Influence of surface roughness on vacuum flashover characteristics of PMMA

Nowadays there are still some disputes about the effect of surface roughness of insulation material on its surface flashover characteristics in vacuum all over the world. We prepared polymethyl methacrylate (PMMA) samples with various surface roughness through polishing with abrasive papers of different mesh numbers, and used the samples to conduct vacuum surface flashover experiments. The results indicate that flashover voltage firstly decreases and then increases with increasing surface roughness. We also investigated the effect of polishing direction on the flashover characteristics. It is found that when surface roughness is high, certain polishing direction effectively increases flashover voltage. Especially when the polishing direction is vertical to the line connecting the two electrodes, the flashover voltage gets obviously increased while holding rather low dispersity. However, when surface roughness is low, polishing direction barely influences flashover voltage. Finally, based on the experimental results and the secondary electron emission avalanche model, the mechanism of surface roughness influencing flashover characteristics is discussed, i.e., the inhibition effect and promotion effect, and a game model is proposed to describe the connection between the two kinds of effects.