Tricky wind turbine question
Tricky wind turbine question
(OP)
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!
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!





RE: Tricky wind turbine question
Second option, design the propeller shaft with a brake system that would be applied in situations of a run away.
Third option, design a transmission box that would increase the gearing ratio in favor of a stall. You could put a heavy viscous oil liquid in the gear transmission casing to act as a dashpot.
Hope this helps.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: Tricky wind turbine question
how about having the pitch control dump so that the blades go into a "wind-mill" mode ?
could you apply an electrical load onto the generator, an electrical brake ??
RE: Tricky wind turbine question
RE: Tricky wind turbine question
Or call the "Jolly Green Giant" and have him stick a finger in it.. That's how I used to stop my model airplane engines. Kind of painful - but worked.
RE: Tricky wind turbine question
Regards,
Mike
RE: Tricky wind turbine question
Got water?
Aim a firehose at the advancing blades.
That's something you can do without climbing the tower and without adding anything, until you can get the controls straightened out.
Actually, I might be inclined to put a nozzle on the after end of a big old truck so I wouldn't have to be near the blade plane while adding the water impact stress to the overspeed stress.
Mike Halloran
Pembroke Pines, FL, USA
RE: Tricky wind turbine question
I'd look for a way to apply a heavy electrical load.
David
RE: Tricky wind turbine question
//signed//
Christopher K. Hubley
Mechanical Engineer
Sunpower Incorporated
Athens, Ohio
RE: Tricky wind turbine question
Also, couplings and gearboxes sometimes fail, again resulting in overspeed.
If I had the option of adding something, I'd consider a spring-set brake as close to the propeller hub as possible, triggered by an external paddle or panel that could be impacted by a rifle shot.
Mike Halloran
Pembroke Pines, FL, USA
RE: Tricky wind turbine question
RE: Tricky wind turbine question
RE: Tricky wind turbine question
Thanks for the fast responses and good ideas!
Someone got it right when they assumed we do already have variable pitch. Indeed there is a pitching brake mechanism in the wind turbines, but it is not 100% reliable, thus disconnection from the controllers in combination with the emergency feathering mechanism failure can sometimes result in a runaway.
My favorite idea so far was the water cannon pointed against the motion of the blades. This may be able to slow the turbine blades down enough to implement an electrical braking mechanism, and could possibly be done while avoiding the rotational plane of the blades. Stopping the machine is more important than saving the blades.
Thanks again for the feedback.
RE: Tricky wind turbine question
Most larger wind turbines have friction brakes (usually a disc brake) located on the gearbox output shaft. The disc brake system would be sized to absorb and dissipate the inertia of this type of rotor overload/overspeed condition. This is probably the cheapest and most reliable method, since it can be made fail-safe.
If the rotor is already overspeeding, then using the generator to brake it is likely not an option. Most larger wind turbine generators use inverter/rectifier electronics to condition their power output, and these electronic devices do not have much excess thermal capacity to absorb drivetrain overloads.
Finally, I would recommend taking a second look at redesigning your pitch control system to make it fail safe and fault tolerant. Loss of pitch control on a single blade can produce extreme rotor cyclic hub moment loads, which can also quickly lead to catastrophic structural failures.
Loss of just part of a blade can create a dangerous out-of-balance condition in the rotor, which can quickly lead to catastrophic structural failures, so I'd also forget the "water cannon".
RE: Tricky wind turbine question
RE: Tricky wind turbine question
RE: Tricky wind turbine question
RE: Tricky wind turbine question
RE: Tricky wind turbine question
ok, from the upwind side, you'd need a "reverse" fan.
how about a great big trough of mud (or jelly, it'd be more fun) to deploy into the path of the blade tip ... something to great a ton of drag ? mind you you'll need to pick up the pieces of the tower, 'cause it'll probably disintergrate from the imbalance of losing a blade).
as ivymike has asked ... are you looking to retro-fit a design, developing something new, or do you have a design working that you have to make good.
i think you need to analyze the fault tree ... what is failing that creates the overspeed situation ? and address these rather than trying to recover from the overspeed situation.
what do you do with increasing wind speeds ? you use pitch control to tailor the power output and to depower as wind speed increases (so the blades travl slower and slower as wind speed increases ?? ('cause you'd want them to stop (or be stoppable) at some design speed, no?)
RE: Tricky wind turbine question
RE: Tricky wind turbine question
Dan
www.eltronresearch.com
Dan's Blog
RE: Tricky wind turbine question
RE: Tricky wind turbine question
Retracts automatically as speed is reduced, no controls required. Comments above indicated a disc brake could already exist, although the concept might be more straight forward to apply to a drum brake.
RE: Tricky wind turbine question
That would stop them - but then they would also start spinning in opposite direction.
Some of these hubs are 200-300' in the air. Not too many water cannons and such can reach such a height.
RE: Tricky wind turbine question
RE: Tricky wind turbine question
If it pivots freely, Bergey, I think uses a steering vane that deflects in an overspeed situation, causing the rotor to turn off of the wind.
RE: Tricky wind turbine question
RE: Tricky wind turbine question
http:
RE: Tricky wind turbine question
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Tricky wind turbine question
There used to be a system called "reefing" a wind mill, AKA wind turbine, where the yaw control turned the rotor 90 degrees to the wind.
Is your system not capable of doing this?
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
RE: Tricky wind turbine question
Mike Halloran
Pembroke Pines, FL, USA
RE: Tricky wind turbine question
26 Sep 11 9:51
I think the challenge presented assumes that _all_ of the controls have "gone off to see God", and are therefore unresponsive to external stimuli, and not behaving as they should.
This is correct. Significant retrofits to the turbine could obviously address the issue, but if this is not possible, what about when the worst case occurs?
