Author Topic: Reducing power in high winds  (Read 8462 times)

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frackers

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Reducing power in high winds
« on: September 10, 2014, 07:51:00 PM »
Greetings all

I've been flying my 3m Piggott mill for 6 1/2 years and apart from jumping off the yaw bearing once (taking out the blades and bending the tower) its been pretty reliable but the stator, which is a 24v standard Otherpower one,  is getting a bit scorched.

What I'd like to do is keep it quiet, maintain the output up to 30km/hr winds but stop the peaks that occur with gusts taking it up to over 400rpm and heading the other side of 2kw. Should I be:
  • Shortening the blades
  • Make new blades with a different profile
  • Smaller tail fin
  • Other changes to the furling geometry

When furling, the tail is pretty much parallel to the plane of the blades, but the whole mill doesn't really turn out of the wind much - its more the tail coming round!! I've made the tail as light as I can without compromising the strength and it is furling, just not limiting the power :(

Cheers
Robin Down Under (Or Are You Up Over)

gww

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Re: Reducing power in high winds
« Reply #1 on: September 10, 2014, 08:53:36 PM »
Interesting post, can't wait to see the outcome.
Good luck
gww

ChrisOlson

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Re: Reducing power in high winds
« Reply #2 on: September 10, 2014, 11:48:00 PM »
Those generator designs are flawed from the word "go".  A 3 meter turbine should be able to produce 2 kW continuous without overheat, and those things don't even come close.

You're not getting enough reactance in the core so the generator self-limits to fit the capability of the winding, and they don't have good enough cooling.  You need to get the voltage up and the amperage down to reduce the watts/cm2 that the stator is dissipating.  Or reduce the flux in the core.  The weaker the flux and the faster you spin it, the more reactance you'll get, so the rpm/volt increases as output increases instead of being a flat rpm/volt curve.

You can get rid of the big round magnets and replace them with 2 x 1 x 1/2" N42's.  That will help.  Or you can open the air gap some.  Reducing core flux will increase rpm's and improve furling reliability, as at 400 rpm you're only running TSR 5 @ 12 m/s.  I run my 3.5 meter turbines at 500 rpm @ 3 kW output, just to give you an idea.  500-550 rpm is no problem for a 3.0 meter rotor.  At 550 rpm you're at TSR 7.0 @ 12 m/s, which is about ideal to develop maximum thrust for good furling reliability.

You can also add some resistance in the 3-phase line and dissipate some of the power there instead of in the stator.  The resistance will have the effect of increasing voltage at the stator (and also rpm's), and reducing amp output.

Flux

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Re: Reducing power in high winds
« Reply #3 on: September 11, 2014, 04:16:20 AM »
Shortening the blades will work but will reduce the low wind performance, which you say you don't want to do.

New blades are an uncertain option, any form of high lift profile will make things worse. A profile designed for stall limiting may work in theory but in real life it is a gamble that probably won't work out. May be possible with lots of experiment but not a simple one off fix.

My feeling is that a smaller tail fin could easily make it worse, in fact you describe the characteristic of wind seeking and the tail won't have much control. Probably not easy but increasing the alternator offset is likely to be the only useful furling mod.

Altering the alternator characteristic as Chris suggested would most likely increase the prop thrust and you may get it furling properly, this will come with an increase in speed and noise, which again you didn't seem to want.

If you add a resistor in the line the immediate effect could easily be not what you want, it may increase the current. You have to add enough that the current falls otherwise stator heating won't be helped. Try it and see if it kicks the furling in, in which case it will do what you want. If you get it to furl properly the current will fall as it furls ( or in the perfect world, stay constant) and the prop will turn from the wind. If the tail turns to the prop and current keeps rising it is not furling.

The best but expensive option is to fit a Midnite Classic mppt controller and have 3 times the output with less stator heating.

