Fieldlines.com: The Otherpower discussion board

Homebrewed Electricity => Wind => Topic started by: DaveP68 on October 23, 2017, 01:41:03 PM

Title: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on October 23, 2017, 01:41:03 PM
A question re Power factor correction capacitors. Has anyone on here tried using them to increase the output power of a wind turbine PMA?

If so what was the method used to calculate the value of the capacitors used?

David
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on October 25, 2017, 01:17:41 PM
Hi Dave,
Welcome to Fieldlines.  Seen your stuff on the backshed.

I've goofed around with capacitors on my turbine's AC leads from time to time.  Mostly inspired by your confederate, Gizmo, in fact.

From my point of view, it's not power factor correction at all, though.
If you asked me to describe the promised advantages of installing capacitors on the WT output leads just before the rectifiers, it is to absorb ripple.  This could suppress some of the flickering torque that causes vibration.

In combination with a second rectifier circuit in parallel with the direct-connected rectifiers, the capacitors also promise to advance the turn-on time of the rectifiers, lowering the apparent cut-in speed.  If effective, and if sized correctly, this would offer some extra energy in very low winds.

So far I have no measurable benefit to show for it.  That doesn't mean I'm not still trying.
Actually, it's uncanny how well timed your question is - I did a test run with 10,000uF caps on the turbine last night, and when I'm done work tonight I'll be reducing the data from my new datalogger to see if they made a difference.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on October 26, 2017, 03:44:37 PM
Hi

Yes spent a bit of time on the The Back Shed site, especially in the last year and was mostly helping Fred flc1 out with his new wind turbine build. This has turned out very successful for him.

That wind turbine has both a capacitor doubler using dual rectifiers which is what I think you are making reference too and power factor correction capacitors. It's has 3x PMA's (F&P triple stator set up) and the power factor correction capacitors as I refer to them are on 1 PMA only.

That PMA (F&P stator) is wired delta and has a phase to phase winding resistance of 10.7 ohms. The 3x capacitors are also wired in delta are only 5.6 uF each in value and rated at around 350 VAC peak across the PMA output pre rectifier.

Without these capacitors, this single PMA's output is around 475 W at 450 RPM. After fitting the capacitors the output power went up to 950 W for the same 450 shaft RPM (the drive torque increased too).

Why I asked the question was, it took a a bit of trial and error using the most basic calculations to work out the optimum capacitor value to get this doubling in output power from a single PMA. Was quite close first time around using 1.7 uF capacitors and power out put went up from 475 W to 800 W with same drive RPM.

I no longer advocated using the capacitor doubler arrangement on F&P stators as they account for around a 22 % through put loss. The F&P stators can be rewired into many combinations to get both low wind performance and high output power using power factor correction as I put it.

David
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: joestue on October 26, 2017, 07:35:45 PM
The capacitors draw leading power factor which pushes the voltage of the pma up.

Since the actual value of the current flowing through the coils is what increases the flux, as the frequency increases with the voltage, the current flowing through the capacitor increases with the square of the wind speed (assuming constant tsr) so the effect of the capacitor is mostly noticeable at higher rpm.

since i don't have one of these machines i can't comment on what portion of the output is reduced due to high leakage inductance.. but adding a capacitor to any synchronous generator (permanent magnet or not), will increase its voltage. since you're dealing with a mostly constant voltage rectifier load, it probably doesn't take much increase in voltage to significantly increase the current.

for example I usually add in a 55uF capacitor to the 240v output of my folk's 5000watt generator, it pushes the voltage from 225-230 volts at full load up to 240, and 255 no load.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on October 26, 2017, 09:30:48 PM
Interesting - you're doing something completely different from what I expected.

I take it the F&P drives you're using may or may not be re-wound, but are all wired up for 3-phase, IIRC.  And they have lots of poles... 24?  This would mean that 450 RPM sets the AC frequency at 90 Hz.  Mine is already furling at 450 RPM, so with 4 poles its peak is 15Hz.  If I wanted to try something like this I would need 6x your capacitance...  22uF or 47uF roughly...

