Oil-solid surface flashover phenomena with sub-microsecond pulse excitation

Abstract

Summary form only given. In accelerators, the beam is generated and accelerated in vacuum where the vacuum region is comprised of appropriate solid insulating supports. The maximum operating voltage is limited by surface flashover across the vacuum-solid and/or oil-solid interface. The pulse shape, insulator shape/size and other operating conditions like electrode area, profile and environmental radiation govern this flashover voltage. However, in the LINAC system, small gaps comprising of solid-vacuum, oil-solid and oil-solid-vacuum insulation are subjected to voltage pulses with rise time up to 50 ns. Therefore, it was of interest to investigate breakdown behavior under linearly rising voltages. There is considerable amount of work reported on flashover across vacuum-solid interface for flat sub-microsecond pulses. This paper presents the experimental results of surface flashovers in oil-solid interfaces under pulsed input excitation. The effect of dV/dt and angle of spacer have been studied and reported here. The test parameters have been varied over a range of (i) rate of rise of input pulse, dV/dt rates viz 50 kV//spl mu/s, to 215 kV//spl mu/s and (ii) the semi-conical angle of spacer /spl theta/: -70/spl deg/ to +70/spl deg/. The effect of dV/dt shows the presence of flashover process is not thermionic, but electronic too. The dependence of the angle of spacer on flashover field is similar to vacuum-solid surface flashover. A theoretical models has been developed based on secondary electron avalanche and charge distribution method. Experimental results showed good agreement with proposed analysis.