Single Line-to-Ground Fault Protection Method Considering Three Phase-to-Ground Parameters Asymmetry in Active Flexible Grounding Systems

The asymmetry of three phase-to-ground parameters is common in distribution networks, and the asymmetry of each feeder has the random difference. However, most of existing single line-to-ground (SLG) fault detection and arc suppression methods ignored the influence of asymmetry on fault protection reliability. In response to this problem, this paper firstly establishes a new zero-sequence equivalent model considering three phase-to-ground parameters asymmetry in an active flexible grounding system. Based on the zero-sequence voltage and current before and after the adjustment of the injected current in this model, the distribution characteristics of the injected current and the grounding parameters of each feeder are calculated, which can be used as the criteria for faulty feeder selection. Then, the unbalanced ground-fault current caused by the asymmetry is discovered, and the voltage-based arc suppression method is proposed to fully compensate these unbalanced components. Finally, considering the asymmetry of three phase-to-ground parameters, an SLG fault protection synchronous control strategy with a coordinated process of arc suppression and fault detection is proposed in active flexible grounding systems. The high reliability of the proposed method is confirmed by comparative experimental results with the theoretical analysis.