During differential protection of transformer, the factor which influence the magnitude and duration of magnetizing current inrush is:

Inrush Currents: In a practical power system, when a transformer is switched on to the line by switching these circuit breakers, it produces a high current in the transformer and causes the circuit breaker to trip or it can blow off the fuse. The basic reason for the above-mentioned problem is the heavy magnetizing current drawn by the transformer. The value of the current may reach a level exceeding the full load current. This current is known as the Inrush Current.

Factors affecting the magnitude of Inrush currents:

• The value of residual flux in the transformer core.
• The non–linear magnetizing characteristics of the transformer core.
• The phase of the supplying source voltage at the instant of energizing the transformer.
• The impendence and short circuit power of the supplying source. 
• The size of the transformer.