Ferrite Gen with a Classic 150

[SparWeb]

That's a good thought: keeping the blade tips wrapped until it's outside and mounted.  Prevents abrasion on doors and floors etc.  Just something I noticed in the photos.

Is there a counter-weight on the tail yet?

[bj]

   Chris--that is just plain sweet.  The photos make it clear how many hours you spent sweating the details.

[Menelaos]

Nice job Chris!

What I always wonder about, not just on your project but on nearly everybodys here:

None of you seem to consider a manual braking system in terms of a disc or drum brake.
I feel that every turbine with more than 3 m diamter should have something like this. What happens if there is a failure to the alternator- it burns or some wires break or shake loose...
Then the prop will speed up enormously and furling does not help with that....or even worse...it does not work properly anymore. I would be so scared of those blads breaking and flying somewhere and damaging or hurting/killing somebody.

I really think there should be a way of stopping the turbine independent from the alternator manually.

For my next turbine i have constructed a disc brake system that works automatic and will be activated by overspeed, alternator failure or vibration with the option of also closing it manually.

It is a system of levers held back by a small elektro magnet that during operation consumes about 5 Watt for that 5 m Machine. If that magnet is switched off, the brake will close. This will be controlled by a controller that observes rpm, vibration and voltage/current of each phase. In case of a disfunktion the turbine will be gently stopped...

OK, that solution might seem a little overcareful but what do you guys do in case of da disfunktion, run away and hope that the turbine survives and windspeed decreases soon???

[kenl]

 Looks really nice Chris. Watching the video where you were lifting it above the stand made me wonder how you get that beast out of the shed and on to the tower?

 I never realized how big these things really were until the video of you next to it. What are you using for a tower and what height is it?

kenny

[fabricator]

Looks really nice Chris. Watching the video where you were lifting it above the stand made me wonder how you get that beast out of the shed and on to the tower?

 I never realized how big these things really were until the video of you next to it. What are you using for a tower and what height is it?

kenny

He's got more equipment than an equipment store.

[ChrisOlson]

Looks really nice Chris. Watching the video where you were lifting it above the stand made me wonder how you get that beast out of the shed and on to the tower?
 I never realized how big these things really were until the video of you next to it. What are you using for a tower and what height is it?

Skid steer loader.  It's going on a free-standing lattice tower, 74 feet.
--
Chris

[Flux]

Interesting question from Menelaos.

That has always been one of my concerns. If you live in a remote place and have plenty of space then it may not be much of an issue, but an out of control turbine close to a lot of people is not the best thing to have.

The snag with any form of back up is that it spends a long time not used and on the day it is needed it will most likely fail.

I have always used a means of shutting down by making the tail go at right angles ( full furl position). If done correctly you can make it shut down even if the control cable breaks.  Brakes seem less attractive to me, they are fine if used and checked regularly but there are a lot of things that can fail and they can be tricky to use in regions likely to freezing.

Tip flaps are used on larger machines, but I don't think any attempt I made would be reliable and it adds a lot of complication.

I think everyone will have their own ideas on back up control and the success will largely depend on how good the construction is and how often it is tested.

My tail shut down schemes generally have worked well but they are not really compatible with hanging cables down the middle of the tower.

I have to admit that I did have one frightening incident with a machine with too little offset and it didn't furl ( it went wind seeking).  No attempts at making it furl worked but it would shut down reliably with the tail. I ended up using it with a wind speed sensor and using a motor to shut it down by the tail in high winds.

Everything was fine until the day the tail fell off, I assumed this would result in shut down as it attempted to go down wind. No that didn't happen, it went wind seeking and went straight into the wind at full power ( fortunately the alternator stayed on load ). I had no control of it except that it would come out of the wind for a few seconds and then seek the wind again. We managed to stop it in one of those moments but if the load had let go nothing would have stopped it.

I just mention this to remind everyone that a back up scheme has to be foolproof under all conditions and it will fail when you most need it and in the most unexpected way. Some of the lovely brake schemes I see here I know will fail sometime, somehow. Only the best thought out best constructed and most rigorously tested will do the job when the real need arises.


This is one of the problems I see of active pitch control but those could probably be designed to fail safe with a bit of added mechanical ingenuity to feather the blades.

This is one of the best arguments in favour of the passive pitch control schemes but again some of the lovely ideas I see proposed will fail for sure with pins in slots and other dream ideas.

A wind turbine is the best life testing rig ever devised.

Flux

[Menelaos]

Ok...I do not want to get too much off topic with this but this issue really makes me wonder when I look at those beautiful machines like Chris has built as it is not that much of an issue to install a brake.

As Flux' example shows, manually furling the tail is not a guaranty for the prop to stop sipnning. Pitch control, wheater active or passive is a nice thing and I have also played with different variations of this but I do not trust in electronic solutions and the passive systems only protect from overspeed but still cannot completely stop the prop which might be essential in some situations. Of course, such a brake must be constrcted to work fail-safe. In my case it is spring loaded and if power cuts off, it will still work. It should have few moving parts that could fail...in my case it is only one moving part, one bearing...thats all, there is nothing that could get rusty and get stack and everything has a weatherprrof cover...

Such a brake will also be handy when doing repairs or maintenance works.

And I personally do not want to watch my turbine all day and check if it is working properly. As ist will be a grid tied turbine, it is supposed to work all the time and I would like to go on holiday without having to fear that something goes wrong and there is nobody to see whats going on and doing something against it...

[ChrisOlson]

None of you seem to consider a manual braking system in terms of a disc or drum brake.

