Certain investigations on discrimination of inrush current and fault current in power transformers using hybrid ann

Abstract

Power transformers are one of the most essential and expensive components with respect to the operation of electric power system. On the occurrence of internal fault in a transformer, immediate disconnection of the faulty transformer is necessary and highly important to protect the power system module. Differential protection is commonly employed for transformer protection. When an unloaded transformer gets energized, high magnitude inrush current flows only on the energized side of the transformer, it ends up as spill current and the differential relay possibly malfunctions, which is basically not desirable. Thus the differential relay is expected to operate only for internal faults and not for inrush current, external fault, normal and over excitation conditions. Fundamentally, inrush current contains second harmonic component which is at least 15% of the fundamental component whereas the internal fault contains only negligible amount of second harmonics components on comparison with the fundamental component of the differential current. Conventional transformer protection scheme employs the percentage of second harmonics as criteria to discriminate internal fault from inrush current. Thus discriminating internal fault from inrush current is always a challenging power system problem. This research thesis aims to discriminate internal fault from inrush current and external fault, normal and over excitation conditions accurately and as well to minimize fault detection time. newline newline newline