Direct Drive for Economically Sustainable Wind Energy
slow turbine blades and high-speed generators – namely the use of gearboxes (see Figure 1). Reliability issues with wind turbine gearboxes is common knowledge (a quick look at the provisions on the balance sheets of some of the major gearbox manufacturers highlights this). Problems with reliability stem from the extreme engineering challenges that gearbox technology faces in wind applications. The most common approach is to use a three-stage gearbox with a high gear ratio (i.e. 97:1). Operating large complex gearboxes in wind turbines is causing a number of difficulties for both developers and turbine manufacturers and it is very difficult to see from where significant improvements in gearbox technology can come. There are very serious limitations surrounding:
• •
• • gear wearing (leading to failure and downtime);
handling of multidirectional forces (turbine blades tend to flex in multiple directions as they pass the wind shadow of the turbine tower);
need for replacement of large quantities of oil (an increasing concern in environmentally sensitive areas, such as offshore); and
component weight (the Winergy three-stage gearbox used in REPower’s 5M machine weighs 63 tonnes).
Any real improvements are hard to envisage in what is an old and mature technology. These problems are increasing as the industry moves towards larger, more powerful turbines which subject gearboxes to ever greater forces. There has already been a shift away from traditional high-speed copper generators.
Figure 2: Direct-drive Wind Turbine with Simple Gearless Arrangement
Optional obstruction light
Nacelle cover Blade
Power converter and system controller
(below mainframe) Mainframe
Service platform Yaw assembly
Tower
Generator Rotor hub
Meterorological instruments (’met mast’)
Figure 1: Conventional Wind Turbine with Complex Gearbox Components 1. Blades 2. Rotor 3. Pitch 4. Brake 5. Low-speed shaft 6. Gear box 7. Generator 8. Controller 9. Anemometer 10. Wind vane 11. Nacelle 12. High-speed shaft 13. Yew drive 14. Yew motor 15. Tower
3 2 5 1 4 12 7 13 14 11 6 8 10 9 15
Mechanical brake (behind generator)
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Ajax Rolled Ring and Machine Phone: +1 803 684 3133
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