A Single-Phase Grounding Fault Line Selection Method for Flexible Grounding Active Distribution Networks Based on the Ratio of Zero-Sequence Current Changes

Single-phase grounding faults (SPGFs), especially high-resistance faults, significantly weaken the electrical characteristics of active distribution networks (ADNs), thereby posing considerable challenges for faulted line selection (FLS). To address these challenges under flexible grounding conditions, this paper proposes an FLS method based on the ratio of zero-sequence current variations. By establishing the zero-sequence equivalent circuit of SPGFs in flexible grounding ADNs, the variation patterns of zero-sequence currents in both faulted and nonfaulted feeders are analysed before and after the parallel insertion of a small grounding resistor. Using a designated reference feeder, the proposed method evaluates the magnitude and phase characteristics of zero-sequence current variation ratios of other feeders relative to the reference. These features are then used to construct a reliable line selection criterion. The effectiveness of the method is validated through fault simulations carried out in PSCAD/EMTDC. Simulation results confirm that the proposed approach achieves high selection accuracy and demonstrates strong robustness against transition resistance.