BTPWE 504 Electrical Machines II

Transcription

KARNATAKA STATE OPEN UNIVERSITY
COURSE NAME:
B.TECH IN POWER ENGINEERING
YEAR/SEMESTER:
5TH SEMESTER
PAPER NAME:
ELECTRICAL MACHINES II
PAPER CODE:
BTPWE 504
NATIONAL COLLABORATIVE PARTNER
INDEX
INTRO£
BLOCK -J
Alternator
This bei~
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Basic Principle and Working of Alternators
. (\lJ§t 2: Types of Alternator
M1nit 3: EMF Equation
~Unit 4: Performance of Alternators~)
BLOCK 2 Synchronous motor
Unit
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1: Working Principle
2: Vector Diagram
3: Effect of Change in Excitation~
4: Power factor • improvement~
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concept(
have been
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types:oft,
equation ~
This hloO
Unit1:.
BLOCK 3 Thret: phase in~uction motor
Unit
Unit
Unit
Unit
1,: 'Principle of Operation
2: Slip-Torque Characteristics
3: Circle diagram
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4: Speed Control
BLOCK 4 Single phase motor
Unit
Unit
Unit
Unit
1~Construction and Principle of Operation> ~Y
2: Spilt Phase Motore
3: Shaded Pole Motor-Y .
4: Universal Motor vV'
BLOCK 5 Maintenance of inductance motor
Unit 1: BIS Code of Practice rt('
Unit 2: Rating ~
Unit 3: Selection of Induction Motors
jJ,hit 4: Start.;n~
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BLOCK 1: ALTERNATORS
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INTRODUCTION:
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This being the first block' of the course, an attempt has been made to define and consolidate
concepts with the help of examples, The important concepts that one must be able to describe
have been discussed in the block.
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One must ~ 'clear about these basic concepts in order to use a lot of functioks ·aJ.1dfacilities,
which' does exist in a alternator. These blocks describes the concept of alternator and focus the
types .of alternator, This basicfocus bf the 'block being that you should be able to study emf
equation and performance of alternator.. ~_
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This block consists of four units:
Unit 1: Defines the basic principle and working of alternator.
Unit 2: Fecus-onthe ~
of alternator
Unit 3: Prevldes the focus on ~e EMF·equaf:ion
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Unit 4: Provides the overview of performance ~f alternator
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UNIT 1: Bask Principle and Working of Alternators
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1.0 OBJECTIVES
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1:1 INTRODUCTION
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1.1IN'C'1
1.2 PRINCIPLE OF OPERATION
i.s SY]'fCHRONUS
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An altl;
energy.
aItern~ton
alternate
. internal c.
SPEED .:
, 1.4 AUTOMOTrVEALTERNATOR
,.
turbO-a.
1.5 MARINE ALTERNATOR
1.2 Prill
1.6 BRUSHLESS ALTERNATOR
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1.6.1. CONSTRUyTION
. 1.6.2 MAIN ALTERNAToR
1.6.3 CONTROL SYSTEM
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1.6.4 AUTOMATIC VOLTAGE REGULATOR (AVR)
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1.7 HYBRID AUTOMOBILES
1.8 RADIO ALTERNATORS
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The rotan
setsof.
currents, l
1.9 LET US SUM UP
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] .10 SOME USEFULL BOOKS
1.11 ANSWER TO CHECK YOUR PROGRESS EXERCISE
1.12 GLOSSARY
The ro....
permantTt
through.
winding. '
which '.
windinc. )
arc rest.
is constur
gcnerat<.
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1.0 OBJECTIVES
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• . The main objectives of this lesson is to give basic introduction of alternators.
Here, we will also discuss the different types of alternators and its actions.
After study this lesson you will be able to:
• Define the principle of alternator
1.1 INTRODUCTION
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An alternator is an electromechanical device that converts mechanical energy to electrical
energy in the form of alternating current. Most alternators use a rotating magnetic field but linear
alternators are occasionally used. In principle, any AC electrical generator can be called an
alternator, 'but usually the word refersto small rotating machines driven by automotive and other
internal combustion engines. Alternators in power stations driven by-steam turbines are called
turbo-alternators.
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1.2 Principle of operation
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Diagram of a simple alternator with a rotating magnetic
core (rotor) and stationary wire' (stator) also showing the
current induced in the stator: by therotating magnetic -field
of the rotor.
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Alternators generate electricity by the .same principle as
DC generators, namely, when the magnetic field around a
conductor changes, a current is induced in the conductor.
Typically, a rotating magnet called the rotor turns within a
stationary set of conductors wound in coils on an iron core,
called the stator. The field cuts across the conductors,
generating an induced EMF, as the mechanical input
causes the rotor to turn.
The rotating magnetic field induces an AC voltage in the stator windings. Often there are three
sets of stator windings, physically offset so that the rotating magnetic field produces three phase
currents, displaced by one-third or a period with respect to each other.
The rotor magnetic field may he produced by induction (in a "brushless" alternator). by
permanent magnets (in very small machines), or by a rotor winding energized with direct current
through slip rings and brushes. TIll' rotor magnetic field may even be provided by stationary field
winding, with moving poles ill the rotor. Automotive alternators invariably use a rotor winding,
which allows control of the alternator generated voltage by varying the current in the rotor field
winding. Permanent magnet m.uhinc-, avoid the loss due to magnetizing current in the rotor hut
are restricted in size. owing tp the co"t (If till' magnet material. Since thc permanent magnet fickl
is constant. the terminal \ ()ha~,' \ ~Iril'"directly with the speed ofthe gcncratoL Rrllshle" ,:'\C
generators are usually largcr m:« hill," than those used in alltol1loti:._t'upplic.uion-.
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1,4 Auto~
1.3 Syw:.:iLronoU!." speeds
The output frequency of an alternator depends on the number of poles and' the rotational speed.
The speed corresponding to a particular frequency is called the S),IlChroIlOUS speed for that
frequency. This table [6} gives some examples:'
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1.500
1.800
6
8
1.000
750
900
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600
720
12
14
16
500
600
428.6
514.3
450
18
375
333.3
20
300
Cut-awa)(
constructiP
alternatint"
station~')
of the ope
drives thC'l
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1.200
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is.ru~m~
current gel
themsime
generator, ;
life. The e
400
360
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Poles RPM at SOHz RPM at 60 Hz
3,600
3,000
·2
4
Altemat«' •
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More generally. f?n~cycle of a1te~ating curreitt ~sproduced each time a pair of field poles passes
over a point
the stationary winding. The relation between 'Speed and frequency is N
120/ I
P. Where/is the frequency in Hz (cycles per second). P is the number of poles (2,4,6 ...) and N
is the rotational speed in revolutions per minute (RPM). Very old descriptions, of alternating
current systems sometimes give the frequency in terms of alternations per minute, counting each
half-cycle as one alternation; so 12;000 alternations per minute corresponds to J 00 Hz.
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Check Your Progress ~ 1
the rectife
Note:
I. Give your answer in the space given below.
2. Chec~ your answers with those given at the end of the unit.
to
I.Define alternator?
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Typicalt-e
where the
looking
salient-~
driven at ,/,
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constant fn
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Modern at
operates"
output.
70-amp a"Pr
rotor win.,
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1.4 Automotive alternators
mal speed.
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alternating
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Alternators are used in modem automobiles to charge.the ,.
battery
to Powera car's ,electricsystem when its engine
is running. Altern,atorShave the great advantage over direct. ciiirent generators of not using a commutator, which makes
themsimpler, ligbJer,less costly, and more rugged than a DC
generator,and the slip rings:aJiowfor greatly extendedbrush
'life:The stropgerconstructionof automotivealternatorsallows them
to'
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.improving output when the engine is
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. '. 'low-cost solid-state diodes !frommanufacturers to .substitute 'iilkrfiato~' ior' OCR" e'].il'e~rators
(major Amencim rtiahtifactiire~ bhlt t#adb th~ctraflsiti'().ii to
alternators by 1962, for example). Automotive hl~ernatots
use a set of rectifiers (diode bridge) to convert AC to nc.
To provide direct current with low ripple, automotive
alternators have a three-phase winding. In addition,' the
pole-pieces of the rotor are shaped (claw-pole) so as to
produce a voltage waveform closer to a square wave that,
when rectified by the diodes, produces even less ripple than
the rectificationof three-phase sinusoidal voltages.
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Alternatormounted in the lower right front of an automobile engine with a serpentinebelt pulley
Cut-away of an alternator, showing the claw-pole
construction; two of the wedge-shaped field poles,'
alternating N and S, are visible in the centre and the
stationary armature winding is visible at the top and'bottom
_of the opening. The belt and pulley at the right hand end
drives the alternator.
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Typical passenger vehicle and light truck alternatorsuse Lundell or claw-polefield construction,
where the field north and south poles are all energized by a single winding, with the poles
looking rather like fingers of two hands interlocked with each other. Larger vehicles may have
salient-pole alternators similar to larger machines. The automotive alternator is usually belt
driven at 2-3 times the engine.crankshaft speed. Automotive alternators are not restricted to a
certain RPM because the alternating current is rectified to direct current and need not be any
constantfrequency.
Modern automotive alternators have a voltage regulator built into them. The voltage regulator
operatesby modulating the small field current in order to produce a constantvoltageat the stator
output. The field current is much smaller than the output current of the alternator;for example. a
70-amp alternator may need only 2 amps of field current. The field current is supplied to the
rotor windings by slip rings and brushes. The low current and relatively smooth slip rings ensure
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greater reliability and longer life than thaI obtained by a DC generator
higher current being passed through its brushes.
with its commutator
sinzle
and
Efficiency of automotive alternators is limited by fan cooling loss, bearing loss, iron loss, ~opper
loss, and the voltage drop in the diode bridges; at part load, efficiency is between 50-62%
depending on the size of alternator, and varies with alternator speed.!" In comparison, very small
1.6BrfJ
. high-performance permanent magnet alternators, such as those used for bicycle lighting systems,
achieve an efficiency around ~60%. Larger permanent magnet alternators can achieve much
higher efficiency.By contrast, the large AC generators used in power stations run at carefully
controlled speeds and h~v~ no constqints -on size or weight. Consequently, they have much
higher efficiencies, onthe order of 98% from shaft to AC output power.
. The field windings are initially supplied via the ignition switch and charge warning light, which
is Why the Jightglows when the ignition is on but the engine is not running. Oncethe engine is
ruoiling and the atteniatorjs'~eilerati!1g, a diode feeds the field current from the alternator main
output. thus equalizing, t1l~:voltage across the warning light which goes out. The wire supplying
the field.current.is often referred to as the "exciter" wire. The.drawback ofthis arrangement is
that if the warning ligbHalls or the "exciter" wire is disconnected, no excitation current reaches
the alternator field windings and so the -alternator, due to low residual magnetismin the rotor,
will not generate any power. However. some; alternators will self-excite when the engirie is
revved to a certain speed. Also. some warning light circuits are equipped with a resistor in
parallel with the warning light that will permit excitation 'curreht to t}ow eve'} if the warning light
falls. The driver should check that. the warning light is glowing wpen.the,'er)gine,'is stopped;
otherwise, there might not be any indication of a failure of the alternator drive belt Which
normally also drives the cooling water pump.
Very large automotive alternators used on buses, heavy equipment or emergency vehicles may
produce 300 amperes. Very old automobiles with minimal lighting and electronic devices may
have only a 30 ampere alternator. Typic3J passenger car and light truck altemators 'are rated
around 50-70 amperes, though higher ratings are becoming more common, especially as there is
more load on the vehicle's electrical system with, for example, the introduction of electric power
steering systems. Semi-trucks usually have alternators around 140 amperes. Very large
automotive alternators may be water-cooled or oil-cooled.
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or hou'~
switCh~
typical y
connect
1.6.((
A bru~',
brushle
versions.
The exe
uses thi.>.'
called. ;..
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The
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from the
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The reI
altema'li
1.6.3!
Many alternator voltage regulators are today linked to the vehicle's onboard computer system
and, in recent years, other factors including air temperature (obtained from the intake air
temperature sensor or battery temperature sensor in many cases) and engine load are considered
in adjusting the battery charging voltage supplied by the alternator.
1.5 Marine alternators
Marine alternators used in yachts are similar to automotive alternators. with appropriate
adaptations to the sail-water environment. Marine alternators are designed to be explosion proof
so that brush sparking will not ignite explosive gas mixtures in an engine room environment.
They may be 12 or 24 volt depending on the type of system installed. Larger marine diesels may
han: two or more alternators to cope \\ ith the heavy electrical demand or a modern yacht. 0"
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single alternator circuits, the power is split between the engine starting battery and the domestic
or house battery (or batteries) by use of a split-charge diode (battery iso.ator) or a mechanical
switch. Because the alternator only produces power when funning, engine control panels are
typically fed directly from the alternator by means of an aux iliary terminal. Other typical
connections are for charge control circuits.
mutator and
t
loss, ~opper
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very small
ing systems,
hieve much
at carefully
have much
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1.6 Brushless alternators
1.6.0 Construction
A brushless alternator is composed of two nlternatore built end-to-end on one shaft. Smaller
brushlessalternators may look like one unit but the two parts are readilyidentifiable on the large
versions. The larger of the two sections is the main alternator and the smaller one is the exciter.
The exciter has stationary field coils' and a rotating armature (power coils). The main alternator
uses the opposite configuration with a rotating field and stationary armature. A bridge rectifier,
called the rotating rectifier assembly.tis mounted on plate attached to the rotor. Neither brushes
nor slip rings are used, which reduces the number of wearing parts.
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light, which
ae engine is
mator main
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mgement
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'ent reaches
n the rotor,
e engine is
resistor 'in
arriing light
'is st<>P'Ped;
belt which
!hicles may
evices may
'S are rated
, as there is
ctric power
Very large
1.6.1 Main alternator
The main alternator has' a rotating field as described above and a stationary armature (power
generation windings).
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1.6.2 Control system
Varying the amount of current through the stationary exciter field coils varies the 3-phase output
from the exciter. This output is rectified by a rotating rectifier assembly, mounted on the rotor,
and the resultant DC supplies the rotating field of the main alternator and hence alternator output.
The result of all this is that a small DC exciter current indirectly controls the output of the main
alternator"
1.6.3 Automatic' voltage regulator (AVR)
Iter system
intake air
considered
ippropriate
ision proof
vironmcnt.
icsels may
yacht. On
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An automatic voltage control device controls-the field current to keep output voltage CO[]',I ;1111 I r
the output voltage from the stationary armature coils drops. due to un increase in demand, more
current is fed into the rotating field coils. This increases the magnetic field around the field coils
which induces a greater voltage in the armature coils. Thus. the output voltage is brought back up
to its original value.
Alternators in central power station lise may also control the field current to regulate reactive
power and to help stabilize the power system ag~lil1stthe effects of momentary Iault-;
Check Your Progress - 2
Note:
I. Give your answer in the spacl' given below.
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L. Chccl: your answer ~ v,itl. tho:, given at the end of the unit.
1. Explain brushless alternator?
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8. Ele.ctt~
9.Electnca
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1.7 Hybrid automobiles
1.11AIf'
Hybrid' automobiles replace the separate alternator and starter motor with a combined
motor/generator that performs both functions, cranking the internal combustion engine when
starting, providing additional mechanical power for 'accelerating, and. charging a large storage
battery when the vehicle is running at constant speed. These rotatihg'ma.chiiies have considerably
more powerful electronic devices for their control than the automotive alternator described
above.
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1.8 Radio alternators
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1.12G~
High frequency alternators of the variable-reluctance type were applied commercially to radio'
transmission
the low-frequency radio bands. These were.used for transmission of Morse code
'anP, eXPfrimentally, for transmission of voice and music. .
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Altern.
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1.9 LET US SUM UP
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• .An alternator is an electromechanical
device -that converts mechanical energy to
electrical energy in the form of alternating current.
• The output frequency of an alternator depends on the number of poles and the' rotational
speed. The speed corresponding to a particular frequency is called the synchronous speed
• Alternators are used in modem automobiles to charge the battery and to power a car's
'electric system when its engine is running.
• Marine alternators used in yachts are similar to automotive alternators, with appropriate
, adaptations to the salt-water environment.
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• A brushless alternator is composed of two alternators built end-to-end on one shaft.
Smaller brush less alternators may look like one unit ·but the ·two parts are readily
identifiable on the large versions.
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High frequency alternators of the variable-reluctance type were applied commercially to
radio transmission in the low-frequency radio bands.
1.10 SOME USEFl.JLL BOOKS
l.Elecrrical Machines by SK Bhattacharya, TataMcHill Publishers
2.A Text Book Electrical Technology hy BL Theraja, S.Chand Publishers
3.0peration and Maintenance of Electrical Machines hy B.Y.S. Rao, Khanna Publishers. ;'\Tl°\'.'
Delhi.
4.Elcctril'al Technology by Ed« ;mi Hughes, Addision -- Wesley International Student Editioll
5, Pertormance & Design of AC Muchine-, by MG S~ty. CBS Publication. Nl'\\ Delhi
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6, Electrical Energy Systems Theory by Elegerd, Tata McGraw Hill Co, New Delhi
7.EJectric Machinery by Fitzerald, Tata McGraw Hill Co, New Delhi
8. Electrical Machinesf'Sigma Series) by Kothari, Tata McGraw Hill Co, New Delhi
9.Electrical Machines by Kothari & Nagarth, Tata McGraw Hill Co, New Delhi
10.Electrical and Electronics Engineering by Vikramaditya Dave, Lakshmi Publications (Pvt)
Ltd, New Delhi
1.11ANSWER TO CHECK YOUR PROGRESS EXERCISE
1. ,See section 1.0
1. See section 1.5
1.12GLOSSARY
. Alternator:
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An alternator is. an electromechanical device that converts mechanical energy .to
electrical energy in the form of alternating current.
The output frequency of an alternator depends on the number of poles and the rotational
speed. The speed corresponding to a particular frequency is called the synchronous speed
Alternators are used in modem automobiies to charge the battery and to power a car's
electric system when its engine is running. .
Types of alternator
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Marine alternator
Brushless alternator
Automotive alternator
Hybrid alternator
Radio alternator
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2.00B
UNIT 2: Types of Alternator
Thisless~'
Structure
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2.0 OBJECTIVES
t'!
2. 1INTRODUCTION
.2.1INTC:'
2;.2LINEAR ALTERNATOR
Alternatl'
isc_onve.
the batter
control
alternator.
i.•
23TRANSFORMER: ALTERNATOR
2.3.0 FICTION
2.2LJNC)
2.3.1 LISTOFAL~R;NATOR
A linear'
2.4 ELECTRIC MOTOR
a type
11
. equivaleri
2.5 DC MOTOR
flows. ~
electrical
2.6 PERMANEl\T'f-MAGNET MOTOR
linear at.
workwi~
straight nr
2.7 UNIVERSAL MOTOR
Theory
2.8 LET US SUM UP
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When a
through.
2.9 SOME USEFULL BOOKS
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A linear ;
directly.
would oy..
compatie-'
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2.11 GLOSSARY
Applicati
The simp'
(USA) •
forth, thlla.
to charg?",
usually.,
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2.0 OBJECTIVES
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This lesson is intended to discuss various criteria for alternators, and you wi,ll be able to : s
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Define the basics of principles of alternator.
•
State the types of alternator
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2.1 INTRODUCTION
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Alternators produce A.C current. If your are talking about automobile alternators this AC current
is converted in to DCto charge the battery. Earlier Dynamo's were in use before 1980's to charge
the' batteries .. Dynamo produces DC current directly and only electrical regulator is used to
control its voltage and current. In case of alternators' an Electronic regulators are.fitted in side the
alternators along with diodes to convert AC to DC.
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2.2 LINEAR ALTERNATOR
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A'linear alternator is essentially a linear motor used as an electrical generator. (An alternator is
a type of alternating 'current (AC) electrical generator.) The devices are often physically
. equivalent. The principal difference is in how they are used and which direction the energy
flows. An alternator converts mechanicalenergy to electrical energy. whereas a motor converts
electrical energy to mechanical energy. Like most electric motors and electric- generators, the
linear alternator works by the principle of electromagnetic induction, However, most alternators
work with rotary motion, whereas "linear" alternators work with "linear" motion (i.e. motion in a
straight line).'
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Theory
When a magnet moves in relation to a coil of wire, this changes the magnetic flux passing
through the coil, and thus induces the flow of an electric current, which can be used to do work,
A linear alternator is most commonly used to convert reciprocating (i.e. back-and-forth) motion
directly into electrical energy. This short-cut eliminates the need for. a crank or linkage that
would otherwise be required to convert a reciprocating motion to a rotary motion in order to he
compatible with a rotary generator.
Applications
The simplest type of linear alternator is the Faraday Flashlight. This is a torch (UK) or flashlight
(USA) which contains a coil and a permanent magnet. When the appliance is shaken back and
forth, the magnet oscillates through the coil and induces an electric current. This current is used
to charge a capacitor. thus storing energy for later use. The appliance can then produce light.
usually.from a light-emitting diode, until the capacitor is discharged It can then be re-charged hy
further shaking.
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unde: development which usc linear alternators to generate electricity; these
devices include the opposed-piston free-piston engine, and the free-piston Stirling engine.
Other devices
iUI.',
launch uf{'
the Decept
Binaltecl('1
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Note:
Among
Ravage, ~\
Wars, w~·
2. Check your answers with those givenat the end of the unit.
1.Define linear alternator?
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2.3 TRANSFORMER:ALT~RNATOR
2.3.0 Fiction
The Binaltech story WClS told through chapters accompanying the Binalt~h toy releases, either in
the booklet provided, or later, on the boxes themselves, There lias been no official storyline for
Alternators on any Hasbro material, though ~ American, Mazda website oted the Binaltech
'storyline and the Nemesis Prime exclusive had a story featuring
Arkeville.
Dr:
While no fiction was written for .the Binaltech Asterisk line, character profiles were pro' ided
with each of the three figures. These profiles 00 oat specifically place them in the Binaltech
universe, however they are also not incompatible with the Story outlined in the main Binaltech
line.
.
The Kiss Players fiction was told through a series of radio plays in Japan, the recordings of
which were included on CDs accompanying the toys. The Kiss Players saga takes place in a
continuity separate from Binaltech, as it depends on the events of the original animated feature,
in which Optimus Prime dies, Unicron reformats Megatron into Galvatron, and both are
eventually defeated by Rodimus Prime.
Binaltech Story
the event"l
history, i~
Prime an,,,
army in a
dooming.,
toberdea:
. .e
The Aut~
Their atte'!!"
thefutur~
Binaltech ,
The Pro.
titrteline. n
andleveri.'
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from the,
fighting a
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Binaltech
Autobot~
AD
A~ the
a showd<jA
with PrinT
called ...
"Altemity
••
Kiss Play'
In the year 2003, prior to the events depicted in The Transformers: The Movie. a pathogen is
released by one of the Decepticons which destroys the Cybertronian bodies of the Autobots
based on Earth. In order to save their lives. not just from destruction by the disease but by attack
from the .Decepticons in their vulnerable stale, the Autobots team up with car manufacturers
from Earth, including Subaru, Mazda, Chrysler and Ford to construct new bodies from Earth
materials. which would be immune to the disease, This initiative is the Binaltech Project
The initiative is successful. and several Autobots are returned to duty, allowing them to fend off
assaults by the Decepticons. However. the Dccepticons take advantage of the developments of
the Project. and several of them manage to obtain Binaltech bodic-, of their 0\\ 11 The AUloboh
14
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of crashiri]
of guilt,,,,
. As a res.
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launch an investigation, however it is determined 11::1: none of the Autobots' allies are to blame the Decepticons' skill at deception and brain-washing is what allowed them to get their hands on
Binallech technology.
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Among the Decepticons given Binaltech bodies is Ravage. This is not the 2003-era cassette
Ravage, but a Ravage from the future, who had travelled back into the distant past to the Beast
Wars, was deactivated onpre-historic Earth and unearthed by archaeologists. With knowledge of
the events beyond the year 2003, Ravage is able to enact several plans which alter Transformers
history, including preventing the Battle of Autobot City (and therefore the death of Optimus
Prime and the reformatting of Megatron into 'Galvatron), and trapping the bulk of the Decepticon
army in a temporal rift' to protect them from Unicron who would soon be appearing, thereby
dooming the Autobotsto fight him unassisted, and providing the opportunity for the Decepticons
to be released and easily defeat whoever was left standing.
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The Autobots become aware of Ravage's tampciingl3Jl4J,and attempt to undo the damageIS).
Their attempts are unsuccessful and trigger the crumbling of reality itself, but a "Protector" from
the future unexpectedly arrives, stabilizes the multiverse, andsplinters the altered timefine of the
Binaltech saga into its own' universe, parallel to the restored timeline in the original universe.
The JP-rotectoi"•explains .that the Binaltech universe, although originally a -corruption : of the
1imeline, must be IDlowedto continue as it will lead to an evolution of the Transformers species,
and-eventually to "the great'Atternity".
..
'When Unieron arrives, the Autobots prevail, but per Ravage's pian, the Decepticons are released
from the rift to conquer the battle-weary Au' obots. In order to put an end to' all Transformer
.fighting across the universe, the Autobots resort to activating an ancient device to freeze all
Transformers across the universe, but it has the unexpected effect of only freezing the nonBinaltech Transformers. Since Binaltech Autobots outnumber Binaltcch Decepticons, the
Autobots once again triumph.
As the Autobots adjust to life in Binaltech bodies, experiments with Binaltech technology lead to
a showdown between Optimus Prime and an evil twinlS] in which the Protector's spark merges
with Prime's to ensure his victory over the doppelganger, and to the discovery of
element
called "Alterniurn" which, unbeknownst to the Autobots, will be key to the prophesied
"Alternity" .
an
Kiss Players
iogen IS
..utobots
y attack
[lcturers
11 Earth
end off
lents of
lItobots
When Galvatron was defeated by Rodimus Prime and tossed out through Unicron's eye, instead
of crashing on Thrull, as seen in the original events. he crashed on Earth. decimating Tokyo. Out
of guilt, Rodimus Prime stepped down as leader. p;Jssing the Matrix 'to Ultra Magnus.
As a result of this incident. even Autobots were no longer welcome on Earth. and the EDC
(Earth Defence Command) took on the duties of ensuring all Transformcr-, were kept away, Thi-,
was accomplished by creating Earth's own transforming robot force. the AutoJ"Ooperlllll. from
Mazda RX)) vehicles.
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~
Galvatron's crash on Earth also had the unexpected effect of distributing Unicron-infected
cells
from his body across Tokyo, which resulted in the rise of a new type of menace, the: Legion creatures created by these Galvatron cells invading Earthen objects and' animals. But it was
found that these cells could also be utilized on humans and the Autorooper squads, to create a
more powerful force to fight the Legion - the Kiss Players. A kiss between the Autorooper robot
and its human partner would cause the two to fuse, with the Autorooper becoming several
magnitudes more powerful and deadly than it originally had been. The process did have one
particular limitation - after-a certain amount of time, the. human would be automatically
disgorged from the Autorooper, even if the battle was still ongoing. Atari Hitotonari wasa
notable Kiss Player whose fusion with her Autorooper resulted in'unmatched power levels.
Binaitfch
fii,
features fUlf1
I. BT-!\
2. BT-<f
3. BT-O::
4. ,BT-('
5". BT-g;....
6. BT-~
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This ability to fuse human and Transformer would eventually spread to Optimus Prime, whose
lifeless body was in the custody of the EDC and who was resurrected and reformatted into a
Dodge Ram truck by a kissgiven by the human MarissaFairebom, and to Hot Rod, who wasin
seclusion on Earth trying to make amends for the' destruction which resulted from his fight with
Galvatron, when he reformatted into a Ford GT car by a kiss from a human named Shaoshao Li,
a former EDC Autorooper operator.
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operat~ .thro~
it·~
although
, rneehanica)·.,
, electric motor'
In spite of the EDC's anti-Transformer policy which saw them being hunted down by the EDC,
Optimus Prime and Hot Rod, along with their human partners, helped battle the Legion on
numerous occasions -.But this was not a happy co-operation, ~s the two Autobots fought each
other on several occasions. This was partly due to the fact that Hot Rod was convincedthat the
reformatted Optimus Prime was an imposter. Hot Rod had, afterall, witnessed Optirnus' death in
the aftermath of the Battle of Auto-or City, and as Rodimus Prime, had briefly replaced Optimus
as the new Autobot commander.
'
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,generatols .ar~
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wristw~l~he.
Eventually, a secret plot by the EDC went awry, resulting in all the dispersed Galvatron cells and
Legion being gathered -back together to reform Galvatron's body. The removal of-these cells
eliminated the unique powers of the Kiss Players and undid the reformatting undergone by both
Optimus Prime and Hot Rod, including undoing Optirnus's resurrection. Galvatron was ejected
into space, to ultimately crash on Thrull, and the original timeline seen in the animated movie
was effectively resjored.
.
2.4 List of Alternators
I. Smokescreen - Subaru Impreza WRC (#8 only)
2. Side Swipe - Dodge Viper
3. Autobot Hound - Jeep Wrangler
4. Silverstreak - SubaruImpreza WRX
5. Autobot Tracks - Chevrolet Corvette C5 Z06
6. Dead End - Dodge Viper
7. Meister (aka Autobot Jazz) - Mazda RX-8
convement
.m
<0
propulsion
Electric moto:
by their app(.)
The physiCa~
and a magn.
constructed iT'"
large scale ...
Some devi~
mechanical lila
actuators anJ-'
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Note: I. Gi.
List of Binaltech
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J. BT-Ol Smokescreen - Subaru Impreza WRC 2003 (#7 & #8)
2. BT-02 Lambor - Dodge Viper SRT-IO
3. BT-03 Streak - Subaru Impreza WRx
4. ,BT-04 Hound - jeep Wrangler
5. BT-05 Dead End - Dodge Viper Competition Coupe
6. BT -06 Tracks - Chevrolet Corvette Z06 (Millennium Yellow & LeMans Blue Metallic)
2.5 ELECTRIC MOTOR
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Billa/tech figures arc the Japanese version of Altemators. Unlike Alternators. the Binaltech line
features fully painted car bodies and die-cast metal parts.
An. electric motor converts electrical energy into mechanical energy. Most electric motors
.operate through interacting magnetic fields and current-carrying conductors to generate force,
although it few use .electrostatic forces. The' reverse' process, -producing' electrical eil~rgy from
mechanical. energy, .is Aone 'by generators such. as an alternator or it dynamo. Many .types of
" ~lectricinotors can be run as generators, and vice versa. For example a starter/genel"!ltorfor a gas
turbine, or .traction motors used Ion vehicles, often perform both tasks. Electric motors and
;,generato.rs;rre commonly ref~ed to.as electric-machines.
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Electric motors are found in .applications as diverse: as jndustrial faps; blowers llnd'pumps,
machine tools, household appliances .. power (ools,'and disk drives. They maybe pOwe.red by
direct current (e.g., a battery powered portable device or motor vehicle), or by alternating current
from a -central electrical distribution grid. The smallest motors may be found in electric
wristwatches. Medium-size motors 'Ofhighl ¥ standardized dimensions ~nd characteristics provide
convenient ..mechanical power forindustrial uses. The very largest electric motors are used for
propulsion of ships, pipeline compressors, and water pumps with ratings in the millions of watts.
Electric motors may be classified by the source of electric power. by their internal construction,
by their application. or by the type of motion they give.
The physical principle of production of mechanical force by the interactions of an electric current
and a. magnetic field was known as early as l821. Electric motors of increasing efficiency were
constructed throughout the 19th century, but eomrneroial exploitation of electric motors on a
large scale required efficient electrical generators and electrical distribution networks,
•
Some devices, such as magnetic solenoids and loudspeakers, although they generate some
mechanical power. are not generally referred to' as electric motors, and are usually termed
actuators and transducers, respectively,
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2.6 DC l\10TOR
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A DC-motor is in electric motor that runs on direct current (DC) electricity ..
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The brushed .D~ electric motor generates. torque directly from DC -power supplied to the motoj
.by using mternal commutation. stationary .permanent magnets; and rotating electrical magnets] ·'Permanent -I
Like all electric motors-or generators, torque is produced by the principle Of Lorentz.force, whic~
pe~er6
dfltatesJhat'any current-carrying conductor placed within ali external magnetic field experiences ~ '.:produce tore
Aorq1,le or force kbowll' as Lorentz force. Advantages 'of.a brushed DC motor include low ,initi~
:to inlpr()~
..cost, high reliability, and simple control of motor speed. 'Disadvantages are high maintenance
, and low life-span for high-intensity uses. Maintenance i~voJves regularly replacing the brushes
", and springs which carry the electric' current. as-well-as cleaning.or replacing the commutatof
, "req~~~s ~.
Th~e componenrs are necessary for transferring electrical power from outside the motor to th~
.~s'pin~ng'wire windings of the rotor inside.the motor .. '
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Synchronous DC motors, such as the brushiess DC motor ~nd the stepper motor, require external
«commutetion to generate torque. They lock up if driven directly by DC power. However, BLOC
motors are more similar to a synchronous ac motor.
Brushless
.
BC
. Brushed.
r
I
. Brushless
moto", use a rotating permanent .magnet in the rotor, and stationary electrical
magnets on the motor housing ..A m~tor ~o~troller converts .DC. to A~. Thi~ d~sign is Sin~Pkrl.•..
than that of .brushed motors' because It eliminates the complication of transferring power from]
outside th~.motor to the spinning rotor. Advantages of bnfshl~ss motors include long life span,t
litt~e ~r no maintenanc"e, and. high efficiency. Disadvantages include high initial cost, and ITIllret
complicated motor speed controllers.
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Oth!!r types of DC motors require no nmllllLltation.
•
HOl1lopt1iar
f
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motor - A homopobr 1ll01()f has a magnetic field alon!! the ;1Xis of Tlltatipn
and an electric current that at some point is not paralld to the m,lgnetic field. The n;II11Ct
hOJnopolar rders to the absence of pub'it) I.·hange.
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Homopolar motors necessarily have a single-tum coil, which limits them to very low voltages.
This has restricted the practical application of this type of motor.
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.' 2.7 PERMANENT MAGNET MOTOR
to the moto:
ical magnets]
.permanent-magnet motor does not have a field winding on, the stator frame, insteadrelying on
force, which .
perni~nent magnets to provide the .magnetic field against which the rotor field interacts to
experiences i ",-'produce torque. Compensating windings in series with the armature maybe used on large motors
Ie low initia1
unPfQve commuation under load. Because this field is fixed, it cannot be adjusted for speed'
maintenance;
control. Permanent-magnet motors are convenient in miniature motors to eliminate the power
~ the Qrushe~ consumption of the field winding. Most larger DC motors are of the "dynamo" type, which
~
commutator. . ieqti~~!:!current to flow in fieldwindings toprovid~'tqe stator'inagileticfield.
motor to'lh·
., .. :..
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., lifo rilinirniie overall weight andsize, ni'iniatui'f·petiIlIlIlent-magnet,motors may use high energy
. magnets, made with neodymium or other strategic -elem~ntS. 'Wjth the higher flux il~nsity
provided, electric machines with .high energy permanent magnets are at least competitive with all
optimally designed singly-fed synchronous and induction electric machines.
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Ball bearing motor - A ball bearing motor is an unusual electric motor that consists of
two ball bearing-typebearings, with the inner races mounted on a common conductive
shaft, and the outer races connected to a high current, low voltage power supply. An
alternative construction fits the outer races inside a metal tube, while the inner races are
mounted on a shaft with a non...conductive section (e.g. two sleeves on an insulating rod).
This method has the advantage that the tube will act as a flywheel. The direction of
rotation is determined by the initial spin which is usually required to get it going .
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iry electrical
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DC motor design generates an oscillating current in a wound
rotor, or armature, with a split ring commutator, and either a
wound or permanent magnet stator. A rotor, consists of one or
more coils of wire wound around a core on a shaft; an electrical
power source is connected to the rotor coil through the
commutator and its brushes, causing current to flow in it.
producing electromagnetism, The commutator causes the
current in the coils to be switched as the rotor turns, keeping the
magnetic poles of the rotor from ever fully aligning with the
magnetic poles of the stator field, so that the rotor never stops (like a compass needle does) but
ruther keeps rotating indefinitely (as long as power is applied and is sufficient for the motor to
overcome the shaft torque load and internal losses due to friction, etc.)
Many of the limitations of the classic commutator DC motor are due to the need for brushes to
! press against the commutator, This creates friction, Sparks are created by the brushes making and
, breaking circuits through the rotor coils as the brushes cross the insulating gaps between
,,
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19
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commutator sections. Depending ,on the commutator design, this may include the brushes;
shorting together adjacent sections-e-and henee coil ends-momentarily while crossing the gaps .. ,
Furthermore, the inductance of the rotor coils causes the voltage across each to rise when its ~
circuit is opened, increasing the sparking of. the brushes. This sparking limits the maximurn
speed of the machine, as too-rapid sparking will overheat, erode, or .even melt the commutator ..:
The current density per unit area of the brushes, in combination with their resistivity, limits the;
'output of the motor .The making and breaking of electric contact a1so causes electrical noise, and
the sparks addit.iomilly cause RFI. Brushes eventually wear out and require replacement, and the'
commutator itself -is -subject
wear' -and ·maintenance (on .larger 'motors) or replacement (on' 'i .
small. motors). 'The 'Comm_lltatorassembly on aIarge motor .isa costly element, requiring]
precision assembly ofmany.parts. On small motQrs,the ~oinmutato(is usually permanently1
integr~ted-int_othe rotor.so replacing it usually reqllires\(eplacin~ ~e·whoieTotor:
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B: series
C: compound
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There are five types of brushed DC motor:
'c~
.A.·DC shunt-wound-motor
I
B. DC series-wound motor
C. DC compound motor (two configurations):
•
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•
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Cumulative compound
Differentially compounded
•
D. Permanent magnet DC motor (not shown)
•
E. Separately excited (sepcx j
(not
shown).
Brushless DC motors
20
•
•
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the brushes ; Some of the problems of the brushed DC motor arc eliminated in the brush less design. In this
ng the gaps: .~' motor, the ,me~hanical "rotating switch" or commutator/brushgear assembly is replaced by an
ise when its.,:.: external electronic switch synchronised to the rotor's position. Brushless motors arc typically 85"
.
e maximum':.,' .../90%
efficient or more (higher
efficiency for a brushless -clectric motor of up to 96.So/c were
commutator.' -,;;·~ported by researchers at the Tokai University in Japan in 2009), whereas DC motors with
y, limits the) .J ;f,rushgear are typically 75-80% efficient.
11 noise.and] "'::'{~~;.:
..,
.
lent, and the ~idway
between ordinary pC motors and stepper motors lies the realm of the brushless DC ,
icement (on' ~4D6tC!r.Built in a fashion very similar-to stepper motots, these Often use a permanent magnet
It, requiring 'i~tefnal rotor" three.phases of drivingcoils, one or more Hall effect sensors to sense the position
permanently~ 1~:;!ittherotor, and the associated drive 'electronics. The' coils are activated, one ,phase .after the
-t>y,thedrive electronics as cued by the signals from either Hall effect .sensors or fromthe
, .: . /EMF,(electromotive
force) of the undriven. coils, In ,effect,;they .act .as three-phase
"J;lc:hronous motors containing xheir.own variable-fr~uency Qri~:el~grQniq;~.A ;speciali:Z-¢,
:' ,5. of .brushless ,DC·, motor; controllers utilize EMF feedback through, the main .phase
.
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• 9DS instead of.JIall effect.sensors.to determine P9si~ip!1i!n,d~~locity, These motors ,a{e
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in :Iectnd'c TbadiO-Cod°D1trolled
vehicles.When
configured .with the magnets on the
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.~~bless DC motors are commonly used where p!ecise speed c¢l~trol is necessary, as in
osses (lower;
.,tpilter 4isk drives or in. "ideo cassetterec9~4e.~;
'tlJe spi'Qdle~;"-'.i.tqin:
CPlo CP~RQ~~{,{e.tc:
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,rq~..h i
metbani~ms' within qffice pr~utt~ ~uch as '.fanS, .\ils~r,.printers and ,photocopiers.
r~~y"~;a"e'Several advantag~s over>CQliv~uonal inot~r~:
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Compared to AC fans usipg shaded-pole motors, they are very efficient, running much
:COOlerthan-the equivalent ACmotors. ThiscpoJoperation·)eac:ls to much-impro~ed life of
;:lbefan's bearings.
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• "Without a commutator to wear·out, the life of a DC brushless motor can be significantly
longer compared to a DC motor using prushes and a commutator. Commutation also ,
tends to cause a great deal of electrical and RF nOIse; withouta ~mrnutator or brushes .•
brushless motor may be used in electrically sensitive devices like audio equipment or
.comput~rs.
• .The same Hall effect sensors that provide the comm.utation can also pro\'ide a convenient
. ~chometer signal for ~Qsed-lqop cOl}trol.(s~rvo~contrQned) applications. In fans, tru;
tachometer signal can be used 10 derive a :'fanOK" signal.
.
• The motor can be easily synchronized to an intci'nal or external clock., leading. t~)precise
speed control.
• Brushless motors have no chance of sparking, unlik~ brushed motors. making them better
suited to environments with 'volatile chemicals and fuels. Also, sparking generates ozone
which can .lcculilulate in poorly ventilated buildings risking harm to on:upants' health.
• Brushless motors are usually used in small. equipment slIch as computers and are
generally used to get rid of unwanted heat.
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affected ny vihrations,
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Modern 0:: brushless motors range in power from a fraction of a watt to many kilowatts. Larger .. Because ~he(
of operatmg1'
brushless motors, up to about. 100 kV,r rating are used in electric vehicles. They also find ...
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significant use in high-perf0n11anCe electric model aircraft.
: An advantag'
Coreless or ironless DC motors
some chara'
.
