Can anyone tell me what the inrush current of a 480/208 75kva transformer would be if it was typically loaded on the secondary side at around 135 amps? I know it goes way high, but I need a ball park figure for argument sake. My boss wants to know why they keep popping the breaker when the transfer switch goes back to normal power. I need a ball park figure
Alan: I calculated the maximum inrush current for a 75 KVA transformer as 990 amps. I do not know the duration. The secondary load is irrelevant for inrush calculations. A circuit breaker with a time trip curve that will permit 990 amps, with a duration necessary to establish core flux, would be required for starting the transformer.
