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Phase field model for electric-thermal coupled discharge breakdown of polyimide nanocomposites under high frequency electrical stress

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Plasma Science and Technology 2024年第2期26卷 114-124页

作者：韩智云李庆民李俊科王梦溪任瀚文邹亮 State Key Lab of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power UniversityBeijing 102206People's Republic of China School of Electrical Engineering Shandong UniversityJinan 250061People's Republic of China

In contrast to conventional transformers, power electronic transformers, as an integral component of new energy power system, are often subjected to high-frequency and transient electrical stresses, leading to heightened concerns regarding insulation failures. Meanwhile, the underlying mechanism behind discharge breakdown failure and nanofiller enhancement under high-frequency electrical stress remains unclear. An electric-thermal coupled discharge breakdown phase field model was constructed to study the evolution of the breakdown path in polyimide nanocomposite insulation subjected to high-frequency stress. The investigation focused on analyzing the effect of various factors, including frequency, temperature, and nanofiller shape, on the breakdown path of polyimide(PI) composites. Additionally, it elucidated the enhancement mechanism of nano-modified composite insulation at the mesoscopic scale. The results indicated that with increasing frequency and temperature, the discharge breakdown path demonstrates accelerated development, accompanied by a gradual dominance of Joule heat energy. This enhancement is attributed to the dispersed electric field distribution and the hindering effect of the nanosheets. The research findings offer a theoretical foundation and methodological framework to inform the optimal design and performance management of new insulating materials utilized in high-frequency power equipment.

关键词： dielectric discharge breakdown high frequency power electronic transformer polyimide nanocomposites phase field model

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Tough polyimide composites synergistically reinforced by carbon nanofiber-grafted carbon fiber and rGO for improved heat dissipation and electromagnetic interference shielding

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Journal of Materials Science & Technology 2023年第18期149卷 225-236页

作者： Zhiqiang Wu Jie Dong Xiuting Li Xin Zhao Wenjun Tan Chengchang Ji Qinghua Zhang State Key Laboratory for Modification of Chemical Fibers and Polymer Materials College of Materials Science and EngineeringDonghua UniversityShanghai 201620China Key Laboratory of Micro-Nano Materials for Energy Storage and Conversion of Henan Province College of Chemical and Materials EngineeringXuchang UniversityXuchang 461000China

The rapid miniaturization and a consequent increase in electromagnetic wave(EM)and heat emission in integrated electronic devices are now urgently desiring for multifunctional polymer composites that simultaneously possess high mechanical properties,excellent electromagnetic interference(EMI)shield-ing ability and heat dissipation ***,a series of novel polyimide-based composite films were constructed by rationally assembling the carbon nanofiber-grafted carbon fiber(NCF)and reduced graphene oxide(rGO)into a highly electrically and thermally conductive pathway within polyimide ma-trix via a sequential bidirectional freezing casting and hot-pressing *** combination of high tensile strength and toughness was obtained by incorporating rGO into the NCF-reinforced PI composite,giving rise to a hierarchical reinforcing structure of NCF and crack deflection induced by rGO *** high electrical conductivity(7.0×10^(3) S m^(-1))endows the PI/NCF30/rGO3.5 composite film with a good EMI shielding effectiveness of 45 ***,the well-aligned thermally conductive NCF and rGO and strong interfacial bonding between the polymer matrix and reinforcing fibers give rise to improved thermal conductivity(λ),particularly along the in-plane ***,the PI/NCF30/rGO3.5 exhibits an in-plane thermal conductivity of 5.18 W m^(-1) K^(-1),∼4.7 times increment compared to the pure PI(0.91 W m^(-1) K^(-1)).Besides,the resultant PI/NCF30/rGO3.5 composite film presents a superior Joule heat-ing performance with some features of fast thermal response,ease of regulation and sufficient ***,the developed multifunctional polyimide-based composite films demonstrate high potential as advanced EMI shielding materials with excellent heat dissipation.

关键词： polyimide nanocomposites Mechanical performance Emi shielding Heat dissipation

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