Very much on topic this post

A monocoque structure is strong as long as it maintains its shape, but dents can cause catastrophic failure. Whether it was a dent or metal fatigue remains to be seen, but either could be the cause. Only a very minor imbalance in the turbine blades could start metal fatigue, and minor dents could accelerate it.

which company/institute will lead the investigation?

I am particularly interested about the results. Which part led to the failure, which alloy...?

15 MPH on the top of a mountain! Must not be a very high mountain. You ever climb one or ride the ski lift? Pretty much 35+ MPH all the time, sort of like the seashore always has wind. That's all just my sarcastic IMHO.

A few have mentioned the failure at one particular point, does look like that part of the shaft has little in there besides hollowness. However I'm sure there is "a shaft" through there, and when the thing was bending over, whatever was turning inside of it could've made a very loud grinding sound, probably further amplified by the fact that the upright tube is mostly a tube and thus potential sound amplifier as also maybe the blades were too. Therefore the wind was turning the blades, thus turning the shaft, it slowly went and once it was enough out of vertical, the shaft was rubbing; could've held that way for a long while, in fact the shaft itself could've been the final holding point until finally the stresses snapped that and then the whole thing finally came down. I saw a video box, but the video never played for me.

A problem with all of that is any change in wind direction, what turns? Not the whole thing, just up top, so you have the equivalent of a flag pole needing to deal with stress from different directions.

@sundialsvcs

Ok, we'll both be OT: the power companies are buying politicians left and right to keep their grid and you paying for it, at least in the US, so don't expect any "rethinking" any time soon. Until the zombie apocalypse anyway....

There is no shaft inside. Just a ladder.

jlinkels

There is no need for any shaft going down the tower. What would it connect to at the ground? The generator is on top, and the whole thing pivots when the wind changes, like a vane on a barn roof. All that is required is a cable to carry the electricity.

Nuff said.

We had one up here in Scotland that ended its self in a shower of sparks and flames because in a high wind the feathering mechanism which adjusts the pitch of the blades failed. The blades should have feathered so that the wind passed straight through without providing any force to turn them.

One of the gripes we have with turbines (Apart from the real estate they take up!) is that the Government pay the Power Utilities a fortune in subsidies during times when the turbines don't generate due to either not enough or too much wind!

Play Bonny!

:hattip:

Why do they have to completely stop when the wind is too high? Why can the pitch be adjusted so they spin at a rational speed?

Good question. I don't know.
One reason could be that strong winds also have large and fast variations. The control system for the blade pitch is slow -- time constants of seconds of not tens of seconds. The control system and mechanics might be too slow for stable pitch control.
Note also that the speed is not controlled by the blade pitch for synchronous generators, but the real power delivered to the grid.
Most turbines do not just feather the blades, they also turn the nacelle perpendicular to the wind direction.

jlinkels

Wind turbines, the big 'uns that is, generally rotate at about eight revs a minute, the gearbox ramps this up to about 1,500 RPM for the generator at the top of the mast. The only way of maintaining this speed is by varying the pitch of the turbine blades. Winds of 90MPH tend to be blustery so I'd go with jlinkels theory above. I think the operating limits are something like between 15 and 50 MPH. If the feathering mechanism fails it's like over reving your car; in this case the gearbox seizes up/burns out rather than the engine. Or the force of the wind blows the mast over!

Some are like this but the ones with the tapering support mast have lifts inside.

They also stop them turning when the demand is low (Hence our Government subsidy payments!) Because you can't store grid electricity, (OK, there are exceptions, see here.) it works on a supply and demand system. Why wear out a wind generator when you don't need the electricity? Wind turbines are OK for fillers, you can spin them up and bring them on-stream fast, but you still need a base supply; coal, oil, gas, nuclear which take a lot longer to ramp up.

In the UK, if there's something particularly good on the television with millions of viewers, you can get a demand spike during the commercial break when everyone rushes through to put the kettle on for tea!, That's "X" million x 3Kw kettle!
(Other countries may have a similar demand dependent on their favourite hot beverage!)
The electric company will be aware of this surge and bring more supply on stream as required.

A final snippet, which may be useful in a pub quiz... Have you ever wondered why Wind turbines are painted that insipid grey colour?

It's apparently because, prior to their installation, someone records the colour of the sky where they're installed over a considerable period of time and the colour they're painted is the "average" of this colour so they don't stand out so much against the sky. Interesting huh?

Play Bonny!

:hattip:

It always used to be "Miss world" in the 1970s.

There was a programme on the grid a year or so back and they still appeared to have TVs tuned to the major channels. There was a lovely moment when one controller shouted out "Coronation Street's finished early, bring Dinorwic online", Dinorwic is a pumped-storage power station. [for non-UK readers: Coronation Street is a long running and popular soap opera.]

Like Cruachan in my link above. One of the interesting things I found with Cruachan Power Station was that they have actually bored holes through Ben Cruachan so they can catch the rainwater run off from the "wrong" side of the mountain and channel it back into Cruachan reservoir!


Here's the turbine in Ayrshire we had fun with back in 2012! :)

Play Bonny!
:hattip:

No, the generator speed is fully determined by the grid frequency. As long as the generator is coupled to the grid, it rotates in sync with the grid frequency. The amount of wind power converted to electrical power is determined by the pitch control. It will never overrev as long as the generator is coupled, but the power might be too high if the pitch is incorrect. That could (and will!) damage the gearbox. And yes, when this damage is so severe the gear teeth are torn off, the blades might overspeed. It has happened. 1500 rpm is quite high for large turbines. The generator can easily be constructed for this speed, but a 8:1500 ratio for the gearbox is large. Generators are constructed for lower speeds like 750 or 375 rpm to relax gearbox design. The newest development is to construct variable speed generators where the field is an AC current instead of DC.

Most turbines are specified at 12 m/s for nominal output. That is 36 km/h. They start at 3 m/s (6.75 km/h). Maximum wind is often at 25 m/s (90 km/h). So 50 mph on the maximum side is quite correct.

jlinkels