Need more load on dumpload

[rickysmartz]

Hi,
Im having some issues with my dumpload not quite taming my 18 footer grid tied 3 phase axial flux machine, design very much like the Dans machine.
Some info-
18 ft
Wound for high voltage /low amperage, inverter set to come on at 70v
individual phase resistance is 6.69ohms so dumpload resistance is sized to 16ohms overall
Aurora inverter
200v at full power around 5000W, inverter will take 580V so plenty of safety margin. Aurora 'wind box' rectifier in place for extra protection but I dont use the crowbar facility.
Omron voltage sensing relay to kick in dumpload if over 300v~, dumpload comes on in PARALLEL with inverter and is timed to stay on until the V drops to 240v-ish.
Dumpload activation relay is 3 phase heavy duty Sneider and is normally closed so default is dumpload on (safer).
Dumpload is commercial 9KW 3 phase nichrome unit, never gets too warm to touch casing.
 
Problem- dumpload does eventually slow the mill to safe speeds after over speed but this happens way too slowly in my opinion, taking about 30 secs to 1 minute. I would expect a much more immediate and dramatic slowing down (it would certainly be better for my nerves). I have seen in high winds the turbine speeding up even when the dumpload is active so Im thinking my load is not quite sufficient at 16ohms. To increase the load should I order another dumpload and reduce the resistance of it to, say, 8ohms? Or should I be looking at 4ohms? Im not sure HOW MUCH a change in resistance will affect the control and how much more load I will need to tame the beast properly. Has anyone had this experience and can they shed light quantitively on how much change in resistance affects performance of a turbine?
Thanks again guys
Richard

[ghurd]

Interesting.

The inverter is making max power output at 200V input?  So there is no reason to go past 200V?
As the wind speed increases, the inverter is making no more load on the turbine.  Then the voltage increases, because the blade speed increases from a lower load:input.

Might try setting it to kick in at say 240V?  Drop out at 190V?  (maybe that's not a great ratio... I don't know)
Start taming it before it gets so far out of hand.


Slowing it down 'too fast' is hard on everything, physically and electrically.

There is a quantity of Watts to deal with.
If the parallel dump load resistance is 'too low', the amps increase 'too much'.  That puts a lot of heat in the stator at a time when it is already warm.

If the parallel dump load resistance is 'too low', it is almost like shorting the PMA.
Since it is automatically kicking in at high winds, that happens at the worst possible time.

In iron core machines, if the parallel dump load resistance is 'too low', and added during high winds, it can run away.
Not sure that is as common with dual rotor air cores.


"HOW MUCH"?   Not Much!
It is taming it, just slower than you think you want it to be tamed.
I certainly would not drastically reduce the load resistance all at one time.
Going from 16 to 14 would be about the biggest single step I would want to try.

G-

[Flux]

If your dump load is in parallel with the inverter and still only just holds things then I wonder if it would hold it without the inverter.

You don't say whether your load is star or delta and I assume the 200v is alternator line volts.

I agree that it would be nice for the dump to hold the speed back fairly instantly. I also assume you have some other back up such as furling and the characteristics of that will have an effect.

If your present load is star then you could try it delta, otherwise it is a bit of an experiment and I would cobble something up out of heating elements or something to find out how much more you need. When you have it sorted then is the time to buy a nice commercial load, not a lot of good guessing and buying something that is not suitable.

Flux

[jarrod9155]

My  turbine setup is almost the same minus I have 20 foot goe222 .what I have found with the aurora inverter over the last year is when a gust comes along the inverter sinces the increase in amps /volts ramps up the mppt curve but not quick enough . On the top end above 20 mph winds I would think you would be approaching 200volts dc  , add more power to the curve the resistance in the stator will absorb the heat and around 220 volts activate the omron  relay and set it to release around half the set voltage say 120 volts dc . What this will do is bring the blades tsr down and close to stall so the dump load is not being turned on when this turbine is starting  to run away ,and the aurora will let it runaway to exstint . The other thing you should try , is to let this turbine run off just the dump load and make sure it's furling at a safe rpm. You never know when the grid will fall out and the inverter go off line. Had it happen even a ground fault will do this .  I know this doesn't answer your question on resistance but with others input  this should help dial it in
   What guage wire and turns plus how many coils ?

[rickysmartz]

Thanks for your input fellas, I'll respond in order-
Ghurd,
The inverter starts with a modest load at 70v (cut in) and progressively increases the load as the voltage rises, same as all MPPT I reckon. Powerone states the most efficiency is attained when 200v is reached at full output so I wound my coils for this (12 coils, 0.95dia 3 in hand, 495grams per coil). It will put out 2500W with a voltage of about 140 and will be full whack at 180 to 200v (5/6Kw but Ive seen 6.5Kw briefly). Ive been having some ground faults which are shutting down the inverter and this is when I noticed it was a little scary in higher winds and why I think I may need a higher load in this condition. The inverter is well capable of taming the machine with its loading method and seems to react pretty quickly in a big gust; but this, of course, is when its behaving itself! Im interested in your comment "Going from 16 to 14 would be about the biggest single step I would want to try." That drop seems quite small- is this going to make enough of a difference?

