Research On Distributed Faulty Line Selection And Sectional Location In Medium Voltage Distribution Network

When the single-phase grounding fault occurs in the medium-voltage distribution network,the line voltage remains symmetrical and the fault current is small,so the system can still continue to operate for 1～2h.With the enlargement of the distribution network,the capacitor current after single-phase grounding will increase.The long-term operation of single-point single-phase grounding fault will be likely to cause more serious accidents.Due to the variable operation mode of distribution network,the accuracy of traditional centralized faulty line selection method is low.In addition,the weak fault signal seriously affects the reliability of sectional location.With the connection of DG to the distribution network feeder,the faulty line selection and sectional location of the medium voltage distribution network will be further affected.Therefore,by using the existing feeder terminal device and advanced communication technology,this paper studies the distributed faulty line selection and sectional location method,greatly improves the accuracy of faulty line selection and location,which has important engineering practical value.The main work and research results of this paper are as follows:1、This paper analyzes the transient and steady-state current characteristics of single-phase grounding fault in distribution network.It focuses on the analysis of the capacitive current distribution after single-phase grounding fault in active distribution network and the influence of distributed generation access location on faulty line selection and location,which lays a theoretical foundation for the subsequent fault line selection and section location criteria.2、A distributed faulty line selection method for distribution network under traditional grounding mode is proposed.Based on the analysis of phase characteristics of zero-sequence current in each section of active distribution network after single-phase grounding fault occurs,distributed faulty line selection criterion is constructed.Considering the influence of the phase of the zero-sequence current and the characteristics of the amplitude of the zero-sequence current after the fault,a distributed faulty line selection method of the zero-sequence current amplitude ratio is constructed for the single-phase grounding fault with large transition resistance.Theoretical analysis and simulation results show that this method can accurately and quickly select fault lines and locate fault sections.3、A method of distributed faulty line selection in distribution network with neutral flexible grounding is proposed.Aiming at the medium voltage distribution network with arc suppression coil and resistor parallel grounding at neutral point,the characteristics of zero sequence current amplitude and phase before and after paralleling resistor are analyzed.Based on the difference of amplitude and phase change of zero sequence current on both sides of feeder section,the faulty line selection and sectional location method is constructed.The simulation results verify the accuracy and adaptability of the proposed method.4、Based on the above distributed faulty line selection principle,a terminal prototype with distributed faulty line selection function is developed.Based on RTDS experimental platform,a closed-loop test system for active distribution network is established and the function of the terminal prototype is tested.The test results show that the developed prototype can accurately identify single-phase ground faulty lines and sections and send alarm signals,and has the ability to withstand the transition resistance.