Structure Design Of Polyimide Nanocomposite Film And Research On Its Electric Heating Performance

China's high-speed railway is developing towards ultra high speed(500km).AC drive system with variable frequency speed regulation is widely used in high speed emu,and Variable frequency speed regulation traction motor is one of the nine key technologies of high speed EMU.Under the operating condition of the super high speed EMU(High temperature field caused by high frequency steep pulse voltage and frequent short time thermal overshoot),The existing insulation system is difficult to meet the actual demand.Nowadays,the insulation material polyimide(PI)is a kind of engineering polymer material with main chain imide ring.It has outstanding dielectric properties,thermodynamic properties and mechanical properties,and plays an irreplaceable role in the field of dielectric insulation.The research on the influence mechanism of inorganic dopants on materials has been research deeply,however,the influence of the structure on the thermal performance of PI film under the power frequency environment is rarely studied.The research on the influence of the structure on the electric heating property of PI thin film is very important to prolong the service life of the inverter.In order to investigate the effect of three layer structure on the electrical properties of PI thin films,a new method was developed for the preparation of polyimide nano composite films with three layers(PI/Al2O3-PI-PI/Al2O3).The microscopic properties of the materials were observed.The dielectric properties of the PI thin films were investigated by testing the dielectric properties such as dielectric spectrum and heat loss.In order to investigate the corona resistance of three layer composite films under the combined action of electric heating and aging,corona resistance test of pure PI film,single layer PI/Al2O3 composite film and three layer composite film under high frequency steep pulse at different temperatures were carried out,and the surface discharge characteristics,dielectric spectrum and infrared spectrum of the samples were tested.Finally,based on the life data of three layer PI thin films under the combined action of electro thermal aging,a new model for the combined aging life of the three layer composite films was established.