Simulation Test And Simulation Research On Internal Defects Of Roof Arrester Of EMU

Roof zinc oxide arrester is an important overvoltage protection equipment for EMU.When it runs outdoors for a long time,it will be affected by adverse factors such as overvoltage,vibration,sand and other foreign body impact and humid climate environment.Compared with the arrester in the power system,it is more likely to break down,which seriously threatens the stable operation of EMU.The analysis of the fault causes of the roof arrester of EMU can improve the reliability of its operation.The research on the artificial simulation and defect simulation of the internal defects of the roof arrester is helpful to explain the fault causes of the roof arrester and provide a basis for the optimization of the design and operation of the roof arrester.The disintegration research of the burst and failed test arrester were carried out.The defective parts of two kinds of arrester valve plates and epoxy cylinder were observed,and their influence on the surface insulation resistance of the valve plates and epoxy cylinder was tested.The microstructure and surface chemical element composition of the defective parts were analyzed by SEM test and EDS analysis,and the causes of the internal defects of the arrester were explained from the microscopic point of view.The results show that the internal moisture and the electric dendritic leakage marking at the interface are the main reasons leading to the crack and unqualified detection of arrester.The artificial defect simulation test platform of arrester was built and the simulation test of arrester defect was carried out.The variation of DC and AC electrical characteristic quantity of arrester under different damp condition and with different length of electrical branches were tested,and the electrical characteristic quantity which can reflect the internal defects of arrester was obtained.The DC reference voltage of the arrester will be irreversibly reduced after it is damp,and the presence of the electric branch of the valve plate will significantly reduce the DC reference voltage.The electric field and thermal field simulation model of arrester were established and the distribution characteristics of internal electric field and thermal field were obtained.The influence characteristics of internal defects on electric field distribution were analyzed under the defects such as displacement of valve plates,surface oxidation,interfacial electrical branches and cracks of epoxy cylinder.Three types of typical overvoltage characteristics suffered by EMU during operation were analyzed.The current field and temperature field variation of defective arrester under the action of overvoltage were studied.The research shows that high amplitude overvoltage is one of the important reasons for the heating of arrester.Under the action of steep wave impact overvoltage,the internal temperature of arrester with electrical branch defects can reach up to 536℃.Roof overvoltage will accelerate the deterioration of arrester performance,and even lead to the formation of internal interface discharge,leading to the explosion accident.