Max, my feeling is that brakes are only useful for parking.  I used to worry about this too, but then experience took over.  In my experience flying these machines, whenever I've had complete stator failures the stators blew up (expanded) and locked the machine up all by itself.  Typically that won't happen unless you grossly under-design the generator for the blade power.  Blowing a single coil and dropping a phase has proven to be not that big of a deal because the machine is still under load and it furls fine.  I only ever had one that ran away, and that was because I didn't have the magnets pinned and it tore all the magnets off when the stator blew.  As long as you got the mags pinned or contained in there, everything will "pile up" and stop it.

The far more common point of failure is wires rubbing thru in the tower someplace.  When that happens I've just had them short out and stop.

With a geared machine, you could have a drivetrain failure.  However, a long time ago I tested a transmission to failure, driving it with a tractor PTO and driving my M&W dyno with the gearbox, and I loaded it with the dyno brake until it failed.  When it failed it let go with a BANG! and the pieces fell into the bottom of the gearcase and locked it up, and it stalled a 125 hp tractor (IH 806 that has a little extra life breathed into it with an AirResearch turbocharger).  I don't remember the exact torque numbers that the gearbox took before it broke, but when I tightened the dyno up to where the 806 was turning the sky black I was thinking I might have to get one of my CaseIH Magnums and hook it up to break it.  But it finally blew when one of the side plates let go on the chain.

So, basically, I've quite worrying about it.  A brake doesn't really hurt anything.  But experience has shown me there's other things that happen.  If the wind is blowing hard enough to blow a wind turbine, it's unlikely that you or anybody else is going to be standing outside in the danger zone going, "Whoooaaa - COOL!" because you're probably more likely to get hit by a flying tree branch or other piece of debris picked up by the wind than broken turbine blades.
--
Chris

[Menelaos]

I get your point Chris and I do not doubt that your turbine is robust and safe...but I have neighbours with children and I feel a lot safer with a backup brake.

What you mentiones about the magnets blocking the stator might be true...but my next turbine will have a non homebrew alternator. I will buy it from Danemark. It is an ironless design but the coils are vertikal, as so is the stator. And even if it wasn't I wouldn rely on that and consider a technical failure just as a broken stator that rubs the magnets as a safety system ;-)

Anyway, thats my point of view and not everybody has to share it...

I really like your turbine :-)

After all your experience with the GOE222, why did you chance the profil again? You always semmed to be quite happy with it?

Max

[ChrisOlson]

I get your point Chris and I do not doubt that your turbine is robust and safe...but I have neighbours with children and I feel a lot safer with a backup brake.

Max, I do have manual furling cables on my other turbines.  The only time I have ever used them is to crank the tail in high wind speeds to limit how much power the turbine puts out so it's not dumping all the time.  When and if the turbine would run away, I would have second thoughts about going out to the tower and manually cranking the tail anyway because that puts you directly in the blast zone of a failed turbine rotor.

Like I said, I see nothing wrong with brake schemes.  But I would not rely on it to stop a turbine in a runaway situation.  The disc brake on a Jacobs turbine, for instance, has to be maintained and rebuilt on a regular basis to make sure it works.  You get water on the rotor, or rust on it, and it'll make an impressive cloud of smoke but it won't stop the turbine.  And it's as big as a brake rotor on a 1/2 ton pickup truck.  You have to figure that a 7 meter rotor can develop 20 hp or so if it's under control, and probably better than triple that if it's out of control.  And you want the brake to stop an out-of-control turbine.

Ok, so go get yourself a 50 hp three-phase electric motor and put a brake rotor on the output shaft, then try to design a brake that will stall that motor.  This isn't like trying to stop an internal combustion engine with a brake.  Obviously you can design a brake that can do it - but will it be light enough and small enough to fit on your wind turbine?

Don't underestimate how much power a wind turbine rotor can make when it's out of control in really good wind.

After all your experience with the GOE222, why did you chance the profil again? You always semmed to be quite happy with it?

For this turbine I wanted high speed, low torque, lots of volts.  The GOE222's are not good for high speed.  Using the faster blades let me use a lower gear ratio, which improves drivetrain efficiency.  I selected the fiberglass ones because they're more durable than wood, and running at high constant tip speeds will require the more durable blades.  And this is not meant to start the old argument about wood being the best material for wind turbine blades.  Jacobs went thru that 30 years ago when Marcellus invented the 23-10 with sitka spruce blades on it.  They had failure after failure of those blades, and when Steve and the guys at WTIC took over in the 80's they switched to glass blades.  They have never a failure since.  So I think for a turbine that is going to run at high speed all the time, the glass blades are going to be needed or you'll be fixing blades all the time.
--
Chris

[midwoud1]

A brake backup in case of storm.
Having pitchcontrolled blades the way Menelaos and Flux mentioned is an option.
A spring preloaded system that can be released by an activated magnet , I haven't yet .
I rely on the actuator who is feathering the blades.
I use already a controller that commands by high rpm. (adjustable) .
Long time ago I had a steel wire 4mm , running down the tower so i could pull the furling tail in to parking position.
The wire was partly guided by tubing not to hurt electrical cables.
Many years worked with an actuator to move the tail in ,also with a controller .
Another way is a yaw drive wich hold the mill  90 degrees on the wind direction ( complex )
Any other sugestions are welcome.

--
Frans.    NL.

[ChrisOlson]

Here's how I look at all this:

A brake backup in case of storm.

How about just leaving it run?  I never shut down during storms, even in the couple tornados we've had.  Sure, the machine will put out some big power spikes, but for the most part it just turns to the side of the tower and it regulates itself pretty well.

