Effect of Different DC Prestressed Time on Flashover Characteristics of Epoxy Resin Under Polarity Reversal Voltage

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 SF
₆
-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 SF
₆
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 SF
₆
gas-insulated equipment.