transformer circuit wiring

[jimmy_mcquade]

Hi everyone,

I am new to ths commercial side of wiring and dad is out on a job site, and
this is my question.
i saw an installation with 3 single phase 37.5 kva xfmrs / 208 secondary voltage, wired in y configuration wired as a 3 phase bank.
i looked up the single phase current capacity in the 2008 Ugly's book, p60 and found that the xfmr was rated 180.3 amps.
i also looked in the 3 ph. side and found that a 45kva xfmr was rated 108.3 amps. Same voltage and wiring.

Would someone please explain the difference.
thanks in advance,
Jimmy

 

[Chamuit]

If you are asking why the amps are different, the simple math is:

1 phase 120/240 45kVA

45000VA ? 240V = 187.5A

3 phase 120/240 45kVA

45000VA ? 416V (240V x 1.732) = 108.2A

3 phase 120/208 45kVA

45000VA ? 360V (208V x 1.732) = 125A

What goes in must come out (basically.)

INPUT______________________XFMR____________________OUTPUT
(208V x 1.732) 360V x 125A = 45000VA = 108.2A x 416V (240 x 1.732)