Measurement of Vector Ratio in Three Phase Transformers

In three phase transformers, it is desirable to know the vector voltages on the secondary of the transformer relative to the primary vector voltages with balanced sinusoidal three phase voltage applied. A method is presented for measuring ratios in three phase transformers, using conventional single phase ratio test sets and the reasonably sinusoidal single phase voltage they use. Then the vector ratio of the output to input voltages for rated three phase excitation can be calculated. Methods for predicting the readings for the ratio tests are given, with tests and calculations on a rectifier transformer with 42.46230°phase shift.