Magnetizing inrush identification based on differential current characteristics

The waveform characteristics of transformer magnetizing inrush and internal fault current are analyzed and a method to identify magnetizing inrush is presented. The internal fault current calculated by full-wave Fourier algorithm is close to that by half-wave Fourier algorithm. Contrastively, the magnetizing inrush calculated by full-wave Fourier algorithm is quite different to that by half-wave Fourier algorithm. Calculate the differential currents by both full-wave and half-wave Fourier algorithms and their difference, then calculate the ratio of the integral of the differential currents calculated by full-wave Fourier algorithm for half power frequency period and that of the differences. The differential current is taken as the magnetizing inrush if the ratio is greater than a setting value, otherwise as the internal fault current. The theoretic analysis and the dynamic emulational test results indicate that, it can distinguish the magnetizing inrush from internal fault current rapidly and can be applied to each phase separately, improving the reliability and security of differential protections.