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#270 - 01/05/01 06:51 PM Transformer inrush current  
Alan McNeil  Offline
Member
Joined: Jan 2001
Posts: 18
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 11:09 PM Re: Transformer inrush current  
Bennie R. Palmer  Offline
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Joined: Nov 2000
Posts: 72
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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