Changing an induction motor voltage

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Johny
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Changing an induction motor voltage

Post by Johny » Mon, 15 Jun 2009, 17:48

It looks like they came of equipment bought in from the USA as they are 60Hz and US voltages. The 12 connections tend to indicate Dahlander configuration.
Do you have any idea of their weight?

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Changing an induction motor voltage

Post by weber » Mon, 15 Jun 2009, 18:23

Oh yes, quite unsuitable. We could come and take them off your hands. Image

Seriously, if they are working, they would be good for a moderately-powered, small car conversion, if you can handle a nearly 700 volt (lethal) battery (with over 200 LiFePO4 cells at 10 to 40 Ah).

So the mythical 12 wire terminal box does exist, and you should be able to get a 3.5 times overvoltage just by installing links in the right places. The shaft height I asked about is an excellent 132 mm (from the part number). And its goot that they have both feet and flange (albeit a small flange).

What is that weight in kg given in the bottom right of the specifications plate? I can't make it out from the photos.

However, it looks like they have been taken out of service. This may be because they failed in some way. It may just be bearings. Or it may be windings. The noise when you spin it will tell you a lot about the former. A multimeter and megger would tell you a lot about the latter (but wont find a shorted turn).
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Changing an induction motor voltage

Post by Johny » Mon, 15 Jun 2009, 18:26

I reckon they would have been removed due to unsuitable voltage for Australia - my not-much-info guess is that they're probably OK.
Oh, and yes (sorry weber), they are completely useless and weber should be allowed to dispose of them for you.

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Changing an induction motor voltage

Post by Bluefang » Mon, 15 Jun 2009, 19:17

58kg is on the panel. I guess i ll just have to suggest to the boss that i ll clean up the workshop.....and just happen to miss place them in my car rather then the dumper.
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Changing an induction motor voltage

Post by Johny » Mon, 15 Jun 2009, 19:26

58kg is a good ball-park weight for a 7.5kW. They are most likely aluminium frame as Dahlanders tended to be heavier. My catalogue has 43kg for an ABB, 2 pole, 7.5kW alu. frame. (M2AA 132 SB, 3GAA 131 002-••E)

Depending on your car maybe you better do one half of the workshop first, then the next day...

Seriously though. At 277/480V they would have been difficult to use in Australia and most people wouldn't have thought of using a VFD. Just don't mention VFDs.

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Changing an induction motor voltage

Post by Richo » Mon, 15 Jun 2009, 20:24

double shafts too!
So the short answer is NO but the long answer is YES.
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Changing an induction motor voltage

Post by weber » Mon, 15 Jun 2009, 20:35

Not sure about the dahlander thing. You only need 6 terminals for that. I'm thinking it has 2 independent pole windings per phase and so they can be wired for parallel 4-pole, not just series 2-pole and series 4-pole.
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Changing an induction motor voltage

Post by woody » Mon, 15 Jun 2009, 20:41

Yep Bluefang, you have quite a find there. The 12 terminals give you access to each end of the 6 windings. This is a dahlander wound motor, hence the two speeds. (~3600 rpm and ~1800 rpm)Image

Having two the same gives you all sorts of possibilities, connecting them inline to each other and winding in series or parallel to one VFD, or one to front diff, one to rear diff on a 4wd with a VFD each. Small & light, you've hit the AC jackpot.

It looks like they may have an encoder on them too (the wire from the terminal box to the pulley end).

Which state are you in ? West or East Coast you'll have AC nuts to help you out :-)
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Changing an induction motor voltage

Post by woody » Mon, 15 Jun 2009, 21:13

weber wrote: Not sure about the dahlander thing. You only need 6 terminals for that. I'm thinking it has 2 independent pole windings per phase and so they can be wired for parallel 4-pole, not just series 2-pole and series 4-pole.
Weber makes sense (as usual), separate windings is possible.

If it's separate windings, 6 of the terminals will be the 2 pole windings. The other 6 will be the 4 pole windings.

Also the "S4" rating means the 7.4kW is not continuous.

Looking at an ABB catalogue, the constant torque / separate windings 2/4 poles have a 2:1 ratio of power, whereas the the dahlander ones it's more like 4:3. So I still guess dahlander for these twins.

cheers,
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Changing an induction motor voltage

Post by coulomb » Mon, 15 Jun 2009, 22:32

My own toe in the water for this rewiring idea.