Flux

Smithson

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Re: Reducing power in high winds
« Reply #4 on: September 11, 2014, 08:12:33 AM »
Hi:  If it is a "standard Otherpower stator" that is a big problem from the "get go".   A 3m stator from Otherpower is made from 1 strand of 14awg wire.   On the other hand the Piggott design calls for 2 strands of 15awg wire.  A 14awg wire is going to heat up faster than a 12awg wire (two 15awg wires in parallel).  No wonder there was a problem with their stator heating up.  I don't know how your stator is wound but the Otherpower stator is suspect.     Arch

ChrisOlson

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Re: Reducing power in high winds
« Reply #5 on: September 11, 2014, 08:49:05 AM »
The problem with both of them, and why they won't sustain more than 1 kW output, which is less than 50% of what the blades can do, is the fact that they are 12 pole 9 coil generators.  The stator has nine hot spots and the coils are insulated in plastic that does not transfer heat.  So the nine individual hot spots keep getting hotter until it finally melts down.

It's kind of counter-intuitive, but cramming more copper in those stators with the coils as close together as possible yields a generator that cools better.  The Otherpower stators I've seen are mostly plastic with a few coils scattered around their circumference.  What you want for proper cooling (and more power) is the exact opposite - more copper and less plastic.

Smithson

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Re: Reducing power in high winds
« Reply #6 on: September 11, 2014, 09:31:10 AM »
Yes, and what I forgot to mention, the otherpower plans call for 6 lbs of copper vs 12 for Hugh's.  I was thinking the price of the Midnite Classic was coming down.  Arch

ChrisOlson

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Re: Reducing power in high winds
« Reply #7 on: September 11, 2014, 09:55:53 AM »
Yes, and what I forgot to mention, the otherpower plans call for 6 lbs of copper vs 12 for Hugh's.  I was thinking the price of the Midnite Classic was coming down.  Arch

MidNite has a less expensive version of the Classic 150 called the "Lite" for quite awhile.  It is the ideal solution in the long term, however a 12 pole generator is not ideal with it.  16 is better.  20 is better yet.  This is a stator for a 20 pole for my 3.5 meter turbines.  There's no room for more copper in it and it will produce 2.7 kW continuous on a 24V system driven by a 3.5 meter rotor, without burnout.  It'll do 3.0 kW continuous on a 48V system.  It is only a 331mm diameter generator:





It must be realized that the homebrew designs in the books were derived for ease of construction, not maximum performance and durability.  You can almost build two of the 12 pole 9 coilers for what one of these 20 polers costs to build.  But in the end you WILL be building 2 of the 12 polers after the first one burns out, because they don't stand up beyond 1 kW continuous output.

frackers

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Re: Reducing power in high winds
« Reply #8 on: September 11, 2014, 07:20:07 PM »
Had a good hard look and listen yesterday afternoon in a decent wind and it looks like the yaw bearing needs attention. Its sticking by the looks of it, either dried grease or none at all (its time for its annual service anyway).

We're now into typical spring weather (changes from minute to minute) but if I get the chance I'll drop the mill over the weekend and give it a going over. A picture or two of the stator may help the conversation ;D

I'm running 2x1x.5 N42 magnets on 300x8mm plates - I'll have to see if I can liberate some of the 1.5mm wire I saw a while back and wind my own 2-in-hand stator, maybe a bit thicker to increase the effective gap and see how that goes...

Thanks for the input from everyone.
Robin Down Under (Or Are You Up Over)

gww

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Re: Reducing power in high winds
« Reply #9 on: September 12, 2014, 04:50:53 PM »
Chris
Is that a direct drive turbine you are building with that stator and when you say 24 volt or 48 volt are you talking of these when using a classic lite controller.  Also is my convertion correct and the rotors are about 13 inches.  I wan't to build a bigger turbine using about 40 mags 2"x1"x.5" for battery charging direct connect and simple as I am not the greatest welder or fabricator.  I was looking at hughs 12' or 14' plans.
Thanks
gww.

PS  I don't want the classic light cause I don't get enough wind to make up for the tare losses, I just think that turbines are fun to look at and bigger may be more fun.

