Negative creeping discharge characteristics of a gas/solid composite insulation system under pulse voltages

Creeping discharge characteristics of a composite gas/solid insulating syst em have been studied by inserting a solid insulator between a needle electr ode and a plane electrode. Considerable differences have been found in the creeping discharge behaviors of N-2/SF6 and CO2/SF6 systems. With the addit ion of three-percent of SF6 gas to CO2 gas, the creeping discharge of the C O2/SF6 gas mixture was clearly seen to be strongly affected by the nature o f SF6 gas, as revealed by photon emission measurements in a corona and obse rvations using an ultrahigh-speed digital imaging system, On the other hand , the addition of a small amount of SF6 to N-2 caused a significant decreas e in the flashover voltage and a peculiar creeping corona extension. The cr eeping discharge characteristics of N-2/O-2 mixtures are similar to that ob served in N-2/SF6 mixtures. Both an electronegative gas (negative ion) and nitrogen play important roles in this behavior.