Author Topic: Yet another Stator Failure.  (Read 4493 times)

0 Members and 1 Guest are viewing this topic.

Herr Snefl

  • Newbie
  • *
  • Posts: 7
Yet another Stator Failure.
« on: December 01, 2009, 01:56:03 PM »
Thought I'd post the details of my failure. Failure is perhaps more educational than success!


My 3m machine died last week after feeding a little over 100kWh into the grid. The stator seems to have heated up, expanded and struck the magnets.





The machine seemed to furl O.K. Certainly the tail would fold up to the vertical. Did not appear to really go edge-on to the wind though. Maybe this is the wind seeking behavior people talk about?


Peak output was a tad over 1000W as measured by the WindBoy 1700 inverter. I guess thats about 1100W from the alternator. Voltage would have been around 320v at that power level so current would be a little over 3 amps. Coil resistance was 60 Ohm between terminals of the star. I'm not quite sure how to calculate the actual current in the coils. Presumably it goes in brief surges when the alternator output exceeds the smoothing capacitor voltage and the rectifiers start conducting? Anyway its clear too much power was being dissipated in the stator!


The stator was of the usual 3 phase, 9 coil star variety. Each coil was 475 turns of 0.45mm diameter wire. Coils where heavily super-glued then potted in polyester resin and baby powder.


The alternator was probably generating slightly too many volts/rpm. The inverter showed a tendency to cut in at very low wind-speeds where there was insufficient power available to cover the inverters losses, then drop out immediately. (Increasing the cut-in voltage to 200v helped here.) I suspect there's some scope for reducing the number of turns and increasing the thickness of the wire.


Looks like I'll be spending Christmas winding coils. The low voltage folk have it easy there!


Neil.


Oh: And just to show that it did fly...









« Last Edit: December 01, 2009, 01:56:03 PM by (unknown) »

David HK

  • Hero Member
  • *****
  • Posts: 509
  • Country: hk
Re: Yet another Stator Failure.
« Reply #1 on: December 01, 2009, 02:19:42 PM »
It looks as if you have taken a jigsaw cutter around the stator and cut off the outer extremities of the coils.


Do you have an original photograph showing the full scope of damage?


David in HK

« Last Edit: December 01, 2009, 02:19:42 PM by David HK »

wpowokal

  • Hero Member
  • *****
  • Posts: 1271
  • Country: au
  • Far North Queensland (FNQ) Australia
Re: Yet another Stator Failure.
« Reply #2 on: December 01, 2009, 02:26:03 PM »
That's paint, and I see only 3 wires.


allan

« Last Edit: December 01, 2009, 02:26:03 PM by wpowokal »
A gentleman is man who can disagree without being disagreeable.

ibeweagle

  • Jr. Member
  • **
  • Posts: 62
Re: Yet another Stator Failure.
« Reply #3 on: December 01, 2009, 04:14:21 PM »
redesign rotors to 16 mag 12 coils for increase of 30 percent and change to vinal ester resin 200c wire 30 percent less turns will work look at you tube ibeweagle cheers Mike Johnson
« Last Edit: December 01, 2009, 04:14:21 PM by ibeweagle »

willib

  • SuperHero Member
  • ******
  • Posts: 2414
  • Country: us
Re: Yet another Stator Failure.
« Reply #4 on: December 01, 2009, 04:44:56 PM »
It would not hurt any to add some more mechanical tie points to the stator , snefi.

A real good stator has one standoff/ tie point per coil.

This keeps the flexing to a minimum.

.

bill

.
« Last Edit: December 01, 2009, 04:44:56 PM by willib »
Carpe Ventum (Seize the Wind)

Jerry

  • Hero Member
  • *****
  • Posts: 1519
Re: Yet another Stator Failure.
« Reply #5 on: December 01, 2009, 07:10:52 PM »
Yet another stator failure. I think I'll try to find how many times I've seen that posted.


Every time I see it one thing is consistant. You gotta love the star connection.


May the stars keep the fire in the wind.


Jerry

« Last Edit: December 01, 2009, 07:10:52 PM by Jerry »

Dave B

  • Hero Member
  • *****
  • Posts: 1014
  • Country: 00
    • DCB Energy Systems
Re: Yet another Stator Failure.
« Reply #6 on: December 01, 2009, 08:32:37 PM »
 Sorry to see that but thank you for posting as yet another reminder that this design has limitations. My following thoughts and comments are in no way intended to down play your build or design but rather to try to clarify a few points learned from the past.


