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Ground to phase measurement on Wye 3 phase motor curcuit

Ground to phase measurement on Wye 3 phase motor curcuit

Ground to phase measurement on Wye 3 phase motor curcuit

(OP)
Hello,

I was tasked with measuring a 3 phase motor for imbalance. The imbalance is less than 1% for current and phase to phase voltage. The phase to ground imbalance is 8% at the max deviation. Is there a standard as far as the phase to ground imbalance? It is a Wye 3 phase 120 phase to phase circuit.

Thanks,
Rachel

RE: Ground to phase measurement on Wye 3 phase motor curcuit

Not sure what you are asking or why. There is no relationship to the Y connection of a motor to ground (or Delta connected for that matter). "Phase to ground imbalance" is essentially meaningless.

RE: Ground to phase measurement on Wye 3 phase motor curcuit

Your phase to ground voltage is a characteristic of the system. It is not seen by the motor and does not affect the motor directly.
respectfully

RE: Ground to phase measurement on Wye 3 phase motor curcuit

Are you saying the source voltage is derived from a wye transformer, phase-to-phase voltage imbalance is under 1%, and that the phase-to-ground voltages are imbalanced by 8%?

How are you calculating imbalance?

What are the phase-to-phase and phase-to-ground voltages you've measured?

What type of meter was used (i.e. - Fluke 87, etc.)?

So far as I know 'phase-to-ground phase imbalance' is as waross stated, and should not affect motor operation, but it seems an odd variance if you indeed have a solidly grounded wye power system (but not too uncommon if power is derived from a delta transformer).

I've seen cheap throw-away digital multimeters give all sorts of odd readings in the presence of harmonics (which is why I asked about the meter).

RE: Ground to phase measurement on Wye 3 phase motor curcuit

(OP)

Hi,
 The Phase to Phase looks to be balanced. I just thought the differences in voltage on the phase to ground would have been closer. But I have learned from this thread that this is not the case.

Phase to phase:

 L1-L2 =122.1V, L2-L3 = 121.9V, L3-L1 = 121.8V

 
Phase to Ground

 L1 64.3 V, L2 75.4, V L3  69.4

 Thanks to all.

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