Suppressing Charge Accumulation and Enhancing Interface Insulation for PI/EP Composites by Fabricating Al2O3 Coating

Interturn insulation made of polyimide (PI) is considered to be the weakest part of the solid-state transformers (SSTs) composites insulation system due to the existence of an interface between the cast epoxy resin (EP) and itself. Ion-exchange strategy can be used to regulate the dielectric and electrical properties of PI insulating dielectric to ensure the stability of the composite insulation system. Therefore, this article intends to investigate the effects of the ion-exchange strategy on the space charge accumulation and interface insulation performance between PI and EP composites insulation. Our experimental results demonstrate that the wide bandgap alumina (Al2O3) nanoparticles can effectively improve the dielectric compatibility of PI and EP and significantly suppress the space charge accumulation on the PI/EP interface. The novel PI/EP composite structures insulation with breakdown strength about 39.5% higher than that of traditional PI/EP is obtained. The improvement mechanism is that the Al2O3 layer introduces a large number of deep traps on the surface of the PI film as well as reduces its dielectric compatibility with the EP, suppresses charge accumulation at the PI/EP composites insulation interface, and thus enhances the high-frequency insulation performance. In this article, the proposed surface engineering strategy is convenient and scalable, providing new insights into the regulation of composite insulation interfacial compatibility in high-voltage power equipment.