Estimation of Phase-to-Phase Flashover Rate of 6.6 kV Distribution Lines

For the past decades the rate of installation surge arresters attached to 6.6 kV distribution lines has been increasing in Japan. As a result, for one of Japanese electric power companies, wire breaking near the insulator has markedly decreased and the ratio of wire breaking at the midspan of distribution lines to total number of lightning outages has increased. Since phase conductors falling to the ground surface as a result of wire breaking in the mid-span may cause not only outage but also a public injury, it is important to clarify the mechanism and effective countermeasures against this phenomena. In this study, we first experimentally examined the characteristics of the lightning overvoltage generated on phase-to-phase, which is considered to be one of the factors causing wire breaking in the mid-span, using actual-scale test distribution lines. Next, on the basis of the experimental results, we proposed an analytical method for evaluating phase-to-phase flashover rates and clarified that the phase-to-phase flashover rate depends on the arrangement of the phase conductors.