I won't assume my converted industrial motor is similar to your F&P's, but I'm game to try new things, and I have the equipment to test and measure things now.
Thanks for the idea!
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on October 27, 2017, 12:55:54 AM
You have both picked up on two very important points.

First is power factor correction capacitors used on F&P stators do increase the AC voltage at X RPM. At the their sweat spot they are putting the PMA (F&P stator) into a from of resonance which just so happens to work to our advantage on wind turbines with the cube law of power extraction. From my observations when the voltage doubles, the optimum current drops slightly but power output significantly increases.

The second factor which is a big advantage when using an F&P stator, is their 36 pole configuration which is 3 phases by 12 poles per phase. This provides a high frequency at a modest RPM range. The rotor cap contains 48 magnets, so 60 RPM translates to 24 Hz. Hence the small capacitor values that can be used to over double the output power.

At 400 RPM F&P stator output frequency is 160 Hz and 200 Hz at 500 RPM.

Question on being a new member, understand I can't add photos or links until I reach at least 10 posts?
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DamonHD on October 27, 2017, 01:48:46 AM
Question on being a new member, understand I can't add photos or links until I reach at least 10 posts?

Hi,

I can't actually find the right setting at this moment to verify (I found a whole new group of settings instead!), but that sounds plausible.  Is the material something you can link to externally for now?

Rgds

Damon
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: Bruce S on October 27, 2017, 08:22:23 AM
Dave P68;
I cannot see where even a newbie (on this forum) is barred from posting pics. Barred from seeing before 50+ posts sure but not merely posting.
What kinda of error(s) are you getting when you try?

Bruce S
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on October 27, 2017, 12:08:39 PM
I have always looked on the converted motor as a limited machine, and those limits come from the reactance due to the iron in the core.  While we agree on that, I think, Dave, I think something different is happening after that.  I don't think the capacitors are giving you an advantage.  I think they are taking away a disadvantage. 

It sounds to me like the capacitors in parallel with the windings of the motor/generator apply a reactance opposite to the inductive reactance in the iron.  Both of these reactance values are at 90 degrees to the flow of current in phase with the voltage (and there's the rub in power factor correction).  With the right values, the reactance of the caps will oppose and cancel out the reactance in the iron.  The result would be a reduction in the total impedance of the system.  Presto: more power!

I'm anxious to try this out.  My estimate above for caps to suit my low pole-count motor conversion and speed range is a start but I think I'll also sit down and estimate the inductive reactance of the core (or measure it with a meter) and compare to the reactance I would get from the caps.  If the figures match up, then I'm buying shares in your company, Dave.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on October 27, 2017, 07:23:00 PM
I'm in agreement with you re the capacitors taking away a 'disadvantage' from your perspective which turns into an advantage on a wind turbine with the capacitors added to the PMA output verses no capacitors used.

Here is a photo of my test rig.
[attach=1]

Shown to the right is a Fisher & Paykel washing machine bowl upside down with a 36 pole copper stator and black rotor cap. Above that is the set of what I call "power factor correction capacitors" blue in colour on a board. Further to the right is a 1200 W drill.
On the left is 2x multimeters and a modified Fisher & Paykel motor control module acting as load to extract the power from the stator. This module has a dynamic brake unction and can operate up to 1500 W for short periods.

Have no wind turbine yet, but own to different sets of blades hence the TSR question relating to the GOE 222 blades.

Added photo now, so not sure what happened last try.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on October 27, 2017, 08:15:47 PM
Glad to see you now posting pix.  :)

Those look just like the filter caps found in half the power supplies in the world.
I thought you were using just 3.  Looks like about 30 there.

PS that power drill is sold under the Bosch brand name in Canada.  I probably paid more for mine than you did for yours :(
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on October 27, 2017, 10:38:58 PM
Well spotted and in fact they are all 0.47 uF 305 VAC capacitors for EMI filtering, recovered from Fisher & Paykel Motor Control Modules. There are 36 in total on that board comprising of 3x 12 in parallel which give 5.6 uF phase to phase, which is the value I mentioned earlier in this topic.

