The Finite Element Simulation And Experiment Of Insulating Material’s Arc Erosion

For today’s electromagnetic conversion technology, how to reduce and eliminate theeffect of electric erosion was the key issue for electromagnetic conversion. Especially forthe insulator materials, electric erosion would seriously affect the life of the entireapparatus, and caused destructive results. Al₂O₃as an insulating material demonstratesgood insulation and heat-resistant properties. It has been used as insulating materials inmany industrial fields. Its typical application was plasma sprayed Al₂O₃coating whichused in aerospace crafts, electromagnetic conversion fields.In this thesis, the ANSYS thermodynamic finite element method was used tosimulate the electric erosion behavior of electromagnetic conversion process. Differenttemperature fields were calculated during different inputs of voltages. The glass fiberreinforced epoxy insulating material and Al₂O₃coating were selected as experimentalmaterials to simulate the temperature field of the insulated rail. Four factors were analyzedwhich have influence on the Al₂O₃coating’s breakdown. Two voltage resistance testsamples were fabricated using the thermal spray method with two different Al₂O₃powders.Before the voltage test, tow Al₂O₃powders were characterized by EDS componentanalysis and SEM structural analysis. The results of the Al₂O₃voltage resistance test werecarried out and coincided with that of the finite element simulation.The results show that the Joule heat would result in serious damage of the insulationrail through the arc erosion, however, Al₂O₃protection layer can decrease the effect of thedamage；Micro-size pores and cracks in the Al₂O₃coating will reduce its dielectricstrength. The influences are transverse pores, circular pores, vertical pores. The structureof as-sprayed Al₂O₃coatings is dense and good bonding according to the SEM structuralanalysis. Under the high temperature environment and high voltage, the coating with theimpurities was easily broken. The bigger the impurities’ size, the leakage current isstronger, which result in serious arc erosion. In the insulating experiment, all breakdownsoccurred in the coatings with impurities. And the erosion appearance was coincided withthe finite element simulation results. Because of the geometric effect, the thinner coatingsseem to have more breakdown points in the experiment. When the thickness of the coating was less than50μm, the coating collapsed. So the critical thickness of the coating d0＞50μm. When the thickness of as-sprayed coating was more than400μm, the anti-breakvoltage can be more than4000V. The thermodynamic finite element method can providethe satisfactory instruction for arc erosion study.