A novel method for discrimination of internal faults and inrush currents by using waveform singularity factor

A novel algorithm using waveform singularity factor (WSF) for distinguishing between inrush currents and internal fault currents in transformers is proposed, which is derived from the singularity features of the waveforms of currents. First, the definition and the calculation method of WSF are presented and then the criterion to identify the internal faults and inrush currents are developed. In a total of 162 experimental cases, the WSF represents different characteristics between the inrush current and an internal fault. The experimental results verify that the WSF calculated in real time is able to clear internal fault even low level internal turn-to-turn fault rapidly, correctly, and reliably.