Variable-speed drives for belt-conveyor systems

Variable-speed drives for
belt-conveyor systems
A project report of the revamp of a lignite conveyor line
ABB Process Industries - Open Pit Mining & Materials Handling, Cottbus/Germany
Variable-speed drives for belt conveyor systems, Nov 2000
2
Introduction
More and more frequently, modern beltconveyor systems are equipped with
variable-speed drives on the basis of
frequency converters connected with
standard squirrel-cage motors and
gearboxes. As compared with conventional
drives used in constant-frequency systems
they have the major advantage that both
power consumption and mechanical wear
can be significantly reduced. This makes it
possible, in conjunction with powerful
control and process management systems
as well as modern diagnostic tools, to
design efficient belt-conveyor systems
characterised by low operation costs and
high availability.
Fig. 1: View of a coal conveyor
This is the description of such a drive concept covering five belt conveyors
implemented recently by ABB. For the first time ABB Automation has used here grid
converters according to the latest developments of drive technology.
M
U
Drive
1482 m
U
M
44
U
U
U
M
3 x 630 kW
(152
m)
735 m
Drive
1552 m
5
M
778 m
Drive
1 x 900 kW
M
inclined conveyor
U
M
906 m
U
Drive
M
M
U
910 m
3
M
Drive
672
m
U
Drive
U
U
M
3 x 900 kW
225 m
381 m
M
1
2
M
1 x 630 kW
Legend
x
- Drive station (of a variable-speed conveyor)
U
- Transfer point (of a conventional conveyor)
1 x 630 kW
Coal dispatch
Fig. 2: Belt-conveyor scheme
ABB Process Industries - Open Pit Mining & Materials Handling, Cottbus/Germany
Variable-speed drives for belt conveyor systems, Nov 2000
3
Quality criteria
Introducing speed control for belt conveyors, the customer has defined precise
economic and technological objectives:
• power savings through a load-dependent control of the belt speed
• efficiency increase
• minimisation of system perturbations
• reduction of gear and belt wear
Demanding quality criteria have been specified as benchmarks for accomplishing
those objectives. They include in particular:
• dynamic torque characteristics at starting and stopping
• efficiency with different belt speeds and loads
• power factor (cos ϕ ≥ 0,95)
• system perturbations (THD ≤ 10%)
ABB Automation, the supplier of the electrical-engineering part of the system, could
successfully prove that all agreed criteria have been attained.
Efficiency of the whole system
(incl. transformer, frequency converters, motors & air
conditioning)
M/MN
[%]
100
75
50
stipulated in contract
[%]
at 100% speed
90.1
90.2
89.2
proved
[%]
92.4
92.0
90.6
at 75% speed
100
75
50
89.8
90.0
89.1
91.3
91.1
90.3
at 50% speed
100
75
50
88.3
88.7
88.1
89.0
88.7
88.4
Fig. 3 Efficiency
ABB Process Industries - Open Pit Mining & Materials Handling, Cottbus/Germany
Variable-speed drives for belt conveyor systems, Nov 2000
4
Drive technology
All conveyor drives are equipped with HXR
type six-pole totally enclosed fan-cooled
squirrel-cage motors fed by ACS 600
frequency converters. They are low-voltage
drives for a supply voltage of 690 V, all
designed for 4-quadrant operation, i.e.
working as motors and generators. The
electrical energy generated during the
braking process is fed back into the grid
through grid inverters.
Two different concepts have been
implemented on the frequency-converter
systems, depending on the number of
motors in question:
• single drive
• multi drive
Fig. 4: Motor HXR 450 LM6
While the single drive, simply speaking, consists of one grid-side and one motor-side
inverter, the multi drive is more complicated. Here one diode rectifier and one grid
inverter each feed in parallel on one common DC busbar which, in accordance with
the drive configuration, supplies up to three inverter units.
6 kV
2 x 0,69 kV
6 kV
0,69 kV
ACA 635-900-6
ACA 635 1710-6
ACA 6312600-61
f
ACA 610-900-6
ACA 610 1385-6
f
ACA 610 1385-6
f
ACA 610 1385-6
f
M
3
630 kW
Fig. 5: Single drive
M
3
M
3
M
3
3 x 900 kW
ABB Process Industries - Open Pit Mining & Materials Handling, Cottbus/Germany
Fig. 6: Multi drive
Variable-speed drives for belt conveyor systems, Nov 2000
5
All the ABB frequency converters used are based on IGBT power semiconductors
and are characterised, in particular, by a modern control concept called direct torque
control (DTC®). Contrary to the well-known pulse-width modulation (PWM) the DTC®
controls directly the torque and stator flow of the motor. That lends the drive a higher
control accuracy and better dynamic properties, especially in the starting and braking
phase.
Guiding principles for dimensioning the drives have been not only the mechanically
required torque but also the objective to use common hardware as far as possible.
Another important criterion has been the demanded high availability of the system.
This is why a so-called emergency operation has been foreseen for the multi drives,
permitting the continued use of the conveyor system with reduced performance in
case of failure of a supply unit or inverter.
