H How to reduce wearing on gears while pitching from 0-degree

WIND ENERGY
EDUARDO VICENTE
G.T.RIVI – LINCOLN SPAIN
How to reduce wearing on gears
while pitching from 0-degree
From the beginning of the wind energy industry, 30 years ago, wind turbine models have grown
up to high energy power per each wind turbine. This power installed per wind turbine leads to the
needing to optimize the maintenance and to increase the reliability; a new technical challenge for
wind turbine designers. A lack of lubrication can bring WTGs to a standstill. The increased cost
of lubricants and maintenance duties, coupled with a higher equipment value, drives the need
for automatic and centralized lubrication systems.
H
arsh conditions such as vibration,
mechanical loads, contamination
and moisture cumulatively result
in a high wear rate for gears and friction
points. Proper Lubrication is absolutely necessary in order to provide the right protection.
A poor preventive maintenance in a wind
turbine might lead to continued nondesired breakdowns and to apply corrective maintenance. Predictive & preventive
maintenance are being optimized in order
to maximize energy generation. For this
reason new multimegawatt WTGs house
autonomous systems that contribute to
decrease the maintenance tasks.
By using Automatic Lubrication Systems,
the lubricant is automatically delivered in
time-controlled and metered quantities to
all connected points in the system, while
the WTG is in operation. Lubrication “in
motion” ensures that the lubricant is optimally and evenly distributed within the
bearings.
But it actually does not happen in Pitch
Gears systems, due to here only a 90-degree cog segment is actually used. Automatic Lubrication becomes more difficult
by the fact that for around 90% of the
production time of a wind turbine the
rotor blades remain in what is known as
the 0-degree setting and is adjusted by
only minimal values. Two to three teeth
of the open gear drive are therefore exposed to extremely high loads for 90% of
the time that the turbine is in production.
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Excessive wearing on gear tooth flange
Conventional lubrication of this cog segment can therefore only be achieved if the
rotor blades pass through the complete
90º segment during a maintenance session. However, as maintenance normally
cannot be carried out without taking the
turbine offline there are only two options
for lubricating the rotor blade adjustment
gear:
• Lubrication during the natural idle
phases (no wind)
• Compulsory maintenance intervals,
associated with additional loss of production
The idea of adapting the lubrication task
to natural idle phases is attractive to wind
farm operators but not at all to designers or maintenance staff. The fact is that
production phases may be extremely long
during extended periods of windy conditions. These periods tend to be longer for
offshore plants than for onshore installations. In such cases there is a possibility
that the lubricating film will degenerate
and fail before the end of the natural wind
production phase, thus causing damage
to the gear drive.
For gear drive lubrication there are essentially two acceptable methods that
can be applied to wind turbines:
• Spray lubrication with compressed air,
which due to lack of pneumatics in
WTGs makes it unfeasible.
• Mechanical pinion gear lubrication,
which is the most used.
Regardless of the lubrication method
that be used, it is important that the
proper type of lubricant be applied in the
required amount, at the right time, and
on the right tooth.
Right lubrication on gears not only reduce wearing, but it also eliminates risk
of pitting, micropitting, scuffing, bending fatigue, and other mechanical failures
inherent to high loads on open gears.
It is also important to take into account
that protection to corrosion is becoming
critical issue; due to Wind Turbine market tends new developments for offshore
environment and cold climate conditions,
where C4H or C5M comes to be mandatory.
MicroLubGear (MLG) is a novel technology to avoid the energy generation loses
to lubricate the pitch at 0º position. Microlubgear – combined with a right Automatic Lubrication System – lubricates the
tooth in contact while the wind turbine
operates and pitch system is working. It’s
just so simple. It’s just so accurate. It’s just
so efficient.
energetica
international
· Nº 4 · MAR14