Rpc: Balance And Phasing

[Uglydog]

I've been dragging my feet on getting my new lathe powered up until I was certain that my RPC was running correctly. I've always figured that the old induction motors on my Vintage Iron was pretty tolerant. Not so sure about the additional circuitry (which I don't understand) in this Colchester (expensive parts).

Friend of the family stopped by on Saturday with his ohm meter and oscilloscope.
First he confirmed that all three legs are balanced within about 1ov of each other.
Then he connected his oscilloscope to my elderly 20hp commercially built RPC up through an isolating device he had built from transformers.

Turns out that two of the legs nearly overlap. Thus, not phasing correctly.
He also observed that everything seems to work well enough and suggested I not worry about it.
Any thoughts on the matter?
Should I hire the electrical company that built it come and replace capacitors?

Meanwhile, on his recommendation I've powered up the lathe and "none of the smoke got out".
No real chips yet. Still aligning the tailstock.

Daryl
MN

 

[Ulma Doctor]

10v between phases is perfectly fine, the generated phase will be slightly behind the supplied phases.
as long as you utilized supplied power for running your control circuit you shouldn't have problems
you can monitor the amps per leg, to see how much it's pulling.
if it sounds good, & the voltage is within 10%- i'd say you have a functioning unit, USE IT!!!!

 

[Uglydog]

Thank you Ulma!
I'll move forward....

Daryl
MN

 

[Tony Wells]

Key thing is to know which is the generated leg and avoid it for anything that feeds a transformer, like a stepdown transformer for any controls, or to get 120V for lights or pump, or any electronics that are tapped off the feed power like a DRO. The main motor is much more tolerant to phase shift. Treat the generated leg like you would the "wild" leg in some commercial 3 phase. This is the same as Mike is saying, pretty much. It might be of interest to use a clamp on ammeter to check each leg of the motor as it runs. They probably won't be the same, but close enough.

 

[Uglydog]

Thank you Tony!!

Daryl
MN