Physics of pulsed unipolar dielectric surface flashover at atmospheric conditions

Dielectric surface flashover along insulators in atmospheric conditions has been empirically characterized over the years. However, the underlying physics involved in atmospheric flashover has yet to be extensively analyzed and understood with variable parameters such as background gas, humidity, surface roughness, and temporal characteristics of the applied voltage. Understanding the fundamental physical mechanisms and the extent to which these processes influence discharge behavior is vital to characterizing and modeling surface flashover for various structures and conditions.

Previous dc and unipolar excitation experiments show distinct spark behavior in air and nitrogen. Specifically, flashovers in air form along the dielectric surface. This is possibly due to relatively high UV emission from a discharge forming in atmospheric air which contributes to photoemission. Discharges in nitrogen develop along the electric field lines, above the surface of the dielectric. Given this behavior, experiments with UV surface illumination in nitrogen were performed to study the impact on flashover behavior. Also, it was of importance to alter the temporal characteristics of the applied voltage to simulate lightning situations and investigate the resulting discharge behavior. Based on these results, the physical mechanisms primarily involved in pulsed unipolar surface flashover will be discussed. Note that the research presented here led to a total of three publications, including an invited paper presented at the 27th IEEE Power Modulator Conference.