Prototype uhv compressed-gas-insulated transmission system

Development, manufacture, testing and installation of a 1200 kV compressed gas insulated transmission line (CGIT) and an SF6-air bushing are reported. Gas insulation studies of SF6 and mixtures with nitrogen, air or carbon dioxide were conducted. Pure SF6 at .45 MPa (50 psig) was selected for use in the prototype. Various materials and construction alternatives for the enclosure and conductor were investigated. Aluminum was chosen for both the enclosure and conductor. These provide the 5000 A 75% load factor thermal rating under standard burial and grounding conditions. Effects of alternate burial, grounding and bonding conditions are reported. For the solid support insulators low dielectric constant materials and epoxy were studied. An arc resistant epoxy formulation was developed and used for both conical and Tripost insulators. A high performance plug in contact for conductor joints was developed. Two versions of an SF6-air bushing were built and tested.