I have hundreds of these boards laying around in my workshop as repair them (only ones that can be). My day job involves repairs and servicing to Fisher & Paykel washing machines. Hence why I have an interest in focusing on the Fisher & Paykel stators for generating power on wind turbines.

I plan to build a MPPT inverter from mostly recovered parts from F&P motor control boards. It will be a high input voltage range 50 to 500 VDC and have 3 kW rating. First stage will be a battery charger version for 24 or 48 VDC systems then progress to making a grid tie one just for the share challenge.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: XeonPony on October 28, 2017, 10:07:06 AM
http://schams-solar.de/download/WIND/prospekt-WMR1500_EN.pdf

Been looking for MppT wind charges as of late as it is superior IMO even with solar I still say it is well worth the money over pwm

In my search I stumbled across this, they give some handy data that will lend its self to home brew style projects! Out side of my skill set sadly, best I can do is make a VCO driven voltage clipper by pwm to a load bank to keep the volts to a set limit, goal here is 120VDC Limit.

Midnight Solar has a voltage clipper but their price is out outrageous for what it is IMO and the Midnight classic can work in wind mode with mppt as well, so seems there is three all ready out there. Third being Morning star Mppt 600VDC unit is configurable to wind or solar.

The idea for my clipper was to take the DC side tap and feed it into a 555 VCO then feed the out put to a pwm unit to a fet bank to run the dump load. Opt 2 was to take a tap off one of the phases and do much the same only a triac or SCR to drive a AC 3 phase resister dump load.

For matching was to use an auto transformer at native out put voltage then down to my battery bank voltage then filter/rectify for now till I can get a good Mppt

I like how they did their in the above link as it is modular so in hypothesis you can expand the wattage by simply buying modules not sure if they do it that way, but again super pricey there as their prices are in Erus
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on October 28, 2017, 02:53:32 PM
Checked out the link, looks a good efficient system and can be configured for 12, 24 or 48 VDC battery systems. Personally I would never use a 12 VDC system as looses are too high due to amount of current flow at high power levels.

http://www.thebackshed.com/forum/forum_posts.asp?TID=2164

This is a true Wind Turbine DIY Analog MPPT system, but requires a bit of fine tuning/complex procedure to follow in order to match the PMA to the wind power curve.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on October 28, 2017, 05:42:48 PM
Dave,
Thanks for the look back at that great thread from Bob.
Reminds me of my big plans when I thought I knew so much about electronics. Turns out I had a lot to learn!
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: XeonPony on October 28, 2017, 06:02:41 PM
Seems to me it is  a nice simple boost converter , so the turbine needs to be matched to the batteries, then it just matches thing up at low speeds.

I am doing the exact opposite I am trying to design my mill to run at highest voltage then buck down to do the V/A flip to match the batteries via the mppt route ideally, then under high winds clamp the volts by a pwm diversion system on the high tension side to the dump load

So run the motor at its native voltage at 2xx volts or split it to 1xx volts to the control system which will be inside the house then do either mppt or auto transformer matching, and again diversion control on the AC side of things

here thank fully the design window is fairly simple far as known average wind speeds (10 to 15mph average daily)
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on October 28, 2017, 06:03:10 PM
OK now things aren't so clear...  Sat down to work out the numbers (always a risky thing) and tried to calculate the reactance in your system and compare it to mine.  It brings up some questions...
Knowing your F&P's pole count(48) means that I can work out the frequency at any RPM, so as you say, at 400 RPM the frequency is about 160 Hz.  I'm with you there.
Next I speculate about the inductance in the coils that I was assuming to be counteracted by the capacitors.  This is where I get in trouble.
The formula for reactance with inductors is X=2*pi*f*L and it doesn't matter what I guess as the inductance in the F&P's coils I get the same problem:
As the frequency goes up the reactance goes up too - but that doesn't make sense because reactance resists out of phase current.
I was thinking that there could be MORE out of phase current at higher speed, because that would lead to lower power factor... somehow I get the opposite: at higher speed the power factor goes up nearly to 1 even if it may have been bad at low speed.

So now I can tell I'm not understanding something, and again, wondering what I've missed.

