Study On The Dielectric Property And Corona-Resistant Mechanism Of Nano-Inorganic-Polyimide Composite Film

The progress in nano-science and technology provided a new train of thought and a way for developing new materials and modifying the present materials. The appearance of nanodielectrics opened a new application field of the dielectrics. The electrical, thermal and mechanical properties of nanodielectrics were better than those of conventional ones. With the development of power electronics technology and new semiconductor devices, more and more AC frequency conversion adjustable-speed motors have been widely used especially after 1980's. However, the life of the motor was only about one or two years due to partial discharge, what is more, the insulations in some motors were breakdown during the test running. Cooperating with ABB and Siemens, Dupont developed the corona-resistant polyimide film, the corona-resistant time of which could be up to 105 hours under 20kV/mm field, approaching the level of mica paper. The further research on the mechanism of corona resistance from the dielectric theory has not reported.The construction of Dupont corona-resistant polyimide film was analyzed by means of SEM and AFM, and the surface morphology of the original film and the corona- resistant film were compared with each other after aged. We found that Dupont corona-resistant film is three layers in construction and the two surface layers containing more Al-compound are inorganic-organic composite. The reason of the corona resistance of this film may be that the inorganic substance concentrating in the surface layers has higher heat conductivity, which can dissipate the heat produced by corona, and thus reduces the danger of thermal breakdown. Meanwhile, corona acts on the inorganic substance, which has good corona-resistance and ability to tolerate the corrosion of the corona products. After corona aging, the inorganic phase in the corona-resistant film appears flocculating cluster and infiltrated organic phase well. On the contrary, there is no such phenomenon taking place in original film.The investigation of the characteristics of dielectric spectrum, the conduction current, the depolarizing current and the thermally stimulated current of Dupont original and corona resistance films shows that the threshold of the corona-resistant film is higher than that of the original film and decreases with the increase of the...