# Help with 3 phase tranformer readings



## KenB (Feb 5, 2014)

Recently expierencing some odd equipment faliures in a industrial facility. Phase to ground readings have got me confused for sure. This is right off the Utilies transformer feeding their substation.

Phase A to ground 25v
Phase B 473v
Phase c 503v

Phase to phase readings look normal.

Im told that this has always been the case, "it's a high leg". To me this is indicating a phase shorting to ground. This is not a 4 wire system why would a phase be grounded?


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## bkmichael65 (Mar 25, 2013)

Corner grounded delta


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## Big John (May 23, 2010)

It's an ungrounded delta with what sounds like a high-resistance fault on one AØ.

Ungrounded systems often have screwball L-G readings because there's no hard connection to keep them stable. That said, they usually don't have that severe an imbalance, so it suggests a problem.

If you can schedule an outage, start at the service and shut off feeder breakers one at a time until you see the L-G voltages approximately balance. Then start chasing the problem down your suspect feeder.

The other option is look to see if they have a pulser system. Turn that on and use an ammeter to try and chase down the source of the ground fault.


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## KenB (Feb 5, 2014)

Thanks for the replies. Apparently a similiar problem occured in the past and was resolved just as you suggested Big John. I need refrsh myself on transformer wiring, if dont use it you lose it I guess.


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## JW Splicer (Mar 15, 2014)

You should put in ground fault detection. It can be as simple as 3 pilot lights...


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