Influence Of The Non-thermal Plasma On The Surface Discharge Of Polyimide Nanocomposite Films

Inverter-fed traction motor is the power equipment of the high speed train.Its reliable operation is related to the safety of the passenger’s personal and property.Because the pulse width modulation（PWM）technology is used to speed the inverter-fed traction motor,the turn to turn insulation system will be strongly impacted by the high frequency and steep pulse.Furthermore,a strong partial discharge is generated in the air gap of the surface of the interturn insulating material,causing premature failure of the insulation.Polyimide（PI）is widely applied to the inverter-fed traction motor because of its excellent electrical and mechanical properties.Adding nanoparticles can enhance its insulation life.As the speed increase of high-speed rail,the power of traction motor will also be increased.How to make use of economic and convenient way to further enhance the insulation life of interturn insulation materials is of great significance.The surface modification of PI and PI/Al₂O₃ films by the non-thermal plasma produced by dielectric barrier discharge（DBD）was executed in this paper.The performance changes of the films before and after modification was studied,focusing on the surface discharge characteristics,and the mechanism of its action was analyzed.The main research work is as followed:The PI/Al₂O₃ and PI thin films were prepared by in-situ polymerization.The microstructure of the two films was observed by scanning electron microscopy（SEM）,and their morphological differences were also analyzed.The chemical structure of PI/Al₂O₃ and PI films was tested by fourier transform infrared spectroscopy（FTIR）.The difference of chemical structures between the two films before plasma treatment was comparatively analyzed.The DBD platform was set up to adjust the related parameters,and the non-thermal plasma for the surface modification of the film was obtained.The PI and PI/Al₂O₃ films were modified by non-thermal plasma.Meanwhile,the contact angle,surface energy and surface conductivity of PI and PI/Al₂O₃ films under different plasma treatment time were tested,and corona resistance of single layer films and modified double layer films at different positions were also tested.Furthermore,the changes of the properties of two kinds of thin films before and after plasma modification were studied,and the performance differences of the PI and PI/Al₂O₃ films before and after the modification were compared and analyzed.By means of emission spectrum,SEM and FTIR,the influencing factors of the surface contact characteristics of thin films after plasma modification were studied,and the chemical structure change,the type of introduced group and the possible mechanism of action were discussed.Besides,the influence of plasma treatment on the dispersion characteristics of residual charge under square wave pulse was revealed and the influence mechanism of plasma treatment on the surface discharge of single layer film and double-layer superimposed thin film was analyzed.The mechanism of nanoparticles in the plasma modification process of PI films and the main reasons leading to the difference of the properties between the two films after plasma modification were compared and analyzed.