Underground Power Transmission with Isolated-Phase Gas-Insulated Conductors

A 345-kV underground transmission system using isolated-phase construction, with concentric aluminum tubes insulated with sulphur hexafluoride (SF6) gas is described. A 600- foot (183-meter) long three-phase installation of this type made late in 1969 at Consolidated Edison's Buchanan substation, on the tie between the Keystone 500-kV system and the New York?New England 345-kV grid is discussed. The link will be capable of carrying 2000 MW in a single trench, backfilled around the enclosures with sand having relatively low thermal resistivity at low moisture levels.