 I'm waiting now on the rash of comments and concerns about why all heat in the stator and then all the armchair quarterbacks with their ideas of how to keep things cooler. It's simple, limit the output of your machine. Past posts will show that it is often assumed that the 10' machine as commonly built is a 1000 watt machine. Yes, it will put out 1000 watts and can peak much higher and even survive if ... and the big if is ... if it FULLY furls properly before this output thus limiting this high output for any extended period of time.


 Flux can chime in here any where about furling. For what ever reason, if a machine does not furl far enough to reduce it's out put significantly then watching the tail partially rise and fall only has entertainment value until the fire. This 10' design has proven over and over that running it at a constant 1000 watts plus for any "good wind" length of time will fry it, period.


 If you want a constant 1000 watts with no worries then build a larger machine, heavier wire etc. etc. and have it FULLY furl at no more than 1000 Watts. The constant "good winds" will not fry it and it should be fairly well protected for brief peaks in power for gusty conditions.


 I know it's hard to accept, I fried 2 stators myself before realizing I had 2 options. #1 limit the "1000 watt" machine to possibly 500-700 watts constant or #2 spend more money to build a machine that could run at 1000 watts constant without burning up.


 Without major improvements in it's current design for disipating more heat (some have helped and there have been some wild ideas thrown around besides) it is what it is.


 Limit the 10' design to well below 1000 watts constant or when the good winds come (and they will) you will burn it up. End of a rant I guess, sorry but from someone who has his share of re-dos I'm only trying to help.  Dave B.      

« Last Edit: December 01, 2009, 08:32:37 PM by Dave B »
DCB Energy Systems
http://dcbenergy.com/

Shadow

  • Sr. Member
  • ****
  • Posts: 473
Re: Yet another Stator Failure.
« Reply #7 on: December 01, 2009, 08:58:19 PM »
Hear! Hear!  I totally agree.
« Last Edit: December 01, 2009, 08:58:19 PM by Shadow »

Flux

  • Super Hero Member Plus
  • *******
  • Posts: 6275
Re: Yet another Stator Failure.
« Reply #8 on: December 02, 2009, 01:15:29 AM »
Not sure about the machine details, I assume it is 10ft, does it have the rectangular magnets.


One thing is very obvious from your pictures, you have only wound about half the available space. You could just about have doubled the wire size and made the coils bigger so that they touched on the outside, this would probably have reduced your resistance to 1/3.


You are probably right about too many turns and too low a cut in speed. That would have given you the option of getting below 1/3 of the present value and that would have cut stator losses by 3.


If it is 10ft and they are rectangular magnets then I agree with others that 16 magnets is a better option but if you reduce your winding resistance you should get the 1kW into a mppt inverter ( not for direct battery charging).


When you get it to furl it will drop power as it goes hard into furl and the prop will be virtually edge on to the wind. I strongly suspect that didn't furl at all.


These windings may handle 1kw peak during gusts but not 1kW sustained for long periods.


On a bench test I suspect your winding with only half size coils would struggle to hold 400W.


If you had the inverter programmed correctly the thing should be running well clear of stall. If you used the original furling for stalled battery charging it would not furl at any sensible speed if at all. I suspect you have to increase the offset a bit anyway to get it furling and you will need to reduce the hinge angle or make a much lighter tail.


It looks from the pictures as though the wire is cooked but it might not be, I don't know what temperature superglue will stand but it may have disintegrated below a temperature that would damage the wire coating and expanded the coils.


I have never found a use for superglue, I tried to stick fingers together and it failed there as well. I would never put it near a winding. If the temperature was high enough to fry the wire coating then the superglue may not have been a major factor.


Polyester will not stand the limiting wire temperature long term but it will probably stand it for wind duty for several years. Vinyl is better and there are a few epoxies that are just as good but normal epoxy will not do as well as polyester.


My immediate thought is to reduce turns, use the thickest wire that will get the coils in the space and you could squeeze the holes a bit more triangular if needed.


Wet wind the coils with vinyl or high temperature epoxy and make it furl so that it drops power in very high winds and I think you can get the 1kW.


Thanks for posting the pictures, a description alone would not have let me realise how much you could have reduced the resistance but using more wire.


Flux

« Last Edit: December 02, 2009, 01:15:29 AM by Flux »

TomW

  • Super Hero Member Plus
  • *******
  • Posts: 5130
  • Country: us
Re: Yet another Stator Failure.
« Reply #9 on: December 02, 2009, 02:59:43 AM »
David;


I had to look closer at that stator picture to get a sense of whats what. Confusing because it looks like the stator was painted after the magnet rotors were installed giving a bit of an illusion it has been cut off around the perimeter of the magnet rotor.


