Delta wye?
Delta wye?
(OP)
Please assist with the following situation. I am looking to see if anyone else has ever encountered this phenomenon.
Power logged secondary of a delta wye 480/208/500 KvA xformer for six hours. After about four hours, the RMS on one leg(L3) dropped to about 40 volts from 120 volts, with simultaneous jump in voltage from about 120 volts to 145 volts on the other two legs(L1&2). current on L3 at the time went from~170a to ~120a,L1 current went from ~260a to ~180a,L2 current had no appreciable change.Here's the kicker....
A neutral current jump occurred simultaneously, from about 160 amps to 760 amps,and remained that way till the logger stopped
(2 hours)---Following morning all systems were normal
xformer feeds office building tenant outlets mostly L-N loads
Power logged secondary of a delta wye 480/208/500 KvA xformer for six hours. After about four hours, the RMS on one leg(L3) dropped to about 40 volts from 120 volts, with simultaneous jump in voltage from about 120 volts to 145 volts on the other two legs(L1&2). current on L3 at the time went from~170a to ~120a,L1 current went from ~260a to ~180a,L2 current had no appreciable change.Here's the kicker....
A neutral current jump occurred simultaneously, from about 160 amps to 760 amps,and remained that way till the logger stopped
(2 hours)---Following morning all systems were normal
xformer feeds office building tenant outlets mostly L-N loads






RE: Delta wye?
respectfully
RE: Delta wye?
RE: Delta wye?
Is the length and impedance of the neutral from the transformer to the data logger consistent with a voltage drop of about 80 volts at 760 amps?
Is this the only transformer in the building?
I see two possibilities, a heavy current on the neutral from another system, possibly a ground fault combined with improperly interconnected grounds and neutrals, or a problem with the data logger.
respectfully
RE: Delta wye?
There is one other 25kva emergency xtransformer --have not ruled out a bad logger---although it's new--
Thanks
RE: Delta wye?
I am sure that if one phase actually went to 40 volts you would hear about it.
respectfully
RE: Delta wye?
An open neutral on the other system could force neutral current through the ground and some could flow through the 120/208 neutral if it were grounded in two places. Voltage drop in the neutral could produce imbalanced voltages at the transformer but balanced voltages at the load.
This explanation only is possible if the neutral measurements were made on the load side of the transformer neutral ground.
It might even be utility primary neutral current flowing through the ground.