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局部放电是导致高频电力变压器绝缘劣化和失效的重要因素,为准确评估高频正弦波形下电压频率和温度对局部放电特性的影响,设计了高频局部放电测试系统,研究了聚酰亚胺薄膜在不同电压频率(0.5~40kHz)和温度(30~200℃)下的局部放电相位谱图、放电次数、放电幅值和绝缘寿命.实验发现,平均放电次数和幅值随电压频率的升高先增长后减小,存在“频致拐点”现象,且拐点频率随着温度的升高向低频段转移,而放电次数和幅值随温升单调增加.从空间电荷与放电特征参量的关联规律,以及温度对局部放电特性的影响机制分析着手,结合高频致热效应和电压频率对空间电荷耗散过程的影响,建立了“频致拐点”现象的数学模型,并揭示了其产生机制,为解释高频下的局部放电机制提供了理论依据.“,”Partial discharge (PD) is one of the most important causes of insulation aging and failure in high frequency power transformers. In order to accurately evaluate the influences of frequency and temperature on PD characteristics of polyimide films under high frequency sinusoidal waveform, a PD test system with variable frequency and temperature was established. The phase spectrum, repetition rate and amplitude of PD pulses along with insulation life were investigated at different frequencies (0.5~40kHz) and temperatures (30~200℃). Experiment results indicate that with the rising of frequency, the average number and amplitude of PD pulses in a cycle increase first and decrease afterwards, showing an inflection point in the variation curves, and the inflection point will move gradually toward the low frequency direction when the temperature is higher; while the discharge number and amplitude increase monotonically with temperature rise. Based on the correlation between spaces charges and characteristic parameters of PD pulses, influence mechanism of temperature on PD properties, combined with frequency-induced thermal effect and the impact of frequency on space charge dissipation process, the mathematical model and formation mechanism of inflection point phenomenon are presented in this paper, which presents theoretical reference for elucidating the partial discharge mechanism under high frequency stresses.