Vector Group test is done in order to know the phase displacement between the high voltage and low voltage winding.
Without earthing the winding neutral points, interconnect one phase of HV winding (say 1U ) to the corresponding phase of LV winding 2U and apply a balanced 3 phase low voltage to the HV winding. The phase sequence of the supply should be the same as the specified phase sequence of the transformer winding. The phasor will show you how to measure the voltages between any terminal.
Connections for Dy11 and Dy1 transformers and the corresponding vector groupings are given in figure:
Measure the voltage between the primary and the secondary terminals. The following requirements shall be fulfilled depending on the vector group of the transformers :