Zero-sequence voltage trajectory analysis for unbalanced distribution networks on single-line-to-ground fault condition

Faulty phase recognition under single-line-to-ground (SLG) fault condition is critical for some arc suppression methods in medium voltage (MV) networks. Traditional methods usually assume that the distributed parameters of the network are symmetrical, thus are unsuitable for the asymmetrical networks, especially when the ground-fault resistance is relatively high. In this paper, the trajectory of the zero-sequence voltage with the change of ground-fault conductance is analyzed in detail. The magnitude and phase angle variation rules of the voltage under different asymmetry ratios are presented. Then, the ranges of their unique variation rules on SLG fault for each phases are separately and strictly discussed both for the under-compensated and over-compensated grounding conditions. Furthermore, a faulty phase recognition method is proposed based on the variation rules of zero-sequence voltage on faulty condition. Simulation results verify the concluded variation rules and validate the effectiveness of the proposed fault phase recognition method, which ensures exact recognition of faulty phase in asymmetrical network and high-resistance ground fault condition.