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Nothing in the' principle of any of the motors described above requires that the iron (steel)" short life pft.
portion~ of the rotora~ually rotate. If the softmagn~tic mate~al of the rotor is made i~ th.eform
mix.ersand t;
of a cylinder, then (except for the effect of hysteresis) torquers exerted only on the windings of : r demands. C~
the electromagnets. Taking advantage of this fact is the .coreless or-oironJess ,DC motor; a :: . of a thyrist('1
specialized form- of a brush or brusliless DC motor. Optimized Jor rapid aoceleration, these i, '~ontroJ. Hou
motors )lave a rotor rhatis-constructed without any iron core. The rotor can take the form of a ,~, several tapC'
winding-filled cylinder, or a self-supporting structure comprising only the magnet wire and the ..~ half~wave re
:bonding material. The rotor can fit inside the. stator magnets; .a .magnetically soft stationary' '1
C'
cylinder inside ,the ..retor provides a return path for'<the stator .magnetic flux. A second '.~ induction Ji;:,
arrangement has the ,[()tor wmding basket .surrounding the stator magnets. In 'that design,. the .:~_uroversal .n1f'
rotor fits inside, a niagnetically soft 'cylinder that can serve as the housing fOr the motor; and'~ blenders,
likewise provides a return path for the flux,
'
.
are also corr'
.'
where the C>
,B~ca~se the rotor i~ rm.c.h !ifht~rin weight'(mas.s) than a conv~niion1!1ro~or fofmed from'C~pper~: exceed 10,0<
windings on steel1!uninauons,. the rotor can accelerate much more rapidly, ;often achtevlng 11 <' :RPM.
I)
-meehanical time constant unded. ms, This is especially true if the wi,nding~ use aluminuin·rather j
than the heavier copper; But ~ause there is no metal mass inlhe rotor
aetas a heat sink, even .~ Universal "
choice for.
small coreless motors must often be cooled by forced air.
.
forwards an,
can also bee
Related limited-travel actuators have no core and a bonded coil placed between the poles of
high-flux thin permanent magnets. These are the fast head positioners for rigid-disk ("nard disk")
MotordanO
drives.
.
limits) if thf
be avoidec()
2.8 UNIVERSAL MOTOR
and controlr'l
5
Vt'l
to
A series-wound motor is referred to as a universal motor when it has been designed to operate
on either AC or DC power, The ability to operate on AC is bec~\1se the current in both the field
and the annature (and hence the resultant magnetic fields) will alternate (reverse polarity) in
synchronism. and hence the resulting mechanical force will occur in a constant direction.
Operating at normal power line frequencies, universal motors are often found in a range mrely
larger than 1000 watt, Universal motors also form the basis of the traditional railway traction
motor lIT' electric railways. 1n this application, the use of AC to power a motor originally
designed to run on DC w(\u1d lead to efficiency losses due to eddy current heating of their
magnetic components, panicularly the motor field pole-pieces that; for DC, would have used
solid (lin-laminated) iron. Although the heating effects arc reduced by using laminated polepieces, as llsed for the cores of transformers and by the lise of laminations of high permeability
e1ectric"il sted. one solution available at start of the 20th century was for the motors tll be
operateLi from vcry low frcyucncy AC supplies, with 25 and 16.7 Hz operation being common,
j,
1:~":~~~;
l2.9LETte
f
i
t
I
I
i
•
A (,
altel
«A.
•
•
•
•
•
o
•
•
•o
Cj
o
~.
,
(
vatts, Larger 1 Because they used universal motors, locomotives using this design were also commonly capable
:y also find;; of operating from a third rail powered by DC.
.
,
.~"An advantage of the universal motor is that AC supplies may be used on motors which have
. some characteristics more common in DC motors, specifically high starting torque and very
.
.:Ii cdrnpact design if high running speeds are used. The negative aspect is the maintenance and
iron (steel):
life problems caused by the commutator. Such motors are used in devices such as food
: i~ th.eform _ mfxers and power tools which are used only intermittently. and often have high starting-torque
windings of
d¢1nands.Continuous speed control of a universal motor running on AC is.easily obtained by use
C .motor, a~~ oLa thyristor circuit, while multiple taps on the field coil provide (imprecise) stepped speed
anon, these,: : iontrol. Household blenders that advertise many 'speeds frequently combine a field coil With
~ form of'.a : se~eral taps and a diodethat can be inserted in series with the motor (causing the motor to run on
vire and the ,half~waveredified AC).··
..,
.'
'1 stationary'
. '(A second ·jnQuction motors can't turn faster than allowed by the power line frequency. By' contrast.
design, the' ·:Uhlvirsal motors generally run at high speeds, making them .useful fot appliances. such as .
.motor, and' blenders, vacuum cleaners, and hair d~is where high speed and light we{ghtisdesirllbl~, They
.also commonly used in portable power tools, such as drills, sanders, cin.:ulaLAn~ji,gsaws,
where the motor's characteristics work welt Many vacuum cleaner and weed trimmer' motors
.:e~ceed 10,000 RPM. while Dremel and dther similar.miniature grinders willoften exceed 30,000
. ro~'C~p~r";
.
achlev~ng a:. ~M.
l in~m'rathe~ ': .
1sink, even .' Universal motors a1~0 lend themselves t~ electronic speed control and, as such, .af~ ah ideal .
' choice for "domestic washing machines. The motor can be used to agitate th~ drum (both
· forwards and in reverse) by switching the field winding with respect to the armatore. -The motor
he poles of '":; can also be run up to.the high speeds required for the spin cycle.
'hard disk ") . •
Motor damage may occur from overspeeding (running at an rotational speed in excess of design
• limits) iflhc unit is operated with nOliigpificant load. O~ larger motors, sudden loss ~f1oad is to
be avoided, and the possibility of such an ocCurrence is incorpomted into the' motor's protection
· and control schemes. In some smaller applications, a fan blade attached to the' shaft often acts as
(
(
6;
short
.,
C
f'
>
c
.'
.-
a;~
'j
•
e
•
•
"
•
I tooperatc
ith the field
JO]arity) in
an artifi.Icialload to Ii.mit the motor spe.ed to a safe level, as well as a meansto C1'r~UI.ate
cooling
.. airflow over the.armature ,and field windings.
'..
.
~
"'"
.'
fl.·
_,
·
-
.
.
,
-~
2.9 LET US SUM UP .
In.
mge -Tarely
ay traction
originally
19 of their
have used
tated pole~rme;'lbility
ltors to be
~common.
-
I
•
I
t
I
!
•
..
•
.
.
A linear alternator is .essentially a 1in~ar mO.torused as an electrical generator. (An
alternator is a type of alternating current (AC) electrical generator.)
A series-wou.nd motor is referred to as a unh'crsal motor when it has been designed to
operate on either AC or DC power.
DC motor design generates an oscillating current in a wound rotor, or armature, with a
split ring comrnutator. and either a wound or permanent magnet stator
permanent-magnet motor does not have a field \\inding on the stator frame.. instead
relying on permanent magnets to provide the magnetic field again~.;twhich the rotor field
interacts to prodllCL' torqllt:
An electric motor ctll1verh electric;'11energy in1<1mcch:ll1icllcncrgy ..
_.'
)'
_-
t
C
I.Electrical Machines by SK Bhattacharya, Tatalvlcflill Publishers
2.AText Book Electrical Technology by BL Theraja, S.Chand Publishers
'.,'
Structure ..
3.0peration and Maintenance of Electrical Machines by B.V.S. Rao, Khanna Publishers, New'.
3.00BJE
Delhi.
4.Electrical Technology by Edward Hughes. Addision - Wesley International Student Edition
.5..performance &1)esignof ACMachines by MG Say, CBS Publication, New penii
3.1IN~<f
6. Electrical Energy Sy~tems 1;heQry by Elegerd, Tata McGra\V ijill Co, New Delhi.
.
"3.2 E.M.F)!'
7.E!ectDc Machinery by Fitzerald, Tata McGrawH.iJl Co, New Delhi
"
8. Electrical Machi~~~(Sigma Series) by Kothari, taiaMcGr.a~ I:lill..Co,,~ew Delhi
A .
3.3FLUXf'
9.Electrical Machines by Kothari & Nagarth, Tata-McGraw-Hili Co, New Delhi _ ;. .
:~
1O.Electri~l and Electronics Engineering by" Vikrarnaditya Dave, Lakshmi :Publications (pYt)"~
Ltd, New Delhi
.'
."!
<f
.\
_,
, ..~. +
J.~MAXWe
.•
2.llANSWER
zo CHECKYOUR
" ' ~Your
, 3.5ELE~
PROGRESS 'EXERCISE'
Progress - 1
"3.6El~C'
L :Selsectian U)
,
•
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0.'
.t·,
Clit~ Your"Progress - 2
-·3;1ELEC.
.!
.
~ec!iQn7.3
-;' .;
1. See
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;..
3:8LETltP
3.9S0M~
2.12 GWSSARY
3.10AN~
e
Linear alternator,
3.11 GLO~
• A linear alternator
'}
•
,
',••
"
•
•
is essentially a linear motor used as an electrical generator:' (An
alternator is a type of alternating current (AC) electrical generator.)
The devices are often physically equivalent: The principal difference is in how they are
used artd Which direction the energy flows.
'
An alternator' converts mechanical energy to electrical energy, whereas a' motor converts
electrical energy to mechanical energy.
.'
Like. most 'electric motors and electric generators, the linear alternator works by the
principle of electromagnetic induction.
Electric Motor
•
•
•
•
An electric motor converts electrical energy into mechanical ellergy.
Most electric motors operate through interacting magnetic fields and current-carrying
conductors to generate force. although a few use electrostatic forces.
The reverse process. producing electrical energy from mechanical energy, is done bv
generators such as an alternator or a dynamo.
Many types of electric motors can he run a!' generators. and vice versa,
C
:t
3.00BJ"
After stu'
l' . D.•
.•
·tJF
f
,
t
t
•
•
3.1INTF
Electro~
in 18316
i
I
I
•
•
•
••
•
•
•
•
••
()
f
I
Ul\TJT-3 El\1F EQUATIO~S
I
..t'
. h
IS
ers,
N··'
,. Structure
ew : ".
Edition
••~ ..:7<3.0 OBJECTIVE
:Lil
INTRODUCfION
p.,-. '."
-.'
,. \,~i0;2E.M.FEQtJ.ATION OF AN ALTERNATOR '
.-'~ :9f'.~
~t':3.3FLUX TIIR{)UGH A SURFACE AND EMF AROUND A LOOP
-;:.:~::':.: .
.
••
"
"
• f'
••
.
.'
0".
:".
':0:<$.4 MAXWELL.FARADAYEQUATION
.~::'"
.
.'
_---....,._ ....5.. i",;:.
<,
•
~-----"'.:."f.';; '3.5 E(,ECTRICAL GENERATOR
,~
~(~
..
,
~~_.3.6ELECTRICALMOT{)R
•
~ 3.1 ELEcm.CAL TRAlNSF()RMER '
.....
,
3:811IT:US'SUM UP
••
•
, ';t9S0ME USBFULL BOOKS
W
3.11
.\•
•
••
•
•
•
I'
)w
they are "
3.0 OBJECfl~ES
.
:or converts
After studying this unit, you should be able to
irks by the
-nt-carrying
ix done by
I
Understand the concepts of Maxwell faraday equation.
Electromagnetic induction W<I' discovered independently by Michael Faraday and Joseph Henry
in IX31: however, Faraday wa-. the first 10 publish the results of his experiments.
I
t
..
Dt:fine emf equation.
•
f
I
-\)
•
3.1INTRODUCfION
l
.,
GLOSSARY
25
Faraday's
(
disk:
(
of
In Faraday's first experimental
demonstration
electromagnetic induction (August 1831), he wrapped two
wires around opposite sides of an iron torus (an
arrangement similar to a modern transformer). Based .on
'his assessment of recently-discovered
properties of
electromagnets, he expected that when current started to "
flow In one wire, a sort of-wave would travel through the
ring an'd .cause some electrical effe~t on the, opposite .side.
plugged one wire into -a
galvanometer, and watched' it' as he connected the other wire to. a battery, Indeed, he. saw a ..
transient current' (which he -ealled a "wave of electricity") when .he ~Connect~~the 'wire to the
battery, and another when he disconnected it.[41Within two months, Faraday had found several ,
other manifestations of electromagnetic induction. For ex,~ple,llesaw
transient currents when
he quickly slid a bar magnet in and out of a coil of
andbe generated a steady (DC) current "
by rotating a copper disk ~ear a bar magnet with a sliding.electrical Iead ("Far8day's disk").
(
RM.svalue~
. Er.m.sf
',He·
"IfKpahd
~)
C;)
••
.Er.m.~
(ti)Sorndirres 1
wileS,'
'becQmes:
•
Er.in.s I pha'
Faraday explained electromagnetic induction using-a Concept he called lines of force. However,
~)1beJine~
. scientists' at the time. widely rejected: his' theoretical ideas', mainly because they' were not.
,_.
forinulated mathematically.
An exception was'. Maxwell, who used Faraday's .ideas as the basis of
..
'r
.',
.,_
his quantitative electromagnetic theory. In: Maxwell's papers, the time varying aspect of
; electromagnetic induction is expressed as a differentialequation which Oliver-Reavisidettfer:red , '; '3.3 'Flux ....
to as Faraday's law even though it is slightly different in form from the original version of
'..
..
Faraday's law, and doesn't.cater for motionallyinduced EMF. Heaviside's version is
form
'Faraday's la'
recognized today in the group of equationsknown as Maxwell's equations.
integral ove
,:.
.
.
"
the
,
3.2 E.M.F EQUATION OF AN ALTERNATOR
'
~B
Let Z = No. of conductors or coil sides in series per phase
•c
••
cp=FluX per pole in ~
P= Nwnber of rotQrpo1es
N = Rotor speed in r.p.m.
•
a"
where dA ~
S·dA is
curve gen~
[done (peT'
electro mot.
In one revolution (i.e., 60IN -second), each stator conductor is cut by P cpwebersi.e.,d
cp=Pcp; dt = 60IN
Average e.m.f. in<:iured in one statoc ronductor
, ::d cp=pcp=p cpN
Ii ffi'N (Jj
lei-
volts
Since tiler are Z co.'1ductore in series per phase,Avetage e.m.fltDase
26
= PtpN*Z
ro
•
IEb"
where
I in webers._
\
\
I
L
•
••
•
••
•
•.,
()
,
=P<pN* 120f
ffi
P
C
(
f
•
•
C
I,
.'
= 2f<pZvolts
ation of
ipped two
oms (an
Based .on
erties of
started 'to
rough the
re into .a
he saw a
ire to the
id several
:';RM.s value of ernfphase =Average value/ phase * form factor
~>¥J, .' E!.m.s/).Xlase
.""
'·;j.lfJ(P
and K d arc the pitchfactorand
·...,,:·i···.::''.~''f'
•
•
•
the form
.
'
.
."
(ii)
..
'4JJecqmes:
were not'
e basis of
•
.
.
~,:'ii~thetums(I)perphasernther1hancOOductor.;Pei~arespecifiei:J,·in
However;.
"
.
1....
aspect of
e referred
'ersion of
distribution factoroftre armature winding,ihen,.
"
',-
:) current
k").
I'
",'
( i)
:Er.ntsl phase= 2.22 Kp Kd f<pZvolts
ents when
• '
=2f<pZ* 1.11 =2.22f<pZ volts
= 222 fcpZ volt'>
;,
.'1'
.
:l~r.in.s I phase
:.::_. ~
:;:-rJii1~lirie voltage will deJxni upoo ~the
~ "-
r.»
windingissti (x-:delta connected.
•
.'
t "i~';";';3""~""'F1""""""'u"""X"""Ih""''1,'00-'-.'' ' ' '
"
(ill)
= 4.44 Kp Kd f<pTvolts
,'"
J
that case.teq.fji)
•
gb-. -a-s-urf-' -a ....ce-,·-an-d-·
-EM
.....
· ·-F--·ar-ou~.·-:o....
d-1l-·.-oo,-· -.p-"----"----;__------
.,
,
,.'
.
farad~y's.lawof induction makesuse of the magnetic flux '<1>8 througha surface L., defined by an
integral :over a surface:
'.
.
~B
=
ff
B(r,t). dA,
1:(1)
where dA is an element of surface area of the moving surface L.(t), B is the magnetic field, and
B,dA is a vector dot product. The surface is considered to have a "mouth" outlined hy a closed
curve denoted OL.(t). When the flux changes,' Faraday's law of induction says thai l11" ',\ (lih
Edone (per unit charge) moving a test charge around the closed curve c~(i), called the
electromotive force (EMF), is given by:
lei =
i
I
where I£~s the maanitude
of the electromotive force (EMF) in volts and q)/i is the maenetic
flux
~
~
in webers. The direction of the electromotive force is given bv Leuz's law,
[
27
I
l
~.
II
.'•,
I
I
dcI>u
dt
For a tightly-wound
of N identical loops, each with the same <liB,
coil of wire, composed
Faraday's law of induction states that
1£1 = IV
dCPB
dt
(
<l? B
(
a single:
where N is the number of turns of wire and «l>8 i~the magnetic flux in webers through
"
,1"" ,
'
•,
loop.
"
,
.
'
.
'"
'
==('
::,
"
,..'
a! 1" The sign
.In choosing a .palhID.:(t) to find EMF. the path must satisfy the basic requirements ~at (i) it is
,closed path, and (ii) thepath must capture the relative motion"'ofthe partsof th~ circuit (th{,:
origin of the r-dependence in o:E(t». It is nota requirementJh~t}ge .PCithfQ}J.?rfa !ipe of~urrentt
flow, but of" course the.EMF that is found using the flux' law"
the chosen]
, be the EMF around ',,'
path. If a current path is not, followed, the EMF
might
not
Qc;,
the
EMf
d]jvjng'tlle
current,
.
' _'' "
.,
will
Example:
Spatially varying Magnetic
field
~
.
- ••
Figure 3: Closed rectangular wire'loop moving along x-)'
'axis ~t ve~9City v in magnetic field ,~ dllt, varies witq?~
-
...
'j'
,
•
.
.~
'
y-al(is'
~1
:,;~ "orin:('1
~',.~~e·ct,
ion,' .!
-,
.
'f;;{luX. lS t ',
'"
.
"'" ~iffer~ntll~
~
,.• "
POSition
-,F."
, .,
x.
,
~'.
>-',....
-~'-"
.•' ":" ,
,,::.-
}' ~_"-"
; ,"
•. ~
.."-
.;
, ..
,:,
'(where v =
C(),n~~er
~ase 'in
loop of wire in the xy-pJarie -tians1ateo in .tbe.:;r-~ite<:tloii"
at velocity v, Thus, the center of the loop at Xc satisfies:
~
, v = dxr idt. The loop has
In the y-direction and :
width :.t' in the x-direction. A time-independent but ,:.
spatially varying magnetic field B(.:c) points in the z- ' . as bef6r
direction. The magnetic field on lhe'left side is'B( Xc ~
The equ~
w I 2), and on the right side, is B( "xc + w / 2). The
xc-w/2
other meu
x~+w/2
electromotive force is to be found by using either the
Lorentz force law or equival~ntly by using Faraday's'inductiun law abOve.
me
ri~re'~~~~~2it!B~,:~~tar
·
,
e•
leqgdr[
.,
,Lorentz force law
Check.
Note: .,
methOd
=
A charge q in the wire on the left side of the loop experiences aLorentz force q v!< B k -q l'
W /2) j (j, k lJnit vectors in the y. and ;:.-directions; sec vector cross product), Icading to '
an EMF (work per unit charge) of v >{ B(xc - U' / 21 al~ngthe length ofthe left side of the loop.
On the right side of the loop the same argument shows IheEMFto
B(TC + wI2).The
two
EMFs oppose each other, both pushing positive charge toward the bottom of the loop, In the'
case where the B-field increases with increase in x, the force on the right side is largest, and the
current will be clockwise: using the right-hand rule, the B-field generated by the current opposes
the impressed field,ll~1The EMF driving the current must increase as we move c~llInterdockwise
(opposite to the current), Adding the EMF's in " counterclockwise tour of the loop we tind
B(.'(c -
be·""r
[= 1'1[[:1.1'('
l"
+ 1/'/21,t
i
B(I"
.
- I/'/:?\j
..
2X
......
," •
1. Defi~
•
•
••
•
••
•
•
•
................
............•
•
••
It
re same
q'B,-
, Faraday's law method
At anY'position of the loop the magnetic flux through the loop is '
c
v
»
1
<1) B = ± [, dy
c
,= i
•
•' v
(
•
..
••
•
.'
•
• '
•
±C' XC
,+
<
that (i) it is a~
! circuit (the ~
e of currentt
d the 'chosen]
rrent.
ring along x- "
t - varies
with';~.
,:~..'
•
'-.
'
B(:r)d.l:
.
' xc-wj2
B(x)dx .
xc-tc/2
'
~~.flux
1'!';
-:.
2
U'/
.
,..'
}'The sign choice is decided by whether
,;~,;~;
.or in .the opposite,direction. If. we
:/;airection as theB..:fleld of the induced
is -then (iIsing 'the <:hain' nile of
,'.: .'_.
_
..
.
'.'
,
"~~ifferentiation of an integtalj..
?:.:~';.'
-:-
l: ~taqgular Ii
e'-i:Oir~tio~ =
t Xc satisfies \
iiiection arid :t,
pendent but
its in the zIe is B( Xc 'W / 2). The "
19 either' the
< B k = -q
.'
•
.0
rIC+W/2
",'
the
the normal to the surface points-In
same direction as
take the normal to the surface as pointing in, the same
current, this sign is negative. The time derivaiive of the
differentiation or·.the general form 'of Leibnizrule for
.
. t
'
..'
.r: -]-
~. -'.
..
"Ii- tody
'd<I>n
.- -d
_,'_,=" (_)-,_.,
dt
. dxc
- (_ )vf[B(Xc
0
XC~W
/'2
dxe d:.rB(x) --.-,
dt
+ w/2) - B(xc - u,/2)]',
.>(where v = dxc I dr is ~herate of rrtotion of ~l}eloop in the x-direction ) I~ding
\'
, " ' n4> B'
E = - -of'
to: •
,;,. .
"
. .
-= i1t[B(xc + w/2)
. '.
- B(xe :_ w/2)] ,
as bef6re.
The equivalence of these two apprl}aches is general and. depending on the' example. "ODeor the
other method may prove more Iml.ctica1.
'.
Note: I.Give your answer 'in the space given below
2. Check your answers with those given at the end of the 'unit.
I'
t),leading·to
of t'he l;op.
'2). Thelwo
loop. In the
gcst, and the
rent opposes
terclockwise
~ find
1. Define Lorentz force method.
...............................................................................................................................................................
............................................................................................................. _
.
,
faraday's,
Example: Moving 1001' ill uniform Magnetic field
·_····c
~
"-= .""~. . .: ';'
CD.....
t .t
. An il~tuit~(
.'the circuit \
independe(
argument is
Figure 4: Rectangular wire loop rotating at
(
angular velocity.o in radially outward pointing
" To u~e th~
magnetic field B'of fixed magnitude. Current is
, the nrns 11
collected by brushes attached to top and bottom;
discs', which have conducting. rims:
-
~~:hs:;~
J__
.
,
,,.
C~l1{ntz force
law method
. ';
.'-
C)
a
F.i~ure.4 sho~s
~pi~dle..forrned oLt~odist;s·;
_
with-conducting zims 'and "a conducting loop"
attached y~rtjc~lly between these rims, :The entire Assembly spins~n a magnetic field that points 7
radially outward, but is, the same' magnitude regardless .of" Its lli{¢ctiQn. A radially oriented
collecting return loop picks up current from the conducting rhos. At the location of-the collecting
.return loop, the radial Bvfield lies' in the plane .of the collecting Ioop, so the collecting loop
contributes no flux to the circuit. The electromotive force is to be found directly and by using;
Faraday's law above.
. .
.
As an exarr
~directipn •
In th.is.ta~e
~ of area A
,to the flu,.,
Ie
<1>.
..
where~h.
current Ioo
:~orti9~q.
..n·}I-,;~
..
In this case the Lorentz force drives the current in 'the two vertical arms of the moving loop
downward, so current flows from the top discto the bottom disc. In the conducting rims' of the
discs, the Lorentz force isperpendicular to the rim, so rio EMF is generated in tbe rims. nor in
the horizontal portions of the moving loop. Current is transmitted from the bottom rim to the top
rim through the external return loop, which is oriented so the B-field is in its plane. Thus, the
Lorentz force in the return loop is perpendicular to the loop, and no EMF generated in this
return loop. Traversing the current path in th~ direction opposite' to the current flow, work is
done against the Lorentz force only in the vertical arms of the moving loop, where
_",
"
-yo
is
in agree~
Now let'.
segments.
suggest.
for the fir.
i~mlater.
F=qBI',
where v= velocity of moving charge
••
Consequently.the EMF is
{; _:_Bet = 81' tv': .
(~r
where v = velocity
conductor or magnet and I ~ vertical length of the loop. In this case the
velocity is related to the angular rate of rotation by \' = r co, with r radius of cylinder, Notice
that the same work is done on any path that rotates with the loop and connects the upper and
lower rim.
•
=
II •
.,/1·l.
!
r
...•.
•
•
o
E:
,,_..
.'~
r:~
,_.
••
••
•
•
••
••
C1
J
I
Farad<Jj"s law method
I
. An intuitively appealing but mistaken approach to using the flux rule would say the flux through
, the circuit was just <l>B
B w I, where w
width of the moving loop. This number is timeindependent, so the approach .predicts incorrectly that no EMF is generated. The flaw in this
argument is that it fails to consider the ~ntire current path, which is a-closed loop.
=
I,
I
I
I
••
•
•
.'•
I
I
rotating at
ard pointing
" To use the flux rule, we have to look ,at the entire current path, which includes the path through
e. Current is
, the rims .in the. top and bottom discs. We can choose an arbitrary closed path through the rims,
and bottom ;' ,
:.and the rotating loop., and the flux Jaw will find the EMF around thechosen path. Any path that
has a segment attached to the rotating loop captures the relati ve motion of the-parts of the circuit.
,
.
)f .two discs. .
As an example path, let's traverse, the circuit in the direction of rotation in the top disc, and in the
ucting loop
. direction opposite to the direction .of .rotation in the bottom' disc ,(shown 'by arrows in '~igure 4).
i that points i
In thiscase, for the moving loop at
angleB fromthe collecting loop, a portion of the cylinder
Ily oJiented .•
, ~' of area A = r £ 9 is part ofthe circuit. This area is perpendicular to the B~fietd, and so contributes
ie collecting, S
to the flux an amount:
lecting loop \
an
nd by using
•
••
"eJ
«
••
loving loop
rims of the
rims. nor in
11 to the top
!. Thus, the
ated in this
-w, work. is
.~
c!
c;
.'•
.'
<]) B
= - Br()f ,
,
.'..,~
.l
•
.,.'
f
=
,is case the
jCJ:. Notice
upper and
.
.·where the sign is nfgative because the right-hand rule. suggests the B~field g_!!nerated.by' the
~urr~"t loop .is opposite Jnrdir~1-io~ to, .the applied B field. As this js the .only time-dependent
;.portion of the flux, tl,teflux 'lawpredicts .an EMF of
. .,
'c
d<J>'B (_,
- ----
,, dt
:::;::
Bd"" ,
-.
B''1'{-;df]
'df
in agreement with the Lorentz fo~ceJaw calculation.
Now let's try a different path. Follow a path traversing the rims via the opposite choice of
segments. Then the coupled flux would decrease as e incre.ased, but the right-hand -rule would
suggest the current loop added to the applied B-field, so the EMF around this path is the saine as
for the first path. Any mixture of return paths leads to the samc result for EMF, so it is actually
irllmaterial which path is followed .
Direct evaluation of the change in flux
Figure 5: A simplified version of Figure 4. The loop slides with'
velocity v in a stationary. homogeneolls B·field.
a
The use of closed path to find EMF as done above appears to
depend upon details of the path geometry. In contrast. the
Lorentz-law' approach is imkpcndcllt of sllch restrictions. The
followinf dis(ussion is in!clll.kd to provide a hetter understanding
llf the cyui\akncc
01 paths ~lI1dc"cal'c the particubrs of path
31
selection when using the flux Jaw .
(
.• Figure 5 is an idealization of Figure 4 with the cylinder unwrapped onto a'plane. The same path- .
related analysis works, but a simplification
is suggested. The time-independent
aspects of the'
circuit cannot affect the time-rate-of-change
of flux. 'For example, at a constant velocity of ;
_ sliding the loop, the details of current flow through the loop are not time dependent. Instead of ~.
'concern over details of the 'closed loop selected to find the EMF, one can focus on the area of B-)
\ix
.
(
i;
field swept out by the moving loop. This' suggestion amounts to finding the rate at which flux is
cut by the eircuit.(lsllhat notion provides direct evaluation of the rate of change 'of flux, without ;;
concern over the time-independent,de!ails of various path choices around the circuit. just 'as with ..~.
the Lorentz law approach, it is clear that any two paths attached to the sliding loop, but differing
. in how they cross the loop, produce the same tate ..of-change of flux.
v>f
..
Els"
.B.is'
t
",nfigure 5 the area swept out in: unit time is simply;z0 / dt ;:;:_
v !,,~ardless
sel~e.d closed path, so Faraday's 'aw of induction -provid~s the EMFas:' .
~
. -'
d<l!B
e..- -.d t
.. ,.
~
.~This equatic
of the details of the ,~ ~;;;taw,'How.
:t:Situations w
~'~o"re'lectro.
':!~01'
';J<.
~rfield.
;;,-:1t tan also.
.
tI
f
l
'
.·e
= tsoe
'.
.f
r._
,
(
J
..
1~
~
ttt,e
''ibis ~th'independence of ~F'shows
that if
~i~Jit~ j~p i§ ~l~J~Y a. solid ~nd~~i~g ':~ f;
plate;or even some complex warped sQrf~, the anWYS1S1s'1:1\e same:"fJiid fhe flux JD tbe area :. .'
swept out by the moving portion of the circuit. In a-similar W;iY, if the .liding loop in the drum
generator of Figure 4 is replaced by a 360° solid c~)Oducting.cylinder,tl.e swept area calculation
is exactly the same as for the case with only a Ioop ..That is, the EMFpredicted by Faraday's law
is exactly the same for the case with a cylinder with solid conducting walls or, for that matter, a .
cylinder with a cheese grater for walls, Notice, though, tharthe current that flows as a result of
this EMF will not be the same because the resistance of the circuit determines the current.
~..
r
.
1
.•
•
CheckYourProgress -2 '
-Note:
'!
1. Give your answer in the space given below.
2. Check your answers with those given at the end of the unit.
.!
1. Define faraday'S law method .
....._
••••••••••••••••••••••••••••••••
_
.."! ••••••••••••••••
3.4 The Maxwell-Faraday
_ •••••••••••••••
_ ••••••••••••••••••••
-.._
_ •••••••••••••••
_ .•._
_
__
dr'
Both
cxplaine.
of curve (
when the
equation
Figure 6: An illustration of Kelvin-Stokes theorem with surface
boundary fir:. and orientation 11 set by the right-hand rule
z
.
•••••••••••
I: its
I
,
t
I
.....
"
lI
y
II,
--
!
The int.
hand sid,
thlough.
•
••
•
••
•
••
()
l
changing· magnetic field creates an electric field; this phenomenon
well-Faradayequation:I17J
I
I
I
e same path.pects of the
velocity of ••••
it. Instead of
J
I
I
'r
v X
" ,
E('I 1 t)' _-
-
lS
described by the
DB(r,
t)
_ _;;_ _ __:_
at
V xdenotes curl
Eis the electric field ,
'B is the magnetic field
I
I.
~11A'lLIIUIl'
appearsin modem ·Sc!s.pfMaxwell's «iuahons>and I~
~f~~'~~to as Faraday's
. becauseit contains 9nlY-pa(liai time derivative~,~ts'illmli~!liioil'is restricted to'
11UQ"V"" where the test charge 1s'statiopary ina.time
~aryi9gm~giJeti~fi~!a;~lfdoesnot account
b{;elecIDomugJllet'icinduction 'in sjtuations whe¢ '~;c~ged ~cl¢.:~s m9ring ina magnetic
I
I
•
•
•
I
•
'
.,
•
c
•c'
e,
••
••
C:
.'.'.;
t.
.'
I.'
also be written in an i~tegral fonD by the Kelvin-Stokestheorem~181
.
'~()nducti'ni'
in 'the;,area
in the drum .
calculation'
iraday's law
,~ij"7\whf~te;the
movement
ent,
.:
of the derivative before the integration requires: a time-'-indepe~dent surface
(considered in, this context to be PM of the .Interpretati9n of the partial derivative), and as
indicated in Figure 6:
' -" . ,
.l: is ~ surface bounded by the.closed contour (Jl:;both 'E and ol: are fixed, independent
lime
.,
E is the 'electric field, ,
, df an infinitesimal vector element of the contour ~l:,
B is the magnetic field,
,
dA isan jnfinitesirnal vector element of surface l: , whose magnitude is the area of
. infinitesimal patch of surface, and whose di.r:ec.lj~ is orthogonal to that surface patch.
of
is
:1i1
Both d( and dA have a sign ambiguity; to get the correct sign, the right-hand rule is used, .IS
explained in the article Kelvin-Stokes theorem.For a planar surface ~, a positive path element lIf
of curve
is defined by the right-hand rule as one that points withthe fingers of the right hand
when the thumb points in the direction of the normal n to the surface L
ar.
uface
I: its
The integral around ill: is called a path integral or line Il1legml, The surface integral al the righthaud ~ide of the Manvdl-Faraday equation is the expliclt cxpreSSi('!1for the magnetic nU\ <Ill{
through:r.. Notice that a nOll/,ero path inter-ral for E is different fro 11 1 Ihe hehavior of till' cieclril..'
c
field gcncra.ed by charges. A C!iill£l-gen-::r4ltcd
E-field can be expressed as the gradient
scalar field that is a solution to Poisson's equation, and has ~1 zero path integral. See g
of
,
Example:(
theorem ..
The integral equation is true for all)' path if£, through space, and any surface 1: for which
, connectioIl""
path is a boundary. Note, however, that irE and 1: are understood not to vary in time in th
observer ot
formula. This -integral form cannot treat motional EMF because '1: is time-independent. Notice
using bot~
well' that this equation makes no reference to EMF -E, and indeed cannot do so wi'mo'ut.:'~'- the 'lo~
introduction of the Lorentz force law enable a calculation ofwork.
v~
"
.;~
Figure 7: Area swept out by
element dC'of curve pl:.jn time-_-._. lit when moving
with. -,,,"llnI' ••ti •.,,,.
~ vector
-.
-.
v,
to
,
..
"
n;;;,"
0
':
.u~ng(he
.
.
CQlfiplbte';Lbrenti-1"orte ·to"callcUl'ltelt;':~
-'theitMF,
.:<_
!;.'
. _
'f\,
"",'
Max'W'h
...•direction gT"
,
~
~ ' __~'~,'.
-.._\,;
1
-
.
:
" .. ,. .
~ statement (:If Faraday's IlfW'of induction
, general _than ih.e irl~~grill
torm of the Maxwell-Faraday equation is (see 'LO.reqtt force);
-_
,,:
......
II>
•
~3/1(t) dA::~;r,'i{:
/."
. .L(:)i~(r,t)~' vx)(r, t)).~
: ~
-:
_
":...~.
" _
•
..,
'''.=.
'.
Here.the .c~
where o:E(t) is the moving closed path bounding the moving surface 1:(1), aitd v is the velocity
movement: &>.e~gure 2. NOtice that the ordinary time derivative is
not:3 partial"
derivative; implying the time variation of };(I) must be ind~ded' in the .differentiation. In
integrand the element of the curve df moves with velocity v. .
usea,
Figure 7 'provides an interpretation of the magnetic force contribution to t~_EMF on the left side
of the above equation. The area swept out by segment df of curve 01: in time dt when movj ng ,
with velocity v is(see geometric meaning of cross-product):
.
~
dt
Q
Solving fOI)
Using theft
EMFaroulfp
,so the change in magnetic' flux 8«1>B through the pOrtion of the surface enclosed by i1L in time dt
IS:
,d.6«PB
dt
•
••
••
•
••
= 'l
.
= -B· df X
.S.
'l'
=-V
X
B· d£ .
and if we add these 8$wcontributions
around the loop for aU segments dl, we obtain the
magnetic force cbntribution to Faraday's law. That is, this term~s related to motional EMF.
which i~ e.
advanced I,
impressio"
thought the
•o
•
(.9
,
I
I
.Example: viewpoint of a moving observer
f
I
. (:.;Revjsiting the example of Figure .3 in a moving frame of reference brings out the dose
connection between £- and B-fields,.and between motional and induced EMF's.II<J1·Imagine an
{)bserver of the .loop moving with. the loop. The observer calculates the EMF around the loop
.._.,"'
....__ both the Lorentz force .law and Faraday's law
induction. Because this observer moves '.'
the loop, the obs~rver sees no movement of theloop, and zero v' X B. However, because the'
'~f':t~~R~fiel'ld
va?es with position x, the moving observer sees a t~rile-varyi~g magnetic field, namely:
<
•
of
~.
I
I
I
I
k is a u~it vector pointing in the z-:directioil.I20~
e 'to'
I
'YI·>i:·.JAlI,\:UU;
•
••
B(r~.f)).~
force law versjon '
Maxwell-Faraday equation says the moving observer. sees an electric field Ey in the ygiven by:
. .
.'.
.'
... , ......... ". "n'
I
•e
-.
iducfion
:e):. ' ....
t)
Here the .chain rule is used:
1
dB
dt
0
•
••
.,
•
••
•
C)
dB
d(x + t,t)
---;----'---:-----'= -.dB-11 . .
d(x
+ ,vt)
dt
'dx
Solving for Ey, to .within a.constant that contributes nothing to an integral around the loop,
Using the Lorentz force law, which has only an electric field component, the observer find,' lhe
EMF around the loop at a time 1 to be:
• .
.
ill:. in time dt
= '['([B(.re
Ie obtain the
IEMF
+ w/2, I) - E,A:rc - 'll'j2, t)]
+ u'/2 + 'vt) - B(x~'. - tl'/2 + rt)]
, .£ = -f[Ey{l'C
which is exactly the same result found by the stationary observer: who sees the centroid Xc has
advanced to a position Xc + \' I. However, the moving observer obtained the result under the
impression that the Lorentz force had only an electric component. while the stationary observer
thought the force had only a magnetic component:
CJ
.1
t,
.'.'
•
I'
t
«
(
35
€
Faraday's
When a pe_p:
. is created~.
law of induction .
Using F.araday's law of induction, the observer moving with Xc sees a changing magnetic n,
but, the' loop does not appear to move: the center of the loop
is fixed because the mov
observer is moving with the loop)'he flux is then:
.
'xc
d.ectri ca.Ii'
. , Fot exampt.;
-: --1:
is the Farat
5, or direct
same way_
where the micus sign comes from the normal to the surface pointing-;Oppositely to the applied
fie1d. The EMF ,rom'Faradafs law of.induction is now:
.....
..•.
"
>il~; ...'.'
E' ==
- ....'... B
fit
. ·il··:
;..:_
j~titfl,'Z'
o
.
-..
>
J.!f
·X.····
e
,c -.". •.•• .
.".0
·l' :r:c+w/2' d ;.: ':~~"..
dy...".
_'.
.• B(
dt
~(itwI2 d '.. ... .' ..
'~-!:.:'~":~B(x'+ t)t)'f)
xc-w/2
'. «c:-;11,)/2 . t:lx ,
X
..'.0 •.
+- vt)i!.x
.'
•
a.r..'
1¥trc:+1t!/2 +}It)-- B(xc
.:
r:
"
- 'W/2 + vt)]
; '.
.", ~.;
.~
l :", ,'.
. ~.
;same ~iIJt_;
f,d~riv~tive passes. through" the. Jnt~wt!()I)~be~allS€t .the lim.its
-:igi¢gritioo"haYe :nQ·:.t{~:'!~peqdeoce.· Aghln; the .chain J\11e[w~·.)!Se4.~()~t)'riY~rt.
'{lOU~,~I~iihieffiicie:nt.
derivative to an:x-d~vative.. . . l<..: "
.'
',;0
-1'h~.~tjJllC
t~e
< '-C
-'.
,"';
-
.:
,
.
-.
"
The: stationary bbserVer1hought the ·EMF was a motional,£MF, while the moving
thought
it was
.. __ .
.... a.ni.n!l~ed EMF.
L\n!~I".n./p.r,_
-'
Cbeck Your PrOgress'~ ~.
Note: ) . Give your an'swe~in the sPlice given below.
2, Check your answers with those given at t.}1eend of the unit.
1.Define 'Ma:t~t1f1a~a.y equation. '
•.. '.,._i.
•-
••••••
!
~••••••••••••
'
-~
__
~~_~
•••••
.
••••
_••_~
••••
_ •••••
- •••••
- ••••••••••••
~••~.-•.••~•••~~--
- •• - •• '1.-••• - ...............••
- ••••••••••
_ ••••••••••••••••••
'!•••••• ~••••••• - ••••• ~.-.-
•• -
••••••.
Although .J..
mecbanis •
c(}nducto_
Fara~ay eq
an ititlue('.,J
the '1T1Q~in,[
magnetIc.
more infor
above ex•
- ••••••.••••••••••••••••
3.6Elect'
Figure 8: Faradllyis disc electric gene(titor>The disc rotates with angular
rate (I). sweeping the conducting radius circulady in th~ static magnetic
field B. The magnetic Lorentz force v x B drives the current along the
conduCling radius to the conduCting rim, and frOJll there the circuit
completes through the lower brush and the axle supporting the disc.
Thu~, C'urrentis generated from 'meC'hanical motion.·
The EMF generated by Faraday's la\\ of induction due to relative
movement of a circuit and a magnetic field is the
electrit;;.li generators.
- phenomenon ·underlying
.
.
36
...---
..... _
....."'- .....
•
An electtj._
Faraday.
Then by W.
that will.
irreversittt
f/> Ii I dt eqtl
••
•
••
••
•
•
•...
e
When a permanent magnet is moved relative to a conductor, or vice versa, all electromotive force
;is cr~ated. If the. wire is connected through an electrical load, current will flow, and thus
.:electrical energy is generated, converting the mechanical energy of motion to electrical energy.
UA.'."'''' . exa,mple, the drum generator is based upon Figure 4. A different implementation of this idea
Faraday's disc, shown in simplified form in Figure 8. Note that either the analysis of Figure
direct application of the Lorentz force law, shows that a solid conducting disc works.the
way.
' .
.
.
Faraday's disc example, the disc 1S rotated in a uniform magnetic field perpendicular to the
causing a currentto flow in the radial arm due to the Lorentz forcedt is. interesting ;,to
~'''''''''T''n', how it arises jhat mechanical work is necessary to drive this current. When the
flows through the conducting rim, a fuagnetic field is ;generated
thls;~ertt
ruV"l';H,··Ampere's.circuital law (labe1ed "induced 13":.in FigJre _8):;.The'pmt_tlills·:beComes')fu
:fecltrorna'~
~.n
e.t thatresists rotation oftheui'sc (an 'CxampJe'c>f:Leriis ;law)r:un~the-tfai,igidi.Qf ihe';~
. the return current flows from the rotating arm through the far-side of the rimjo tbeJ;ottom :
The B-fi~ld induced by this return current.opposes the.applied a-field, ten~ingto'detre(ls~ ,
through that side of the circuit; opposingthe increase influx due to fota~ion..On the
figure; the return (!UITeOrtlOw8 from the rotating .arm .through:the "ear sl(te--'of ille''dili'
bottom bnish~The 'induced ~~fie)d increa s es the flux -on this side ofthe circuit, oPposiQ.g.
