Maloperation of differential protection of transformers due to magnetizing inrush current is prevented by
1
setting the current of the relay higher than the maximum value of inrush current
2
keeping the time-setting long enough for the inrush current to fall to a value below the primary operating current of the relay.
3
bypassing the inrush current from the operating coil of the relay
4
filtering third harmonic content of the inrush current flowing through the operating coil and passing through the restraining coil