Are those capacitors in parallel across each phase, or in series with each line?
Is your stator wired up in Delta when you use these capacitors?
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on October 28, 2017, 09:22:19 PM
There are 12 poles per phase, with 200 turns "per pole" 0.6 mm wire diameter with approx 1.33 ohms per pole. That's 2400 turns across the entire 12 poles if wired in Delta. The stator has 36 poles total, with "48" magnets in the rotor cap which is where the 160 Hz is derived at 400 RPM or another way is to state it's 40 Hz per 100 RPM. Frequency comes from number of "magnet pairs" (N+S) in rotor cap which is 24, so 1 rotation creates 24 cycles (Hz).

In Star mode (factory configuration) the resistance between phases is 32 ohms.  I always use them in Delta mode so the resistance drops to 10.67 ohms between phases.

Here is a photo of a stator wired Star with capacitors wired in Delta as I described before.
[attach=1]

Hope this is of help for you to make some useful calculations from.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: joestue on October 28, 2017, 10:59:04 PM
Next I speculate about the inductance in the coils that I was assuming to be counteracted by the capacitors.  This is where I get in trouble.
The formula for reactance with inductors is X=2*pi*f*L and it doesn't matter what I guess as the inductance in the F&P's coils I get the same problem:
As the frequency goes up the reactance goes up too - but that doesn't make sense because reactance resists out of phase current.
I was thinking that there could be MORE out of phase current at higher speed, because that would lead to lower power factor... somehow I get the opposite: at higher speed the power factor goes up nearly to 1 even if it may have been bad at low speed.

So now I can tell I'm not understanding something, and again, wondering what I've missed.

Are those capacitors in parallel across each phase, or in series with each line?
Is your stator wired up in Delta when you use these capacitors?


yes what you're missing is that the capacitors are not canceling out the inductance of the air gap.* they are increasing the flux density in the generator. and the increase in flux density is proportional to the amps flowing through the capacitor. The amps flowing are proportional to the rpm squared.

-------------
there may be an improvement if the capacitors are connected directly across each coil group. so if the coils are delta, delta capacitors. if they are wye, then wye capacitors with the neutral connected.

the reason why has to do with the third harmonic. the 9th probably doesn't matter. yes, the 3rd harmonic cancels but it cancels out through an rms voltage reduction at the generator terminals. (delta connection cancels the third harmonic by circulating the current around instead, causing waste heat) so for instance, my 10 pitch 24 slot 2 pole generator makes 145 volts per phase, but only 235 volts phase to phase instead of 250 like it would have, if each phase put out a sine wave

anyhow, you will probably see a bit more output (or lower rms current in the coil) if the capacitors are directly connected to the coils rather than delta caps on a wye generator.

it might actually be worse because the capacitors will be 3 times better at nulifying the 3rd harmonic than the first, so you'll probably see a much cleaner sine wave out of each phase, at the expense of increase copper losses in the generator.

If you reconnect the capacitors in wye, then put an amp meter between the generator neutral and the capacitors, you might see an improvement, or reduction in efficiency if you make or break that connection. (the difference should be accounted for by the increase or decrease in rms amps through each phase)


*the reactance of the generator is a fundamental property of the generator and cannot be improved without a physical re-design of the generator.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: XeonPony on October 29, 2017, 09:04:50 AM
http://projekter.aau.dk/projekter/files/43280847/masterthesis_chf_version02.pdf

Here's a PDF of a buck boost system for ideas and more inline with what I'm aiming for.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on October 29, 2017, 06:47:13 PM
Thank you Dave for clarifying, and for the schematic, which shows that I was picturing your capacitors correctly.
I had to refresh my memory on how to deal with the reactive components correctly (vectors). 

Have you ever taken measurements of the inductance in your F&P stator?  I can only guess. 
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on October 30, 2017, 03:19:06 AM
Thanks for all your valued input to my question.

Here is a graph of the open circuit voltage for both normal stator setup Delta mode and with the PFC capacitors connected.
[attach=1]

That is a big difference. The reason I stopped at 375 RPM is the DC rectifier is only rated to 400 VDC and as can be seen voltage reached a peak of 442 VDC.

