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Is it practical for a RPC to generate 440 volt 3-phase from 220 single phase?

I had a perhaps dangerous thought.

Many 3-phase motors are wound for 220/440 volt 3-phase, with coils in parallel for 220 and in series for 440 operation. It seems to me that if such a motor can be wired in the Wye configuration, one could feed

220 single phase to the center tap of one of the three 440-volt inputs, and take 440-volt three phase off the three 440-volt "inputs". Actually, delta could work as well, so long as one can access a center-tapped coil.

The big disadvantage that comes to mind is that that one coil (half of a

440-volt input, so one of six coils) has to handle the entire power input, but then again large used 3-phase motors are not that expensive for their capacity, and one avoids the need for a big 220 to 440 transformer.

Joe Gwinn

Reply to
Joseph Gwinn
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Um, OK. Your 220 voltage comes out of your panel on L1 and L2. You hook L1 to the center tap, and where do you hook L2?

This can never ever work. The voltage at the center taps may be 220 from one center tap to another, but there are 3 center tap points and the voltage waveforms need to all be 120 degrees out of phase at those center taps. No way to get the 120 degree out-of-phase from single phase using your scheme, seems to me.

Grant

Reply to
Grant Erwin

Sounds very interesting, I think that it is a good time to find a cheap 3 phase motor and experiment. It is a fascinating thought.

i
Reply to
Ignoramus13308

Imagine three windings (ASCII art)

*C / \ . . / \ *---.---* A x B

The OP was proposing to apply 220V to points x and B. If one winding can act as its own transformer, which is kind of possible, then it would induce 440 volts between A and B.

That 440v can possibly keep this idler motor spinning and generating out of phase voltage in point C. That would be your 440v three phase.

I think that it is an interesting idea, though its efficiency may not be great, but I would sacrifice a motor to try it.

i
Reply to
Ignoramus13308

You have it right. And, yes, a winding can act as an autotransformer. The question is how good an autotransformer it will be.

Joe Gwinn

Reply to
Joseph Gwinn

Joe, why don't you find out, this is a very exciting development. I will be VERY interested in outcome. I have a 2 HP dual voltage motor that I could use for such an experiment, but I am very pressed for time and am leaving on vacation this Sat.

i
Reply to
Ignoramus13308

Well, for one thing, I don't have such a motor, so you are way ahead of me. Nor do I have anything that must have 440, but there seems to be a lot of 440 volt 3-phase stuff available fairly cheap, presumably because it's an awkward kind of power for a HSM to handle.

Joe Gwinn

Reply to
Joseph Gwinn

It's perfectly practical. Conceptually, very little different from me feeding

240V into a star wound motor and getting 415V out. The downside to both is that the output rating of the convertor is a lot less than rating plate power. If you could get a 220/220 isolating transformer then you would obviously do better by using it to feed the other half of the winding. But 220/220 transformers aren't common as surplus in decent sizes :-(

What about using the two windings of the input phase in parallel, isolated from the other two phases, and using the other two phases to generate a wild-leg three phase. It'd be messy, but could be made to work.

Mark Rand RTFM

Reply to
Mark Rand

This should certainly work well, but it may be easier to come up with surplus 220:440 transformers. It will probably come down to which kind of transformer one comes upon first.

It should work, but it seems simpler to me to get a larger motor.

Joe Gwinn

Reply to
Joseph Gwinn

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