Modification of HVDC GIS/GIL Basin Insulators Based on Electrical and Mechanical Collaborative Design

Abstract

Gas insulated metal enclosed switchgear(GIS) and transmission line (GIL) have basically the same basin insulators which are used for gas chamber isolation and conductor support. They are the weak links in the electrical insulation and mechanical strength of GIS/GIL equipment, and are related to the safe and reliable operation of high-voltage transmission lines. Under AC voltage, the basin-shaped insulator weakens the tangential field strength, reduces the flashover voltage, and ensures the bonding strength between the conductor and epoxy. Unlike the AC, in the DC GIS/GIL, space charged particles drift, diffuse, and accumulate on the surface of the insulator, distorting the initial capacitive electric field. At this time, although the tangential field strength of the basin-shaped insulator is small, its strong normal component attracts a large number of charged particles to accumulate on the surface, which increases the risk of flashover along the surface. The use of low basin insulators or plate insulators can effectively reduce the normal electric field component and reduce charge accumulation, but it cannot meet the requirements of mechanical characteristics at the same time. In this paper, an AC steady-state electric field model, a DC transient electric field model based on space charge transport, and a stress field model during a pressure test are established. Firstly, the characteristics of electric field distribution along the surface of basin insulators under AC and DC voltages are compared and analyzed. The electric charge accumulation and electric field distortion of basin insulators under DC voltage conditions are obtained, and the key structural parameters that affect the charge accumulation under DC voltage are determined. Secondly, the electrical and mechanical characteristics of basin and plate insulators are compared and analyzed. An electrical and mechanical collaborative design scheme of the high-voltage DC GIS/GIL insulator structure is proposed, which provides important theoretical support for the modification of insulator structure.