We connected 3-75kVA transformers (%Z = 1.5) in a Delta (Primary - 12kV) and Delta (Secondary -480V). When we measured the voltage on the secondary, we read 500V Line to Line; but the line to ground voltage readings were not what I expected (230V, 240V, and 430V). I was expecting to read 277V on all three phases. Any clue of why the variation in line to ground voltages?