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!

 

[1gibson]

Perhaps Windar hasn't responded because he has been montioring the turbine with a fire hose nearby.

 

[moon161]

Couple the output shaft by a clutch to a rotor w/ the opposite pitch.

 

[rb1957]

i saw this online news article today, and remembered all of us "slagging off" about that they must have overspeed protection designed in ...

 

[leisure17]

http://www.telegraph.co.uk/news/pic...-battered-by-gale-force-winds-and-storms.html

 

[rb1957]

by the look of it only one turbine "exploded" so i guess it was an individual issue, not a systemic design problem.

the way it exploded looks like it uses a mechanical brake (that broke ?)

 

[moon161]

Use a failsafe vane to point it off the wind. The actively controlled position of the vane shall point it at the wind. If any control fails, a spring returns it to a position that steers it off the wind.

 

[ivymike]

I'm blown away.

 

[IFRs]

The water, if pointed at the hub rather than at the blade tips will run outwards along the blades, possibly slowing them down uniformly. I wonder if there could be a hose running up the tower to just behind the blades that could be turned on when needed.

 

[IFRs]

Incorporate into the blade design a small plate that is automatically (mechanically) deployed from the over speed that acts like the air brakes on aircraft wings. Positioned at the tip.

 

[racookpe1978]

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 powerpac and couple up. Then slew it around 90°, to the "reefed" position that berkshire brought up. Fairly cheap 'fix'.

But you've got some physical problems responding, and your response team (the truck and its hydraulic pump and tank and crew) would be parked directly under the over-speeding wind turbine in the line of fire of the breaking blades, underneath the (probable) burning nacelle and generator, and underneath the falling parts and debris. Not a place I'd send a crew!

Response time? These things are widespread apart (by miles down winding dirt and gravel roads) always in the boondocks (off of even paved roads, much less convenient high-speed highway exits. So you'd have to detect the overspeed turbine, get your crew going, get to the highway exit, get to the county roads, get to the dirt roads, get down the dirt road, get to the right turbine, then hook up the hydraulics and start pumping - before the overspeeding turbine got fast enough (past the trip detection point of the overspeed sensor) to start destroying the turbine and drive gears.

 

[akarcticengineer]

Windar,

I am familiar with your predicament.

What could work in this situation is to grab a bow and arrow.

Attach a very strong light weight cord to the arrow tail (about 200ft long).

Tie the small cord to a larger rope that is a bit longer.

Tie that rope to larger rope and so on until you have some large line like a barge halyard at the end.

Shoot the arrow above the top of the rotor and the rope will start to be pulled in...

STAND BACK!

Eventually the rope/line should create enough drag to slow down the rotor...

Good luck!

 

[MikeHalloran]

I think you mean 'hawser', not 'halyard', but it's a workable idea.


Mike Halloran
Pembroke Pines, FL, USA

 

[rb1957]

i think that by the time the blade is whirling around out of control that the horse has bolted. any attempt to 'restle the sucker back under control is frought with peril, such that the outcome is obvious and unavoidable (fun though it has been to dicuss).

IMHO, either the control system is designed so that complete failure is very improbable (and systems can be designed for this, think nukes, aircraft, spacecraft, railways, ...) or if failure is possible (it might be too expensive to design a fail-proof control system) then either you adopt Ford's Pinto economics (and we know how well that worked for Ford) or you design the blade so that it will depower itself through aero-elastic response, not though blowing itself into a million shards.

 

[berkshire]

It strikes me that if you have a mechanism of the type that total failure is possible. It should be sited far enough away from people and other mechanisms, that it should be allowed to self destruct without creating other problems.
Just stand back and let it do its thing.
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

 

[gadkinsj]

Can you design it in a way that there are counter-balancers in the root of the hub that can be pushed out in the case of high inertia to shorten the turbines?

Or just have some fluid that will fill the internal passages of the blades if they get out of control?

Or, how about it pivots itself on the other axis and points up?

Explosive bolts that just blow measured bits off at a time? like 5 feet?

 

[akarcticengineer]

All you are trying to do in this situation is slow the rotor to keep it from self destructing. A self destructing turbine is also a safety issue for personnel and the public obviously.

If you can keep it from destructing then it is possible to the reuse the blades, tower and gear case (usually new gears and bearings are needed).

Turbines in this power range (<100kW) are built as simply as possible... The tip-brakes at the blade tips are the over speed control on these usually.

However, they sometimes don't deploy as designed... overspeed results...

 

[hemisboats]

The designers/engineers need to apply a tether on the opposite side of the hub and connect it to a slip-ring so it can be quickly accessed. Then it could be attached to a vehicle (or winch w/block) so the blades can be pulled out of the wind. IMHO!

 

[moon161]

//The designers/engineers need to apply a tether on the opposite side of the hub and connect it to a slip-ring so it can be quickly accessed. Then it could be attached to a vehicle (or winch w/block) so the blades can be pulled out of the wind. IMHO! //

In a runaway or potential runaway, you wouldn't want to be anywhere near the turbine.

 

[hemisboats]

Hence the beauty of the tether. You don't have to be close. Agreed, you would not want to be close enough to be hit with flying pieces.

 

[racookpe1978]

I'm going to expand on something gadkinsj began to think of ... But am going to reverse his thought:


gadkinsj (Mechanical)
16 Dec 11 15:07
Can you design it in a way that there are counter-balancers in the root of the hub that can be pushed out in the case of high inertia to shorten the turbines?

Or just have some fluid that will fill the internal passages of the blades if they get out of control?

Rules:
you must have something completely automatic (NO manual involvement because of time to detect and get to the wind turbine, access on site to the over-speeding turbine, height of the blades, climbing time, danger when near the turbine on the ground, etc.)
Whatever slows the whole turbine down MUST trip or deploy on all of the blades at the same time from the same trip setting: otherwise, one blade gets slowed (or gets a force thrown on it and it breaks, or the others get unbalanced forces on them and they get torn off, the root bearing breaks because of unbalanvced forces as it tries to slow down.
The mechanism must be re-setable or re-useable without destroying the turbine or its blades.

Therefore, I recommedn that each blade tip be "covered" with an "overspeed scoop tip" closely fitting to the current blade end contour. The overspeed scoop tip is pivoted at one side so that, when open, the scoop catches the wind and slows the blade. At slower speeds - safe speeds less than rotor maximum - the tip is held in the closed position by a latch to resist centrifugal forces.

The "overspeed scoop" is held in its closed position on the tip, and thus the scoop is held firmly onto the blade tip with almost no air resistance, by hydraulic forces routed inside the blade via an internal "hose" (or thin diameter pipe) to the latch holding a scoop in the closed position. This hydraulic pressure is retained by a set of two (or three) relief valves, and pumped up by a hydraulic pump fed by the turbine blade when the blade is rotating.

(Zero rotation speed, hydraulic latch pressure = bearing oil pressure. At higher turbine velocities => more hydraulic pressure => hydraulic pressure comes closer to the trip points of the relief valves. At the required overspeed velocity, first (or second) relief valve opens => dumps latch pressure to all blades at the same time => opens latches => overspeed tips open on all blades => blades can't go faster => turbine is safe.)

When problem is overcome (whatever caused the original overspeed fault is corrected) the safety tips are pushed back to closed position, the latches are reset and turbine can restart when the vented hydraulic fluid is reloaded.