A Test for the Effect of High Energy Arcs on the Flash-over Strength of Insulators in Compressed SF6

A test method for evaluation of solid insulating material for insulators in Compressed Gas Insulated Transmission (CGIT) systems has been developed. The test measures the ability of an insulating surface to withstand voltage after being subjected to a high energy power arc across its surface. The test has been used to evaluate several different solid insulators in SF6 at 0.4 MPa. The test circuit is designed to effect an efficient transfer of energy from a capacitor bank to an arc on the insulator surface. Voltage reversals in the capacitor bank are minimized. Flash-over of the insulator is initiated using an impulse generator. After exposing the insulator to the arc, the power frequency flash-over voltage is used as a relative measure of the ability of the material to withstand power arcs. The test circuit, sample geometry and representative measurements are described. Epoxy systems with the best performance in these tests showed little or no decrease in power-frequency flash-over voltage after arcing, while large reducitons were observed in other epoxies after only a few power arc-overs. This arc damage test was developed as part of an ERDA Contract to develop a prototype 1200 kV CGIT system.