You can use one single-phase 75kVA transformer or three 25kVA transformers for this load.
AN, BN, and CN are 120? Voltage Transformer Polarity Testing Below is the test set up for testing a Voltage Transformer or Potential Transformer polarity testing.
If you were feeding a single piece of 480 equipment that had no need for 277 then why add the expense of a Wye wound secondary on a transformer? In wye configuration, the loads are unbalanced in a Y configuration.