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ungrounded delta #72960
12/12/06 09:56 PM
12/12/06 09:56 PM
frank  Offline OP
Joined: May 2001
Posts: 376
windsor ontario canada
I have a 600v ungrounded delta with voltage readings of 309v,309v and and 513v phase to ground instead of the typical 347v at the sevice enterance.
Voltage phase to phase is 619v and the ground indicator light panel is Fried.
Opinions please.

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Re: ungrounded delta #72961
12/12/06 10:33 PM
12/12/06 10:33 PM
u2slow  Offline
Joined: Sep 2003
Posts: 200
Salt Spring, BC, Canada
Those readings have the same proportions as a high-leg delta.

Are there any single-phase distribution transformers in house? If the X0 and H0 points on such a transformer became inadvertently tied together, I think you could get that result.

Re: ungrounded delta #72962
12/12/06 11:46 PM
12/12/06 11:46 PM
JBD  Offline
Joined: Jul 2001
Posts: 599
Your readings probably mean nothing. You are probably seeing the effects of an unbalanced load on the coupling capacitance of your system. The phase to ground voltages will only be equal under balanced loading. The "better" (high impedance) your meter the more sensative it is to this effect.

You should not try to measure a voltage without a constant reference point except for historical purposes. I have seen ungrounded systems with voltages to ground as high as 2x the phase-phase voltage.

Re: ungrounded delta #72963
12/12/06 11:49 PM
12/12/06 11:49 PM
gfretwell  Offline

Joined: Jul 2004
Posts: 9,184
I would be curious what happened if you put a small load from line to ground. It would indicate if this was some kind of high resistance path to ground or a real bolted ground.
What kind of ground fault indication are you using?

Greg Fretwell


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