In this context, the Tokyo Electric Power Company has observed lightning strokes to
overhead ground wire or transmission tower (shielding success), for the first time as far as the
authors are aware, and direct lightning strokes to a phase conductor (shielding failure). The
present study analyzed and compared the ratios of shielding success or failure, and the
(forward) flashover or back flashover outage rates based on the observation results of UHVdesigned
and 500 kV transmission lines. The number of lightning strokes to transmission
facilities is 167.3 cases/100km/year for UHV-designed transmission lines and 130.8
cases/100km/year for 500 kV transmission lines, meaning the taller the facilities, the more
lightning strokes occur.