Here is my 7.5 kW 4 pole 132 frame cast iron (unfortunately) motor that I'm considering for White Suzi:

Image
Edit: updated image pointing out room for joining and insulating.

Those ties are rather in the way. So I'll snip one and see what happens:

Image

Oops. Where the tie came off, the enamel looks different (red oval). In fact, it looks like fresh copper. Out with the ohmmeter... no, it's not bare copper. I think what's happened is that the enamel has darkened over the ages from UV light or heat, and where the tie was covering it, it hasn't darkened as much. Or something like that. Phew.

You might notice that the tie didn't so much untie as snap off. It's brittle as glass. In fact, I found this dentist's tool to be the best for getting behind it and pulling forward to snap it off:
Image

I've found my first crossover wire; it's really hard to see in the photo, and not much easier in real life:
Image
The wire just seemed different to the others somehow. You can see that it runs from slot 2 on the left to slot 3 on the right. I think if I cut it in the middle, I should be able to get it to the outside of the windings where there is a moderate amount of room for joining and insulating.

But there are a lot of red herrings, like this one:
Image
This wire (above yellow scribble) goes from outer to outer slot. (Edit: Where the white arrow points also looks a bit different; I'll check it out too, but it's also likely to be a false positive.)

So I think I have a fair bit of eyeballing to do.
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Changing an induction motor voltage

Post by weber » Mon, 15 Jun 2009, 22:36

Hey Woody, you have a good point about the 3:4 power ratio thing too. So maybe it's in some sense a 12-wire dahlander? Can you direct me to something that explains how dahlander windings are physically arranged in the stator.

I was imagining something that changed speeds by reversing the phase of one pole in each phase to create consequent poles and thereby go from 2-pole to 4-pole. But I guess that's not dahlander.
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Changing an induction motor voltage

Post by weber » Mon, 15 Jun 2009, 23:01

coulomb wrote: I've found my first crossover wire;

So unlike acmotors' case, you're looking for crossovers between the 3 concentric coils making up a pole, as well as the crossovers between the poles making up a phase.

Well done. Only 14 more to go. My previous more pessimistic claims of how many you had to find were wrong.

I still think you'll get currents circulating between coils and overheating the motor. But I really hope I'm wrong.
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Changing an induction motor voltage

Post by coulomb » Mon, 15 Jun 2009, 23:34

So do I have other realistic choices? I'm still catching up on coils verses windings etc.

If I parallel the two poles per phase (correct me if I'm wrong there), then I only get 1/2 voltage, right? Is it possible that only paralleling poles per phase will minimise circulating currents in delta?

I might be forced to run in star, or at least use a star/delta contactor so is in delta only at the highest speeds. But that's still a problem for highway driving.

With the circulating currents, does the extra resistance of the outer coils per phase come into play? I thought surely induced voltage is all about amp-turns, so the motor should be as balanced as it was before (in delta mode). As far as I know, motors don't have any special procedure to balance the resistance and/or voltage when connected in delta.

In fact, I think I'm still wanting to keep each pole in series to make each phase. Otherwise, it's 1/6th voltage. Each phase has two (real) poles, each made up of 3 coils taking up 2 slots each. So that's 2 slots per coil times 3 coils per pole times 2 (real) poes per phase times 3 phases, for a total of 2*3*2*3 = 36 slots. At present, everything up to the phases is in series, so that's 12 coils to rearrange.

So it seems to me that I only need to find the crossovers from coil to coil within one pole, not the pole to pole making up a phase. So that's just 2 connections per pole, times 2 (real) poles, times 3 phases, or 12 extra connections. The three pole cross overs don't need touching.

Edit: In fact, if the circulating currents are a big problem, I'm better off paralleling the poles per phase for 1/2 voltage (415/2 = 207), rather than 1/3 voltaging and operating in star (720/3 = 240). So to be able to do both, I should find all 15 points and bring them all out after all. Or just live with 1/2 voltaging, and only find 3 new points (ignoring the one I've already found).
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Changing an induction motor voltage

Post by woody » Mon, 15 Jun 2009, 23:36

weber wrote: Hey Woody, you have a good point about the 3:4 power ratio thing too. So maybe it's in some sense a 12-wire dahlander? Can you direct me to something that explains how dahlander windings are physically arranged in the stator.
Nah, I've got nothing. Google found this which has a 12 terminal winding, so a 3rd possibility of what these motors are.

