Transformer KVA calculations

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ezterms

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Maybe you can settle this arguement.

If I have a 480 volt variac rated at 70 amps continuous current feeding a 480 to 240 gen purpose transformer , what KVA should the transformer be rated at to produce approximately 140 amps out the secondary.

The input is 3 phase - delta
and output is same

Thanks
 
Re: Transformer KVA calculations

The source of power (i.e., your variac) has no bearing on the question you are asking. 140 amps times 240 volts times the square root of three is about 58.2 KVA. The transformer must have a rating of at least that number. I believe the next higher standard size is 75 KVA.
 
Re: Transformer KVA calculations

Thanks Charlie, 75 KVA was the original selection.

How about this one.

A 480 to 240 gen purpose transformer for a 180 amp secondary load.

Single phase 480 input - single 240 output
 
Re: Transformer KVA calculations

For a single phase calculation, just drop the factor of the square root of three. 180 amps times 240 volts equals 43.2 KVA. The next larger standard size is 50 KVA.
 
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