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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]

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 micron metal particles are inevitably produced in long-term operation condition of high voltage direct current SF6 insulated apparatus, which could frequently cause the surface discharge. Degradation of long-term surface discharge will be a severe threat to the insulation strength. Aiming at this problem, the surface charge accumulation and flashover voltage of epoxy itself before and after discharge degradation by particles were compared in this paper. The composition after degradation was measured by EDS and FTIR. The microstructure was observed by SEM. The roughness was measured as well. The trap distribution was measured by SPD. The mechanism of degradation and its effect on insulation characteristics were analyzed. The results show that the surface charge accumulation increase three times after degradation. Additionally, flashover voltage decreases 19% after degradation. The smoothly surface after degradation decrease the trap energy level for 14%, which might be the change reason of surface charge accumulation and flashover voltage. This paper can offer as a reference for the effect of micron metal particles on insulation degradation in SF6 gas insulated equipment. [ABSTRACT FROM AUTHOR]

DC wall bushing is one of the key equipment in high-voltage direct current (HVDC) transmission project. At present, post insulators based on epoxy composites are widely used for supporting insulation in SF6-insulated apparatus. However, the flashover faults caused by surface charge accumulation can be a severe threat to the long-term operation of the post insulators under dc field. Therefore, the issue of charge accumulation on epoxy post insulators in HVDC wall bushing and its effect on flashover has been widely concerned. Aiming at this problem, the flashover characteristics of epoxy samples in SF6 gas under polarity reversal conditions with dc voltage prestressed for 10–600 min were measured in this article. The flashover process is analyzed through surface charge distribution measurement and electric field computation. The results show that with the increase of prestressed time, the accumulated negative charge density could reach $-14.8\,\,\mu \text{C}/\text{m}^{{2}}$ , which led to a 12% increase in maximum field strength. As a result, the polarity reversal flashover voltage could decrease by 12% and the flashover time delay could decrease by 84.6%. This article can offer as a reference for the effect of surface charge accumulation on flashover in SF6 gas-insulated equipment. [ABSTRACT FROM AUTHOR]