A fault line selection method for flexible grounding systems based on zero-sequence current phase variation

To address the poor tolerance to transitional resistance and incomplete utilization of fault information in grounding protection for flexible grounding systems， a fault line selection method based on current phase variation is proposed. First， the phase variation trends of zero-sequence currents across lines before and after small resistance insertion are analyzed based on the zero-sequence equivalent circuit of single-phase grounding faults in flexible grounding systems. Then， it is observed that during high resistance grounding faults， the phase variation of zero-sequence currents in healthy lines shows significant differences from that of the fault line. Based on this observation， a fault line selection method using zero-sequence current phase variation is proposed. Finally， the correctness and effectiveness of the proposed method are verified in PSCAD/EMTDC simulations. Results show that the method only requires phase information of zero-sequence currents before and after small resistance insertion， offering strong transitional resistance tolerance and immunity to issues such as zero-sequence CT polarity reversal， asynchronous sampling， and fault distance variations.