Influence of nano particles on partial discharge of polyimidefilms

Stator insulation in inverter-fed traction motors may lose its function earlier due to continuous square impulses voltage of converters, whose insulation failure mechanism is different from that under power frequency AC voltage. Partial discharge (PD) is one of the key factors in insulation failure of inverter fed traction motor. Investigation of partial discharge is to understand aging and failure mechanism of insulation material under high frequency impulse more clearly, which is foundation for improvement of insulation material. There is overvoltage at the end of motor and windings because of high frequency impulse, which will lead to partial discharge and accelerating aging on the insulation. Life test are performed on three kinds of polyimide film. They are common polyimide and nanocomposite film produced by DuPont company, as well as nanocomposite film produced by Jiangsu ice-city insulation materials stock Co. LTD in China, respectively. The results show that the life of nanocomposite films is much longer than that of common ones. Thermal gravimetric analysis (TGA) and scanning electron microscope (SEM) analysis are performed on three types of films. The results show that thermal stability of common film is better than that of other ones. Nano particle adding into composite film made of DuPont company is aluminum oxide (Al₂O₃), and nano particle adding into composite film made of Jiangsu ice-city company is silica (SiO₂). PDIV(partial discharge inception voltage), mean discharge quantity and discharge number are tested with different impulse frequency and rise time, respectively. Results show that PD activity are enhanced with increase of impulse frequency as well as decrease of rise time. Furthermore, PD activity of common polyimide film is stronger than that of the other nanocomposite ones.