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Topics Covered
Introduction
Wind Turbines
Lubrication
High Loads
Specialty Greases
Smart Lubrication Tip
Tag Links: Lubrication | Wind Turbine Lubricants
Introduction
Wind-generated electricity is becoming an increasingly attractive source of
power, as it is recognized as providing an environmentally compatible source of
electricity. Wind energy is the world's fastest growing energy source on a
percentage basis (with an annual increase approaching 32%) and its growth is
forecast to continue at a double-digit pace into the next decade. The process of
the wind turbine is a fairly simple one. The wind is used to generate mechanical
power or electricity. A range of different wind speeds passing over the blades
is converted into mechanical power. Wind turns the blades and the power from the
rotation of the wind turbine rotor is transferred to the generator through the
nacelle that houses the gearbox, low and high speed shafts, generator,
controller, and brake. To get the most reliable energy production possible,
machines have to be kept in excellent condition. Lubrication is another
important aspect that contributes to turbine reliability and long service
intervals.
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Key Wind Turbine Lubrication Points |
The promise of clean, unlimited wind energy presents many technical
challenges for the components in the windmill nacelle. Often located in
extremely remote locations and tens of meters in the air, reliability is
paramount and failure not an option. Components need to be compact and
lightweight yet provide exceptional service life in the most demanding of
operating environments. For manufacturers and operators of wind energy
generating turbines, reliability, remote monitoring and ease of component
maintenance are critical factors in their successful and viable operation. High
efficiency lubrication should be an integral part of wind turbine design and
maintenance.
Wind Turbines
Wind turbines are complex mechanical installations which require three types of
special lubricant: for the hydraulic circuits and brakes, greases for the
slewing rings and bearings. Among the most critical components of the nacelle
are the blade bearings which have to operate under extreme stresses and
operating conditions. The higher power of the latest wind energy technology is a
consequence of design changes and component development including much longer
blades, taller towers and improved mechanical and electrical components like
gearboxes and generators. Also, improved lubricants and adapted maintenance
intervals together with automatic lubricant dispensing systems have contributed
to this growth.
Lubrication
The points to lubricate in an indirect drive wind turbine are:
1. Blade bearings with pitching gears, Azimuth bearings
2. Main
shaft bearing
3. Releasable shaft connections i.e. shrink disc
connections
4. Gear boxes
5. Generator bearings
6. Disc
brakes
7. Most of the external and internal threaded
connections
Many bearings, including the blade bearings, are
lubricated with an automatic greasing system. Greases for blade bearings and
azimuth bearings have to show the following properties:
- High load
resistance
- Resistance to vibrations as a result of the light weight
design and the unsteady wind
- Medium to low speeds
- High
temperature resistance and broad service temperature range
- Resistant
to corrosive environments etc.
- Good compatibility to the sealing
materials and varnishes involved
- Good pumpability in centralized
lubricating systems
High Loads
High loads are occurring due to the wind gusts and inner vibrations in the
turbine. The intermediate bodies of the bearings like balls or rollers are
pressed against the outer and inner rings under vibrations so that the grease is
squeezed out of the highly loaded contact zones. Wear marks in form of the
contact area of the intermediate bodies against the rings are generated. This
'riffeling' effect is damaging the bearings severely. The effect can be
reproduced in screening tests, and at the same time the corrosion of the bearing
is checked.
Specialty Greases
Specialty greases i.e. Lithium or Calcium soap greases with Mineral, PAO or
Ester base oils are in use (the later when compatibility to the plastic
materials involved is assured). In addition, solid lubricants and anti-corrosion
additives can ensure high wear reduction and less corrosion leading to the long
service intervals needed.
With a trend in wind farms moving offshore so as to capture maximized wind
speeds and therefore run more efficiently, maintenance will increasingly become
more difficult. This emphasizes the importance of proper lubrication at the
design stage. To date, very poor maintenance of wind turbine lubrication has
been seen in the field. But Molykote hopes its expertise will be called
upon to improve this.
Smart Lubrication Tip
Problem: You are faced with short life of your bearings which operate under
high load in a wet, corrosive environment
Solution: You can extend the equipment life by applying Molykote G-0102 heavy
duty bearing grease, which is well suited in the presence of water
Source: Dow Corning
For more information on this source please visit the Dow
Corning supplier profile on AZoM.com