Improvement of Flashover Strength and Reduction of Surface Charge-induced Field Enhancement of Insulating Material

ac surface flashover voltage in air (ACFOV) and the effect of surfactant-painting are studied with several polymeric tubular insulators which have a back-side (inner) electrode. The insulating materials used are Nylon-6 (NY), Polymethyl - methacrylate (PMMA), Polyvinylchloride (PVC), Polypropylene (PP), Polyethylene (PE), and Polytetrafluoroethylene (PTFE). The surfactant used is alkyl-benzenesulfonate. ACFOV chareristics for non-painted specimens can be classified into two types according to the insulating material used: With PTFE, PE, and PP specimens (A-type), the diagram of the relation between ACFOV and electrode distance does not have an extremely saturated curve and a definite minimum; these are characteristics of the B-type specimens: PVC, PMMA, and NY. ACFOV of the A-type is higher than that of the B-type. When the surfactant is painted on the B-type, ACFOV increases, and the ACFOV characteristics are similar to those of the non-painted A-type: The extreme saturation and the definite minimum cannot be seen. With the painted A-type, ACFOV and the characteristics are similar to those of the original non-painted. These experimental results can be explained by the condition of the electric field enhancement due to the accumulated surface charge.