A novel detection criterion for transformer inrush based on short-window filter algorithm

This paper presents a novel detection criterion for transformer inrush. The current magnitudes calculated by one-cycle Fourier filter will not change or change little with time, no matter for inrush current or internal fault current, because the filter window length is just the same as the power cycle. However, the magnitudes of inrush current calculated by short-window filter algorithm have distinct difference from the magnitudes of internal fault. The inrush current magnitudes calculated by short-window filter algorithm will fluctuate significantly around the magnitudes calculated by one-cycle Fourier filter, but the internal fault current magnitudes calculated by short-window filter algorithm are close to those by one-cycle Fourier filter. Based on the magnitudes calculated by Fourier and short-window filter, a novel inrush detection criterion is presented. Extensive simulation results show that the presented criterion can correctly distinguish inrush current from internal current.