CABLE SIZE FOR 500KVA TRANSFORMER

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PatStrachan41767

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I want to calculate the Amperes of a 3-phase system using 3 - 500kva transformers @ 480V Secondary.

Am I correct in saying that:

Amps = (3 x 500kva x 1000)/(480V x 1.73)
= 1800 Amps (each phase)

Thanks.
 
Re: CABLE SIZE FOR 500KVA TRANSFORMER

Originally posted by PatStrachan41767:= 1800 Amps (each phase)
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You were right until you got to the "each phase" part. You should not look at current in terms of "each phase." It will get you confused. You will be tempted to multiply 1800 per phase times three phases and get 5400 amps, and that will be very wrong. Just say "equals 1800 amps," and you'll have it.
 
Re: CABLE SIZE FOR 500KVA TRANSFORMER

Why not use only one tranformer of 1500KVA, it will yield the same result, and perhaps will be more economical than using 3 Numbers of 500KVA transformers.
 
Re: CABLE SIZE FOR 500KVA TRANSFORMER

Thank you very much!

I have one more question! Now that 1800Amps total is established for the 3 - 500KVA Transformers, is it safe to say that 3 - 500MCM cables per phase is adequate to withstand the full load current of the transformers?
 
Re: CABLE SIZE FOR 500KVA TRANSFORMER

Originally posted by PatStrachan41767:
Thank you very much!

I have one more question! Now that 1800Amps total is established for the 3 - 500KVA Transformers, is it safe to say that 3 - 500MCM cables per phase is adequate to withstand the full load current of the transformers?
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No. 500 Kcmil is a 380 amp conductor. You would need 5 sets of 500 to get that.
 
Re: CABLE SIZE FOR 500KVA TRANSFORMER

I have to ask this cause it is something I see all the time and I can't quite figure why its done.

Would it not make more economic sense to set the three xfmrs somewhere closer to the point of use and run HV to them at a much smaller wire and conduit size?
 
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