Author Topic: Once again in 3-part (phase) harmony  (Read 8570 times)

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joestue

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Re: Once again in 3-part (phase) harmony
« Reply #27 on: December 16, 2016, 01:31:56 PM »
I meant they are extremely easy to design and build.

kitestrings

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Re: Once again in 3-part (phase) harmony
« Reply #28 on: December 16, 2016, 06:08:14 PM »
Ahhh...I got it.  Too funny.  I was reading inconsequential, ineffective (at low frequencies).  Hard to read expression, intonation on these darned things....

Jason Wilkinson

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Re: Once again in 3-part (phase) harmony
« Reply #29 on: December 17, 2016, 05:33:54 PM »
 After some of magnets corroded and lifted off the  fiber  glass potting , i remade the rotors with out the potting . Same 18''  rotors 16 mag/ 12 coils  and now there is this deep growl, wasn't there when the rotors were potted.  I checked and the growl starts at about 10 amps   and disappear as the amps gets higher.  Surprisingly, when the smaller turbine  10 footer  12/9  and not potted was on the same tower, that growl /hum was only heard if you placed your ear on the tower. When your tower is only 10 to 12 feet from the house  the growl can be annoying especially to those who don't know what it is.
 Jason

SparWeb

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Re: Once again in 3-part (phase) harmony
« Reply #30 on: December 18, 2016, 09:20:10 AM »
Hi KS,
Some reading material on the subject:
http://literature.rockwellautomation.com/idc/groups/literature/documents/wp/mvb-wp011_-en-p.pdf

The white paper isn't too technical so even I can follow it.  The current waveform at the beginning is the kind of thing our generators experience.  The reasons are different - the paper is written for VFD drives, after all - but the effect is the same.

In my case, I have a "parallel resonance" situation with my motor-conversion. That's why a bank of capacitors proved to be so effective in my system when I tried it.

In your case, you could have the "series resonance" but not necessarily.  The capacitance due to long AC lines from tower to rectifier could be the culprit.  There isn't a lot of inductance in Axial-flux genny windings (compared to an iron-core motor/generator, that is) making an inductor installed close to the rectifier effective at getting out of the resonance zone.  In series, however, the two will increase the total impedance so don't go overboard or you will reduce the current that can flow.

Do you still have the low-speed noise that you heard earlier?  Or has the tower-tightening solved the most of it?

Jason,
Sorry to hear you have similar trouble.  Are you considering similar solutions?
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

kitestrings

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Re: Once again in 3-part (phase) harmony
« Reply #31 on: September 29, 2017, 09:36:08 AM »
Ive been tracking this and taking some vibration recordings and output screenshots for a while.  I think I have it narrowed down a bit more.  It seems where this is most pronounced is actually not right at, but slightly above cut-in, likely at a resonant frequency that is exasperated by the tower and or turbine itself.  The rough point is when the turbine is putting out ~300 watts; the DC voltage is in the low to mid 70V range, and Im estimating that the AC frequency is 15 Hz.

Id like to experiment with an inductor.  After researching inductive filtering for rectifiers a bit, I found this formula:

RF= 0.4714/√[1+(4πfiL/R)2]

ref:
http://www.irjes.com/Papers/vol2-issue6/Version-1/E02064249.pdf

where fi = input frequency, L = inductor value (mH), and R = resistance (ohms)
I thought I might try an off-the-shelf unit in series with the first controller, which is current limited at 40A.  If my math is correct, a 50A, 2.5 mH choke with a resistance of .008 should result in a ripple factor of less than 1%.

What am I missing?  Is this worth a try?  How do I calculate the loss that it introduces?
I think there may be some other mitigation measures that could be employed rope in tube, vibration damping tape on stator bracket, tower damping but if I can reduce the source of the problem, thatd seem logical to me first.

SparWeb

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Re: Once again in 3-part (phase) harmony
« Reply #32 on: September 29, 2017, 12:51:44 PM »
The article you found barely mentions impedance.
That would be the reactive resistance, out of phase with the voltage, but still there, working against the current. 
Read the author's Table 3.  Look at the column Irms, which goes from 0.6A to 0.15A as he selects values that correct the ripple.
The author's goal was to reduce ripple in the output current, not to optimize power transfer from the source to the load.

I'd try some of your mechanical ideas first.