I have a 10 footer myself. Running at 24 volts it can do 40+ amps. With an extremely light tail it never sustains higher outputs for long. I like it that way. Much rather get long life producing safe power levels than squeeze every watt out of it all the time and have it fail early. It furls but I have never seen it hold fully furled with the prop edge on to the wind.







The tail is PVC sheet 3/16th inch thick and was sized according to the latest book on the 10 footer by the Dans. Sorry, I cannot recall the exact specs now.


My soon to be flying 12 footer will be done the same. Light tail, low cut in with early furling to keep it going low and slow.


Just what I do here.


Tom

« Last Edit: December 02, 2009, 02:59:43 AM by TomW »

tecker

  • SuperHero Member
  • ******
  • Posts: 2183
Re: Yet another Stator Failure.
« Reply #10 on: December 02, 2009, 08:06:51 AM »
25 Gauge wire is the main problem the limit per coil would be 3 amps and slightly warm So when hitting 9 amps would have to be limited to pre furl and the gen set should be held to around 7 amps continuous. It does look like it warped and hit the rotor . If your looking for 3 amps at 200 plus I would go for a single phase set . I've found 10 ohms per phase is the edge of the resistance for  furling with power anyway. The machine drops down with any load and has to unfurl at that point.Go bifillar with the 25 gauge I assume your looking for transmission efficiency with the higher voltage .(just a guess) Working with 150 to 200 volts will be a better power factor 300 volts has a tendecy to arc over easily .
« Last Edit: December 02, 2009, 08:06:51 AM by tecker »

jlt

  • Sr. Member
  • ****
  • Posts: 368
Re: Yet another Stator Failure.
« Reply #11 on: December 02, 2009, 01:29:00 PM »
Not all coils are black from high heat . i have a piggot 8 ft that has been very hot and all the coils are black. but mine is still working. it looks as though the problem started with some rubbing on the magnets.sorry that you have make a new stator.but with bigger wire and more stator support your next one should much better.
« Last Edit: December 02, 2009, 01:29:00 PM by jlt »

wpowokal

  • Hero Member
  • *****
  • Posts: 1271
  • Country: au
  • Far North Queensland (FNQ) Australia
Re: Yet another Stator Failure.
« Reply #12 on: December 02, 2009, 02:57:16 PM »
The interesting part of this is that of the blackened coils most are only so across part of them, I vote for moisture ingress and a breakdown of insulation at those high volts as the catalyst for this failure.


allan

« Last Edit: December 02, 2009, 02:57:16 PM by wpowokal »
A gentleman is man who can disagree without being disagreeable.

ADMIN

  • Guest
Re: Yet another Stator Failure.
« Reply #13 on: December 02, 2009, 05:52:57 PM »
What power curve did you program into the Windyboy?

That's the tricky part about direct grid tie.

Batteries do a good job with no computer. With no batteries, you need to get the power curve computer programming right or else the turbine will not be loaded correctly, and will burn up. Not just homebrew turbines -- ANY wind turbine.

There are LOTS of folks interested in this, please post any further information.

DAN FINK

« Last Edit: December 02, 2009, 05:52:57 PM by ADMIN »

DanB

  • Global Moderator
  • SuperHero Member
  • *****
  • Posts: 2151
  • Country: us
    • otherpower.com
Re: Yet another Stator Failure.
« Reply #14 on: December 02, 2009, 08:03:35 PM »
Yes that's a big factor I expect.  Also - as Flux has pointed out there is a lot more room for copper in the stator.

It's surprising to me some, because with teh right power curve in the inverter ~ the thing should be operating at much higher efficiency that it would in a simple battery charging application.  I should think a machine in this application should have half the losses in the stator at full output as a battery charging machine would.
« Last Edit: December 02, 2009, 08:03:35 PM by DanB »
If I ever figure out what's in the box then maybe I can think outside of it.

imsmooth

  • Sr. Member
  • ****
  • Posts: 425
Re: Yet another Stator Failure.
« Reply #15 on: December 02, 2009, 08:44:40 PM »
I have a 10.5' using an Aurora Inverter with 16 programmable points.  My wire is 17g, 110T, 9 coils in Star.  It has seen over 1400W in gusts; I am not sure what it has run sustained.  I know during testing of the coils I fed several amps into them and measured the temperature with an IR thermometer to make sure I stayed well below 200C.


You can see the details at http://www.mindchallenger.com/wind/axial1.html

« Last Edit: December 02, 2009, 08:44:40 PM by imsmooth »

Flux

  • Super Hero Member Plus
  • *******
  • Posts: 6275
Re: Yet another Stator Failure.
« Reply #16 on: December 03, 2009, 12:50:58 AM »
In wet areas I can see problems with insulation , it will be much more of a problem than low voltage machines.


