disconnection and connection of wind turbines 1

[royclh]

hi,

i wonder if any expert in wind turbines can help me to clear my doubts. at a very low wind speed, i understand it's sensible to disconnect the wind turbine generator (WTG) from the grid to reduce the losses. one of the papers that I have recently read about wind farm connection has however suggested to keep the WTG running as a motor at a certain low wind speed (intermediate stage) and only switch off when there is absolutely no wind or at a very low wind speed. i cant remember exactly what are the advantages of doing that but i guess it would allow the turbine to pick up easily as the wind speed increases. Also, this reduces frequent connection and disconnection of the WTG that may reduce its life expectancy. also, keeping the motor running is one form of energy storage or sth.

I wonder if this has been put into the practice? have the wind turbine manufacturers ever considered this approach? So far, what I heard is that the WTGs will disconnect from the grid as the wind speed drop below 3 - 5m/s.

Look forward to your reply. Many thanks.

 

[jan63]

although not an expert in that subject but you are right as far as keeping the WTG are concerned.Frequent operation is avoided in this way.Also please do remember that most WTG do not have their own excitation and rely on external source for excitation.

 

[jraef]

With an induction generator, if the rotor speed of the generator EVER falls below synchronous speed, the generator becomes a motor and CONSUMES rather than creates power. But if you have CVT* between the turbine and the generator, the wind speed can often drop quite a bit before there is an uncompensated drop in generator rotor speed. So it's really not the best idea to disconnect from the grid based on wind speed alone. It's better to base it on power flow; if power is "gazinta" instead of "gazouta", that's when you want to disconnect to avoid losing the revenue you have been creating.

But...

A turbine is NOT a good prime mover when it comes to accelerating torque. When at a standstill or very low speed, air tends to spill off the blades for a long time before it creates enough radial torque to make them move (or move faster). If for example it takes 2 extra hours of high wind speed to get the rotor to a speed where it generates, that is 2 hours of lost generating time. So usually, an induction generator acts as a motor to bring the turbine up to motor slip speed and then let the wind just take it super synchronous. To that end there is a case to be made for leaving it connected to the grid if you think the speed drop is temporary, because if it returns, you may not have to waste a lot of time re-accelerating. But if it gets too slow you will have to re-accelerate it and that causes mechanical stress, especially on the transmission. Typically a WTG controller takes all of this into account as a programmed algorithm.

*CVT = Constant Velocity Transmission; usually a variable pulley or hydraulic transmission that maintains a constant speed at the generator rotor when the turbine speed varies.


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[alehman]

As jraef said, the controls are normally programmed by the manufacturer. As a customer you would typically have very limited influence on how the unit operates (at least if you value your warranty). Even some of the smaller units motor up to near operating speed automatically.

Alan
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"It’s always fun to do the impossible." - Walt Disney