Effect Of Al₂O₃ Nanoparticles Plasma Modified On Dielectric Properties Of PI Composite Films

The increasing speed of high-speed railway trains requires higher parts of high-speed trains.Variable frequency traction motor is one of the key parts of high-speed trains.Polyimide film,as an excellent dielectric material,is applied to turn to turn insulation of traction motor.Doping nanoparticles in the film can improve some properties of the film,such as dielectric constant and dielectric loss,partial discharge The dielectric properties such as electric,breakdown field strength,conductivity and space charge behavior,but the agglomeration of nanoparticles will restrict the further improvement of the dielectric properties of the film.As a method of material surface modification,plasma modification is rarely applied to the study of the modification of nanoparticles in polyimide nanocomposite films.Therefore,it is of great significance to study the dielectric properties of polyimide nanocomposite films modified by plasmaIn this paper,the plasma generation platform was built,and the dielectric barrier materials and discharge distance needed for the proper discharge effect were determined through many tests.The surface of nano alumina was modified.Two kinds of PI/Al₂O₃films with different interface control methods were prepared by in-situ polymerization.The dielectric spectrum of the film was measured.It was found that the dielectric constant of the film was decreased and the dielectric loss was increased.The breakdown field strength and corona resistance life of the film are tested.The insulation life of the film meets the Weibull statistical distribution.Based on the Weibull distribution function,the corona resistance performance of the film is analyzed.By using the surface potential attenuation test platform,the surface attenuation characteristics of the film were tested.It was found that the plasma modification increased the surface potential attenuation rate of the film.The micro morphology of the film was observed by scanning electron microscope,and the volume fraction of nano particles increased after plasma modification.Fourier infrared spectroscopy was used to analyze the functional groups of the film and the nano alumina particles modified by different methods.It was found that the absorption peak related to the hydroxyl dimer was enhanced after the nano particles were modified by plasma.The broad-band dielectric spectrum of the film at-60-200℃was measured.The dielectric spectrum was analyzed based on the Havriliak-Negami model.The relaxation time,relaxation intensity,activation energy and other related characteristic parameters were obtained.The surface potential decay curve was analyzed by isothermal surface potential decay method,and the trap distribution of the film was obtained.Based on the trap characteristics and breakdown field strength of the film,the relationship between trap characteristics,charge transport,conductivity and breakdown characteristics is established.The influence of plasma modification on corona resistance life is explained from the point of charge transport dissipation.The mechanism of plasma modification on conductivity is explained from the interface level by using the multi-core model.In combination with the dielectric characteristic parameters and trap characteristics,isoionization is proposed The mechanism of the influence of sub modification on the polarization process of the film reveals the relationship between the microstructure and the macroscopic properties.In this paper,the macroscopic dielectric properties and microstructure mechanism are linked,the mechanism of plasma modified nano particles is studied,and the method of improving the insulation life of polyimide nano composite film is explored,which is of great significance for improving the insulation performance of variable frequency motor and safe and high-speed operation of railway.