Flux,
Its star configured and has a standard furling tail which works very well although I think its furling a bit early; when I get my power dashboard/davis anemometer system working I'll refine the furl and have a much better picture of the wind system as a whole. The 200v is DC into the inverter and leaves plenty of safety room before the inverter fries (which wont happen because the fuses in the wind box will blow first, protecting the expensive inverter). I designed the dumpload to come on in parallel with the inverter and stay on for a delay to keep the inverter in sell mode and ready for exporting when the spike was reduced. This seemed the most logical solution to a big gust when the system is already outputting full power and just needs a little control. Shutting the inverter off completely means it will have to go through its start up tests etc and waste good energy. As i said the dumpload keeps the machine under control when its started from stop, its the grid fail/ground fault at high speed that seems to stretch the capability of the DL. Unfortunately Ive already purchased and fitted a commercial Dumpload @ 16ohms, which is what was calculated would be the right value (with some help from the supplier).

Jarrod,
Thats great someone is out there, on grid, with a similar machine. The ramping speed is an adjustable setting and mine works good at 5000w per second, much higher than the default setting and probably plenty quick enough for a gust. have you tried adjusting this? 12 coils, 89 turns 0.95dia 3 in hand, 495grams per coil but you have a couple of extra feet on my rotor so the maths/voltages will be a bit different from mine.

"...On the top end above 20 mph winds I would think you would be approaching 200volts dc "
No, I dont hit 200v til much higher wind speeds (maybe 33MPH), my rig starts to furl at 35MPH and is fully furled by 55MPH- I cant confirm this yet without any hub height wind measurements but thats what I reckon and these figures seem to be acceptable according to 'those who know' on this forum.
"...add more power to the curve the resistance in the stator will absorb the heat and around 220 volts activate the omron  relay and set it to release around half the set voltage say 120 volts dc ."
I set it for 300v so it really only kicks in at all in a serious and very rapid gust or in a gridfail/ground fault situation. As stated earlier your rig is a bit bigger so again different readings.
 ..."What this will do is bring the blades tsr down and close to stall so the dump load is not being turned on when this turbine is starting  to run away ,and the aurora will let it runaway to exstint"
Not sure what you mean here; Yes the dumpload will slow and stall the blades and hopefully deal with whatever event happened to create overvoltage, thats its job here. But what do you mean by the Aurora will LET it runaway (dont know what 'exstint' is either , is that a typo?)
I am very interested that you have also been experiencing ground faults. They are at present the bane of my life and are very difficult to sort out. Ive had a megger on site and it saw no problems with the turbine but after tearing the rest of the system asunder (changing the inverter, replacing the wind box with a standard rectifier, removing relays from the system etc) Im thinking it must be at the tower/turbine after all, very annoying and time wasting. I'll take it down again on Wed when the wind dies a bit and hopefully find the bugger. Can you shed any light? There is only one other possibility as follows; Italy work on a very high earth resistance value of 20Mohms and here in Ireland we work on 5Mohms- is it possible our grid is just too 'dirty'?? Id love some feedback on this also from you boys who are grid tied.
Thanks everyone
Richard

[rickysmartz]

Sorry, my reference above to Italy is because that is where the Powerone Auroras are manufactured.
R

[Flux]

If the dump load is star then you could try connecting it delta. It's a fairly drastic change and probably more than you would want long term but it would let you see how things behave with much more dump load.

Changing to delta would be effectively a reduction to 1/3 of the resistance. You may have to watch the rating but it will stay on for a much shorter period and I think it would be ok for a trial.

Flux

[Dave B]

Ricky,

  I do not have my machine grid tied but I have a few comments based on many years of realizing the potential of these machines. Your 18' machine if it is reasonably built is capable of 3500 - 7000 watts from 20-25 MPH winds. Look at this again, 3500 watts increase for 5 mph increase in windspeed !!!! It is not "if" but rather "it will" if not controlled. You are asking the inverter to over speed control your turbine above 25 mph, can you imagine where the curve is at say 33 MPH like you state ? Furling your machine at 35 MPH and not seeing it fully furled until 55 MPH I am sorry to say will be catostrophic. Talk with Jarrod in great depth if you can, nobody wants to limit the output of their machine but if you are not well on your way to slowing this down just above 20 MPH either with furling or proper load or both you are going to loose it. It will accelerate beyond control in a heartbeat, just look again at the curve. I hope you get the components of your system balanced out to work together. It's just my opinion but I think right now you are running way above the upper end of disaster. Be careful.  Dave B.

