Characteristics of impulse-driven surface flashover across polymers with different surface conditions

Power-centric research conducted in the past few decades has identified many influencing factors that affect and contribute to the development of surface flashover. Among them, the surface condition—morphology, roughness, and texture—is one such physical characteristic of a gas-solid interface that is believed to be exploitable, relatively inexpensively, as a method to improve surface flashover strength. High-voltage (HV) pulsed power systems and equipment face similar issues, but there presently exists limited literature focused on impulse-driven flashover and the effects of surface roughness. In this work, the impulse-driven surface flashover strengths of five polymers relevant to pulsed power system design [polyvinylchloride (PVC), Delrin, Ultem, Torlon, and Perspex] are reported under two different (~20 ns and ~100 μ s rise time) impulsive waveforms in atmospheric air. Samples of different surface conditions—“as received” and “machined”—were subjected to flashover tests, complemented with surface profilometry measurements to evaluate the effects of various roughness characteristics on the impulse-driven breakdown strengths and times-to-breakdown. The obtained results indicate a general enhancement of the impulsive flashover strength with increased roughness with a corresponding prolongation of the time-to-breakdown. Rougher “machined” surfaces were therefore found to outperform the smoother “as received” surfaces. A correlation analysis between the measured surface roughness parameters and the breakdown data suggests that the short-wavelength components of the surface profile contributes more toward the enhancement of the flashover strength compared to longer wavelength “waviness” components. The consistency of this result with the theory of increased streamer path length and streamer inhibition is discussed, as are the potential consequences to insulator surface modification for flashover mitigation.