Damage processes of polyimide film caused by surface discharge

Partial discharge (PD) under a sequence of high-frequency square pulses is one of the key factors which lead to premature failure of insulation systems of inverter-fed motors. In order to explore the damage mechanism of PI film caused by discharge, an aging system of surface discharge under bipolar continuous square impulse voltage (BCSIV) was designed based on the ASTM 2275 01 standard and the Dupont 100HN PI film was experimented. The micro-morphology and micro-structure changes of PI film aged above partial discharge inception voltage (PDIV) were investigated through Scanning Electron Microscopy (SEM). The chemical bonds of PI polymer chain were analyzed Through Fourier Transform Infrared Spectroscopy (FTIR). The results show that the degradation mechanism of PI film is the fracture of chemical bonds, such as ether bond (C-O-C) and imide ring (C-N-C), caused by the physical and chemical erosion of surface discharge.