Thanks for your input fellas, I'll respond in order-
Ghurd,
The inverter starts with a modest load at 70v (cut in) and progressively increases the load as the voltage rises, same as all MPPT I reckon. Powerone states the most efficiency is attained when 200v is reached at full output so I wound my coils for this (12 coils, 0.95dia 3 in hand, 495grams per coil). It will put out 2500W with a voltage of about 140 and will be full whack at 180 to 200v (5/6Kw but Ive seen 6.5Kw briefly). Ive been having some ground faults which are shutting down the inverter and this is when I noticed it was a little scary in higher winds and why I think I may need a higher load in this condition. The inverter is well capable of taming the machine with its loading method and seems to react pretty quickly in a big gust; but this, of course, is when its behaving itself! Im interested in your comment "Going from 16 to 14 would be about the biggest single step I would want to try." That drop seems quite small- is this going to make enough of a difference?

Flux,
Its star configured and has a standard furling tail which works very well although I think its furling a bit early; when I get my power dashboard/davis anemometer system working I'll refine the furl and have a much better picture of the wind system as a whole. The 200v is DC into the inverter and leaves plenty of safety room before the inverter fries (which wont happen because the fuses in the wind box will blow first, protecting the expensive inverter). I designed the dumpload to come on in parallel with the inverter and stay on for a delay to keep the inverter in sell mode and ready for exporting when the spike was reduced. This seemed the most logical solution to a big gust when the system is already outputting full power and just needs a little control. Shutting the inverter off completely means it will have to go through its start up tests etc and waste good energy. As i said the dumpload keeps the machine under control when its started from stop, its the grid fail/ground fault at high speed that seems to stretch the capability of the DL. Unfortunately Ive already purchased and fitted a commercial Dumpload @ 16ohms, which is what was calculated would be the right value (with some help from the supplier).

Jarrod,
Thats great someone is out there, on grid, with a similar machine. The ramping speed is an adjustable setting and mine works good at 5000w per second, much higher than the default setting and probably plenty quick enough for a gust. have you tried adjusting this? 12 coils, 89 turns 0.95dia 3 in hand, 495grams per coil but you have a couple of extra feet on my rotor so the maths/voltages will be a bit different from mine.

"...On the top end above 20 mph winds I would think you would be approaching 200volts dc "
No, I dont hit 200v til much higher wind speeds (maybe 33MPH), my rig starts to furl at 35MPH and is fully furled by 55MPH- I cant confirm this yet without any hub height wind measurements but thats what I reckon and these figures seem to be acceptable according to 'those who know' on this forum.
"...add more power to the curve the resistance in the stator will absorb the heat and around 220 volts activate the omron  relay and set it to release around half the set voltage say 120 volts dc ."
I set it for 300v so it really only kicks in at all in a serious and very rapid gust or in a gridfail/ground fault situation. As stated earlier your rig is a bit bigger so again different readings.
 ..."What this will do is bring the blades tsr down and close to stall so the dump load is not being turned on when this turbine is starting  to run away ,and the aurora will let it runaway to exstint"
Not sure what you mean here; Yes the dumpload will slow and stall the blades and hopefully deal with whatever event happened to create overvoltage, thats its job here. But what do you mean by the Aurora will LET it runaway (dont know what 'exstint' is either , is that a typo?)
I am very interested that you have also been experiencing ground faults. They are at present the bane of my life and are very difficult to sort out. Ive had a megger on site and it saw no problems with the turbine but after tearing the rest of the system asunder (changing the inverter, replacing the wind box with a standard rectifier, removing relays from the system etc) Im thinking it must be at the tower/turbine after all, very annoying and time wasting. I'll take it down again on Wed when the wind dies a bit and hopefully find the bugger. Can you shed any light? There is only one other possibility as follows; Italy work on a very high earth resistance value of 20Mohms and here in Ireland we work on 5Mohms- is it possible our grid is just too 'dirty'?? Id love some feedback on this also from you boys who are grid tied.
Thanks everyone
Richard

[rossw]

The 200v is DC into the inverter and leaves plenty of safety room before the inverter fries (which wont happen because the fuses in the wind box will blow first, protecting the expensive inverter).

Ahhh, I see you've yet to meet my friend Mr Murphy.

Fuses rarely (if ever) blow first and protect equipment - especially expensive equipment!!

[jarrod9155]

12 coils 89 turns per coil you must really be spinning some fast rpms to get your volts up , what is your tsr on the blades and if you don't mind the mppt curve per wind speed . And for ground falts the biggest problem I had was if the magnets or rotors so much as just rub a little on the stator instant ground fault ,or  rain on some of your 3 phase leads leaking to ground  . I ran 18 foot blades before my current setup and the  higher winds over 50 mph would destroy the bearrings and allow that little play and cause the ground faults .With real quick math in my head I would think you are spinning this turbine a little to fast  , for instance I am 12 coils at 300 plus turns per coil to reach the higher voltage range . Now at 60 rpms at the rotor plates I see 60 volts dc output  , And the aurora doesn't start putting power out till over 60 volts dc .  As for how quick it ramps up I am set at 10000watts per second . And for safety try to get that machine to furl closer to 25 mph to 30 mph  . I have had some really scary moments but the machine furling  has been the one thing that has saved my a$& .