If you get a rub between magnets and coil the a high voltage machine is in real trouble and that almost certainly was the final cause of failure.


I think larger clearance from magnets to stator is likely to be needed and I am not sure polyester is totally satisfactory if used in the normal way with glass cloth and a thin coating over the coils. If you live in a dry area then it may not be an issue.


I don't think this was the start of the problem but I agree that it may have been the final cause of the failure. Low voltage machines will actually run burnt out for quite a long time but with moisture and high voltage you are relying on the integrity of the wire coating and any failure there means the start of trouble.


Flux

« Last Edit: December 03, 2009, 12:50:58 AM by Flux »

Flux

  • Super Hero Member Plus
  • *******
  • Posts: 6275
Re: Yet another Stator Failure.
« Reply #17 on: December 03, 2009, 12:54:19 AM »
This may be an issue but from his description of early cut in and running up to 300v I suspect the was holding the speed up reasonably well.


It is certainly an issue that needs checking,the volts should track wind speed fairly closely if the programme is near enough. Holding it stalled will cause the same problems as battery charging.


Flux

« Last Edit: December 03, 2009, 12:54:19 AM by Flux »

Junkie

  • Jr. Member
  • **
  • Posts: 84
  • Country: 00
    • Scraptopower.co.uk
Re: Yet another Stator Failure.
« Reply #18 on: December 03, 2009, 05:32:55 AM »
Looks like you could get a bit more copper in there on the next model. I would try more turns of a thicker wire.
« Last Edit: December 03, 2009, 05:32:55 AM by Junkie »

Herr Snefl

  • Newbie
  • *
  • Posts: 7
Re: Yet another Stator Failure.
« Reply #19 on: December 03, 2009, 02:05:42 PM »
Wow, what a lot of replies! Thanks everyone.


Where to start? I'd not considered water ingress. That may well be the crux of it. I'm in a dry area but we have had a wet spell.


The paint confused some people. That was an after-thought. I slapped it on after assembling everything. Makes it look a bit nicer against the sky.


People have asked about the inverter power curve. The WindyBoy-1700 doesn't really have a power curve (except perhaps in the mathematical sense). Just a straight line. You can set the 0 and 1700W voltages, that's it. It seems you can't even set the 1700W point to be above 400v should you have a small turbine (despite what the manual says!)


I think part of my problem is that the inverter cuts in at about 200v and rises to a bit over 300v at peak power, never actually reaches the 400v limit because the inverter is over-dimensioned. So though it's doing a form of MPPT there's probably only a 60% or so voltage tracking range. Probably not all that much more than a lead acid battery!


Someone mentioned the Aurora inverter. They look fantastic on paper. I considered buying one but they seemed to cost about twice as much as the WindyBoy here in the UK.


I've taken on board all those tips about stator winding. Using all the available space, thicker wire, slightly fewer turns, no superglue and a high temperature resin seems to be the way to go.


I was intrigued about the recommendation of one stator mount per coil. That seems extreme. Surely all the force on the mounts is in the direction of rotation? There can't be much incentive for the stator to buckle under load, can there? I've hit the emergency stop switch a few times without anything breaking. The turbine is made from BMW brake discs on a Volkswagon hub. It wasn't too easy to find three good stator mounting points.


Some people have hinted the tail is a bit heavy. Actually this is the mark-II tail. The first tail didn't seem to provide enough torque to keep the rotor facing the wind. I added tail area and inevitably a fair bit of weight in order to support it. I'm not convinced the the rotor was running square to the wind even with the larger tail. I've been intending to add a streamer to check. Despite the weight the tail does end up vertical in a strong enough wind. Its just that the rotor angle to the wind doesn't seem to change much as it furls!


Flux, I'm amazed you failed to stick your fingers together with superglue. I glued mine together nicely winding the coils. That scared me a little so I tried gloves. I punctured the glove and got the glove stuck to my hand. Maybe I'm just accident prone?


Neil (aka Snefl).

« Last Edit: December 03, 2009, 02:05:42 PM by Herr Snefl »

Flux

  • Super Hero Member Plus
  • *******
  • Posts: 6275
Re: Yet another Stator Failure.
« Reply #20 on: December 04, 2009, 06:47:06 AM »
If you are in the uk then I agree that your cut in is too low, you need to run the windy boy up to near maximum volts on full load. I thought you might be working at 110v.


The big snag is that the higher the volts the more you need to worry during synchronising but reducing the turns would help this issue as well.


