A Zero-Mode Inrush Current Identification and Zero-Sequence Protection Method for Transformers Based on Circulation Similarity
With the fast expansion of China's power system and the rapid increase of transmission capacity,Yd-connected high-impedance transformers are widely used.The traditional transformer zero sequence differential protection adopts the second harmonic ratio for inrush identification,but this method often malfunctions energizing on internal faults.In this paper,a zero-mode inrush identification and zero-sequence protection method for transformers based on circulation similarity is proposed,which calculates the waveform similarity between the primary zero-mode inrush and the secondary circulation,and then identifies internal faults based on the saturation coefficients of the three phases of the transformer,and comprehensively realizes the accurate inrush current blocking of the transformers.The simulation and experiment results show that the proposed protection method can correctly operate under the conditions of transformer energizing under sympathetic interaction and on internal faults.
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