Having pitchcontrolled blades the way Menelaos and Flux mentioned is an option.

I look at the amount of maintenance a Jacobs governor requires, which is one of the simplest and more robust ones out there, and it's just not a good option for small wind turbines.  There's a reason Jake service guys always carry a complete governor and set of blade sleeves in the service truck.  There's always something broke, bent, stuck or cracked on the governor.  If you like working on your wind turbine all the time, then a governor is cool.

A spring preloaded system that can be released by an activated magnet , I haven't yet .

On a turbine of any decent size it would take a helluva spring on a brake to apply much braking power.  Take a look at the caged spring in the emergency spring brake chambers on a truck with air brakes.  You're talking several hundred pounds of spring pressure there, even on a small Type 30 chamber.  And that spring is applying braking pressure thru the mechanical advantage of the slack adjuster, plus the cams.  And you got eight of them, and at best they will only slow the truck down gently if they have to used.  The hydraulic cylinders and air brake chambers apply force in the thousands of pounds to the actuator rod during braking.  It's just not feasible to use springs to do that if the brake is to have any real amount of power.

I rely on the actuator who is feathering the blades.

I have yet to see any sort of blade pitch changing mechanism, including those used on aircraft, which are hydraulic and oil bath, that do not require a lot of maintenance to keep them working.  It's not a matter of IF it will fail, it's WHEN.  Blade feathering mechanisms on wind turbines are fine if you're prepared to do the maintenance on it.  But even the largest turbines have hatches where the tech crawls into the blade governor area to work on it and maintain it, and replace parts.  They don't throw 'em up there and it "just works".  They have to be worked ON to keep them working.

I played with various blade pitch changing mechanisms a long time back.  I finally decided I couldn't really come up with anything that was any better than a Woodward governor used on Hamilton-Standard aircraft props.  And the thing with those is - they have be rebuilt every 1,500 hours.  My turbines get better than 4x that amount of hours on them in a year.  And on a rebuild they dye penetrant, or x-ray, check parts in the governor and it's not usual to find cracked spiders and/or blade roots and you end up replacing most of the governor.

So with any blade pitch changing outfit the key word is maintenance.  I don't care if it's the old flyball governor used on the Jake Model 25's or the latest and greatest made from stainless steel and 4140 chromemoly - it WILL fail if it's not inspected and maintained on a regular basis.
--
Chris

[Menelaos]

Hi Chris,

^{The only time I have ever used them is to crank the tail in high wind speeds to limit how much power the turbine puts out so it's not dumping all the time.  When and if the turbine would run away, I would have second thoughts about going out to the tower and manually cranking the tail anyway because that puts you directly in the blast zone of a failed turbine rotor.}


Well that is you living in a remote area and probably beeing home most of the time and you are using your setup in combination with a battery bank.
For me there is no need for that. Germany is a small place compares to the USA and you really have to search for places without grid power. I build the turbines for the fun of constructing and building them and not because I need the power, want to save money or for beeing one of those green guys...

Anyway I do not want my wind turbine to be my everydays project and I do not want to go there and pull this string and fix tails or regulate anything. I feel a turbine should be able to do this without human interference. If my turbine enconters a problem I want it to be intelligent and stop working and I think that disfunctions can also accur during normal operation and not only in storms.

Of course the brake has to fit the forces that can occur during operation. The brake is calculated (!) and designed to be able to completely take the torque that the turbine will deliver in winds of 14m/s. My furling is calculated to already set in at about 9-10 m/s. Once the prop has slowed down a little, it will stall anyway and braking will be easier. I do not underestimate the power of the blades (!) and furling will help it as well. If it turns out not to be powerful enough, I can still take harder spings and apply up to 7.000 pounds of force...that really is plenty on a 300mm diameter brake disc.

Short gusts will hardly effect the torque of the prop as it takes quite a while for the prop to speed up and thus adjust tsr. In the meantime the blades are stalled. Looking at diagrams for various blade profiles, one can determine the torque and power values that will have to be handled. Practical tests are always good but there still is some science behind that ;-)

After all, this brake will still be better than no brake...right? :-)
It is not only to be useful in high winds but also when other problems occour that I might not realize when not watching the turbine all day. If there is a failure to the alternator, the turbine an stp before it burns out. If I have an imbalace on the blades because of damage (maybe a bird is still sleepy in the morning and gets caught damaging the blades) or vibrations of the tower (caused by whatever) I just like to know that things are taken care of if I am not there to do something manually.

A wile ago I was really keen on those pitch controls but I came to the same conclusion than you- there is a lot of maintenance required...earlier or later or maybe never....but who knows... so I am back to fixed pitch and alternative controll systems. For me personally I feel that furling only is not enough and I have read many reports and talked to many people that were really scared in storms standing under the turbine in winds of 60 miles an hour trying to rescue their turbines risking their lifes. I am not one of those "idiots" going outside in such situations trying to pull some wires to furl the tail and hoping to get that beast under control... ;-)


Max

[ChrisOlson]

Of course the brake has to fit the forces that can occur during operation. The brake is calculated (!) and designed to be able to completely take the torque that the turbine will deliver in winds of 14m/s. My furling is calculated to already set in at about 9-10 m/s. Once the prop has slowed down a little, it will stall anyway and braking will be easier

Yes - the turbines I have seen and worked with that have brakes can rely on them to stop the machine when there is generator load, to prevent overspeed or possibly stop the turbine.  But when there is a generator failure, the turbines I have seen do not have enough brake to stop it.  And that is my point.  At 14 m/s, that is mild.  In storms where the wind speed can exceed 30 m/s and you have a total generator failure so the turbine is a runaway, there is no brake that will physically fit on the turbine that will stop it.  You're dealing with a rotor that is running out the top side of its optimum TSR, then applying load to it with a brake that is going to try to pull it down.  When it passes thru its optimum TSR it will turn the brake to smoke because the torque from say a 7 meter rotor is just about beyond comprehension in 30 m/s wind.  You may as well have a blown and injected Keith Black Hemi on that tower and try to stop it with a rubber band.

