Investigation Of Holdoff Conditioning In Surface Discharges

The experimental findings are reported for the observed (surface holdoff voltage) conditioning effects for a group of ceramic and polymeric insulators tested in a surface discharge switch producing 300 kA, 20 p current pulses. The surface voltage holdoff response (i.e., the surface breakdown voltage versus the number of discharges) for the surface discharge switch is shown to have two phases: 1) the conditioning phase, and 2) the decomposition phase. The conditioning phase occurs during the initial series of discharges and is manifested by a successive increase of the surface breakdown strength of the insulator lasting up to /spl tilde/45 discharges. The decomposition phase follows and results in the surface of the insulator becoming conductive or semiconductive. The mechanism responsible for the conditioning effect is attributed to water vapor absorption in the insulator. Empirically, the calculated conditioning response is proportional to the product of the decomposition resistance of the material and its water absorption.