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ungrounded delta #72960 12/12/06 09:56 PM
Joined: May 2001
Posts: 376
F
frank Offline OP
Member
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
Joined: Sep 2003
Posts: 200
U
u2slow Offline
Member
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
Joined: Jul 2001
Posts: 599
J
JBD Offline
Member
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
Joined: Jul 2004
Posts: 9,575
G
gfretwell Online Content
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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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