And this is the type of situation where a lot of folks think a brake is going to help, or would be useful.

This Vestas turbine has it all - powered yaw drive that can turn it out of the wind, feathering blades, and a huge brake in that is designed! to stop it.  And yet watch what happens - and I guarantee you that huge brake was applied:
http://www.youtube.com/watch?v=kBYJul2ykZs

It's my opinion after studying the situation, running these machines, and applying all my engineering knowledge to it, there is no brake that will fit on the turbine that will save your butt in any real wind if you have a runaway and that baby is facing dead-on into the wind.  And I have seen fully loaded turbines (with the generator and furling working) come out of furl and face the wind at wind speeds over 20 m/s.  I don't fully understand what causes it - Flux and Hugh have explained it to me - but I have seen it.  And it puts The Testâ„¢ to your generator when it does it.  It makes you also consider upgrading your downstream equipment, like ammeter shunts and dump loads and stuff.

Bergey Wind Power's method of dealing with this is to unload the turbine by kicking the inverter out.  Those machines have variable pitch (PowerFlex) blades, turn to the side furling, crankable tail, but no brake.  They have designed blades that can run at something like 121 mph wind speed unloaded, and survive.  My blades aren't that good.  So my course of action would be to grab the video camera, retreat to a safe distance and try to catch the explosion on video for future generations to enjoy.  If you got a brake in it, you're not going to get the good video footage because your first reaction will be to just stand there expecting that the brake should be kicking in any second now.   
--
Chris

[ChrisOlson]

So my course of action would be to grab the video camera, retreat to a safe distance and try to catch the explosion on video for future generations to enjoy.

And that's no kidding - when your daughter is telling the grandkids not to do something because it's too dangerous, they can always whip out the Wind Turbine Explosion Video and tell her, "Well, lookit what grandpa did!"   
--
Chris

[birdhouse]

a run away turbine without load, seems to me, to be about like a hugely overloaded 1 ton truck going down a VERY steep VERY long hill. 

without exhaust braking or down shifting, YOU WILL burn up your brakes. 

i warp rotors all the time in my little dodge truck.  it's because i over work it for its size.  it's a consequence of maint. that i live with.  the difference is, i chose when and where to drive my truck with various payloads, but a wind turbine has no choices.  it just runs harder as the wind speed increases. 

disk brakes are great, but have their limitations!

adam

[Menelaos]

oh oh :-D

Anyway I don't know why you always pick this 7m machine as an example...this is not what "normal" folks put in their front garden...
I am talking about machines of 4-5m diamter. If I was to setup a 7m machine I wouldn't dare using that slow furling mechanism to protect it anyway....although there are machines that are setup this way and seem to work well undless the alternator gives up...

You might be right Chris about the brake not beeing stron enough or maybe you are wrong...I think it depends on the brake system, the braking force, the diamter od the disc and friends like furling that support the stopping procedure.

If there is a problem of vibrations or the inverter blowing up or overspeed, I still have the alternator and dumploads to help me braking the turbine...as well as the furling...so far my turbine will do the same thing that yours does excep that the brake will help it and support bthe alternator. Once the turbine is stopped, it will not be able to start up again, that for sure.

If I have an alternator problem, the brake will close imidiately (thats probably wrng spelling)...as the electronics do observe all 3 phases and "know" if something is wrong. The prop will then not have time to speed up.

Even if the turbine does speed up, furling will not stop working within seconds. Furling definitively does support the brake. When you were talking about 30 m/s second...of course, the brake alone will not help much but also on your machine you do not get 15 KW of power in those winds, do you?
The blades turn out of the wind and leave only a fraction of the power they would support when they would directly face the wind so also the brake only has to take a fraction of torque from what could be calculated.

Have a look at car brakes...If you go with 100 mph with your car weighting 2 tons....how much torque is that ?
And look at those tiny brakes and discs...and still if you keep accelerating and push the brake at the same time, the brake will win (unless you have some kind of really freaky engine)

Now imagine this disk brake kit on a 5 m turbine....do you really think that would look enormously big on top of a 15m tower...compared to the alternator...?
And do you really think such a car automotive brake wouldn't be ale to stop that 5m turbine...?

I think this would be the point to make some calculations rather that guessing. I know that you have plenty of knowledge and engeneering skills and I agree with you in many points of view but I am not sure on this one...

Max

[midwoud1]

We have to deal with the challenge to improve our windmills .
I rely on it.
Very soon a barrel crude oil will be over 200 dollar  ...hi.

Frans.

[ChrisOlson]

And do you really think such a car automotive brake wouldn't be ale to stop that 5m turbine...?

No, it won't in any real wind.  A brake's job has nothing to with torque, really, except at the mount for the caliper or brake anchor point.  A brake's job is to convert kinetic or mechanical power to heat - and to dissipate the heat fast enough so as to not damage the components of the brake.

A typical disc brake on a small sedan will generate approximately 20kW in heat for about 20 seconds before it "fades" and braking effectiveness is lost.  And this is at maximum braking, without locking up the brake (which would be disastrous for a wind turbine to just suddenly lock up).

