EDM in FHP split phase induction motors?

[Skogsgurra]

I do lots of work on EDM (bearing currents) in large AC induction and synchronous machines and also DC motors. Coupling mechanisms and failure mechanisms are well understood and most situations can easily be handled. Sometimes at a cost. But so far, all cases I have been in contact with has been solved.

Now, I start to see EDM also in FHP split phase motors. I can explain why we have it, but the problem doesn't seem to be severe enough for anyone to care. My question is, thus:

Do you know about any situations where motors fed from Line-Neutral or Line1-Line2 have unexpectedly short bearing life?

There may also be anecdotes about motors emitting HF interference even if they are constant speed (no VFD).

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[electricpete]

I saw your waveform on slide 39 in the other thread and it was thought provoking.

http://www.gke.org/presentatiofner/files/GE Bearings and their electric environment w O and E.pdf

Our plant has many single phase motors, but none are powered off three phase system line-to-neutral or line-to-line.

I think it would apply also for household 120 vac motors powered line to neutral where neutral is grounded at service entrance (center tapped 240vac)?




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(2B)+(2B)' ?

 

[Skogsgurra]

Yes. As soon as the vector sum of the terminal voltages isn't zero, there will be a rather large common mode voltage. BVR is quite high in FHPs, so the effect is readily observable also in 120 V motors. As you can see, there are also lots of lower voltage breakdowns. They occur quite often and that is why I ask about EMI from such motors.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[electricpete]

So then, the vast majority of single-phase ac motors would see common mode from their voltage supply. The only ones not included would be those connected to the non-grounded outer phases of a grounded-center-tapped winding (for example household 220 vac motors).

It makes it all the stranger that we don't hear more about it (as you've mentioned). I've certainly never heard of it. I'll look forward to learning more as you (hopefully) present your findings/conclusions to the forum at some point.



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(2B)+(2B)' ?

 

[Skogsgurra]

Actually, one guy brought the problem up last week. There seems to be a problem with small cooling fans that emit radiation from the motor shaft "mainly in the 108 to 152 MHz aeronautical band".
There is probably more emission below that frequency band, but the victims were in the "aeronautical band". I will certainly be on my toes!
Anyone else seen this?

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.