[fabricator]

Fuses are meant to stop fires in the wiring, not protect expensive electronics.

[rickysmartz]

Flux,
I cant change to Delta that I know of because I have no access to the centre of the star it being encased in resin at this stage. Maybe a mistake but too late now.

Fabricator,
Normally you are quite right but the Aurora wind box is specifically designed to protect the inverter and has lots of other circuitry in place to do so (or so they say). Its an expensive bit of kit ($450) which could instead have been a simple rectifier, much cheaper.  Im assured it will blow before the inverter is fried, this gives me some peace of mind that at least in the event of a catastrophe I may only have to replace the wind box and not the inverter.

rossw,
As MrMurphy is Irish Im well aquainted with him unfortunately. Ive tried to design the control circuitry so he doesn't know where I live and therefore cant visit : )

Jarrod,
TSR 6.5
Cut in 65rpm~
Max speed 260rpm
12 coils, 4 per phase, 16 neo48s custom wedge, 81 turns of .96mm dia, 3 in hand
open circuit voltage on 1 coil at 72rpm was 7.3v when testing (and I wound a lot of different variations , the 3 in hand was to squeeze a little more copper in), so help me with the math-
7.3 x 1.4 (peakv from RMS meter) x 4 (coils per phase) x 1.73 = 70.72vAC  rectify this to dc (x 1.33) = 94.06 minus a little for losses. Im thinking 1.1v per rpm ish.
I set my inverter to engage at 70v, math seem ok so far?
Lookup table -
70v -0W
80v -300w
91.33- 850w
144v- 2500w
192 -4200w
220v -5200w
250v -6000w
270v -6500w
300v - 6500w

Thanks for the tip on stator/magnet contact causing ground faults, I'll pursue this. My stator has exposed brass connection bolts but the whole machine is insulated from the tower by nylon bearings, I never liked the metal on metal set up commonly used by these homebrew designs. Cant think how a ground fault could occur here because of the nylon but could the brass bolts with rain cause a fault? The bolts are spaced 2.5inches apart  but maybe I should paint them with wax or insulate them with high voltage putty? What do you think?
My furling was based on observation and since my design has an adjustable tail pivot angle I can increase or decrease the angle and adjust the furl easily. I set it at 13.5 degrees and when I saw how quickly it furled I have set it now for 15.5 degrees and it seems to work good as long as there is a load providing thrust, hence the topic here and my need, i think, for an increased load on the dump. As I said earlier I have no hub height wind speed gauge yet, soon to come. I'll revisit furling windspeed then.

DaveB,
Thanks Dave for your warning which I will heed immediately. I was lead to believe start furl at 16m/s (35mph) and full furl at 25m/s (56mph) was the right configuration for these designs and this size. This comes from the Dans book and Hugh piggott and a few other eminent sources and Im not sure how I could have got it so wrong. Perhaps a start furl of 16MPH and full furl of 25MPH is what I should be aiming for and the MPH to m/s conversion got forgotton! Oops! Either way I have seen the turbine perform well and furl well so I cant be too far off in my configuration.
To get back on topic, how much should I reduce my dumpload resistance by to get a bit more control? Does a 50% reduction result in 50% more magnetic drag on the mill?
Cheers all
Richard

Richard

[ghurd]

Powerone states the most efficiency is attained when 200v is reached at full output so I wound my coils for this (12 coils, 0.95dia 3 in hand, 495grams per coil). It will put out 2500W with a voltage of about 140 and will be full whack at 180 to 200v (5/6Kw but Ive seen 6.5Kw briefly).

So there is NO reason to go past 200V?
Then why go past 200V?

The inverter is well capable of taming the machine with its loading method and seems to react pretty quickly in a big gust; but this, of course, is when its behaving itself! Im interested in your comment "Going from 16 to 14 would be about the biggest single step I would want to try." That drop seems quite small- is this going to make enough of a difference?

Will it make a difference?  IMHO, Yes.  Enought, I do not know.
The inverter is 'almost' keeping it controlled, and the additional dump load is 'almost' keeping it controlled.

It sounds like it is furling late, not early.
Not many people begin to furl at 35MPH (16m/s) and fully furl at 56MPH (25m/s).  That is getting uncomfortabbly close to hurricane wind speed energies.
Some people furl at 25MPH.  (25m/s vs 25MPH)   Maybe there is a translation issuue?