A four meter turbine rotor running at 35% efficiency @ 20 m/s will put 20.7 kW to the shaft.  So at 20 m/s that brake would be barely adequate.  At 30 m/s, which is a more usual thunderstorm wind speed (at least around here), that little 4 meter rotor will put almost 70 kW to the shaft.  Just do the math on it.  That car brake will not even come CLOSE to stopping that little 4 meter rotor in thunderstorm wind.

Like I said, never underestimate the power a wind turbine rotor can put to the shaft when its running out of control in real wind.

The other thing with wind turbines is, do not get carried away with putting electronic controls and actuators, etc., on a wind turbine to keep it under control.  All you're doing is reducing the reliability of the machine.

It's kind of like diesel engines - one of the last devices left on earth that can run without needing any electricity to make it work.  And what do they do?  Some engineer at Mercedes had a nightmare back in the 80's, woke up, and still in a stupor strapped electronics on diesel engines to control fuel injection.  And then Detroit Diesel and the rest of the industry decided to follow suit so Mercedes wasn't the only idiots running electronic fuel injection on diesels.  But to this day, in mission critical diesel power applications like marine and genset engines, mechanical injection is still used.  There's a reason for that.  All the electronics did to diesel engines was put them in the shop being worked on more, and dramatically increased the failure rate of what was a reliable power source.  And, actually, it did the same thing to the rest of the automotive industry - approximately 86% of all the repairs done these days on modern automobiles is electronic in nature.
--
Chris

[Menelaos]

^{a run away turbine without load, seems to me, to be about like a hugely overloaded 1 ton truck going down a VERY steep VERY long hill.}

No it is not, it is exactly the other way round. When the prop is not under load, it will spin up far above design TSR. In some cases it can spin up to double design TSR. When doing that, the efficiency of the prop decreases dramatically...not as fast as due to stall but still fast. Finanlly there is a point when all the energy of the prop is used to keep that verry high rpm and basically no power is deliverd to the shaft. All thats left then is the kinetic energy stored in the rotation of the blades.
With the truck it is different. When it goes down hill, it releases all that kinetic energy that was created when going up hill in advance....

Anyway... When the brake starts working now, it will in the beginning quickly slow down the prop. When doing that, the prop again gets closer to its design TSR and the efficiency will increase and of course in a 20 or 30 m/s wind we then have a problem as chris' numbers do show correctly.

^{At 30 m/s, which is a more usual thunderstorm wind speed (at least around here), that little 4 meter rotor will put almost 70 kW to the shaft.  Just do the math on it. That car brake will not even come CLOSE to stopping that little 4 meter rotor in thunderstorm wind.}

That is so true Chris but we still have furling and at 20 or even 30 m/s the furling mechanism should be definitively already doing its job, dramatically reducing the swept area of the prop.

I never stated that a stand alone disc brake system could substitute that furling safety feature and I do not argue about the fact that it wouldn't but the combination of both can, in my opinion, make the turbine completely stop. As soon as it stalls, the wind has "lost" anyway because as soon as the tsr drops belos design tsr, the prop will loose efficiency verry fast and gusts comming now will not change that but even support the stopping progress as it even more drops tsr.

If it was any different, your system with furling wouldn't work either Chris. All you have is furling and the chance of shorting the alternator ( or at least load the prop ) or getting rid of power using dump loads. According to your calculations, your dump loads for that 4m machine would also have to take 70 KW of power in order to keep the turbine under control and also the alternator would have to able to withstand that load....but I guess that you neather have a 70 KW backup dump load nor an alternator that can handle something like 2900 Amps (on a 24 V system)...and if you had it, your alternator wouldn't survive the 20 seconds that you stated the disc brake could... If you know the resistance of your winding, you can calculate the maximum amps that your alternator could possibly produce as there is a limit.
Knowing the maximum system voltage, you can then calculate the maximum power that the alternator can use for braking process which will be during shorting all phases simultaniously ( but I know that you are familiar with this )
This limit will be far below the numbers that you stated for the automotive brake- I bet on that...!
So in verry high winds, in order to keep the turbine under control, you have to keep the turbine stalled and not have it reach design tsr or you need to furl in order to reduce swept area, which you do...but the this applies to my calculations as well ;-)

So I wonder why for my example you set up new conditions...

I totally agree about what you said about those electronic solutions- I distrust and hate them as well...!...but they can be verry useful and sometimes make life a lot easier :-)
This is why I would never design in such a way that I need micro electronics or an electric motor to CLOSE the brake. In my version, the brake is kept open by elektronics and I do not need it to close the brake. Even if I have a power cut or if the whole thing "explodes", the brake will still be able to close which it does as soon as the electro magnet gets a power cut. That will happen eiter way, if the electronics is not working and also if it is working and the sensors dectect "danger". This is what I mean by "fail safe- System".

But anyway, I do not want to get too much offtopic with this braking issue, destroying the red line about your turbine and maybe this topic would be better off beeing moved somewhere else or to a seperate threat...

Max

[ChrisOlson]

We have to deal with the challenge to improve our windmills .
I rely on it.
Very soon a barrel crude oil will be over 200 dollar  ...hi.

Well Frans, I been throwin' 'em up as fast as I can build 'em.  My dino-fueled generator is starting to feel a little dejected because it don't run much anymore.

Everything will be fine until the politicians figure out some reason that people with wind turbines should be paying an extra tax because they're getting something for "free".  Governments make a lot of money off crude oil.  If it gets too expensive and people stop using it, the governments won't have enough money.  And then they'll start eyeballing your wind turbines as a revenue source.
--
Chris

[ChrisOlson]

That is so true Chris but we still have furling and at 20 or even 30 m/s the furling mechanism should be definitively already doing its job, dramatically reducing the swept area of the prop.

