Dangers of Wind Power

YouTubers have been enjoying some spectacular footage of the disintegration of a Danish wind turbine which ended up a bit broken after its brakes failed:
The suicidal turbine was located at Hornslet near Aarhus. According to the Telegraph, the 60m-high structure was ten years old and manufactured by Vestas. Engineers who attended the scene were unable to prevent the break-up, and wisely retired to a safe distance.

Its death was one of two in the space of a week, and Denmark's climate minister has called for a probe into the failures.
that is a textbook example of turbine structural failure due to overspeed. That speed is far outside the design parameters, and the forces on the structure far beyond the design as well. Asking it to be able to survive that is like asking for your car to not be crushed when you crash it into a wall at 60 mph.

Turbine rotor speed is generally controlled in three basic ways. The first is simply the resistance of the generator itself. However if the generator fails or is disconnected from the power grid this source of resistance fails as well.

The second speed control method is by changing the aerodynamics of the rotor. On most modern pitch regulated turbines this involves changing the pitch of the rotor blades into the wind. When the blades are pitched 90 degrees out of the wind they generate essentially zero rotational force. On simpler stall regulated machines, which cannot adjust blade pitch, a tip brake is activated; the last few feet of the blades are pushed out a few inches and turned out of the wind. This achieves a similar aerodynamic effect. Either method is usually enough to stop a turbine fairly quickly, and this is the primary control mechanism. These systems have either springs or hydraulic accumulators and should automatically activate in case of other systems failure.

The third method is a mechanical brake. This is generally a massive disk brake, and may be mounted either on the low-speed input shaft, or, more commonly, on the high speed shaft connecting the gearbox to the generator. This brake is typically used as a parking brake during maintenance, but can be activated as an emergency brake as well.

Overspeed like this would require the turbine to be offline and not generating power, and for both the aerodynamic and mechanical brakes to fail. It can happen, but is very rare, and I am extremely curious as to exactly how this happened.
And some general information on speed:

Most turbines shut down when wind speeds reach 25 meters per second (56 mph). Some shut down at 20 meters per second (45 mph). They can survive much higher wind speeds when they are not running.

Rotational speeds vary by model but generally range from 10 to 20 revolutions per minute. 15 RPM is a fairly common number. Most turbine models rotate at one or two fixed speeds. GE turbines have more sophisticated power electronics (and a patent) that allows them to vary their rotational speed as wind conditions change.

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