exfrmer primary ocpd

[Toros]

Hi,
I have a 500 kVA , 3-ph. @ 480/600v dry type transformer ,
if the primary is 400A C.B, what is the current of secondary @ 120/208v ???????

900A @ 120/208V ??????

Thank you

 

[don_resqcapt19]

500,000/208/sq rt 3

 

[kwired]

I agree with don, you have a 500 kVA coil. If you only have a 400 amp breaker on the primary you will trip it before you ever can deliver 500 kVA for any sustained period of time though. @ 480 volts that 400 amp breaker sort of limits you to only 332.5 kVA.

Not sure what you mean by 480/600 volt primary, unless it has taps for both voltages. I would think that would be sort of rare to have though.

 

[Toros]

500,000/208/sq rt 3

you meant,
332,000 /208/sq rt of 3

???

 

[kwired]

you meant,
332,000 /208/sq rt of 3

???

That is essentially what you have available with the primary breaker you have, though the transformer is capable of 500,000.

 

[don_resqcapt19]

Even with a 600 volt primary, I would be surprised if a 400 amp breaker would hold when you turn the primary on.

 

[Jraef]

A circuit breaker makes for a poor current limiting device because it only has a binary method of accomplishing that function.