Question from one that does not know much

[Mauro Gaetano]

I have a few question about the operation of utility size wind generators, 1MW size class.

Is the rotor RPM fixed and synchronously geared with the grid frequency or is variable?

I assume that power generated varies with wind strength. In such case how is controlled?
Are blades variable pitch? If RPM is constant is more power extracted by
controlling the alternator to produce more current demanding more torque?

I am curious about all these new windmills popping up.

Thanks
Mauro

[Rob Beckers]

Mauro, both types exist: Those turbines that run essentially fixed speed and use an asynchronous generator (basically just an induction motor on a gearbox) to produce power. Their RPM is related to the grid frequency and it has to stay within a very narrow RPM band to produce power.

The other type uses a permanent magnet alternator to produce power, and an inverter. They make those now too in the MW class of turbines. PMA based turbines are variable RPM.

In both cases power varies with wind speed, the PMA type is just better at following along with the wind speed.

For the large turbines I don't know if variable pitch is used as a mechanism to optimize power output. It is used by many turbines to feather (or turn to stall angle) in case of high winds or mechanical trouble, together with a brake.

-RoB-

[Mauro Gaetano]

Thank, very informative.