# Two transformers 'trick' for 3 phase

Discussion in 'Electrical Engineering' started by Michael Moroney, May 25, 2004.

1. ### Michael MoroneyGuest

Question: If you need a certain amount of power (kva) 3 phase, are 2
transformers each with half the total kVA rating cheaper than 3 each with
1/3rd the total?

I was thinking of the Scott-T transformer configuration, which generates
90 degree 2 phase from 3 phase with 2 transformers. It also can produce 3
phase from 90 degree 2 phase when used "backwards". So if you have two
Scott-T configurations back-to-back you have 3 phase to 3 phase with 4
transformers. Not very useful. But since one transformer simply feeds a
second, they can be combined. So now you can have 3 phase to 3 phase with
only 2 transformers. But they are different: Transformer 1 has primary
and secondary A-CT-C and Transformer 2 is wired B-CT(1) (CT(1) means to
centertap of 1) The two transformers have different voltage/current
levels but have the same turns ratio.

Is there any reason why this configuration isn't used for commercial power
systems? The need for different transformers outweighs the fact you need
only 2 instead of 3? I don't know what the minimum kVA of a pole pig
is but I would think this combo might be useful for serving low power