Analysis And Location Method Of Single Phase Break Fault In Small Current Grounding System

In recent years,the insulation rate of distribution network has gradually increased,accompanied by more and more lightning break-off fault events,coupled with external damage and line aging and other multiple factors,the frequency of single-phase break-off fault in distribution network has become higher and higher.When single-phase line break fault occurs in the distribution network,the fault current is very small,and the system cannot accurately judge the fault.If the fault is not solved for a long time,it may lead to electric shock accident,and the electrical equipment will also be damaged due to long-term phase loss operation.Therefore,it is necessary to study the fault characteristics and location methods after single-phase line break fault occurs in the distribution network,which is of great significance to reduce personal safety and property losses caused by single-phase line break fault,and improve the power supply stability and reliability of the distribution network.In this paper,the small current grounding system as the research object,respectively ungrounded system and resonant grounding system under different factors to do a detailed analysis of the fault voltage characteristics of the change law.For ungrounded system,the fault voltage characteristics of single-phase ungrounded fault,single-phase ungrounded fault and single-phase ungrounded fault and single-phase ungrounded fault and single-phase ungrounded fault are analyzed respectively.Considering the influence factors such as the location of the broken line,the proportion of the capacitance to ground of the faulty part of the line to the total capacitance to ground of the system,the size distribution of the load impedance and the size of the transition resistance to the ground of the broken line,the neutral offset voltage and the voltage characteristics of the three phase voltage and line voltage before and after the single phase break fault in the ungrounded system are analyzed.For the resonant grounding system,the damping rate,detuning degree,line break position,the proportion of fault line capacitance to ground capacitance in the total system capacitance to ground,the size distribution of load impedance and the size of line break ground transition resistance are analyzed.Considering load impedance symmetry,the fault voltage characteristics of single-phase ungrounded fault,single-phase ungrounded fault and single-phase ungrounded fault of power side and single-phase ungrounded fault of load side in resonant grounding system are analyzed respectively.The voltage characteristics of neutral offset voltage after fault,three-phase voltage and line voltage before and after fault are derived.Based on the analysis of voltage characteristics of single phase break fault in small current grounded system different locating methods of single phase break fault for ungrounded system and resonant grounded system are proposed respectively.For the ungrounded system,the method of locating the fault interval of the broken line using the amplitude and phase relation of the downstream phase/line voltage of the broken line is proposed respectively.For the resonant grounded system,the method of locating the fault interval of the broken line using the amplitude relation of the downstream line voltage of the broken line is proposed.By adding a software analysis module to the existing distribution network automation platform,the proposed fault location method can quickly identify the fault interval of line breaking.Finally,using the simulation software MATLAB/Simulink,the simulation model of single-phase line break fault of 10 kV distribution network was established.The simulation results verified the correctness of the proposed fault identification and fault location method.