Max, the furling is not too reliable in really strong winds from what I've seen if you have a runaway.  A 4 meter rotor running at TSR 6 @ 30 m/s is turning at almost 1,100 rpm.  Trying to turn it is like trying to derail a train with a broomstick (assuming the blades are still on it).  If you do get it to turn at any rate decent enough to reduce swept area the chances of the blades still being on are reduced to almost nothing.

Most of these wind turbines do not have rigid aluminum blades like an aircraft prop to take that kind of speed.  They flex - a lot.  So if you count on furling to work at that speed, you'd better have some sort of furling that turns it really, really gentle or you'll break it.

The one time I had that happen with a 4 meter turbine, it busted the mast on the tower and I just about lost the turbine off it.

Edit: Which, BTW, was caused by a blown breaker.  The breaker kept the rectifier from turning into a glowing, smoldering pile of goop.  But it didn't do the turbine much good.
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Chris

[Menelaos]

^{The one time I had that happen with a 4 meter turbine, it busted the mast on the tower and I just about lost the turbine off it.}

Well thats kind of scarry 
What did you do about it, what happend after that gust had passed and wind speed decreased again and what would have happend if you weren't home to observe what happend to that turbine and do whatever you did....? This kind of practical experience is like a treasure to me :-)

Anyway, I am not yet convinced ;-)

For my next turbine I will use the same profile that you have already used on some of your turbines, the GOE222
For various reasons, I am a fan of untwisted blades with a constant pitch and chord length and I am about to order a couple hundret meters of aluminium profile from china that I have designed as I didn't like the ones available...That one will have a cordlength of 190mm and be a good fit for turbines of 3-6 m diameter, depending on blade configuration...

As stated in your example, I plan to have them run at about TSR 6-6.5.
It is really also interesesting to do simulations on those blades to see what happens on exrtemely high raynolds numbers.At 30 m/s, the blade tips would spin with something like nearly 200 m/s which is about 700 km/h or 400 mph... from your experience with aircrafts, please tell me if you feel that is possible... ;-) - I don't think so! I guess that maximum possible RPM is somewhere around 600 RPM for a 4 m turbine....still spooky though....!

Did you have the chance to measure RPM during that incident? - That would be really interesting to me!!! Anyway, these numbers can be roughly calculated but it would be nice comparing them to practical results...
The characteristic of this type of blades is that they basically limit themselves to a maximum RPM and power output caused by the great width of the profile on the tip ends...so even if the turbine spins up with no load, there is an RPM limit using those blades and all yoi have to to is to make them strong enough to withstnad this maximum rpm :-) Thanx mister Raynolds ;-)

So those blades at some point will start to stall  by themselve which is a nice contribution to safety.

^{Which, BTW, was caused by a blown breaker.}

This is exactly what I was refering to in the verry beginning of this discussion. Some stupid electric component decides to stop working and leaves the alternator and blades without load and after a few seconds the whole thing willstart to seek for the wind and furling will be likely to fail.

A disfunction like that is exactly what I think that kind of intelligent braking system like the one I am planning can help with. Within a fraction of a second, the controller would have known about the "no load situation" and kickes in the brake before the prop gets the chance to spin up. So it then basically behaves like a 20 KW dump load for something like half a minute.

Do you think that would have helped you in that situation you were talking about to keep the prop under control?

[ChrisOlson]

What did you do about it, what happend after that gust had passed and wind speed decreased again and what would have happend if you weren't home to observe what happend to that turbine and do whatever you did....? This kind of practical experience is like a treasure to me :-)

I shut it down with the shorting switch.  The wind side brace broke on the tower and it bent the mast so the top of the tower was leaning at a 30 degree angle, about.  Once I shut it down it took the load off the tower but the wind was blowing at 20 m/s sustained with gusts higher than that.

I lowered the tower the next day and fixed the mast.

I do not know how many rpm's it was going.  The data recorder said 140 some amps on a 24 volt system when the breaker let go, with a spike to about 175 when the breaker reset.  The turbine was actually fine in free-wheel.  It was when the auto-reset breaker reset that it broke the tower.  The turbine made a violent turn the right when it became loaded again, and that broke the tower.  It kind of shocked me for a second or so when the top of the tower tipped.  It was point up and still running.  I thought it was going to come off but the lee side struts sort of held (they were bent).  I ran for the switch at the base of the tower, which is a big SquareD three-pole safety switch and threw it.  That shut the turbine down.

The generator on that turbine, BTW, was a geared ferrite magnet dual stator.  The rotor was a two-blade 4.0 meter.  I took the turbine off the tower when I fixed it and put up a three-blade 3.8 meter machine instead.  That two-blade machine had a violent head shaking problem when it yawed, and I believe that's what broke the tower.

For my next turbine I will use the same profile that you have already used on some of your turbines, the GOE222

You will like the GOE222.  But I would run it at TSR 6 at where you tune for peak performance (for your wind site), and let it "lug down" on the top end of the power curve.  That airfoil works really good down to TSR 4.  If you run it at TSR 6.5 you will lose power.  I have calculated that it develops Cp .35 @ TSR 6 and CP .27 @ TSR 4.  It has a very flat torque curve, and it is just about impossible to get those blades to fully stall and stop making power.  Another member of this forum can attest to the fact that a set of those blades started up his turbine with the parking brake set, squealed the brake until it burned it up, then took off running.  They develop raw torque like no other blade I have flown.

