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聚酰亚胺(polyimide，PI)薄膜作为特殊工程塑料在变频电机绝缘设计中得到了广泛应用，方波脉冲电压下的局部放电是造成变频电机绝缘系统失效的主要原因之一。为探讨放电对电机绝缘的损伤作用过程，基于ASTM 227501标准设计一套表面放电老化试验系统，并对PI薄膜进行老化试验。表面放电使介质表面碳化，增加了PI薄膜的表面电导率，这对表面放电活性有较大的影响；借助扫描电子显微镜聚酰亚胺(polyimide，PI)薄膜作为特殊工程塑料在变频电机绝缘设计中得到了广泛应用，方波脉冲电压下的局部放电是造成变频电机绝缘系统失效的主要原因之一。为探讨放电对电机绝缘的损伤作用过程，基于ASTM 227501标准设计一套表面放电老化试验系统，并对PI薄膜进行老化试验。表面放电使介质表面碳化，增加了PI薄膜的表面电导率，这对表面放电活性有较大的影响；借助扫描电子显微镜观察了不同放电老化阶段下PI薄膜表面及横截面的微观形貌，发现PI薄膜的降解是从试样表面逐渐向内部发展的过程；采用傅里叶红外光谱(Fourier transform infrared spectroscopy，FTIR)分析了PI薄膜在老化前后的FTIR图谱，发现 PI 分子主链上的醚键(C-O-C)和酰亚胺环(C-N-C)键在放电老化作用下断裂，表面放电侵蚀造成有机分子链断裂是聚合物降解的本质原因。“,”Polyimide (PI) film is an important type of insulating material used in the inverter-fed motors. Partial discharge (PD) under a sequence of high-frequency square impulses is one of the key factors which lead to premature failure of 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) was designed based on the ASTM 2275 01 standard and the PI film was tested. The surface conductivity of PI film increases because of the carbonized surface layer caused by surface charge, which would affect the characteristic of surface discharge. The micro-morphology and structure change of PI film aged above partial discharge inception voltage (PDIV) was investigated by Scanning Electron Microscopy (SEM). The degradation path of PI film is initiated from surface and then gradually extends to the interior with continuous aging. The chemical bonds of PI chain were analyzed through Fourier Transform Infrared Spectroscopy (FTIR). The results show that the degradation mechanism of PI film is the fracture of chemical bonds, such as ether bond (C-O-C) and imide ring (C-N-C), caused by the physical and chemical erosion of surface discharge.