[jarrod9155]

Next time it's down try checking resistance from the pole to turbine to see if the nylon bushings are as insulated as you think . And if there aren't any tell tell marks of stator rub your good there , and then you might need a transformer on the output side of the inverter to isulate   the inverter from the grid if this is causing the ground fault .  As for exposed brass connections  on the stator , I haven't ran in to that with my current setup .

[rickysmartz]

Ghurd,
Yes, in normal operations there is no need to exceed 200v. In reality the voltage does sometimes go to 250 in a gust but the inverter then applies a little more load and it drops back to 200ish. The remaining margin (up to 600v) is the safety margin and is recommended by the inverter manufacturers, the rule of thumb being 1/3 for generation and 2/3 for safety. In a high wind full power grid fail situation one may get a spike of 350v before the dumpload (which comes on via a voltage sensing relay) tames the turbine. Ive never seen this situation YET which potentially could happen in a violent storm which is exactly when the grid is most likely to fail anyway.
When you say "Some people furl at 25MPH" do you mean that its reached full furl by then, or it starts to furl then?
Has anyone ever done any kind of testing with different dumpload resistance values and charted the results and the behaviour of the turbine?
How low a resistance would it have to be for the turbine to 'see' something like a dead short? Im trying to get some idea of proportion here.

Jarrod,
Good plan, Its at least 8mm of nylon at its thinnest insulation point so I expect complete insulation. Funny thing is the ground faults only started happening after 6 weeks, it got colder and wetter then. Its the only thing other than increased bearing wear that was different. Damn intermittent faults are sometimes so hard to trace!
I'm gonna paint tar onto the brass bolts at the stator and rewire the connection at the base of the tower to eliminate any dampness issues.
Isolating transformer is a great idea but expensive, Google search says 800 to 1000 Euro for a 6Kva unit! Wow!

Richard

[Flux]

Everything is a compromise with wind. In the perfect world your furling would hold power constant once you get beyond the range of the inverter. In real life even if you furl too early to the point where you are reducing power capture you will still get spikes that your dump load will probably have to catch.

It seems from your description as though your furling is fairly close.

Now the awkward bit, your inverter should be programmed to load as a cube law and the furling will behave differently from being loaded with resistance, which loads as a square law. There is no properly stable value of fixed load and if your dump just holds things as furling is starting to come into effect it may nor be enough to keep things under control and if it gets away and starts wind seeking you will loose control of it.

If you are mainly concerned with protecting against loss of the inverter then I would use a lot lower value of dump resistance so that the prop goes into stall and brings the speed way down.  This is not the best situation to use in the region where you are just trying to catch a few spikes from poor furling in the region where the inverter is loading properly.

It looks as though the best thing would be to keep things much as they are but have another dump resistor that comes in perhaps at 260v and has a lot lower resistance. This would look after the case where the inverter comes off line.

You still have a bit of a dilemma in that you have to either choose a load resistance that keeps the mill under control when fully furled and rely on furling to protect your stator or go for a very low load resistance that effectively acts as a stall brake and just lets the blades crawl slowly and rely on prop stall to keep your stator safe.

The braking mode is nasty mechanically  and it would be messy to do it in 2 stages but it should be safe. The 2 stage could be a fairly low Resistance that brings the speed down fairly quickly but without severe shock and the final stage could be a short for best brake effect without any danger of break away.

I don't have direct experience of machines of that size to give you the best advice. Much depends on whether a short circuit brake can stall your prop in any wind.

If you want to try keeping things running into the resistor and rely on furling for protection then I suspect about half the present resistor value may be a good starting point.

The snag is that any resistor will be too low for low winds and the machine will stall. Once it pulls through stall in high wind you will need enough load to hold it to a similar power level to the inverter at furling point. It will need to provide more load than the inverter at full load if it is going to have any chance of dealing with the inevitable high wind that will come one day.

I think I would go for the braking approach or accept that when off the inverter you need a fully developed cube law heating controller, loading into a fixed resistor is very much a compromise. Just as a fail safe scheme it's not worth the complexity of a proper heating controller, when things are out of control the best protection is shut down until the wind drops.

Flux

[nekit]

Richard,
Great to see another person with a similar setup as mine.  Now that their are several of us with 17-20' Axial Flux wind generators with Power one inverters we should be able to learn off of each other.  Mine is a 17' based off of the Dans design.  Mine is wound a little higher voltage than yours.  It's on a tower just under 100' in USA.  Here's a link to details of mine.  http://fieldlines.com/board/index.php/topic,144309.0.html

I made my tail angle adjustable too.  I would love to see a picture of how yours is setup.  I also added removable end sections of the tail that lead shot can be added to. Currently mine is furled at 25mph and starts furl about 15mph.

I set my dump load to switch for the inverter when it comes on.  I thought it might be safer for the inverter, but I'm sure it would transition between load and inverter if it was setup to leave the inverter on.  I also figured this way the load condition wouldn't be different if the grid was lost.  I'm still not sure which is best?

