Silicon carbide (SiC) is widely used to improve the non‐linear conductivity of non‐linear resistive field grading composite. In this paper, the SiC nanoparticles are modified into core‐shell nanoparticles with silica (SiO ₂ ) coating on the surface and are characterised by transmission electron microscopy and X‐ray diffraction, respectively. The 7 wt% SiC@SiO ₂ /epoxy nanocomposite is then prepared, and the pure epoxy and 7 wt% SiC/epoxy nanocomposite are prepared as a contrast. The relative permittivity, thermally stimulated current, conductivity and breakdown strength are studied, respectively. The presence of SiO ₂ shell around SiC nanoparticles has a great effect on the relative permittivity and trap distribution. The epoxy nanocomposites show non‐linear conductivity characteristics, compared with pure epoxy. The 7 wt% SiC@SiO ₂ /epoxy nanocomposite has higher switching electric field and breakdown strength than the 7 wt% SiC/epoxy nanocomposite, which is helpful for the application of non‐linear resistive field grading composite in higher‐voltage equipment or components.

In dielectric science, the electrical breakdown strength of a polymeric material significantly decreases with elevated temperatures, which restricts the development of advanced electrical and electronic applications toward miniaturization. In the present study, to clarify the temperature-dependent DC breakdown mechanisms of epoxy resin (EP)/TiO₂ nanocomposites, the effects of nanoparticle incorporation and temperature on charge transport and molecular chain dynamics were studied. The results indicate that space charge accumulation and electric field distortion are reduced by nanoparticle incorporation to enhance the deep trap level, while space charge accumulation, electric field distortion, and molecular displacement are all accelerated as temperature increases. To further investigate the influence of carrier traps and molecular chain dynamics on temperature-dependent breakdown, a DC breakdown simulation model that involves bipolar charge transport, molecular chain dynamics, and breakdown criterion equations is established. The calculated breakdown strengths of EP/TiO₂ nanocomposites show great accordance with the experimental results, which indicates that temperature-dependent DC breakdown mechanisms are dominated by the synergetic effects of carrier traps and segment chain dynamics. Through the analysis of the breakdown model, a transition of the dominant mechanism (from segment chain to backbone dynamics) near the glass-transition temperature for DC breakdown of EP/TiO₂ nanocomposites is discovered.

Core-shell structured filler is helpful for the improvement of the nonlinear conductivity characteristics of nonlinear resistive field grading materials, but the effect of its filler loading on the charge transport characteristics of these materials is rarely reported. To aim at this, the core-shell SiC@SiO ₂ nanoparticles were fabricated at first, and were filled into epoxy matrix to prepare nanocomposites with 0, 1, 3, 5 and 10 wt%. The nanoparticles’ microstructure were characterized, whereas the relative permittivity, thermally stimulated current, conductivity and surface potential decay characteristics of epoxy nanocomposites were measured, respectively. Experimental results show that the relative permittivity decreases at first and then increases with the increase in filler loading. New shallow traps were introduced by core-shell nanoparticles when the filler loading is larger than 1 wt%, and increases with the filler loading. Only when the filler loading is no less than 5 wt%, the nanocomposites show distinct nonlinear conductivity characteristics, which are attributed to the presence of large amount of new shallow traps. The enhanced nonlinear conductivity characteristics are responsible for the surface potential decay.

Surface flashover is an inevitable insulation issue for basin-type insulators in gas-insulated switchgears/lines, which significantly challenges the reliability of the electrical power systems. Previous studies have indicated that polymer/semiconductor-filler composite coatings effectively improve the insulation properties; however, the influence mechanism of the coating materials on flashover has not been demonstrated from a molecular perspective. In this work, epoxy/silicon-carbide (EP/SiC) composites were coated onto an EP substrate. The energy-level structure, surface trap, surface charging, and DC flashover voltage in SF₆/N₂ were calculated and characterized, and the process by which the tailored molecular energy level influences surface charge transport and flashover characteristics was elucidated. The incorporating of SiC particles reduced the width of the bandgap and introduced shallow traps, which improved carrier mobility and surface conductivity. Quantitative analysis of charge transport indicated that the improved carrier mobility and reduced surface trap level accelerated the surface charge dissipation. This reduced the tangential electrical field distortion and surface charge density and further impeded gas ionization. When the SiC concentration was 15 wt%, the flashover performance improved by 20.88%. This study describes the mechanism by which the EP/SiC coating regulates the surface charge distribution to improve the surface flashover performance by establishing a relationship among the microscopic molecular energy-level structures, mesoscopic charge transport, and macroscopic discharge phenomena.