;ilp,,.rpn~" in flm .
rotai1on?rhus, both sides of the circuit ~~n~te ~~r~frig'~~~
14eeniet.2~v·
.• _ .
moving.;·despite this r~tivefo~.
i~:tC~aclly.
._.....
~.~ .~._. ·.,nel.]~Y l'~eilC~r~j~ed.{plus
,ene:n.
i?;.Y~fl~t~.~e ~(l,f~ion, ..1QlIJ~·bAAting;' <,u.l~ ~ller .
~(ttnlmoIJ-to all ,g~~tofS,;CP.J1Vqt},iJgJmeQbarii~;jl.;eJ.l¢Igy10·"
by
near
to
e9iJ~!
'u..,
ng oh.serverifi:·Ahhough Faraday's law always describes the working of .electrical .~eqt!ratot:S...the:detail~d
mechanism can differ 'in different ,Cases. When the magnet is rotated an>und ,a ,stationary'
~onductcir, the changing,'inagn;tic}ield .create!; an electFi'c field, as deScribed;.J;>y thlf l"1axw~1J- .
Fiira~ay equatioo; an~ that electric 'field pushes the chwges throughthe wire~ 'f\li.s.case is called
an mdueeil EMF. On the' other haiid~ when the magnet i~ st<ltionary a_n~the'conducwr 4~~fltated,
themQving charges experience a magnetic force. (as described by thelore_ntz fo,r~_law), and tgis
'. magn·etic·force p~hes the charge~ !hrough the wire. This case'is c~lled~lilqiiop(zI~,
(~or
more iDformatron on moti6nal EMF,.iriduced EMF, FaTaPay's law, and the Loretitz force, see
above
example,~ and
'see GriffithsJ; ~.j.:.
.
-.,'
: ..... , ',~
~ _': •• ~) .•-e_-:-: ~'U
•
•
•
•
t
tic l11:.tgnetic
,nt along the'
. the circuit
ng the disc.
1(\ relative
I generators.
An electrical generatOr can" be run ~'back\\',Irds" to become ,a mO~9r~~
f:oLex~~ple~ 'Yft!\ W~
Faraday disc, suppose a'DC currenlls driven, through the ~()riducting T~dial pnn"by .a yol~agc.
Then by the Lorentz force law. this, tr<lVclingcharge experiences a force in the Ilwgrictic fteld IJ
that will .turn the disc in
direction ,given by :I;leming's left hand rule. )n .the, absence of
irreversible effects, like friction or Joule heatin&. the dISC turns at the rate necess~ry t~, make d
cjJ8! dt equal to the voltage driving the current.
'u'
~..,
."
.1
3.7 Elcclrica: transf ormcr
The EMF predicted by Faraday's law is also responsible for electrical transformers. When the
electric current in a loop of wire changes, the changing current creates a changing magnetic field.
A second wire in reach of this magnetic field will experience this change in magnetic field as a
change in its coupled magnetic flux, ad (l)s I d t. Therefore, an electromotive force is set up in .'
the second loop called the induced EMF or transformer EMf. If-the two ends of this loop are
_connected through an electrical load, current will flow.
.'
'.
.Magnetic fi.o,,"meter
" F~day's I!lW IS used for measuring th€!flow of.electrically cOr\ductive'Jiquids and slurries. Such
instruments are"called magnetic flow meters ..The,il)du.ced voltage '£ generated in the magnetic
field B que to a conductive liquid moving at.velocity. v is,thUs given by:
where { is the distance between electrodes in the ~~gn~tic flow meter.
?-••8 LET
US SUM
·UP
.....
'•. The Lorentz force. drives' the ~u~nt in Ute two ~e~ical arms of the movingJoop
downWard, so current flows fmin the top disc.to the bottom d.isc. ,
• The stationary observer thought the. EMF was a motional EMF, while the moving
. observer thought it was an induced EMF .
.~ The EMFgenerated by Faraday's law of Induction due to relative' movement of a circuit
imd a magnetic field is the' phenomenon underlying electrical generators.
• 'When the magnet is rotated.around a statiOllary c~dLJctor, the changing magnetic field
creates anelectric field. as described by the Maxwell-Faraday equation, and that electric.
field pushes the charges through the wire. This case IS called an induced EMF.
• .' An electrical generator can be run "backwards" tp.~ome a motor.
• When the electric current in, a loop of wire 'ctumge~. the changing current.creates a
changing magnetic field. A second wire in t:each of this magnetic field will experience
this change in magnetic field as a change .in its coupled magnetic flux, a d q>B I d r.
Therefore, "an electromotive force is set upin the second loop called the induced EMF or
transformer ~MF.
'e1ectr<J.
..
If the'"
•
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, Farad ~
voltat
• Then, :'
field.
• In the
rate n.
trIJ
•
l Electrica! Macbines bySK Bhaua~barya, TataMcHill Publishers'
2.A Text Book Electrical Technology by BL Theraja, S.Chand Publishers
3.0pemtion and Maintenance of Electrical Machines by B.V.S, Rao, Khanna Publishers. New
Delhi.
4.Electrical Technology by Edward Hughes. Addision - Wesley Intcrn.uionul Student Edition
5. Performance & Design of AC Machines by MG Say. CBS Publication. New Delhi
(I. Electrical Encrgy SystemsTheory by Elegerd. Tata McGraw Hill Co. Nc\\' Delhi
•
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:Electric Machinery by Fitzerald, Tara McGqlw Hill Co, New Delhi
Electrical Machines(Sigma Series) by Kothari, Tat" McfirawHill Co, New Delhi
'~lt:;"UJ'''''UMachines by Kothari & Nagarth, Tata McGraw Hill Co, New Delhi
1I..1::J"",
and Electronics Engineering by Vikramaditya Dave, Lakshrni Publications (Pvt)
New Delhi .
.
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section 3:0
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magnetic
section 3,0 ..
'Your Progress - 3
section .~.2'''
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!The.EMF generated by Faraday's law ofinduction due ttl reJati~ ID{)veriienrof a circuit
.1·~d a:Qlagneb.cfield is'the phenomenon underlying electri.~!tl:~~-9-eraw%..
'
. ~'.~':,"--1_" _~ :~.~
•. : ... _ __ •. __ , _ ._".:
. ;Wll~n a. permanent magnet is moved relative to ::t; conol1ctof;"'or 'vice' versa, .an
I
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._
,
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moving
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'electromotlveforce is created. .
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If the' wire is connected through an electrical load, currerit will
and tHus'eJci;ttlcal
energy is generated, converting the mechanical energy of 010ti6n to electrical energy.
.le<:tl'i.caJ motor
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flow:
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f a circuit
.An electrical generator can be run "backwards" to become a motor.' For example, with the·
ietic field
11electric
•
creates a
cperience
ct>u I d 1.
IEMF or
'.
Faraday, disc. suppose a DC current..is driven through the conducting radial ann b) a
voltage.
'
Then by the Lorentz force law, this traveling charge .experiences a force in the magnetic
field B that will turn the disc in a direction given by Fleming's left hand rule.
In the absence of irreversible effects, Eke friction or Joule heating, the disc turns at the
rate necessary to make d cjJB / di equal tothe voltage driving the current.
t :
'f
.
•
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ers, New
it ion
•
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The EMF predicted by Faraday's law is also responsible for electrical transformers. ,
When the electric current in a loop of wire .changes, \be cntirlglng 'current creates ~
changing magnetic field, A second wire ill reach of this magnetic field will experience
this change in magnetic field as a change in its coupled magnetic flux, a d <VI! / d 1.
Therefore: an electromotive force is set up in the second loop called the induced EMF or
transformer EMF. If the two ends of this loop are connected through all electrical IO;JJ,
currenl will flow.
e
. pump,
Unit 4: Performance of Alternators
wI(
mechanical
.turbine orf
.. air or any
i
Structure.
4.00BJEct,IVE
4.1 INTRODUCfION
f'
C'
-
4:2 EXCITATION
.4.3 DC ,EQUIVAI:ENT CIRCUI!
·4.4 VECHILE-MOONTED
GENERATOR
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A.n e~ectf1(
requires •
LEt US SUM UP
coils are D'
energy,'""
.4.10 SOME USEFULLBOOKS
4." J ANSWER TO CHECK YQURPROORESS EXERCISE
.' ·Smaller·~
. curren~p.
4.12 GLOSSARY
- -:the .annan'
4.0 OBJECTIVE
magnetise
current in
generate.
the
1.
Very lar.
• ~fine
•
COre
pC~~'J4;v;alent circ~it.
State the performance Qf~D alternator:
coils of til
stations •
.largestgeT
4.1 INTRODUCTION
In electricity generation, an electric generator is a device that converts mechanical energy to
electrical energy, The reverse conversion of eleorrical energy into mechanical energy is done by
a motor; motors and generators have many similarities. A generator forces electrons in the
windings to flow through the external electrical circuit. It is somewhat analogous to a water
jo
40
•
••
•
••
•..
••
•
C)
o
, pump, which creates a flow of water but does not create the water inside. The source of
mechanical energy may.' be a reciprocating or turbine steam engine, water falling through a
turbine or waterwheel, an internal combustion engine, a wind turbine, a hand crank, compressed
air or any other source of mechanical energy.
-,
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, I
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....
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"
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.
"
small ~lY 1906s.75 ;f(Y~~d,_irectMye'n power station AC a1temat~r, with~a separate;be"lt-
,-:....",".'.......
".... ex(:ityr,generator.
or
;',
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.
,
'.
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.
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An' electric ;ge~eiator
~l~c~motor
that 'uses field coils rather than perman~t rnagncls
requires a current to be present
the field coils for the device to 'be' able 10 work. If~. field'
coils are not-powered, the ~r
m:a generator can spin without producing any usable ,electrlC31
energy, while the rotor of a motor may not spin at all.
.
•
•e
••
••
•
Smaller generators are sOIlletinieS ~elf-ixcited,which means the field coils are powered-by the
current produced by the generator Itself. The field .coils are connected in series or panul¢l With
the arinattire winding. ~en.. the generator first' starts to turn, the small amount of remanent
magnetism present U;i the iron W~ pI'Ovides a magnetic field to .get it started, generating a smaIl
current in the armature, This flows through the field .coils, creating a larger. magnetic field whiCh
generates a larger anIlatUre--cqrr.em.Tb,is "bootsttaP"process continues until the magnetic field In
.the core levels off due to saturation and the generator reaches a steady state .power output.
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Very large po~er station generatOrs often utilize a separate smaller .generator to excite; the field
coils of the larger. In the event of a severe widespread power outage where islanding of power
stations has occurred, thy stations may need to perform a black start to excite the fields of their
'largest generators, in order to restore customer-power service .
.1 energy to
! is done by
rons in the
to a water
41
4.3 DC Equivalent circuit
,G- - - -
I
R~,
Equivalent circuit of generator and load.
,.G = generator
VG=generator open-circuit voltage
, RG=generator internal resis.tance
, Vr=generatoron-load voltage
RL=loadresistance
'
The equivalent circuit of a generator and.load-is shown
. ' j.,
,.' '-,',
in the diagram to
right The 'g~neratoi's)V o an~ ,RG ,para.nei~:~#ih ~}d~{~in$Q- by
"!eas,uring the' windin~, resistance (corr'7t~ t(;;pp~~~smt}elJlpe~~~~~;~~~~~~e
?pen.circuit and loaded voltage for a defined currentt~d. ~~,.;, "
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J. Give your answer inthe space given below.
Note:
~ 2.. Check
your answers with those givenat the end of the-dnit, ,
1. Define ex~itation.
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generators
Early motor vehicles until about the 19605 tended to use DC generators with electromechanical
, regulators. .These have now been replaced by alternators with built-in rectifier circuits, which are
less costly and lighter for equivalent output. Automotive alternators powerjhe electrical systems
on the vehicle and recharge the battery after starting. Rated output will typically be in the range
5Q-l00'A at 12 V; depending on the designed electrical load within the vehicle. Some cars now
have .electrically-powered steering assistance and air conditioning, which places a high load on
the;el~rical'~ystem.
Large commercial vehicles-are more liketytol~se/24 V to give ~Ifficient
power at the 'S~rter motor to turn over a large diesel 'engi ne. Vehiole :alternators 'do not use
pern1unenJ in~gnets and are typically only 50-60% efficient ''O'!6r a wide -speed range:I.!1
Moto':Cyc1ealternators often use permanent magnet stators Illade with hire ~1rth m~gneis. since
they can be'made smaller and .lighter than other types. See also hybrid'vehic1e.
Sonie of the smallest generators commonly found power b~'ycle lights.' These tend 10 hc 0.5
ampere, permanent-magnet alternators supplying 3-6W at 6 V,or 12 V. Being powered hy the
rider. efficiency is at a ·premilllll. ~l) these may incorporate rare-earth magnets and arc cksigncd
and manufactured v.ith greal precision. Nc\eJ1hekss. the Ilw,imum efficiency is onl) ,IWUlld
8Wk for the best of th~se generators-6()'.1c is more typicat--duc in part to the rollill!,' fridiOIl <it
the tyr!?-gellcmt5)r interface from poor ,i1igl1l1lcnl. the smal! sill' uf the generator. bearing i()sse~
and cheap design. The liSt' oj' PCllll,Ult'll( Illa~"d ...mC,IIl' Ihai l'lficicllCY falls even ftinhci ,I{ hi~h
speeds because the magnetic field slrL'll~th l'<lIln6t be controlled in any way. Hub gL'llcralol~
-.f2
. 'tluman p0WJ1r.
,of some DPP
trainer, or ~
'cases are d~
watts on
" complete exl
Portable mQ
al$
cJOCkWO~
riD
" 4.7 Linear
tID
In the simp.
t
solenoid - a
Far~lday'sla.
the Faraday.
·1
••
•
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••
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remedy many of these flaws since they arc internal to the bicycle hub and do not require all
interface between the generator and tyre, Until recently, these generators have been expensive
" , and hard to find. Major bicycle component manufacturers like Shimano and SRAM have only
just entered this market. However, significant gains can be expected in future as cycling becomes
more mainstream transportation and LED, technology allows -brighter lighting at the reduced
I, current these generators are capable of providing.
(
! '
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:'Sailing yachts may use a water or windpowered generator to trickle-charge the batteries. A small
;propellerl wind turbine or impeller-is connected to a low-power alternator and rectifier to supply
~currents of up to 12A .at typical cruising speeds. '
,','
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~4.5' Engine-generator
I'
L~,n'engine-generatotis the combination of an electrical generator and an engine tprime mover)
~moiJnted together to 'form a single piece of self-contained equipment. The engines used are
~sWlIJypiston engines, but gas .turbines call also be,i!se<J.'Many different versions are available .,
~gfng from verysmall portable petrol powered sets to-large turbine installations. ,,'
,,'
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41
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;,A generator can.also be (lovell by human muscle power (for instance, in field radio s~ti~n
:tquipme~t).
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hanical
!ch are
ystems
~range
}Iuman powered direct current generators arecommercially' available, an.I have been the project
of some DiY enthusiasts. Typicallj operated by means of. pedal power, a converted bicycle
trainer, or a foot-pump, such generators can be practically used to charge batteries, ~i1d-jnsome
cases are designed .with an integral inverter. The average adult could generate abou(125-200 '
watts on a pedal powered generator, but at a power of 200 W, a typical healthy human will reach
,:- 'complete exhaustion and fail t~' produce any more power after approximately '1.3 hours,ISI
Portable radio receivers with a crank are made to reduce battery purchase requirements. s}!e .'
'clockwork radio.> '
.
rs now
4.7 Linear electric generator
in the simplest form of linear electric generator. a sliding magnet moves back arid forth through 11
sol~noid - a spool of copper wire. An alternating current is' induced in the loops of wire hy
Faraday's law of induction each time<the magne.t slides thn.)ugh. This type of generator is lIsed in
the Faraday flashlight. Larger linear ele<;tricity generators are'used in wave pOwer schemes.
0.5
the
;igncd
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•
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r~~6Human powered .electrical.generators
.
i
43
"
Ct.eck Y(Ju: Progress - ')
•
Note: 1, Give your answer in the space given below.
I O.EI ectrict
pd, New 1"',
C1
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1. Define linear electric generator.
..................................................................
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i
:1 'f'~'I. See secf'l
~A·
------~--~------------------------------~~--~------------~---------~'
4.8 Tachogenerator
{:; .~,:.'.~.;~.
~,
_:_:.:.:.....::~=e.=::::.:===-...:......------------_,...,.------------...:......----~---..,--~,...,--___,.---·h~: _-'-----
I>
Tachogenerator are frequently used
power tachometers i~ measure .the speeds '<)f electric's :~"~..12GL0i)
1",'
motors, 'engines, and the equipment 'they power, Generators :'generate 'voltage . roughly~d
:,.i_ Engine gc>
proportional to shaft speed. With precise construction and design; generators can ·be built to"
produce very precise voltages for certain ranges of shaft speeds
~,
~
to
• Ar8
mox
4.~LETUS SUM UP
•
An electric .generator is a device that converts mechanical energy to electrical energy. :.~
The reverse conversion of electrical energy into mechanical e~ergy is done by a motor; \'
motorsand generators have many similarities.
• .An electric generator or electric motor that uses field coils ratherthan permanent magnets
requires a current to be present in the field coils forthe device tobeable to work.
• . An engine-generator is the' co'mbination of 'an electrical generator and an engine (prime
..mover) mounted together to form a single piece of self-contained equipment.
• Tachogenerator are frequently used to power tachometers to measure the speeds of
electric motors, engines. and the equipment they power.
•
"
1
l.Electrical Machines by SK Bhattacharya, TataMcHill Publishers
2.A Text Book E1ectrical Technoiogy by BL Theraja, S.Chand Publishers
3.0peration and Maintenance of Electrical Machines by B.V.S. Rao, Khanna Publishers,
Delhi.
4,Electrical Technology by Edward Hughes, Addision - Wesley International Student Edition
5. Performance & Design of AC Machines by MG Say. CBS Publication. New Delhi
6. Electrical Energy System- TI,c()ry by Elegerd. Tata \lcGraw Hill Co, New Delhi
7.Electric Machinery b) Fil/.er,dd. Tala McGraw Hill Co. New Delhi
8. Electrical MachinestSium.: Series) by Kothari. Tara McGrav. Hill Co, NL'\\ Delli!
I).Electrical Machines b:, i-(oth:!il s: Nagarth, Tal;, I\k(irdW Hill Co. NCII Del:l:
I
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Publications (Pvt)
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ra,lt·C:l.r
. is the fOnl~ih*iaK_6fan·.ele~n~riext~ot.zall~,c~n
engi:ne (~rjme
~~ffJr1~S~:l~'~~!~~~:
cinij~t)J'nQ\;:lltl~..lOgetli¢f Jo~f.()WJ:,~,!!p~l~~i~
h~enlgin~s:JlS(_~_.areuswdly p17ston-e~glD~s!,blltgaS.t_~thm~~~SQb¢used.
',-.'
,~l!ll\y~!!f(ler~ot versions:areav~l*ble ~;'-i:a.nging
V¢ry$tn~ll])()rtabiepetrolpowered
c.. t,~ t",. J""r:"...
e installations.
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fr<»n
UI"· ..·..
Tacihoi~n:¢rator.are
frequently used -to power tachometers to measure the speeds of
el~tripmolots, 'engines. and the equipment they power.
'~ne~(jrs
generate voltage roughly proportional to sh:lft spe¢:
precise construciion and (leSig~; generators can be built to: produce very precise'
:,vol~agesfor certain ranges of shaft speeds
<
, .:with
ishers, New
Edition
.'
45
- ---.f
BLOCK 2:
(
SYNCHRONOUS l\1.0.'rOR
Struct~
1.00(1
This being the first block of the course, an attempt has been made to define and consolidate
concepts with the help of examples. The important concepts that one must be able to describe.
have been discussed in the block.
One must be clear about these basic concepts in order to lise a lot of functions and facilities/ ..
which does exist in a synchronous motor. These blocks describes the concept of synchronouj],
motor of Working'Principle, vector diagram and power factor, This basic focus of theblock being;'.
that-you should be able to study effect of change in excitation.
..
.
:;'
This block consists of four units:
.
1.1llCJ;
1.2P...fi'
·i.30~
Ij4s~l
••
-Unit I: Defines the basic principle and working of synchronous motor,
1.5SPB
Unit 2: Focus on the vector diagram.
1.6USE
.
Unit 3:. Provldes the-focus
on the effect of change
in excitation .:
··f.
.
Unit 4: ,-'Provides
the overvie'J' ofPow~r factbr improvement.
..
.
,
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1.7A1fY
l.8ue
J.9S~
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l.Il ~
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After stu~
.tf'-
· 1\.
V
A classic'
pa...sing '.
\\ hich dri \'
conditior.
motor.
\~';l
flt>qIlI:IK'_
46
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block bein~;
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OF SYNCHROl'\OUS l\10TOg
Structure
1.1INTRODUCTION
id facilities';:
;ynchr~>nou~:;
~
--_._- ._----------_._----------
----UNIT 1; WORKING PRINCIPLE
I.OOBJECfIVES
,
•
•
•
••
•
•
•
•
.,
•
••
•
•
•
•
•
•
.•,
•
•
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_------------_._-_._---
1.2PARTS
. 1.30PERATIONS
1;4~TARTING METHODS
1.5SPECIAL PROPERTIES.
I.~USES
J.7ADVANTAGES
.,1.8LET US SUM UP
. J .9S0~E USEFULL BOOKS
1.11 GLOSSARY
1.00BJECfIVES
•
•
Understand the Basic principle of synchronous motor
Analyse the concepts such as : the special properties of synchronous motor.
1.1 INTRODUCTION
A classic synchronous electric motor is an AC motor distinguished by a rotor spinning. with coils
passing magnets at the same rate as the alternating current and resulting rotating magnetic field
which drives it. Another way of saying this is that it does not rei) on slip under usual (lj1crating
conditions and as a result. produces torque at synchronous speed. Contrast this with an induction
motor. which must ~;!ip in O]"(kT to produce torque. They operate xynchronou. ..j.\ ,\ iil-! liuc
frequency A~ with ~qullTt:l-,:;t~e induction motors. speed i-, determined by the number ()l p:lir" oi
·n
(
ailablc in sub-fractional self-excited
sizes to high-horsepower direct-current excited industrial sizes. In the fractional horsepower
range, most synchronous motors are used where precise constant speed, is required. In highhorsepower industrial sizes, the synchronous motor provides two important functions. First, it is
a highly efficient means of converting ac energy to work. Second, it can operate at leading or'
unity power factor and thereby provide power-factor correction.
poles and the line frequency.
Synchronous
motors are
.!\
1'=(
"
where.v is the
number .of (
brushless wo
synchronou.
There are two major types of synchronous motors; non-excited and direct-current excited, which
have no self-starting capability to reach synchronism without extra excitation means, such as.
,Check YourC"
electronic control or induction. But with -recent advances in independent brushless excitation
control of the rotor winding set that eliminates reliance on slip for operation, the brushless
C'
wound-rotor doubly-fed electric machine is the third type of synchronous motor with all the}i!': Note: I. Gt)
theoretical qualities of the synchronous motor and the wound-rotor doubly-fed motor combined, ~ ,
2.Ch(
. such as power factor correction, highest power density, highest potential torque density, low cos.t11
electronic controller, highest efficiency, etc.
'.,
-,~,
1. Define sye
Non-excited motors are -manufactured in permanent magnet, reluctance and hysteresis designs.'J
......................
. Reluctance and hysterisis designsemploy a self-starting circuit and require no external excitations',
supply. Permanent magnet designs require electronic control for .practical operation (see~~
Permanent magnet synchronous generator).
.
..~:
PARTS.
~
Reluctan~e designs have ratings tnat range from sub-fractional to .about 30 hp. Sub-fractional·;.
horsepower motors have lowtorque, and are generally used for instrumentation applications.}
A synchron.
Moderate torque, integral horsepower motors use squirrel- cage construction with toothed rotors .. [
When used with an adjustable frequency power supply, all motors in the drive system can be
• The •
controlled at exactly the same speed. The power supply frequency determines motor operating .
windja
speed .:
rotat!'!"'"
• The •
Hysteresis motors arc manufactured in sub-fractional horsepower ratings, primarily as'
suppli
servomotors and timing motors. More expensive than the reluctance type, hysteresis motors are
mage
used where precise constant speed is required.
The sl
The.
DC-excited motors ~ Made in sizes larger than 1 hp, these motors require direct current
supplied through slip rings for excitation: The direct current can be supplied from a separate
Large mach.
source or from a de generator directly'conn~cted to the motor shaft
lubricating ••
<
0
..
....................•
.
Slip lings and brushes are used to conduct current to the 'rotor. The rotor poles connect to each
other and move at the same speed - hence the name synchronous motor.
Synchronous motors tull under the category of synchrouous machines which also includes the
alternator (synchronous generator). These machines are commonly used in analog electric
clocks. timers and other devices where correct time is required.
The "synchronous
speed" of a synchronous
motor
h
dCiL'rIllllled by the follow ing formula:
1.2
•
J.30PER4
1
!J".
t
TIll: llperat_ji'
b) it poly-pie
field winding
field andro.
! field. ihl'
•
•
•
•
•
••
•
:1)1);'.
•.,
()
,
(
(
self-exci ted
norsepower
d. In high. First, it is
leading or
(
ns, such as .".
C
(
..
ited, which
.j
,Check Your Progress - 1
t,
•
.1
1. Define synchronous motor?
.
_
......................... ~
sis designs; .: '
J .excitation
ration .: (see ~ ,
:*
.
.
,1.2 PARTS
.'
'1:
.a-fractionalf ~
..
c
•
••
•
•
•
•a)
e
.'•
.•,
.1
•el
.'
f
.e.
vith all the~'
Note: I.Give your answer in the space given below.
combined,
.y, low co~tt ,
C'.
••
•w
120 ~< f
where v is the speed of the rotor (in rpm),Jis the frequency of the AC supply (in Hz) and 11 is the
number. of magnetic poles. Different from all other synchronous motors, the synchronous
brush less wound-rotor doubly-fed electric machine operates from sub-synchronous to supersynchronous speeds or twice synchronous speed.
.
; excitationx
e brushless.i
f'l
•
1'=
~
',..,
pplications ..,;
thed rotors ..
tern can be
of operating
,
A synchronous motor is composed of the following parts:
•
•
imarily as
motors are
•
current
a separate
ect
-ect to each
ncludes the
00 electric
'"
rula:
II
The stator is the outer shell of the motor, which carries the armature" winding. This
winding is spatially distributed for poly-phase AC current. This armature~ creates a
rotating magnetic field inside the motor.
.
The rotor is the rotating portion of the motor. It carries field winding, which may be
supplied by a DC source. On excitation, this field winding behaves as a permanent
magnet. Some machines use permanent magnets in the rotor.
The slip rings on the rotor, to supply the DC to the field winding.
The stator frame contains and supports the other parts and may include bearing housings.
Large machines may include additional parts for cooling the machine, supporting the rotor,
lubricating and cooling the bearings, and various protection and measurement devices.
],3 OPERATION
I The operation
a synchronous motor is simple to ilTldgine.The armature winding. \\ hen excited
Ii h) a poly-phaseof (usually
3-phase) supply, creates rotating magnetic field inside the motor. The
iI
I field winding. which act-; "" iI permanent magnet. simply locks in with the rotating magnetic
i
l field and rotates al\)n~ \\ ith it. During operation. ~I'thl' fit'ld lock-, in with the rowtin~' magncric
field. the motor is said tn hi III -ynchronization.
UI1L'l' (ill'
motor
fr'_'l)u'..:'!i() \\'hLn
is
the
ill
'lPIT~lti()n.
n1tli~H
load
the speed 01 tIll' 111(lt,l: t-, dependent onlv Ill' th, supply
~!h." h;~
..'a< du\\-n load. th(' iihHOC illll" llUI
1;-.. increased beyond
_fl)
ur
wi«,
JeaJ
synchronization
i.e., the applied load i~ large enough to pull out the field winding from following
the rotating magnetic field. The motor immediately stalls after it falls outof synchror..izatioli.
1.4 STARTING
thet
•
METHODS
The(
indue
•
Synchronous motors are not self-star-ting motors. This property is due to the inertia of the rotor.
When the power supply is switched on, the armature winding'and
field windings are excited. . . The leadinj,.
correction. ~ ,
Instantaneously,
the armature winding creates a rotating magnetic field. which revolves at the
designated motor speed. The rotor. due to inertia, will not follow the revolving magnetic field. In ,factor, wh~
practice, the rotor should be rotated by some other means near to the motor's synchronous speed , Josses. In s~·
'excited, sotl
to overcome the inertia. Once the rotor nears the synchronous speed. the field winding is excited,
lagging pow
and the motor pulls into synchronization.
.
'.
factor).
increasing tl
The following techniques are employed to start a synchronous motor:
toco~ect tl>
A separate motor (called pony motor) is used to drive the rotor before it locks in
•
l.{j USES
synchronization.
..
.
•. The field winding is shunted or induction motor like arrangements are made so that the
_ synchronous motor starts as an induction motor and locks in to synchronization once .it
• Sync
is.
reaches speeds near its synchronous speed; •
• . Reducing the input electrical frequency to get the motor starting slowly. Variable-frequency:'
drives can be used here which have ReCtifier-Inverter circuits or Cyclo converter circuits.
• lm'_
If.
e
•
· Lo'
an.
• MQ
I.What are the starting methods in synchronous motor?
.•........................................................................................................................................................
.................................................................... -
1.5 SPECIAL P·ROPERTIES
.
I
When the field excitation voltage is decreased, the motor runs in lag)2.ing.p\>\,.er faeloff'
The PO'\ cr factor b) which the motor lags varies directly with tl1l: drop in cxcitution]
voltage, Thi-, condition ie, called under-exclt;\tiol1.
When the field c\L'lI~ili(lll \oltagc i:-- III<td,:equa) to the rated \(llta~,' Ih,' IIHl\()l rnn- :II
unity power betllr.
•
•
--I ~~
Synchr?nolls motors show some interesting properties, ~hich ~nds applic."tions ~n power factor,
correction. The synchronous motor can be run at lagging, unity or leading power factor. The.
control is with the fH?IJ excitation. as described below:
f:~
,
•
1.7 ADVA9
~
Synchronou
•
Spec
Al.
•
• Th.
loud
ob.
con,
The
..
(d..,
!
Th•
•
•
••
•
••
•
•
•
(J
..
(
(
(
c
(
€
f"
•
•
•
.'•
•
•
•
xu following
nization.
When the field excitation voltage is increased above the rated voltage, the motor runs at
leading power factor. And the power factor by which the motor leads varies directly with
the increase in field excitation voltage. This condition is called over-excitation.
• The most basic property of synchro motor is that it can be use both as a capacitor or
inductor. Hence in tum it improves the power factor of system.
of the rotor.
; are excited.
valves at the . The leading power factor operation of synchronous motor finds application in power factor
correction. Normally, all the loads connected to the power supply grid run in lagging power
netic field. In
,factor,
which increases reactive power consumption in the grid, thus contributing to additional
ronous speed
losses.
In
such cases, a synchronous motor with no load is connected to the grid and is run overng is excited,
excited, so that the leading power factor created by synchronous motor compensates the existing
'lagging power factor in the grid and the overall power factor is brought close to I (unity power
factor). If unity power factor is maintained in a grid, reactive power losses diminish to zero,
increasing the efficiency of the grid. This operation of synchronous motor in over-excited mode
to
correct the power factor is sometimes called as Synchronous condenser.
locks in into
I
1~6USES
e so that the
.ation once it
o
••
..••
•
•
•
.
'Synchronous
motors find applications in all industrial applications where constant speed
.
IS necessary.
•
Improving the power factor as Synchronous condensers.
•
Low power applications include positioning machines, where high precision i-. required,
and robot actuators.
•
Mains synchronous motors are used for electric clocks.Record player turntables
ble-frequency
r circuits.
Q
.,
•
,
1.7ADVANTAGES
···············_·····1
Synchronous motors have the following advantages over non-synchronous motors:
I
facloll
power
zr factor. The,
I
•
•
•
•
P()\'.
.
, In
er faci(lLi
..
I
eXClta1H'11
•
•
Speed is independent of the load. provided an adequate field current is applied.
Accurate control in speed and poxition lIsing 0pen !(IOP controls, egostepper motors
They will hold their position \.\hell a DC current is applied to both the stator and the rotor
windings.
Their power factor can be adjll'tcd to unity by using a proper field current relative 10 the
load, Also. a "capaci Ii\c" pth\ cr Iactor, (current phase leads voltage phase). can he'
obtained by increasing thi-, CUII\'nlslightly. which can help achieve a better power factor
correction for the whole install.uion
Their construction "il()\\\ I"l! ilkll';t.'c'd electrical efficienc , when a low speed i~,l'l'LjUlrcd
(as in ball mill, and <imil.n ,IPi~,,!;lltl,!,
They run either .u ihc <vnchronou-, ',pct'd 01 the y do not run at all.
~
"I
f
(
~.
swring metl
Lxamples
bruxhlesv DC electric motor.
•
•
.•
stepper motor.
Three-phase AC synchronous motors.
Switched reluctance motor.
Synchronous brushless wound-rotor doubly-fed electric machine.
•
4'
1.8 LET US SUM UP
• Synchronous electric motor is an AC motor distinguished by a rotor spinning with coils
passing magnets at the same rate as the alternating current and resulting rotating magnetic
field which drives it.
• The~e are.two major types of synchronous motors: non-excited and direct-current excited.
('
C'.
•
•
•
•
•
•
•
o
I.Electrical Machines by SK Bhattacharya, TataMcHill Publishers
3.0peration and Maintenance of Electrical Machines by B.V.S. Rao, Khanna Publishers, New
Delhi.
4.Electrical Technology by EdwardHughes, Addision - Wesley International Student Edition.
5. Performance & Design of AC Machines by MG Say, CBS Publication, New Delhi
6. Electrical Energy Systems Theory by Elegerd, Tata McGraw Hill Co, New Delhi
7.Electric Machinery by Fitzerald, Tata McGraw Hill Co, New Delhi
8. Electrical Machines(Sigma Series) by Kothari, Tata McGraw Hill Co, New Delhi
9.Electrical Machines by Kothari & Nagarth, Tata McGraw Hill Co. New Delhi
IO.Electrical and Electronics Engineering by Vikramaditya Dave, Lakshrni Publications (Pvt)
Ltd, New Delhi
1.10 ANSWER TO CH~CK
voun PROGRESS
'.
EXERCISE
o
•
1.11 GLOSSARY
A se"
synchrom;
The fiel«'
synchrono
reaches
Reducin~,
drives ca!
--------
----------------------------------------------------------
Synchronous motor
• Synchronous electric motor is an AC motor distinguished hv a rotor spinning with coils
;
-(
t
passing magnets at the same rate as the alternating current and resulting rotating magnetic i
field \\ hich driv cs it.
f
Anothe: \\ay of s,lying this is that it docs not rdy on sl;p under INial operating condition, 1
and a~ ;t result. pruduL'cS torque at xvnchrunous speed
Contra-a this \\ ith an induction 1l101(l1. which must slip in order 1(' produce It'H.jUC.
•
••
•
•
•
•
•
•••
•
•
•
•
•
•
"
(J
Staring methods
•
•
.'
A separate motor (called pony motor) is used to drive the rotor before it locks in into
synchronization.
The field winding is shunted or induction motor like arrangements are made so that the
synchronous motor starts as an induction motor and locks in to synchronization once it
reaches speeds near its synchronous speed.
Reducing the input electrical frequency to get the motor starting slowly, Variable-frequency
drives can be used here which have Rectifier-Inverter circuits or Cyclo converter circuits. .
~ with coils
Ig magnetic
€'
e"
~nt excited.
I
.,
shers, New
.'
Edition
•
•
•
•
uions (Pvt)
i)
Q
•
•
.;.'
•
•
•
•
.'.'
f.;
•
•e)
•.j
.'
(
{
with coils
;g magnetic
i!
l
I
z- condition- f.
l
que.
I
I
I!
t
53
(
drives. If th.
such that
t'
UNIT 2 VECTOR DIAGRAM
be very cl~,
Structure
speed driv~>
from the illf'
are known':
2.00BJECTNE
•
2. I INTRODUCTION
2.2 SYNCHRONOUS MACHINE STRUCTURE'
2.2. I STATOR AND
The pn
allows fort'
.
.'
Vector.di~'
ROTOR
2.2.2 DISTRIBUTED WINDING
2.3 LET US SUM UP
.
2.5 ANSWER TO CHECK Y.QUR PROGRESS
f6GLOSSARY
2.0 OBJECTIVE
In this lesson we are going to discuss in detailed manner about:
,.
Basics of vector diagram
• Synchronous machine structure .
2.1 INTRODUCTION
A synchronous machine is an ac rotating machine whose speed under steady state condition is
proportional to the frequency of the current in its armature, The magnetic field created by the
armature currents rotates at the same speed as that created by the field current on the rotor, which
is rotating at the synchronous speed, and a steady torque results,
Synchronous machines are commonly used as generators especially for large power systems,
such as turbine generators and hydroelectric generators in the grid power supply. Because the
rotor speed is proportional to the frequency of excitation. synchronous motors can be used in
situations where constant speed drive is required, Since the reactive power generated by a
synchronous machine can be adjusted by controlling the magnitude of the rotor field current,
unloaded synchronous machines are also often installed in power systems solely for power factor
correction or for control of reactive kYA 11m'. Such machines. known a~ synchronous
condensers, may be more economical in the large sizc~ than static capacitors,
With power electronic variable voltage variable lrcqucnc , I V\'\T) Pl)\\ L'J'slippliL". synchronous
motors. especially those with permanent mugnct rotors. arc widely lISL'dfor \ ariable speed
l
I
1
Youcan:t
factor is a ~
canalsoae
reactance,'
create
rep:esent'
th.
resistance;
variation.
changes.
•
•
•
•
•
•
•
•
•
()
I
-----_
drives. If the stator excitation of a permanent magnet motor is controlled by its rota; position
such that the stator field is always 900 (electrical) ahead of the rotor, the motor performance can
be very close to the conventional brushed .de motors, which is very much favored for variable
speed drives. The rotor position can be either detected by using rotor position sensors or deduced
from the induced emJin the stator windings. Since this type of motors do not need brushes, they
are known as brushless de motors
I
(
I
I
\
The principles of an A~ synchronous machine are illustrated with dynamic vectors. This
allows for an understanding of the interaction of various machine parameters.
l
r
Vectordiagram of synchronous motor
~
I
•
S'nwu ... ous.u.daiae
I-
••
.'•
'M
•
•
8
••
•.'
•
•
•
•
condition
rotor, which
I;
e:
•
,
Ii
(
IS
.atcd by the
.'.;
.'•
••
lpower mg1e = i:50 I
•
Ipower factor = lagging I
I
er systems.
3ecause the
be lIsed in
erated by a
eld current.
-ower factor
vnchronous
~nchronouiublc speed
!ii
-
You can adjust three bus parameters, terminal voltage, lirte current, and power factor. The power
factor is adjustable, as it is the phase angle between the terminal voltage and the line current. You
can also adjust two machine parameters, the armature resistance {~) and the sum of synchronous
reactance, and armature reactance (x$ + x.:£). These values are multiplied by the line current to
create the appropriate voltage drops. The synchronous impedance voltage drop js then
represented by the black vector. This is the vector sum of the voltage drops due to armature
resistance, synchronous reactance, and armature reactance. You can observe the power angle
variation as the angle between the terminal voltage (green) and the generated voltage (Eg)
changes.
55
1.Explain'
-
·············
....·C·
....................
f
izSYNc..
~ ."_:k'
f'l
t
2.2.1 Statoe
The armatC'
and is usual1
;.current, or'
1~.",,2S.ool
--
~·::~n
'~IXtac~"'1
- - -
•
.~'
used with ,.
rotoraru/s('
rotor 8trUFe
while salien
The pictun4t
turbine gen.
-
•
•
---
•
IJIO'Wl' qIc = 18.00 I
I,_...rxa = aaly I
- -- - -
•
•
••
Note: I. Give your answer in the space given below.
56
Ii
t
.
••
•
•
•
•
••
•
•
fJ
1. Explain synchronous condenser?
......................................................................................................................................................................
..............................................................................................................................
2.2 SYNCHRONOUS MACHINE STRUCTURES
2.2.1 Stator and Rotor
The armature winding of a conventional synchronous machine is almost invariably on the stator
and is usually a three phase winding. The field winding is 'Usually on the rotor and excited by de
- current, or permanent magnets. The de power supply required for excitation. usually is supplied
-rhrough a dc _generator known as exciter, which is often mounted on the same shaft as the
synchronous mac.hine. Various excitation systems. ~s.ivg ac excit.er and solid state rectifiers are
used with large turbine generators. There are two typt;s of rotor structures: round or cylindrical
rotor and salient pole rotor as illustrated schematically in the diagram below. Generally. round
rotor, structure is used for high speed synchronous machines, such as steam turbine generators.
while sa1ient pole structure is used for low speed applications. such as hydroelectric generators.
The pictures below show the stator and rotor t1f 8.' hydroelectric generator .and the rotor .of a
turbine generator.
.
.
I
I
I
Flux
peti'l$
•r
t
J,
(b)
(3)
Schematic illustration of synchronous machines of
(a) round or cvlindrical rotor and (b) salient rotor structures
57
•
the induce('
the diagral
and the PIt'
is ready to
in electric(
SI
where ~
€',
t,
Cl
e
C)
,
"..t-cooled I'OlCiI'd the 100-MVA ~
~
(Brown
..
•
•
•
Bovtri OotpotWiOtl.)
4.
of
•
e
C'
e
•
•
C
A great
nf
1t
consider
varies for
I"
e=-•
Angle in Electrical and Mechanical Units
Consider a synchronous machine with two magnetic poles. The idealized radial distribution of
the air gap flux density is sinusoidal along the air gap. When the rotor rotates for one revolution,
58
For a ge~
•
•
•o
••
•
•
•o
t
\
the induced emf, which is also sinusoidal. varies for one cycle as illustrated by the waveforms in
the diagram below. If we measure the rotor position by physical or mechanical degrees or radians
and the phase angles of the flux density and emf by electrical degrees or radians, in this case, it
is ready to see that the angle measured in mechanical degrees or radians is equal to that measured
in electrical degrees or radians, i.e.
