The Effect Of SiO₂Nano-hybrid On The Electrical Properties Of Polyimide Film

Since entering the21st century, due to the rapid development of high-speed railway and electricity system, variable frequency motor has been more widely used. As the power equipment of high-speed EMUs, the life of variable frequency motor has an important impact to the stable operation of EMUs. With enhancing the speed of EMUs, the power requirements of variable frequency motor are higher. For the majority of variable frequency motor using PWM modulation driving, at the beginning of each frequency, pulse polarity from positive to negative or from negative to positive, the motor windings generate partial discharge for withstanding twice the peak voltage value of the full-size voltage and as the power increasing, which produces a partial discharge will be more serious. Since the wave impedance of variable frequency motor being significantly greater than the wave impedance of the cable, making variable frequency motor suffer approximately the twice of pulse leading edge voltage, the coil insulation layer of variable frequency motor occurs partial discharge during operation. Insulating materials get damaged under the influence of partial discharge, which reduces the span of frequency conversion motor. Therefore researching modified polyimide film of variable frequency motor, the major issue for design and manufacture of variable frequency motor to improve its electrical properties to extend the frequency control motor life has been became.A test platform was built based on the experimental principle of the sol-gel method preparing polyimide/SiO2composite films, the purchase of instruments equipment and chemical reagents. According to the sol-gel method, prepared the composite film of SiO2nanoparticle content of2%,5%,10%,15%,20%, analyzed the influencing factors of preparing a polyamic acid, laying of the membrane with polyamic acid, the process of imidization.Using of developed composite films with different content of SiO2, the surface morphology and internal structure feature of the composite films were characterized by SEM and FTIR, have tested and analyzed the variation of the different SiO2content of composite films with frequency, temperature variation, analysis of the breakdown strength and corona-resistant, assessment of excellence of its electrical properties of the homemade composite film.