A facile method using a nanocomposite coating is proposed to suppress surface charge accumulation and enhance the surface breakdown strength of polymeric insulating materials like epoxy resin, by covering a thin 1,1,2,2-tetrahydroperfluorodecyltrimethoxysilane modified alumina (Al₂O₃) flake/UV curable resin nanocomposite coating. Due to the peculiar characteristics of perfluorooctyl chains at the microscale and the intricate topographical structure of morphology at the mesoscale, the coating exhibits enhanced water/oil repellence, surface charge accumulation resistance, and flashover withstanding capability. It is found that increasing the content of modified Al₂O₃ is conducive to decreasing the surface free energy of the specimens, rendering them superhydrophobic. Experimental tests in air show that the presence of nanoparticles generates numerous carrier traps at the surface layer, contributing to a much faster charge decay rate. Furthermore, impulse flashover voltage tests under vacuum show a >100% improvement of surface electrical strength. Further experimental results reveal that lower secondary electron emission yield remarkably alleviates the surface charging phenomenon, thus relieving electric field distortion caused by hetero-charges. We envision that such a multifunctional strategy for surface discharge mitigation is efficient, adaptable and easy to scale up, and thereby exhibits great prospects for applications in electronics and electrical power systems.

Dielectrically graded insulation (DGI) serving as an embodiment of functionally graded materials in electrical insulation field displays extraordinary insulation strength compared with conventional uniform composite materials. In recent years, the design and fabrication of DGI toward industrial applications have become urgent issues. Here, we reported a construction strategy of DGI for gas-insulated equipment. A topology optimization method was applied to optimize the electric ( $E$ ) field distribution of a 126-kV disk-type spacer with actual size. The spatial distribution of relative permittivity ( $\varepsilon _{r}$ ) inside spacer was designed to improve the $E$ -field distributions along the spacer surface and near the triple junction region. Influences of design parameters on $\varepsilon _{r}$ distributions and the resultant $E$ -field mitigation degree were analyzed. Appropriate values of design parameters that balance the structure processability and $E$ -field mitigation results were selected. A three-layer dielectrically graded spacer, including high, medium, and low $\varepsilon _{r}$ regions, was constructed based on the topology optimization results. In addition, the influence of the area of design domain on the optimization results was analyzed. Numerical results indicate that the $E$ -field distribution of designed dielectrically graded spacers is significantly improved compared with that of a homogeneous spacer. In the situation with simplified electrode configuration, the maximum $E$ -field strength along the spacer and at triple junction area could be decreased by 10.5% and 43.4%, respectively. This three-layer DGI construction strategy is promising to apply industrially.

Epoxy/alumina composite materials are widely used in support insulators in air/SF ₆ switchgear. However, epoxy resin is difficult to be recycled or reprocessed because of its cross-linked structure. With the worldwide promotion of net-zero strategy, it is necessary to investigate suitable replacement for the epoxy resin. For this purpose, this paper investigates the applicability of several thermoplastic alternatives in support insulators, and selects an optimal material for future research. The first study is the comparison of basic electrical and mechanical properties among several typical thermoplastics, in which the standardized material requirements for solid insulators were used as a reference. Subsequently, polycarbonate (PC), polyoxymethylene (POM), and polyamide 66 (PA66) were selected for the detailed evaluation on dielectric properties, i.e., electrical conductivity and broadband dielectric spectra (BDS). Electrical conductivity was measured in –40 °C to 125 °C temperature range and 1 to 8 kV/mm electric field range. BDS were tested under the identical temperature range. Results on electrical conductivity indicate that PC has the lowest value among three studied materials, which varies slightly with electric field. An Arrhenius study was carried out to understand the variation mechanism of the conduction process. For dielectric spectra, the results of PC show little temperature-dependence, whereas the other material has significantly increased dielectric loss when operating under high temperature (>65°C). The fitting results of the Havriliak-Negami model reveal the mechanism of dielectric spectra variation for the investigated thermoplastics. These results suggest that PC has lower conductivity, lower dielectric loss and less temperature- and field-dependence than the other thermoplastics, making it a potential, environmental-friendly replacement for epoxy resin in support insulators.

To prepare high-permittivity composite materials for dielectrically functional gradient materials (d-FGMs) by the stereolithographic 3D-printing technique, three ceramic powders (i.e., alumina, barium titanate, and strontium titanate) are selected as functional fillers for a UV-curable resin matrix. The viscosity and UV curing depth of the uncured slurry are tested for feasibility of 3D printing. Comprehensive electrical properties, including volume resistivity, permittivity, dielectric loss, and breakdown strength of the cured composites are measured. The effects of the filler types, morphologies, particle sizes, and volume fractions on the UV curing characteristics of the slurry and dielectric properties of cured composites are systematically analyzed. The experimental results show that spherical fillers with large particle sizes, smooth surfaces, and high permittivity are conducive for reducing the slurry viscosity, increasing curing depth and adjusting the composite’s permittivity over a wide range. We believe that the proposed strategy for material system establishment can improve the 3D printability of high-permittivity composites and promote other applications of the d-FGMs by the stereolithography technique.