Tricky wind turbine question 5

[Windar]

Hello everyone,

I have a difficult question regarding wind turbines that I was hoping to get some feedback on.

Situation: There are a number of ~90 kW turbines mounted on 60-foot lattice towers. Due to the design of the machine, it occasionally happens that the turbine will go into what's called runaway mode. This means that there is no effective way to stop the turbine blades from spinning faster than they should be. We are looking at ways to bring a runaway turbine to a stop.

First of all, I realize the common answer is: you don't do anything. However, assuming that something HAD to be done, do people have suggestions for ways to bring an out of control wind turbine to a stop. The rotor diameter is about 17 meters, three-bladed, mounted on a 60' tower.

Any action taken would have to be done from the upwind side because these are downwind machines.

Thanks!

 

[dhengr]

Windar:

I think what you should do is hire a couple, out of work, Samurai with large swords and long step ladders. When things get out of hand, they would set up right next to the blade path and start wacking away, at the same elevation on all three blades, thus maintaining some balance in the rotating system. After they’ve wacked off the first six or eight feet of the blade tips, they move up a few rungs and repeat. If they do this on the down stroke side of the blade path, they should be able to pile up the blade parts like chord wood at the foot of their ladders, thus making clean-up easier. Soon enough, you will have little airfoil left to over speed.

Alternatively, you could do about the same thing in 6' blade lengths with a machine gun. They call this rotary blade nipping or trimming. Although, given the systems that you seem to be operating, where all fail safe systems do not work, these final solutions will probably fail in your neighborhood too.

 

[SWComposites]

Paul Bunyon and a lasso ...

Explosive bolts at the root of the blades ...

 

[zeusfaber]

You might want to ask yourself why you can't leave the runaway turbine to its own devices until some day when there's no wind.

If the answer to that is that you think it will be too dangerous and runaway turbines are already a known problem, then you probably ought to be looking at ways of immobilising the turbines today, and keeping them all immobile until somebody has brought the design to an acceptable state.

A.

 

[MiketheEngineer]

I saw a clip of one these self-destructing - probably on YouTube. Pretty impressive and s&&t flew everywhere...

 

[btrueblood]

1gibson, you are closer to the right answer, yes, than many of us that are posting cheeky responses. The right answer is that you should never have a full runaway, blade-shedding, building-destroying scenario develop; the blades I'd think would have a design that makes them auto-feather in the event of overspeed and/or loss of control signals, etc.

Rb,

A Canada goose can weigh much more than a chicken (tastier too, imo), and fly up to 50 mph. If flying downwind in 40 mph storm, what is the effective impact speed? We know these flying foreign terrorists can take down a jetliner...

...and if it's migrating in December, in Alberta, it might just be pretty well frozen...

I don't think the big 3-bladed rotors can survive a loss of one blade at operating speeds, at least not from the videos I've seen. Lose 30% of the rotating mass, and something's gonna wobble, somewhere.

 

[berkshire]

Didn't the OP mention that these were also mounted on lattice towers.
I seem to remember reading somewhere, that these can come apart when things start wiggling violently.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[rb1957]

i'd reckon that if a goose was somewhat below it's normal operating temperature so that it's tissues were more rigid than normal, then it wouldn't be flying, plummeting maybe.

also doubt if a goose can make headway against a 40mph gale.

at the OP ... all the smart a$$ suggestions are telling you that your scenario (all controls going "tits up") is unreasonable.

here's another one ... invent an inertial field (like ST's sub-space inertial dampening field) to control the uncontrollable, or possibly a time machine (for obvious applications). then market these inventions and forget about making money from the wind.

 

[1gibson]

Flying downwind, not upwind.

40mph wind speed + 50 mph goose speed (relative to the air) = 90 mph giant-long-necked-chicken-projectile

 

[telecomguy]

I'm not in the industry but it sounds like a very hazardous situation to deal with. Obviously the designed-in solutions would be best, but from the way the question is posed, it sounds like you are in the middle of a hurricane and don't have time to go back to the drawing board.

Would there be a way to freeze up the bearings? Maybe by applying heat/cold or injecting a sand/powder mixture? Of course the issue is getting up there to do it in the middle of the storm. Interesting topic.

<tg>

 

[KENAT]

Put a big tank under the turbine filled with a suitably viscous liquid.

Gradually raise the tank (or the water level in the tank) so that the tips of the blades drag through it.

Are the blades metallic or at least conductive? Might be able to do something with big magnets/electro magnetic if they are.

Of course, both options will likely damage the turbine.

Posting guidelines faq731-376

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(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[rb1957]

kenat, check post 23 sept 8:06 ...

 

[btrueblood]

Kenat, you can only brake one blade at a time that way, which is going to put an unbalanced load on the blade and rotor. Not saying it couldn't work, but I'd definitely want to be standing on the upwind side, out of the plane of rotation, before opening the hydrant.

Look at some YouTube videos - search term "wind turbine failure".

 

[rb1957]

sensibly, i wonder if you can use the centripedal load on the blade to unload the blade ? or tailor the blade construction (assuming graphite plies) so that the blade will flex under load to depower (sort of like how you can design a forward swept wing to deflect in a stable manner). ??

 

[KENAT]

fair point rb1957, I read the thread originally a few days back and didn't re-read the same thing.

btrue, just 'cause Zdas said I might be management material hopefully doesn't mean I'm a complete moron. I was hoping "Of course, both options will likely damage the turbine." might cover it.

Also when I said suitable viscous liquid, I was actually wondering if fairly low viscosity might be the way to go, rather than thick mud or similar. Minimize the load on the blade.

Oh, and both suggestions are fairly tongue in cheek.

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[rb1957]

careful you don't bite your tongue ...

 

[MikeHalloran]

Mine wasn't tongue in cheek. And I said fire hose, not water cannon, so as to minimize the additional stress. All that's needed is enough drag to decelerate the rotor assembly, however slowly. If it hasn't exploded already, nobody will care if it takes an hour or two or six to bring the rotor to a stop.

Further, complete control failure is not a remote possibility; I get the impression that it already happened. ... and I have yet to see fully redundant or even fail-safe controls featured in wind turbine fluffery. The competitive nature of the market means that nobody is going to put extra money in controls until they are forced to do so.



Mike Halloran
Pembroke Pines, FL, USA

 

[rb1957]

i note that Windar hasn't marked the thread and he hasn't chimed in for awhile ... maybe he's given up on us smartie pants ??

 

[SnTMan]

...or maybe...

 

[btrueblood]

Dunno, Kenat, you sound managerial from time to time.

No, you may be right, as I said if you read the whole post. I guess I'm hung up (i.e not convinced) that losing a part of a blade won't unbalance those flimsy contraptions I see in the hills, and result in a complete blade-shedding, tower-crumpling fiasco, complete with ambulance-chasing lawyers and TV news crews. I.e. more than just damaging the turbine, but a complete write-off of the whole installation plus collateral damage. The link I posted suggests that it's been happening, at least over in Europe.

But maybe that would be the point, design the dang thing to be damage tolerant enough so that it could survive throwing one of 3 blades.

I like the centripetal balance to auto-feather and/or blade washout by means of tailored layers of fiber composites. I think some of the bigger units use these techniques already...

 

[Duwe6]

Try adding a hydraulic motor to the slewing ring, and attach it to the tower. Leave the supply/return tubing that you ran to the ground open. With a runaway, you drive up with a truckmounted hydraulic powerpacl and couple up. Then slew it around 90°, to the "reefed" position that berkshire brought up. Fairly cheap 'fix'.