中国物理B ›› 2014, Vol. 23 ›› Issue (2): 27703-027703.doi: 10.1088/1674-1056/23/2/027703

• CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES • 上一篇    下一篇

Microscopic degradation mechanism of polyimide film caused by surface discharge under bipolar continuous square impulse voltage

罗杨, 吴广宁, 刘继午, 彭佳, 高国强, 朱光亚, 王鹏, 曹开江   

  1. School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, China
  • 收稿日期:2013-05-02 修回日期:2013-07-16 出版日期:2013-12-12 发布日期:2013-12-12
  • 基金资助:
    Project supported by the National Natural Science Foundation of China (Grant Nos. U1234202, U1134205, 51177136, and 51107104).

Microscopic degradation mechanism of polyimide film caused by surface discharge under bipolar continuous square impulse voltage

Luo Yang (罗杨), Wu Guang-Ning (吴广宁), Liu Ji-Wu (刘继午), Peng Jia (彭佳), Gao Guo-Qiang (高国强), Zhu Guang-Ya (朱光亚), Wang Peng (王鹏), Cao Kai-Jiang (曹开江)   

  1. School of Electrical Engineering, Southwest Jiaotong University, Chengdu 610031, China
  • Received:2013-05-02 Revised:2013-07-16 Online:2013-12-12 Published:2013-12-12
  • Contact: Wu Guang-Ning E-mail:gnwu@swjtu.cn
  • About author:77.55.-g; 52.80.Wq; 68.55.-a
  • Supported by:
    Project supported by the National Natural Science Foundation of China (Grant Nos. U1234202, U1134205, 51177136, and 51107104).

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摘要： Polyimide (PI) film is an important type of insulating material used in inverter-fed motors. Partial discharge (PD) under a sequence of high-frequency square impulses is one of the key factors that lead to premature failures in 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) is designed based on the ASTM 2275 01 standard and the electrical aging tests of PI film samples are performed above the partial discharge inception voltage (PDIV). The chemical bonds of PI polymer chains are analyzed through Fourier transform infrared spectroscopy (FTIR) and the dielectric properties of unaged and aged PI samples are investigated by LCR testers HIOKI 3532-50. Finally, the micro-morphology and micro-structure changes of PI film samples are observed through scanning electron microscopy (SEM). The results show that the physical and chemical effects of discharge cut off the chemical bonds of PI polymer chains. The fractures of ether bond (C–O–C) and imide ring (C–N–C) on the backbone of a PI polymer chain leads to the decrease of molecular weight, which results in the degradation of PI polymers and the generation of new chemical groups and materials, like carboxylic acid, ketone, aldehydes, etc. The variation of microscopic structure of PI polymers can change the orientation ability of polarizable units when the samples are under an AC electric field, which would cause the dielectric constant ε to increase and dielectric loss tan δ to decrease. The SEM images show that the degradation path of PI film is initiated from the surface and then gradually extends to the interior with continuous aging. The injection charge could result in the PI macromolecular chain degradation and increase the trap density in the PI polymer bulk.

关键词: surface discharge, polyimide film, micro-morphology and micro-structure, degradation process

Abstract: Polyimide (PI) film is an important type of insulating material used in inverter-fed motors. Partial discharge (PD) under a sequence of high-frequency square impulses is one of the key factors that lead to premature failures in 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) is designed based on the ASTM 2275 01 standard and the electrical aging tests of PI film samples are performed above the partial discharge inception voltage (PDIV). The chemical bonds of PI polymer chains are analyzed through Fourier transform infrared spectroscopy (FTIR) and the dielectric properties of unaged and aged PI samples are investigated by LCR testers HIOKI 3532-50. Finally, the micro-morphology and micro-structure changes of PI film samples are observed through scanning electron microscopy (SEM). The results show that the physical and chemical effects of discharge cut off the chemical bonds of PI polymer chains. The fractures of ether bond (C–O–C) and imide ring (C–N–C) on the backbone of a PI polymer chain leads to the decrease of molecular weight, which results in the degradation of PI polymers and the generation of new chemical groups and materials, like carboxylic acid, ketone, aldehydes, etc. The variation of microscopic structure of PI polymers can change the orientation ability of polarizable units when the samples are under an AC electric field, which would cause the dielectric constant ε to increase and dielectric loss tan δ to decrease. The SEM images show that the degradation path of PI film is initiated from the surface and then gradually extends to the interior with continuous aging. The injection charge could result in the PI macromolecular chain degradation and increase the trap density in the PI polymer bulk.

Key words: surface discharge, polyimide film, micro-morphology and micro-structure, degradation process

中图分类号:  (Dielectric thin films)

  • 77.55.-g
52.80.Wq (Discharge in liquids and solids) 68.55.-a (Thin film structure and morphology)