中文摘要：

变频电机绝缘长期承受高场强方波电压的作用,出现了绝缘过早失效的情况。聚酰亚胺是变频电机中重要的绝缘材料,为了解它不同承受电压形式时其绝缘老化过程和失效机理与传统交、直流电压下存在的很大差异,在高场强方波电压下对聚酰亚胺膜进行电老化,测试了不同老化时间后聚酰亚胺膜的电导电流和热刺激电流（TSC）以分析聚酰亚胺膜活化能和陷阱密度等微观参数的变化规律。结果表明：聚酰亚胺膜TSC曲线可能由2个单峰曲线叠加而成,随着电老化时间的增长,聚酰亚胺膜活化能发生变化,浅陷阱可发展成深陷阱,导致浅陷阱密度逐渐减小,深陷阱密度逐渐增大,总体陷阱密度逐渐增大。

英文摘要：

Thermally stimulated current（TSC） is the depolarization current in dielectrics after polarization.It is a powerful technique to study the space charge accumulation and the trapping parameters in the dielectrics.These parameters could reflect the ageing degree of dielectric.In order to study the change regularity of trap parameters in polyimide under high stress step voltage,the thermally stimulated current and conductive current were measured during the electrical ageing process.The test results show that the TSC curve of polyimide is a compound curve of two single-peaked curves.Low temperature single-peaked curve corresponds with structure of shallow traps and the other one corresponds with structure of deep traps.The activation energy of traps varies with the increasing of ageing time.The shallow traps turn into deep traps,resulting in the density of shallow traps reduced and the density of deep traps increased.The increase in the total density of the trap in polyimide indicates that the ageing degree would be more serious.