Identifying inrush currents from internal faults using symmetrical components in power transformers

This paper presents a novel technique for three phase transformer protection, which the method effectively identify magnetizing inrush currents from internal fault currents. This technique employs symmetrical components. When transformer is switched, inrush current happens. This current have some features, which it is enough for identify itself. In this paper, by extract these features, a new criterion is proposed to discriminate inrush currents from internal faults in power transformers. In faulty time such as switching or short circuit, the value of negative sequence for differential current is different from positive sequence value. Helping this feature, new criterion is introduced. Simulations show this criterion works properly in over-flux and CT saturation condition too. The simulated results presented clearly, the proposed algorithm can accurately discriminate between an internal fault and a magnetizing inrush current in power transformer protection in all cases.