Also, if you want to take a peek at my old postings (ca 2012?), you can see the vibration isolators in my motor-conversion mount which wouldn't be too hard to adapt to a pancake alternator.
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

joestue

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Re: Once again in 3-part (phase) harmony
« Reply #33 on: September 29, 2017, 01:42:41 PM »
If you only need a 2.5mH inductor at 15hz when the turbine is putting out 5 amps at 70v, then you dont need to build a 3.1 joule inductor, which would weigh about 20 pounds or more.

A mot core with a dozen turns of 6 gauge wire might work for you. A paper thin airgap, and the core will be saturated at 50 amps.

kitestrings

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Re: Once again in 3-part (phase) harmony
« Reply #34 on: October 02, 2017, 07:23:37 AM »
Thanks for the responses.  I've done a few things that helped mechanically, and I have several more in mind, but it still makes sense to me that if there's a way to filter out some of the unwanted AC residue from the rectifier output we'd be starting at the likely source of things.  It seems like there must be similar applications where inductive filters are applied without having to build one from scratch.  Unfortunately, I have no feel for scale of the units involved here - a mH isn't readily tangible in the same way as amperage, voltage or mpg might be (for me) - I'd really prefer not to be desiging and building an (and my first) inductor for this task; and adding yet another list of unmeasured variables.

Spar I'll search some of your related archives.  On the mechanical front, it occurred to me that a potential issue could be movement of the coil sectors.  They are held, it part, by sandwiching the stator sectors between a pair of outer polycarbonate rings.  These likely have some flex.  I was considering putting some longer stainless supports in place of washers that might bridge from one to the next; picture like a low-profile piece of framing angle.


I've added rubber isolation to the PVC conduit and various minor things.  it all helps, and over the turbine is working well.  I'd just like to close in on this one detail if at all possible.



joestue

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Re: Once again in 3-part (phase) harmony
« Reply #35 on: October 02, 2017, 02:08:29 PM »
If you place a resistive load on the turbine that closely matches the amps that the turbine pushes into the batteries at the nominal resonance rpm, does the resonance go away?

SparWeb

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Re: Once again in 3-part (phase) harmony
« Reply #36 on: October 03, 2017, 12:50:49 PM »
Hi KS
I have done the same math as you have, and come up with similar results (turbines working in similar speed ranges etc.)
Just for fun, let me show you the FIRST Google hit I get when I searched for "motor choke size":

https://www.schneider-electric.com/en/product/VW3A4555/line-motor-choke---0.5-mh---60-a---3-phases---94-w---for-variable-speed-drive/

0.5 mH, 3-phase, 60 amps... It weighs 11 kilograms (24 pounds)!
The 2mH version is smaller - about half the weight.

So I'd say your instincts about the inductors are right.

As for the relative vibration of the coil sectors - Hmm I thought you had taken steps to prevent that.  I forget what exactly.
Does the stack of materials in the stator go like this?
-polycarbonate sheet
-Coil
-polycarbonate sheet
-backing ring

If that's correct, is there any sealant between the layers?
Or any other material that prevents vibration?
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

kitestrings

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Re: Once again in 3-part (phase) harmony
« Reply #37 on: October 04, 2017, 09:54:04 AM »
Quote
If you place a resistive load on the turbine that closely matches the amps that the turbine pushes into the batteries at the nominal resonance rpm, does the resonance go away?

Hmmm, I'm trying to think how I might be able to do this.  Of course, normally the thing is always tied to the batteries...maybe I could program the load diversion into a matching load, but it would still be in parallel with the batteries.

In light winds, about this speed, I have tried dumping the output into my 3-phase load bank which is similar, but different.  Here we're putting out 300, 400, 500 watts say, and we don't short the 3-phase output, but connect the alternator output via relay to a relatively low resistance 3-phase load.  It brakes the turbine, though less abruptly.

Quote
Does the stack of materials in the stator go like this?
-polycarbonate sheet
-Coil
-polycarbonate sheet
-backing ring

If that's correct, is there any sealant between the layers?
Or any other material that prevents vibration?

