Influence of Surfactants on the Flashover of an Interrupted Insulator Surface

AC flashover voltage (ACFOV) between insulation surfaces coated with surfactant and interrupted by an air gap depends on the surfactant. The surfactants used are alkyl-benzene sulfonate (Neogen T®), alkyl-trimethyl-ammonium chloride (Catiogen L®) , and polyoxyethylene-sorbitan monolaurate (Tween 20®). The insulating material is polymethylmethacrylate (PMMA). In the ac prebreakdown discharge, the luminescence at the positive phase is streamer-like and that at the negative phase is glow-like. The intensity of the positive streamer luminescence for the coatings increases in the order: Catiogen L, Tween 20, Neogen T. This ordering may be caused by two factors: polarity difference of ions in the surfactant, or mobility difference between the surfactant ion and its counter ion. When violent positive prebreakdown discharge is generated, ACFOV should be lower than that for weak discharge. For this reason, ACFOV of an air gap between insulation surfaces decreases in the order shown above. Non-coated specimens have almost the same ACFOV as Tween 20 coated ones.