SparWeb
Haven't taken an inductance reading of the stator coils yet as my set up just works in doubling of the output power. Will a do some testing later in the week as you've stirred my curiosity so will find out the answer.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: XeonPony on October 30, 2017, 09:53:47 AM
I been gathering allot of data, and been looking into impedance matching transformers, any thoughts?

I want to run as a high as practical voltage down the tower to house, then do all conversion and power factor correcting there.

Has any one tried making an impedance matched Xfrmer for their wind turbine be for? and would PF caps help in such a case?

So far setting all the variables for the end calcs, so at this point I need real world experiences of others!
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on October 30, 2017, 12:58:35 PM
Dave,
I paid a visit "down under" over the weekend and did a lot of reading to catch up with you guys.  You've really run the ball down the field.  Also re-read a bunch of old stuff since Gordon's original thread went back to 2008.  Very reassuring to read the old stuff, and still see names we know and trust like Oztules participating in those ones, too.

A couple of tough questions got asked during that debate.  Answers were not found in the course of the discussion, and the same questions haven't been brought up yet in the one you're having now, either.  One of the hardest ones was about taking measurements - this is going right down to the basics.  If reactive currents are flowing, your multimeter won't know the difference between true power and reactive power and start making up exaggerated stories.  That one stopped me and I'm still pretty stuck by it.  Gordon tried not to get tangled in the matter, but I think some of his responses undermined the enthusiasm that was initially created.

I'm pretty sure you (Dave) are measuring your output power on the DC side of the rectifier, which takes reactance out of that measurement, which means the graph you just posted up is still in good shape. But every time you, I, or any other guy goes to the AC side of the WT rectifier with a clamp-on ammeter, there's no way to know if there's a reactive component in the reading.  And it can be large.  The only way to know is to measure phase angles between voltage and current.  I don't think any of us have that stuff.  The original discussion 10 years ago left me with a distrust of any reading I measured on the AC side, but until I went back to read it again yesterday I had forgotten many of the pitfalls.

Something else you said - about the harmonics - may be more true than the power factor issue.  If we set aside PF for a while, and just looked at harmonics, then I think I'd want to follow that lead a little more, especially now that you've confirmed that the stator you're testing is Delta wired.  Lots of chances for currents to circulate around the windings.  You could even do some estimates of how big they could be if you want to do a bit of reading (you know, homework problems...  "allaboutcircuits.com" makes it interesting at least).


XeonPony,
You've got a lot of great questions but I can't help feeling they're going to get lost before I can get my head above water on the capacitors question first.
Some thoughts - just shooting from the hip.
Mass-produced transformers are cheap, special transformers are very expensive.  Self-made transformers require a very special set of skills and tools to do well.
I had a neighbour who installed a WT, with a 20 KVA autotransformer to match it up to his battery voltage, but that was a professional installation and he must have spent 20k USD on that setup.
You are right that any power factor problems would be magnified in such a setup.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: XeonPony on October 30, 2017, 02:33:43 PM
Transformers are actually quite forgiving in practice and by special you mean handling mind numbing tedium then guess so. You can make a functioning moderately efficient unit from metal strapping they use on pallets! proper silicon steel is just that much better.

I was just going to retask some microwave transformers unwind them and rearrange the cores for a 3 phase caged after crunching the math (Where the real head ache is)

After careful thought I am putting my primary on the inside winding with a 3mm air gap from the secondary low voltage winding for good cooling at a cost of some efficiency allow for easy swap to different battery voltages for when I make the great swap to 48 volts down the line.

Harmonics play a big role in system transfer efficiency and heat build up it by far is the largest head ache in AC electronics, why I try to avoid A/C as much as I can but for a use full wind tower in any way seems the only way to go is high voltage AC or wire thick as the truck its self for DC transfer efficiency, that and I want Every thing on the ground as much as plausible!

http://www.electronics-tutorials.ws/transformer/transformer-construction.html

Hardest part is winding a clean well shaped coil and varnishing it solidly so it doesn't hum excessively! just a bit more picky then a stator coil winding.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on October 30, 2017, 09:36:30 PM
Very nice tutorial website, Xeon, thank you!

Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on October 31, 2017, 04:05:15 AM
Would like to outline some important observed facts (data collected) relating to F&P stators output power potential.

As can be seen in the photo posted earlier I mainly use a Ozito HDR-5000 drill which produces up to 1200 W shaft power to drive my stators in test mode. There is some information missing from the published raw data.

Test 1: The maximum output power from any stator I've tested was 1032 W gained in direct drive mode with the drill at 912 RPM. Lets brake that down into some unpublished numbers. The input shaft power was 1200 W going into the stator. When we calculate the efficiency of the stator power transfer it comes out to 86 % which is pretty good.

Test 2: Adding a capacitor doubler to another stator (different configuration) tested in the lower gear on the drill (3 to 1 ratio) so 1200 RPM becomes 400 RPM on the shaft. The maximum output I reached was 710 W at 400 RPM. That is with the same 1200 W maximum input power. We are now down to only 59 % power transfer.

Test 3: Adding what I call "power factor correction capacitors" running a test again as above in lower gear on the drill I get 950 W peak at 395 RPM. With the same 1200 W maximum input power, we are now back up to 79 % power transfer.

The one big factor that I'm trying to point out here, when applied to wind turbine with a TSR of 7, 3 m blade diameter running at 9 m/s wind speed there should be 1 kW of output power available from a PMA at 400 RPM "if correctly set up".

With test 1 running at 912 RPM gain to get 1 kW we lack sufficient RPM to get that 1 kW output power potential.

With test 2 we match the 400 RPM, but the output is only 710 W so a bit down on an efficient match.

Now with test 3 we again come close with 395 RPM, but very close to the 1 kW power output potential reaching 950 W output.

It all comes down to optimization and my test results speak for them selves. Yes they have all been logged on the DC side of the rectifier as you have already picked up on.

I'm will now make an decent effort to make some measurements on the AC side within Delta windings to extract the data you chaps are after. This will be of much use to others to transfer the knowledge gained and to apply to other types of PMA's.

Also check out this video linked below and you will see a hint to why I'm achieving the results above, but with no gearing.
https://www.youtube.com/watch?v=8aPIEsnKb6o

I'm no longer contributing to 'The Back Shed' if that is what you are referring to by making reference to a visit "down under".
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: XeonPony on October 31, 2017, 06:09:58 AM
https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&cad=rja&uact=8&ved=0ahUKEwiZyYa66ZrXAhVBVmMKHbdWDtMQFghiMAw&url=http%3A%2F%2Felectrical.theiet.org%2Fwiring-matters%2F18%2Fpower-factor.cfm%3Ftype%3Dpdf&usg=AOvVaw2Ry_KsuJ8lRPYUTr267X9U

https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=15&ved=0ahUKEwiZyYa66ZrXAhVBVmMKHbdWDtMQFgh0MA4&url=http%3A%2F%2Fwww.eaton.com%2Fecm%2Fgroups%2Fpublic%2F%40pub%2F%40electrical%2Fdocuments%2Fcontent%2Fsa02607001e.pdf&usg=AOvVaw2sjmGHftKxYoBE7bsoCFLs

http://www.rapidtables.com/calc/electric/power-factor-calculator.htm

A pdf on power factors and their correction
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on October 31, 2017, 04:37:57 PM
Dave,
I think you could be underestimating some of your efficiency numbers.

Do yourself a favor and check that the power drill is actually delivering the mechanical power that you think it is.  Remember, efficiency cuts all machines, so the efficiency of your power drill is dependent on its speed, gearing, and the voltage you get out of the wall.  Measuring the drill's power consumption is a start, and relatively easy to get an accurate number.  If the drill uses 1200W of electric power, you can be very certain it can't create 1200W of mechanical power.  Probably 80-90% efficient.  No reason to expect it to consume exactly 1200W either.  My 500W power drill uses 750W of electricity.  When you snap in the speed reducer that could change its mechanical efficiency too.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on October 31, 2017, 05:38:12 PM
Hi SparWeb

It's not about the drill actually having a shaft power of 1200 W exactly, it was for illustration purposes only. All those efficiency numbers could be 10 % lower. It's the difference between them, that is the most important factor. My testing outlined above to illustrate it another way is about Watts output vs RPM. So test # 1 is 1.13 W per 1 RPM, test # 2 is 1.775 W per 1 RPM,and test # 3 is 2.41 W per 1 RPM.