But at 10 degree pitch they do not like to run over TSR 6.
--
Chris

[Menelaos]

Those 2- bladed props are tricky with those vibrations when they adjust do the wind. This is why they stopped producing the big 2 bladed commercial turbines here in germany. They had broken or abused yaw bearings all the time...

Thanx for the hints with optimum TSR. With a slightly changed pitch angle I could use it with TSR 7 as well but than of coures I will have a little less Cp. I have to check out on that once I have the alternator. As I will buy that one, I cannot adjust windings to make a perfect fit this way. I want to be able to use that turbine for working with a grid inverter, a 48 V system and also to be compatible with the CLASSIC that you use right now...

What was the width of your blades Chris? I calculated 190mm to be perfect for a 3 bladed prop of 4m diameter...

I shut it down with the shorting switch......The data recorder said 140 some amps on a 24 volt system when the breaker let go, with a spike to about 175 when the breaker reset. 

If you managed to get it under control using the shorting switch I think it would have worked with the disc brake as well- why shouldn't it...?!? If it applies the same braking moment that the shorted alternator can deliver, then there is no doubt about that
I would really like to calculate for the maximum power/amperage that alternator can theoretically deliver when shorted to have something to compare that brake caracteristics with. What was the resistance of the windings (line to line)?

You seem to get bored by me always picking on that disc brake stuff again but I do find this really interesting...also for others...

OK, in your incident that brake wouldn't have helped a lot as your alternator was working ok but I am sure, if it didn't, wou would have been happy having had one of those brakes ;-)

Max

PS. with those magnet prices we have right now, buying these complete ironless alternators from danemark might be a solution for some people and they have qiute a number of models to choose from.

Here is the website where you can download the datasheets:

http://www.dvetech.dk/?page=PMG

Price is about 800-1000 Euros / KW

Max

[ChrisOlson]

What was the width of your blades Chris? I calculated 190mm to be perfect for a 3 bladed prop of 4m diameter...

The chord is 160 mm on those.

OK, in your incident that brake wouldn't have helped a lot as your alternator was working ok but I am sure, if it didn't, wou would have been happy having had one of those brakes ;-)

I have bench tested a ferrite generator with one stator shorted and failed to burn it out.  So it's my opinion that the generator can be used for the brake probably more reliably than a brake itself.  If I had a neo generator in the turbine I would've had second thoughts about shorting it out.  I think with the ferrites, the armature reaction from shorting it is more severe and it sort of "bends" the weak flux, turning the generator into more of an eddy brake than a neo does.  A neo just "locks up".  A ferrite generator is more gentle.

The other issue is that all my turbines are geared.  The generator has a huge advantage in torque over the mainshaft due to gear reduction from the PTO to input.  When you short a geared generator the torque load on the stator mount, rotors and stator is considerably less than a direct drive, and provides more effective braking.

So, no - until I see a reason to have one I won't be putting a brake on any time soon   
--
Chris

[Menelaos]

the reason is exactly what happened to you with that limit switch. It did something funny and let the turbine spin up, getting out of control. I well believe that by shorting the alternator, yo can safely stop the turbine....but what is that good for if there is nobody out there shorting it in such a situation. You stated that you run outside to the base of the tower shorting your turbine...and maybe that is ok for you beeing home watching your turbine from time to time. For me that would not work at all as I am sometimes not home for weeks and as I will have my turbine grid tied I do not see the point of swiching it off when beeing on holidays or at work and losing all that power...

Max

[ChrisOlson]

For me that would not work at all as I am sometimes not home for weeks and as I will have my turbine grid tied I do not see the point of swiching it off when beeing on holidays or at work and losing all that power...

Yes, it is a different thing because we have no grid power.  So when we leave I shut the wind systems down.  We have a large battery bank and it will run the critical stuff like 'fridge and freezer for about 10 days with no other loads on in the house and my shop.  I leave the solar going, but if the bank would get low our standby generator automatically starts and takes care of the problem.

Our "normal" loads in the winter time are about 30 kWh/day.  In the summer about 17 kWh/day. 

So I don't look at it as "losing out on all that power".  If we get a really good day with both wind and sun and the bank gets full I shut the wind off and let the solar carry the load.  If we're not there to use it, we don't need it.

I guess I have never seen the logic behind grid-tied systems.  I know a lot of people do it, but it really does you no good during a power outage unless you have battery backup.  Our power never goes off   
--
Chris

[Menelaos]

For me there is no need for a turbine and my place is even too small to put it up so it will be installed at a friends place. I build turbines because I like building them and see them fly and to check if things work out the way I designed them to work :-)

Its like buying an expensive car that I give to friends to drive it...why? - because I can :-D

I like the idea of turning nature into energy. I also have a few other projects running. My biggest one is a high frequency carbon reactor that we have recently patented...some kind of wood gasifier with a combustion engine to produce electricity working with microwaves to get rid of the tars. With that device, people will be able to heat their house for free as the grid feed will pay for way more than the wood it consumes and leaves 20 KW of permanent heat for the house...and again I also do not have the space to use that one myself...a 300 KW unit did already run for thousends of hours without problems.
but thats a different story- so why do I develope that kind of machines beside building wind turbines? - because I can... :-D

So of course I could switch off the turbine when I am away for a longer time or when storm is announced in the media...but I don't like to do so because I want that turbine to be able to do its job unattended and I want it to be fool proof and safe, especially as it will not be installed in my place.

Max

[Menelaos]

Chris,

I again read through your other topics to again checked about the braking forces when your alternator is shorted.

