Epoxy casting composition for UHV service in compressed SF6 insulated equipment

A prototype, 1200 kV (nominal voltage) compressed gas insulated transmission line (CGIT) is being developed on a program for the U.S. Energy Research and Development Administration (ERDA). A critical component of this system is the insulator, which supports the aluminum conductor concentrically within the aluminum sheath. The line is filled with sulphur hexafluoride (SF6) gas at a pressure of 4.4 atmospheres absolute (50 psig) for the high voltage insulation and to help dissipate the heat from the conductor to the sheath. Two types of insulators are being considered for the prototype, to be made from either a cast epoxy, or a low-dielectric constant material. A comprehensive materials evaluation program has therefore been made, together with a detailed investigation of the required profile and construction of the insulator.