Wind turbine cut-out behavior

[gsdesena]

Hello all,

I'm working on a research project about the impact of wind farms on the electrical grid in extreme weather. I'm trying to understand the behavior of wind turbines near their cut-out wind speed. A post from a few years ago (

https://www.eng-tips.com/viewthread.cfm?qid=402063#post)

gave exactly the kind of details I'm looking for, but I'd like to know if anyone can confirm that this is a typical control strategy. The main question is: how fast do wind turbines react to a change in wind speed when determining when to cut-out and when to cut-in again?

Thanks for any information you can share!


Geoffrey De Sena
PhD researcher
Uppsala University

 

[FluidPowerUser]

You would have to ask the manufacturer about their own particular design criteria.

From a control point of view, the anemometer input can prompt a response from the turbine to either turn away from the wind with the yaw control, or change the blade pitch in a few seconds. However, that will put stress on the turbine and shorten the running life. The last thing the turbine needs is to be constantly adjusting to wind strength and direction. On this basis, there will be a control algorithm that is averaging the wind conditions and making the necessary adjustments to get the best efficiency.

It's expensive to build a wind turbine and you don't want to have too much mass up there and you don't want to be moving it around constantly.

Ultimately, it's up to the turbine manufacturer to set the duty cycle and design criteria for assembly and operation.

There are plenty of turbines that sit still while the wind is blowing and there are not that many instances of turbine failure, per capita. The indication is therefore that these things are very slow to respond.

 

[gsdesena]

Thanks for the explanation! By "very slow to respond", do you mean something on the order of 100 seconds as in the linked post? I know the anemometer is typically sampling at 1 Hz, so reacting to every time step would be absurd. But reacting to the 10-minute aggregated data seems way too slow. I guess it's somewhere in the middle.

 

[FluidPowerUser]

Yes, somewhere between 10 and 100 seconds of aggregated data is to be expected.

The control side of the system can respond in ms and provide a constant blade speed relative to the wind speed. However, the costs of doing that in terms of hardware and installation are prohibitive. I'd expect a 4MW turbine to see constant windspeed for at least a minute before it turns into the wind or changes the pitch of the blades. Anything less than that will have a dramatic affect on the life of the turbine.

Vestas offer Power Optimised or Load Optimised for their 4MW, but they don't mention any performance optimisation vs wind conditions. That suggests to me that they use software and real time monitoring to effectively tune the turbine to the local climate and offset the performance depending on the commercial agreement for installation, design life and return on investment.

 

[gsdesena]

Thanks for the additional details!

 

[rb1957]

A couple of things ...

1) the turbine has to have some electrical "post-processing" to convert the variable input frequency (from the local windspeed) to constant frequency output. This is stuff about which I know not.

2) A wind turbine blade should (IMHO) be optimised for torque (rather than a conventional propeller, optmised for thrust). I'd've though they had a "constant speed" beta (pitch) control, like a conventional propeller (to match the propeller speed to the airplane speed and maxmise propulsive efficiency).

3) I'd've thought that wind turbine blades were designed to "wash out" (de-load) the blade as the wind speed increased, to control the maximum torque. So in high winds, the blades would go into a "feather" mode and the blade would "wind-mill".

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.