I
f
(;
t
€,
where
e is the angle in electrical
degrees or radians and
em the mechanical
angle .
.•
'
•
•.,
B(G) & e(wt)
_<, /.~_.
Q
\/
j\
c
••
••
•
•
•
•.)
•
.;
Ii
••
.'."
II
C
(
I---.
B(6)
/
C(ltJt)
\
\
\'
;r
n
em
0\
o
i2:IT
1l"
\
\
i
\
,
\
\1
J!
\. X ,
•
s
!
.\._...\j
3rr
\
I
\ i
4IT
6&wt
;
\\_/·V
Y /
(b)
Flux density distribution in air gap and induced emf 1D the phase
winding of 3 (3) two pole and (b) four pole synchronous machine
A great many synchronous machines have more than two poles. As a specific example, we
consider a four pole machine. As the rotor rotates for one revolution (qm=2Cj), the induced emf
varies for two cycles (q = 40); and hence
.tribution of
~revolution,
It
(J
= ::.e",
For a general case, if a machine has P poles, the relationship between the electrical and
I
59
(
§~
mechanical units of an angle can be readily deduced as
p
AC'
&
e =-fj
-,
con
,!;
• Taking derivatives on the both side of the above equation, we obtain
P
(u =-(U
"
'"
where w is the angular frequency of emf in electrical radians per second and wm the angular
speed of the rotor in mechanical radians per second. When wand wm are converted into cycles
per second or Hz and revolutions per minute respectively, we have
-
P n
•
ij
•
Tli{
stf'l
thC'
I.Electri.
2.AText B
3.0peratC>
120f
Delhi.
4.Electri~
5. Perfo",
6. Electric
7.Electri.
8. Electric
9.Electri.
IO.Electri.
Ltd,Ne~
n·=--
or
S~
2.4S0~,
f=-2 60
,
•
p
where w=2pf, wm=2pn/60, and n is the rotor speed in rev/min. It can be seen that the frequency
of the ind uced emj' is proportional. to the rotor speed.
2.2.2 Dlstributed Three Phase Windings
2.SANSf
The stator of a synchronous machine consists of a laminated electrical steel core and a three
phase winding. Fig.(a) below shows a stator lamination of a synchronous machine that has a
number of uniformly distributed slots. Coils are to be laid in these slots and connected in such a
way that the current in each phase winding would produce a magnetic field in the air gap around
the stator periphery as closely as possible the ideal sinusoidal distribution. Fig.(b) is a picture of
a coil.
'Q
Check \
). s
•
Check'"
2.•
Note:
•
I, Give your answer in the space given below,
2.6GL.
J.\\'hat arc the synchronous machine structure?
..........
................................................................................ -
~~
.."
••
-.
•
••
•
•
•
•
•
Svnchrc:
..~.~
,
- ~
•
•
~~~
l
!
l
•
I
"
(J
"
_----2.3 LET US SUM.
(
(
e
c
•
•
cC'
.'•
•
•
•e
Cl
•
C'
••
c
c
&
•
eJ
e)
.'.,
(
..
..
_------_
...
--_ .. -
-- ------
2.4 SOME tJSEFULL BOOKS
rito cycles
I.Electrical Machines by SK Bhattacharya, .Tatalvlclfill Publishers
3.0peration and Maintenance of Electrical Machines by B.V.S. Rao, Khanna Publishers, New
Delhi.
4.Electrical Technology by Edward Hughes.Addision - Wesley International Student Edition.
5. Performance & Design of AC Machines by M" Say, CBS Publication, New Delhi
6. Electrical Energy Systems Theory by Elegerd, Ta\a McGraw Hill Co, New Delhi
8. Electrical Machines(Sigma Series) by Kothari, Tata McGraw Hill Co, New Delhi
9.Electrical Machines by Kothari & Nagarth, Tata McGraw Hill Co, New Delhi
J O.Electrical and Electronics Engineering by Vikramaditya Dave, Lakshmi Publications (Pvt)
Ltd, New Delhi
frequency
ld a three
that has a
I in such a
:ap around
picture
2.5 ANSWER TO CHECK YOUR PROGRESS
or
I.
•
e;.
•
•
•
•
-----------_._-_
re angular
••
.'•..
--_._.-
ur
A synchronous machine is an ac rotating machine whose speed under steady state
condition i~ proportional to the frequency of the current in its armature.
Synchronous machines are commonly used as generators especially for large power
systems, such as turbine generators and hydroelectric generators in the grid power supply.
The armature winding of a conventional synchronous machine is almost invariably on the
stator and is usually a three phase winding.
The stator of a synchronous machine consists of a laminated electrical steel core and a
three phase winding
•
«
------_
See section 2.1
2. See Section 2.2
2.6 GLOSSARY
Synchronous machine
.................
t
l
machine
an uc rotating
•
A synchronous
c
condition is proportional to the frequency of the current in it" arrn.uurc
T;11.' magnetic field created by the armature current, rot.ue-. ;:1 ILL' <urnc speed
IS
61
machine
whose
"'jl~'cd under
steady
,h
<uue
that
created by the field current on the rotor, which is rotating at the synchronous speed, and a
..
_~___f
steady torque results.
Synchronous machines are commonly used as generators especially for large power
systems, such as turbine generators and hydroelectric generators in the grid power supply.
STRI
0,
f
1.0
Synchronous Machine Structure
•
•
•
Stator and rotor
Distributed winding
Angle in electrical and mechanical units
J.l
It)
1.2
.~
1.3
IC,
..
3.4
L'
3.5
~
3.6
••
••
3.7
A
3.8
Gi
3.00B"
•
•
•o
•
II'
B
3.11Nit
•
changes
gene rat.
altcrnatj,
parallel,
\entric~
l'onducfl!!"
hlond
t
I
1
I.
•
••
•
•
•
•
•
•
•
•o
"I
reed, and a
f
rge po wei
ver supply.
-----'----------
--------------
STRUCTURE
(
C
1.0
OBJECTIVES
t
J.l
INTRODUCTION
.,.'
1.2
EFFECT OF CHANGING EXCITATION IN ONE OF ALTERNATOR
1.3
PARALLEL OPERATION
3.4
IN FREEQUENCY CONDUCTANCE
3.5
LET US SUM UP
3.6
SOME USEFULL BOOKS
'3.7
,ANSWER TO CHECK YOUR PROGRESS
3.8
GLOSSARY
.,
•
•.,
•
•
.'•
3.0 OBJECTIVES
G
Ct
.,
•c'
•
•
•
•
•.,
.'.'
••
c)
'J
.,
.J
C'
f
f
,_-_-
UNIT 3: EFFECT OF CHANGE IN EXICITATlON
_.
•
In this lesson we shall discuss about CHANGE IN EXICITATION.
going through this lesson you will be able to:
Basic effect of changing excitation
After
3.1 INTODUCTION
Change in excitation of one of the alternators does not change wuttful components but
changes wattles components resulting ill change in power factors of alternator-. The l'1.·Ollnmic
generation of alternating
current frequently involves parallel operation of two or PI', ,!-alternators. Direct-current generators excited to the same terminal voltage may he connected in
parallel merely hy Cl'lllleL'ling together terminals of like polarity. An important component of the
ventricular \O!U!11l' l11l';"1IIl'd lISill~ the conduct;llIce catheter technique
i~ due It' parullcl
conductance (Vc ). \\ hich results from the extension of the electric field beyond the ventricular
blood pool,
,
t
l
t'
Cbecl Your Progress=
Note:
I
(
e
f
1. Explain the effect of change in excitation?
..................................... _
C
.
...................................-
.
(I
f'\
€\
3.2 EFFECT OF CHANGING EXCITATION OFQNE OF THE ALTERNATORS:
Change in excitation of one of the alternators does not change watt full components but changes
wattles components resulting in change in power factors of alternators.
,:-'
~~
.. When thA)
If alternators (a) and (b) in Fig. 20-8 are supplying a load jointly and the field excitation of
machine (a) is reduced, the division of power load will not be affected. However, a circulating
current will be caused to flow around the load circuit formed by the two alternators. "This
circulating current will be leading with' respect to the voltage of alternator (a) and willthus
supply the excitation deficiency by armature reaction. Furthermore, the circulating current will
be lagging with respect to the voltage of alternator (b) and so willdetract from its excitation. The
line volta ~e will decrease somewhat because of the increased impedance drops in the two
alternators. but the division of power load will remain constant.
! Fig. 20-8 jJi..
."]f the syn!f'
. "wouidbeA
.' circuit culT,
•
•
•
•
3.3 PARALLELOPERATION
Q
The economic generation of alternating current frequently involves parallel operation of two or
more alternators. Direct-current generators excited to the same terminal voltage may be
connected in parallel merely by connecting together terminals of like polarity. However, before
two or more alternators can safely be connected in parallel, their frequencies must be almost the
same and their terminal voltages must be almost the same. Furthermore, theterminal voltages of
the machines must be almost in phase. Fig. 20-.8 shows a circuit diagram of two three-phase
alternators arranged to be operated in parallel, and shows also the ideal vector relationship
desirable at the instant of closing the synchronizing switch. If the speed of the incoming
alternator (a) is slightly greater than that of alternator (b). there will be alternate instants when
the respective phase voltages of the two machines will be in phase. as in Fig. 20-8, and )80 out
of phase. as in Fig. 20-9.
0
o
•If
••
If, howe,.
20-8. the ,
cin:ulatir.
FIi2.20-1e
S(lI1l(\' hili
have ap_
L<tfCk",
64
til
•
•
•
•
•
••
•
..
o
(
I
cl,
t, ..................
,
C'
II
•
•
•
.'•
E'b
lo.d
s:
nit
.•
'
{.\u,:n,tc' (tv
changes
ccitation of
circulating
ators. This
d will thus
current will
itation. The
in the two
E.~kF."
Fig. 20-8. Circuit Connections for Alternators to Be Operated in Parallel,
When the respective phase voltages of the two generators are exactly out of phase, the lamps of
, Fig. 20-8 will receive the combined voltage of both alternators in series and will be fully lighted .
')f the synchronizing switch were closed at that instant. the combined voltages of the alternators
"would be applied to their combined impedances only,and there would result a tremendous shortcircuit current which would possibly damage the alternators,
.'
C'
6
CI
•
•
••
•
••
•
.'.)
•
&"
.'
.;
••
.',1
«
<:
1 of
two or
be
may
~e
.ver, before
almost the
voltages of
.hree-phase
elationship
~ incoming
tants when
id 180 out
0
Fig. 20-9. Alternator Voltages Exactly out of Phase
If, however, the switch be closed when the voltages of the two alternators are in phase. as in Fig.
20-R. the resultant voltage across the lamp' wil] be zero. the 1~'lllrs will be dark. arid no
circulating current will now. This method i~ ,:aBed 'dark-lump" '-' iil'llrllni/alion
fig, 20-10 shows the vectors ,,)1 Fig, 2(P: :.;up,'rpI'scd
~Ilan il1,;t~\jll
when alternator ("lila" drifted
past the proper \\I$'hr(l!':!II1~' jh;inc ,liLl rt'slIlullt \$:\~iC'l': I' iclhh. E~clr:~h
.;\11\1
h<lEJ,
han: appeared across til( s:,i1c!;;,,;;i/tn/ l;"l1i-' Thl' ':hod, [(1 til'_' ;dll'rI1~!\l'r' rl'SlIllin'.' rn->l11
somewhat
l'~l'-L'1c_'<,
riming
ofthe ~,yn'
__
'hr~~~:i/\\:~'-,,,\:~·~'h
i:-',
rn-ll~),_'ni\_);IJll11
tl··:_,v'
1"t~...lllt~l!11
\t.)lt~l~i.".
(
Signifcance
of Phase Sequence.If
the phase sequences
of the alternators
in Fig. 20-8, as seen at
group 2).(
signific~
was poor'
the synchronizing switch, arc. the same, all the lamps will brighten and darken in unison as
synchronism is approached. If they do not so brighten and darken in unison, but the brilliance
. seems to "rotate," then the phase sequences are not the same and the synchronizing switch must
not be closed. The phase sequence may be corrected by reversing only two leads on either side-of
the synchronizing switch.
CONcuf
current ....
eonductam
method i~l
this is clea
·cannot~
Note:
L Give your answer in the space given below.
3.5LET~)
'C1.
1. Explain parallel operation?
........................................................................................
_ ••• _ •• _-_
••• ~.••••••••••••••••••••••
_._
...................................................•..................................__
- ••••••••
-
.•
e,
.
• 'fIC\
two
3.4 THE EFFECT OF CHANGING. EXCITATION FREQUENCY ON PARALLEL
, CONDUCTANCE IN DIFFERENT SIZED.HEARTS:
-
.
.' D'
.
.
~h~
pae
OBJECTIVE: An important component of the ventricular volume measured using the
conductance catheter technique is due to parallel conductance (Vc), which results from the
extension of the electric field beyond the ventricular blood pool. Parallel conductance volume is
normally estimated using the saline dilution mel rod (Vc(saline dilution», in which the.
conductivity of blood in the ventricle is transiently increased by injection of hypertonic saline. A
simpler alternative has been reported by Gawne et al. [I2l Vc(dual frequency) is estimated from:
the difference in total conductance measured ilt two exciting frequencies and the method is based .
on the assumption that paral' .!l conductance is mainly capacitive and hence is negligible at low .
frequency. The objective of this study was to determine whether the dual frequency technique
could be used to substitute the saline dilution method to estimate Vc in different sized hearts.
METHODS: The accuracy and linearity of a custom-built conductance catheter (CC) system was
initially assessed in vitro. Subsequently, a CC and micromanometer were inserted into the left.
ventricle of sev.en 5 kg pigs (group I) and six 50 kg pigs (group 2). Cardiac output was
determined using thermodilution (group I) and an ultrasonic flow probe (group 2) from which
the slope coefficient (alpha) was determined. Steady state measurements and Vc estimated using
saline dilution were performed at frequencies in the range of 5-40 kl-lz. All measurements were]
made at end-expiration. Finally. Vc was estimated from the change in end-systolic conductance
between 5 kHz and 40 kHz using the dual frequency technique of Gawne et ul. 1121-
• ~a.
3.6S0Mt
•
1.Electric~
2.A Text flJ(I
3.0perati<,Y \
Delhi.
....,
4.Electric_'
5. Performa
6. Electri.
7.Electric ~.
8. EJectri.
9.ElectricL
J O.EJectric!'
Ltd, New.
3.7ANS.
RESULTS: There was no change in measured volume of a simple insulated cylindrical model
when the stimulating frequency was varied from 5-40 kHz. Vc(saline dilution) varied
significantly with frequency in group I (8.63 +/- 2.74 011 at 5 kl-lz: 11.51 +/. 2.65 m! at 40 kHz)
(p = o.on Similar results were obtained in group 2 (69.43 +/- 27.76 1111 at 5 kHz: 101.24 +/15.21 ml at 40 UV I (P < (WOI )_Howe.ver, the data indicate that the resi sl ive component of the(
parallel conductance is substantial (vc at 0 Hz estimated as ~{_Olml in group I and 62.3 IIII in~
66
Check Yo.
I. Se.
Check Yo.
•
2. See S
l ••
•
•
•
••
c
(J
I
l
(
(:
-8, as seen at
in unison as
the brilliance
~switch musi
either side'{)f
(
I:
('
.',
•
•
PARALLEL
•
•
•
•
•
..
~,
C
I
C
•
•
•
CONCLUSION: At a lower excitation frequency 0(5 kHz a smaller percentage of the electric
current extends beyond the blood pool so parallel conductance is reduced. While parallel
conductance is frequency dependent, it has a substantial resistive component. The dual frequency
method is based on the assumption that parallel conductance is negligible at low frequencies arid
this is clearly not the case. The results of this study confirm that the dual frequency technique
cannot be used to substitute the saline dilution technique.
3.5 LET US SUM UP
....................,..
t
group 2). There was an increase in alpha with frequency in both groups but this did no! reach
significance. The correspondence between Vc(dual frequencyjand Vc(saline dilution) methods
was poor (group I R2 = 0.69; group 2 R2 = 0.22).
sd using the
alts from the
tee volume is
n which the.
onic saline. A
stirnated from
:thod is based
ligible at low
lCY technique
ed hearts.
:) system was
I into the left
:: output was
) from which
timated using
rements were
: conductance
•
Change in excitation of one of the alternators does not change watt full components but
changes wattles components resulting in ch.ange in power factors of alternators.
•
The economic generation of alternating current frequently involves parallel operation of .
two or more alternators.
•
Direct-current generators excited to the same. terminal voltage may be connected in
parallel merely by connecting together terminals of like polarity.
'.
.
•
An important component of the ventricular volume measured using the conductance
catheter technique is que to parallel conductance.
,
.
.
3.Operation and Maintenance of Electrical Machines by B.V.S. Rao, Khanna Publishers, New
Delhi.
4.Electrical Technology by Edward Hughes, Addision - Wesley International Student Edition
5. Performance ~ Design ofAC Machines by MG Say, CBS Publication, New Delhi
6. Electrical Energy Systems Theory by Elegerd, Tata McGraw Hill Co, New Delhi
8. Electrical Machinest Sigrna Series) by Kothari. Tata McGraw Hill Co. New Delhi
9.Electrical Machines by Kothari & Nagarth, Tara McGraw Hill Co, New Delhi
)Q.Electrical and Electronics Engineering by Vikramaditya Dave, Lakshmi Publications (Pvt)
Ltd, New Delhi
idrical model
ution) varied
111at 40 kHz)
z: 101.24 +/.
ponent o( the'
nd 62.3 ml ill
I. See section 3.1
2. Sec Section :U
67
(
----(
(
STRUC'J'
3.8 GLOSSARY
Effect of change hi operation
•
•
•
4.0°1\
In one of the alternator
Parallel operation
Frequency on parallel conductance.
4.1
11ft
e
4.2p
4.3~
4.4.
4.5~
4.6L~
4.7
t .
.---'
••
sor
4.8 ..
4.9<e
4.00B.
.After
•
•
st.
Un~
Ana.
4.1INTt
•
The po~
flowing'"
betwee~
capacity (
the CUlT.
or due to
"pparen.
III an el.
a high ..
iIKT~<lse"
(IS
•
•
•
•
••
••
"
CJ
I
,UNIT 4: POWER I MPROVEMEI-.;'l
I
I
STRUCTURE
I
(,
4.0 OBJECTIVES
I
4.1 INTRODUCTION
f
I,
4.2 POWER FACTOR IN LINEAR CIRCUIT
4.3 NON-LINEAR LOADS
•
•
•
•
•
••
4.4 IMPORTANCE OFPOWER FACTOR IN DISTRIBUTION SYSTEM
4.5 MEASURING POWER FACTOR
4.6 LET US SUM UP
t\
"
.'
4.9 GLOSSARY
4.0 OBJECTIVES
, After studying this unit, you should be able to
W
•
•
•
••
••
a;'
4.1 INTRODUCTION
.'C;
6;
•
.l
II
CJ
GJ
Understand the Basic power factor of synchronous motor
Analyse the Importance of power factor
The power factor of an AC electric power system is defined as the ratio of til..: renl power
flowing to the load to the apparent power in the cin:uil.l'1I21and is a dimcnsionlcs- HlI11lb j
between 0 and I (frequently expressed as a percentage, e.g. 0.5 pf = 509r pf). Real power is the
capacity of the circuit for performing work in a particular time. Apparent power is the product of
the current and voltage of the circuit. Due to energy stored in the load and returned Iu the source.
or due to a non-linear load that distorts the wave shape of the current drawn from the source. the
apparent po\\'er will be grealer than the real power.
,
.'
.
4.8 ANSWER TO CHECK YOUR PROGRESS EXER<:ISE
In an electric power system. a load with a low puwer r"CIOf dr~I\\ s more current than ~I load with
~I hit!h pl)wer tuctor for the same amount of useful P(I'.',C: !r~\I1skrrL'd The hi~hl'r ,'lItTcnto.;
II1(re"sc the energy 10',1in the dlstrihlltion
s)stel1l. ,lI1d ll'qlllrL' 1;11'):'.'.:'1 \\ ire- ,1I1c!1)IIlL'1l'qllipi11<.'nt,
1
.,
f
of the costs of larger equipment and wasted energy, electrical utilities will usually
charge a higher cost to industrial or commercial customers where there is a low power factor.
linear load de
timing (pha£,
Linear loads with low power factor (such as induction motors) can be corrected with a passive
network of capacitors or inductors. Non-linear loads, such as rectifiers, distort the current drawn
from the system. In such cases, active or passive power factor correction may be used to
counteract the distortion and raise the power factor. The devices for correction of the power
factor may be at a central substation, spread out over a distribution system, or built into powerconsuming equipment.
£
Because
'_'Circuits
_:;stoves, etc .• ,
;(electric mote
"
-'"Definition
' ,-C:a
Note:
col
AC power,
,measured in '
;'(Q), measll_
1. Give your answet: in the, sl,'ace given below.
C!
1. Define power factor?
........... -..-
-TbepbwerCl
--
. .......•.......................... ~
.......................................................
~
_
.
_
_. _ ..
!
,
In
. the
,,'~ case.
a vector tria.
4.2 POWER FACTOR IN LINEAR CIRCU'IT
,
In a purely resistive AC circuit, voltage and
current waveforms' are in step (or in phase),
changing polarity atthe same instant in each cycle,
All the power entering the loads is' consumed.
Where reactive loads are present, such as with
capacito
rs
or
inductor
s,
energy
storage
in
the
loads
result in a time difference between the current and
voltage waveforms, During each cycle of the AC
voltage, extra energy, in addition to any energy,
"'" consumed in the load, is temporarily stored in the load
in electric or magnetic fields, and then returned to the
power grid &4Taetion of a second later in the cycle The "ebb and flow" of this nonproductive
power increases the current in the line. Thus, a circuit, with a.low power factor will use higher
currents to transfer a given quantity of real power than .i circuit with a high power factor. A
·!C·.
~-
70
If <Pis the ,.
cosine of th.
IPI.
Since the u.
and I. W~
in the loa~
supplied bYe
"lagging" to ;
o
•
If a purei y re
in step, th.
across the ne
wound coi.
loads such "
the voltage
•
•
•
•
•
••
.•,
e
(J
(
I)
actor.
linear load does not change the shape of the waveform of the current, but ruav chance the relative
timing (phase) between voltage and current.
~
a passive
ent
drawn
(
! used to
(. he power
to power-
Circuits containing purely resistive heating elements (filament lamps, strip heaters, cooking
stoves, etc.) have a power factor of 1,0. Circuits containing inductive or capacitive elements
,(electric motors, solenoid valves, lamp ballasts, and others) often have a power factor below J .0.
l
C'
USU31ly
,_
Definition and calculation
f
AC power flow 'has the three components:
real power (also known as active power) (P),
measured in watts (W); apparent power (S), measured in volt-amperes (VA); and reactive power
(Q), measured in reactive volt-amperes (var).13J
"•
I'
e
The power factor is defined as:
C' ................
•.
In me case
•
••
a
&;
«
II
.'.'
.'
a·
t
(
of a perfectly sinusoidal waveform, P, Q and S can be expressed as vectors that form
'a vector triangle such that:
If lPis the phase angle between the current and voltage, then the power factor is equal to the
cosine of the angle,
C>
l
• "
S.
'
•
••
•
••
•
•
e
P
,--I
,/"
"
I PI
/.
"
=
[cos :pI, and:
ISlleos 'PI·
Since the units are consistent, the power factor is by definition a dimensionless number between
and 1. When power factor is equal to 0, the energy flow is entirely reactive, and stored energy
in the load returns to the source on each cycle. Whev the power factor is I. ;'11the energy
supplied by the source is consumed by the load, Power .ictors are usually stated as "leading" D;
"lagging" to show the sign of-the phase angle.
o
urrent and
If the AC
ly energy
in the load
rned to the
productive
use higher
factor. A
If a purely resistive load is connected to a power supply, current and voltage will change polarity
in step, the power factor will be unity (I), and the electrical energy tlows in a single direction
across the netwcrk in each cycle. Inductive loads such as transformers and motors (any type of
wound coil) consume reactive power with current waveform lagging the voltage. Capacitive
loads such as capacitor banks or buried cable generate rcacti ve power with current phase leading
the voltage. Both types of loads will absorb energy during pan of the AC cycle. which is stored
t:
71
I;
in the d",\'iCt\ magnetic or electric field. only to return this enerpy had to the source during the
simply. b1:
, analYSIS.
c
rest of the cycle.
For example. to gel I kW of real power: if the power factor is unity, I kVA of apparent power
needs to be transferred (1 kW -;- I = 1 kVA). Allow values of power f..ctor, more apparent power
needs to be transferred to get the same real power. To get 1 kW of real power at 0.2 power
-factor, 5 kVA of apparent power needs to be transferred (1 kW -;-0.2 = 5 kVA). This apparent
power must be produced and transmitted to the load in the conventional fashion, and is subject to
the usual distributed losses in the production and transmission processes.
Electrical loads consuming. alternating current power consume both real power and reactive
power. The vector sum of real and reactive power is the apparent power. The 'presence of
-reactive power, causes the real power to be less than the apparent power, and so, the electric load
has a power factor of less than 1.
Power factor correction of linear loads
It is often desirable to adjust the power factor of a system to near l.0. This power factor
correction (PFC) is achieved by switching W or out banks of inductors or capacitors. For
-example the inductive effect of motor loads lp.ay be offset by locally connected capacitors. When
reactive elements supply or absorb reactive power near the load, the apparent power is reduced.
Power factor correction may be applied by an electrical power transmission utility to improve the
stability and efficiency of the transmission network. Correction equipment may be installed by
individual electrical customers to reduce the costs charged to them by their electricity supplier. A
high power factor is generally desirable in a transmission system to reduce transmission losses
and improve voltage regulation at the load.
'
Power factor correction brings the-power factor of an AC power circuit closer to 1 by supplying
reactive power of opposite sign, adding capacitors or inductors which act to cancel the inductive
or capacitive effects of the load, respectively. For example, the inductive effect of motor loads
may be offset by locally connected capacitors. If aload had a capacitive value, inductors (also
known as reactors in this context) are 'Connected to correct the power factor. In the electricity
industry, inductors are said to consume reactive power and capacitors are said to supply It, even
though the reactive power is actually just moving back and
forth on each AC cycle.
'
1. Reactiv,
Limiting (
Transform
€\
An autoljrc,
correctici~
contacto~
electricalJ
tomeasuC'
Dependi.~
the necess
valu~ (us,
0'
'Instead
pow~r. ,.,
This is re .
network..
suppprt_
The co~
advantage
electric.
proportio
networ}<Q
transmisb
re
4.3NO
Anon-It>
The reactive elements can create voltage fluctuations and
harmonic noise when switched on or off. They will supply or
sink reactive power regardless of whether there is a
corresponding load operating nearby. increasing the system's
no-load losses, III a worst case. reactive elements can interact
with the system and with each other to create resonant
conditions. resulting in "ystem instability and severe
overvoltage nucruaiions. As such, reactive elements cannot
72
•
•
•
•
•
•
•
G
(1
\
during
litt'
simply
be applied at
will. and
PO';CI
fucto: correction
I'
normally subject
10
engmeenng
analysis.
rent power
.rcnt power
0.2 power
is apparent
s subject to
nd reactive
iresence of
lectric load
1. Reactive Power Control Relay; 2. Network connection points; 3. Slow-blow Fuses; 4. Inrush
Limiting Contactors; 5. Capacitors (single-phase or three-phase units, delta-connection); 6.
Transformer Suitable voltage transformation to suit control power (contactors, ventilation, ...)
An automatic power factor correction unit is used to improve power factor. A power factor
correction unit usually consists of a number of capacitors that are switched by means of
contactors. These contactors are. controlled. by a regulator that measur~s power factor in an
electrical network. To be able to measure power facl9r, the regulator uses a current transformer
to measu~e the current in one.phase.
.
.
Depending on the load and power factor of the network, the power factor controller will switch
the necessary blocks of capacitors in steps to make sure the power. factor stays above a selected
value (usually demanded by the energy supplier), say 0.9.
..
.
)wer factor
icitors. For
itors. When
; reduced.
improve the
installed by
supplier. A
ssion losses
,.... y supplying
ne inductive
motor loads
luctors (also
CJ e electricity
nply it, even
,_J
e
CJ
e
•
••
•
Instead of using a set of switched capacitors, an unloaded synchronous motor can supply reactive
power. The reactive power drawn by the synchronous motor is a function of its field excitation.
This is referred to as a synchronous condenser. It is started and connected . to the
electrical
,
network .. h operates at a leading power factor and puts vars onto the network ,~s .required to
support a system's voltage or to maintain the system power factor at a sp'ccified level. '
.
The condenser's installation and operation are identical to large electric motors. Its principal
advantage is the ease with which the amount of correction can be adjusted; it behaves like an
electrically variable capacitor. Unlike capacitors, the amount of reactive power supplied is
proportional to voltage, not the .square of voltage; this improves voltage stability on large
networks. Synchronous condensors are often used in connection with high voltage direct current
transmission projects or in large industrial plants such as steel mills.
4.3 NON-LINEAR LOADS
A non-linear load on a power system is typically a rectifier (such as used in' a power supply), or
some kind of arc discharge device such as a fluorescent lamp, electric welding machine, or arc
furnace. Because current in these systems is interrupted
by a switching action, the current contains frequency
components that are multiples of the power system
frequency. Distortion power factor is a measure of how
much the harmonic distortion of a load current
decreases the average power transferred to the load.
Sinusoidal voltage and non-sinusoidal current give a
distortion power factor of 0.75 for this computer power
supply load.
c>
t,
,
,
e
t
C
r
«
(
73
w.
Non-sinusoidal
components
Non-linear loads change the shape of the current waveform from a sine wave to some other form.
Non-linear loads create harmonic currents 'in addition to the "original (fundamental frequency)
AC current. Filters consisting of linear capacitors and inductors can prevent harmonic currents
from entering the s'-!pplying system.
from a rev.
incOrporatl(
voltage exce
8yerage in"~hase and
i'
A
In linear circuits having only sinusoidal currents and voltages of one frequency, the power factor"
arises only from the difference in phase between the current and voltage. This is "displacement
power factor". The concept can be generalized to a total, distortion, ortrue power factor where
the apparent power includes all harmonic components. This is of importance in practical power
systems which contain non-linear loads such as rectifiers, some" forms of electric lighting.
electric arc furnaces, welding equipment, switched-mode power supplies and other devices.
A typical rnultimeter will give incorrect results when attempting to measure the AC current
.drawn by a non-sinusoidal load; the instruments sense the average value of a rectified waveform.
The average response is then calibrated to the effective,"RMS value. An RMS sensing multi meter
must be used to measure the actual RMS currents and voltages (and therefore apparent power).
To measure the real-power or reactive power, a wattmeter designed to work properly with nonsinusoidal currents must be used.
I
Distortion power factor
1
I1,r111s
_distortion power fector = --;==== -
vl1 + THD}
" Irms
THD; is the total harmonic distortion of the load current. This definition assumes that the voltage
stays - undistorted (sinusoidal, without harmonics). This simplification is often a good
approximation in practice. hmlS is the fundamental component of the current and Irons is the total
current - both are root mean square-values.
The result when multiplied with the displacement power factor (DPF) is the overall, true power
"factor or just powerfactor (PF):
Switched-mode
e
,.;:s:=,
power draltl,
correction YtJ,
t'l
_Regulatory:
factor. DeG
comply witt
J>ower mo.
IF<luiresa
ia
,
PassiveP.
the averagepower transferred to the load.
=
~'
power.fa~
The pistortion powerfactor' describes how the harmonic distortion of a load current decreases
PF
tYI:ical
- cirCUIt. The
rectifier is C'
current has e
DPF II .rms
Irills
The simple
that passei.,
current, vJfII!
power "fac\p-,
requires Ia}{
•
•
A passive P
This is a sin
effective I}
Passive P~
confused.
PFC on a sv
PFChas.
Active PI.
power supplies
1\
A particularly important class of non-line ar loads is the millions of personal computers that
typically incorporate switched-mode p,nWf supplies (SMPS) with rated output power ran~in~
74
j,
0.
...
."'\n actlv~
amount
•
•
•
•
•
•
•
•
•e
her form.
equency)
: currents
VeT factor
,lacement
:or where
ial power
lighting,
ces.
::::current
/aveform.
uiltimeter
It power).
with non-
from :J few watts to more .than 1 lW. Historically, these very-low-cost power supplies
incorporated a simple full-wave rectifier that conducted only when the mains instantaneous
voltage exceeded the voltage on the input capacitors. This leads ,to very high ratios of peak-toaverage input current, which also lead to a low distortion power factor and potentially serious
phase and neutral loading concerns.
A typical switched-mode power supply first makes a DC bus, using a bridge rectifier ,or similar
circuit. The output voltage is then derived from this DC bus. The problem with this is that the
rectifier is a non-linear device, so the input current is highlynon-linear. That means that the input'
current has energy at harmonics of the frequency of the voltage.
This presents a particular problem for the power companies, because they cannot compensate for
.the harmonic current by adding simple capacitors or inductors, as they could for the reactive
power drawn ,by a linear load. Many jurisdictions are beginning to legally require power factor'
correction for all power supplies above 'a certain power level.
Regulatory agencies such as the EU have set harmonic limits as a method, of improving power
factor. Declining component cost has' hastened 'implementation of two different' methods. To
comply with current EU standard EN6}()()()"3-2, all switched-mode power supplies with output
power more than 15 W must include ~ssive PFC, at least. 80 PLUS power supply certification
requires a power factor of 0.9 or more. 4J
•
Power factor correction in non-linear loads
decreases
PassivePFC
voltage
a good
s the total
ie
.;:
""liepower
C;
•
••
•.i
•.;
•
•
I
.'
I)
e:
(,
f
,
The simplest way to control the harmonic current is to use a filter: it is possible to design a filter
that passes current only at line frequency (e.g. 50 or 60 Hz). This filter reduces the harmonic
current, which means that the non-linear device now looks like a linear load. At this point the
power factor can be brought to near unity, using capacitors or inductors as required, This filter
requires large-value high-current inductors, however, which are bulky and expensive.
A passive PFC requires an inductor larger than the inductor in an active PFC, butcosts 1ess,15116]
This is a simple way of correctinfi the nonlinearity of a load by using capacitor banks. It is not as
effective as active PFc.17Jl8Jl9JlIOJl
II
,
Passive PFCs' are typically more power efficient than active PFCs. Efficiency is not to be
confused with the PFC, though rnany computer hardware reviews conflate them,!?1 A passive
PFC on a switching computer PSU has a typical power efficiency of around 96%. while all active
PFC has a typical efficiency of about 94%.112J
Active PFC
An "active power factor corrector" (active PFC) is a power electronic system that controls the
amount of power drawn hy a load in order to obtain a remer factor as dose as possible to unity,
uters that
!r ranging
75
1
In most applications, the active PFC controls the input current of the load so thai tilL current
waveform is proportional to the mains voltage waveform (a sine wave). The purpose of making
the power factor as close to unity (I) as possible is to make the load circuitry that is power factor
corrected appear purely resistive (apparent power equal to real. power).1131In this case, the
voltage and current are in phase and the reactive power consumption is zero. This enables the
most efficient delivery of electrical power from the power company to the consumer.1141
The signiff
volt-ampere,
than the ~
generation",
'·apparent p'"
would alsct,
be doupled
componenC]
.'increased in
Specifications taken from the packaging of a
:"·i.fow
conti' uc&i'$-~"4DC~"iWjfG.lk'·'t
,,','",':' " ,;,".,'"",,,,JJ'''''''i'''~":''''
",,<,.,~;J'~
;,J 610W ~C power supply showing Active PFC
";'Yi:",",'','"
?CJp ft) 90% {1t:),d8J. f..e$S':N~t~e.pcr'~att
:,~;;:;":',rating
:"'IJPS12VI:NVIDIA@$Us#.~ltW
~~kfbtivrrt1l!;jeylt1l,~JIt':9g,·ttW"l'
'
."'If2 2'VDC'(!t·~9J\Xt.~,'SI~e,:fI~
,'~;.~",~~,
~ .Some typcs
,,·24-pJn.8-pl,,~;
...pJnHIBfonn«tors"<
:2 PCl·£:tnd 15 Drive Coit,rit(d.Of-5,.
AufCrtJifticF;m Sl'c.;d
GI.'1Ck finish (Coppi!l
e·
of active PFC are:
Utilities fY,4.
limit, whi<!J
as one of tty
'
• Boost
• 'Buck
• Buck-boost
Contr6ICirc:U'it
en
i~que~)
S·l·car Wamlnty (lruJ ret:h,Support
Active power factor correctors can be single-
stage or multi-stage.
, Iri the 'case of a switched-mode power supply, a boost converter Is inserted between the bridge
rectifier and the main input 'capacitors. The boost converter attempts to maintain a constant DC
bus voltage on its output while drawing current that is always
phase with 'and at the same
frequency as the line voltage. Another switchmode converter inside the power supply produces '.
the desired output voltage from the DC bus. This approach requires additional semiconductor
switches and control electronics, but permits cheaper and smaller passive components. It is
frequently used in practice. For example, SMPS with passive PFC can achieve power factor of
about.O.7-O.75, SMPS with active PFC, up to·0.99 power factor, while a SMPS without any
power factor correction has a power factor of-only about 0.55-0,65.1151
a
in
Due .to their very wide input voltage range, many power supplies with active PFC can
automatically adjust to operate on AC power from about 100 V (Japan) to 230 V (Europe), That
feature is particularly welcome in power supplies forlaptops.
2. Check your answer" with those given at the end of the unit.
1. What is non linear loads'?
....
~
- ~.
,;
..
~ ~
7(1
J
•
4.5Meas'i
Power fa~
watt meter-s
measured.
that of any
•
J. Give your answer in the space given below.
.......
•
In Europe,
A direct re:
. type. ca~
instruillena
connectelrr'
the st?L'lll1.
current in r
A pro\id.
zero POWt"
Note:
With there
become mo
(ENERG.
> 0.9 at 10(
Intel and.
require th.
Requirem~
'
..
torque to•
.,
prt'\ i(~t~d..
•
•
••
•
•
•
•c.
o
ie current
)f mating
wer factor
case, the
tables the
I
19m9 of a
ctive PFC
_----_._----
_-...
4.4 Importance of power factor in distribution
.-~.-
svstcms
...
The significance of power factor lies in the fact that utility companies supply customers with
volt-amperes, but bill them for watts. Power factors below 1.0 require a utility to generate more
than the minimum volt-amperes necessary to supply the real power (watts). This increases
generation and transmission costs. For example, if the load power factor were as low as 0.7, the
apparent power would be 1.4 times the real power used by the load. Line current in the circuit
would also be 1.4 times the current required at ).0 power factor, so the losses in the circuit would
be doubled (since they are proportional to the square of the current). Alternatively all
components of the system such as generators, conductors, transformers, and switchgear would be
, increased in size (and cost) to carry the extra current: ,
Utilities typically charge additional costs to customers who have a power factor below some
limit, which is typically 0.9 to 0.95. Engineers are often interested in the power factor of a load
as one of the factors that affect the efficiency of power transmission.
be 'single-
the bridge
nstant bc
t the same
I produces ,_.
iconductor
.ents. It IS
r factor of
ithout any.
PFC can
ope). That
With the rising cost of energy and concerns over the efficient delivery of power, active PFC has
become more common in consumer electronics. Current Energy Star guidelines for computers
(ENERGY STAR® Program.Requirements for Computers Version 5.0) call for a power factor of
~ 0.9 at 100% of rated output in the PC'!spower supply. According to a white paper authored by •
Intel and the U.S. Environmental Protection' Agency, PCs with internal power supplies will .
require the use of- active power factor correction to meet the ENERGY STAR® 5.0 Program
Requirements for Computers.'
.
In Europe. IEC 555-2 requires power factor correction be incorporated into consumer products .
4.5 Measuring power factor
Power factor in a single-phase circuit (or balanced three-phase circuit) can be measured with the
waumeter-ammeter-voltmetcr method, where the power in watts is divided by the product of
measured voltage and current. The power factor of a balanced polyphase 'circuit is the same as
that of any phase. The power factor of an unbalanced polyphase circuit is not uniquely defined.
A direct reading power factor meter can be made with a moving coil meter of the electrodynamic
. type, carrying two perpendicular coils on the moving part of the instrument. The field of the
instrument is energized by the circuit current flow. The two moving coils, A and B, are
connected in parallel with the circuit load. One coil, A, will be connected through a resistor and
the second coil. B, through an inductor. so that the current in coil B is delayed with respect to
current in A, At unity power factor. the current in A is in phase with the circuit current, and coil
A pnn ides maximum torque, driving the instrument pointer toward the 1.0 mark on the scale. At
zero power factor. the current ill coil B is in phase with circuit current, and coil B provides
torque to drive the pointer towards O. At intermediate values of power factor, the torques
prm ulcd hy the two coils add and the pointer takes up intermediate positions.II'!1
77
Another electromechanical instrument is the polarized-vane type.1201 In this instrument 2.
stationary field coil produces a rotating magnetic field, just like a polyphase motor. The field
coils are connected either directly to polyphase voltage sources or to a phase-shifting reactor if a
single-phase application. A second stationary field coil; perpendicular to the voltage coils, carries
a current proportional to current in one phase of the circuit. The moving system of the instrument
consists of two vanes which are magnetized by the current coil. In operation the moving vanes
take up a physical angle equivalent to the electrical angle between the voltage source and the
current source. This 'type of instrument can be made jo register for currents in both directions,
giving a 4-quadrail.t display of power factor or phase angle.
.
Digital instruments can be made that either directly measure'the time lag between voltage and
. current waveforms and. so calculate the power factor, or by measuring both true and apparent
power in the circuit and calculating the quotient. The first method is only accurate ·ifvoltage and .
•current are sinusoidal; loads such as rectifiers'distort the waveforms from the sinusoidal shape.
·4.6 LET US SUM UP
The ~wer facror of an AC electric power system is defined IlS ~he ratio of the real power
flowing to the load to the apparent power in the circuit,l'1t2J and is a dimensionless number
.•
between 0 arid 1.
•
•
•
•
Real power is the capacity of the circuit for performing work in a particular time. Apparent
power is the product of the current and voltage of the circuit.