Anyway enough on that subject for now, I have an inductance reading 62.518 mH for 1 set of 12 poles (coils) of a 36 pole F&P stator. Hope this number is of use to you with the calculations you would like to make.

Next measurement will be voltage vs current phase angles in the AC winding in Delta mode.

David

Found an error so have edited the inductance value.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: joestue on October 31, 2017, 11:33:48 PM
how much additional current is flowing through the coils, as a percentage of practical load, when you add the capacitors?
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on October 31, 2017, 11:59:15 PM
Thanks XeonPony for the links re power factor correction, taking a bit of reading to get though them.

SparWeb has given me the clue to what is probably going on here. Now that I know the inductance of the coils 62.518 mH per phase, I've been able to calculate a resonant frequency 219 Hz 6 uF AC capacitors are connected.

That translates to 548 RPM which is why I notice such a large increase in the output power above 300 RPM.

Next step is to plot the power difference on a graph with output power no capacitors added 60 to 600 RPM and then carry out the same test with the capacitors connected over the same RPM range.

joestue

Was given a 3 channel storage scope today, so plan on taking some AC volts and current readings in the Delta windings this weekend.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on November 01, 2017, 01:12:56 PM
Dave,
Glad to see you pursuing this.

Back in 2008, I tried to crunch the numbers - using my machine's stats - and published to Gordon's long caps-mod thread.
Below is a calculation sheet that I tried to "make pretty" for those interested in the math.
(http://www.thebackshed.com/forum/uploads/SparWeb/2008-09-29_030034_Stator_Reactance.gif)

Later in that thread, I posted this, given some of Gordon's F&P parameters:

(http://www.thebackshed.com/forum/uploads/SparWeb/2008-09-29_124455_Stator_Reactance_Gordons_Graph.gif)

400 RPM, eh?

A few months after I posted that, an accident with my tower destroyed that wind turbine.  When I built the next one I never did pick up this subject again, until now.
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: kitestrings on November 01, 2017, 08:20:46 PM
Welcome to OP.

Quote
I'm no longer contributing to 'The Back Shed'

I'm sorry to hear this Dave.  As you know I murk about in the margins of several sites including The Back Shed.  I have less to contribute due to the alternator of predominant choice there, but still some interesting ideas.

With solar far and away the more popular choice these days, it's getting harder to find folks who are stubborn enough to still muck about with small-scale wind design.  Still watching a turbine is immensely more satisfying than a sunbathed PV array IMO.

~ks

Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on November 01, 2017, 11:15:34 PM
Hi Dave,
The thing about the power drill is not trivial.
If you test in condition 1 and get one output curve, and then test in condition 2 and get another output curve, then all you know is that something changed.
But if you aren't watching the input power, then you could be mistaking a change in power with a change in speed range, or worse, fooling yourself that there is any improvement at all.  Even in the best case, you would want to know input power, to get the blades to match the generator characteristics.  If the blades get stalled, then no amount of capacitors on the generator will correct it.

As I said, I went back to the old threads on the Backshed and started re-reading them.  You'd better take a look at the comments from "HerbNZ" in the "Visual effect of capcitors" thread from GWatPE in particular, approximately page 20.  I don't think the inductance explanation has legs.  The other theories have merit, but by the time they were put forward, nobody still reading was interested in figuring out the rest.

I may have jumped to the wrong opinion when you started this subject.  Since that old thread was poorly resolved, and didn't offer any method to judge what capacitors to use when, despite being 40+ pages long, I think there's still room to step in and offer a better solution.  If you're willing to help, this will go faster than if I have to figure it out on my own.