ChrisOlson

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Re: Reducing power in high winds
« Reply #10 on: September 12, 2014, 09:03:02 PM »
gww - yes it is a direct-drive machine:
http://dairylandwindpower.us/projects/Direct-Drive_3.2meter_MPPT/index.html

It runs at 140V and was designed specifically for use with the MidNite Classic 150 controller.  For direct hooked applications not using a MPPT controller the stator has to be wired in delta configuration, and will only work on a 48V battery system.  Alternatively,  without MPPT, I recommend the use of a three-phase step-down transformer ahead of the rectifier.  This is the method used by the Bergey Excel-R so the turbine can run at more efficient voltages with less losses in your transmission cables.  A 2:1 stepdown transformer works nicely with the stator wired wye on a 48V battery.  Using the transformer provides much higher efficiency than direct-hooked with a delta stator because it cuts the amps in half coming from the turbine.

gww

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Re: Reducing power in high winds
« Reply #11 on: September 13, 2014, 12:53:37 AM »
Chris
I have hughs book.  I am not building now and may never get to it.  I don't know if you remember, But before I bought my batteries, I posted here and during that for about three days you responded to my post and during that, dense as I am, I finally understood some about hot water heating opertunity load, which I use now. I don't understand the transformer thing.  With hughs book I can figure the delta/wye thing.  If I ever get serious, do you mind if I pm you as I am sure this thread will get lost and the search engine never really works for me on this site.  For example I was trying to look up lattice tower raising.  I know you built a lattic tower but no matter how I typed in I got nothing on the search.  I can't spell and that could be part of the problim.  Any way, Maby a pm coming your way sometime in the future?
Thanks
gww

ChrisOlson

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Re: Reducing power in high winds
« Reply #12 on: September 13, 2014, 09:35:35 AM »
I hardly ever get time to look at those PM things.  If you bookmark the link to our website and navigate thru the links there you'll eventually get back to the homepage and you can find the Contact link and call me if you decide to build a turbine at some point.  I'm usually busy or working around noisy equipment so don't always answer my phone right away either.  But if you leave a message on it I'll call you back.  It's way easier to explain all the details talking direct on the phone than it is to email.  The links and my contact info is also on Hugh's website and quite a few folks in Europe have built that high voltage turbine.  So you can find it there too.

I recently built and tested a smaller 2.6 meter version of it with a Morningstar TS-MPPT60-150 too if you don't want to tackle a large turbine.  The TriStar MPPT's also have programmable wind curve capability now and Hugh and I sorted out the details of it with Douglas Grubbs at Morningstar.  So that's another option if you want to build a turbine that is smaller and more economical to build.  A 3 kW 3.5 meter puts as much loading stresses on the tower as the 17 and 20 foot homebrew designs that used to be popular on this site and they are quite expensive to build because of the tower requirement.  So that's why I designed the 260 for folks who don't have $8-10,000 laying around to build a 350.

gww

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Re: Reducing power in high winds
« Reply #13 on: September 13, 2014, 12:25:42 PM »
Chris
Sounds good.  I may never follow through or may just build hughs out of the book.  If I call you and it is a bother, don't be shy in saying so, I'm a big boy and smart enough to reconize that most poeples lives are quite busy without extras.  That's also the reason I may never get to building again, but I might also.
Thanks
gww

frackers

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Re: Reducing power in high winds
« Reply #14 on: September 14, 2014, 07:08:23 PM »
Status update

I've dropped the mill and removed the genny ready for a stripdown. No pictures yet (its mostly the state of the stator that I'm interested in and it doesn't look as bad as I remembered) but I'll get to that in a couple of days.

Immediate issues of note are that the thrust yaw bearing was dry (its a delrin/fibreglass composite on the mast running against a flat steel face on the genny) and the lower bush yaw bearing grease had the consistency of cold porridge:( The other problem was that the 3 phase cable was wound up really tight down the mast (unless its caught up on something part way up the pipe). Must have had a lot of depressions going past the south of the island recently - causes the wind to direction to change consistently anticlockwise!! The grease in the furling bearing was pretty sticky as well. Looks like there may have been a lot of dust blowing about recently (or maybe grease+pollen = sticky).

Cleaning everything up is in order, split the genny and check the bearings in the hub (they are still original and clocked over 1.5MW-hrs so far!) and get new grease into everything.

Cheers...

Robin Down Under (Or Are You Up Over)

gww

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Re: Reducing power in high winds
« Reply #15 on: September 14, 2014, 08:11:57 PM »
How long since you last had it down?  If it's just the geases (elbo and axil) don't sound bad.
gww

frackers

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Re: Reducing power in high winds
« Reply #16 on: September 21, 2014, 07:33:53 AM »
Split the genny down and the stator looks to be wound 2 in hand which explains the lack of scorching. Can't get to any of the wires to see what gauge it is. The black on the back is due to some scuffing 3-4 years ago and is the Hammerite paint from the magnets transferred to the stator.

