Applicability of surface functionally graded materials for flashover mitigation: from vacuum to compressed SF₆ gas

Surface functionally graded materials (SFGMs) exhibit promising prospect in flashover mitigation of solid insulation in high-voltage apparatus. The construction methods and their applicability of SFGMs in various scenarios are systematically investigated in this work. Coating materials with different functional fillers were prepared to fabricated different types of SFGMs. Flashover testing results show that coating with graded permittivity (ε-SFGM) and coating with graded permittivity / conductivity (ε/ σ-SFGM) exhibit excellent electrical strength enhancement effect in compressed SF₆ gas at power frequency. In contrast, the improvement effect of SFGMs are limited in vacuum. Only ε/ σ-SFGM constructed by SiC fillers shows a better flashover mitigation effect in vacuum due to the dissipation capability of surface hetero-charge. σ-SFGM constructed by carbon nanotube fillers would deteriorate surface electrical strength both in SF₆ gas and in vacuum due to its excessive conductivity. Furthermore, numerical simulations were conducted to build the relationship between SFGMs construction methods and flashover threshold both in vacuum and compressed SF₆ gas, which are in agreement with the experimental results.