Faulty Line Selection Method Based on Differentiation of Zero-Sequence Current Characteristics for Flexible Grounding Systems

To effectively address the challenge of faulty line selection during high-impedance grounding faults in distribution networks with a flexible grounding system, a novel fault line selection method that integrates both the amplitude and phase characteristics of zero-sequence currents is proposed. The characteristics of zero-sequence currents under single-phase grounding faults in a flexible grounding system are thoroughly investigated, with a particular focus on analyzing the phase relationship and amplitude differences between the zero-sequence currents of each feeder and that of the neutral point. Upon the switching of the parallel low-resistance device, the zero-sequence current of the faulty line is approximately equal in amplitude but opposite in phase to that of the neutral point. In contrast, the zero-sequence current amplitude of a healthy line is significantly smaller than that of the neutral point, and its phase is nearly orthogonal to the neutral point zero-sequence current. To capture these characteristic differences, the projection of each line’s zero-sequence current onto the neutral point zero-sequence current is employed. A projection coefficient criterion is subsequently constructed to enhance the reliability of line selection. Furthermore, by utilizing the neutral point zero-sequence current, the method can effectively extract the weak zero-sequence current of healthy lines, thereby mitigating the risk of misjudgment by the fault line selection device caused by the inability of zero-sequence current transformers (CT) to accurately acquire such faint signals. Simulation results obtained via PSCAD validate that the proposed method remains effective for single-phase grounding faults with transition resistances up to 3000 Ω, even under extreme operating conditions such as reverse polarity of zero-sequence CT or the presence of strong noise interference.