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 is given. The waveform has the nature of sine function during normal operation of transformer and internal fault, but the magnetizing inrush current possesses fastigium wave characteristic with non-periodic components and intermittent angle during no-load switching. By identifying the extreme point of the waveform in all cases, a corresponding half cycle sine waveform is constructed. Then K function of sine degree of nearness is defined and used to distinguish magnetizing inrush current from fault current of power transformers. Results of dynamic tests show that the proposed method is feasible and correct.