Engineering and Construction of a Gas-Insulated Substation in an Area of Potential Seismic Activity

A large 500/220 kV gas-insulated switchgear (GIS) for bulk power transmission has been installed in the extra high voltage (EHV) network in California. The station is situated outdoors in a region with potential seismic activity, a desert type climate and close to residential areas. These circumstances, together with long and complicated connections to incoming high voltage lines, presented a set of requirements that could best be served by a GIS type of substation. This was the first large EHV GIS to be installed on the Edison system. Experience from design, testing and installation of the GIS equipment is reported, as well as various means to cope with problems and items such as insulation coordination, disconnector transient overvoltages, thermal dimensioning of buses in trenches and seismic dimensioning.