Digital protection method for power transformers based on an equivalent circuit composed of inverse inductance

An algorithm for the protection of power transformers is described in which transformers are represented by a universal equivalent circuit composed of inverse inductance, without reference to an internal fault. The circuit is derived from multiterminal network analysis of the windings. The intrinsic characteristics of the equivalent circuit elements are clarified by calculations for actual power transformers. The characteristics of the inverse inductance obtained by sampling voltage and current at each terminal are used to discriminate between internal faults and magnetizing inrush. Computer simulations for large power transformers and experimental studies on actual model transformers have confirmed that the algorithm can distinguish internal faults from a magnetizing inrush at very high speed