Yes, that's right Spar.  There are SS washers against the polycarb. rings, but otherwise you have it.  There is no sealant.  What you are remembering correctly is that we have some movement along the T &G edge over time, and we resolved that by adding a second thru-bolt at every other sector.  This might help:
10828-0
10829-1
10830-2

BTW, I visited a Bergey Excel site yesterday.  It was fairly windy, and the thing had wa- wa-WA-Wavvbbbb rumble at one octave where it shook the wind instruments, and then the EMT conduit violently until the rpms increased.

kitestrings

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Re: Once again in 3-part (phase) harmony
« Reply #38 on: October 04, 2017, 10:00:14 AM »
My apologies to mod.  I didn't grab the re-sized version of one photo.  Doesn't appear to be anything I can fix after the fact.  ~ks

SparWeb

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Re: Once again in 3-part (phase) harmony
« Reply #39 on: October 04, 2017, 01:27:35 PM »
...And I think I can see 2 of these inter-sector bolts in your photo from October 2nd.  Yes I remember that, now.
So this means that out-of-plane motion is still possible, but requires bending of the poly sheet. 
What about the ring around the edge of the stator: are all of those bolts already fastened through the big ring too?
I think I see that in your last (small) photo.  If so, then maybe there isn't much freedom of motion between sectors after all.

I found my isolator bolt picture:
http://www.sparweb.ca/Forum/Turbine_Inspection_lrg.jpg

I was inspired by this arrangement:
http://www.hutchinsonai.com/products/product.cfm?cid=7&fid=35

I'm also interested in seeing what happens if you can try Joe's suggestion. 
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

kitestrings

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Re: Once again in 3-part (phase) harmony
« Reply #40 on: October 06, 2017, 07:20:44 AM »
Quote
So this means that out-of-plane motion is still possible, but requires bending of the poly sheet.

Yes, that's right.

It is possible I suppose that the whole stator bracket assembly (SB1 drawing) is flexing, or "ringing" is what I'm envisioning.  It is constructed out of 1/8" SS.  There may be a natural frequency where the the thing shudders.

Nice pic.  I've seen some of those isolation mounts on generators and motor-drives.  Something like this could work on the six (1/2") bolts that mount the bracket assy. to the frame, but it would require taking the thinbg down, disassembly, and a fair amount of work.

I'll try to see if I can load the thing as suggested.  I think I can set the voltage such that we divert to the load a bank in light wind at/about the speed in question.

Thanks for all the suggestions.  ~ks

kitestrings

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Re: Once again in 3-part (phase) harmony
« Reply #41 on: October 06, 2017, 11:55:29 AM »
I could try some of this vibration dampening tape (as ULR point to) on some of the braket surfaces to see if it had any impact.

I also have an aluminum tail-boom and vane (the vane to strut is rubber isolated).  While not the source of vibration, they could be amplifying it.  I think Dan had said he preferred wood veneer for this reason.

kitestrings

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Re: Once again in 3-part (phase) harmony
« Reply #42 on: October 09, 2017, 07:49:12 AM »
I'd written to Hugh P. to see if this was anything that he might have wrangled with -

He responded that it was pretty common, and worst just above cut-in where the ripple is maximum.  He didn't have any simple solution, but shared some work these folks in Greece had been working on:
10839-0
10840-1

but, he also said that the approach "but it saps power and leads to overspeed and only partially reduces the noise.", which seems a lot like the laundry list of side-effects accompanying some new drug.  You can remedy your dry eyes, but you have to live with incontinence, rectal bleeding, memory loss, increased propensity for suicide, etc., etc.

DamonHD

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Re: Once again in 3-part (phase) harmony
« Reply #43 on: October 09, 2017, 08:19:32 AM »
I haven't gone back to the beginning of the thread, but can you just use something a bit gentler than rectifiers straight to the batteries to make the cut in more gentle, eg a crude MPPT tracker?  Or maybe some caps instead somehow to smooth the corners.

Here's an unorthodox thought.  What if you made the rectifiers slightly asymmetrical, eg 2 diodes in series in one of the arms (with one as usual in the others), to spread the full cut-in load slightly.  If that works at all you could then do clever things later to make it more efficient.

Rgds

Damon

SparWeb

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Re: Once again in 3-part (phase) harmony
« Reply #44 on: October 09, 2017, 09:30:38 AM »
KS,
Have you been following my datalogger thread?

One of the major obstacles to my progress in cleaning up the noise in my WT (yes I admit it still does make noise) is that I haven't been able to accurately measure its speed without leaving an oscilloscope connected to it.  All previous efforts at making a tachometer have been foiled by the harmonic noise.  Which is ironic, since that's the main reason I want to measure it!  The attached picture below is the form at just ONE narrow speed range.  The harmonics shift and change as the speed changes.  Damping the 7th could work between, say, 100-200 RPM but wouldn't matter if the 5th and 11th dominate at other speeds.  Damp ALL the harmonics and 25% of the power gets turned into heat instead of battery charge... then what's the point...

