A new technique for current differential protection of transformer

Abstract

This paper proposes the application of moving window averaging technique for differential protection of transformer. The instantaneous currents of primary and secondary are transformed by using moving window averaging technique for the window width of one cycle. The steady state values of transformed currents are zero for a sinusoidal signal. However, the presence of harmonic and dc offset may deviate it from its nominal zero value. The energization of transformer leads to decaying transient inrush current which mal-operate the differential relay. The power transformer is modeled in ATP-EMTP environment considering core nonlinearities and losses so as to capture inrush current. The moving window averaging technique based current differential protection algorithm is implemented in MATLAB. The relay is tested for various internal and external faults. The result promises applicability of proposed algorithm for protection of transformer.