I imagine that something had noticeably failed to begin with. Wind turbines such as those are suppose to have a braking system to slow it down and also when they've been spinning for a certain amount time they're suppose to turn out of the wind and come to a stop to cool off. This one obviously did neither of these.
I think Ã88 has got the right idea. They are designed to run at certain speeds and have safe guards built in to keep this from happening. I get the feeling that this one was spinning at a speed that it wasn't designed to handle.