BISAM wrote:

The maximum current through each transformer stays the same whether it is connected single phase or three phase. Therefore, for a Wye connection the kVA is E X I X Sqrt 3. --> 37.5 X 1.73 = 65 kVA. In Wye, the phase current = the line current. If you were making a Delta connection the total kVA would be 37.5 X 3 since the line current = the phase current * sqrt 3. In delta, kva = E X I X sqrt 3 X sqrt 3 = E X I X 3. Hope this helps.

I don't think so, or perhaps both yes AND no.

The KVA RATING of each transformer stays the same, regardless of the configuration. [And in the above I assume you are talking primary side configuration]

To do an apples to apples comparision, you still have to be applying 1PU voltage across the winding.

In your Wye case, your Line voltage also needs to be multiplied by Sqrt3 to get you back to 1PU on the transformer, getting you back to an overall KVA rating of E*I*3.

Or if you want to look at it the other way, you need to recalculate the NEW transformer KVA 1PU base at the "new" 1PU voltage, and the new total KVA will still be 3 * the new KVA base. [Yes, the new total KVA would be 65]