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!

 

[FeX32]

Ok guys.
Now seriously I think this one has not been mentioned. Since the most feasible and easy solution is the breaking mechanism on the gearbox sid of things. Why not rely 100% on mechanical design (as it is less likely to fail) and design a centripetal clutching break system. Such that when it reaches a certain rpm it automatically starts to engage, with that engagement becoming more intense if the rpm further increases.
Done deal. Agree?


Fe (IronX32)

 

[Duwe6]

Waaaay too much energy to run through a mechanical brake - it would melt the metal portions, might melt ceranics.

 

[FeX32]

Good point. I guess it would depend on the size of the break and energy transfered (size of turbine). I'm not saying it would still work, I just think it's something to put on the possible solutions board.
What about a liquid cooled centripetal break? (I know the complexity just increased)


Fe (IronX32)

 

[berkshire]

racookpe1978
Expanding on your thoughts but at the same time not re-inventing the wheel.
During the manufacture of the blade, install Schempp Hirth dive brakes in it activated by a weight, counterbalanced by a spring.
Set the spring to keep the brakes closed up to just over the safe operating speed of the blade. Above that speed centrifugal force would pull the weight agaist the spring and open the dive brakes, closing them when RPMs had dropped to safe limits.
You do not need hydraulics for this and the technology is well established.
The major question would be whether or not the manufactures would install such a safety device or consider it too costly?
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

 

[FeX32]

Interesting idea B.E.


Fe (IronX32)

 

[rb1957]

sorry to disagree but if you "trip" something as it detects an over-speed (ie the blade is already whirling around at a high rate of knots) and you deploy something to brake the blades, i reckon that's exactly what you'll do ... break the blades.

btw, as we're focusing on the blades, what's happening inside the motor as the drive speed increases ? from the pix above it looks like the motor gives out first, before the blades distribute themselves over a wide area.

 

[potteryshard]

I've thought of using a water brake. Essentially a low-efficiency hydraulic pump mounted on the main rotor shaft with no fluid outlet. The only outlet for the pressurized fluid is the pump clearances. Under normal running circumstances the water brake is dry; no seals, no losses. If the turbine runs away, water is released from an overhead tank into the brake... Braking force can be controlled by varying the water flow. With the amount of energy available, most of the water would be vaporized, and so should be easily ducted overboard. Vaporization of the water should also serve to control the pump component temperatures.

 

[berkshire]

The speed limiting dive brake has been used on composite aircraft wings for 50 years now.
A wind turbine is nothing but several aircraft wings stuck on a common hub.
The idea would be to deploy the things in an overspeed situation before structural limits are reached.
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

 

[tbuelna]

The OP described a "run away" turbine condition. If you consider the basic wind turbine drivetrain consisting of a rotor driving against the generator load, a "run away" condition would imply that there is a failure somewhere between the rotor hub and generator. Thus any proposed solution should be capable of directly stopping rotation of the rotor hub itself.

While the ideas proposed using absorbers could slow the rotor, unless they include some form of locking function they would not be capable of continuously absorbing/dissipating the rotor power. The only practical solution to slowing the rotor without damaging the blades would be some form of mechanical fuse in the blade pitch control. Once the blades are free to feather, they should naturally assume a neutral lift position, and the rotor rotation should cease.

Here's what can happen with even very small turbine blades that run away.

http://www.dailymail.co.uk/news/article-2083149/Wind-turbines-cope-UK-weather-3-blown-pieces.html