The phase sequence or the order , by which the phases attain their highest positive voltages , should be similar for 2 paralleled transformers . Other-wise , during the cycle , each pair of phases would be short circuited .

The several secondary connections are available in respect of different primary three phase connection in a 3 phase transformer . So for similar primary applied 3 phase voltage there might be different 3 phase secondary voltages with various magnitudes and phases for different internal connection of the transformer . Let's have a discussion in detail by example for better understanding .