A non-linear load on a power system is typicaJly a rectifier (such as used in a power suppl; ),
or some kind of arc discharge device such as a fluorescent lamp, electric welding machine, )r
~ furnace.
.
Power factor in a single-phase circuit (or balanced three-phase circuit) can be measured with
the wattmeter-ammeter-voltmeter method, where the power in watts isdivided by the product
of measured voltage and current.
.
4.7.SOME USEFULLBOOKS
I. IEEE Std. 1459-2000 Trial-Use Standard Definitions for the Measurement of Electric Power
Quantities Under Sinusoidal, Non sinusoidal, Balanced, or Unbalanced Conditions, Institute of
Electrical and Electronics Engineers Inc., 2000,0-7381-1963-6.
2. Fairchild Semiconductor (2004). Application Note 42047 Power Factor Correction (PFC)
Basics.
.
3.Bollen, M. H. J., (1999). Understanding -Power Quality
Interruptions. Piscataway, NJ: Wiley-IEEE Press
Problems:
Voltage Sags and
4.Sugawara, I., Suzuki, Y, Takeuchi. A.. & Teshima, T. (1997). Experimental studies on active
and passive PFC circuits. Telecommunications Energy Conference, 1997. INTELFC CJ7 19th
International 19-23 Oct 1997. 571-578. doi 10.II09/INTLEC.11J97.646051.
78
4.~AN~
Check"¬ ''
1. Sf;
Check".
1.
s-
C>
C'
I:"
Cl
•
••
•
••
•
o
o
••
•
••
••
•
•
•
•
•
•
••
•
••
.,
strument
a
'. TIle field
reactor if a
(
oils, carries
instrument
• ' rving vanes
rce and the
directions,
•
1. See section 4.1
1. See Section 4.3
(
(
•
voltage and
ld apparent
voltage and .
lal shape.
I
•
real power
•
tess number
CI
e. Apparent
•
ver suppl; ),
machine, )r
•
-,
$ .asured with
CCI
."
••
•
•
&;
.'
II
el
C·
«
(
the product
ectric Power
Institute of
ction (PFC)
Sags and
es on acti ve
97" 19th
:c
7l)
(
______ ---BLOCK 3
THREE PHASE INDUCTION MOTOR
_____c
(
INTRODUCTION:
S'fRUcnI
This being the first block of the course, an attempt has been made to define and consolidate
concepts with the help of examples. The important concepts that one must be able to describe
-have been discussed in the block.
1.oosf
l.1J
order to use a lot of functions and facilities,
which does exist in a three phase induction motor. These blocks describe the concept of
induction motor of Working Principle, slip-torque characteristics. This basic focus of the block
being that you should be able to study the circle diagram and speed control.
One must be clear about these basic concepts
10
.'
1.2PRf'
}.3 COt-
e
This block consists of four-units:
1.4E,\,
Unit 1: Defines the bas~cprinciple and working of three phase induction mo!or.
1.5L~
1.6S~
'1Jnit 2: Focus on t.Jleslip-torque characteristics.
Unit 3: Provides the focus on the circle diagram.
1.7~
Unit 4: Provides the overview of speed control
1.8G.
•
•
1.00BJ.
After stut
• Basi.c~
•
EqUlW
•
•
•
1.1 INT.
An in(Ju.
is supplitl
I.
An deem
calkd
are distill'
slir-rin~.
called c~
the
xo
f
l.;.
_
rolO~
•
•
••
••
•
•
()
(J
I~
t
-
.--------.------.-.~~-.
UNn~J FFJ},CrfLU Of-OPERATION
C
(
STRUCTURE
,
msolidate
) describe
t
facilities,
;)ncept of
the block
(
C'
1.00BJECfIVE
).1 INTRODUCTION
) .2 PRlNCIPLE OF OPERATION
1.3 CONSTRUCTION
1.4 EQUIVALENT CIRCUIT
1.5 LET US SUM UP
.
) ,6 SOME USERJLL BOOKS
1.YANSWER. TO CHECK YOUR PROGRESS EXERCISE
1.8 GLOSSARY
1.0 OBJECTIVES
..
•
•
Basics of three phase induction motor
Equivalent circuit of three phase induction motor
1.1 INTRODUCTION
An incJuction motor or asynchronous motor is a type of alternating current motor where power
is supplied to the rotor by means of electromagnetic induction.
An electric motor turns because of magnetic force exerted between a stationary eledromagnet
called the stator and a rotating electromagnet called the rotor. Different types of electric motors
are distinguished by how electric current is supplied to the moving rotor. In a DC motor and a
slip-ring AC motor, current i~ provided to the rotor directly through sliding electrical contact"
called commutators and slip rillg~. In ali induction motor. hy contrast. the current is induced in
the rotor without contacts by till' lllagnftic field of the stator. through electromagndic inducuon
ei
Cl
e)
e,'
.'
f
Ali i:;duCi!U;i
motor
is sometimes
called a rotating transformer because the stator (statioHary
part) is essentially tile prima')' side of the transformer and the rotor (rotating part) i~ th~
secondary side. Unlike the normal transformer which changes the current by using time varYing
flux, induction motors use rotating magnetic fields to transform the voltage. The current in the
primary side creates an electromagnetic field which interacts with the electromagnetic field of
the secondary side to produce a resultant torque, thereby transforming the electrical energy into
mechanical energy. Induction motors are widely used, especially polyphase induction motors,
which are frequently used in industrial drives.
conducto{
effect cal
Induction motors are now the preferred choice for industrial motors due to their rugged
construction, absence of brushes (which are required in most DC motors). and-thanks to modern
power electronics=-the ability to control the. speed of the motor.
and spee",
between
of the
. aSynchron<
Howevel{
speed of t!.
lllagneticC.
:~~~~
m
nl'
G
.
Synchr0i;)
1. Explain induction motor?
._
_
Note: 1. Give your answer in the space given
below.
•
To unde~
a synchro~,.J
frequenc.
induction n
2, Check your-answers with those given
at the end of the unit.
It can be,
_
.................................................................. _
l.tPRINCIPLE
.
ntt
.
OF OPERATION
•
•
where ns.
Hz) and
P6
A 3-phase power supply provides a rotating magnetic field in
an induction motor.
Forexanl)
•
1/,
The basic difference between an induction motor and a
synchronous AC motor with a permanent magnet rotor is that in
the latter the rotating magnetic field of the stator will impose an
electromagnetic torque on the magnetic field of the rotor
causing it to move (about a shaft) and a steady rotation of the
rotor is produced. It is called synchronous because at steady
state the speed of the rotor is the same as the speed of the rotating magnetic field in the stator.
Note on tWj
poles per
Theequaa
By way of contrast, the induction motor does not have any permanent magnets on the rotor;
instead. a current is induced in the rotor. To achieve this, stator windings are arranged around the
rotor so that when energised with a polyphase supply they create a rotating magnetic field pattern
which sweeps past the rotor. This changing magnetic field pattern induces current in the rotor
with P bee
82
tI
rr
II.•
Slip
••
•
••
•
••
•
•e
f
,r (stationary
part) IS the
time varYing
urrent in the
ietic field of
I energy into
.tion motors,
I
I
I'
•
(
their rugged
ks to modem
I
('
I
•
conductors. These currents interact with the rotating magnetic field created by the stator and in
effect causes a rotational motion on the rotor.
'
However, for these currents to be induced, the speed of the physical rotor must be less than the
speed of the rotating magnetic field in the stator (the synchronous frequency ns) or else the
magnetic field will not be moving relative to the rotor conductors and no currents will be
induced. If by some chance this happens, the rotor typically slows slightly until a current is reinduced and then the rotor. continues as before. This difference between the speed of the rotor
and speed of the rotating magnetic field in the stator is called slip. It is unitless and is the ratio
between the relative speed of the magnetic field as seen by the rotor (the slip speed) to the speed
of the rotating stator field. Due to this, an induction motor is sometimes referred to as an
asynchronous machine; .
speed
Synchronous
I
space given
I
•
••
•
.
L
To understand the behaviour of induction motors, it is useful to understand their distinction from
a synchronous motor.A synchronous motor always runs at a synchronous speed- a shaft rotation
frequency .that is an integer fraction of the supply frequency. The synchronous speed of an
induction motor is the,same fraction of the supply.
.
.
,
those given
It can be shown that the synchronous speed of a motor is-determined by the following formula:
120 X
ll,,=
.....................
f
p
'
.'
I>
.'
•
••
•
•.i
II
tJ
e)
.1
II
'1I'
f
f
where n, is the (synchronous) speed of the rotor (i n rpm), f is the frequency of the AC suppl y r in
Hz) and p is the number of magnetic poles per phase.
ietic field in
For example, a 6 pole motor operating on 60 Hz power would have a speed of:
'II ., =
rotor and a
nor is that in
ill impose an
of the rotor
tation of the
.se at steady
he stator.
120 X 60
----6
= 1200
1'1)111
Note on the use of p - some texts refer to number of pole pairs ·per phase instead of number 01
poles per phase. For example a 6 pole motor, operating on 60 Hz power, would have 3 pole pair';'
The equation of synchronous speed then becomes:
II-,
tiO ><
p
t
m the rotor;
d around the
field pattern
in the rotor
with
P being
the number of roil: pail s pel phase.
Slip
typicu] torque curve as a tuner ion of slip
IItC!l arc
Sqr
slip is a ratio relative to the synchronous speed and is calculated using:
;S
=- ( H;< - Ill')
\
t
(,
The most c
common)€'
strips can
semiclostC"
skew to re
n.~
Where
f';
s is the slip, usually between 0 and 1
n, = rotor rotation speed (rpm)
ns = synchronous rotation speed (rpm)
• SIt:
A slip ri'C;
slip rings.
they cane,
beneficial
'.
•
1.3 Construction
.
-
Typical winding pattern for a 3 phase, 4 pole motor- (here phases
are labelledW, U, V). Note the interleaving of the pole windings
and the resultant quadrupole field.
The stator consists of wound 'poles' that carry the supply current to
induce a magnetic field that penetrates the rotor. In a very simple
motor, there would be a single projecting piece of the stator (a
salient pole) for each pole, with windings around it; in fact, to
optimize the distribution of the magnetic field, the windings are
distributed in many slots located around the stator, but the
magnetic field still has the same number of north-south
alternations. The number of 'poles' can vary between motor types
but the poles are always in pairs (i.e. 2,4,6, etc.).
Induction motors are most commonly built to run on single-phase or three-phase power, but twophase motors also exist. In theory, two-phase and more than three phase induction motors are
possible; many single-phase motors having two windings and requiring a capacitor can actually
be viewed as two-phase motors, since the capacitor generates a second power phase 90 degrees
from the single-phase supply and feeds it to a separate motor winding. Single-phase power is
more widely available in residential buildings, but cannot produce a rotating field in the motor
(the field merely oscillates back and forth), so single-phase induction motors must incorporate
some kind of starting mechanism to produce a rotating field. They would, using the simplified
analogy of salient poles, have one salient pole per pole number: a four-pole motor would have
four salient poles. Three-phase motors have three salient poles per pole number, so a four-pole
motor would have twelve salient poles. This allows the motor to produce a rotating field,
allowing the motor to start with no extra equipment and run more efficiently than a similar
single-phase motor.
84
So
e
c.
~ rotor.
Speed
r--".
I.
Ii
,i
\
i
-.
,t
/
't-
l-g
f
l
0
•
L-_
be run
ja
range a'fll'
and de.
constant
run ate
Before.
the fre~
Asan"
heine ,-
applied
•
••
•
Co
•
••
•
•
"
(;
'1 herl an. three t yp:;~of roto :
•
Squirrel-cage rotor
The most common rotor is a squirrel-cage rotor. It is made up of bars of either solid copper (most
common) or aluminum that span the length of the rotor, and those solid copper or aluminium
strips can be shorted or connected by a ring or some times not, i.e. the rotor can be closed or
semiclosed type. The rotor bars in squirrel-cage induction motors are not straight, but have some
skew to reduce noise and harmonics.
•
Slip ring rotor
A slip ring rotor replaces the bars of the squirrel-cage rotor with windings that are connected to
slip rings. When these slip rings are shorted, the rotor behaves similarly to a squirrel-cage rotor;
they can also be connected to resistors to produce a high-resistance rotor circuit, which can be
beneficial in starting
•
Solid core rotor
A rotor can be made from a solid mild steel. The induced current causes the rotation.
tere phases
! windings
'current to
ery simple
e stator (a
In fact, to
ndings are
r, but the
iorth-south
iotor types
but twomotors are
in actually
90 degrees
e power is
the motor
ncorporate
simplified
zould have
l four-pole
uing field,
I a similar
:f,
I'
I
(
Speed control
ypicaJ torque curves for different line frequencies
The synchronous rotational speed of the rotor (i.e. the
theoretical unloaded speed with no slip) is controlled by the
number of pole pairs (number of windings in the stator) and
by the frequency of the supply voltage.
.-_.-------------.
-~
However. for a loaded rotor. for any given drive frequency
and current and mechanical load, synchronous motors should
be run in the 'operating zone' for that particular induction motor. This is the shaft rotation speed
range above the peak torque. In this zone slightly increasing the slip speed increases the torque,
and decreasing the slip decreases the torque. Hence in this zone the motor will tend to run at
constant speed. Below the operating zone. the run speed tends to be unstable and may stall out or
run at reduced shaft speed, depending on the nature of the mechanical load.
Before the development of economical semiconductor power dCLlronics. it was difficult to \ ary
the frequency to the motor and induction motors were mainly used in fixed speed applications.
As an induction motor has no brushes and is easy to control. many older DC motors arc nov,
being replaced with THR induction
rnotor-: and ,tlT()lllp,"1yin~'
inverters 111 in.JlI~lrja!
uppl ic.ui. lIlS.
'IIi.
This section was recently translated by machine from the German Vlikipedia site. and partiattv
human I ranslated. If you can continue the translation, please do so
To understand the behavior of an induction motor when the rotational speed and suppJy
frequency varies, it is helpful to look at the equivalent circuit. The equivalent circuit shows an
electrically equivalent circuit to the motor's construction, where the two leftmost terminals would
be connected to a power supply.
an ari)[(lX Im:
i~not incluf
motor.can,
effective.
I
(
frequently to
c:Onected -£
torque or s~\
problems d·
Equivalent circuit
Check You'~
On the left side of the circuit, the equivalent resistance of the
and core
resistance in series, is shown as Rs. During asynchronous
operation, the stator also induces some reactance, which is
represented by the inductor Xs. The next inductor X,. represents the effect of the rotor
(commonly a squirrel-cage) passing through the stator's magnetic field. The effective resistance
of the rotor (again with rotating in a magnetic field), Rr, is composed of: .
Rr stator, which consists of the copper resistance
•
•
the equivalent value of the machine's real power (which changes with the torque and the
load on the machine)
the ohmic resistance of the stator windings and the squirrel cage of shorted rotor
windings.
At idle, the induction motor equivalent circuit is essentially just Rs and Xs, which is why this
machine only takes up mostly reactive power. The idle current draw is often near the rated
current, due to the copper and core losses which exist even at' no load. In these conditions, (his is
usually' more than half the power loss at rated load. If the torque against the motor spindle is
increased, the active current increases by R,., and thus in the rotor.
Due to the construction of the induction motor, the two resistances both induce a magnetic field.
.in contrast to the three-phase synchronous machine, where the magnetic flux is induced only bv
the reactive current in the stator windings.
The current produces a voltage drop in the cage portion of the R,., but only a slightly nigher
voltage drop in the stator windings. Consequently, the losses increase with increasing load in the
rotor faster than they do in the stator. The
., copper resistance R..ami the "copper" resistance from
the cage portion of R,. both cause I-R·losses, and therefore the efficiency of the machine
improves with increasing load. The efficiency of the machine reduces with temperature.
In contrast with a smaller frequency of the reactance X., also getting smaller. In compliance \\ ith
the rated current 'must shrink by the drive voltage delivered. Thus. the ratio of the voltage di \ idcr
R.~to X, and R, and this increases engine power I()~.~c:s.In continuous operation this can llnh he
C)
Note: I. Gf;,
2'~i
.
:::::::::::::::::::.
l.5LETU~
•
An indue
poweri.
In a DC.
sliding If/P
Aslip~
to slip nn
rotor; th<",
can be be!
•
_1.6SOME ~
I.Electrical •
2.AText Bo~
3.0peration.
Delhi.
-l.Electrical •
). Performal",
6. Eleclrical~
7.Ekctril· [Via.
~. Electrical
"r"
n.
ll.EkctriLal.
IO.EkL"l1
i..:,d
Ltd. NL'I\
86
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1.Explain
•
•..
•
•
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,.
.'I
d partially
f
,
•
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•
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•
•
•
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e
•
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C
CJ
nd supply
shows an
nals would
t
mce of the
and core
nchronous
, which is
the rotor
resistance
(
2. Check .your answers with those given at the end of the unit.
1. Explain equivalent circuit of induction motor?
................................... _
......................................
.ie
~
.
.t.•••~••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
and the
1.5 LET US SUM UP
rted rotor
, why this
the rated
lOS, (his is
spindle is
etic field .
d only hy
I)'
higher
xrd in the
met.' from
machine
mcc \\ Ith
.e divider
.~
C'
Frequently today, Rs / Rr are measure automatically and are thus in a position for any motor
cO"nnectedto automatically configure itself and thus to be protected from overload. A holding
torque or speed dose to zero can be achieved with a vector control. Here,too though, there can be
problems with ~ooling since the fan is usually mounted on the rotor.
-
.
.'
'
nil api)roximation because a nominal torque is generated because the cooling (If rotor and stator
is not included in the calculation. At higher than the rated speed or rated frequency induction
motor can, however - in the context of isolation - are working on higher voltages and is more
effecti ve.
An induction motor or asynchronous motor is a type of alternating current motor where
power is supplied to the rotor by means of electromagnetic induction.
In a DC motor and a slip-ring AC motor. current is provided to the rotor directly through
sliding electrical contacts called commutator and slip rings.
A slip ring rotor replaces the bars of the squirrel-cage rotor with windings that are connected
to slip rings. When these slip rings 'are shorted. the rotor behaves similarly to a squirrel-cage
rotor; they can also be connected to resistors to produce a high-resistance rotor circuit, which
can be beneficial in starting
1.6SOME USEFULL BOOKS
2.A Text Book Electrical Technology by BL Theraja. S.Chand Publishers
3.0peration and Maintenance of Electrical Machines by B.V.S. Rao, Khanna Publishers, Nev.'
Delhi.
.:I.ElectricalTechnology by Edward Hughes. Addision - Wesley International Student Edition
). Performance & Design of AC Machines b) MG Say, CBS Publication, New Delhi
6. Electrical Energy Systems Theory by Elcgerd, Tata McGraw Hill Co. New Delhi
7 Electric Machinery by Fitzerald. Tala McGraw Hill Co. New Delhi
X.Ekdrical Machincst Sigrna Series) by Kothari, Tala l\L(;;,I\\ Hill C(). New Odili
9.Electril"d Muchine« by Kothari 8:, Nag.mh. Tutu 1'l'kCilJ\\ Hili Co. New Delhi
'\(LEJel'lril',\1 .md Electronics Engincerin~ I)" Vikr<lilu,Jit\;! Dave. Lnkshmi Pl!hli'_':ltion, ,p\t}
Ltd. N,'\\
n-u.
__(.
r
Cheek Your Progress -1
I. See-section 1.1
Check Your Pregress=
f
STRlf'
2
1. SeeSection 1.4
~
C£
82
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•
AfteAt
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o
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t.
It
--------------_-
--_------------------------_
UNlT-2 SLIP-TORQUE
CHARACTERISnCS
STRUCTURE
2.0 OBJECTIVE
2.1 INTRODUCTION
2.2 LET US SUM UP
2.5 GLOSSARY
2.0 OBJECTIVES
. After studying this unit, you should be able to
•
•
To study the slip-torque characteristics.
Can differentiate the motor concepts and it functionalities .
2.1 INTRODUCTION
Basic Induction Motor Concepts:
The Development of Induced Torque in an Induction Motor
[;.,./= kB ..it xB \
,',\.,
L .-
_
..
--.------.----
....
('i;/,
,)' I
tile let:;.'
If tile mouc ticn u-ctcrs
r c lcr \''':1 C
tumir«; at svl\f. ...hrcnous SI·h2C"C
bc1l:o
tc
-;
,',oule tJC stalicllcH Y IC!dti v·,_
u., Ihl,)IKUC
~.
.'IIlii.
C:
fi,;k;
Slip may
uc induced voltaqc
s
C
!he Elect.;
W.henthee
. speed , the..
And rotor
Slip of induction motor
The speed of induction motor inust always be less than the synchronous speed and as the' load .
increased the spree of the motor will decrease. The difference between the speed of the stator and
the actual speed of the rotor is known as the slip speed of induction motor,
11111 .
.';-
= slip speed of the machine
,PFl.,. ,-
" -:
;<t}1t
Ai
•
••
..
list;p
••
••
•
e
Where
,
i,.
= speed of the magnetic
This show.
determine
tt
field.
TorqueCh.
11
111
= mechanical
shaft speed of the motor
A self st~
starting and;
thepermane
The slip can be expressed in rpm and radians per second, but usually it is expressed as a fraction
or percentage of synchronous speed,
90
••
••
in househo!rl
••
•
•
,
C
C
"I'
t
(
c·
I'
J
:.:...s_ x 1 (lO" •.
n
.t.:,
x I(Hl""
II
Slip may also be described in terms of angular velocity,
s
"
(
COsync - COm
X 100%
co sync
(
(
•
•..
-
~----~
The Electrical Frequency on the Rotor
J.
,
wpen the rotor is stationary, rotor conductor are being cut by therotating flux at the synchronous
speed, the frequency of rotor current (or emf) is the same as that of supply frequency,
And rotor frequency may be expressed as:
(
&)
•
the load
:ator and
••
f~·#.'/:'·,:
· s1nde·~tJp
is
,,,,,,
And since n~, =120( JP.
II
~
~
,
Ci
I)
I)
•
••
•
II
•
III
~
t
I;
II
t
I;
I'
t
P
I
t, =-\11
I 20'
,1,1'1<
-11
hi
This shows that the relative difference between synchronous speed and the rotor speed wilJ
determine the rotor frequency
Torque Characteristics
fraction
Analysis of a Self Starting Type Permanent Magnet Motor
A self starting induction motor that has a rotor and cage operates as an induction motor when
starting and as a synchronous motor when the motor reaches synchronous speed with the poles of
the permanent magnets, Self starting type permanent magnet motors, often used in industrially or
in household appliances, do not require a starting device while providing high-efficiency.
91
Analyzing 'the current
induced in the rotor
bars
is
important
because the induced
current
essentially
determines
the
performance when the
motor operates as an
induction motor. For
this reason, it is
important to evaluate
the current that is
induced in the self
starting
type
permanent
magnet
motor.
Stator core
Rotor core ----,..
---Cage
Magnet
The alter&because iW.
As a res!;
inducti0f'( .
~:
Despite its
machine,.
requ~re c~
contmue.~
Coils
This example presents
•
the use of a magnetic field analysis to obtain the current density distribution and- the slip versus
torque curve of a self starting type permanent magnet-motor,
:=:~~
~thecool'
Slip vs. Torque Curve
The slip versus
torque curve is
indicated
in
Fig. 3.
12
10
-
...--.-----:------
..-.--"'"!-.- ..---------:'
:
...;
•
. :
~
!
I
I
:
:
I
The torque of
the self starting
type permanent
magnet motor
gets smaller as
the slip gets
larger, reaching
a
maximum
torque at a 0.4
slip.
AC induction
motor slip
E
~
(J)
5-
. (5
8
•
·_··--·1
I
~
----.J
-I
I
I
."..-
/.?
--.-~
I
I
:
:
I
I
I
I
.. ----~---------~------------~------------~-----------:
:
:
:
6
2
,:
.-----------!----------- +.//.-~-------~-------------l---- ---- ----I
4
...-.······_··--:--·__
:
,,/:
1,/
!
I-
..----.-.-
:
7.t:.~
,
I
I
I
I
,
•
..
I
I
------------1------------1------------1------------1-----------·-1
..
...
•
,
~..
...
I
I
..~
I
I
0.8
0.6
..
I
I
I
I
I
I
04
0.2
... -:-. - -- - - - _. - - ...!-- - -- ...-------1
,,
.
I
(I
Slip
Fig. 3. Slip versus torque curve
92
•
The rotor J
laminatie
and posili...
hence,_
"indu~
The in.
generate .J...
the roto~
called sl~
o
••
Slip dep'
..
The form
•
••
••
•
C
c
c
____
1
•
The alternating current (Ae) induction motor is often lr.'fem:d to ax the workhorse of the industry
because it offers users simple, rugged construction, easy maintenance and cost-effective pricing.
As a result of these factors, more than 90 percent of motors installed worldwide are AC
induction.
ator cors
(
C
t, ----Cage
Despite its popularity, the AC induction motor has two limitations: It is not a constant-speed
machine, and it is not inherently capable of providing variable-speed operation. Both limitations
require consideration, as the quality and accuracy requirements of motor/drive applications
continue to increase .
Motor slip is necessary for torque
C.
•
t:
,
.\
••
•e
.(
generation
t'l
~
slip versus
,_~
Figur~ 1. Cutaway of ,squirrel c~ ACinductiQn motor opened to
st>owthe sbIIor lind rotor construction. the stHIft '<lith bearing.;
and the cool ing fan.
II
An AC induction motor consists of two
asscmblies,stator and.rotor. The stator structure
is composed of steel laminations shaped to
form poles. Copper wire coils are wound
around these poles. These primary windings
are connected to a voltage source to produce a
rotating magnetic field. Three-phase motors
with windings spaced 120 electrical degrees
apart are standard for industrial, commercial
and residential use.
The rotor is another assembly made of laminations over a steel shaft core. Radial slots around the
laminations' periphery house rotor bars.cast-aluminum or copper conductors shorted at the ends
and positioned parallel to 'the shaft. Arrangement of the rotor bars resembles a squirrel cage;
hence, the term squirrel-cage induction motor. The name "induction motor" comes from the AC
"induced" into the rotor via the rotating magnetic flux produced in the stator.
......
- - - - - --I
I
- - - - - --1
,
!
;
- - - - - --i
I
,
!
The interaction of currents flowing in the rotor bars and the stators' rotating magnetic field
generate torque. In actual operation, rotor speed always lags the magnetic field's speed, allowing
the rotor bars to cut magnetic lines of force and produce useful torque. This speed difference is
called slip speed. Slip also increases with load and is necessary for torque production.
o
Slip depends on motor parameters
The formal definition of slip is:
93
1
S = (ns , n) x 100 percent/us
ns
= synchronous
, where
speed
«
=
e
n actual speed
At low values, slip is directly proportional to the rotor resistance, stator voltage frequency and
load torque, and inversely proportional to the second power of supply voltage. The traditional
way to control wound-rotor-induction-motor speed is to increase slip by adding resistance in the
rotor circuit. The slip of low-hp motors is higher than that of high-hp motors because rotorwinding resistance is greater in smaller motors.
D
As seen in Table 1, smaller and lower-speed motors are associated with higher relative slip.
However, high-slip large motors and low-slip small motors also are available.
~
6\
C'
Q)
:"
cr
lo..
.,
..
Figure2.,.,
tho!
.
""the.
••
•e
(_.\}~Tent r:
Motor slip of selected aluminium and cast iron NEMAmotors, with synchronous speed ranging
from 3600 RPMto 900 RPM.
As one can see, full-load slip varies from less than I percent (in high-hp motors) to more than 5
percent (in fractional-hp motors). These variations may cause load-sharing problems when
motors of different sizes are connected mechanically. At low load, the sharing is about correct;
but at full load, the motor with lower slip takes a higher share of the load than the motor with
higher slip.
As shown in Figure 2, rotor speed decreases in proportion to load torque. This means that rotor
slip increases in the same proportion.
Key:
A
= Synchronous
e" I"(!!lf(;
,':,ue_
••
•
•
•
f-tgure"3 Tc
!":':':-I~-:sr·:!C
!"'';:- ;
&
speed
•
•
B = Rotor speed
94
••
•
••
,
C
c
_____
---f
..
(
c
«
D = Torque
=:
Rotor slip
(
c
(' quencyand
C'
«
•
e
•
D
A
Synchronous
speed·
: traditional
lance in the
ause rotor-
:lative slip.
Ii'
e;
•
•
•
•
e
•
•
.,•
•
•
•
•.)
.)
•
•.1
IJ
~
~
II
I,
f
t
Speed
Figure 2. Tho?!.pe.;c curve ,::"f :;n indlJctio~motor.
Ih;;1 01 the .yr.chr,.r.ous
,.p,•.j
CO
Slip is tho:- diffo::rence irl rotor $pecd ri:la1i\l~ f.:.
= P.D . E;D = AB.
Relatively high rotor
impedance is required
for good across-theline
(full
voltage)
starting performance
(meaning high torque
against low current),
and
low
rotor
inlpedance
is
necessary for low fullload speed slip and
high
operating
efficiency. The curve';
in Figure 3 show how
greater
rotor
impedance in motor B
reduces the starting
current and increases
the starting torquebur
it causes a gr Iller slip
than ill standard motor
A.
Torqlf!-i« ur.-ent
id ranging
ore than 5
ems when
ut correct;
actor with
Methods to reduce slip
Synchronous motors. reluctance motors or
permanent-magnet
motors
don't
slip.
Synchronous motors commonly are used for very
high-power and very low-power applications, but
to a lesser extent in the medium-hp range, where
many typical industrial applications arc found.
Reluctance motors abo are used. but their
output/weight ratio is not good and. therefore,
they are less competitive than squirrel-cage
induction motors.
that rotor
Permanent magnet (PI\·ll motor-; which are used
\\ ith electronic acljll~;[;t!:k-:,pl'l'd dri ve-, prov ide
To reduct
the speed
cornpen!('
compensat
80 perce~.,
benefits such as accurate speed control without slip, high efficiency with low rotor losses and the
flexihility of choosing a very low base speed, eliminating the need for gearboxes. PM motors are
limited to special applications, mainly because of
high cost and the lack of standardization.
Rotor speed
Selecting an oversized AC induction motor also
reduces ~lip. Larger motors exhibit less slip, and
it gets smaller with a partial (rather than full)
t'
C
motor load.
I :: Synchronous speed
For example, refer to Table I. The required
power is 10 hp at about 1,800 rpm and 1.5
percent speed accuracy is required. We know
that a 10-hp motor has a slip of 4.4 percent. Can
we achieve an accuracy of 1.5 percent with a 15-
2 :: Without slip compensation '
=
3 With slip compensation
hp motor?
Torque
FiglJr~ .:1. lhe effo:ci of the slip oornpensGtion
4
•
Answer: The full-load slip of the i5-hp motor is
2.2 percent. but the load is only 10115 = 0.67.
The slip will be 67 percent of 2.2 and equals 1.47 percent, which fulfils the requirenents. A
disadvantage to oversizing is that 'larger motors consume more energy, increasing investment and
•
•
Figure 5...
Vector.
operution costs.
Adjustable-speed AC drive often is the best solution
Using adjustable-speed control can solve AC induction motor limitations. The most common AC
drives lise pulse-width modulation (PWM). Line voltage is rectified, filtered and converted to a
variable voltage and frequency. When frequency-converter ouput is connected to an AC motor,
it's possible to adjust motor speed.
When an AC drive is used to adjust motor speed. motor slip is no longer a problem in many
applications. A number of drive applications still exist. including printing machines, extruders.
paper machines, cranes and elevators, in which high static speed rlccuracy, dynamic sped
accuracy or both are required.
Rather than oversizing the motors to eliminate the slip-induced speed error, it may he better to
use sectional drive line-ups with separate inverters for each motor. The inverters are connected to
a direct current (DCl-voltage bus bar supplied hy a ~'(lmI110nrectifier. This is an energy-efficient
solutiul1 because the driving sections lISl' the braJ...ing energy from decelerating sections
(rcgencr<ltion ).
The ne~
and ~ir~
algonthms
PWM~
fixed swiu
the load.
minimizes
operatio.
What is!
•
DTC is ar
flux and.
Theinp"
from the
r
to-anae"
•
•
•
•
•
•
•
•
•
•o
pC
«
,
{
(,
es and the
notors are
,ecause of
1.
notor also
; slip, and
than full)
To reduce motor slip, compensation can be added to AC drives. A load torque signal is added to
the speed controller to increase the output frequency in proportion to the load. (Slip
compensation cannot be 100 percent of the slip because rotor temperature variations cause overcompensation and unstable control.) But the compensation can achieve an accuracy as great as
80 percent, reducing slip from 2.4 percent to 0.5 percent.
(
f'\
.'
1
•
C
.'.'
•
•
required
and 1.5
We know
rcent. Can
with a 15-
p motor
is
0.67.
er ients. A
strnent and
15
=
Figure 5. Bloel-;diagram of Direct Torque ContrOl. OTC
Vector and direct torque control improve speed control
nnmon AC
verted ('0 a
AC motor,
c)
m
III
many
, extruders.
unic speed
•
•
better to
onnected to
g) -efficient
Ole
Ig scctiou-.
The newest high-performance technologies in adjustable-speed drives field are vector control
and direct torque control (DTC). Both use. some type of motor model and suitable control
algorithms to control torque and flux, 'rather than the voltage and frequency parameters used in
PWM drives. The difference between traditional vector control and DTC is that the latter has no
fixed switching pattern for each voltage cycle. DTC switches, instead, the inverter according to.
the load 40,000 times per sec. This makes OTC especially fast during instant load changes and
minimizes the need for and effect of dramatic speed changes once the load or process is in
operation.
What is DTC?
DTC is an optimized AC drives control principle. ill which inverter switching directly controls
nux and motor torque.
The input van abies for DTC arc motor current and DC link and voltage. The YoltaL!1' is defined
from the DC-bus voltage and inverter switch positions. The voltage :1I1dcurrent signals are inputs
to an accurate motor model, which updates stator flux and torque every 25 microsec.
<)7
motor torque and flux comparators compare the actual values to the reic.rence value',
produced by torque and flux reference controllers. The outputs from these two-level controller,
are updated every 25 microse~. and they indicate whether the torque or flux must be changed. '
Two-level
(1
• f10
Depending on the outputs from the two-level controllers, the switching logic optimizes inverter
switch positions. This means that each single voltage pulse is determined separately at "atomic
level." The .invener switch positions determine motor voltage and current, which, in turn:
influence the motor torque and flux (this closed loop control eliminates the need 'for encoders in
· i,
(',
It
many applications).
i
It
The reason DTC 'control reacts' faster than PWM· control is shown in Figure 6."The motor is ..
running ~ith low load at p<?int.A an~ the load has ~ stepwise increase to'ohi§l.t:?a~. Th.e higher
torque with th~ PWM control.is achieved by reducing speed from A to B,;"'fhISh.:ls quite slow.
The higher torque with .the DTC control is achieved by direct increase e.t.tQrqy.~,fr:qrn A' to C
.
.
about 10 times faster than that''br}>V\'Mcontrol.
Slip compensation with DTC is instantaneous
and produces a nominal slip of 10 percent. This
translates into a speed accuracy of 0.1 percent to
0.5 percent. This enables OTC drive use.in many
applications. where a tachometer-based vector
control was needed previously. For applications
demanding an even higher accuracy, it's possible
to add a pu1se encoder to a DTC drive.
Torque
Check Your Progress ,...1
. Note: 1. Give your answer in the space given
below.
2. Check your answers with those given
at the end of the unit.
Speed
1 Explain slip-torque cbardcteristics?
~
.
_
.
...............................................................................
FiglJrlt? ~'. CC1rr,p3rise.rl t,t:t·,I.'-~,:;:n FV';t.~,'(I('(jijf::::r::;-,~nj
C. \\-Uh [lTI:' (:ontrc·j
(lTe: drh~
"'I"':~,~Gc·ntrci ""fd
.fI, to
CI
1·. Electrfl
2. A Tex!J..
3. Opera""
4..Elec~
•
2.4ANS'
•
•
CheckYo\
•
1.
•
'i
2.5GL
•
e .
.................
.........................
(.ontcc,1during IO:;li,j~m~,~d:
P.t:, E···
...itr , f
2.3S0M
.-
.
Self-sta •
•
•
2.2 LET llS SUM UP
•
The Development
•
or Induced Torque in an Induction
9X
Motor
••t.
•
•
•
•
•
•
•
•
•
•
,
crencc vulu-.
C
/el controller,
~changed.
(
l1izes inverter
(
ely at "atomic
(
or encoders in
tlll( j·=.k" ...BR· xB).,..
•
hich, in turn,
•
•
(
..
C"
I
C'
C')
C'
•
•
•
•
•
The motor is
rd. The higher
.is quite slow.
: from A to C
WM control.
i nstantaneous
percent. This
0.1 percent to
'e use.in many
-based vector
)r applications
y, it's possible
ive.
·1, Electrical Machines by SK Bhattacharya. TataMcHill Publishers
2. A Text Book Electrical Technology by BL Theraja, S.Chand Publishers
3. Operation and Maintenance of Electrical Machines by B.V.S. Rao, Khanna Publishers, New Delhi.
4. Electrical Technology by Edward Hughes, Addision -Wesley International Student Edition
..
.'
e space gi ven
.].
~
The speed of induction motor must always be less than the synchronous speed and as the
load increased the spree of the motor will decrease.
An AC induction motor consists of two assemblies, stator and rotor.
DTC is an optimized AC drives control principle, in which inverter switching directly
controls flux and motor torque.
.
The voltage is defined from the DC-bus voltage and inverter switch positions.
See section 2.1
:h those gi veil
2.5 GLOSARRY
e
C>
•
•
•
•
•
•
•
sties?
Self-starting induction motor
•
•
•
•
A self starting induction motor that has a rotor and cage operates as an induction motor
when starting and as a synchronous motor when the motor reaches synchronous speed
with the poles of the permanent magnets.
Self starting type permanent magnet motors, often used in industrially or in household
appliances, do not require a starting device while providing high-efficiency.
Analyzing the current induced in the rotor bars is important because the induced current
essentially determines the performance when the motor operates as an induction motor.
For this reason, it is important to evaluate the current that is induced in the self starting
type permanent magnet motor.
~
I,
I;
99
+Re(
lI
u,t
UNrT-3 CIRCLE DIAGRAM
(
STRUCTURE
-
3.0 OBJECTIVE
~,
3.1 INTRODUCTION
3.2 LET US SUM UP
. 3.3 SOME USEFULL BOOKS
r
~
3.5 GLOSSARY
3.0 OBJECTIVES.
,. ,
•
After studying this unit, you should be able to analyse:
•
•
•
Paramee
Circle diagram of an induction machine.
The concepts in operating methods.
3.1 Il'lTRODUCTION
•
!I
.
The circle diagram of an induction machine is the orbit of the stator current.
Preconditions are:
• U I is in y-axis
• the rotor is short-circuited
• Rl = 0
The locus of the stator current II is a circle. The middle point of the Circle lies on the
negative imaginary axis (y-axis), the diameter of the circle is (I1-10), Figure 7 shows
the circle diagram of the induction machine.
.
For the
slip line~
the line
For the •
Powerit!+
From th_
11 foral".
the air-gal
the line.
Thediffj
through
•
•
Operat.
The thr.
as follow:
• Motor.
100
•
•
•
•
•
•
•
•
C)
0
-_
..
_£
(
f --_
+Re
(
(
(
C["
(,
C;"
-lm
M
«
.,--
c'
•
•
•.,
e
I
.:
C'!
.
Figure 7: Circle diagram of an induction machine
Parameterization
For the construction of slip a tangent to the circle at the point 10 should be drawn. The
slip line is an arbitrary straight line parallel to the x-axis (-1m axis). The extension of
the line 12 will divide the slip line proportional to the slip .
For the parameterization another point besides the no-load point must be known.
Power jn the circle diagram
From the circle diagram of induction machine it is not only possible to read the current
11 for any operating point.but it is also possible to directly determine the torque M.
the air-gap power PD, the mechanical power Pmech and the electrical power Pel from
the line segments.
&:
•
•
•
•
•
•
•
•
•
c,.
I)
"
f
f
(
,
The different powers are shown in the circle diagram in figure 8. The straight line
through s = 0 and s = I is called mechanical power line.
Operating ranges and specific operating points
The three operation mode- ot induction machines arc represented in till' circle di~l",ral1l
as follows:
_ Motor operation: () < s < ,. Brakint: operation: I < s < I- Generator operation: s < ()
Io I
Ched; You,'
,
Note; 1. G~Y
+R<
2. Ch(
1.Explainc,
......................
.................
C'
'..
,
-.~-
~
Br;ske s > 1
,~
~LET-Ui\
• Th'-;
•
•
For th
Froe
'.1:.3 SOMEi)
Figure S: Power'in the circle diagram
I
1. Ele~tric.
'
2. A Tex't4
The following points can be distinguished:
3.0perati.
No-load: s = 0, n = nl: No-load current lies on the x-axis and should be as small as possible,
considering the absorbed reactive power of the induction machine.
•
3.4ANSWi,
Ch~
Breakdown point: At this point the induction machine has the maximum torque. This is the peak
point of the circle, the real part and imaginary part of the current J; are the same. Starting- or
short-circuit point: s = 1. n = 0; At the start-up of. the machine the short-circuit current I I K is
several times the rated current liN. So it has to be limited. Typical values arc II K = 5...7 . II N.
Ideal short circuit: s = I, n = I: This is the largest theoretically occurring current which also lies
on thex-axis. The values reached in practice are 11 5.:.8 . liN
=
Optimum operating point: The rated point is chosen at the point where cosl is maximum. This is
fulfilled if the rated current line is a tangent to the circle. In practice the optimum value cannot
be always kept exactly.
I. See.
3.5GL0S9
operating'
• Motor o~
• Brukina jt
• Gcncratoi
102
•
The three o.£.
asfollov,s.
,
•
•
•
•
•
•
•
•
•
•
•
G
"
CheeL Your Progress - J
Note: 1. Give your answer in the space given below.
2, Check your answers with those given at the end of the unit.
1.Explain circle diagram?
.
;
...................................................................•.....................................................
3.2 LET- US SUM UP
.
,
t.'
•
•
•
The circle diagram of an induction machine is the orbit of the stator current.
For the construction of slip a tangent to the circle at the point 10 should be drawn.
From the circle diagram of induction machine it is not only possible to read the current
I, Electrical Machines by SK Bha,na<;harya,Tata1v!cHill Publishers
2. A Text-Book Electrical Technology by BL Theraja, S.Chand Publishers
3. Operatio.i and Maint~nance of Electrical Machines by R VS. Rao. Khanna Publishers. New Delhi.
ossible 3.4 ANSWER TO CHECK YOUR PROGRESS
Check Your Progress - I
re peak
I. See section 3.1
ing- or
IlK is
liN.