One story which makes sense to me is that these motors were installed in a common piece of equipment, and the manufacturer required two speeds, but didn't know what voltage the customer would have. So you have a dual-voltage dual-speed.
weber wrote: I was imagining something that changed speeds by reversing the phase of one pole in each phase to create consequent poles and thereby go from 2-pole to 4-pole. But I guess that's not dahlander.
From the diagram:Image

There are 6 windings. I imagine as you say, 4 pole is consequent winding:

In 2 pole they are in pairs opposite each other in the stator with flux in the same direction (e.g. North at top of motor, South at bottom of motor)
In 4 pole one end is reversed, so both point inward with a consequent pole at 90 degrees (between the other 2 poles).

cheers,
Woody
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Changing an induction motor voltage

Post by woody » Mon, 15 Jun 2009, 23:54

coulomb wrote: So do I have other realistic choices? I'm still catching up on coils verses windings etc.
OK, so 6 sets of windings, all separate, each taking 6 whole slots each, no sharing.

So it looks like classic 2 pole motor, except it's a 4 pole with consequent poles.

Directions you could go:

parallel up each set of 3 concentric windings - this may backfire as the inner winding has less resistance and would take more than its fair share of the current and you wouldn't be very sinusoidally distributed any more -> efficientcy downwards.

reverse the opposite pole - giving you a real 2 pole motor with same torque as current motor, but double power / same current?

parallel opposite poles in same polarity - double current @ half voltage

parallel opposite poles in opposite polarity - double current @ same voltage @ double speed (2 pole)?

Parallel up each coil : extreme difficulty in locating the mid (or 1/3 + 2/3 or 1/4, 1/2, 3/4) point of each winding and paralleling.

not sure on the 2pole/4pole switching here. Treat with extreme dubiousness.
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Changing an induction motor voltage

Post by coulomb » Tue, 16 Jun 2009, 00:08

woody wrote:
parallel up each set of 3 concentric windings - this may backfire as the inner winding has less resistance and would take more than its fair share of the current and you wouldn't be very sinusoidally distributed any more -> efficiency downwards.
Ah, right! That's what I was missing; different currents in the coils.

Also, the windings with different currents would be in parallel, which could cause circulating currents within the pole, even if the motor was wired in star.

Ok, I think I'm finally getting it. Sorry to be a bit slow, guys   Image

Edit: spellink
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Changing an induction motor voltage

Post by acmotor » Tue, 16 Jun 2009, 01:27

Just a thought on the ellusive circulating current.

If I have the 4 poles (coils) in my little emotor in parallel then that should leave me open to current unbalance ?
This would show up as temperature rise when I hold 6000RPM with the 2 amps or so magnetising current flowing. However temp rise is minimal.

Does that mean that things are balanced or just that balance is less of an issue than we are thinking ? (or little motor ? or relatively high working voltage 415V so unbalance is relatively low ?).

Would unbalance be more of an issue if there were only 5 turns per coil ?

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Changing an induction motor voltage

Post by coulomb » Tue, 16 Jun 2009, 02:27

I think that the difference is that you are paralleling (up to?) 4 identical poles.

I'm thinking about paralleling three coils within the one pole, where the three coils have different lengths of copper.

My instinct is that the difference will be negligible, since magnetising current is all reactive, which is about amp-turns, not ohms. The turns are very well matched, but the ohms may vary by (wild guess) 20%.

Now I just have to figure out how to make suitable loads for the motor. Raising weights? I could regen them back into... into the cap bank. Ick. I guess it's time to get a shonky battery bank together.
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Changing an induction motor voltage

Post by coulomb » Tue, 16 Jun 2009, 03:35

Acmotor,

is this roughly the arrangement of your motor?

Image

I likely have several large errors... and it's obviously incomplete. But is the gist correct, i.e. each phase winding is 6 slots wide?

Do you have access to the two red windings I've drawn?

How have you gotten quarter voltage from this? I'm thinking you can't get more than half voltage from this, without centre taps. I'm thinking you get 6000 rpm just by pushing the frequency up to 200 Hz. Feel free to tear this to shreds, though   Image

PS if anyone modifies this, please save it in .png (or at least .gif) format. NOT JPEG! Image
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Post by weber » Tue, 16 Jun 2009, 04:52

coulomb wrote:Ah, right! That's what I was missing; different currents in the coils.

