Novel theory of identifying inrush current based on half-cycle sine waveform

A novel theory of identifying inrush current and fault current based on the different characteristics of waveform, which is a sine function during normal operation and internal fault; the magnetizing inrush current possesses fastigium wave characteristic with non-periodic components and intermittent angle. By identifying the extreme point of the waveform in all cases, a corresponding half cycle sine waveform was constructed. Then K function of sine degree of nearness is defined, according to the K value of differential current, both inrush current and fault current of power transformers can be distinguished. Results of dynamic tests show that the proposed method is feasible and correct.