Surface Flashover over a Microprofiled Cylinder in Air

Increasing the lightning impulse (LI) flashover voltage of insulators can require significant changes to the geometry and material properties of the insulator or electrodes. In some cases, such changes can be difficult to implement as they may require more volume or may compromise e.g. mechanical properties of the insulating parts. In this work, a new micro-scale surface profile which inhibits streamer discharge propagation without introducing major changes to the insulation system geometry or materials is demonstrated. Polyoxymethylene (POM) cylinders with 25 % glass fibre in air were machined with 0.5x0.4 mm rectangular grooves spaced 0.6 mm apart and stressed with LIs. A non-profiled cylinder and a cylinder with a larger, semi-circular grooves were tested for comparison. The cylinders were tested in a 48.5 mm atmospheric air gap with an exposed triple junction as the positive electrode. The rectangular surface profiles increased the LI flashover voltage (U 50 %) from 70.0 to 96.5 kV peak . High-speed imaging showed positive 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.