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#270 - 01/05/01 02:51 PM Transformer inrush current
Alan McNeil Offline
Member

Registered: 01/05/01
Posts: 18
Loc: Buzzards Bay, MA U.S.A.
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

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#271 - 01/06/01 07:09 PM Re: Transformer inrush current
Bennie R. Palmer Offline
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Registered: 11/09/00
Posts: 72
Loc: Milwaukie, OR 97267 USA
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.

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