Digital simulation of the transient phenomena in high voltage power transformers with particular reference to accurate fault detection

This paper presents a technique developed to accurately model a power transformer for the purposes of simulating its transient phenomena both under faults and due to magnetising inrush, under a whole variety of different system and fault conditions. The transient characteristics of magnetising inrush currents and internal faults, including symmetrical and asymmetrical faults as well as the winding turn-to-turn and turn-to-ground faults of the power transformer are studied in detail. The simulation also includes a model of a current transformer (CT) used for measuring current flowing through the power transformer under faults; in the latter case, the effect of CT saturation on the measured current is also modelled. The purpose of the simulation is to develop alternative techniques for satisfactorily protecting the power transformer under a whole variety of practically encountered faults and at the same time being able to distinguish internal faults from magnetising inrush current.