Studies On Preparation And Insulation Properties Of PI/Al₂O₃ Nano-Composite Film

In recent years, the high-speed railway is developed fast. With the running speed of EMU promoting, the invert-motor power is increasing. Due to volume of EMU, The invert-motor is subjected to the strong electric field and high temperature field, which can lead to the insulation of motor premature aging and affect the safety of EMU. Polyimide (PI) film is widely used in the insulation of invert-motor. Nano-materials modified is an effective means to improve insulation properties of PI. Compare with the tradition insulating medium, the nano dielectric has the excellent electrical properties and complex reaction mechanism. Therefore, Research the influence mechanism between nano particals and PI’s insulation properties has an important significance to improve the insulation of invert-motor. This paper choose the Al2O3 (60nm) as the filler to modify.Some samples of PI/Al2O3 have been made by in-situ polymerization to study the influence of nano Al2O3 on the electrical characteristics of PI film. The microstructure of PI/Al2O3 is observed. Under the square wave pulse voltage, PI/Al2O3’s breakdown voltage value, corona aging time, partial discharge parameters were tested. Meanwhile the influence of temperature on corona aging time and partial discharge parameters was also researched. Then, the reaction of mechanism between nano Al2O3 and PI/Al2O3’s electrical characteristics was revealed.The different between pure PI film and PI/Al2O3 film on molecular structure has been compared by Fourier transform infrared spectroscopy(FTIR) to study the influence of nano Al2O3 on the material properties of PI film. Besides, the changing of chemical group in the process of PI/Al2O3’s degradation was analyzed. Microstructure of the PI/Al2O3 film before and after discharge was observed by Scanning Electron Microscope(SEM). The thermal conductivity property and dielectric property of PI/Al2O3 with different content was tested, which the influence mechanism were discussed.In the end, the interaction model between hot electron and PI/Al2O3’s internal structure has been set by the data of influence of nano Al2O3 on PI film in the aspects of electrical and material. The paper analyzed the nano Al2O3’s reaction mechanism in aspects of extending the composite film’s corona-resistant lifetime and enhancing the stability of composited film’s structure. The model and mechanism analysis can provide a theoretical basis to improve the insulation property of inverter-fed traction motor.