Study On Characteristics Of Fault Leakage Current And Its Protection Methods

With the continuous improvement of social and economic level,people’s production and life are closely related to electric energy,and the problem of power safety caused by electric energy has attracted more and more attention.Human electric shock and electrical fire are problems when using electricity.At the same time,there is leakage current when the line is running normally.In the short line,the influence of normal leakage on leakage detection is very small,but with more and more feeder branches and longer feeder length,the influence of normal leakage on leakage detection increases gradually.The detection and protection of leakage is usually realized by residual current protector and multi-level protection strategy.However,the current residual current protection technology can not distinguish between normal leakage and fault leakage,resulting in frequent refusal and misoperation of residual current protector.Based on the analysis of normal leakage and fault leakage,this paper puts forward a method to measure the insulation resistance of each phase of TN ground supply network,which is used to distinguish the fault leakage from normal leakage,a novel multi-stage fault leakage protection strategy is proposed to reduce the failure probability of the residual current protector.The main research work and conclusions are as follows:(1)Study the causes of normal leakage,analyze the influence of environmental change and line switching on line insulation resistance and distributed capacitance,analyze and experiment three common leakage models of human body,wood and cement in fault leakage,study the variation characteristics of normal leakage and fault leakage,and put forward the identification method of normal leakage and fault leakage.(2)A new measurement method for TN system,TN system three-frequency method,is proposed.The additional voltage source of other frequencies is used to measure the line to ground parameters.The frequency selection method of three frequency method for TN system is proposed.According to the error comparison between the simulation results under different frequency combinations and the actual insulation resistance,it is verified that the frequency selection method can effectively reduce the relative error.(3)This paper analyzes the problems existing in the traditional leakage protection strategy,and puts forward a new multi-level fault leakage protection strategy.Through simulation analysis and comparison,it is verified that the new protection strategy has more complete leakage protection ability than the traditional protection strategy.