Windmill Failure

No information given, as usual.

Never mind.

Fenner Wind Farm - Wikipedia, the free encyclopedia

I saw the article in the dispatch about coming attractions. Thanks for the other source. I wanted more than the press release.

This is an international forum. Stating your country is a good beginning, then state...

Sorry about not being location specific. I personally am located in central New York State, USA. The windmills in question are located also in NYS south of me in an area known as Fenner. One of the units actually fell over. Available news pictures showed the tower base intact with bolts apparently attached to a layer of concrete. It looked like a rough surface still in the ground, hence my impression of a cold joint.

The answer appears to be "unknown" and "all of the above."

According to the article below, in Dec 2009 the wind farm operator shut down all 20 turbines while they inspected #18. By Aug 2010, neither they nor contracted inspectors had found the smoking gun.

So they poured some more concrete (always a good idea; the moment arm on a GE 1.5 MW of that vintage is 80 meters) and re-started the turbines one by one.

It wasn't written up in one of the trade rags that I read, North American Windpower, but then again, it was not likely to have been.

http://www.wind-watch.org/news/2010/08/13/fenner-turbines-power-up-while-cause-of-collapse-remains-unknown/

I worked for an aerospace company that erected many antenna poles in Alaska. To make a long story short, these poles kept falling down even though their design strength exceeded all published engineering specifications. It took years of study in top universities to uncover a new failure mechanism. I am not aware of this data being published. Many of the failure mechanisms that have been studied and documented for military programs don't make it into text books and aren't well known. It's unnerving to find that although best practices were employed in the design and manufacture of an item, nature still can find a way to defeat us.

So did the "gumbo" melt in Alaska, allowing the tower(s) to fall? I would expect that a large moment (high wind pressure in a prevailing direction) over time could conceivably produce enough pressure in permafrost to pressure melt the soil(mud), and allow miscule shift(s), and in the end weaken the resistance to toppling.

So, what was that failure mechanism? Years ago I worked for a company that made round tubular poles for street lighting (I actually worked in transmission tower division, not street lighting.) For the smaller poles there was a phenomenon called vortex shedding. Vortices came alternately off opposite sides of the pole; if the frequency happened to match the resonant frequency of the pole, it would vibrate badly, even to destruction. This typically happened at low wind speeds. Could it be happening to the larger towers?

I don't recall the failure mechanism, and the failures were attributed to vortex shedding, but in this case, the vortex action was assisted by unusual ice build-up on the round poles. I do remember that whole fields of poles would be leveled when these conditions occurred.

According to published reports today, the failed unit is being replaced with a newer, more efficient, bigger,65 feet taller, unit. The blade and hub went on yesterday. Thanks all for your input.

Situations such as this are often due to fatigue failure of the bolts.

Most tower foundation bolts are tensioned rather than torqued. Nevertheless, in either situation, there is rarely, if ever, a bolt preload verification step specified in the erection procedure. As a result, nobody actually knows how "tight" the bolts are. The safety and reliability of the turbine is thus left unknown.

It just baffles the mind when authorities accept "guesses" as to the residual bolt preload in critical fasteners such as these

The failures described in #6 were traced to unusual weather conditions. A combination of temperature, precipitation, and wind, turned the supporting structure into an airfoil and resulted in amplified stresses that not even perfectly tensioned bolts could have survived.

With the high tension transmission towers I worked with years ago, my impression (I didn't work in the field with installation) was that the nuts were tightened by "turn-of-the-nut" method, perhaps using sledge wrenches. There was a leveling nut under the base plate, which meant that the part of the anchor rod between the nuts was tensioned, but from the leveling nut into the foundation was not. Most of ours were 2.25" high strength (I don't remember the yield for sure, but maybe 104 ksi.)