A weighted mathematical morphological method for the identification of transformer sympathetic inrush

Sympathetic interaction between transformers would lead to mal-operation of transformer differential protection. Based on the fact that the waveform of internal fault current has the sinusoidal features while the sympathetic inrush has not, a weighted mathematical morphological method is proposed for the identification of sympathetic inrush. In the simulation studies, the identification results have proved that the proposed method can identify sympathetic inrush even when the current transformer is seriously saturated, where as the traditional second harmonic restrain method may misjudge the differential current as an internal fault current. Moreover, with the data window of half a cycle, the proposed method can reduce the processing time and achieve a better performance.