| With the rapid development of power electronic technology, frequency control technology was used widely. It caused insulation system degradation in advance with some practice virtue. Dupont corona-resistant polyimide films have excellent characteristic of corona resistance and were used widely in conversion system. No one know the synthetic method but Dupont company and corona resistance mechanics. In the paper, one experiment set-up was designed for measuring the breakdown characteristic of PI films, another for measuring the corona resistance characteristic. The testing results coordinate to Dupont's by our device experiencing. When the percentage composition of SiO2 or micro-sialic was 4%, the breakdown characteristic was more excellent. The minimum electric field which causes material appearing space charge accumulation was electric degradation threshold. It can be used for the maximum safe field when the material was used. The electric conduction current characteristics of both Dupont original and corona-resistant polyimide films (100HN and 100CR) before and after corona-aged 8 hours under electric field of 10kV/mm and 20 kV/mm were measured respectively. The results show that the conduction current of 100CR is larger by about one order of magnitude than that of 100HN. The electric degradation threshold was 40 kV/mm for 100CR and 35 kV/mm for 100HN, and decreases with the increasing of corona-aged field. By measuring the depolarization current of two films at 170oC, the decay of depolarization current of 100CR is faster than that of 100HN can be observed. Based on the depolarization current curve, the apparent carrier mobility and the trap depth can be calculated respectively during depolarizing. The apparent carrier mobility change from 1.2×10-13 m2/Vs to 3×10-14 m2/Vs for 100CR and from 1.12×10-13 m2/Vs to 8×10-14 m2/Vs for 100HN with depolarization time, the trap depth change from 1.052eV to 1.105eV for 100CR, and from 1.054eV to 1.069eV for 100HN.
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