The only time I have had a ground fault problem with the inverter was when I first hooked it up.  One of the Delta brand lightning arrestors that I had hooked to the power leads at the tower was leaking across the terminals internally.  Replaced it and haven't had a problem over the past 6 months.

Would love to see you Aurora Power curve.  Mine is posted in the link above.

My dump load is 20.4ohms when measured between any two legs of the three phases.  I'm not sure how this compares to your system.  I've turned it on at 300VDC and it slows the turbine more than the inverter, but does not make it stop.  One nice thing about my dump is that I can wire the resistors differently to adjust the Ohm rating.

I'm not using the Power-one Wind Box rectifier.  I attempted to build a frequency generator to be able to hook to the inverter to see the frequency and rpm on the communicator software, but can't seem to get it to work correctly.  Are you using the frequency outputs on the Wind Box? 

The way the fuses in the Wind Box are suppose to work is that at around 550VDC it automatically shorts the legs together.  This is suppose to blow the fuses, but according Rob Becker of Solacity, just blows all the capacitors in the box.  Which I guess is better than blowing up the inverter.

I've been getting pretty good output out of mine.  Average low wind day I get 6-10kwh, windy days 25kwh, and my best day so far was 36kwh.  What are you seeing?

Would love to see more about your system.

Thanks,
Rob L

[rickysmartz]

Hi Rob,
Its really excellent to find a few people running similar machines grid tied as theres not much in the way of support for us.
Unfortunately we had a severe wind storm on Christmas eve and my mill self destructed, and I mean completely; I may be able to salvage the tower stub but thats all, theres bits of stator, winding wire, tail, stator star, magnets all over the field- BooHoo!
Anyway, onwards and upwards, Ill build a new one and have it up in a couple of weeks. I had been trying to squeeze more power out of it and playing with tail angle configurations and inverter power lookup tables etc, maybe I changed too much all at once and something happened. I dont quite know yet what because its so windy I havn't been able to bring it down. Im not sure I'll ever truly know as there are so many parameters and the 'event cascade' is difficult to unravel- did the tail boom metal fatigue and bend first or did it bend after the stator roasted and caught in the magnet rotors? I'll never know now. Ive been working closely with Dan Lennox (well known on fieldlines) to develop his 'PowerDashboard' monitoring software and we had just finished a working version on Xmas eve but I hadn't installed it yet, wanting to do more testing in the workshop before I put it on site. Damn, I wish Id installed it because it may have given clues as to what happened to cause such a calamity. Anyway , next time Im gonna have every parameter logged.
I should add this machine was functioning well for two months and putting out 6.5kw in a good wind, then I started getting those dreaded ground faults. I pulled the whole thing apart, completely rebuilding it, increasing the stator gap just in case there was an occasional rub (which Ive been told can cause a Ground fault), adding some bits like a neoprene washer above the slip rings to avoid grease dropping down onto the rings and affecting conductivity. Tweaking is important to get the most from a particular machine but I tweaked something wrong or mis-connected something and payed the ultimate price. $#|+, its so dissapointing to see all that work ruined- excuse me blowing off steam at your expense!
I'll deal with the points you raise in your mail in order-

Great to see another person with a similar setup as mine.  Now that their are several of us with 17-20' Axial Flux wind generators with Power one inverters we should be able to learn off of each other.  Mine is a 17' based off of the Dans design.  Mine is wound a little higher voltage than yours.  It's on a tower just under 100' in USA.  Here's a link to details of mine.  http://fieldlines.com/board/index.php/topic,144309.0.html
Mine is on an 18m hydraulic tower, a big piece of engineering but very permanent and easy to use when made. Its galvanized and will last 70 to 100 years.  Its 18ft diameter, Dans design based but with lots of extra development. I wound lots of different coil configs and eventually settled on 81 turns of 3 in hand 0.95mm dia 200*C wire. Each weighed in at 485grams of copper, as much as I could cram in- I will wind my replacement coils with 2 in hand to raise the voltage a little as I see this as a potential problem, it worked fine for a while but I decided to increase the stator gap from 2mm each side to 3.5 mm because of the ground faults.
What increase in voltage would you expect from this change? Going from 3 in hand to 2 in hand I reckon should give me a third extra voltage but is this the way it works?


I made my tail angle adjustable too.  I would love to see a picture of how yours is setup.  I also added removable end sections of the tail that lead shot can be added to. Currently mine is furled at 25mph and starts furl about 15mph.