The equipment of the belt-conveyors is shown here:
Conveyor
Motors
number
type
HXR…
1
2
3
4
performance
supply unit 1
type
rated current
synchronous
speed
supply unit 2
type
rated current
1
630 kW
450 LM6
1000 min
1
630 kW
450 LM6
1000 min
3
900 kW
500 LR6
1000 min
1
*)
500 LR6
Frequency converters
inverter
type
rated current
ACA635-0900-6
695 A
ACA610-0900-6
755 A
supply unit:
grid inverter
ACA635-0900-6
695 A
ACA610-0900-6
755 A
supply unit:
grid inverter
ACA631-2600-6
2176 A
ACA610-1385-6
1156 A
(3x)
supply unit 1:
diode unit
-1
-1
-1
ACA635-1710-6
1320 A
ACA631-2600-6
2176 A
900 kW
1000 min
Remarks
-1
supply unit 2:
IGBT grid inverter
ACA610-1385-6
1156 A
*)
(2x)
ACA635-1710-6
1320 A
supply unit 1:
diode unit
supply unit 2:
IGBT grid inverter
*)
5
3
630 kW
500 LR6
1000 min
ACA631-2600-6
2176 A
-1
ACA610-1385-6
1156 A
(3x)
ACA635-1710-6
1320 A
final stage: 3 x 900 kW
supply unit 1:
diode unit
supply unit 2:
IGBT grid inverter
Fig. 7: Drive design
ABB Process Industries - Open Pit Mining & Materials Handling, Cottbus/Germany
Variable-speed drives for belt conveyor systems, Nov 2000
6
Owing to the arrangement in closed and insulated
electric containers it is necessary to get the loss heat
out that is produced by the frequency converters.
Split-type air conditioners have been installed for that
purpose with a particular view to having closed
cooling circuits. This has led to an almost total
elimination of dust from the interior of the frequency
converter room being deposited on the powerelectronic components.
Cooling air coming in
through cable basement
Switchgear
Fig. 8: Container cross-section
Control concept
Compact programmable controllers – so-called application controllers (APC) are
integral parts of the frequency converter system. These controllers are used for timecritical control and supervision functions close to the drives, such as
• conveyor speed control
• speed control of individual drives
• speed and belt-slip control
• load equilibration between two driving drums
• speed difference control between two motors on one driving drum
Thus the application controllers are the interface between the frequency converters
and the decentralised control system based on ABB Advant OSC® that performs
overriding operation control functions and general control and supervision tasks.
Optimum belt load
An optimum loading of the belts is achieved by way of controlling the belt speed,
depending on the load volume, in the range of 3.0 … 6.0 m/s. A laser scanner is
used to supply reference values by monitoring the cross-section of the load on the
belt.
The value determined is the input for a complex mathematical model called “virtual
conveyor” integrated in the control system. It is there that the reference values are
calculated for all downstream conveyors and transmitted via Ethernet (optical-fibre
connections) to local controllers and from there to the frequency converters.
Diagnostics
Every frequency converter system has an interface for DrivesWindows®, a powerful
Windows-based software tool for commissioning and maintenance. DrivesWindows®
runs on conventional personal computers or laptops and is easy to handle. It covers
the following functions:
• displaying and editing of signals and parameters (online or offline)
• storing of parameters
• recording and graphically displaying of signals
• recording of fault and failure reports with time stamp
In addition, the frequency converter systems are equipped with a touch screen for
fast menu-supported display of major operational signals, such as speed, torque,
fault and status reports.
ABB Process Industries - Open Pit Mining & Materials Handling, Cottbus/Germany
Variable-speed drives for belt conveyor systems, Nov 2000
7
coax
PITOUCH
drive
drive
YPK112A YPK113A
APC 2
YPP110A
YPK112A
drive
DDCS
YPQ112
drive
Ext. I/O
YPQ111A
1 2 3 4
+2LS
drive
APC 2
YPP110A
Ext. I/O
YPQ111A
drive
drive
DDCS
YPQ112
YPH 107
1 2 3 4
-X2
-X2
Control Cubicle
-A21.3
-A21.1A
-A21.1B
RELAYS
YPT111A
YPT111A
ISU
DSU
INU
INU
INU
=1B01A
=1B01B
=1B10
=1B20
=1B40
+2IG11
+2IG2
+2IU1
+2IU2
+2IU3
-A17
NDBU91
8
1
Diagnostic Tool
DRIVES WINDOWS
Control Cubicle
Fig. 9: Diagnostic tools on a conveyor
Summary
Some of the benefits of controlled drives are
• an optimum loading of the belts through controlling the belt speed, depending on
the load volume, in the range of 3.0 … 6.0 m/s; reference values are supplied by
a laser scanner monitoring the belt load
• a reduction of gear and belt wear through smooth starting and stopping of
conveyors
• the elimination of belt slippage at driving drums
• more even torque on driving drums through load equilibration
• control of speed differences between motors on one driving drum
Moreover, the electric drives are characterised by high availability and efficiency as
well as little system perturbation.
For further information, please contact
ABB Process Industries GmbH
Gaglower Str. 17/18
03048 Cottbus
Germany
Phone: +49 355 596 225
Fax: +49 355 596 832
Email: Cottbus.deasy@de.abb.com
www.abb.com/mining
ABB Process Industries - Open Pit Mining & Materials Handling, Cottbus/Germany