Breaker trpping upstream a transformer while grounding its neutral
Breaker trpping upstream a transformer while grounding its neutral
(OP)
In our system, we have a 2km, 600V distribution line, where we have a 150 kVA Y/D step-up transformer 600/4160V at its beginning and a 150 kVA D/Y step-down transformer 4160/600V at its end, to lower the voltage drops across the line. A SQD 200A breaker TM with an instantaneous of 1000A protects the primary of the step-up Transformer 600/4160V. Whenever we try to ground any of those transformers neutral, the 200A breaker trips. We do not know what is the reason go that.






RE: Breaker trpping upstream a transformer while grounding its neutral
If the source is at the other end, then you can'y ground the neutral of the step-up transformer for the same reason.
RE: Breaker trpping upstream a transformer while grounding its neutral
RE: Breaker trpping upstream a transformer while grounding its neutral
What is source to the 600V system?
Breaker is at (600V?) _____
Then transformer
600V winding = ________ (wye, grounded wye, delta)
4160V winding = ________ (wye, grounded wye, delta)
Protection on transformer secondary/sending end of 4160V line = ______________
Then line
3 wire, 4 wire, or _________
Protection on receiving end of 4160V line/transformer primary = ________________
Then transformer
4160V winding = ________ (wye, grounded wye, delta)
600V winding = ________ (wye, grounded wye, delta)
Then what?
RE: Breaker trpping upstream a transformer while grounding its neutral
I will pick up all details soon and come back to you with it.
Thanks,
RE: Breaker trpping upstream a transformer while grounding its neutral
Step-up.
If the primary neutral of a wye/delta bank is connected to the supply neutral (as usually happens when a connection is grounded) any primary voltage unbalance or primary phase angle error will cause circulating currents in the delta winding. These currents are limited by the impedance of the delta winding.
This connection may be used for large scale power transmission but power transmission loads are generally well balanced and single phasing is rare. (Single phasing is an exreme form of voltage unbalance.) Also the typical PU impedance of a power transformer is typically much more than the impedance of a distribution transformer.
Bottom line, don't ground the wye point of the wye/delta step-up transformer. This is not a code violation in North America and is the RUS recommended connection for a wye/delta transformer or transformer bank.
Step-down.
Delta/wye with the wye point grounded is a commonly used connection for distribution circuits. Look for a ground fault in either the transformer or in the system that it is feeding.
Bill
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"Why not the best?"
Jimmy Carter
RE: Breaker trpping upstream a transformer while grounding its neutral