What happens in the event of an anemometer failure?
Many people will not realise that wind speed is not involved in the closed loop control of wind turbine output.
That is, how much torque the excitation control system puts on the generator is not based on the magnitude of the wind speed, but on the impeller speed, an indirect variable.
This is because the anemometer we currently have at the rear of the nacelle does not measure the effective wind speed value. In fact, with a sweeping area as large as the entire impeller, the wind speed is not at all described by a single number.
In most control systems, wind speed measurements can only be used to make logical judgements:
Whether the wind speed is high enough to get the unit started -- that is, the cut-in wind speed;
Whether the wind speed has reached a level outside of the unit's tolerable range ---- - also known as the cut-out wind speed;
Whether there is an extreme change in wind speed - so-called extreme wind condition detection.
It doesn't seem that complicated. But what happens if the anemometer fails?
In the first case, if this failure can be self-tested by the anemometer and reacted to the control system, then it is generally a fault shutdown, which is the simplest case;
In the second case, the unit is in shutdown and an anemometer failure generally results in very low wind speed data, then the unit will not cut in;
(c) In the third case, the unit is in grid-connected operation, but the anemometer has failed, making the wind speed a zero value, or on the small side. As a general rule, the unit will only judge that the wind speed is too large and cut out, but the wind speed is small and will not trigger any action.
In this case, it is easier to get out of the situation. Because, if the wind speed is much higher than the cut-out wind speed without triggering the cut-out condition, resulting in overloaded operation of the unit, which is very dangerous, especially in some extreme weather.
Typically, due to icing on the anemometer, the wind speed is measured at less than 2 m/s, but the unit is running at full load. If the wind speed continues to increase above the cut-out speed in this situation and the unit continues to run due to a failure of the anemometer, the unit could be potentially overloaded, or an accident could occur.
Icing is just a typical example, and quality problems with the anemometer itself can also cause this phenomenon.
