High Phase to Ground Voltage

[dcheser]

I am dealing with a 1,000KVA transformer (Delta-Delta) 13.8kV to 575Volt system and all phase to phase voltages read around 580 but the Phase to ground on the "A" Phase reads 470 to 480 volts while "B" and "C" phase are right where they should be around 300 volts. Never seen anything like this!! Any Ideas? We have checked the voltage with a multimeter under load and no load conditions and get the same results.

 

[StephenSDH]

How is the Delta Secondary of the Transformer Grounded?

 

[dcheser]

Not Sure how it is grounded. Was looking into it moments ago and I opened all of the branch circuits and the problem cleared. Began closing breakers until the problem appeared again. Ended up tracing it back to an MCC Bucket that feeds an Elevator. The Elevator has a built in capacitor bank, so I am guessing a capacitor may be the culprit.

 

[mivey]

How is the Delta Secondary of the Transformer Grounded?

Sounds like it isn't.

 

[zog]

Sounds like a low resistance ground fault on phase A

 

[mivey]

Sounds like a low resistance ground fault on phase A

How about a fault from B to C?

PS: the B & C 300 volts seems low to me

 

[mivey]

dcheser,

What are the current readings with and without the elevator?

 

[zog]

How about a fault from B to C?

PS: the B & C 300 volts seems low to me

Seems about right to me for ungrounded delta, all depends on the length of bus/cables, etc on the load side.

 

[zog]

I am dealing with a 1,000KVA transformer (Delta-Delta) 13.8kV to 575Volt system and all phase to phase voltages read around 580 but the Phase to ground on the "A" Phase reads 470 to 480 volts while "B" and "C" phase are right where they should be around 300 volts. Never seen anything like this!! Any Ideas? We have checked the voltage with a multimeter under load and no load conditions and get the same results.

Megger the load side yet?

 

[Cold Fusion]

I am dealing with a 1,000KVA transformer (Delta-Delta) 13.8kV to 575Volt system and all phase to phase voltages read around 580 but the Phase to ground on the "A" Phase reads 470 to 480 volts while "B" and "C" phase are right where they should be around 300 volts. Never seen anything like this!! Any Ideas? We have checked the voltage with a multimeter under load and no load conditions and get the same results.

Not Sure how it is grounded. Was looking into it moments ago and I opened all of the branch circuits and the problem cleared. Began closing breakers until the problem appeared again. Ended up tracing it back to an MCC Bucket that feeds an Elevator. The Elevator has a built in capacitor bank, so I am guessing a capacitor may be the culprit.

Your numbers are real close to an un-grounded system, with a fairly low resistance ground on the centertap between B and C.

If the caps are Y connected, I wouldn't suspect them.. But if they are Delta connected - maybe.

cf

 

[ptonsparky]

Your numbers are real close to an un-grounded system, with a fairly low resistance ground on the centertap between B and C.

If the caps are Y connected, I wouldn't suspect them.. But if they are Delta connected - maybe.

cf

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