--------~----------------------------------.------------~--------
Iso lies
Operating .rangl~
3.5 GLOSARRY
The three operation modes of induction machines are represented in the circle diagram
•
This is
cannot
as follow s:
• Motor operation: 0 < s < I
• Braking operation: I < s < I
• Generator opera! ion: s < ()
1
103
UNIT-4 SPEED
(enter (':
CONTROL
factor)
(
STRUCTURE
4.0 OBJECTIVE
4.1 INTRODUCTION
4.2 CONTROLLING
4.3 SPEED CONTROL
4.3.1
4.3.2
THE SPEED OF THREE PHA5I;: INDUCTION
FOR A.C INDUCTION
MOTOR
MOTOR
VARIABLE FREQUENCY'DRIVES
PHASE VECTOR DRIVES
4.3.3 . DIRECT TORQUE CONTROL DRIVES
4.4 LET US SUM UP
A motor c
and pr,·,;
be bolted
maint~~:r
overload r
and a ~.>c
throug~s,_
. centers~r'
.
C'
Each mot
controiIJ,
of bi-metr
of circe
c~n.nec~)
wmng It{;
f)l
Motor
resistare
4.7 GLOSSARY
Check.
4.0-:0BJECTIVES
Note:
•..
•
2.
.•
•
·1I(
Speed control of induction motor
Control the speed of a.c induction motor
4.1INTRODUCflON
A motor control c~nter (MCC) is an assembly of one or more enclosed sections having a
common power bus and principally containing motor control units.!'! Motor control centers are in
modem practice a factory assembly of several motor starters. A motor control center can include
variable frequency drives, programmable controllers, and metering and may also be the electrical
service entrance for the building. Motor control centers are usually used for low voltage threephase alternating current motors from 230 V to 600 V. Medium-voltage motor control centers
. are made for large motors running at 2300 V to around 1500uV, using vacuum contactors for
switching and with separate compartments for power s w'itching and control.
1. Expl~
............•
•
----4.1COi
ThesP"
voltage. r
convert.
voltages a
controll •
Note th~'
Motor control centers have been used since 1950 by the automobile manufacturing industry
which used large numbers of electric motors. Today they are used in many industrial and
commercial applications. \\'her~ very dusty, or corrosive processes arc. used. the motor control
J04
}~OU
for.
this parag
work.') ..
•
•
•
•
•
•
•
•
•
f)
I.
(
center may be installed in a separate air-cunditioncd
factory floor adjacent to the machinery controlled.
«
A motor control center consists of one or more vertical n'ictal cabinet sections with power bus
c
and provision for plug-in mounting of individual motor controllers, Very large controllers may
be bolted in place but smaller controllers call be unplugged fromthe cabinet for testing or
maintenance.
Each motor controller contains a contactor or a solid-state motor controller,
overload relays to protect the motor, fuses or a circuit breaker to provide short-circuit. protection,
and a disconnecting switch to isolate the-motor circuit. Three-phase power enters each controller
through separable connectors.·The
motor is wired to terminals in the controller. Motor control
centers provide wire ways for field control and power cables.
t,
(
f"
€~
.\.'
1'\
•
•
•
I
•
("
I
I
I
I
I
•
Chetk Your Progress - I
Note:
2. Check your answers withthose given at the end of the unit.
e
.;
f
>:
I)
•
•
•
•
Each motor controller in an MCC can be' specified with a range of options such as separate
control transformers, pilot lamps, control switches, extra control terminal blocks, various types
of bi-metal and solid-state overload protection relays, or various classes of power fuses or types
of circuit breakers. A motor control center can either be supplied ready for the customer to
connect all field wiring, or can be an engineered assembly with internal control and interlocking
wiring t~a central control terminal panel board or programmable controller.
Motor control centers (MCC) usually sit on floors, which are often required to have a -fircresistance rating. Firestops may be required for cables that penetrate fire-rated floors and walls.
e
••
••
•
room, nul (lite! I all [VjCC wil] be on the
1. Explain motor control?
..............................................................................................................................................................
............................................................
_
•••••••••••••••••••••••••••••••••••••••••••••
'! ••••••••••••••
having a
ers are in
1 include
electrical
ge threeI centers
ctors for
The speed of a normal 3-phasc induction motor is a function of the frequency of thO::supply
voltage. Changing the speed of such a motor-hence requires building a 3-phasc power frequency
convertor. The driver can be realised using power mosfets (or IGTB's) capable of han~lIing high
voltages and fast switching speeds. The generated frequency can be programmed in a small PIC
controller and even in a fast Basic Stamp.
industry
trial and
I control
Note that at lower (hall 11orrna I frequencies. the \'olta~l; should be decreased proportionally.
It
you forget thi·s. the motor may overheat and evcntuull , even burn out. (S.:,_'note at tilt' bottom of
tillS paragraph). The circuits shown here sene mere educational purposc-, (;dth(lu~1! they do
\\ or" I) and arc not a hI ~t\ ... tIll' most suitable nor \;:1 ext xollut ion.
4.2 CONTROLLING THE SPEED OF 3 PHASE INDUCTION MOTORS
I!)'i
_
For
till
bipolar drive circuit shown below, tilt' motor should bc
Jiltl~11 highf
rectifIed 3'1,:
insulati.on
.1
dcliii-COI1I1CLlC(L
expenSIve ttl,
since we dC';
APplicati<Ci
•
chat:;
:- ~;~:
• Bn.
----:-_.:::---==-=t==========---== -------
--
----,~---.,----,~"G~-l
NOTE:'
e
'If you are
1ft
_______ I_~'-=L=.;b_Jt .. 'ml..'~..
_--+--~_=!==--L..:::.-
.ihe many
m:
(Micromas~
the speed ~
(~10V most
'commands f)
1~F.:=:~====f'=~==''====F=,--------l----,
,3J(;8.".~
~
1____-..11."1
as a motor £I
~ircuits sh.
_~:t:_._.J_
The optocouplers used 'can be either TIll I J or eNY} 7- ~_Do not try to save on the transformers:
these are very small and cheap types (2VA is enough) and the floating way they arc connected
here (no grounded negative poles!) is essential to this design. Be careful! when playill~ around
with .this kind of circuitry. since there are high voltages everywhere. The digital input and the
microcontroller are,completely and optically isolated from the power circuitry.
The bit-pattern to be programmed in the controller software could look like:
4.3SPEE~
Recent
•
deve
these motofj;.
torque geneb!
Note the' 120 degree phase shift. The pattern, was designed to generate a lot of thirth harmonic
distortion
'
.
on
the
wave.
resulting
.•.. 'j
j
mcrcusing
thus
yoltagc
the
RMS
mot or
over
the
I
windings.
I "','..''',''"
.
If
you
motor to be
connected,
problem
111:11
'~"",'
I
I
I.-j' ~;,;
II I
1
,"",-'
,
1
I
!
"
!
I
I
,_L
i
t '1'" .. ,
I
1
you
Iii
'"
..
I
want
!
the
ill
he'
need
"
\1
I
111'
!I
i
I
I, ,
the
y-
II ;'.
•
•
•
•
•
•
•.,
f
...
much higher voltage to wori. from. Using a 3-plias·. rccnuei bridge, you can ur course USc
rectified 3-phase mains current. but that presuppose- its availability. Ass an alternative an
insulation transformer 230V/ 400V can be used. However. at the end this will tend to be more
expensive than the circuit given above. The circuit below however
become a lot simpler,
since we do not require 6 mosfets and no floating powers supplies:
€
«
will
(
(
Applications:
".-
• changing! adjusting the wind pressure inwindblown organs.
• Motor controllers for lathes, large saws etc...
• . 3-phase current generator
• Brushless DC motor drives
f;
'-
NOTE:
«
.'
:If you are in need of a controller for a 3-phase motor, you should always consider using one of
the many modules the industry offers these days. Factories such as' Lust gmbh, Siemens
(Micromaster 410), Toshiba, Hitaclii., all have controll modules in their catalogues. Controlling
the speed of the motor using such a standard solution canbe done by sending an analog voltage
JO-IOV most of the time) to the appropriate input. or, on some models, by sending RS232
'commands to.their. port. The advantage of these modules is, amongst other things, that they serve
as a 'motor protector at the .same time. Also, it might at the en'd be cheaper than building the
circuits shown above yourself.
c)
•
•
•
•
&1
0
C;\
•
•
•
•
•
•
..
C)
C
C!
'-
•
C;
1-'
I
I
I
I
.n'rners:
mected
around
1I1U the
nnolllc
thc
wave,
reusing
voltage
motor
III
the
ythe
he
·d
;1
4.3 SPEED CONTROL FOR A.C INDUCTION MOTOR
Recent developments in drive electronics have allowed efficient and convenient speed control of
these motors, where this has not traditionally been the case. The newest advancements allow for
torque generation down to zero speed. This allows the polyphase AC induction motor to compete
in areas where DC motors have long
dominated, and presents an advantage in
robustness of design, cost, and reduced
maintenance.
4.3.1 Variable frequency drives
A variable-frequency
drive (VFD) is a
system for controlling the rotational speed of
an alternating current (AC) electric motor by
controlling the frequency of the electrical
power supplied to the motor.[1)[2lf3] A variable
frequency drive is a specific type of adjustablespeed drive. Variable-frequency drives are also
known as adjustable-frequency drives (AFD),
variable-speed drives (VSD). AC drives.
07
l11icrodrives or inverter
sometimes
drive».
Since the voltage
is varied along
also called VVVF (variable voltage variable frequency)
with frequency.
these are·
speed
0'
reliability
drives.
("
Variable-frequency
drives are widely used. In ventilation systems for large buildings. variablefrequency motors on fans save energy by allowing the volume of air moved to match the system
demand. They are also used on pumps, elevator. conveyor and machine tool drives.
VFD types
All VFDs use their output devices (IGBTs. transistors. thyristors) only as switches. turning them
only on or off. Using a linear device such as a transistor in its linear mode is impractical for a
VFD drive, since the power dissipated in the drive devices would be about as much as the power
delivered to the load.
.
Drives can be classified as:
•
•
•
Constant voltage
Constant current
Cycloconverter
In a constant voltage converter. the intermediate DC link voltage remains approximately constant
during each output cycle. In constant current drives. a large inductor is placed between the i~put
rectifier and the output bridge,
the current delivered is nearly constant. A cycloconverter has
':'0 input rectifier or pC link and instead connects each output terminal to the appropriate input.
so
phase.
The most common type of packaged VF drive is the constant-voltage type, using pulse width
modulation to control both the frequency
Sine'i,'av(,
. 'Jallab'e
Mcd1aOical
and effective voltage applied to the motor
Power
Fro;:q"CflCY
Power
load.
~
[.
Pcr,·.':"
AC Mota' '
----V· I
VFD system description
~~"
1i;Jllat;l.::
_8.__
c-ri;:::;:~:;:J.,.
t2:.~.r,'D"'"C~,e,"o,
VFD system
F
LuI
"".w C~,a,,~
Opera:,,:
'nteda-::c
A variable frequency drive system generally
consists of an AC motor. a controller and an operator interfaee.1411''I
VFD motor
The motor used in a VFD system is us"ual1ya three-phase induction motor. Some types of singleph:ISl' motors Gill be used. hut three-phase motor" arc usually preferred. Various types of
'ynl..hrono\,', motors offer achantages in some situations. hut induction motors arc suitable for
Ill""! pUrp(hcs and are Ilcner:t1ly the most economical choice. ~d()l(lrs that are designed Ior fixedIO~
VFDcl
~~~
Variab1iP·
usual dis
circuit. .,
energy im
.improv.l
sequ~c~
DC. md!:
convert.,
phase inp
•
•
•
As new
appliecte
availabl~
device~
. AC moto
freque[e
operate ~
freque.
value (JI.
adjustr&;'
rule.
-re
In add.
control a
wayth.
The ust!
WithPiI
wavefon
pseud.
.Opemte
(base ~
do not'l!"
motur.i.
ACm<T
•
•
•
•
•
•
•
•..
G
tE,
(
(
, these are
,
s, variablethe system
(
(
C
,C)
irning them
ictical for a
s the power
C\
t
•
.'•
•
•
•
&
0
ely constant
en the inpJt
mverter has
priate input
pulse width
Mcchanocal
Pi)\'iCf
speed operation are often used. Certain enhancements to the standard motor designs offer higher
reliability and better VFD performance, such as MG-31 rated motors 1(·1
VFD controller
Variable frequency drive controllers are solid state electronic power conversion devices. The
usual design first converts AC input power to DC intermediate power using a rectifier or
converter bridge. The rectifier is usually a three-phase, full-wave-diode bridge. The DC
intermediate. power is then converted to. quasi-sinusoidal AC power using an inverter switching
circuit. The inverter circuit is probably the most important section of the VFD, changing DC '
energy into three channels of AC energy that can be used by an AC motor. These units provide
. improved power factor, less harmonic distortion, and low sensitivity to the incoming phase
sequencing than older phase controlled converter VFD's. Since 'incoming power is converted to
DC, many units will accept single-phase as well as three-phase input power (acting as a phase
converter as well as a speed controller); however the unit must. be derated when using single
phase input as only part of the rectifier bridge is carrying the connected loadpl
As new types of semiconductor switches have been introduced, these have promptly been
applied to inverter circuits -at all voltage and current ratings for which suitable devices are
available. Introduced in the ]980s. tlie insulated-gate bipolar transistor (lOBT) became the
device used in most VFD inverter circuits in the first decade of the 21st century:18Jl91llOJ .
AC motor characteristics require the applied voltage to be proportionally adjusted whenever the
frequency is changed in order to deliver the rated torque: For example. if a motor is designed to
operate at 460 volts at 60 Hz, the applied voltage must he reduced to 230 volts when the
frequency is reduced to 30 Hz. Thus the ratio of volts per hertz must be regulated to a constant
value (460/60 = 7.67 V/Hz in this case). For optimum performance. some further voltage
adjustment may be necessary especially at low speeds, but constant volts per hertz is the general
rule. This ratio can be changed in order to change the torque delivered by the motor.!" 1
In addition to this simple volts per hertz coritrol more advanced control methods such as vector
control and direct torque control (DTC) exist. These methods adjust the motor voltage in such a
way that the magnetic flux and mechanical torque of the motor can be precisely controlled.
The usual method used to achieve variable motor voltage is pulse-width modulation (PWM):
With PWM voltage control, the inverter switches are used to construct a quasi-sinusoidal output
waveform by a series of narrow voltage pulses with
Pulse \I'Ij,dt!' floch, atcd
pseudosinusoidal varying pulse durations.
",Ia:!aDle FrccJcnv,' Controtle:
O"tput WO'ief(lrr1) II ,,1(;to Line)
~s or singkIS types of
suitable for
d Ior fixed-
Operation of the motors above rated name plate speed
(base speed) is possible. hut is limited to condition- that
do not require more power than nameplate rating of the
motor. This is sometimes called "field weakening" and. for
AC motors, mean" operating at less than rated Yoil,,/hcrll
I Ill)
and above rated name plate speed. Permanent magnet synchronous motors' have quite limited
field weakening speed range due to the constant magnet flux linkage. Wound rotor synchronous
motors and induction motors have much wider speed range. For example. a 100 hp, 460 V,
60 Hz, 1775 RPM (4 pole) induction motor supplied with 460 V, 75 Hz (6.134 V1Hz), would be
limited to 60175 80% torque at 125% speed (2218.75 R~M) = 100% pO\~eLILlJAt higher
speeds the induction motor torque has to be limited further due to the lowering of the breakaway
torgue of the motor. Thus rated power carr be typically produced only up to 130...150 % of the
rated name -plate speed. Wound rotor synchronous motors can be run even higher speeds. In
rolling mill drives often 200 ..3.00 % of the base speed is used. Naturally the mechanical strength
.of the rotor and lifetime of the bearings 'is also limiting the maximum speed of the motor. It is .
recommended to consult the motor manufacturer if more than 15.0% speed is required by the,
application.
.
=
PWM VFD Output Voltage Waveform
An .embedded microprocessor governs' the overall operation .of the VFD controller. The main
microprocessor programming is' in firmware that is inaccessible to the VFD user. However, some
degree of configuration programming and parameter adjustment is usually provided so that the
user can customize the \[FD controller to suit specific motor and drive~ equipment
. requirements.
.
VFD operator interface
The operator interface provides a means for n operator to start and stop the motor and adjust the
operating speed. Additional operator control functions might include reversing andswitching
between manual speed adjustment and automatic control from an external process control signal.
The operator interface often includes an alphanumeric display and/or indication lights and meters
to provide information about the operation of.the drive. An operator interface keypad and display
unit is often provided -on the front of the VFD controller as shown in the photograph above. The
keypad display can often be cable-connected and mounted a short distance from the VFD
controller. Most are also provided with ..input and output (110) terminals. for connecting
push buttons, switches and other operator interrace ,devices or control signals. A serial
communications port is also often available to allow the VFD to be configured. adjusted,
monitored and controlled using a computer.
tllrqU('
speed I
right €
speed r
due 11'
~~:~1
t.l
In prif'
and
side, th
draw.)
conside
•
C-,
(lj
«2)
.,
We neg
•
Un.In
Um.b.
Given.....
(netw~
With ~
and v8
approac
deceleO
allow~
contr~
front-.
energ)'T
••
A vailal
VFD operation
When an induction motor is connected to a fuJI voltage supply, it draws several times (up to
about 6 times) its rated current. As the load accelerates. the available torque usually drops a little
and then rises to a peak while the current remains very high until the motor approaches full
speed.
B) contrast. when a VFD starts a motor. it initiallj applie-: a h)\\ frequency and voltage: to the
motor. The starting frequency i~ typically 2 Hz or Ic~s. Thus ~Iariing at such a 10\\ frequency
~1\,1i(bthe high inrush current 111;1\occurx when a motor is st;lfkd by simply aprlyil1~
the' utilit ,
Illl~lill~i voltage by turninj; Oil ;i "witch. After the "l;til ul" til\.' VFD. till.' applied rn:qu(,lil'~ alld
lin
Vari~b.ll..
3-phas"
design.
are typl'
severa.
Mcdill
(."iOH.
voltaae
with ~.
•
•
•
•
•
•
•
•
--
"
C'
f
I'
(,
~
C'
e
•
••
•
•
••
•
••
•
e
.1
&>
f
lite limited
illdlronou"
ip, 460 \I,
,would be
At higher
breakaway
%'of the
speeds. In
al strength
notor. It is
red by the,
o
The main
.ver, some
;0 that the
iirernents.
voltage arc inLTc;lsL'd a\ a controlled r.uc III r;J!ll!,cd Ill' til accelerate the load without druwing
excessive current. This starting method tYl'ic·;t1!) ;dlm'. S a motor to develop 150~( of its rated
torque while the VF!) is drawing less th;111)W; (I! ih rated current from the mains in the low
speed range. A VFD can be adjusted 10 produce .1 steady IS(YIr starting torque f.rom standstill
right up to full spccd.!"" Note. howcvcr.uh.u
cool ing of the motor is usually not good in the low
speed range. Thus running at low speeds even with rated torque forlong periods-is not possible
due to overheating .01' the motor. If continuou-, operation with high torque is required in low
speeds an external fan is usually needed. The manufacturer of the motor and/or the VFD should
specify the cooling requirements for this mode of operation.
In principle, thc current on the motor side i~;in direct proportion of the torque that is generated
and the voltage on the' motor is in direct proportion of the actual speed, while on the network
side, the voltage is constant, thus the current on line side is in direct proportion of the power
drawn by the motor. that is UJ or eN where C is torque and N (he speed ,of the motor (we shall
consider losses as well. neglected in this explanation).
(Ij
n
adjust the
. for
network
(grid)
and
m
for
U for voltage IV I, I for current LA], and N for speed [rad/s]
motor
INmJ,
We neglect losses for the moment:
=
switching
rol signal.
nd meters
id display
Jove. The
the VFD
onnecting
A serial
adjusted,
'stands
'(2) C-stands for torque
•
Un.In
Um.lm
(same
power
drawn
from
Um.lm
Cm.Nm
(motor
mechanical
power
Given Un is a constant (network voltage) we conclude: In
(network) is in direct proportion of motor Pll\\ er".
=
•
network
and
from
motor)
motor
electrical
power)
Cm.NnVun That is "line current
=
=
With a VFD, the Slopping sequence is just tile opposite as. the starting sequence. The frequency
and voltage applied to the motor are ramped down at a controlled rate. When' the frequency
approaches zero, the motor: is shut off. A small amount of braking torque is available to help
decelerate the load a little faster than it would stop if the motor were simply switched off and
allowed to coast. Additional braking torque can be obtained by adding a braking circuit (resistor
controlled by a transistor) to dissipate the braking energy. With 4-quadrants rectifiers (activefront-end), the VFD is able to brake the load by applying a reverse torque and reverting the
energy back to the network.
Available VFD power ratings
c>.; (up to
ps ;1 little
.ches full
.:."_.Ii)
the'
reLjucllL'y
lJ~'Itldily
.'1,,".
;llld
Variable frequency drives are available with voltage and current ratings to match the majority of
3-phase motors that are manufactured for operation from utility (mains) power. VFD controllers
designed to operate at III V to 61}()V arc often classified as low voltage units. Low voltage units
are typically designed for use with 11l0tOJ:srated to deliver 0.2 kW or 1/4 horsepower (hp) up to
several megawatts. for example. the 1;lrgest ,-\RB ACSgOO single drives are rated for 5.6 MWI:'11
Medium voltage VFD controllers arc d,'\1 ~Il(d t\) operate at 2,-1.()(Jf
..U 62 V (60 Hz). 3,Onn \
(50 Hz; or lip ((1.10 k\'. In S()llIe applll'''tl\)l1~ ;1 ~tcr up trallsfortllt'r is placed between a 11'\\
voltage dri\'e alld a mediulll volt;tg" 1();ld tvl\'diull1 \Illtagl' units are typically designed for usc
\Vilh J1HHors rated to (it:liYL-'r 375 ~\\ i.!i" ~O(l hi) ~tnd aht)\e. ~1edillll)\'oltage urives r~lted abo\"t' I
It i
k V and 5,000 or 10,000 hp should probably be considered to be one-of-a-kind
4.4LETC
----:-
(one-off)
designs.122]
•
Medium voltage drives are generally rated amongst the following voltages: 2,3 KY - 3,3 Kv - 4
Kv
.6
Kv
II
Kv
The in-between voltages are generally possible as well. The power of MY drives is generally in
.the range of 0,3 to ]00 MW however involving a range a several different type of drives with
different technologies.
A~
co
~
start:
ll:
.
..
• AC'
~~
•
.1
"
Note:
LGive your answer in the sp?ce given below.
•
,
"
1. Explain variable frequency drives? .
.........--.~
. ",
•....•.....................,.
~
"
'!'
4.3.2 Phase vector drives.
""
•....--....••.........................................................
:
_ ••••••••••••••••••
..
.'.
~
.
" •••••••••••••••••••••••••••••
'!' ••••••••••••
.
._
'. ~ .' .Ele~tric.
'~.AText
rati•
. .Ove
.
•" Phase vector drives (or simply vector drives} are an improvement over variable frequency drives
(VFDs) in that they separate the .calculations (If magnetizing current and torque generating
'current. These quantities are represented by phase vectors, and are combined to produce the .. ~
driving phase vector which in tum is decomposed into the driving components of the output
stage. These calculations need afast microprocessor, typically a DSP device.
.ro
fhi.
Unlike a VFD, a vector drive is a closed loop" system, It takes feedback on rotor position and
phase currents. Rotor position can be obtained through an encoder, but is often sensed by the
rl!verse EMF generated on the motor leads,
.
" .
" .Electric.
~. Perforilja
,6. Electric!l"
"1.Electric...
8. Electric~
'9.Electric.
i IO.Electrica
Ltd, New'"
In some configurations. a vector drive may be able to generate full rated motor torque at zero
_4.6A~SJf
.
~~.
•
"
Che,
I.Seet
4.3.3 Direct torque control drives
CI.
Direct torque control has better torque control dynamics than the PI-current controller based·
vector control. Thus it suits better to servo control applications. However. it has some advantage
over other control methods in other applications as well because due to the faster control it has
better capabilities to damp mechanical resonances and thus extend the life of the mechanical
system.
2. See.
4.7GLO~
Speed co'"
.
.
•
•
112
.
'.
Va•
Ph•
Dire
•
•
•
•
•
•
•
••
"
t
(one-off)
4.4 LET US SUM UP
(
(,
~,3 Kv - 4
Kv
{'l merally in
(., rives with
A motor control center (MCC) is an assembly of one or more enclosed sections having a
common power bus and principally containing motor control units.
Motor control centers are in modern .practice a factory assembly of several motor
starters.
.
A motor control center can include variable frequency drives, programmable controllers,
and metering and may also be the electrical service entrance for the building.
Motor control centers are usually used for Jaw voltage three-phase .alternating current
motors from 230 V to 600 V.
.
. .Medium-voltage motor control centers are made for large motors running at 2300 V to
around 15000 V, using vacuum contactors Jar switching and with 'separate compartments
for power switching and control.
•
•
•
C"
•
•
I)
.'.,
.................
C)
••
.,
e
~
I)
ncy drives
generating
'oduce the
the output
.sition and
sed by the
.ue at zero
Ci
'4.5 SOME USEFULL BOOKS
: t Electrical Machines by SK Bhattacharya, TataMcHiII Publishers'
2.A Text Book Electrical Technology by BL Theraja, S.Cha~d· Publishers
3.0peration and Maintenance of Electrical Machines by B.V.S. Rao, 'Khanna Publishers, New
Delhi.
I .
•
,
5. Performance & Design
AC Machines by MG Say, CBS 'Publication, New Delhi
6. Electrical·Energy Systems Theory by Elegerd, Tata McGraw HiIlC6, New Delhi
7.Electric Machinery by Fitzerald, rata McGraw Hill Co, New Delhi
8. Electrical MachinestSigma Series) by Kothari, Tata McGraw Hill Co, New Delhi
9.Electrical Machines by Kothari & Nagarth, Tara McGraw Hill Co, New Delhi
IO.ElectriCal and Electronics Engineering by- Vikrarnaditya Dave, Lakshmi Publications (Pvt)
Ltd, New Delhi
of
4~6ANSWER TO CHECK YOUR PROGRESS
I)
I, See section 4,2
C0
•
•
•
"
Cl
C'
...'
••
C.
I
•,
(
I
iller based
advantage
ntrol it has
nechanical
2. See Section 4.4,1
4.7 GLOSSARY
Speed control for a.c induction motor
'.
•
•
Variable frequency drives
Phase vector drives
Direct torque control drives
113
Motor control centre
• A motor control center (MCC) an-assembly of one or more enclosed sections having a
common power bus and principally containing motor control units. '
• Motor control centers are in modern practice a factory assembly of several motor
starters.
• A motor control center can include variable frequency drives, programmable controllers,
and metering and may also be the electrical service entrance for the building.
.
.
• Motor control centers' are. usuall y used for low voltage three-phase al ternating current
-motors from 230.Vto· 600 V.
..
• Medium-voltage motor control centers are made for large .motors .running at 2;300 V to around 15000 V, using vacuum contactors for switching and with separate compartments
for power switching and control
.
.
is
_---'fi(
----·f=-·.
INTRODUC
.
(:
'[his beingJl
concepts ~ll
have beent
',Onemust.f'
\\'llich does ~
motor of'\\("
able to
Si'
;be
:.Thisblock
iJ
. :Unit 1:DetC,
11nit 2: Fo&:>
'.•
'U~it'3:~1
.
.
-Unit
4:
&on
•e
t"':
••
114
._•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
t)
If.
t
BLOCK 4
SINGLE PHASE MOTOR
(
having a
C'
al motor
INTRODUCTION:
'"
ntrollers,
This being the first block of the course, an attempt has been made to define and. consolidate
~oncepts with the help of examples. The important concepts that one must be able to. describe
-h;lvebeen discussed in the block.
t,
CCl
~ current
300 V to •
iartments
One must be clear about these' basic concepts in order to use a IDt of functions and facilities,
which does exist in a single phase motor. These blocks describe the conceptof single phase
motor of WorkingPrinciple, split-phase motor. This basic focus of the block being that you should
be able to study the shaded pole motor and universal motor. .
. .
.This block consists of four units:
'Unit1: Deflnes the basic principle and working of shigle phase motor.
•
••
.
Unit 2: Focus
. on the split-phase motor.
Unit 3: ~vides
the focus on the s~aded pole mot4)r. _
Unit4: provides the overViewof unlversel motor.
.'
e
115
t,
f.
f
(
1.2 w{r
UNIT 1: CONSTRUCTION
AND PRINCIPLE
OF OPERATION
,
STRUCTURE
1.0.OBJECTIVES
"
1.1 INTRODUCTION
1:2 WORKING.PRINCIPLE
.'
.
, !
1.3 SINGLE PHASE LOADS
1.4 LET US SUM UP
come"
1.6 ANSWER TC)"CHECK YOUR PROGRESS
and, so '
suffice
.
__
"
1.5 SOME USEFULL, BOqKS , .
1.7.GLOSS1\RY
~
.
.
~~
1.0 OBJECTIVES
,red~,',~
~ startll~
i,
~'~'~'~~~
'J~"~~~--~~'-'~(---
"
.This lesson is intended to discuss various criteria for motors .
After studying this Jesson you will be able to:
• \Define sjngle psase motor
'
• Single phase loads '
1.1 INTRODUCfION
The single-phase inductionmachine isthe most frequently used motor for refrigerators, washing
Machines, clocks, drills, compressors, pump, and so forth. The single-phase motor stator has a
laminated iron core with two windings arranged perpendicularly:One is the main and the other is
theauxiliary winding or startingwinding.
.
-
Large'
curre.
the win
induce
Insolt
,by mr)
positi\r(
inCr~
to an 11
runn.
.,
CheIP
Notee
••••••••••
t
••••••••
116
•
••
•
•
•
•
•
••
II
1.2 WORKING PRINCIPLE
In a single phase induction, motor, it is
necessary to provide a starting circuit to start
rotation of the rotor.. -If this is riot done,
rotation may be, commenced by manually
giving a slight-turn to .the rotor. The .smgle
phase Induction .motor .may rotate in either
direction and -it is only -the starting circuit
which determines rot;at!onal.directiQn. '
';','.
'I;";'
~!~-
,.....
-:{'~,::"~:'
_ I,
.For small motors of a few watts, the, start
rotationiis-done by means of one ol';twosingle
.
'
.tum(s) "6fbea.vy:,wppet:.,wire·, arQunc:i one
corner of the .pole. -The current inducedin the single tum is 'out of phase.with the ~plY:®rrent
and so causes .an out-of-phase component ill the .magnetic field, .whlch;imparts.t0 othe:I1eld
sufficient rotational character to start the motor. Starting torque is very low and efficiency is also
reduced, Suc.ftshaded-pole motors are typically used in.low-power applirations. with low or zero
;' 'starting torque requirehients, such as deskfans and record p~ayer:s. ';
• ',)
;,
'
. . ~,~ .
~-'
.
,Larger' motors are' provided with a .seeond stator.winding' ~hich is .fed ,with. an out-of ..phase
current to create arotatingmagnetic field. The out-of-phase currentmaybederived.by.feeding
the winding through a capacitor or it may derive from the-winding havingdifferent.values
of
inductance and resistance from the main winding.'
'.
In some designs, the second winding is disconnected once the motor is up to speed, usually either
,by means
«J
•
•
•
•
&1
washing
nor has a
re other is
of a switch operated by centrifugal force acting on weights on the motor shaft or by a
positive temperature coefficient thermistor which, after a few seconds of operation,' heats
and
increases its resistance to a high value thereby reducing the·current through the second winding
to an insignificant level. Other designs keep the second winding continuously energised \'1,J._ •
running, which improves torque.
:up
Check
Your Progress - 1
Note:
1. Give your answer in the space given below .
.
1. Explain single phase motor?
............- -.~--.......•..............•...................................•..... _
-_._
................................................................_
_
_-_._ _ .
117
.
I
1.3 SINGLE PHASE LOADS
tdi
.,
In a -single phase induction motor, it is necessary to provide a starting Circuit to start rotation of
the rotor, If this is not done, rotation may be commenced by manually ~iving a slight tum to the
rotor. The single phase induction motor may rotate in either direction and it is only the starting
tu
(
circuit which determines rotational direction.
I.5S0~
'For smallmotors of' a few watts, the start rotation is done by means .of one or two single tum(s)
of heavy copper wire around one corner of the pole. The current induced in the single tum is out
of phase with the supply current and so causes ali out-of-phase component .in the magnetic field,
which imparts to the field sufficienfrotational·charactert<> st~ li!e motor. Starting torque is very
, low and efficiency, is also' reduced. Such shaded-pole' inotorS }re. ·t)'pically jised in low-power
applicatiDns with low or zero starting torque requirements,
such
as ;desk fans and record. players.
.
.' .
.'
.: ,.'
-
-
-_.
","-.
1. Elect("
2.ATe£'
3. Operf·
"
1.6ANf
Larger motors are provided with a ,second stator .winding which is fed with all' out-of-phase
current to create a rotating magnetic field. ,The out-of-phase current may be derived by feeding
" "thewincUng through a capacitor or it may derive from the winding-having different values of
inductance and resistance from the main winding.
. '
. . Ii'-r
J
. .
,,'
't:
~,~
•
• ,£\
,2._
.Jn some designs, the second winding is disconnected once the motor is up to speed. usually either
.
~_bymeans fif a switch operated by centrifugal force acting on weights on the motor shaft or by a
, positive temperature coefficient thermistor Which, .after a few. seconds of operation, heats up and
increases its resistance to a high value thereby reducing the current through the second winding
to, an insignificant level. Other designs keep: .re second winding continuously energised when
_ running, which improves torque.'
. .
.
1.7GLfl
a.eck Your Progress - 2
Note:
.
1: Give your answer in the space given below.
,,2;Check your answers with those given at the end of the unit.
~
.t:J
_
_ _._
_ _ __ -_
.~- -..-..•......•..........-
1. Explain single phase loads?
.....
• •
•
_
-
r·
-
-_
.
Singlep
_
-.~.-•....•.
•
.
1.4 LET US SUM UP
e
•
•
.~
.1>
•
The single-phase induction machine is the most frequently used motor for refrigerators, .
washing Machines. clocks, drills, compressors, pump', arid so forth.
The single-phase motor stator has a laminated iron core with two windings arranged
perpendicularly.
.
In a single phase induction motor. it is necessary to provide a s~artinf circuit to start
rotation of the rotor.
118
••
•
••
•
• I
•
•
•e
..
•
•
•e
o
f'
"
(
•
'Larger motors are provided with a second stator winding which is fed with an out-ofphase current to create a rotating magnetic field. The out-of-phase current may be derived
by feeding the winding through a capacitor or it may -derive from the winding having
different values of inductance and resistance from the main winding.
.
•. For small motors of a few watts, the start rotation is done by means of one or two single
tum(s) of heavy copper wire around o.necorner of the pole.
(,
:t rotation of
(I It tum to the
(i
C>
f
1"
' the starting
ingle tum(s)
Ie tum is out ignetic field,
irque is very
iIow-power
xd players.
.'.
'
C'
€l
.)
•
•
out-of-phase
:I by feeding
nt values of
1. Electrical Machinesby SK Bhattacharya,TataMcHillPublishers.
2. A Text BQOkElectrical Technologyby
BL Theraja, S.Chand Publish.ers·
3. Operation and Maintenance of ElectricalMachines by B.V.S.Rao, Khanna Publishers, New Delhi.
•
sually either
shaft or by a _
heats up and
ond winding
rgised when
.
'
0
1. See section 1.2
•
CHeq. Your Progress - 2
2. See Section 1.3
1.7 GLO~ARY
.
Single phase induction machine :.•
C·
C>
....................
The single-phase induction machine is the most frequently used motor for refrigerators,
washing Machines, clocks, drills, compressors, pump, and so forth.
• The single-phase motor stator has a laminated iron core with two windings arranged
perpendicularly..
.
• One is the main and the other is the auxiliary winding or starting winding.
Single phase loads :•
•
-efrigerators, .
•
Ig.S
arranged
•
"Cuit to start
In a single phase' induction motor, it is necessary to provide a starting circuit to start
rotation of the rotor. If this is not done, rotation may be commenced hy manually giving a
slig-htturn to the rotor.
The single phase induction motor may rotate ill either direction and it is only the stm1ing
circuit which determines rotational direction.
For small motors of a few watts, the start rotation -is done by means of one or two single
turn(s) of heavy copper wire around one corner of the .pole.
The current induced ill the single turn is out of phase with the supply current and so
causes an out-or-phase component in the magnetic field, which imparts to the field
sufficient rotational character to start the motor. -
119
The(
UNIT 2: SPILT PHASE MOTOR
power,
rcae".
discoll1
.runnft'i
they
STRUCTURE
2.0 OBJECfIVES
2.1 INTRODUCTION
Capl('·
2.2 SPUT-PHASE INDUcnON
.L C'..
MOTOR
·f',
2.3 PERMANENT SPLIT-PHASE CAPACITOR MOTOR
N
2.4 LET US SUM UP
.,!
e
,
Res£\
1'1
2.7 GLOSSARY
A resu
.•
ins.
Ch,•
• provid
2.1 INTRODUCTION
One type of induction motor, which incorporates' a starting device, is called a split-phase
induction motor. Split-phase motors are designed to use inductance, capacitance, or resistance to
develop a starting torque. The principles are those that you learned in your study of alternating
current. Capacitor-start.---the first type of split-phase induction motor that
be covered is the
capacitor-start type. A. simplified schematic of a typical capacitor-start motor. The stator consists
of the main winding and a starting winding (auxiliary). The starting. winding is connected in
parallel with the main winding and is placed physically at right angles to it. '. :
will.
2:2 SPLIT-PHASE
r,
".
. l.Exp
e
INDUCTION MOTOR
•
I)
Another common single-phaseAC motor is the split-phase 'induction motor,ISI commonly used in
• major appliances such as washing machines and clothes dryers. Compared to the shaded pole
'motor, these motors can generally provide much greater starting torque by using a- special startup
winding in conjunction with a centrifugal switch.
.
..
In the split-phase motor, the startup winding is designed with
a higher resistance than the running
.
winding. This creates an LR circuit which slightly shifts the phase of the current in the startup
winding. When the motor is starting, the startup winding is connected to the power source via a
set of spring-loaded contacts pressed upon by the stationary centrifugal switch. The starting
winding is wound with fewer turns of smaller wire than the main winding, so it has a lower
inductance (L) and higher resistance (R). The lower LlR ratio creates a small phase shift. not
more than about 30 degrees, between the flux due to the main winding and the nux of the
starting winding. The starting direction of rotation 1l1;!) he re\ ersed simply b) exchanging the
connections of the startup winding relative to the running winding.
120
2.31/
-.
Anoll.
and'"
~l··
•
thera
wintF
cet
In
~~
in~
•
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•..
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e
tJ
(
The phase of the magnetic field in this startup winding is shifted from the phase of the mains
power, allowing the creation of a moving magnetic field which starts the motor. Once the motor
reaches near design operating speed, the centrifugal switch activates, opening the contacts and
disconnecting the startup winding from the power source. The motor then operates solely on the
.running winding. The starting winding must be disconnected since it would increase the losses in
the motor.
.
.
(
('
(.
(
Capacitor start motor
(I
L
II"
Schematic of a capacitor start motor.
t.
..
A capacitor start motor is a split-phase induction motor with a
starting capacitor inserted in series with the startup winding,
creating ari LC circuit which Is capable of a much greater phase
shift (and so, a much greater stinting torque). The capacitornaturally adds expense to such motors.
-e-:
N
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Resistance start motor
C·
e
••
•
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~
.'
..
A resistance start motor is a split-phase indu<ftion motor with a starter inserted
in 'series with the startup winding, creating capaeitance. This added starter .
provides assistance in the starting and initial direcCion.9f rotation.
split-phase
esistance to
o alternating.
'ver~d is the
uor consists
onnected
Check Your·Progress - 1
Note:
.2. Check your answers with those given at the end of the unit.
In
I.Explain split-phase induction motor?
• .
......_
_
...........•....................... -.__ _ .._ -.....•.•...•..
_ _ _
_
_.-~
"
.
_
.
CD
only used in
._,
shaded pole
zcial startup
2.3 PERMANENT-SPLIT CAPA('TIOR MoToR
the running
the startup
source via a
Another variation is the permanent-split capacitor (pSC) motor (also known as a capacitor start
and roo illotor).{6]This motor operates sioiilarly to the capacitor-start motor described above, but
there is no centrifugal starting switch,[6] and what correspond to the start' windings (second
windings) are ~rmanently connected to the power source .(through a capacitor), along with the
run windings.' ] PSC motors are frequently used in air handlers, blowers, and fans (including
ceiling fans) and other cases where a variable speed is desired.
•
••
•
.,
(,
I,
t
I
I'
I
I
I
I
I
Ihe starting
'las a lower
.e shift. no!
flux of the
hanging the
.
.
.
A capacitor ranging from 3 to 25 microfarads is connected in series with the "start" windings and
remains in the circuit during the run cycle.l6] The "start" windings and run windings are identical
in this motor,[6] and reverse motion can be achieved by reversing the wiring of the 2 windings.l'"
121
with the capacitor connected to the other windings as "start" windings. By changing tips on the
running winding but keeping the load constant, the motor can be made to run at different speeds.
Also, .provided .all 6 winding connections are available separately, a' 3 phase motor can be
converted
a capacitor start and run motor by commoning two of the windings and connecting
the third via a capacitor to act as a start winding,
to
2.6At-
e.
1.(,
l
2.'S,
Check
Your Progress -1
".' ....
f'
_
Note;
-
t':
2.7G
1. Give your answer in.the space given below.
2. Check your answers with those given arthe end of the unit.
PermE
I.Explain perinanent-splii capacitor motor?
-
..
-_ _._---_._ ...•....._ .........•..._ -_-.-.._
........._ ..-_ _ --.-.._.- .._
_
-
-~ -
_
-_._ _-_- .._ ..-_ .
~
..
2.4 LET US SUM UP
Split~pbas~dnotors.are designed to use inductance, capacitance, or fesistance to develop a
.starting. torque. •
• The principles are those. that you learned in your study of alternating current: Capacitorstart-=the first .type of split-phase iflduction motor that will be covered is the capacitorstart type ..