8385-0

The black on the front of the stator is due to the black tape binding the coils bleeding through the resin.

8386-1

The bearing surfaces are starting to break up although the rollers are OK, not really pitting but on the way out. They have lasted over six and a half years, generated over 3MWh of power so new ones it is.

The coating on the magnets is also on the way out so I've cleaned off the rust with phosphoric acid and sprayed with a high zinc primer.

More cleaning to be done and rust to be scrapped off the body of the genny, this time it will be the zinc paint rather than Hammerite!

Cheers
Robin Down Under (Or Are You Up Over)

gww

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Re: Reducing power in high winds
« Reply #17 on: September 21, 2014, 01:53:31 PM »
Thanks for the pictures and the update.
gww

Smithson

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Re: Reducing power in high winds
« Reply #18 on: September 21, 2014, 07:19:52 PM »
Hi:  If you want to reduce power in high winds and gusts why not hook up a 1:1 gear ratio?  Install one gear at the top of the yaw pivot and the other gear at the top of the tail pivot.  I haven't figured out how to insert a hand drawing or I would show what I mean.

The big selling point of the Otherpower Turbine is that they produce full power while furling.  That is good with mppt but if you have battery charging usually the batteries are already full in high winds.

The feathering governors on early machines reached a set rpm (maybe 300 rpm) and stayed there producing no more power.  They did this by turning the blades so that the leading edge faced the wind and the trailing edge moved downstream from the wind.

If you set the side facing turbine to furl with the leading edge facing the wind (change the blade rotation one way or another) you could reduce the power in high winds along with the gear arrangement on both the turbine yaw and the tail pivot.

An advantage is that if the blades pivot 10 degrees then the tail pivots 10 degrees.  No wind seeking.  No false furling.  It could also save the stator from overheating.  When the wind died down the tail would fall to its original position and drag the blades back.

I think it could be done but hard to explain.   Wild idea.    My original idea was to attach a steel plate (rectangle) to the back of the yaw.  On the long legs of the rectangle build hinges for the tail and the propeller.  The center of the propeller pivot ( on the rectangle long leg) and where the spindle comes back would be the offset.  Have your gears at the top of the hinges.  I haven't thought out how close the blades and tail would come to each other.  It would work fine if you didn't need the full 20 degrees for the tail hinge.  Just angle the rectangle to where you want.    The propeller pivot would also be angled.   Arch

Smithson

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Re: Reducing power in high winds
« Reply #19 on: September 21, 2014, 09:16:39 PM »
After thinking it through I realize you do not want a pivot on the turbine side of the rectangle.  That would cause the blades to crash into the tail.  Only have the pivot on the tail side.  You would still need the gear at the top of the centerline of the propellor shaft side, but fixed in place.  Just fix the propellor shaft in place perpendicular to the steel rectangle.  And set your offset.  As the wind pushes the prop to one side the gear on to, although fixed, would shove against the tail pivot gear and move it reducing power etc.  On the other side of the rectangle you have to slant the tail pivot for your hinge.   Arch
My thinking is not as clear as it used to be.

electronbaby

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Re: Reducing power in high winds
« Reply #20 on: November 24, 2014, 07:05:10 PM »
if you want to reduce power in higher winds, there are two choices,... or a combination of the two.

1) lower feedline resistance in higher wind to stall blades more when you want to.

2) make sure your side furling is working properly (it seems like it isnt if you arent seeing decreased output, and rotor still runs into the wind).

to fix the furling issue, you may want to add length to the tail boom/fin to effectively get it out of the wash from behind the spinning rotor. try adding length, but it would work better if you can add length and height, as to allow the tail to remain higher than the rotor sweep most of the time. Simply put, you need more, -less disturbed air- to make it to your tail.

the feedline resistance issue can be solved with relays if you want to try that (and you have an inverter or CC with aux contacts). if you slow the rotor down in higher winds, your furling will work better. everything is a trade off.

Personally, Id try decreasing resistance in higher wind and seeing how it responds (because that stuff is easy to do on the ground without tilting the tower down). after you get a handle on how that works, you can try playing with tail boom length.