What about a large net propulsion system? (the blades are fairly easily replaced if they were to fail).
RE: Tricky wind turbine question
if all your controls are assumed to have failed then the machine becomes uncontrollable.
rational design works to levels of probability of failure, with redundant systems of control.
RE: Tricky wind turbine question
RE: Tricky wind turbine question
oh, and pick the pieces of broken wind turbine scattered about.
RE: Tricky wind turbine question
see http://www.caithnesswindfarms.co.uk/accidents.pdf
"Pieces of blade are documented as travelling up to 1300 meters. In Germany, blade pieces have gone through the roofs and walls of nearby buildings."
Seriously, you'd need to run some kind of testing to verify that the various blade-braking schemes suggested would not just become blade-breaking schemes. The blades aren't really designed to take any impacts more significant than a frozen chicken when at operating speed. Even the reefing ideas would have issues with slew rate and gyroscopic forces if not controlled precisely.
A more reasonable method might be a means of erecting a series of poles/masts or a more-or-less solid "wall" upstream of the troubled rotor (I'm thinking of a D-8 cat as an anchor, and a couple of big cargo parachutes), in an effort to block all or most of the wind, allowing the rotor to spin down to a lower, safer speed before attempting some method of blade breaking/braking. At least the lower speed will reduce the ballistic distance of the blades...
RE: Tricky wind turbine question
actually they use thawed chickens, since frozen are too solid.
and i wouldn't've thought bird strike was much of a design criteria. a bird, even a 12ld-er, impacting at 15ft/sec (10mph), should be pretty easy to absorb ... at the root the blade is very rigid, at the tip very flexible.
maybe a design requirement is to safely depower if a blade is shed
RE: Tricky wind turbine question
;--
The problem I see with physically snagging the blades with nets, ropes or parachutes, is twofold.
If the rope wraps around the hub, there may be enough inertia and mechanical advantage to lift and maybe even swing a Cat D8 as if launched from a trebuchet. Modern ropes can do amazing things like that.
If the rope managed to snap off a blade, I'd expect the resulting imbalance to take out the tower pretty quickly. Maybe the towers are designed for a missing blade imbalance at above design speed; they don't look like it to me.
;--
Deploying multiple parachutes or a tall screen upwind might slow the rotor a bit, but you don't want to accidentally snag the spinning rotor. You still face the problem of stopping the rotor, but intervention becomes a little less dangerous.
;--
IF the nacelle is free to swing during control failure (not revealed so far), then pre-deploying a weighted rope from its upwind end might allow one to yaw the rotor away from the wind, with the Cat D8.
Mike Halloran
Pembroke Pines, FL, USA
RE: Tricky wind turbine question
i was thinking of a bird flying into the plane of the turbine, bending about the weak axis of the blade. thinking more, the bird could be unlucky enough to be in the prop-plane at the wrong time whihc would resemble a more typical bird strike on the leading edge of the wing. still the tip speed would be much less than an airplane's forward speed, the L/E radius of the balde would be much smaller (for the blade) ... factors which decrease the impact loads, but the section is much smaller than a wing which would increase the effects.
RE: Tricky wind turbine question
I can't tell if some of these suggestions are jokes, or if I missed part of the original post about keeping the machine in one piece not being a requirement.
That's not entirely true, the "strongly worded note on the drawing" was obviously a joke. But some of the others still have me confused.
RE: Tricky wind turbine question
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.
RE: Tricky wind turbine question
Explosive bolts at the root of the blades ...
RE: Tricky wind turbine question
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.
RE: Tricky wind turbine question
RE: Tricky wind turbine question
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.
RE: Tricky wind turbine question
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
RE: Tricky wind turbine question
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.
RE: Tricky wind turbine question
40mph wind speed + 50 mph goose speed (relative to the air) = 90 mph giant-long-necked-chicken-projectile
RE: Tricky wind turbine question
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>
RE: Tricky wind turbine question
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.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Tricky wind turbine question
RE: Tricky wind turbine question
Look at some YouTube videos - search term "wind turbine failure".
RE: Tricky wind turbine question
RE: Tricky wind turbine question
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.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Tricky wind turbine question
RE: Tricky wind turbine question
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
RE: Tricky wind turbine question
RE: Tricky wind turbine question
RE: Tricky wind turbine question
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...
RE: Tricky wind turbine question
RE: Tricky wind turbine question
RE: Tricky wind turbine question
RE: Tricky wind turbine question
RE: Tricky wind turbine question
RE: Tricky wind turbine question
the way it exploded looks like it uses a mechanical brake (that broke ?)
RE: Tricky wind turbine question
RE: Tricky wind turbine question
RE: Tricky wind turbine question
RE: Tricky wind turbine question
RE: Tricky wind turbine question
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.
RE: Tricky wind turbine question
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!
RE: Tricky wind turbine question
Mike Halloran
Pembroke Pines, FL, USA
RE: Tricky wind turbine question
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.
RE: Tricky wind turbine question
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
RE: Tricky wind turbine question
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?
RE: Tricky wind turbine question
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...
RE: Tricky wind turbine question
RE: Tricky wind turbine question
In a runaway or potential runaway, you wouldn't want to be anywhere near the turbine.
RE: Tricky wind turbine question
RE: Tricky wind turbine question
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.
RE: Tricky wind turbine question
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)
RE: Tricky wind turbine question
RE: Tricky wind turbine question
What about a liquid cooled centripetal break? (I know the complexity just increased)
Fe (IronX32)
RE: Tricky wind turbine question
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
RE: Tricky wind turbine question
Fe (IronX32)
RE: Tricky wind turbine question
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.
RE: Tricky wind turbine question
RE: Tricky wind turbine question
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
RE: Tricky wind turbine question
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://