To see the kind of test I'm talking about:  http://www.sparweb.ca/3_Gen_MoCo/Baldy.html

It's not necessary to go nuts with a lathe like that - I just had access to one, and it was big enough to drive the generator up to 2kW+.  For your tests, all you need to do is put the washer drum back in the washing machine and, presto, you have a smooth bearing-mounted axle that the F&P generator can drive, while a prony brake holds the drum.  Torque * RPM = Input power.    Output power / Input power = efficiency
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on November 02, 2017, 12:40:03 AM
Hi SparWeb

I haven't over looked what you are referring too with the drill, as I stated before "input shaft power was 1200 W". Again that isn't an exact figure but close enough.

One thing I've noticed on forums over time is many over read what isn't there in what I post ('m not picking on you here). I have done hundreds of hours of testing and yest do have an AC power meter monitoring what is going into the drill. All power readings you see are maximums taken over several tests taking into account input AC mains voltage to drill, power input reading of drill, temperature, how hot the drill gets, etc, etc.

All peak readings were taken first test of the day under colder conditions.

I can't accurately monitor the torque but that drill is hand held so I get to feel what happens each test so close enough for me.

The drill is providing a "maximum" reference point which just so happens to work in my favor. It has a 3 to 1 reduction gear box so the aim is to get a stator to output 1 kW at around 330 RPM. I know this is possible at in direct drive mode I can easily get 1 kW out of an F&P stator using the drill, but this is only achieved at above 900 RPM.

There is no chance of blade stall every happening when I use some form of MPPT after the stator. I already use a form of MPPT when doing my testing on these F&P stators just check out the voltages they run at which is the big give away (>400 VDC).

The reason why I post the YouTube video of the Pratt & Whitney PW1000G high-bypass geared turbofan, is Aviation is my main interest and I hold a pilots licence. I also worked at ATC at Auckland Airport a few years ago. There is a close relationship between aircraft and wind turbines.

This is just a hobby to me so have never made a dollar from it...
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on November 02, 2017, 12:59:42 AM
Welcome to OP.

Quote
I'm no longer contributing to 'The Back Shed'

I'm sorry to hear this Dave.  As you know I murk about in the margins of several sites including The Back Shed.  I have less to contribute due to the alternator of predominant choice there, but still some interesting ideas.

With solar far and away the more popular choice these days, it's getting harder to find folks who are stubborn enough to still muck about with small-scale wind design.  Still watching a turbine is immensely more satisfying than a sunbathed PV array IMO.

~ks

Hi ks

Thought you would notice my presence on here soon enough :)

It was the resident diesel mechanic and the farmer that drove me away from that website. I suspect some of the same types drove away Gordon who was a bright chap that many still talk about on there and the same chap made reference too in this topic. Shame as I think he still had lots to offer.

Anyway having a much better experience over here so far  :D
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on November 02, 2017, 12:55:54 PM
Cool Dave,
I could tell you had some smarts about you.
I do a bit of aircraft work, too; modifications like the Australian Coast Guard's turboprops (DHC-8-100).

Quote
... with the drill, as I stated before "input shaft power was 1200 W". Again that isn't an exact figure but close enough.
The chances of that being true are small.  Sorry.

Quote
I can't accurately monitor the torque...
Sure you can.  Once you get your head around it, it can be as easy as a C-clamp, a board, and a bathroom scale.

Quote
...drove me away from that website...
Their loss
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: SparWeb on November 02, 2017, 01:03:47 PM
Wait a minute - if you have two F&P motors, and convert 1, you can use the other as the drive for testing. 
Looking at your other thread about mods to the motor controller, it looks like you have already started on this path...
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on November 02, 2017, 02:00:38 PM
Hi SparWeb

Thanks for the endorsement. Yes working on the torque measurement technique using "C-clamp, a board, and a bathroom scale" to capture the input power component. Haven't bother to date as holding drill was just easier.

David
Title: Re: Power factor correction capacitors used on wind turbine PMA's
Post by: DaveP68 on November 03, 2017, 10:23:16 PM
For those following this topic, today graphed the power output difference with capacitors connected to the stator and with no capacitors.
[attach=1]

That is a greater than 2 to 1 gain in power output vs RPM and I didn't even reach the peak which by calculations is at just over 500 RPM.

The peak power was 852 W at 375 RPM as can be seen on the graph (Green line).