RoyR

Have Fun!!!  RoyR KB2UHF

just-doug

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Re: Reducing power in high winds
« Reply #21 on: November 25, 2014, 11:32:42 PM »
a longer tail will aid tracking in shifting winds.it will act heavyer, so a reduction in tail hinge angle,more straight up, will help  lower the furly speed.increasing the offset will lower the furly point also.

electronbaby

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Re: Reducing power in high winds
« Reply #22 on: November 26, 2014, 01:10:15 PM »
well, you are correct. I did not say anything about changing the weight. The tail weight should remain unchanged, but tail should be made longer, or taller preferably.  with a short tail and a rotor that is operating at a higher TSR, there is a lack of interaction from the oncoming wind, to the tail. A good portion of oncoming wind will cone around the rotor and quite possibly pull the rotor back into the wind without the tail doing much of anything (seeking force as most call it) - while the tail vane is in the wake of this. You either have to slow the rotor down (electrical loading induced stall) or at the very least allow the tail to track properly so that it can do its job.   More alternator offset, and a decrease in the tail pivot angle would work also, but I suggested trying one thing at a time. He seemed happy with the performance of the machine, just that he wanted to furl a little bit earlier in higher winds. Having a longer tail (same weight as to not change more than one variable at a time) will always give you a stable reference point as to base further experimentation on, at low to high TSR alike.

RoyR
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electronbaby

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Re: Reducing power in high winds
« Reply #23 on: November 26, 2014, 01:22:25 PM »
"When furling, the tail is pretty much parallel to the plane of the blades, but the whole mill doesn't really turn out of the wind much - its more the tail coming round!! I've made the tail as light as I can without compromising the strength and it is furling, just not limiting the power :("

This is what made me think that the tail boom was too short and getting caught up in the wake of the blades operating at a higher RPM.  A longer tail will keep the tail boom facing down wind while the machine is folded up. Slowing the blades down a tad bit wouldnt hurt either (in higher wind only as to not hurt low wind performance). I suspect that experimentation could be focused in these two areas as the resistance of the feed line can be lowered easily without having to take the machine and tower down just yet.


RoyR
Have Fun!!!  RoyR KB2UHF

frackers

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Re: Reducing power in high winds
« Reply #24 on: November 26, 2014, 03:34:42 PM »
Well, I've finished the maintenance on the mill and run it for a couple of weeks and I'm seeing a lot of improvement.

The changes have come from the following areas:
  • Greased up the yaw bearing and unwound the cable drop so it can swing much much more easily
  • A couple of knot holes in the blades that had been blown by the frost drilled out and filled, another couple of coats of paint on the blades
  • Adjusted the 'preload' on the tail so it goes into furl earlier - now happens at about 800w (where it should be!!)

Item (1) has made the biggest difference, the grease was old and stiff and the yaw was almost locked up due to cable tightness. Item (2) has made it much quieter and item (3) made it safer!

I'm still switching the mill off regularly (shorted to stall) as we are having a very windy spring with winds regularly gusting over 120kph - I shut it down when they go over half that.

Provided the weather calms down a bit, I'll keep it up otherwise it will be for sale - too much hassle compared to solar ;)

Robin Down Under (Or Are You Up Over)

DamonHD

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Re: Reducing power in high winds
« Reply #25 on: November 26, 2014, 04:55:34 PM »
Provided the weather calms down a bit, I'll keep it up otherwise it will be for sale - too much hassle compared to solar ;)

Much as I am a solar man myself by necessity, given where we are this saddens me a little...

Rgds

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kitestrings

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Re: Reducing power in high winds
« Reply #26 on: November 27, 2014, 10:13:45 AM »
frackers,

Glad to hear you've gotten to a workable solution.  Wind can definitely be more challenging, particularly the long-term maintenance.  Still on a good site it can do a lot - at night, winter, and when solar gives little benefit.  It is the perfect compliment to solar in many cases.

Regarding your original question, while getting the furling right is important - for survival if nothing more - with this size turbine, I'd be inclined to have ample load available to keep it clamed.  It's pretty doable.  If you can find a use for the surplus, even better.

Regards, ~ks

MattM

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Re: Reducing power in high winds
« Reply #27 on: November 28, 2014, 02:47:38 AM »
Windmills are the HotRods of the RE world.  Live a little my man.