Simple Question, Quick Answer

[cruzy]

So one of my books says that the turns ratio of a three phase transformer bank of a 13 kV delta - 138 kV wye transformer is 13/ (138/sqrt 3). Is that the single phase transformer ratio of one of the three transformer making up the bank, or is that the total three phase turns ratio?

 

[cableguy]

For a single phase transformer version of that, the voltage of the low side is 13kV, the voltage of the high side of that would be 138/sqrt(3) - so the ratio you are giving would be for a single transformer.

 

[cruzy]

For a single phase transformer version of that, the voltage of the low side is 13kV, the voltage of the high side of that would be 138/sqrt(3) - so the ratio you are giving would be for a single transformer.

So if they had asked for the turns ratio of the three phase transformer as a whole, it would have been 13/138? (Just like NCEES #506 would have been 115/24?)