Trap level distribution dependence of lifetime for polyimide films under repetitive impulse voltage
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Trap level distribution dependence of lifetime for polyimide films under repetitive impulse voltage Yan Yang1, Xueyang Bai1, Yixin Lei2, Kai Liu1,* 1 2
, and Guangning Wu1
School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, Sichuan, China Chongqing Qinan Electric Power Supply Company, Chongqing 401420, China
Received: 20 July 2020
ABSTRACT
Accepted: 22 September 2020
In this paper, polyimide (PI) films were modified by using non-thermal plasma, which was generated by dielectric barrier discharge (DBD) in atmospheric air. Under repetitive impulse voltage, the lifetime of plasma treated PI films increases obviously, which reaches the maximum value of 16.8% higher than that of untreated PI films, obtained by 20 s’ treatment. For further understanding lifetime improvement mechanism, energy level distribution of both electron-type and hole-type traps was calculated based on isothermal surface potential decay (ISPD) measurement. It is found that energy level of both shallow and deep traps decrease after treatment, reaching the lowest value for the films treated for 20 s. Lower energy for shallow trap is beneficial to charge dissipation, so that local electrical field would be mitigated. Furthermore, lower energy for deep trap results in less amount of trapped surface charges. Thus, surface PD intensity would be suppressed, ending up with longer lifetime. Analysis of chemical bonding structure reveals that active groups rich in oxygen and nitrogen were introduced into the near-surface region of plasma treated sample, which are responsible for corresponding change of trap energy level distribution. However, in order to prolong lifetime effectively, plasma treating time must to be controlled in an appropriate range.
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
1 Introduction Polyimide (PI) film has been widely used as insulating material in electrical equipment due to the excellent electrical, mechanical and thermal characteristics [1, 2]. Particularly, it is commonly used as corona resistant material to avoid surface partial discharge (PD) occurring in insulation system that is subjected to repetitive impulse voltage, which is quite
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https://doi.org/10.1007/s10854-020-04539-5
common in power electronic equipment [1, 2]. Under these circumstances, surface charges are easily accumulated on film surface as the voltage reversed in such a short time that surface charge dissipation could be unaccomplished. Local field could be enhanced as a result of the superimposition of the reversed voltage and additional electric field formed by accumulated surface charges [2, 3]. In this case, PD takes place regularly, and the insulation system
J Mater Sci: Mater Electron
should be designed to withstand these partial discharge (PD) activities during operation. For this kind of system, PD induced degradation and corresponding breakdown is one of the most significant causes for insulation failures [4, 5]. Although the
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