Also, the windings with different currents would be in parallel, which could cause circulating currents within the pole, even if the motor was wired in star.

Hi Coulomb, not all the way there yet. But very close. You're right that the circulating currents we're talking about here have nothing to do with delta and can just as easily happen in star. And you're right that we're talking about currents circulating between the 3 different coils making up a pole winding.

But circulating currents can't happen just because the coils have different resistances or even different inductances. This sort of imbalance on its own would only cause some coils to carry more than 1/3 of the current and so the sum of the I^2*R losses would be slightly greater than it would be if the currents were evenly distributed.

Circulating currents can only happen if the voltages induced in the coils are different. This would obviously happen if they had different numbers of turns each. But there is good reason to expect them to have the same number of turns.

What I'm talking about would happen even if the resistances were the same and the turns were the same. It would happen because the waveforms are different due to the different widths of the coils.

That's what Woody is getting at here:
woody wrote:... and you wouldn't be very sinusoidally distributed any more -> efficiency downwards.
The outer coil will make a broad wave with a flat top. The middle coil will make a more spiky wave. And the middle one will be somewhere in between. When connected in series they will add to make a reasonable sine wave.

But when connected in parallel, any instantaneous difference between them will be short-circuited internally.

You could also look at it in the frequency domain and say that the three coils have different harmonic spectra. While they could conceivably all have the smae amplitude and phase of the fundamental, they will differ in the amplitudes of various harmonics and these harmonic differences will be short-circuited between the coils.

These are the harmonic circulating currents I'm talking about.
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Changing an induction motor voltage

Post by a4x4kiwi » Tue, 16 Jun 2009, 06:26

Guys, you would kill for this book I got given last week.
Image

http://a4x4kiwi.blogspot.com/2009/06/i- ... ok-on.html

Let me know if you have any specific questions and I will try and find the answer. The text is heavy going, and only human searchable.
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Changing an induction motor voltage

Post by acmotor » Tue, 16 Jun 2009, 07:16

coulomb wrote: Acmotor,

is this roughly the arrangement of your motor?

Image


Nope

Firstly, the stator in my emotor is round and secondly all the copper wires are the same colour.
....and thirdly, it is nothing like that.

Having set all that, I will offer my attempt at a drawing for the flat earth society.

Image

The new wiring is for 104V (1/4 voltage) mode.
I have connected in star as the original was 415V in star.
I can also connect in 60V delta.

The current direction (start/finish) of each coil in the new configuration is arranged to match the NSNS of the original connection, so it is running in 4 pole at 50Hz at 1500RPM.
I paid careful attention to this with the Faed Flux Finder.Image

Oh and weber, you're making my head hurt. Image

Mal, throw that book of yours at him. Image   
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Changing an induction motor voltage

Post by acmotor » Tue, 16 Jun 2009, 07:58

coulomb, I'd be chasing that dark sleeved wire in the very centre of your picture (not the one your arrow points to) and its mate at the other end of the pole coil. You only need to find the three inter 'pole coil' connections to make your emotor 1/2 voltage. If it is a consequential pole motor then the wire runs nearly 90° around the stator and is likely to be in a sleeve.
This would be a lot less work than the wiring I had to do with 4 pole coils per phase since you only have two.

( or are you still chasing 1/4V ? )

Mal, can you see if your book suggests the same about the inter pole wiring connection ?

[quote="coulomb"]

Image
QUOTE]
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Changing an induction motor voltage

Post by acmotor » Tue, 16 Jun 2009, 08:23

Boy was I slow on the uptake....

Bluefang photoshopped blue to the pic of the motors !!!
Is that like licking them and putting your mark on them !Image
Bluefang wrote:
Image


ABB motors are an industrial grey colour (Only blue in a Melbourne winter). Even a re spray would not have gone inside the terminal box and on the floor ! Image
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Changing an induction motor voltage

Post by coulomb » Tue, 16 Jun 2009, 14:08

a4x4kiwi wrote: Guys, you would kill for this book I got given last week.
Image

That sound you hear is my axe grinding to a smooth, sharp edge ....   Image

Excellent find! I'm getting some great info from just the photos on your blog. I'll see if I can find it at my local state library.

Does it happen to mention anything about "circulating currents"?
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