Research On Fault Line Selection Method Of Resonant Grounding System Based On Tuned Zero Sequence Impedance Characteristics

The medium voltage distribution network in China mostly operates in the mode of small current grounding,which can reduce the tripping rate of single-phase grounding fault and effectively improve the power supply reliability of the distribution network.After single-phase grounding fault occurs,to ensure the normal operation of the system,it is necessary to select the fault line and isolate the fault which can,reduce the harm of arc overvoltage,restrain the occurrence of phase to phase fault and,expand the scope of power outage.Therefore,the research on fast and accurate fault line selection technology has significant for the safe operation of distribution network.When single-phase grounding fault occurs in distribution network resonant grounding system,the electrical characteristics are weak,which leads to great difficulties in accurate fault line selection.For a long time,it has not been effectively solved,which seriously threatens the safe operation of distribution network.Aiming at 10 k V resonant grounding system,the transient and steady-state electrical characteristics after single-phase grounding fault are analyzed in detail,and the fault zero sequence equivalent network is established.It is found that the characteristic of zero sequence impedance is related to the compensation condition of arc suppression coil: when it is under compensation,the zero sequence impedance of sound line is capacitive while,that of fault line is inductive;when it is over compensation,the zero sequence impedance of all lines is capacitive;When it is fully compensating,the system is in resonance state.Based on the above characteristics,a fault line selection scheme for resonant grounding system is proposed.By adjusting the compensation degree of the system and extracting the characteristic frequency band of zero sequence voltage and zero sequence current of each line,the zero sequence impedance angle of each line is calculated for fault line identification.The results show that the zero sequence impedance angle of the sound line is 90 degrees in different compensation states;the zero sequence impedance angle of the fault line is 90 degrees in over compensation and-90 degrees in under compensation.According to the calculation results of the zero sequence impedance angle difference before and after the change of compensation degree,the fault line can be effectively identified.Aiming at the route selection scheme constructed in this paper,Matlab platform is used for simulation verification.A 10 k V distribution network model is built in Simulink environment,and different fault conditions are set to verify the reliability of the method.The results show that the method can significantly enhance the fault signal characteristics,and can effectively identify the fault line in the case of high resistance grounding.Also,it can greatly improve the accuracy of fault line selection,and it is easy to be implemented,which provides a reference for the application research of the technology device in the industrial field.