Study on surface charges accumulation characteristics of insulators for ±500 kV DC-GIL based on multi-physics coupling model

When a DC voltage is applied externally, a large amount of charge accumulates on the surface of the insulating components in the gas insulated metal-enclosed transmission line (GIL), significantly reducing the flashover voltage along the surface and triggering a series of electrical equipment failures. Based on the above issues, this paper considers the internal heat transfer process of DC-GIL under actual working conditions. Using the finite element method, a simulation model of the surface charge accumulation characteristics of DC insulators under temperature gradients is established, and the surface charge accumulation characteristics of basin-type insulators are analyzed. The research results indicate that under the action of direct current voltage, negative charges will accumulate inside the insulator, with a maximum charge density of 4.66 mC/m3. The concave surface of the basin-type insulator mainly accumulates charges opposite to the polarity of the applied DC voltage, while the convex surface mainly accumulates charges of the same polarity as the DC voltage. The charge accumulation effect causes the maximum tangential electric field strength on the convex surface of the insulator to increase by 40% and the maximum tangential electric field on the concave surface to increase by 19.78%, seriously affecting the insulation performance of the system. On this basis, a new type of insulator structure was proposed, which can reduce the maximum normal field strength by 35.1% compared with the basin-type insulator and reduce the surface charge density on both sides by 91.27% and 91.42%, respectively. This study can be referred to in the insulation design of DC-GIL.