Surface Flashover over a Profiled Cylinder in Air

The effect of a small-scale surface profile on the lightning impulse (LI) surface flashover over 30 mm diameter polyoxymethylene (POM) cylinders with 25 % glass fibre in air was studied. The cylinder surface was machined with 0.5x0.4 mm trenches spaced 0.6 mm apart. A non-profiled cylinder was used as a reference. The cylinders were tested in a 48.5 mm atmospheric air gap with an exposed triple junction as the positive electrode. The surface profiles increased the LI flashover voltage (U 50% ) from 70.0 to 96.5 kV peak . High-speed imaging showed surface streamer discharges stopping on the surface profiles. Discharge inception calculations were used to explain the influence of the surface profile on the flashover process. The results are relevant for technological applications with electrically stressed solid insulators in gases.