Optical studies of surface flash-over

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Abstract
An experimental study has been carried out into the optical activities associated with surface flash-over on high-voltage insulators in vacuum, aimed at determining the physical origin of the flash-over process. This involves using a 'transparent anode' to form, with combinations of cathode-insulator regimes, a number of electrode configurations, in order to observe the field electron emission and the optical events occurring during surface flash-over. In particular, the flash-over characteristics of two types of insulator shapes, cylindrical insulators and truncated cone insulators, were investigated. The latter allow spatially resolved imaging of the optical activities at two triple junctions and the surface of the insulators. Using this imaging technique in conjunction with the real-time recording function of a video camera system, four types of optical images have been identified. In addition, the influences of temperature and helium conditioning upon the characteristics of a flash-over were studied. Finally, a new model has been proposed to account for these experimental findings, which assumes accumulation of charges at two interface regions at two triple junctions, and that subsequent initiation of flash-over results from the breakdown of interface layers.