Assuming your total stator resistance including the line resistance is is about 0.5 ohm and your cut in wind speed (now assumed for optimum tsr althoug I know thats not exactly right) is 3.5 m/s with a system voltage of 24 Volts I get the following numbers for a wind speed of 20 m/s:

open voltage : 137 volts
resistance : 0.5 Ohm

137 volts/ 0.5 Ohm = 274 Amps short circuit current

That is the maximum amps that the stator can produce.

274 Amps x 137 Volts= 37.5 KW on optimum tsr. If the prop runs away and thus open voltage rises even more, the breaking power will be even higher.
At that cp of 0.35 that you mentioned that you figured out during your tests, that 4m prop will have a shaft power of about 21.5 KW

So you could definitively get that turbine to stop by shorting even if it is directly facing the wind without having to be scared of it running away.
It would not anymore work if the sum of stator and line resistance is more than about 0.85 ohm. If that was the case, you would need the help of furling to make it work by reducing the prop area.

Anyway, when that untwisted constant cord width profile will be exposed to winds of 20 m/s it will no more have its design efficiency of cp 0.35 but far less due to RE numbers getting funny and the tips producing currents and drag...but lets assume that won't happen and continue the calculations with a shaft power of 20 KW as that number is more easy to handle.

In order to find out how a disk brake has to be designed we need to calculate the torque available at the shaft for that wind speed

That would be 20.000 watts / 570 RPM x 9.55 = 335 Nm

In order to JUST keep the turbine under control with a disc brake we need at least or more than 335 Nm of breaking torque.
The brake disc that I want to use has an diameter of 270mm and my brake pads have their center at a radius of 110mm which is 0.11 meters.
friction coefficient I assume with 0.35 as usual for that kind of brake.

I will use springs made by steinel. If you have those in your hands you wouldn believe those are springs as they behave like a tube that you cannot compress at all. When fully loaded, they have a force of 8000 newtons. I will use 2 of them. This will give me a breaking moment of:

8000N x 2 x 0.35 x 0.11m = 616 Nm

With that setup I can easily get that turbine to a complete stop as well when faced to the wind, still with plenty of room. I could also use softer springs. If I have 400 Nm, that will be enough already and I still have the furling to help it. Anyway, in the catalogue I find springs with up to 25.000 N of force that would still fit in my construction and the whole thing can be built really compact. A 270mm brake disc really is not that big compared to the alternator that most folks use for a 4m turbine, is it? ;-)

And on a geared turbine like yours one could attach that disc brake to the fast end, on the alternator and one would need a breaking moment that is smaller by the same factor as the transmission ratio. In your case with a transmission of something like 1:3 150 nm of brekaing moment would definitively do the job...

Please check my calculations and tell me where I did the mistakes that make you think that this kind of brake would not be able to stop that turbine I do not see any reason!

Why did I do all this math now?

Because I cannot cope with your statement that a second brake system is useless as it cannot control those forces anyway which is simply not true and I do not want people to get the idea that such a system is not wort applying it to the turbine because it wouldn't have any real efeect anyway...

That leads me back to the verry initial question when I asked why people do not use those brakes as I guess that not everybody here lives as rural as you do Chris...

...but please guys tell me if I am getting annoying with this... ;-)

Max

[ChrisOlson]

Max, your calcs look good to me, except some of the resistance figures are off.  The internal resistance of the gen on that machine is .38 and the line resistance from the stator to the switch is .07 ohm.  So it develops well over 40 kW during braking when shorted.

Again, like I said, I see nothing wrong with a mechanical brake.  Just question the logic saying you must have one for the turbine to be safe.  If the generator is robust it makes a very effective braking unit  And neither the gen nor a mechanical brake will be effective once the wind speed increases to 30 m/s with the rotor facing dead-on into the wind.  So at that point you need to have the swept area of the rotor reduced by having it furled, or you will overpower any braking effectiveness delivered by either one.

A brake almost has to be automatic to do any good because you simply can't babysit your turbine every time the wind blows with your hand on the brake lever.  If the machine has an adequately robust generator, and the furling is working properly, it shouldn't have a problem, and mine never have in those wind speeds outside of a few incidents early in my wind power "career" that taught me what it takes to build a machine that will survive.  Lots of people get all worried and shut their machines down when a thunderstorm comes.  I don't.  I figure there's no better way to test it to see what that baby can really take than letting it run flat out in Big Wind.  You either got a real machine on the tower, or you got a toy up there.  May as well separate the men from the boys.

So is it totally worthless to put a brake on your turbine?  IMHO, no.  Would having a brake on it be effective in the situation where it would really be needed? (blown generator and runaway in thunderstorm winds).  Again, no.  Am I going to lose much sleep over not having mechanical brakes on my turbines?  Again, the answer is no.

The reason my answer is no to all the above is because I got thousands of hours on the towers with my machines.  I have spent months studying furling - why it seems to work sometimes, and sometimes not.  And I put enough iron in my machines so the machine won't break (but it'll break the damned tower).  I have run them in tornado winds over 100 mph - we lost the solar array off our house - but the turbines survived - running.  Without a mechanical brake.  And that's why I just don't worry about it anymore.
--
Chris

[midwoud1]

Hey Max .
Why don't you use a hydraulic brake caliper and disk from a car. with a  1/4 " HP hose down  the tower.
A hand ram pump like car panel workers use .
I also had it with a very small hydro-electrical  pump of a dentist chair. ( still have a picture of it )
Simple, lightweight , strong , cheap, and reliable.
I had it succesful working on a 3 meter prop.

Frans.