Contribution of Temperature Gradient to Insulation Performance of Disc-insulator at DC Voltage-Part Ⅱ: Surface Flashover Properties

The temperature gradient is a crucial factor affecting the flashover characteristics at the gas-solid interface in DC GIS/GIL. This paper proposes a “stepwise approximation” method and utilizes it to measure the charge distribution approaching flashover occurrence (CDAFO). The electric field distribution considering CDAFO is calculated to analyze the effect of surface charge on DC flashover voltage at temperature gradients. The results show that with increasing temperature gradient, both positive and negative flashover voltages gradually decrease. The hetero-charge accumulation increases significantly, with high-density hetero-charge clusters appearing at the moment approaching flashover. These charge clusters greatly enhance the electric field near high-voltage electrode: the maximum electric field under negative voltage increases from 3.64 kV/mm to 4.96 kV/mm, and it increases from 3.45 kV/mm to 5.09 kV/mm under positive voltage. This electric field enhancement leads to the reduction in flashover voltage. This work can provide valuable references for the insulation design of DC GIS/GIL systems under temperature gradients.