Study of the Inrush Current Identification Using the Improved Half-Cycle Fourier Analysis

Among the traditional schemes of current differential protection for power transformer, the principles of second harmonic restraint and dead angle restraint to distinguish inrush current from fault current are influenced such many factors as the decrease of transformer core magnetic saturation and CT transient saturation. In fact, the inrush current is characterized of its peaky wave and its relatively big dead angle compared with the internal fault current. So the paper proposes a novel method to identify the inrush current using the improved half-cycle Fourier analysis (HCFA). The improved HCFA can accurately extract the fundamental component and reflect the characteristic difference of the inrush current waveform. The proposed method is tested by a large amount of EMTDC simulation on various conditions, the dynamic analogous test data from different transformers. These test results indicate that the novel method to identify inrush current is basically correct and feasible.