NANOSECOND, PULSED BREAKDOWN OF N//2 AND SF//6.

Pulsed breakdown experiments are reported which were performed with a square wave impulse generator with 150 kV impulse amplitude, 200 ns pulse width, and a rise time below 2 ns. Optical investigations of the mechanism of discharge ignition by UV-illumination are performed in both N//2 and SF//6 . The investigation of the discharge formation shows that in SF//6 an intermediate state in the discharge development exists. Thus, the gap is partly bridged by a narrow discharge channel and in the remaining part, a diffuse discharge with a rather high voltage drop exists. Additional measurements of pulsed breakdown at insulator interfaces are then performed.