High-Low Transformer Fault - What Evidence Would Remain?
High-Low Transformer Fault - What Evidence Would Remain?
(OP)
If there were a fault somehow between the high side and the low side of a medium voltage-low voltage transformer such that the high side voltage were to be seen on the low side, what evidence would be left?
The question is intentionally vague to not bias the answers, but if high side voltage appeared on the low side, what tell-tale signs would be left? Could be in the transformer, what tests would show what? Could be in relay records on the high side circuit that feeds the transformer, what would we see in currents and/or voltages?
Transformer is one of many on an underground distribution circuit. Transformer is pad-mount type oil transformer with dead front bushings on the high side and spade lugs on the low side. High side in loop through with a load-break switch under oil in the tank.
Thanks.
The question is intentionally vague to not bias the answers, but if high side voltage appeared on the low side, what tell-tale signs would be left? Could be in the transformer, what tests would show what? Could be in relay records on the high side circuit that feeds the transformer, what would we see in currents and/or voltages?
Transformer is one of many on an underground distribution circuit. Transformer is pad-mount type oil transformer with dead front bushings on the high side and spade lugs on the low side. High side in loop through with a load-break switch under oil in the tank.
Thanks.






RE: High-Low Transformer Fault - What Evidence Would Remain?
David Castor
www.cvoes.com
RE: High-Low Transformer Fault - What Evidence Would Remain?
But its possible that, for some point on a high side Wye winding close to the neutral point, the fault would just look like a shorted turn. There might not be enough fault current to trip high side protection or a high enough voltage placed on the secondary to cause problems. So the fault would just sit there and fizzle. Oil analysis could reveal its presence. Or you could take the transformer out of service and test winding insulation.
RE: High-Low Transformer Fault - What Evidence Would Remain?
RE: High-Low Transformer Fault - What Evidence Would Remain?
If the secondary side was not well grounded, then arcing fault could cause an elevated voltage via repetitive restrike, but if it is solidly grounded, that seem unlikely, at least theoretically.
That's probably a logical inference, but might there be other scenarios that could explain the same fault data? The substation relay is just giving current and (possibly) voltage data.
David Castor
www.cvoes.com
RE: High-Low Transformer Fault - What Evidence Would Remain?
It's those other scenarios I'd like to find out about. To settle it one way or the other conclusively, or even to find that there are multiple scenarios that work with the observed record without being contradicted by portions of the evidence.
RE: High-Low Transformer Fault - What Evidence Would Remain?
RE: High-Low Transformer Fault - What Evidence Would Remain?
David Castor
www.cvoes.com
RE: High-Low Transformer Fault - What Evidence Would Remain?
Alan
RE: High-Low Transformer Fault - What Evidence Would Remain?
I can't answer about the low side neutral-ground connection, but these are new installations, the events happening fairly soon after initial energization. Multiple tests, but I don't know exactly what, performed prior to energization.
RE: High-Low Transformer Fault - What Evidence Would Remain?
I'm sure you've already thought of all this.
David Castor
www.cvoes.com
RE: High-Low Transformer Fault - What Evidence Would Remain?
RE: High-Low Transformer Fault - What Evidence Would Remain?
Another scenario may be poor or no earthing of neutral and consequent unbalanced overvoltage on any phase.
RE: High-Low Transformer Fault - What Evidence Would Remain?
Under-rated fuses could explain the fuse failures. Restrikes during fuse failures may cause high voltages.
RE: High-Low Transformer Fault - What Evidence Would Remain?
RE: High-Low Transformer Fault - What Evidence Would Remain?
Relay events clearly show a 3-phase low current event, followed by a bit of transition and then a phase-phase high side fault on the high side (for two events, one was cleared on the low side without fuse operation). The high side fuse failure seems to be the result of the low side event rather than a cause. All of the transformer damage found is around the fuses and no damage to the windings or insulation.
RE: High-Low Transformer Fault - What Evidence Would Remain?
ABB