Research On Self-extinguishing Characteristics Of Single-phase Grounding Fault Arc In 10kV Non-effective Grounding System

With the acceleration of the distribution network construction,the system capacitance current level is rising,and when a single-phase ground fault occurs,the fault point arc is difficult to self-extinguish,which has an impact on the safety of the distribution network.The access of the arc extinguishing coil will eliminate the influence very well.However,in the medium-voltage distribution network,there is little research on when to join the arc extinguishing coil.Blindly adding the arc extinguishing coil and adjusting it can not eliminate the arc discharge phenomenon and increase a lot of investment.To this end,this paper is based on the arc self-extinguishing theory,the fault arc self-extinguishing characteristics of simulation analysis,Designed and built a 10k V arc-burning test platform and conducted a large number of arc-burning tests to provide a basis for the reasonable introduction of arc extinguishing coils.First,in order to study the self-extinguishing characteristics of the fault arc of 10k V system,this paper analyzes the characteristics of the AC arc,the mechanism of arc ignition and extinguishing and the influence of system parameters on the arc extinguishing characteristics.Based on theoretical analysis,the fault arc extinguishing and reignition process was simulated using PSCAD software.The results show that the grounding method and system detuning degree have a large impact on the peak recovery voltage and recovery speed.It also establishes the theoretical basis and simulation model foundation for the real 10k V distribution network fault arc self-extinguishing characteristics test.Then,built a 10k V voltage level arc-burning test simulation platform,which can simulate the actual arc-burning of three types of overhead lines（air gap）,cable lines（cable insulation）and combined appliances（SF₆ insulation）.The platform is used to simulate various types of single-phase grounding faults in 10k V systems,including ungrounded neutral,over-compensated and under-compensated via arc extinguishing coil grounding,air gap,cable insulation,and SF₆ insulation at single-phase grounding fault currents of 5 to 30A.Finally,the experimental data are analyzed,the average arc duration under various conditions is counted,the influence of system parameters on the arc duration is analyzed,and the residual current limits for arc extinguishing under different operating conditions are given by fitting the curves to the experimental data.The test results show that the neutral ungrounded system arc extinguishing current is lower than the arc extinguishing coil grounding system;the under-compensated system is easier to extinguish the arc compared to the over-compensated system,but considering the risk of over-voltage of line breaking fault,over-compensation is generally used;With the increase in detuning of the compensation system,the probability of grounded arc reignition increases,and systems with higher fault currents have larger residual current limits for arc extinguishing than smaller systems;When the capacitance current is below 10A,the neutral point is not grounded;If more than 10A can be used arc extinguishing coil grounding mode,the minimum arc extinguishing limit can be set to 12A,with the increase in system capacitance current,the minimum arc extinguishing limit can be appropriately relaxed tuning range;The cable insulation does not have self-recovery capability and the arc extinguishing residual current limit for the cable line can be set at 1A;SF₆ gas has good arc extinguishing performance,no arc reignition under the test current,SF₆ gas insulation arc extinguishing residual current limit can be set to the maximum value of the test 30A.