Surface Charge Characteristics of DC-GIL Insulator Under Multiphysics Coupled Field: Effects of Ambient Temperature, Load Current, and Gas Pressure

In this article, the surface charge characteristics of the direct current gas-insulated transmission lines (DC-GIL) insulator under thermal-electric coupled fields are investigated. A horizontally installed GIL with a basin-type insulator is employed. The 3-D charge distribution under different ambient temperatures, load currents, and gas pressures is obtained based on the finite-element method. It is found that the charge density increases with increasing ambient temperature since the bulk conduction is promoted due to the increasing insulator temperature. At lower ambient temperature, the surface charge distribution shows a more obvious difference in different radial directions along the insulator due to the increasing difference in electric conductivity in different directions. With increasing load current, the charge density increases, and the difference in charge density in different radial directions becomes more obvious. The charge density increases with increasing gas pressure although the temperature decreases, which is attributed to the domination of decreasing ion mobility over decreasing bulk conduction. It can be concluded that attention should be paid to these conditions when dealing with the insulation property of DC-GIL considering the effect of thermal gradient on the charge accumulation. Besides, simulation based on a 3-D model is necessary, especially for horizontal GILs.