Development of Insulation Technology in Compact SF_6 Gas-Filled Bushings: Development of Compact 800-kV SF_6 Gas-Filled Bushings

摘要

Efforts of designers of gas-insulated switchgear (GIS) are currently focused on such features as smaller installation area and economical efficiency. Circuit breakers (CB), disconnecting switches (DS), and earthing switches (ES) have been redesigned in more compact configurations. Compactness and light-weight requirements are applied also to bushings used in GIS. GIS bushings can be divided in three general types: capacitor, gas-filled, and molded bushings. Requirements of the light weight and the economical efficiency of gas-filled bushings can be satisfied by improvements in insulation technology. Size reduction can be effectively achieved by moderation of the electric field strength on the outside surface of the hollow insulator in the area of the inner grounded electrode tip. We devised a new inner grounded electrode structure consisting of a cylindrical electrode and a ring electrode supported by column electrodes. This paper describes the effect of reduction of the maximum value of electric field strength on the outside surface of the hollow insulator by a new type of grounded electrode. Then, improvement of insulation performance for electrodes with insulation coating in SF_6 gas is described as the composite insulation technology. Finally, the efficiency of these insulation technologies is described by the basic insulation test results of a prototype compact 800-kV SF_6 gas-filled bushing.