Dielectric Stimulated Arcs in Lightning-Arrestor Connectors

Substantial lowering of breakdown voltage can occur between electrodes in air when a solid insulator surface bridges these electrodes. The breakdown mechanism involves a type of surface flashover across the insulator. The apparent triggering of the breakdown by the insulator is called a dielectric stimulated arc. This phenomenon, based on previous experimental results, has been incorporated into the lightning arrestor developed by Sandia Laboratories, Albuquerque, NM. The lightning-arrestor connector would be more useful if both the mean and standard deviation of breakdown levels were decreased. With this goal in mind several experiments were performed in order to study the dielectric stimulated arc in detail. Prebreakdown conduction was measured and was shown by image-enhanced photography to be caused by partial discharging. The partial discharge was found to occur in highfield regions far from the breakdown site. Ultraviolet light generated by the partial discharge was shown to sympathetically initiate a surface flashover on the insulator within a few tens of nanoseconds. These studies have led to a better understanding of dielectric stimulated arcs and will undoubtedly lead to improved lightning-arrestor designs.