Study On The Transient Zero Sequence Characteristic And Fault Line Detection Of Single Phase-to-ground Fault In Small Current Neutral Grounding System

Fault line selection is the premise of correct failure removal in power system, and the improvement of fault line selection accuracy is much important for the power system safety and economy operation. The single phase-to-ground fault is most common in distribution networks, while fault line selection of single phase-to-ground has low accuracy as the result of complex grounding, therefore, further research on fault line selection is needed.First, the reasons of fault line selection with low accuracy using the existing method are analysed. The characteristic and application of various fault line selection techniques is described by analysing the methods of line selection. Then the simulation model of small current neutral grounding system is built. By simulating the isolated neutral system and resonant earthed neutral system, We get the simulation results of zero sequence voltage,zero sequence current,zero sequence power and quintuple harmonics current under different operation conditions. At last, this paper analyses the transient zero-sequence characteristics in the case of single phase-to-ground fault in small current neutral grounding system. The transient zero-sequence current changing rate method for the fault line detection of small current neutral grounding system is presented. The simulation results of transient zero-sequence current changing rate among different lines are shown. And the fault line selection criterion based on the difference of transient current changing rate between the fault line and the non-fault line is given.The simulation results show the method, which can be immune to the variation of neutral grounding, voltage initial angle and transition resistance, has the characteristics of high sensitivity, reliability and practicality.