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Nanoparticles can generate charge carrier trapping and reduce the velocity of streamer development in insulating oils ultimately leading to an enhancement of the breakdown voltage of insulating oils. Vegetable insulating oil-based nanofluids with three sizes of monodispersed Fe 3 O 4 nanoparticles were prepared and their trapping depths were measured by thermally stimulated method (TSC). It is found that the nanoparticle surfactant polarization can significantly influence the trapping depth of vegetable insulating oil-based nanofluids. A nanoparticle polarization model considering surfactant polarization was proposed to calculate the trapping depth of the nanofluids at different nanoparticle sizes and surfactant thicknesses. The results show the calculated values of the model are in a fairly good agreement with the experimental values.

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Insulating oil modified by nanoparticles (often called nanofluids) has recently drawn considerable attention, especially concerning the improvement of electrical breakdown and thermal conductivity of the nanofluids. In this paper, three sized monodisperse Fe3O4nanoparticles were prepared and subsequently dispersed into insulating vegetable oil to achieve nanofluids. The dispersion stability of nanoparticles in nanofluids was examined by natural sedimentation and zeta potential measurement. The electrical breakdown strength, space charge distribution, and several dielectric characteristics, for example, permittivity, dielectric loss, and volume resistivity of these nanofluids, were comparatively investigated. Experimental results show that the monodisperse Fe3O4nanoparticles not only enhance the dielectric strength but also uniform the electric field of the nanofluids. The depth of electrical potential well of insulating vegetable oils and nanofluids were analyzed to clarify the influence of nanoparticles on electron trapping and on insulation improvement of the vegetable oil.

Epoxy polymer-based dielectric materials play a crucial role in advanced electronic devices and power equipment. However, high voltage-stress applications impose stringent requirements, such as a high dielectric strength, on epoxy polymers. Previously reported studies have shown promising material architectures in the form of epoxy polymer–nanoparticle dielectrics, which can restrict the movement of high-energy electrons by the interface charge traps associated with the various interfacial regions. However, these high-energy electrons inevitably traverse the epoxy polymer matrix and destroy the molecular structure, thereby creating a weak link for dielectric breakdown. In this study, a general strategy is developed to improve the dielectric strength by constructing interface charge traps in the molecular structure of the epoxy polymer matrix, using the −CF3 group in partial replacement of the −CH3 group. The proposed strategy increases the dielectric strength (39.5 kV mm–1) and surface breakdown voltage (26.9 kV) of the epoxy polymer matrix by 22.08% and 13.3%, respectively, because the interface charge trap hinders the movement of high-energy electrons. At the same time, the strategy does not degrade the mechanical and thermal properties. The results hold potential for wide application in the manufacturing of advanced future electrical and electronic equipment requiring resilience to high-voltage stress.