Sparkover as influenced by surface conditions in D-C Corona

Sparkover between clean electrodes has been investigated extensively but it is found that sparkover between contaminated electrodes exhibits very different results. With corona from a clean metal point to a plane, sparkover occurs at a considerably lower voltage if the point is positive.1 Because of this, it is frequently assumed that positive corona will always result in the lowest sparkover voltage. A few experiments with contaminated electrodes show that sparkover is a complicated phenomenon and that negative corona does not always result in a higher sparkover voltage.