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Epoxy post-insulator is one of the key parts in SF6 gas-insulated DC wall bushing, which is irreplaceable in high voltage direct current transmission projects. Flashovers occur on post-insulators frequently, where a great number of tiny metal particles exist. The micron metal particles attached to the epoxy will change the insulation state of the surface. However, this relation between microstructure of material and macroscopic electrical properties on flashover would still arouse controversy. In order to study the effect of particles on the flashover characteristics, the particles generated from wear of spring in DC wall bushing were selected, the surface potential decay along surface and the DC flashover voltage of epoxy attached with particles were measured. The results show that the discrete particles could increase surface trap level by 0.025 eV under the effect of Van der Waals force. Furthermore, the deeper traps could capture the charge during the streamer development and inhibit the flashover, when the particle amount less than 500 per mm2. If the particles are more enough to form the continuous paths, these conductive paths could promote the streamer to propagate, which shortens the insulation distance, increases the electric field, and decreases the flashover voltage by 50% finally. [ABSTRACT FROM AUTHOR]

The charge accumulation phenomenon at the gas–solid interface under the co-action of DC electric field and temperature gradient is of great significance, but its long-time evolution characteristics are still unclear. In this work, the accumulation and dissipation characteristics of the surface charge on the epoxy-SF6 interface within 216 h were obtained, indicating that, (a) the normal surface electric field is increased by the temperature gradient along the gas–solid interface, which results in a prominent increase in the surface charge density; (b) there are different evolution processes of surface charge in high and low temperature regions under the co-action of DC-temperature gradient, and the increase of the charge trap density caused by the degradation of solid material is considered to be an important reason for the charge evolution; (c) the total charge dissipation ratio within 600 s decreases with the increase of charging time in DC electric field, and the surface charge dissipates mainly to the gas side of the interface; (d) the large amount of charge accumulated at the interface distorts the surface electric field at the triple junction points. The total electric field strength at the low-temperature tri-junction point increases by 35.5%, while the direction of the tangential field at the high-temperature tri-junction point reverses during the long-time co-action of the DC-temperature gradient. The results of this work may be helpful to understand the long-time charge evolution characteristics of the gas–solid interface under the DC-temperature gradient and to reveal the failure mechanism of the gas–solid interface. [ABSTRACT FROM AUTHOR]