How many amps, at 400 volts, can I get from a 300 kva [ 480v/ 400v] transformer?

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Originally Posted by Nathonian

How many amps, at 400 volts, can I get from a 300 kva [ 480v/ 400v] transformer?

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This answer can vary depending on the type of load. Assuming a non-inductive load,(no large motors) then your answer would be 300kva/400volts output=750 amps. This is in an ideal situation. In reality you have a less then perfect energy transfer, the "standard" for industrial applications is usually to caclulate for a 60% efficiency or Power Factor(PF). In this case 300kva*.6PF =180000/400volts yields you approximatley 450 Amps.

Hope This Helps,
Morrowrj

The expression Volt Amps of AC power, will include any power factor consideration on the circuit. A transformer rated in KVA will not need to be derated for any inductive or capacitive load.

Assuming this is a 3 phase transformer, due to the size and voltages involved, the amps available on the 400 volt secondary side is calculated:

300,000 VA / 400 volts * 1.73= 1297.5 or 1300 amps

Hmm, I normally work single phase... However it still seems like your calculation is off? Is it possible that the equation is KVa divided by the quantity of volts times 1.73 ?

300,000VA / (400 V * 1.73)

or

300,000Va / 692 = 433 Amps.

Please see here :Rex Power Magnetics - Home Page

Or here : How To Size Phase Transformers

Please let me know if I am missing something.



Morrowrj

Sorry I missed this, thought I would get subscribed just by answering.

You are right ,I can't believe I said that. The brackets mean to calc phase to phase voltage of 692, then divide.

Morrow is correct, the amps is 433.

Hello There

Sorry New, What Would Be The Right Size Transformer.

Power Coming In Would Be Single Phase 480

Output Is 120v , About 4.2a

I Figure About 1kva Would Be Plenty

Yes, I agree 1kva should be good. Did you check the links I referenced above?



Morrowrj