Polyimide (PI) films used for inter-turn insulation of power electronic transformer (PET) are prone to premature insulation failure. Using ion-exchange technology to modify the surface of PI films effectively improves its high-frequency (HF) insulation strength. In this paper, the HF discharge characteristics of PI films were studied coated a nano-Al₂O₃ layer. The experimental results illustrate that the introduction of nano-Al₂O₃ coating can effectively improve the HF surface insulation strength of modified PIs, in which the maximum discharge lifetime is increased to 5.6 times of the pristine PI, and the creeping flashover voltage raised from the initial 6.34 kV to 11.98 kV, an increase of 88.96%. The enhanced mechanism of HF insulation performance of modified PIs is as follows: On the one hand, formed the functional nano-Al₂O₃ coating improves the thermal management ability and the inorganic–organic phase structure of the modified PIs, which is effective in reducing the temperature rise of materials. On the other hand, the introduction of the nano-Al₂O₃ coating increases the density of the shallow trap, increasing the surface conductivity of modified PIs, and hindering the development of HF surface discharge. This paper offers a prospective strategy for polyimide dielectrics with superior HF insulation performance.

用于电力电子变压器 (PET) 匝间绝缘的聚酰亚胺 (PI) 薄膜容易出现过早绝缘失效。采用离子交换技术对PI薄膜表面进行改性，有效提高其高频（HF）绝缘强度。本文研究了涂覆纳米Al ₂ O ₃层的PI薄膜的高频放电特性。_{实验结果表明，纳米Al 2} O ₃的引入涂层能有效提高改性PI的高频表面绝缘强度，最大放电寿命提高到原始PI的5.6倍，沿面闪络电压从最初的6.34 kV提高到11.98 kV，提高了88.96%。改性PIs高频绝缘性能的增强机制如下：一方面，功能性纳米Al ₂ O ₃涂层的形成提高了改性PIs的热管理能力和无机-有机相结构，有效地降低材料的温升。另一方面，纳米Al ₂ O _3的引入涂层增加了浅陷阱的密度，增加了改性 PI 的表面电导率，阻碍了 HF 表面放电的发展。本文提供了一种具有优异 HF 绝缘性能的聚酰亚胺电介质的前瞻性策略。