why not to have a wind turbine in the back yard

[travelin01]

http://my.break.com/Content/view.aspx?ContentID=457780

anything mechanical will malfunction eventually, at least these
are really cool when they do. Don't think anyone was killed in
this malfunction like the one in eastern Washington a while back.

[rreidnauer]

Yea, I posted that vid in the windmill thread on Saturday, though it said this mill is in Denmark, not Montana. I haven't found a news article on the net about it yet, only the video spreading like wildfire now. Odd. :-|

I'll tell ya though, a couple things really amazed me about that. First, I had no idea something that big could get going that fast, and stay together. (as long as it did) There must be a huge amount of safety lead way built into those blades. I had to keep telling myself that isn't a 20 foot wind turbine, but something over 300 feet across!!! Second thing was, when it did finally let go, the blades didn't go flying thousands of feet at high velocity. They just sort of broke up and fell to the ground.

Best I can tell, it looks like a massive control systems failure. (probably ran on a Windows based system) ;-) Anyhow, it appears a single blade finally began to fail under wind pressure, (NOT root failure) and struck the tower. Once that happened, the rest was history.

[bkleber]

Rod,

I used to work in a lab where we studied breakdown of turbines under extreme rotational stresses. It was a lab run by Dan Lathrop, http://complex.umd.edu/ who is trying to replicate, in a lab setting, the geodynamo of the earth's magnetic molten core - which generates the earth's magnetic field due purely to the tremendously turbulent rotation of said molten core. As we made bigger models and spun them faster and faster, we had to be VERY careful to engineer the things to be able to withstand the centripetal forces required to not explode.

I got to take a tour of Calvert Cliffs, MD's nuclear power generation facility when one of the two turbines was shut down for repair - got to check out the blades, shaft, and most especially, the specs on the housing that the actual reactor is located in. While generally the several-feet-thick-concrete, clad-in-eight-different-kinds-of-steel is advertised as being able to withstand a such-and-such earthquake, a tsunami, AND a jetliner crash all simultaneously, the actual most dangerous thing that could possibly happen is that a blade on the turbine break down and go flying. Take a 20-foot-radius solid metal turbine blade, spin it up to 3600 RPM, and you've got a tip velocity around 5,100 MPH.

The reason the blades didn't fly far in the video is because they're constructed for maximum turbulence and minimal mass. Hollow formed fiberglass seemed to be the tower construction, and to make good blades you just need something that won't explode outward violently with centripetal force - "light" is your best bet. As soon as they cracked off near the hub, they tumbled on their long axes, and performed their other job really well - catching turbulence - thus slowing themselves down a bunch.

As for the control systems failure - I dunno. if that's really 300 feet across , the amount of braking power needed to slow it down more would be immense. Could have been a hardware limit, not just M$ bloatware. The hub sure slowed down fat once the props were no longer forcing it, so the generator sucks up mechanical energy and turns it into current pretty well. i'm impressed as well - that was doing phenominally well for a good long while. I'd love to see high-speed video, and know what was the first to go.... a gust knocking the tri-prop off-axis, one blade torquing a tiny bit too much and coming off... the resulting imbalance immediately cracking off the other two, and one taking out the tower in the process. Hooray for destruction.

[rreidnauer]

I agree about the heavy blades thing. The guys over on www.fieldlines.com ever so often talk about their homebuilt solid wood blades failing in a storm and finding pieces of them a long ways off from their original location. It's interesting to note that most failures are due to trying to squeeze too much power from their mills by setting their furling system at too high a wind speed, and the second is just shoddy construction. Really, it's not an inherent or likely event to occur if one doesn't try to push the limits.

That commercial mill is able to feather the blades by rotating them at the hub, to control speed. It didn't. Definitely a control system failure. Here is an image of one fully feathered for service. A far as I know, mechanical brakes are not used. (except maybe for full-stop service)
http://img.photobucket.com/albums/v328/titantornado/ge15_wind_turbine.jpg

[travelin01]

the original poster of the thread I saw the video was answered by someone from Denmark who knew a little
about it. Said the technicians were working until noon of that day and were pulled out as the wind was
rising and they could not solve the problem. http://www.komotv.com/news/local/9383316.html
Here is the link of some pictures of the one that fell out west. Oregon, not Washington, my mistake this time.
Was the same story, the software system failed and they were unable to feather the blades to prevent the
overspeed. Guy that was killed rode it down was the story. The picture on the bottom I was told doesn't show
how hard it hit. The rest of the turbine is supposed to be shoved 6 feet down into solid rock.

The turbines in my area have towers made of metal and the blades are fiberglass. Structural integrity must be
very high. When transporting the pieces some the trailers are a short front trailer attached to the semi-tractor
and the back is just a dolly chained onto the rear of the tower or blade.

[rreidnauer]

It's funny, you'd think even with a feathering servo failure, you could still turn the rotor away from the wind with the nacelle directional servo as a backup emergency measure. But then, maybe that wouldn't work either when over-speeding, as it would cause an uneven loading of the rotor, and break up just the same. Probably both systems run off the same program, but you'd think it would have a failsafe position if anything goes wrong. Very odd occurrence. Must be one of those "perfect storm" type events.

Wonder how many watts were coming out of her before she went boom? (hint: wattage goes up by a factor of 8, for each doubling of RPM)

[ponyboy]

And I was thinking about applying for a windmill maintenance job... :-(

Do those things have elevators to the top or do you have to clime a 200 ft ladder...

[Timber]

And I was thinking about applying for a windmill maintenance job... :-(

Do those things have elevators to the top or do you have to clime a 200 ft ladder...

On my trip from CALIF. TO WYOMING There was a field of those giant windmills in the Cowboy State. I had this weird sense of being OfF balanced looking up at them while driving 70. Might not of been so bad if I was stopped. Scary taLL

Ron

[rreidnauer]

And I was thinking about applying for a windmill maintenance job... :-(

Do those things have elevators to the top or do you have to clime a 200 ft ladder...
http://www.youtube.com/watch?v=eyrBj1USOXQ

[rreidnauer]

but not nearly as climatic as the first
http://www.youtube.com/watch?v=YCvf61_ebgM
http://www.youtube.com/watch?v=4N4HQv-UyUo