My design is adjustable from 11 to 18.5 degrees. Ill post pics when I work out how to.
You have done a smashing job on your machine and have tackled some of the problems I see with the original Dans design: namely, tail shocks, lack of slip rings, metal on metal yaw bearings

I set my dump load to switch for the inverter when it comes on.  I thought it might be safer for the inverter, but I'm sure it would transition between load and inverter if it was setup to leave the inverter on.  I also figured this way the load condition wouldn't be different if the grid was lost.  I'm still not sure which is best?
I have my dump set to come on in parallel with the Aurora, Im thinking the dump will take off any overspeeding and still allow the inverter to sing to the grid. I have never seen V above 250V even when at full power (6Kw) but as stated I'll wind coils for higher next time. The Powerone is most efficient above 200v (98%) and has a sharp fall off in efficiency below this so Id like it to hit 200V when its putting out anything over 1000/1500W. The inverter applied load seems to keep the voltage way lower than I expected it would; the amperage rises quick and I expected the voltage to rise at the same rate but it seems to rise much slower. Had I known this I would have designed the system differently from the start but I had no experience with inverters to guide design.

The only time I have had a ground fault problem with the inverter was when I first hooked it up.  One of the Delta brand lightning arrestors that I had hooked to the power leads at the tower was leaking across the terminals internally.  Replaced it and haven't had a problem over the past 6 months.

Would love to see you Aurora Power curve.  Mine is posted in the link above.

My dump load is 20.4ohms when measured between any two legs of the three phases.  I'm not sure how this compares to your system.  I've turned it on at 300VDC and it slows the turbine more than the inverter, but does not make it stop.  One nice thing about my dump is that I can wire the resistors differently to adjust the Ohm rating.
My dumpload is a commercial 9Kw 3 phase crane braking resistor bank in an enclosure. I worked out my phase resistance was 6.35ohms  and ordered a 16ohm total resistor. I feel this was too high and will recalculate for the new stator and probably have to buy another Dumpload to match. Speaking of which that calculation was done by working out the single wire resistance for the length of wire in the coil and then multiplying this by 3 (for the 3 in hand), I reckon this is bogus now as doesn't the resistance reduce with extra wires in hand? I reckon my dumpload should have been a third of the resistance I ordered at about 6ohms. This would have been a much harder brake which I see now would have helped. I find the whole resistance thing decreasing with extra copper hard to get my head around when it comes to multiple wires in hand and 3 phase values etc.

I'm not using the Power-one Wind Box rectifier.  I attempted to build a frequency generator to be able to hook to the inverter to see the frequency and rpm on the communicator software, but can't seem to get it to work correctly.  Are you using the frequency outputs on the Wind Box? 
No, the wind box is just an expensive rectifier and does NOTHING else properly as I have found. It need lots more development by Powerone before it could be considered a must have bit of kit. The fusing doesn't work properly, nor does the brake activation.
The PowerDashboard Dan Lennox is working on with me is going to be the BEST measurement, logging and control software available and is designed specifically for the Axial flux machines we build- he has built a mill too and is applying his experience to the problem exactly as I would if I were to develop monitoring software. The PD measures everything without needing to connect the inverter outputs. Itll read volts, amps, watts, RPM, windspeed and direction (with the proper anemometer of course) and allow remote switching and control/shutdown etc.

The way the fuses in the Wind Box are suppose to work is that at around 550VDC it automatically shorts the legs together.  This is suppose to blow the fuses, but according Rob Becker of Solacity, just blows all the capacitors in the box.  Which I guess is better than blowing up the inverter.
Yea, as I said the Windbox needs lots more work.

I've been getting pretty good output out of mine.  Average low wind day I get 6-10kwh, windy days 25kwh, and my best day so far was 36kwh.  What are you seeing?
Ill get back to you with data- Id love to have a graph with every parameter logged, this would be the most informative and remove the guessing Ive been doing so far.
Thats really good output on yours though, well done!

Would love to see more about your system.

[rickysmartz]

Oh and heres some preliminary curves and data-
TSR 6.5
Cut in 65rpm~
Max speed 260rpm
12 coils, 4 per phase, 16 neo48s custom wedge, 81 turns of .96mm dia, 3 in hand
open circuit voltage on 1 coil at 72rpm was 7.3v when testing (and I wound a lot of different variations , the 3 in hand was to squeeze a little more copper in), so help me with the math-
7.3 x 1.4 (peakv from RMS meter) x 4 (coils per phase) x 1.73 = 70.72vAC  rectify this to dc (x 1.33) = 94.06 minus a little for losses. Im thinking 1.1v per rpm ish.
I set my inverter to engage at 70v, math seem ok so far?
Lookup table, PowerOne 6000-W inverter -
70v -0W
80v -300w
91.33- 850w
144v- 2500w
192 -4200w
220v -5200w
250v -6000w
270v -6500w
300v - 6500w

Cheers
Richard

[zvizdic]

7.3 x 1.4 (peakv from RMS meter) x 4 (coils per phase) x 1.73 = 70.72vAC  rectify this to dc (x 1.33) = 94.06 minus a little for losses. Im thinking 1.1v per rpm ish.
Richard

7.3 x1.414 =10.3 x 4 x 1.73 =71.43 VDC  -1.4 diode drop -line drop = voltage at batteries or inverter.
Multiplying with 1.414 is rectify voltage from ac rms to dc.

