Long-term corona behaviour and performance enhancing mechanism of SiC/epoxy nanocomposite in SF6 gas environment

Abstract

Surface coating technology is an effective way to solve the interface insulation problem of DC GIS/GIL basin insulators, but the performance of the coating will change greatly, and the insulation strength will be completely lost, after long-term use in the extreme conditions of corona erosion. In this research, the multi-needle-plate electrode platform was constructed to explore the long-term use performance of SiC-doped nanocomposite exposed to corona discharge in SF6 gas. Samples with a high SiC content have advantages in maintaining physical and chemical properties such as elemental composition, erosion depth, surface roughness and mass loss. The nanocomposite doped with 6 wt.% SiC has prominent surface insulation strength after long term exposure to corona, and the others are close to losing, or have completely lost, their insulating properties. Furthermore, the degradation mechanism of physicochemical properties of composite exposed to corona discharge was investigated with the proposed ReaxFF MD model of energetic particles from SF6 decomposition bombarding the epoxy surface. The reaction process of SF particles and F particles with the cross-linked epoxy resin, and the SiC nanoparticles providing shelter to the surrounding polymer and mitigating their suffering direct bombardment, have been established. The damage propagation depth, mass loss and surface roughness change of nanocomposite material bombarded by SF6 decomposition products is reproduced in this simulation. Finally, the deterioration mechanism of insulation properties for the SiC-doped composite was elucidated with DFT analysis. The band gap of the molecule containing S drops directly from the initial 7.785 eV to 1.875 eV, which causes the deterioration of surface electric properties.