Drive train and generator

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As already noted, a modern wind turbine rotates at between 5 and 20 rpm while conventional generators operating at between 800 and 3600 rpm, so some form of step-up gearbox is usually necessary. This gearbox has to be extremely rugged because it must be able to withstand more than simply the rotational force from the wind turbine rotor.

Since wind speed varies with height, the force on a turbine blade at the lowest point of its orbit will be less than at the highest point. This will create a constant bending force on the rotor which is transmitted through the shaft to the gearbox. The speed of the generator must also be controlled so that it remains synchronised with the grid. If the shaft feeding energy to the generator starts to rotate too fast there will be a countermanding force from the generator resisting this increase in speed. This will set up an additional rotational stress within the shaft. This force will also be felt within the gearbox.

To cope with this, a wind turbine gearbox needs to be a heavy-duty design. Even so the gearbox is the most likely component in a wind turbine to fail.

One solution to this problem is to eliminate the gearbox altogether and use a system where the rotor is connected directly to the generator. Direct drive generators capable of operating at the low speeds encountered in wind turbines are being developed but current designs are much heavier than more conventional generators.

Main Gear-box shaft transmission Brake Generator

Main Gear-box shaft transmission Brake Generator

Figure 11.3 A wind turbine drive train

Another approach which eases the load on the drive train is to use a variable-speed generator. This will generate power at whatever speed the turbine rotor turns. However the variable frequency output must then be converted electronically to the grid frequency, adding to the cost of the wind turbine.

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Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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