High frequency development and discharge characteristics of SiO2 modified polyimide films

Polyimide can be used to coat insulation of high frequency power transformer. Surface discharge will lead to insulation failure. In this paper, nano-SiO2 particles containing 2%, 4%, 6%, 8% and 10% Si element were introduced into polyimide for nano composite modification (Si0, Si2, Si4, Si6, Si8, Si10). It is found that the lifetime of Si0 is the shortest and that of Si10 is the longest. The development process and characteristics of high-frequency surface discharge of Si0 and Si10 are studied. The results show that: in the process of high-frequency surface discharge of pin plate electrode, the damage caused by flashover is greater. The discharge at positive half cycle and polarity reversal is more severe. Compared with Si0, the amplitude and number of discharge of positive half cycle and overall of Si10 are smaller. At first, the discharge amplitude of Si10 is larger but the number of discharge is less. The discharge amplitude of two kinds of films fluctuates in the middle stage, and the discharge frequency of Si10 is more in the later stage. The discharge amplitude and frequency of Si0 are much higher than that of Si10, which leads to the rapid breakdown of Si0. Further research shows that resistivity of Si10 is less than that of Si0, so discharge of Si10 is more serious in the early stage. The material structure characteristics plays an important role in in the middle and late stage. The interface effect and light energy absorption caused by modification play an important role, so the discharge of Si0 is more serious.