Post-Type Support Spacers for Compressed Gas-Insulated Cables

The flashover performance of post-type support spacers for concentric compressed gas-insulated transmission lines was investigated. The experiments were made with SF6 gas at 4.4 atm. abs. and low frequency AC voltage in the EHV range. Nine cast epoxy spacers with metal inserts at each end shaped to produce different electric field distributions along the solid-gas interface were tested. The results show that flashover voltage is controlled by the electric field distribution and is inversely proportional to the stress enhancement in the gas. This conclusion is shown to be consistent with ionization-initiated breakdown at a certain stress limit about 300 kV/cm in these studies. The better designed spacers were limited by sparkover of the radial gas-gap at 1300 kV peak and not by surface flashover at the insulator.