In this paper, SiO2 particles with three particle sizes of 60 nm, 2 μm, and 25 μm were added as fillers into the composites prepared by epoxy resin and micron silicon carbide to investigate the mechanism of SiO2 particle size on the nonlinear electrical conductivity and breakdown characteristics of the composites. Compared with SiC/EP composites, the smaller the added SiO2 particle size, the lower the current density at high fields and the higher the breakdown field strength of SiO2/SiC/EP composites. The nonlinear coefficients of SiO2/SiC/EP composites increased slightly with the addition of 1phr 25 μm SiO2 and 4phr 2 μm SiO2, and the breakdown field strengths were increased by 55.36% and 66.77%, respectively. The SiO2/SiC/EP composites with the addition of 4phr 60 nm SiO2 particles showed the most significant attenuation of the conductivity current and the most prominent enhancement of the breakdown field strength, but the nonlinear coefficient was reduced by 24.6%. With the increase of SiO2 doping amount, compared with the composites with the same particle size and low doping amount, the larger the SiO2 particle size, the decrease of the current density of the composites under high field intensity is more obvious, and the dielectric constant drops even more.

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Nonlinear composite materials serve to homogenize electric fields and can effectively improve the local concentration of the electric field in power systems. In order to study the nonlinear surface conductivity properties of micro-nano epoxy composites, two types of epoxy micro-nano composite specimens were prepared in the laboratory using the co-blending method. The surface conductivity of the composites was tested under different conditions using a high-voltage DC surface conductivity test system. The results show that the surface conductivity of micro-nano structured composites increases and then decreases with the rise of nanofiller doping concentration. The nonlinear coefficient was 1.781 at 4 wt% of doped nanostructured SiC, which was the most significant nonlinear coefficient compared to other doping contents. For the same doping concentration, the micro-nano structured composites doped with nanostructured SiC have more significant surface conductivity at the same test temperature with a nonlinear coefficient of 1.635. As the temperature increases, the surface conductivity of the micro-nano structured composite increases significantly, and the threshold field strength moves towards the high electric field. Along with the increase in temperature, the nonlinear coefficients of micro-nano composites after doping with nanostructured SiC showed a gradually decreasing trend. The temperature has little effect on the nonlinear coefficients of the micro-nano structured composites after doping with O-MMT.