[Flux]

Yes Zvizdic is right.

I would approach it another way but the answer is very close.

7.3v per coil x 4 gives phase volts rms = 29.2v

Phase volts x 1.73 gives line volts rms = 50.16v.

The peak will be 50.16 x 1.414 = 71.42v

This will be the peak of the ripple and will decide the actual cut in. The figure of 1.4 is the factor to get the dc mean from a 3 phase bridge and is probably a better factor to use than the true peak at 1.414, but when you start guessing at diode drops etc. it makes very little difference.

Flux

[rickysmartz]

Hi Rob,
Heres a pic of my adjustable tail-


Flux and zvizdic,
Thanks for the help with that, im fairly close.  If I want to increase the voltage and decide to wind my coils with two in hand instead of three, do I get one third more voltage? Is it as simple as this? I should still be able to cram 485gms of copper into the space allowed. I should expect an increase in the coil resistance though, as Ill be increasing the number of turns by about a third- does this mean one third more resistance?
To get back on topic- If I keep the original dumpload (3 phase, 16ohms total), am I moving in the right direction to increase the effective braking when the dumpload is activated, or are my coil changes going to make it worse and decrease the braking effect?
Thanks fellas
Richard

[Flux]

If you wind 2 in hand then you have room for 1/3 more turns so you will increase the volts by 1/3.

The resistance is not so simple. You will have increased resistance from the extra turns, but you have also reduced the wire csa to 2/3 of the previous value.

You will in fact about more than double the resistance.

Flux

[rickysmartz]

So, I considered the original 16ohm dumpload too light or soft a brake, and I thought 8ohms may be a better match. Then if my coil resistance is doubled with the new 2 in hand winding, Im actually solving two problems simultaneously? Increased braking, and increased voltage at the inverter. Excellent!
Thanks again
Richard

[Dave B]

Ricky,

  I am sorry to hear of your misfortune. I have 2 suggestions again based on my experience with larger machines. Make sure you have an accurate way to monitor your actual RPM. (Hughs frequency to voltage circuit will work nicely) You cannot assume what it is from voltage readings looked up on your chart and therefore the load settings (curve) might be way out of wack possibly allowing it to overspeed before it can load it down to get it stalled under control. My other suggestion is to make a thin stator and get your magnets closer together. You can get your voltage with the magnets closer together making up for more winds and a thick stator. You will never slow and control your machine in the upper part of the curve with a stator that is too thick and especially if you are running a step load controller that is running the blades at close to their TSR to begin with.

  I really hate to add this again below but I wrote this earlier in your thread before the mishap. Electrically things can look great on paper but the mechanics of the design must be an integral part of the equation. A certain voltage and load on paper does not neccessarily mean that the machine will react as calculated. Biggest part being that if you do not have your magents close enough together pulling at each other with a huge force across the stator then it won't matter what your voltage or your load is, mechanically or flux related wise or whatever you want to call it, you will not be able to control your machine effectively. Things happen very, very fast in the upper part of the curve and once the machine starts to run away or overspeed you usually loose the effectiveness of the gravity type furling sytem also and then it's all over.

  Take it for what it's worth but : get a handle on actual RPM and get your magnets closer together with a thinner stator. Start experimenting with you machnie very hard stalled (maybe just your dump load only) make sure it will not start up and run away from 0 rpm in very high winds and then monitor your rpm and kick on the dump load to make sure it will stall and controll the speed in the upper RPM range you choose to run. Once you are confident of this as your overspeed control then get into experimenting with the inverter curve. It's alot of work I know but much less work and less expensive than building another machine. You have a machine unique to you just like the rest of us, you will need to experiment, observe, change, repeat. Good luck again.  Dave B.

    Ricky,

  I do not have my machine grid tied but I have a few comments based on many years of realizing the potential of these machines. Your 18' machine if it is reasonably built is capable of 3500 - 7000 watts from 20-25 MPH winds. Look at this again, 3500 watts increase for 5 mph increase in windspeed !!!! It is not "if" but rather "it will" if not controlled. You are asking the inverter to over speed control your turbine above 25 mph, can you imagine where the curve is at say 33 MPH like you state ? Furling your machine at 35 MPH and not seeing it fully furled until 55 MPH I am sorry to say will be catostrophic. Talk with Jarrod in great depth if you can, nobody wants to limit the output of their machine but if you are not well on your way to slowing this down just above 20 MPH either with furling or proper load or both you are going to loose it. It will accelerate beyond control in a heartbeat, just look again at the curve. I hope you get the components of your system balanced out to work together. It's just my opinion but I think right now you are running way above the upper end of disaster. Be careful.  Dave B.