• A simplified schematic of a typical capacitor-start motor. The stator consists of the main
winding and a starting winding (auxiliary).
•
~
•
The starting winding is connected in parallel with the main winding and is placed
physically at right angles to it.
A capacitor ranging from 3 to 25 microfarads is connected in series with the "start"
w~ndings and remains ~nthe circuit during the run cycle
I.
Split Phase Induction Motor section in Neets module 5: Introduction to.Generators and
Motors Archived December 20,2010 at WebCite
.
2.'
.George Shultz, George Patrick Shultz (1997). Transformers andMotors. Newnes.
pp. page 159 of 3:36. ISBN 0750699485,9780750699488.
.
3.
Dominion Resources, Inc. (2007). "Bath County Pumped Storage Station".
Archived from the original on April 4, 2007.
4.
. 'EC-max '16 2-wire electronically cornmutated motors available from Maxon
Motor Australia Archived December 20.2010.
122
•
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•
•
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••
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•
•
•
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e
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taps on the
ent speeds,
2.6ANSWER TO CHECK YOUR PROGRESS
tor can be
connecting
~
f
1. See section 2.2
t
.Check Your Progress - 2
2. See Section 2.3
f
"
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.'
2.7 GLOSARRY
I'
•
1
e,
Permanent split capacitor
._
e)
•
•.
I
develop a
Capacitorcapacitor-
•
fthe main
e)
the "start"
is placed
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rators and
.)
. Newnes.
•
Station",
•
n Maxon
•
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I
I
I
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.
••
,
I
I
Another variation is the permanent-split
capacitor starts and run motor) .
•
This motor operates similarly to the capacitor-start motor described above. but there is no
centrifugal starting switch, and what correspond to the start windings (second windings)
permanently connected to the power source (through a capacit~r). along ~i~h the run,
windings. PSC motors are 'frequently used in air handlers, blowers. and fans (including
.ceiling fans) and olber'Case~ where a variable speed is desired. ", _
....
are
•• .'
•
•
_
capacitor (pSC) motor (also known as a
UNIT 3: SHADED POLE MOTOR
STRUCTURE
3.0 OBJECTIVE
3.1.~TRODUCTION
3.2 SHADED POLE MOTOR
3.3 STARTING'ISSUE AND TORQUELIMITATION
--,
3.4 SHADED POLE SINGLE PHASE MOTOR
3.5 LET US
:f.2SID\DE
- . (i
suM UP
~;~~~
. "3.6 SOME USEFUU. BOOKS
"3.7 ANSWER
1'6 CHECK
(
in 'other .-)
create the r
induced 'cCl
the fluxp~
pole face.
tatum bo~
full level
YOUR PROGRESS
3.8 GLo~SARY
3.0 OBJECTIVEs
r
•
•
Define shaded pole inotor.
State the starting issue and torque limitation
Areversi'
field coil"
four "half:;.l
a pair of~
in all.
c>
3.1 INTRODUCTION
A shaded-pole motor is a type of AC sin_gle-phaseinduction motor. It is basically a small squirrel
cage motor.in which the auxiliary winding is composed of
a, copper ring surrounding a portion of each pole.[11This
auxiliary winding is called a shading .coil. Currents in this
coil delay the phase of magnetic flux in that part 'of the
pole enough to provide a rotating magnetic field. The
direction of rotation is from the unshaded .side to the
shaded (ring) side of the pole. [2] The ~ffect produces only
a low starting torque compared to other classes of singlephase motors.
These motors have only one winding, no capacitor nor
starting switch, "making them economical and reliable.
124
The mot<t>
the motor:
motors
we>
·An uous.
advertisi.
with the
was split.
other. ,Bot
farthera.
ar
Applyin"
of the sli:.
tniVellin~
•
,e
•..
•
•
•
C
C
c:.
(
-----
B~cause their starting torque is low they are best suited to driving fans or other loads thai are
. started. Moreover,
are compatible with TRIAC-based variable-speed controls, which
often are used with fans. The)! are built in power sizes up to
about 116hp or 125 watts- output. For larger motors, other
designs offer better characteristics.
The first photo is of a common C-frame motor. With the
shading coils"positioned as shown, this motor will start.in a
clockwise direction as viewed from the long shaft end. The
second photo shows detail of the shading coils,
,3.2 SHADEO.roLE MOTOR:
"trt,
, A common single:phaiie motor' is the' shaded-pole motor 'and is -used
devices requiring -low
, starting torque, such as electric-fans or the drain pump of washing machines and :dishwaShers or
in 'other small household appliances. In this motor, small single-turn' copper "shading coils"
create the moying magnetic field. Part of each pole is encircled by a copper· coil or strap; the
inducet!'ciirferldn the strap'6J'P<>s-esthechange or':Oux through the coil: This causes a timelag in
the flux p~sing 'through the shading roil, so that the maximum field 1n~risity mo\¢s actoss the
pole face on each cycle.
produces a low level rotating magnetic field wliich islarge enough
to turn both the rotor and its attached load. As the rotor picks up speed the torque builds 'up'to its
full level as,the'priricipal magnetic field 'is rotating relative to the rotating rotor. _ - --
This
A reversible shaded-pole motor was made by Barber-Colman several decades ago. It had a single
field coil, and 'two principal poles, each split halfway to create two pairs of poles. Each of these
four "half-poles" carried a coil, and the coils of diagonally-opposlte half-poles were connected to
a pair oftermimils. One tetminal of each pair was common, so only three terminalswere needed
in all.
.
.
.'
c'
&1
G;
•
••
•
.
Ii
mall squirrel
The motor would not start with the tenninals open; connecting the common to one other made
the motor run.one way, and connecting common to the other.made it run the other way. These
motors were used in-industrial and scientific devices.
.An unusual, adjustable-speed, low-torque shaded-:pole motor could be found in traffic-light and
advertising ..lighting controllers. The pole faces were parallel and relatively close to each other,
with the disc centred between them; something like the disc·in a watthour meter. Each pole race
was split. and had a shading coil on one part; the shading coils were on the parts that faced each
other. -Both shading coils were probably closer to the main coil; they could have both been
farther away, without affecting the operating principle, just the direction of rotation.
Applying AC to the coil created a field that progressed in the gap between the poles. The plane
of the stator core was approximately tangential to an imaginary circle on the disc, so the
travelling magnetic field dragged the disc and made it rotate .
'
II
t
C
C
I,
I
(
(
«
,
125
The stator was mounted on a pivot so it .could be positioned for the desired speed and then
clamped in positio,n. Keeping in mind that the effective speed of the travelling magnetic field in
the gap was constant. placing the poles nearer to the centre of the disc made it run relatively
'faster. and toward the edge, slower.
3.3STA'i_"i
" : ('I
. Even by ih
low. Be<~
constant fr.
.,speed w(:
It is possible that these motors are still in use in some older installations.
squirrel,~
synchrot'lil:
Shaded-pole synchronous motors are a class of AC'motor. '
further Pf.
.
,
Like a shaded pole induction motor, they use field coils with additional copper shading coils (see
the illustration) to produce a weakly rotating magnetic field. But unlike a shaded pole induction
motor (which uses a squirrel' cage rotor), 'the synchronous version of this motor uses a
magnetized rotor. This rotor rotates synchronously with the 'rotating magnetic field: if the rotor
begins to lag -oehind the rotating field,' dri ving torque increases and the rotor_speeds up slightly"
until the rotor's position withinthe rotating field is a point-where. torque = drag; similarly, if the'
rotation of the field slows; down, -the rotor will advance relative to the field, torque will decline,
or even become negative, slowing thespeed of the rotor until it again reaches a position relative
to the field where torque drag.
'
,
=
.
: In more f"i
slowly and
('I
.Shaded ~
prodUC~l
~~~~t~
.checklo':
'
Because of this, these motors'
are often
used t~t",,,'drive electric clocks and, ' occasionally.
,
,
phonograph turntables. In these applications, the speed of the motor is as accurate as the
frequency of the mains power applied to the motor. -, .'
Frequently, the rotor and its associatedredr nion geanmin is encased in an aluminium, copper;
or plastic enclosure; the"enclosed f(?tor is driven magnetically through the enclosure. Such geared
motors are commonlyavailable with the finaloutput shaft or gear rotating from 600 RPM down
to as low as II 168 revolutions per hour (I revolution per week !).
"
A further development dispenses with the shading rings altogether. The application of power
gives the magnetised rotor enough of a 'flick' to move it fast enough to establish synchronism. A
mechanical means prevents the rotor from starting in the wrong direction This design' will only
work satisfactorily if the standstill load is near to zero and has very little inertia.
I
•.
Note:
e
1.
~
1. Explain
•
--~,,,.,
•
3.4 SHAD
I)
Like any.L
stator is ~
Check Your Progress -1
The poll
Tbesmae
Note:
L Give your answer in the space given be19W.
2. Check your-answers with those given at theend of the unit.
1. Explain shaded pole motor?
• .
-...............•.........................................................
.......................................................·..···__····················t·························· _ .
116
•
••
•
•
•
•
•"
•
••
•
"o
t
C
3.3 STARTING ISSUES AND TORQUE LIMITATIONS
d then
'ield In
atively
«
Even by the standards of shaded pole' motors, the power output ~f these motors is usually very
low. Because there is often no explicit starting mechanism, the rotor of a motor operating from a
constant frequency mains supply must be very light so that it is capable of reaching running
, speed within one cycle of the mains frequency. Alternatively, the rotor may be provided V(ith a
squirrel, cage, so that the motor starts .like an induction motor, once the. rotor is pulled into
synchronism, with its magnet, the squirrel cage has 'no current induced in it and so plays no
further part in the operation.
(
t
(
t
!ls (see
t'
,
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C'
e
:: In more recent times, the use of variable frequency controls permits synchronous motors to start
slowly and deliver more torque.
.
luction
uses a
e. rotor
lightly
• if the
ecline,
elative
Shaded pole motor is one of the types of single phase induction motors, which are used for
. producing a rotating stator flux.in order to make-the single phase induction motor a self starting
..me, Let us discuss 'the constructional details, diagrams and working of shaded pole .motors in
detail.
"
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onally,
as the
geared
down
power
ism. A
II only
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1. Explain starting issue and torque limitation?
• .
_
_
_ .•................_
,
3.4SHADEI).POLE
SINGLE-PHASE
.
_
.
.
MOTORS
Like any other motors the shaded pole induction .motor also consists of a stator and rotor. The
stator is of salient pole type and the rotor is of squirrel Gagetype. ,
The poles of shaded pole induction motor consist of slots, which are cut across the laminations.
The smaller part of the slotted pole is short-circuited with the help ofa coil. The coils are made
up of copper and it is highly inductive in nature. This coil is known as
shading coil The part of the pole which has the coilis called the shaded
part and the other part of the pole is called unshaded part.
Cl
C)
Note:. 1. Give your answer in the space given below.
.......................... _
(I
t:)
Check Y~ur Progress - 2
2. <::heckyour answers with those given.at the end of the unit.
opper,
~)
•
••
•
,.
.
..........
Now let tis consider that an alternating current is passed through the
excited winding which surrounds the pole. Due to the presence of
shading coil, the axis of the pole shift from unshuded part to shaded
part. This shifting effect is equivalent to the physical movement of the
poles, which is' nothing but the rotation of poles. So the rotor starts
rotating in the direction of the shift from unshaded pan to shaded pan.
127
(
Advantage
('
Why Magnetic Axis ShiftTakes Place?
The variou:
,
(
,
Now let us discuss why the axis shift occurs when current is
passed through the winding and how the shading coil ~ds in
producing the shift.The current carried by, stator' winding ,
produces alternating flux. The-distribution of flux through the
poles is greatly influenced bythe shadingcoils.
#",...<,'
l
ci
• '>.
•
•
•
isildvanl'(
,When the alternating current through the .coil increases, it .induces a
'current in the shading coil. The direction of current in shading coil is
such as to oppose the cause producing it (from Leriz law). The cause is
the alternating current. So the flux in the shading Coil decreases and it
opposes die main flux. Hence the flux mostly crowds or shifts towards
the unshaded part of the 'pole. So the 'magnetic axis Iies along: the
middle of the uiishaded part.It is denoted, as Nein the picturebelow.
'
' ""'.
No~ consider that the a\tem~ting current has reached its peak (or)
somewhere near th,e peak..He~ tM rafei>f change of current is low, as ,
it has already reached the peak (or) it is very close to peak value. Since
the change is current is sosmall, the induced current at shading ring is
also small and negligible. So the shading ring does not affect the
distribution .of main flux. The flux is distributed uniformly and the
magnetic axis lies .at the center of pole face.The magnetic axis is
-denoted as ND in the picture,
.
The alternating current, after reaching the peak starts to decrease
rapidly and in turn decreases the main flux, The 'change in current induces a current in shading
coil. According to Lenz 'law the direction of this current is so as to oppose the cause p~uciDg it
(the decreasing alternating current). So theflux in shading coil oppOses the decrease in main flux
and strengthens it. This' increases the strength
main flux in ·th~ shaded part. SO the magnetic
axis shifts itself to the middle part of shaded pole.The magnetic axis denoted as NE in the picture
below.
"
of
So it is quite 'clear that during the positive half cycle of the alternating
, current, North Pole shifts from unshaded part to shaded pint and during
the negative -half cycle, the South Pole shifts along, from unshaded part
to shaded part. This effect is nothing but the rotation of poles from left
to right.
.
Thus shaded coils aids in producing the rotating flux and thus the single
phase Induction motor is converted into self starting one using the Shading coil. Due to fixed of
position of shading coils, the direction of rotation 'Ofsuch .motors cannot be changed.
128
Uses:
I)
Due to
t!1
electric.
working, c
3.5
••
:LI/
•
.M
I
• Par
b
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4)
•
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pri
3.6S01\.
s.
svst
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•
..•
••
•
•
"e
A.dvantages, Disadvantages and Applications
The various advantages of Shaded pole motors includes
• Very cheap and reliable
• Easy to construct
• Extremely rugged in nature
isadvantages includes,
duces a
~ coil is
cause is
:s and it
1(1 .owards
ong the
C' elow,
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.'
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••
•
•
•
.'
Low efficiency
Low starting torque
Since the shading coil is made of copper, the copper loss is high.
Uses:
Due to their low starting torques they are mostly employed in small instruments, toys, small fans,
electric clocks, hair dryers, ventilators, circulators etc.Thus we have discussed in detail the
working, constructional features and applications of Shaded pole Single Phase motors.
••
•
~
•
•
•
3.5 : LET US SUM UP
•
shading
ucing it
lin flux
~gnetic
picture
•
•
•
mating
during
edpart
A common single-phase motor is the shaded-pole motor and is used in devices requiring
low starting torque, such as electric fans or the drain pump of washing machines and
dishwashersor in other small household appliances.
In this motor, small single-tum copper "shading coils" create the moving magnetic field.
Part of each pole is encircled by a copper coil or strap; the induced current in the strap
opposes the change offlux through the coil.
This causes a time lag in the flux passing through the shading coil, so that the maximum
field intensity moves across the pole" face on each cycle.
This produces ~ low level rotating magnetic field which is large enough to turn both the
rotor and its attached load.
•
As the rotor picks up speed the torque builds up. to its full level as t;
principal magnetic field is rotating relative to the rotating rotor.
om left
~single
ixed of
I.
Wildi, Theodore; Wildi, Theodore (2006). Electrical machines. drives, and power
svsten:s. Upper Saddle River, NJ: Pearson Prentice Hall. ISBN 0-13-177691-6.
')
Wildi, Theodore: Wildi, Theodore (2006). Electrical machines. dri VCS, and pm\ er
SYstCIIIS. Upper Saddle River, NJ: Pearson Prentice Hall. ISBN 0-13-177691-6.
12l)
..
3.7 ANS'VER TO CHECK YOUR PROGRESS
(
STRUCT
(
i(
4.00BJ
1. See section 3.2
4.1 INT('
4.2WCf;
1. See Section 3.3
43 LET'
3.8 GLOSSARY
4.4
soj)
Single phase motor
4.5AN~
•
A shaded-pole motor is a type of AC single-phase induction motor.Jt is basically a small
squirrel 'cage motor in which the auxiliary winding is composed of a .copper ring
4.6GL~~
surrounding a portion of each pole.
.' 'fhis auxiliary winding is caned a shading coil..
."
• • Currents in this coil delay the phase of magnetic flux in that part 'of the pole enough to
4.1INTR
fj
provide a rotating magnetic field.
The direction of rotation is from the unshaded side to the shaded (ring) side.ofthe pole.
The effect produces only a low starting torque compared to other classes of single-phase
•
•
'motors.
Ad~antages of Shaded pole motors includes
•
•
•
Very cheap and reliable
Easy to construct
Extremely rugged in nature
Disadvantages
includes
Auniv~
norrnallr'l
•
You can £
on vacuC)
is the m~
concent.
windin.
brushes"?
rotor wO
motor do(
speed.
horsepow
•
:~a~
• Low efficiency
, •
Ci)
Low starting torque
when-yea
otheran(f"
ac ordc.
"4.2WOtt
A series'
either
the anna:
synchr06
Att
130
••
•
•
••
•
"
Ct
(
UNIT 4: UNIVERSAL MOTOR
f
(
STRUCTURE
t
4.0 OBJECTIVES
f
4.1 INTRODUCTION
(
4.2 WORKING PRINCIPLE
t
4.3 LET US SUM UP
C·
•
.'
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By a small
opper ring
4.1INTRODUcnbN
~
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..
enough to
he pole.
ngle-phase
e
~
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•
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I
4.6 GLOSSARY
I
A universal motor is one that operates on' either single-phase ac or de power. These motors are
normally made In sizes ranging from 1/200 to 113 horsepower.
You can get them in larger sizes for special ccnditions. The fractional horsepower sizes are used
on vacuum cleaners, sewing machines, food n.ixers, and power hand tools. The salient-pole type
is the most popular type of universal motor. The salient-pole type consists of a. stator with two
concentrated field windings, a wound rotor, a commutator, and brushes. The stator and rotor
windings in this motor are connected in series with the power source. There are two carbon
brushes that remain on the commutator at all times. These two brushes are used to connect the
rotor windings in series with the field windings and the power source (fig. 7-35). The universal
motor does not operate at a constant.speed. The motor runs as 'fast as the load permits; i. e., low
speed with a heavy load and high speed with a light load. Universal motors have the highest
horsepower-to-weight ratio of all the types of electric motors.
The operation of a universal motor is much like a series de motor. Since the field winding and
armature are connected in series, both the field winding and armature winding are energized
when voltage is applied to the motor. Both windings produce magnetic fields which react to each
other and cause the armature to rotate. The reaction between magnetic fields is caused by either
ac or dc power.
4.2 WORKING PRINCIPLES
A series-wound motor is referred to as a universal motor when it has been designed to operate on
either AC or DC power. The ability to operate on AC is because the current in both the field and
the armature (and hence the resultant magnetic fields) will alternate (reverse polarity) III
synchronism. and hence the resulting mechanical force will occur in a constant direction.
131
. t
\ffl;~',"
Operating at normal power line frequencies, universal motors arc often found in a range rarely
larger than 1000 watt. Universal motors also form the basis of the traditional railway traction
motor in electric railways, In this application, the use of AC to power a motor originally
designed to run on DC would lead to efficiency losses due to eddy current heating of their
magnetic components, particularly the motor field pole-pieces that, for DC, would have used
solid (un-laminated)
iron. Although the heating effects are reduced by using laminated polepieces, as used for the cores of transformers and by the use of laminations of high permeability
electrical steel, one solution available' at start of the 20th century was for the motors to be
operated from very low frequency AC supplies, with 25 and 16.7 Hz operation being common.
Because they used universal motors, locomotives using this design were also commonly capable
of operating from a third rail powered by DC.
.
An advantage of the universal motor is that AC supplies may be .used on motors which have
some characteristics more common in DC motors, specifically high starting torque and very
compact design if high running speeds are used. The negative, aspect is the maintenance and
short life problems caused by the commutator. Such motors are used in devices such as food
.mixers and power tools which are used only intermittently, and often have high starting-torque
demands. Continuous speed control of a universal motor running on AC is easily obtained by use
of a thyristor circuit, while multiple taps on the fteleJ coil provide (imprecise) stepped speed
control. -Household blenders that advertise many speeds frequently combine a field coil with
severaltaps and a di~e that can be inserted in series withthe rndtor (causing the motor to run on
half-wave'rectified AC): .
..'
..
Induction motors can't turn faster than alhwed by the power line frequency, By contrast,
universal motors generally run at high speeds, making them useful for appliances such as
blenders, vacuum cleaners, and hair dryers where high speed and light weight is desirable. They
are also commonly used in portable power t601s, such as drills, sanders, circular and jig saws,
where the motor's characteristics work ~ell, Many vacuum cleaner and .weed trimmer motors
exceed IO,OOORPM,while Drernel and other similar miniature grinders win often exceed 30,000
RPM:
'
Universal motors also lend themselves to electronic speed control and, as such, are an ideal
choice for domestic washing machines. The motor can be used to agitate the drum (both
forwards and in reverse) by switching the field winding with respect to the armature. The motor
can, also be run up to the high speeds required for the spin cycle.
.
'
.
Motor damage may occur from overspeeding (running at an rotational speed in excess of design
limits) if (he unit is operated with no significant load. On iarger motors, sudden loss of load is to
be avoided, and the possibility of such an occurrence is incorporated into the motor's protection
and control schemes. In some smaller applications, a fan blade attached to the shaft often acts as
an artificialload to limit the motor speed to a safe level, as well as a means to circulate cooling
airflow over the armature and field windings.
C
it
1«'
Vj,,,
(
f
c:'
~~:11'
.'.'
.
e\
•
'
·
••
•
••
·,
••
·
· ,.
••
••
•e
•
••
.Check.
~
•
Tl
~
th
132
",.
"
_---_vv"
rarely
ay traction
originally
1£ of their
have used
rated polemneability
itors to be
~common.
rly capable
mge
f
'('
t
(
('
(
The stator and rotor windings of the
motor are connected in series through
the rotor commutator. Therefore the
universal motor is also known as an
AC series motor or an AC
commutator motor. The universal
motor can be controlled either as a
phase-angle drive or as a chopper
drive.
'
\'00
MeV
Voo
~;
.1",:. '.
/J,.
\;'V~
Voo
/
... ..',.
~~·-····1·'·
i
Substitutes
another
field
winding for DCmotor's permanent
magnets can be driven by AC or
DC (lienee "universal") ,
"
\"
(
,"
.-
\':is
/hich have
: and very
nance and
ih as food
ing-torque
ned by use
ped speed
coil with
r to run on
contrast,
s such as
ible. They
t jig saws,
rer motors
-ed 30,000
CF~T~
High construction complexity
Low reliability
o Low efficiency
o Poor EMI (brushes create sparks and ozone) t
0
Driven by rheostat. chopper or phase angle (ScR or Triac) controllers
o' Some degree of sensorless speed control possible
o Good power to weight ratio
o
/
o
•
I
Note:
1. Explain universal motor?
~ an ideal
'urn (both
Ihe motor
of design
'load is to
protection
en acts as
Ie cooling
..................................................................... .~...•...............................
..................................................................... _ ............................•......... ._
.
4.3 LET US SUM UP
•
•
•
•
A series-wound motor is referred to as a universa:I motor when it has been designed to
operate on either AC or DC power.
'
The ability to operate on AC is because the current in both the field and the armature (and
hence the resultant magnetic fields) will alternate (reverse polarity) in synchronism, and
hence the resulting mechanical foree will occur in a,constant direction.
Operating at normal power line frequencies. universal motors are often found in a range
rarely larger than tOOOwatt.
The, use of AC to power a motor originally designed to run on DC would lead to
efficiency losses due to eddy current heating of their magnetic components, particularly
the motor field pole-pieces that, for DC, would have used solid (un-laminated) iron,
133
•
Although the heating effects are reduced by using laminated pole-pieces; as used for the
cores of transfonners and by the use of laminations of high permeability electrical steel,
one solution available at start of the 20th century was for the motors to be operated from
very lowfrequency AC supplies, with 25 and 16.7 Hz operation being common.
Because they used universal motors, locomotives using this design were also commonly
capable of operating from a third rail powered by DC.
•
.. This bl~'
Unit 1:1'.
4.4 SOME USEFULL-BOOKS
Unit 2: {i
1. Electrical Machines by SK Bhattacharya, TataMcHili Publishers
Unit 3:
2. A Text Book ElectricalTechnolc;>gy ~y BL Theraja, S.Chand Publishers
Unit 4: St
f~
,":,
.. ft:
3. Operation and Maintenance of Electrical .Machines by B.V.S. Rao, Khanna Publishers,
. New Delhi.
it:
4.5 ANSWER TO C~ECK YOUR PROGRESS
•
2. See section 4.2
4.6 GLOSSARY
Universal motor
1.0
A -universal motor is one that operates on either single-phase ac or de power. These motors
ru:e normally made in sizes ranging from 1/200 to II 3 horsepower.
.
•
The fractional horsepower sizes are used on vacuum cleaners, sewing machines.: food
mixers, and power hand tools.
~ The salient-pole type is the most popular type of universal motor.
• The salient-pole type consists of a stator with 'two concentrated field windings, a wound
rotor, a commutator, and brushes.
• The stator and rotor windings in this motor are connected in series with the power
source.
• There are two carbon brushes that remain on the commutator at all times.
1.1
~
••
..
••.,
•
BIS
c<I'
IS 123'
is 123_
IS 12407
IS 124.
IS 1243'
Minera.
IS 124~
Cakiur"
IS 124.
Polyuret
134
•
•
••
••
to
et
e
c
(
,""
"
BLOCK 5: 11AINTENANCE OF INDUCTANCE MOTOR
.ed for the
rical steel,
rated from
(
c.'
commonly
t
This block consists of four units,
Unit 1: BIS Code of Practice
{
Unit 2: Rating
c
Unit 3: Selection of Induction Motors
(\
C'
e
Unit 4: Starters
Delhi.
UNIT 1: BIS CODE OF PRACTICE
l
(!
.,
••
•
STRUCTURE
Cl
1.0 OBJECTIVE
1.1 BIS CODES
1.2 LET US SUM UP
].3 SOME USEFUL BOOKS
].4 ANSWER TO CHECK YOUR PROGRESS EXERCISE
].5 GLOSSARY
.
e
ese motors
~
lines, _food
1.0
•
1.1
1'1
I)
•
••
•
~
the power
In this lesson we shall discuss about BIS code .practise . After going through this
lesson you will be able to: understand the deviations of BlS codes
INTRODUCTION
•
•
c.) ;. a wound
e
OBJECTIVES
Now all IS codes are called BlS codes.
characteristics of three-phase induction motors have been included in the Indian
Standard IS: 4029-1967
BIS CODE OF PRACTISE:
IS
IS
IS
IS
IS
12368 : 1988 Guidelines for Design and Construction of Hot Air Generators
12377 : 1988 Classification and matrix for various categories of hospitals
12407 : 198XGraphic symbols for fire protection plans
12423: 1988 Method for colorimetric analysis of hydraulic cement
12432 : Part I : 1988 Code of practice for application of spray applied insulation Part
Mineral fibre
IS 12432 : Pan 2 : 1999 Application of Spray Applied Insulation - Code of Practice - Part :2 :
Calcium Silicate
IS 12432 : Pan 3 : 2002 Application of Spray Applied Insulation - Code of Practice - Part 3 :
Polyurethane/Polyi ...ocyunurutc
~
(,
I,
I)
I)
1,/
I,
I
I
l
135
IS 12433 : Part I : 1988 Basic requirements for hospital planning.Part I upto 30 bedded hospitals
IS 12433 : Part 2 : 2001 Basic Requirements for Hospital Planning - Part 2 : UP to 100 Bedded
Hospital
IS 12440: 1988 Specification for precast concrete stone masonry blocks
IS ] 2457 : 1988 Code of practice for evaluation repairs and acceptance limits of surface defects
in steel plates, and wide flats
IS 12458 : 1988 Method of test for fire resistance test of fire stops
IS 12459 : 1988 Code of Practice for Fire Safety in Cable Runs
IS 12466 : ] 988 General requirements for builder's hoist
'
'IS ] 2467 : '1988 Method for determination of the ignitability of upholstered composites
seating for furniture by smokers' materials
.
.
IS 12468 : ] 988 General requirements for vibrators for mass concreting; Immersion type
for
IS 12469 : 1988 Specification for Pumps for Fire Fighting System
.'
IS 12506 : ]9.88 Code of Practice for Improved Thatching of Roof with Rot and Fire Retardant
Treatment'
'
IS 12518 : ]988 Shellac Bond Powder - Specification ' ,
IS -l 2583 : ]988 Specification for corrugated bitumen roofing sheets
I
• ,
IS 12584 : 1989 Bentonite for Grouting in Civil Engineering Works ~Specification
IS 12585 : 1988 Specification for Thermoplastic Hoses (Textile Reinforced) for Water - General
Purpose
•
.
IS 12592 : 2002 PrecastConcrete Manhole Cover and Frame - Specification
,
IS 12594 : ]988 Hot-dip Zinc Coating on Structural Steel Bars 'for Concrete Reinforcement Specification
"
' ..
.
.
IS. 12600: 1989 Specification for low heat Portland cement
IS 12608 : ]989 Methods of test for hardness of rock
IS 12629: 1989 Water well drilling - Rotary hose for rotary drilling: Recommended practice for
care and use
.
IS 12634: J 989 Method of determination for direct shear strength of rock joi nts
.IS ]2635 : 2000 Water Well Drilling and Blast Hole Drilling - Rock Roller Bit with Non-sealed
Ball and Roller Bearing Arrangement - Technical Supply Conditions
.',
IS 12643: 1989 Corrosion Protection of Steel by Fiber glass Reinforced Polyester Lining - Code
of Practice
IS ]2645 : 1993IISO 9246 : 1988 Earth-moving machinery - Crawler and wheel tractor dozer
blades - Volumetric ratings .
IS )2647 : )989 Solid Waste Management System - Collection Equipment - Guidelines
IS. )2654 : 1989 Code of practice for lise of low grade gypsum in building industry
IS 12679.: ,1989 Specification for By-product gypsum for lise in plaster, blocks and boards
IS 12680: 1989 Specification for wooden sofa-cum-bed
IS 12682 : 1989 Water.well drilling - Percussion drilling rigs - General requirements
IS 12709: 1994'Specification for glass-fibre reinforced plastic (GRP) pipes joints and fittings for.
use for potable water supply
.
IS )2710: 1989 Glossary of terms used in acoustic emission testing
IS 12722: 1989 Textile floor coverings - determination of flame resistance by Tablet test
IS 12727 : 1989 Code of practice for no fines cast in situ cement concrete
IS 12744 : 1989 Ready Mixed Paint. Air Drying, Red Oxidc Zinc Phosphate, Priming Specification
IS 12747
Definitf~,
IS 127"
test
,IS 127~~
Part 3 Sp<
IS 127~
IS 12776
IS l28f
IS 1281$.
IS 128~
IS ]281¬
IS 128:f!i
IS 128'
system Pr
IS 12s.C~
1.2
-e
-I)
t
•.•,
1.3.
N
.,"
~
1.4
I)
1.5
BIS
>
136
J
••
•
-,••
'"•
••
•
••
•
I;
€I
c
r
(
.d hospitals
00 Bedded
(
(
ace defects
C'
«
C
(,
•
t
posites for
)C
Retardant
,
f
C
.'•
•
•
•
•
e)
•
•
•
•
fI'
1.2
"rcement
l
.'t
.'I
I
Now all IS codes are called BIS codes.
characteristics or three-phase induction motors have been included in th~ Indian
Standard IS: 4029.,1967 .• •
SOME USEFUL BOOKS
-
I.Electrical Machines by SK Bhattacharya, TataMcHill Publishers
2.A Text Book Electrical Technology by BL Tberaja, S.Chand Publishers
'on-sealed
3.Operation and Maintenance of Electrical Machines by B.V.S. Rao, Khanna Publishers,
New Delhi.
ng - Code
4.EJectricaJ Technology by Edward Hughes, Addision - Wesley International Student
Edition
xor dozer
5. Performance & Design of AC Machines by MG Say, CBS Publication, New Delhi
1.4
ttings for
I
-
ractice for
•
I
LET US SUM UP
•
•
1.3.
'ds
I
IS 12747 : Part 1 : 1989 Combined Flexible Materials for Electrical Insulation - Part 1 :
Definitions and General Requirements
IS 12747 : Part 2 : 1989 Combined flexible materials for electrical insulation: Part 2 Methods of
test
IS 12747 : Part 3 : 1998lIEC 626-3 : 1996 Combined flexible materials for electrical insulation:
part 3 Specifications for individual materials
IS 12770 : 1989 Coal for Cement Manufacture - Specification
IS 12776: 2002 Galvanized Strand for Earthing - Specification
IS _l2817 : 1997 Specification for stainless steel butt hinges
,
IS 12818 : 1992 Specification for un plasticized PVC screen and casing pipes for bore/tube well
IS 12823 : 1990 Wood Products - Pre laminated Particle Boards - Specification
IS 12830 : 1989 Rubber based adhesives for fixing PVC tiles to cement
IS 12834: 1989 Solar photovoltaic energy systems-Terminology
IS 12835 : Prot 1 : 1989 Code of practice for design and installation of fixed fire extinguishing
system Part 1 Low expansion foam,
IS 12843: 1989 Tolerances for erection of steel structures
'- General
•
I
I'
I
ANSWER TO CHECK YOUR PROGRESS EXERCISE
'I) Derivate the BIS code tor the electrical insulation?
1.5
GLOSSARY
BIS - BUREAU OF INDIAN STANDARDS
'riming -
137
UNIT 2: RATING
STRUCTURE
2.0 OBJECTIVE
2.1 INTRODUCTION
2.2 TYPES OF RATING
2.2.1 Rated voltage or voltages
2.2.2 Rated full-load amps for each voltage level
2.2.3 Frequency
.
2.2.4 Phase
2.2.5 Rated fuli-Ioad speed
"2.2.6' Insulation class and rated ambient temperature
2.2.7 Rated.horsepower
2.2.8 Time rating
,
2.2.9 Locked-rotor code letter
2.2.10 Manufacturer's name and address
2j.11 OTHERS.
•
2.3 LET US SUM UP
2.4 SOME USEFUL BOOKS
2.6 GLOSSARY·
2.0
• i"
·
{:
• C>
·t
e
• Ir
.••
e
• R
e
'
•
•
OBJECTlVE.'i
..
In add,
NEMA'f
After.,studying this unit, you should be able to
•
•
•
•
•
Explain work holding devices
Discuss various types of mandrels
Describe types of chucks
Finally,
code, •
2.2.1.
2.1
INTRODUCTION
The U.S. motor industry has worked on a standardized basis for more than three-quarters of a
century. The standardization agency - National Electrical Manufacturers Association (NEMA)
_ was established in 1926 " ... to promote the standardization of electrical apparatus and
supplies." As a result of this group's efforts, .you can expect "standard" motors from different
maQufacturers to meet or exceed minimum performance parameters and, for the most part. be
about the 'same size.
A critical part of making motors interchangeable is ensuring that nameplate infonnation is
common among manufacturers. TIle' common language of the motor nameplate enableinstallation and maintenance personnel to quickly understand and recognize exactly what tYpl?of
motor they're dealing with during a new installation or replacement procedure.
l
138
Motor'
combi.
known
distrite
supply
below.
beex~
2.2.2 •
tl.
As
increa:
•
•••
•
•
•
•,
,
C
(
(
t
TYPES OF RATING
(
2.2
(
The NEe states that th_emotor nameplate must show the following information:
"e
•
Rated voltage or voltages
•
Rated full-load amps for each voltage level
•
Frequency
•
•
Phase
•
Rated full-load speed
t
•
Insulation class and rated ambient temperature
I
•
Rated horsepower
I
.• Time-rating
c.
f\
C
•
I;
•
•e
•
Locked-rotor code letter
•
Manufacturer's name and address
In addition to this required information, motor nameplates may also include data like frame size,
NEMA design letter, service factor, full-load efficiency, and power factor.
.
(i
•
Finally, some nameplates may even include data like bearing identification numbers, certification
code, manufacturer serial number, and symbols and logos.
I,
2.2.1 RATED VOLTAGE
I
I
•
•
•
Il
I
f
I
I
I
I
I
I
I
I
I
lers of a
(NEMA)
atus and
different
part. he
nation I~
enables
It type of
Motors are designed to yield optimal performance when operating at a specific voltage Ievcl. or a
combination of voltage levels in the case of dual-voltage or tri-voltage motors. This 'value is
known as the nameplate voltage. In recognition of the fact that voltage changes on your power
distributIOn system occur due to changing load conditions within your facility and on the utility
supply that feeds your facility, motors are designed with a tOo/c tolerance for voltage above and
below the rated nameplate value. Thus, a motor with a rated nameplate voltage of 460V should
be expected to operate successfully between 414V and 506V.
2.2.2 RATED FULL-LOAD AMPERAGE
As the torque load on a motor increases. the amperage required to power the motor ;,i1:-()
increases. When the full-load torque and horsepower is reached. the corresponding amperage 1:1:19
known as the full-load amperage (FLA). This value is determined by laboratory tests; the value is
usually rounded up slightly and recorded as the nameplate value. Rounding up allows for
manufacturing variations that can occur and some normal voltage variations that might increase
the full-load amps of the motor. The nameplate FLA is used to select the correct wire size, motor
starter, and overload protection devices necessary to serve and protect the motor.
2.2.3 FllliQUENCY
To operate successfully, the motor frequency must match the power system (supply)frequency~
In North America, this' frequency is 60 Hz (cycles). In other parts of the world, the frequency
may be 50 or 60 Hz.'
.
2.2.4 PHASE
This concept
::~!o~!
ata ti.v.
2.2.98>
is fairly simple in the United
States. You either have a single-phase
or 3-phase
motor.
2.2.5 RATED
Stand~-.l
~em~u
interrmtte
to 60 ("In
are baser
windi~is
the' te§t,"
motor'~
FULL-LOAD
When.
~:ri:
SPEED
equip.l
This is the motor's approximate speed under full-load conditions, when voltage .and frequency
are at the 'rated values. A somewhat lower value than the actual laboratory test result figures is
usually stamped on the nameplate because ithis value can change slightly due to factors like
manufacturing tolerances, motor temperature, and voltage variations. On standard' induction
motors, the full-load speed is typically 96% to 99% of the no-load speed.
2.2.6 ~NSULATION CLASS AND RATED AMBIENT TEMPERATURE
A critical element in motor life is the maximum temperature that occurs at the hottest spot in the
motor. The temperature that Occurs at that spot is a combination of motor design (temperature
rise) and the- ambient (surrounding) temperature. The standard way of indicating these
. components is by showing the allowable maximum ambient temperature, usually 40°C (104°F),
and the class of insulation used in the design of the motor. Available classes are B, E and H.
••
••.1
b
2.2.1",
Moste
Optional
'.
typica .. j
,...
2~2.11_
.,
'FRAr!
2.2.7 RATED HORSEPOWER
Horse power is the measure of how much work a motor can be expected to do. This value is
based on the motor's full-load torque and full-load speed ratings and is calculated as follows:
Horsepower (hp)=[Motor SpeedxTorque (Ib-ft)).;.-5,2S0
The standardized NEMA table of motor horsepower ratings runs from ) hp to 450 hp. If a load's
actual horsepower requirement falls between two standard horsepower ratings, you should
generally select the larger size motor for your application.
Under t!
size.
digits .&
inch. til'
inch,~
1.
On
the first
woul.
rneasun
2.2.8 TIME RATING
we,
indicae
bet
140
•
•
•
•
•
•
•
•
C)
'{
he val LIe is
allows for
ht increase
size, motor
C'
Standard motors are rated for continuous duty (2417) at their rated load and maximum ambient
temperature. Specialized motors can be designed for "short-time" requirements where
intermittent duty is all that's needed. These motors can carry a'short-time rating from 5 minutes
to 60 minutes. The NEMA definition for short-time motors is as follows: "All short-time ratings
are based upon corresponding short-time load tests, .which shall commence only when the
windings .and other parts of the motor are within SoC of the ambient temperature at the time of
the' test." By using short-time ratings, it's possible to reduce the size, weight, and cost of the
motor required for certain applications. For example, you may choose to install an induction
motor with a I5-minute rating to power a pre-operation oil pump used to pre-lube a gas turbine
unit because it would be unusual for this type of motor to be operated for more than 15 minutes
ata time .
•t
2.2.9 LOCKED-ROTOR CODE LETTER
(
(
tl
t
C
frequency,
frequency
or 3-phase
When AC motors are started with full voltage applied, they create an inrush current that's usually
many times greater than the value of the full-load current. The value of this high current can be
important on some installations because it can cause a voltage dip that might affect other
equipment. There are two ways to find the value of this current:
.
frequency.
t figures is
actors like
. induction
.
•
Look it up in the motor performance data sheets' as provided by the manufacturer. It will
be noted as the locked-rotor current.
• Use the locked-rotor code letter that defines an inrush current a motor requires when
.starting it.
2.2.10MANUFACTURER'S NAME AND ADDRESS
.
._,,
spot in the
ernperature
ting these
C(I04°F),
od
H.
2:2.11 OTHERS
FRAME SIZE
is value is
llows:
It
Most manufacturers include their name and address on the motor nameplate.
Optional nameplate data. In addition to the required items noted above, more information is
typically included on a motor nameplate.
Under the NEf.,,1Asystem, most motor dimensions are standardized and categorized by a frame
size number and letter designation. In fractional horsepower motors the frame size" ~dc [ v, (.)
digits and represent the shaft height of the motor from the bottom of the base in sixteenths of an
inch. For example. a 56-fram~ motor would have a shaft height ("D" dimension) of 56/16 of an
inch, or 3.S inches.
If a load's
'all
should
On larger 3-digit frame size motors. 143T through 449T, a slightly different system is used where
the first two digits represent the shaft height in quarters of an inch. For example. a 326T frame
would have a "D" dimension of 32 one-quarter inches. or 8 inches. Although IW direct inch
measurement relates to it. the third digit of three-digit frame sizes, in thi« case a 6. is an
indication of the motor body's length. The longer the motor body, the longer the distance
between mounting bolt holes in the base (i.e. greater 'T' dimension). For example. a l-lS'Tframe
141
has a larger F dimension than does a 143T frame.
When working with metric motors (IEe type), the concept is the same as noted. above with one
exception _ the shaft height above the base is now noted. in millimeters rather than inches. The
frame size is the shaft height in millimeters.
