Formation Mechanisms of Clean Zones During the Surface Flashover of Contaminated Insulators

The mechanism of breakdown on a contaminated insulator surface under High Voltage dc (HVDC) has been studied. A new laboratory contamination technique is proposed, which yields uniformly contaminated test specimens. Using this method, flashover processes have been systematically studied and recorded on high speed films. These tests reveal the existence of a "clean zone" around the anode for test voltages of both polarities. A theory is proposed to describe the formation of such a "clean zone" and its role in the flashover process.