Novel power transformer differential protection scheme based on improved short-window algorithm

This paper presents a new approach to improve the performance of the power transformer differential relay. The proposed approach enhance its anti-CT saturation performance during serious faults based on short data window improved Prony's algorithm, and is capable of acting rapidly when external fault converts to internal fault. The improved Prony's algorithm can obtain power frequency phasors of the fault current in a short time with unsaturated segment of the CT's distorted current. The reduced order method and optional sampling rate calculation method are employed to improve the efficiency of the improved Prony's algorithm. Moreover, a discrimination region is added into the traditional dual-slope differential characteristic. When the differential current trajectory enters into this discrimination region, an improved equivalent instantaneous inductance of transformer method is proposed to distinguish inrush current from internal fault and reliably block the protection during the transformer inrush current. A 242/66kV power transformer is simulated applying PSCAD/EMTDC for evaluating the performance of the proposed transformer differential protection. Extensive simulation studies show that the proposed approach results in a more sensitive and faster differential protection scheme.