Effects of roughness on surface flashover voltages under DC stress

Investigations about the effect of roughness on the surface flashover voltages were made with different materials under different ambient conditions. The tendency of the investigations appear to be contradictory to the results exhibited in other publications, where only roughness values up to 10 micrometers were investigated and different directions of the roughness in respect to the electrical field direction were not taken into account. The experiments were made using epoxy resin test samples, which have different degrees of roughness and diverse roughness orientation in respect to the electrical field direction. The test samples were exposed to voltages up to the surface flashover. The withstand voltage of the test samples was then analysed concerning the behaviour at consecutive flashover with and without a pause between consecutive flashover. The results of these experiments show a relationship between the roughness value of the insulator surface and its flashover voltages and also an effect of the roughness orientation related to the electrical field direction.