All these machine suffer from not facing the wind below furling. An error of up to 30deg doesn't matter but more than that does start to be an issue. I prefer to set the tail well away from straight back and away from the furling direction. It looks a bit silly but it does no harm. You probably need it set away by at least 30 deg if you don't want a monster tail. It's very hard to increase tail area much without too much weight.


I also prefer a longer boom rather than just increasing the vane area, it helps damp the wagging in turbulent winds.


For grid tie there is little real energy below 9mph so if you cut in below that you probably have too many turns.


It seems as though you are well on the way, just keep going the next stator will probably be fine.


I am not as paranoid about the stator mounting as many others but if you use short circuit braking often then there are many forces on the stator, some in directions you don't expect, but twisting of the stator mounting studs is the biggest worry.


Flux

« Last Edit: December 04, 2009, 06:47:06 AM by Flux »

Jon Miller

  • Sr. Member
  • ****
  • Posts: 316
  • Country: gb
    • Otherpower UK
Re: Yet another Stator Failure.
« Reply #21 on: December 04, 2009, 10:12:10 AM »
Hi Neil,


Where abouts in the UK are you?


Do you have some pictures of the inverter set up?


What device do you have to stop over voltage?


Jonathan


Cornwall

« Last Edit: December 04, 2009, 10:12:10 AM by Jon Miller »


imsmooth

  • Sr. Member
  • ****
  • Posts: 425
Re: Yet another Stator Failure.
« Reply #22 on: December 04, 2009, 08:17:43 PM »
The solution to superglue is having Acetone.  If you get the Superglue on you immediately pour some Acetone on the area and/or rub it with a soaked cloth.  The glue will disolve.  It works much better if you don't let the glue cure.


Also, Acetone will disolve vinyl gloves.

« Last Edit: December 04, 2009, 08:17:43 PM by imsmooth »

Herr Snefl

  • Newbie
  • *
  • Posts: 7
Re: Yet another Stator Failure.
« Reply #23 on: December 05, 2009, 09:50:58 AM »
Hi Jon,


I'm the other side of the country to you, on the prairies of East Anglia. Wind speed is pretty mediocre here but at least there aren't too many obstructions.


You're the first person to ask about over-voltage. That surprises me since it strikes me as one of the biggest problems to solve for a grid connect system. The WindyBoys take forever to boot, test their environment and sync up. During that time the turbine is potentially unloaded and picking up revs/voltage. Plus you can't rely on the inverter being there. We had strong winds a few months ago and the grid went off, a tree on the line I suppose. Grid connect inverters have anti-islanding and will disconnect as soon as the mains goes away.


The simple way to protect the inverter seems to be with a thyristor and a dump load. Trouble is thyristors once triggered conduct until the current drops back to zero. This means the turbine will be brought to a complete standstill and probably not released until a lull in the wind. Fine for emergency protection but not so good should it cut in whilst the inverter is trying to sync...


My solution is a crude pulse-width-modulation controller to load up the turbine should the voltage get too high. See piccies:








The top-left connector goes to the dump load (heater) hung below. The middle connector is the rectified DC in from the turbine. The right hand connector goes to the WindyBoy.


The top-left circuit board is the simple thyristor emergency cut-out. The big golden resistor gets quite toasty when it trips. The bottom board contains a DsPIC micro-controller. These are rather nifty since they have built in analogue-digital converters and PWM controllers. The DsPIC runs a very simple program which monitors the turbine output voltage and ramps the PWM output from 0% at 350v to 100% at 400v. Finally the top right board contains two big MOSFETs and a driver chip. The lefthand FET is driven by the PWM output of the PIC and connects the heater to the turbine. (Note the diode across the the heater socket - the heater is quite inductive.) The right-hand FET sits in the return path from the inverter. This FET is driven by a watchdog circuit. The idea is that if the processor crashes or the power fails the inverter is disconnected. Unfortunately this FET seems prone to failing and going short-circuit, leaving the windy-boy permanently connected. Something I need to get to the bottom of.


Sorry, I do go on a bit once I get started on my favorite subject :-)


Neil.

« Last Edit: December 05, 2009, 09:50:58 AM by Herr Snefl »

Jon Miller

  • Sr. Member
  • ****
  • Posts: 316
  • Country: gb
    • Otherpower UK
Re: Yet another Stator Failure.
« Reply #24 on: December 06, 2009, 03:27:33 AM »
Hi Neil,


do you have an email address, or can you drop me an email on the address above ^^^^


Thanks

« Last Edit: December 06, 2009, 03:27:33 AM by Jon Miller »