'
NE:MADESIGN LETTER
Certain types of machinery may require motors With specialized performance characteristics. For
example, cranes and hoists that have to start with full loads .imposed may require motors with
operating characteristics much different from what is required for pumps 'and blowers. Motor
performance characteristics can be altered by design changes in lamination, winding, rotor, or
nonnal~
(ODP) ..
require~
as 1:2\"
contmuc
startinC
Traditi('i
manufa<
Most
avail!'-t\
f'
any combination of these three items.
Most standard motors for generalpurpose applications meet or exceed the
values specified for Design B motors in
~
MG-l, Standard for Motors and
Generators. Design A motprs are
sometimes used on applications that.
require high breakdown
(pull-out)
torque, such as injection molding.
machines. Design C motors are selected
for applications that require high starting
, (locked-rotor) torque, such as inclined
conveyors. Design D motors, also called
"high slip" motors,' are sometimes used
to power hoists and cycling loads, such
as oil well pump jacks. and low-speed
punch presses.
Fig. 1. These graphs show typical torquespeed curves for Design A, B, C, and D
motors.
It shows th~general shape of torque-speed curves for motors with
NEMA Design A, B, C, and D
GenerP
3-pha.
value t
very.
nomin:
teste~
other.
value.
.-
Guaral
detere
in the
20%.
corre~
MG-"
PO"•
powe
characteristics.
Bear in
shapes.
Asene
and inc
info~
indica~
value~'
Pow.
mind that the curves shown in Fig. 1 and the figure in the sidebar on page 24 are general
In real .motors, each motor would have its own distinct values different from the
percentages reflected in these figures.
incre:
near.
Fina~
item.
SERVICE FACTOR
churn
Service factor (SF) is an indication of how. much overload a motor can withstand when operating
142
•
•
•
•
,
C
C
(
c
<
with one
ches. The
istics. For
nors with
Motor
, rotor, or
IS.
normally withi? the correct voltage tolerances. For example, the standard SF for open drip-proof
(ODP) motors IS 1.15. This means that a 10-hp motor with a 1. I 5 SF could provide 11.5hp when
required for short-term use. Some fractional horsepower motor's have higher service factors, such
as 1.25, 1.35, and even 1.50. In general, it's not a good practice to size motors to operate
continuously above rated load in the service factor area. Motors may not provide adequate
starting and pull-out torques, and incorrect starter/overload sizing is possible.
Traditionally, totally enclosed fan cooled (TEFC) motors had an SF of 1,0, but most
manufacturers now offer TEFC motors with service factors of 1.15, the same as on ODP motors.
Most hazardous location motors are made with an SF of 1.0, but some specialized units are
avail~ble for Class Iapplications with a service factor of 1.15.
F1JLL-LOAD EFFICIENCY
generalxceed the
motors in
rotors and
ItOrs are
ions ·that
(pull-out)
molding.
e selected
~hstarting
s inclined
USO called
imes used
lads, such
low-speed
cal torqueC, and D
As energy costs have increased, conservation efforts have become more important to commercial
and industrial operations. As a result, it's become important to have full-load efficiency
. information readily available on motor nameplates. The efficiency is given as a percentage and
indicates how well the motor converts electrical power into mechanical power. The closer this
value is to 100%, the lower the elecVicity consumption cost is going to be.
.
.
Generally, larger motors will be mote efficient than smaller motors. Today's premium effici \::y.
3-phase motors have efficiencies ranging from 86.5% at 1 hp to 95.8% at 300 hp. The efficiency
value that appears on the nameplate is the nominal full-load efficiency as determined using a .
very accurate dynamometer and a procedure described by IEEE Stand:.rd 112, Method E The
nominal value is what the average would be if a substantial number of identical motors were
tested and the average of the batch were determined. Some motors might have a higher value and'
others might be lower, but the average of all units tested is shown as the nominal nameplate
value.
Guaranteed minimum is another efficiency that's sometimes noted on a nameplate. This value is
determined from a mathematical relationship that assumes that the worst efficiency of any motor
in the batch _ used to determine the average (nominal) value - could have losses as much as
20% higher than the average. As a result, each nominal efficiency value would have a
corresponding minimum efficiency value. You can view these values. in Table 12-8 in NEMA
MG-1.
, C,andD
ire general
from the
POWER FACTOR
Power factor is the ratio of motor load watts divided hy volt-amps at the full-load condition.
Power factor for a motor. changes with its load. power factor is minimum at no load and
increases as additional load is applied to the motor. Power factor usually reaches a peak at or
near full load on the motor.
Final spin. Changing motors out becomes a lot easier \\ hen you can quickly recogni/c the key
items that describe a motor's size. speed, voltage. ph~sical dimensions, and performance
characteristics. All of this information and more is usual! y ;1\ uilublc on the motor's nameplate.
I operating
143
It's your responsibility to be able to correctly interpret the information on this nameplate,
correctly apply it in the fielr' and verify conformance to NEMA, IEC, or other industry
f
Ched
standards.
1. See(e,
Check Your Progress -1
Note:
(
1;·Give your answer in the space given below.
2. Check your answers with those given at 'the end of the unit.
1. Explain types of rating?
•...................................
...............
~
..............•...................................•........................................•..............
:..!
.
:.....•.................................................................................
'
~(
2.3
LET US SUM UP
• ,A critical part of making motors interchangeable is ensuring that nameplate
information is common among manufacturers.
~ Motors are designed to yield optimal performance wheq operating at a specific
~oltage level, or a combination of voltage levels in the case bf dual-voltage or trivoltage nfotors.
•
• ,Standard motors are rated for continuous duty (24n) at their rated load and
maximum ambient temperature.
•
When AC motors are started with full voltage applied, they create an inrush
current that's usually many times greater than the value ofthe full-load current.
•
Service factor (SF) is an indication of how much overload a motor can withstand
when operating normall y within the correct voltage tolerances.
•
Power factor is the ratio of motor load watts divided by volt-amps at the full-load
.condition. Power factor for a motor changes with its load.
•
Horsepower (hp)=[Motor SpeedxTorque (lb-ft)]7S,2S0
2.4 SOME USEFUL BOOKS
I. Electrical Machines by SK Bhattacharya, TataMcHilI Publishers
2. A Text Book Electrical Technology by BL Theraja, S.Chan~ Puhlishers
3. Operation and Maintenance of Electrical Machines by B.Y.S. Rao, KhannaPublishers,
Delhi,
144
New
•
F~
• rtI!
• R!
• Insu
•
•
.. RI
·.T.
• ll'
•
~
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•e
(
f
t.
f
uneplate,
industry
z.s
f
1. See section 2.2
t
C
2.6
C'
C) ..............
•
•
I
Rated voltage or voltages
.- Rated full-load amps for each voltage level
e,
.'.-.'
Types of rating:
•
I'
•
•
••
GLOSSARY
imeplate
•
Frequency
specific
:e or tri-
• , Phase
.'
Rated full-load speed
•
Insulation class and rated ambient temperature
•
Rated horsepower
lad and
inrush
rent.
I
• _TIme rating
ithstand
ull-load
•
Locked-rotor code letter
•
Manufacturer's
name and address
I
I
I
•
•
s, New
t
I
•
I
•t
~
a
t
t
,
l
145
Ie
UNIT 3: SELECTION OF INDUCTION
3) to
Energy-e
For all'i,c
MOTORS
~;e:lff
STRUC'rURE
condit~
Whenpu
Instea<C
To repla(
As
When~t
motorlti
3.0 OBJECTIVES
3.1.INTRODUCTION
pat:~
3.2 INDUSTRIAL MOTOR APPLICATION
3.3 OPERATiNG 60 CYCLES INDUCTION MOTOR AS GENERATOR
..
3.4 LET US SUM UP
3.2INe
•
In 19~
mega~1
electri.,. •
accounte
3.7 GLOSARRY -
Possibe
3.0 OBJECTIVES
•
In this lesson we shall discuss about'llielndu~on
Inoto~s
. After going through this lesson you will be able" to:
Understand the Selection of induction motor.
345 M\\
for 52•
.moto~
•
3.1 INTRODUCTION
This Energy-Efficient Electric Motor Selection Handbook (Handbook) contains guidelines to
help you identify motors that are candidates for replacement with energy-efficient electric
motors. Using readily available infonnation such as motor nameplate capacity, operating hours,
and electricity price you can quickly determine the simple payback that would result from
selecting and operating an energy-efficient motor. Using energy-efficient motors can reduce your
operating costs in several ways. Not only does. saving energy reduce your monthly electrical bill,
'it can postpone or eliminate the need to expand the electrical supply system capacity within your
facility. On a larger scale, installing energy conserving devices allows your electrical utility to
defer building expensive new generating plants, resulting in lower costs for you, the consumer.
Energy-efficient motors are higher quality motors, with increased reliability and longer
manufacturer's warantees, providing savings in reduced downtime, replacement and
maintenance costs. Saving this energy and money requires the proper selection and use of
energy-efficient motors. I There are three general opportunities for choosing energy-efficient
motors:
I) when purchasing a new motor,
2) in place of rewinding failed motors. and
146
•..
Energy-
The effi
input..
.OurplI"
Desig~
premllft"
that
input tl
(NE~
to help.
of mil.
the noa.
NOl11i~
show,.
manufa
machie
are
•
•
•,
.!.- ..
(
(
(
(
(
3) to retrofit an operable but inefficient motor for energy conservation savings.
Energy-efficient motors should be considered in the following instances:2
For all new installations
'
When major modifications are made to existing facilities or processes
For all new purchases of equipment packages that contain electric motors, such as air
conditioners, compressors, and filtration systems
When purchasing spares or replacing failed motors
Instead of rewinding old, standard-efficiency motors
To replace .grossly oversized and underloaded motors
As part of an energy management or preventative maintenanceprogram
When utility conservation programs, rebates, or incentives are offered that make energy efficient
motor retrofits cost-effective
"
3.2 INDUSTRIAL MOTOR POPULATIONS
AND USES
In 1987, industrial sector use of electricity in the Northwest amounted to 6,062 average
megawatts (MWa). This is equivalent to 38.8 percent of
region's 15.618 MWa of total
electricity sales to final consumers. Five industries-food, ehemicals, paper; lumber,' and metalsaccounted for-more than 90 percent of the region' s industrial use of eleCtricity3 A 1988 study of
possible industrial sector energy conservation measures revealed a potential of approximately
345 MWa of-energy savings, with changeouts of standard to energy-efficient motors accounting
.. for 52.7 MWa or 15:2 percent of the total savings.4 Replacing standard with energy-efficient
_motors saves $13.8 million annually given an electricity price of only $.03/kWh,
tJte
Energy-Efficient
e
I
e
I
•
••
Ii
.'
guidelines to
::ient electric
srating hours,
I result from
1reduce your
;leCtrical bill,
y within your
icaI utility to
consumer.
and longer
cement and
I and use of
efficient
Motor Performance
and Price
The efficiency of a motor is the ratio of the mechanical power output to the electrical power"
input. This may be expressed as:
.-
=
.Output Efficiency =Output Input-Losses=
Input Input Output + Losses
Design changes, better materials, and manufacturing improvements reduce motor losses, making
premium or energy-efficient motors more efficient than standard motors. Reduced losses mean
that an energy-efficient motor produces a given amount of work with less energy
input than a standard motor.2 In 1989, the' National Electrical Manufacturers Associ at ion
(NEMA) developed a standard definition for-energy- efficient motors'. The definition, designed
to help users identify and compare electric motor efficiencies -on an equal basis, includes a table
of minimum nominal full-load efficiency values." A motor's performance must equal or exceed
the nominal efficiency levels given in Table 2 for it to be classified as "energy-efficient"
Nominal full-load efficiencies for currently available energy-efficient and standard motors are
shown in Figure 3. Figure 3 clearly indicates that the NEMA standards are easy for motor
manufacturers to exceed. In fact, most motors on the market qualify as "high-efficiency"
machines. It is also apparent that you can improve efficiency hy as much as (1 points through
I
I
I,
I
I:
I,
I
I
I
I
147
f
efficie{
be used.
simply buying a "premium-efficiency"
motor, one whose peiformance lies near the top of the
range of available efficiencies, rather than one that just meets the NEMA minimum standard.
Frequently, one manufacturer's energy-efficient motor performs with approximately the same
efficiency as another manufacturer's standard unit. Average nominal efficiencies and 1990 list
prices for standard and energy- efficient motors are summarized in Table 3.
'In order to help you identify, evaluate, and procure energy- efficient motors, the Washington
State Energy Office has prepared a motor performance database. The
database contains t'ull- and' part-load nominal efficiencies. and power factors for approximately
2,700, 5- to 300-hp NEMA Design B 'polyphase motors. Information contained in the 'database .
was extracted from manufacturers' catalogs with each manufacturer given an opportunity to
review performance information for accuracy. Users can query the database toproduce a
listing, ranked in order of descending full-load efficiency, for all motors within a stated size,
speed, ana enclosure classification. A sample database listing is shown in Table 4. The database
also contains the manufacturers' name, motor model, full-load RPM, service factor, frame size,
and list price. Note that the nominalfull-load motor efficiencies vary from. 86.5 to 9'3.2 percent.
Prices also vary. In many cases, motors with identical list prices exhibit very different efficiency
ratings.
.
"
Motor Losses
and Loss Reduction
..-Te(,:bniques·
•
€
,.
3.3 oi'i
('
Any me
Circurf'
. two mos
C:'
Thet~.\
and ca ,
1"
Althoug
characff;'
connecti
C)
STEP~
~
A motor's function is to convert electrical energy to mechanical energy to perform.useful work .
. The only way to improve motor efficiency is-to reduce motor losses. Even though standard
motors operate efficiently, with typical efficiencies ranging between 8'1 and 92 percent, energyefficientmotors perform significantly better. An efficiency gain from only 92 to 94 percent
results in a 25 Percent reduction in losses. 'Since motor losses result in heat rejected into the
atmosphere, reducing losses can significantly reduce cooling loads on an industrial facility's air
conditioning system. Motor energy losses can be segregated into five major areas, each of which
.is intluenced by design and construction decisions.S One design consideration, for example, is
the size of the air gap between the 'rotor and the stator. Large air gaps tend to maximize
efficiency at the expense of power factor, while small air gaps slightly compromise efficiency
while significantly improving power factor. to Motor losses may be categorized asthose which
are fixed, occurring whenever the motor is energized, and remaining constant for a given voltage
and speed, and those which are variable' and increase with motor load. I I These losses are
described below.
I .Core loss represents energy required to magnetize the core material (hysteresis) and includes losses
due to creation of eddy currents that flow in the core. Core losses are decreased through the use
of improved permeability electromagnetic (silicon) steel and by lengtheningthe core to reduce
magnetic flux densities. Eddy Current losses are decreased by using thinner steel laminations.
2. Windage and fricti~n losses occur due to bearing friction and air resistance. Improved
bearing selection, air-flow. and fan design are employed to reduce these losses. In an energy-
148
•
STEp·.
such as
either.
•
STEP,
. (usual "
turnin~
connect
••
STEP.
below.
STEP~
a ligh.
test for
, mode .•
STEP'
the ge.
methoc
genene
equally
•
•
•
•
•
•
•
C
"c
r
(
sp of the
( jar-d.
(
(
t
t
(""1
efficient motor, loss minimization results in reduced cooling requirements so a smaller fan can
be used. Both core losses ~nd windage and friction losses are independent of motor load.
the same
1990 list
3.3 OPERATING 60 CYCLE INDUCTION MOTORS AS GENERATORS
ishington
iximately
database
tunity to
ned size,
(.> latabase
(", arne size,
~.percent.
(: fficiency
Any motor can be used as a generator and any generator will motor under the proper
Circumstances. The purpose of this paper is to describe the connections required to convert the
, two most common types ofinduction motors intoAC generators.
The two types of motors most readily Converted are three phase Squirrel cage Induction ~otors
and capacitor start single-phase induction motors.
Although, the connections are different, both types of machines exhibit similar operating
characteristics. Below is an outline form applying to either type.of generator? The instruction, for
" connecting the machines and small parts that you will need are discussed later.
(')
STEP 1- Electricaly connect the unit as outlined under the connection section.
CI
•e
f)
C}
.)
fa
I)
II
I,
~
••
I
I'
I·
I
I
I
I)
,
fi
t
r
t
•
ful work.
standard
, ent<rgyent
i into the
ility's air
of which
ample, is
naxirnize
ifficiency
.se which
Ii voltage
()Sses are
includes
h the use
to reduce
ions.
Improved
1 energy-
'.
.
STEP' 2- Connect the machine 'by belt or other-suitable means to a Source of mechanical power
such as it gasoline engine. Tum the machine at about its nameplate speed.' Most machines will be
either about 1800 RPM or about 3600 RPM.
STEP 3- With no loads of any kind connected to the. generator, its voltage should build-up
.fusually a faint generator hum is audible). If you are using a Single-phase machine, be sure it is
turning the same direction that it turned as a motor, Build up can be checked by momentarily
connecting a light bulb across theoutput terminals to check for power.
STEP 4- Reduce generator Speed until the machine will just keep the light bulb lit. You will find
below this Speed, the generator will simply stop generating.
.
-
STEP 5- with the generator Operating at minimum speed where it continued (0 generate, connect
a light bulb load to the averageload for the generator. If you have been using a smaller load to
test for generator build-up, it may' be necessary, to increase the Speed 'a hit 10 maintain generati ng
~~.
'
STEP 6- set the generator speed by checking the generators output voltage. The faster you turn
the generator the higher its voltage will become, etc. If a voltmeter is not available, a sirnple
method is to compare the brightness of two bulbs of the same type. one plugged into the
generator and the other plugged into the wall. The speed is about right when the bulbs arc
equally bright.
149
r
RA TING- your generator can be rated at 500 watts per motor horsepower, This is a
comfortable rating and allows for some short time Overload capacity. When selecting the loads
for the generator remember that most electric motors require six to ten times their rated power
when starting. As' an example, a 1/3HP-freezer motor may require up to 3 HP worth of
generating capacity to start it. High Speed portable tool motors are the .main exception. These
Series wound motors usually start quite successfully at 2 or 3 times their rated power current at
rated voltage) level, Motor loads are best estimated by multiplying their nameplate volts times
nameplate amps. This product is really V\ but can be used safely as watts for the purpose of
generator rating. Your generator will produce sine wave power generally at a frequency slightly
below'60 HZ. An eJectricdock with a second hand will read the exact frequency in seconds in
one' minute.
.
I. You are generating lethal voltages- use appropriate care.
2- The generator will pot build-up its voltage when loaded. It must alwaysbe started 'with no
load connected.
"
.
3- Running the generator at speeds higher than the nameplate rating-may generate very high
voltages and cause the capacitors to explode or the machine to flash over inside and catch fire.
Speeds in excess 0\ 4000 RPM may even cause the rotor to fly apart in~id~ the \nachine.
4- DonOt leave the generalor unattended until it has run about 2 hours without overheati ng. A
safe motor temperature is :when'you can barely hold your hand on the generator for 5- ,I 0 se~onds
and no hot or oily smell is coming from the machine. .
.
Faults or dead shorts may be placed on the generator without 'harm since it will simply stop
generating.
.'
. .
:.
TROUBLE SHOOTING- If the generator will not build-up voltage when initially operated at or
near nameplate speed, the capacitors may be too small, If single phase it may be turning
backwards, the connections may be incorrect, the machine may be faulty or the iron in the
machine may have lost its residual magnetism and need to be flashed. All the fixes are evident
except flashing. To flash it' momentarily, connect a car battery across the generator output
. terminals while it is running full speed Owith no loadO. ONE second is more than enough time
to flash the machine.
MACHINE SELECfION:=Either a three-phase squirrel cage induction motor or a capacitor type
motor may be used.
.
.-
Of the two choices, the old three-phase motor makes .a better selection. These usually can be
located in motor .shops, junkyards, etc. for very little investment. The size machine to use
depends on the rating you need from the generator but generally should not exceed about 10 HP
for a three-phase machine or 3 HP for a single-phase machine, Poor
results can be expected below about 1I2HP for three phase or 116 HP for single phase, The best
generators are machines rated at 1700 RPM or higher. Lower speed machines can be used, but
will require larger capacitors.
tSO
excitation to
moving p<f,.
are determin
load is ap~ ..
C
REGULAl'
regulation cr
f"
CONNE~
nameplate~.
should sa~i.
#1
<;::AUTION.
..rHEORY(
Thecorre~
abouU/301
use care rC'1
•
CONNECi
the type
refrigeratJ
applies to t
J
•
I>
STEP 1~
you shOU~
voltage u
I
STEP 2- ~
be a cent.
controls or
switch so8
3-fI
STEP
moving ."
4-.
STEP
have two (
or in the.
wires .
•
•
•
•
•
••
•
STEP 5- I
capacitor.
C
(
(
(
(
(
(
(
t.,
(,
his IS a
the loads
xl power
worth of
m. These
:urrent at
IItS times
irpose of
'I slightly
sconds in
'1'
THEORY OF OPERATION- For either type of machine, capacitors will be used to provide
excitation to the machine. The excitation magnetizes the machineOs rotor. The magnetized rotor
moving past the windings generates vo I tage in the windings. The-machine voltage and frequency
are determined by how many turns are in the.windings, how fast the rotor turns and how much
load is applied to the generator.
REGULATIQN~At -constant speed" capacitor excited Induction generators have rather poor
regulation curves often running Iron 140 ~olts no load to lOOvol~sf411)ofl~
~,
THREE
CONNECTIONS FOR
MACHINES Three-phase machines willsay 3 phase on the
nameplate along with the voltage rating and speed. For a 120 volt 60hz output, the nameplate
should .say'208 or 230/460 volts andthe motor should have nine .leads
as shownbelow.:eHART
#1
i '
' .,'
.'.,..
"
(,
1"
t',
.1
e
••
•
C)
.C'
C;
I with no
It
••
•
I,
"
eating. A
) seconds
..
ated at or
e turning
:)0 in the
e evident
or output
nrgh time
citortype
Iy can be
re to use
rut 10 HP
The best
used, but
+
.
~..'
',,'.
a
l
t
~
~
t
•
~
~__ ':.'~:'
•
~o
-.
:-.,-~-
-:-
_:,~.~
if/
......
, ~--_-.
STEP I~Run the machine as a motor to verify that it operates and note the direction or rotation.
You should tum the machine this direction when operating it as a generator. If the motor is dual,
voltage use the I20-volt connection.
I
STEP 2- Carefully disassemble the motor. Inside, attached to one end bell of the machine, will
be a centrifugal switch mechanism. This starting switch will have contacts such that the circuit it
controls opens when the machine speeds up. Solder a short section of insulated wire around this '
switch so that the circuit the switch controls is permanently engaged.
'
STEP 3- Carefully reassemble the motor watching that no wires are where they will be hit by
moving machine parts or cut by the end bells as you assemble the motor.
STEP 4- Locate the capacitor and cut the two wires leading to the capacitor. Large motors may
have two capacitors hooked together. A few motors have thecapacitors located inside an end bell
or in the base of the machine. In any case, the capucitorrs) will be a cylinder shaped object with 2
wires.
STEP 5- Connect an ac oil capacitor to the wires that went to the original capacitor. The oil
capacitor may be selected from the capacitor selection graph or lise a capacitor of about _ the
~
I
__
CONNECTIONS FQR SINGLE. PHASE CAPACITOR TYPE AC MOTORS- these motors are
the type with the little can on the outside of the motor. General.~x".:tJ:l~.Y~~e ,fo~~d.on older
refrigeratcrs and freezers, air compressors, pumps, washing machines"etc. The ouOine below
applies to these single-phase motors only.
nply stop
(:
(;
The correct size capacitor can be selecied from the following graph. Each plug will be capable of
aboutll3 of $he generators rating. There wil'l be approximately 480 volts ac at the capacitors, ,so
use care not to touch them when the generator is operating C~ART #2 '
lery high
atch fire.
151
•
i
i
value shown on the capacitor you removed. This step completes the conversion for single (I)
phase motors.
---(
{
~
('
3.4 LET US SUM UP
('
&
The efficiency of a motor is the ratio of the mechanical power output to the electrical
t·
•
powednput. This may be expressed as:
.
.
Output Efficiency =Output Input -Losses= = Input
Input Output + Losses
Any motor can be used as a generator and
generator will motor under the proper
Circumstances.
C'
any
•
3.6 S,OME USEFuLL BOOKS
1. Electrical Machines by SKBhattacharya, TataMcHilI Publishers
. 2. A Text BOOkEleCtrical Technologyby BL Theroja, S.Chand Publishers
3. Operation and Maintenance of Electrical Machines by B.V.S. Rao, Khanna Publis~rs,
..
I'
.
New Delhi.
•
e
4~O •
Aft_
••
•..
_.
--.
Check.Your Progress - 1
t. See section 3.3
3.S'GLOSARRY
Two types of motors
4.1
Itmost readily Converted are
• Three phase Squirrel cage Induction
•
C
motors
Capacitor start single-phase induction motors.
AsfI
mOL*,
the
•
••
Qe
~
and.
152
••
•
••
&
C.
C
(
(
If
single (I)
UNIT 4: STARTERS
(
«
Structure
4.0
4.1
4.2
,4.3
4.4
4.5
4.6
4.7
c
.'
te electrical
C'
" ' ~ the proper
C
OBJECTIVES
INTRODUCTION
HISTORY
ELECTRIC STA~TER
GEARS- REDUCTION STARTERS
PNEUMATIC STARTER
HYDRAULIC STARTER
OTHER METHODS
4.7.1
'4:7.2
C
.'
4.8
4.9
4.10
4.11
4~O
MANUAL STARTING
SELF STARTING
lEI' US SUM UP
SOME USEFUL BOOKS
GLOSSARY
.
.
OBJECTIVES'
'.
.
After studying this unit, you should be able to define and state the .
4.1
•
Starters
•
•
•
•
Gears-reduction starters
Pneumatic starter
Hydraulic starter
Other methods
INTRODUCTION
A starter motOr (also starting motor, or starter) is an electric
motorfor rotating an intemal-combustion engine so asto initiate
the engine's operation under its own power
4.2
HISTORY
Typical starter installed underneath and toward the rear of an automobile engine both OUo cycle
and Diesel cycle internal-combustion engines require the pistons ,to be moving before the
·153
,.
\
ignition phase of the cycle, This means that the engine must be set in motion by an external force
before it can power itself.
Originally, a hand crank was used to start engines, but it was inconvenient.
difficult, and
dangerous to crank-start an engine, EVen though cranks had an overrun mechanism, when the
engine started, the crank could begin to spin along with. the crankshaft and potentially strike the
person cranking the engine. Additionally, care had to be taken to retard the spark in, order to
prevent backfiring; with an advanced spark setting, the engine could ,kick back (run in reverse),
pulling the crank with it, because the overrun safety mechanism works in.one
direction only,
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a
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While the need was fairly ~bvious~asearly as 1899, Clyde']. 'Colem~n applied for U.S. Patent
745,157 for an electric automobile self-Staiter~inventing one that worked s~ccessful1y in most
conditions did not occur until 1911 when Charles F. Kettering 'of' Dayton Engineering'
~boratories Company {DELCO) invented an<ffiled for U.S. Patent. 1,150,523 for the first useful
• electric starter. (Kettering had replaced the hand crank bn ~CR's cash re_gi~t~is'with an eledt\c
motor five years earlier.) One aspect of the invention lay in the realization that a relatively small.
motor, driven with higher voltage and current than would be';feasible for continuous 1>peration;
could delive> enough power to crank the engine for starting. At 'the voltage and current levels
required, such a motor would bum out in a few minutes of continuous operation, but notduring
the few seconds needed to start the engine. The starters -were first. installed by Cadillac on
production models in 1912. These starters also worked as 'generators once the engine was
running," a concept that is now being revived in hybrid vehicles. The Model T relied on hand
cranks until 1919; by 1920 most manufacturers included self-starters, thus ensuring that anyone,
regardless of strength or physical handicap, could easily start a car with an internal combustion
Before Chrysler's 1949 innovation of the key-operated combination ignition~starter s~itCh,r l] the
starter was operated by the driver pressing a button mounted on the floor or dashboard,
:.Main HOUsing(yoke)
Dyerrunning dutch
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the st.
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Although users were advised, to cup their fingers .under the crank and pullup, it felt natural for
operators to grasp the handle with the fingers on one side, the thumb ori the other. Ever) a simple
backfire could result in a broken thumb; it was possibleto eng 'up with broken wrist, or worse.
Moreover, increasingly larger engiries with higher 'compressiol} ratios made hand cranking a
more physically demanding endeavour,
!
starting(
engages a
with th£.
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Field coils
Brushes
Solenoid
The modern starter motor is either a pLTmancnt-magnet or u series-p,lralkl \\ ound direct current
electric motor with a starter solenoid (similar to a relay) lllountL'd on ir. \VhL'1lcurrent from the
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and per
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starting battery is applied to the solenoid, usually through a key-operated switch, the solenoid
engages a lever that pushes out the drive pinion on the starter driveshaft and meshes the pinion
with the starter ring gear on the flywheel of the engine.
The solenoid also closes, high-current contacts for the starter .rnotor, which begins to turn. Once
the engine starts, the key-operated switch is opened, a spring in the solenoid assembly pulls the
pinion gear away from the ring gear, and the starter motor stops. The starter's pinion is clutched
to its driveshaft through an overrunning sprag dutch which permits the pinion totransmit drive
in only one direction. In this manner.drive.is transmitted through the pinion to the flywheel ring
gear, but if the pinion remains engaged (as for example because the operator fails to release the
key as soon as the engine starts, or if there is a short and the solenoid remains engaged), the
pinion will spin independently of its driveshaft. This prevents the engine driving the starter, for.
such backdrive would cause the starter to spin so fast as ~o f1¥ apart. However, this .spragclutch
arrangement would .preclude ,.the.use of the starter as a generator if employed in .hybrid scheme
mentioned above, unless modifications .are made. Also, a standard starter lTIotoris only desi gned
, for intermittent use' which would preclude its use as, it generator; the electrical component~ are
designed only to operate for typically, under ~O seconds before overheating (by too-slow
dissipation of heat from ohmic losses), to save weight and cost. ThIS is the same reason why
most automobile owner's manuals instruct the operator to pause for at least ten seconds after each
. ten or fifteen seconds of cranking the engine, when trying to start an engine that does not stan
immediately. ,.
'
This overrunning-clutch pinion arrangement was phased into use beginning in the early 1960s;
before that time, a Bendix drive was used. The Bendix system places the starter drive pinion on a
helically-cut driveshaft. When the starter motor begins turning, the inertia of the drive pinion
assembly causes it to ride forward on the helix and thus engage with the ring gear. When the
engine starts, backdrivefrom the ring gear causes the drive pinion to exceed the rotative speed of
the starter, at which point the drive pinion is forced back down the helical shaft and thus out of
mesh with the ring gear.
An intermediate development between the Bendix drive developed in the 19305 and 'the
overrunning-clutch designs introduced in the 1960s was the Bendix Folo-Thru drive. The
standard Bendix drive would disengage from the ring gear as soon as the engine fired, even if it
did not continue to run. The Folo-Thru drive contains a latching mechanism and a set of
flyweights in the body' of the drive unit. When the starter motor begins turning and the drive unit
is forced forward on the helical shaft by inertia, it is-latched into the engaged position. Only once
the drive unit is spun at a speed higher than that.attained by the starter motor itself (i.e., it is
backdriven by the running engine) will the flyweights pull radially outward, releasing the latch.
and permitting the overdriven drive unit to be spun out of engagement. In this manner, unwanted
starter disengagement is avoided before a successful engine stall,
current
'Om the
155
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Check Your
Note:
assem~v
1. Explain electric starter?
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........•.•... ~... .....•............................•........................•..............•.........................
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4.4
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5.
Progress - 1
GEARS- REDUCTION STARTERS
6.
This 8('
conceptu
, 'volt to¬ -current S'
u~e unt
4.5
Chrysler Corporation contributed materially to the modern development of the starter motor. In
1962, Chrysler introduced a 'starter incorporating a geartrain 'between the motor and the driveshaft. Rolls Royce had introduced a conceptually similar starter in 1946, but Chrysler's was'
tlie first volume-production unit. The motor shaft has integrally-cut gear teeth forming a ,drive
gear which mesh with .a larger adjacent driven gear to provide a gear reduction ratio of 3;75: I..
This permits the use of a higher-speed, lower-current: lighter and mote compact motor assembly
while increasing cranking toique.[2] Variants of this starter design were used on most vehicles
produced bfChry,sler Corporation from 1962 through 1987. The Ch:yster st~er.made a unique,
readily identifiable seund when cranking the engine.
"
This starter f6nned the design basis for the offset gear reduction starters now employed by about
half the vehicles on the road, and the conceptual basis for virtually all of them. Many Japanese
automakers phased in gear reduction starters in the 1970s and 19.80s. Light aircraft engines also
made-extensive use of this kind of starter, because its light weight offered an advantage.
Those starters not employing offset geartrains like the Chrysler unit generally employ planetary
epicyclic geartrains instead. Direct-drive starters are almost entirely obsolete owing to their
larger size, heavier weight and higher current requirements. Ford also issued a nonstandard
starter, a, direct-drive "movable pole shoe" design that provided cost reduction rather than
electrical or mechanical benefits. This type or"starter eliminated the solenoid, replacing it with a
movable pole shoe and a separate starter relay. The Ford,starter operated as follows:
t
if,
Some
The syst.
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compre)
On lar.
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slots cli.
the dru'ft"
the
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ar.
On lar,
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provide!
suPPO.
I.
The operator closed the key-operated starting switch.
distribu'
thee
radiallMa
distrib~
start
from a
valve.
011
2.
A small electric current flowed through the starter relay coil, closing the contacts and
sending a large current to the starter motor assembly.
3.
One of the pole shoes, hinged at the front. linked 10 the starter drive, and spring-Iuaded
away from its normal operating position, swung into position. This moved i.l pinion gear to
engage the flywheel ring gear, and simultaneously closed a pair of heavy-duty contacts supplying
current to the starter motor winding.
4.
The starter motor cranked the engine until it started. An overrunning clutch in the pinion
gear uncoupled the gear from the ring gear.
.
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Since I'
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5.
The operator released the key-operated starting switch, cutting power to the starter motor
assembly.
6.
This starter was used on Ford vehicles from 1973 through 1990, when a gear-reduction unit
conceptually similar to the Chrysler unit replaced it: Light motor vehicles have now adopted 9.6
.. volt to lOA volt starter motors for use with 12 volt systems to give increased power. The lower
current starter will give increased torque, but will tend to overheat and burn out with prolonged
use under load
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4.5·
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r and tile
Isler's was '
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of 3;75:1. ,
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;t vehicles
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supplying
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he pinion
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On larger diesel generators found in lar&eshore installations and especially on ships, a pneumatic
'Starting gear is used. The air motor is normally powered by compressed air at pressures of 10-JO
bar. The air motor is made up of a center drum about the size ofa soup can with four or more
slots cut into jt to allow for the vanes to be placed radially 0.1 the drum to form chambers around
the drum. The drum is offset inside a round casing so that tne inlet air for starting is admitted at
the area where the drum and vanes form a small chamber compared to the. others. The
coin pressed air can only expand by rotating the drum which allows the small chamber to become
larger and puts another one of the cainbers in the air inlet. The air motor spins much 100 fast to
be used directly on the flywheel of the engine, instead a large .gearing reduction such as a
planetary gear is used to lower the output speed. A Bendix gear is used to engage theflywheel.
Iby about
; Japanese
gines also
It
PNEUMATIC STARTER
Some gas turbine engines arid 'Diesel engines, particularly on trucks, use a pneumatic self-starter.
The system consists of a geared turbine, an air compressor and a pressure tank. Compressed air
released from the tank is used to spin the turbine, and through a set of reduction gears, engages
the ring gear on the flywheel, much like an electric starter. The engine, once running, powers the
compressor to recharge the tank.
€I
e
A spring retracted the pole shoe, and with it, the pinion gear.
f
I
On large diesel generators and almost all diesel engines used as the prime mover of ships will use
compressed air acting directly on the cylinder head. This is not ideal for smaller 'diesels as it .
provides too much cooling on starting. Also the cylinder head needs to have enough space to
support an extra valve for the air start system. The air start system operates very similar to a
distributor in a car, There is an air distributor that is geared to the camshaft of the diesel engine,
on the top of the air distributor is a single lobe similar to what is found on a camshaft. Arranged
radially around this lobe are roller tip followers for every cylinder. When the lobe of the air,
distributor hits one of the followers. it will send an air signal that acts upon the back of the air
start valve located. in the cylinder head causing it to open. The actual compressed airis provided
from a large reservoir that feeds into a header located along the engine. As soon as the air start
valve is opened the compressed air is admitted and the engine will begin turning. It"can be used
on 2-cycle and 4-cyde engines and on reversing engines. On large 2-stroke engines less than one
revolution of the crankshaft i~;needed for starting.
Since large trucks typically use air brakes, the system does double duty. supplying compressed
air to the brake system. Pneumatic starters have the advantages of delivering high torque,
157
..
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inca(
andi
mechanical simplicity and reliability. They eliminate the need for oversized, heavy storage
batteries in prime mover electrical systems.
~:cp~:
4.6
HYDRAULIC STARTER
sec~
4.7 •.-
Some diesel erigines from 6 to 16 cylinders ate started by
'means of a' hydraulic motor,' Hydraulic starters and the
associated systems provide a sparkless, reliable method of
. engine starting at a wide temperature range. Typically
hydraulic. starters are found in applications such as remote
generators, lifeboat propulsion engines, offshore fire.
pumping engines, and hydraulic fracturing rigs.
SonC"'
~~~
t·
4.8~
The system used to support the hydraulic starter includes
valves, pumps, filters, a reservoir,' and piston accumulators. The operator can manually recharge
the hydraulic system; -this cannot readily be done with air or electric starting systems, so
hydraulic .starting systenis are favored in applications wherein emergency starting- is a
requirement."
.III
"•
.'
•
•.,
•
•
Note:
•..
2. Check your answers with those given at the end
of the unit.
1. Explain bydraulic starter?
. __
.................
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4.7
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OTHER METHODS
Other ways of starting have included a spring wound by regenerative braking, gun powder
cylinders, windmilling the propeller of an engine while the airplane is flying and putting a car in
gear when it is moving.
4.7.1
MANUAL STARTING
Early internal combustion engines were generally started with energy supplied by a human
operator. The methods included cranking, pushing, flipping the propeller, pulling a cord, foot
pedal starters, and indirect methods such as springs and fly wheels. Since these methods are
158
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inconvenient and sometimes dangerous, they have: gradually 'been replaced by electric motors
and compressed air, starting in the larger engines.
storage
In case of failure of the battery or starter motor, a car with a manual transmission can be started
by pushing it or rolling it downhill and then engaging the clutch while it is moving, usually in
second gear
'
4.7.2 SELF STARTING
Some modern gasoline engines with twelve or more cylinders always have at least one piston at
the beginning of its Power stroke and are able to start by injecting fuel into that cylinder and
igniting it.
4.8
C'
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e
.•,
•
..•.'
r-
ly recharge
ystems, so
rting -is a
•
-
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;
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Iow,
at the end
4.9
..................
....._ ...........
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I
3. Operation and Maintenance of Electrical Machines by B.V.S. Rao, Khann.: Publishers,
New Delhi.
powder
ng a ,car in
In
5. Performance & Design of AC Machines by MG Say. CBS Publication, New Delhi
6. Electrical Energy Systems Theory by Elegerd. Tara Mcfiraw Hill Co, New Delhi
7.Electric Machinery by Fitzcrald, Tara McGraw Hill Co. New Delhi
8. Electrical MachinesrSigma Series) by Kothari. Tara McGraw Hill Co, New Delhi
. a human
cord, foot
ethods are
9.Elcctrical Machines by Kothari & Nagarth, Tata !\kGr,l\\ Hill Co. Nc\\ Delhi
I
II
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SOME USEFUL BOOKS
2.. A Text Book Electrical Technology by BL Theraja, S.Chand Publishers
~
••
A starter motor (also starting motor, or starter) is an electric motor for rotating an internalcombustionengineso as to initiate the engine's operation under its own power.
Both Otto cycle and Diesel cycle intemal-cornbusticn engines require the pistons to be
movingbetore
the ignition
phase , of','the cycle.;
,
. .
.._
_
4-.
•
The fnodem'starter motor is either a pennanent-magftet or a series-parallel wound direct
: currentelectric motor with a starter solenoid (similar to a relay) mounted on it.
Hydraulic starters and the associated systems provide .~ sparkless, reliable method 'of
engine starting at a wide temperature range.
Some modern gasoline engines with twelve or more cylinders always have at.least one
piston at the beginning of its power stroke and are able t~ start by injecting fuel into that
cylinder and igniting it.
I. Electrical Machines by SK Bhattacharya, Tatalvlcl-lill Publishers
CJ
•
LET US SUM UP
1St)
I
j
{,
10.Electrical and Electronics Engineering by Vikramaditya Dave, Lakshrni Publications (Pvt)
Ltd, New Delhi
<;
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4.10
(
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fi
l , -See section 4.3
Check Your Progress - 2 '
) . See Section 4.6
4.11
f'i
I{l
GLOSSARY
,
'
CJ
Electric starter
•
•
The modem starter motor is ejther a permanent-magnet or a series-parallel wound direct
current electric motor with a starter solenoid (similar to a relay) mounted on it. '
When current from the starting batteryis applied to the solenoid, usually through' a keyoperated switch, the solenoid' engages a lever that pushes out the drive pinion on the
starter driveshaft and meshes the pinion with the starter ring gear on the flywheel of the
engine .:
•
The solenoid also doses high-current contacts for the starter motor, which begins to tum.
Once the engine starts, the key-operated' switch is opened, a spring in 'the solenoid
assembly pulls the pinion gear away from the ring gear, and the starter motor stops.
•
The starter's pinion is clutched to its 'driveshaft through an overrunning sprag clutch
which permits the pinion to transmit drive in only one direction.
C"
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Types of starter
•
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Electric starter
gears- reduction starters
pneumatic starter
hydraulic starter
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NATIONAL COLLABORATIVE PARTNER
KOLKATA OFFICE:
114/D Garfa Main Road
(Opp. 12 No. Municipality Office)
Jadavpur, Kolkata – 700075
West Bengal, India
Ph- 033 65002166
Email- santanu.sikdar@gmail.com
DELHI OFFICE:
M-7, Old DLF Colony
Sector – 14
Gurgaon
Haryana 122011
Ph- 0124 4284798
www.ksouoel.com

BTPWE 504 Electrical Machines II

Transcription

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