Insulation Design of Prefab Insulating Covers in Overhead Distribution Lines Concerning the Protection from Animal Contacts and Surges

In order to prevent the accidents due to the contact of animals, trees and etc., prefab insulating covers are installed in overhead distribution lines. However, sufficient effect is not realized. To make their protection performance at high level, they should to be designed taking the combination with the lightning protection equipments into consideration. With arrestors, they are required to withstand the lightning and switching surges smaller than the operation voltage of the lightning arrestors. With high-speed circuit breakers, as the breakage by the lightning surge is permitted and the following current is intercepted, the covers should withstand the switching surge when the lines are re-closed. In this study, the impulse-withstand voltage of a gap between the conductor and the contact object was examined assuming that the conductor cover and the prefab insulating cover were damaged. And the authors proposed a design method of the prefab insulating cover by comparing the withstand voltage of the air gap with the operation voltage of the arrestor and the magnitude of the switching surge.