Tranformer Calc question?

[deharoj]

I have 3 ph 480V primary. I need to get 400A on the secondary (120v - 208v)>

Can someone tell me the size of the transformer and what amperage my primary should be?

Thanks in advance, I'm just checking myself.
I came up with Primary amps at 175 and the transformer at 112kva.

 

[jatrottpe]

400A per phase secondary
400A * 208V * 1.732 = 144.102kva ~ 150kva transformer

Primary
144102 / (480 * 1.732) = 173a

150000 / (480 * 1.732 ) = 180a

 

[charlie b]

I agree with jatrottpe's math. Please note, however, that the values of 400 (secondary) and 180 (primary) are the transformer's approximate current ratings, not the ratings of the associated overcurrent protection device.

 

[micromind]

The primary (480) current on a 112 KVA xfmr is 135 amps; the secondary current is 312. On a 150 KVA, it's 180 and 416.