So it's been several years that I've been trying to crack the nut, and now that I do have an accurate and reliable RPM, I can now tell WHICH speeds are the actual noisy ones, rather than just guess and suppose.  Then view the waveform at just THOSE speeds and see if I can do something about just them.

Reliable RPM measurements also opens the door to other experiments, some I've already found will reduce the cut-in noise, by shifting the cut-in speed.  There wasn't much point trying out those things (such as capacitor-bridge triplers, similar but not the same as the linked graphic from Hugh) when my RPM guess was my thumb in the wind.


No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

Mary B

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Re: Once again in 3-part (phase) harmony
« Reply #45 on: October 09, 2017, 05:14:01 PM »
You need to build a low pass filter that cuts off at the maximum frequency the turbine puts out. Schematics on the internet.. http://www.wa4dsy.net/filter/hp_lp_filter.html

kitestrings

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Re: Once again in 3-part (phase) harmony
« Reply #46 on: October 10, 2017, 06:14:30 AM »
One of the challenges, from what I'm reading & understanding, is that these things are operating at comparatively very low frequency.  In your link it says,
Quote
These filters are most effective between 50 kHz and 500 MHz. Below 50 kHz
  Our turbine at cut-in is running only about 12 Hz, and top end - roughly 300 rpm - it still is only about 42 Hz.  A trade off appears to be how much gain is afforded relative to increased losses.  It is likely further complicated by resonance due to the variable speed nature of the thing.

I'm trying to keep in perspective that overall this does not have any effect of performance.  It really is just an annoyance when the wind settles in at a range overlapping the trouble spot.

BTW, below is the source of the paper I referenced above, from Hugh.  The pdf was a bit too large a file, and the best I could do and keep it legible was to carve it up.
10841-0

SparWeb

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Re: Once again in 3-part (phase) harmony
« Reply #47 on: October 10, 2017, 09:02:06 PM »
Thanks Mary.
My low-impedance low-pass filter needs 20mH inductors (2 per phase) to suppress transients 40Hz and above.
It's a lot of copper.
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

Mary B

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Re: Once again in 3-part (phase) harmony
« Reply #48 on: October 11, 2017, 05:50:59 PM »
Yup the huge coils needed are also inefficient... adds loss

SparWeb

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Re: Once again in 3-part (phase) harmony
« Reply #49 on: October 11, 2017, 11:59:20 PM »
So this is the appeal of the doubler/tripler circuits, silly as they may sound at first.
The point is not to boost the power boost the power boost the power
Actually, if the components are selected carefully, what it CAN do is add a new battery charging circuit but with higher impedance than the main one.  With that circuit in action at speeds below cut-in, the WT is already loaded when the main circuit cut-in is passed.  Why this matters...

To make a mechanical analogy (which isn't such an analogy in this case):
Lightly loaded joints are easily moved by vibration and conduct it to other parts.  Heavily loaded joints do not, because the load and the mass damp out the motions.
Similarly, lightly loaded electrical circuits with low impedance (ie. rectifiers are off) allow transient currents to flow, but these same circuits can damp them out when currents are allowed to flow through loads (ie. rectifiers are on).
ALSO similarly, electrical circuits that have high transient currents experience mechanical vibrations, and those mechanical vibrations are objectionable if the other mechanical loads (weight, thrust and drag) are also low.  That's what's happening at cut-in, too.

So that may be where the doubler/tripler circuits can help.  They put an electrical load on the system where the wasn't before.  Once the main circuit turns on and begins throwing up the transients, the system already has current flowing through the other circuit.  I'm hopeful the mechanical loads in play can damp down the cut-in jiggles.

...and so in theory, a properly selected doubler/tripler could do two good things: increase the trickle of power at low wind speed, and add mechanical damping to the cut-in vibrations.

It's all a beautiful theory in my head...  don't spoil it!
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

kitestrings

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Re: Once again in 3-part (phase) harmony
« Reply #50 on: October 18, 2017, 09:55:40 AM »
You reminded me of one thing that I could/should experiment a bit more with - with Classics I can manipulate the power curve to have it load heavier, at lower rpm, or later after more speed is reached.  I tried the latter a bit, with little or no improvement.  Again, where we experience the most noise/shudder is quite a bit above cut-in ~300 watts or so, and about 70V in/ 110 rpm.  We cut-in at ~59V; 92 rpm.