Ratios-based universal differential protection algorithm for power transformer

Abstract

For safe operation of power systems, it is essential that the transformer protection operate reliably if a fault occurs. There are many challenges in developing a fast and accurate differential protection scheme that not only disconnects the transformer during internal fault conditions but also restrains during energizing and external fault conditions. A universal algorithm based on the ratios of primary and secondary voltages and currents, supplemented by current direction and wave-shape criteria, for power transformers with any type of winding connection, star or delta, is proposed. The ratios are the ratio of the absolute difference and absolute sum of primary and secondary line currents and the terminal phase voltages. The primary objective is to avoid incorrect operation of the conventional differential protection approach during energization, energizing on an existing internal fault and external faults under current transformer saturation. Performance studies confirm that the proposed algorithm can provide fast, efficient and reliable protection of a power transformer for all types of winding configurations.