Multiline simultaneous faults on transmission lines due to winter lightning

The transmission line exposed to thunder storms in the winter manifests a series of unique behaviors substantially different from those observable during the summer season. The share of multiphase simultaneous faults as a percentage against the total number of faults is more numerous for winter than for summer. In addition, simultaneous flashing occurs onto different towers on several occasions. Since most of the transmission lines, including 500-kV ones, are built on a double circuit principle in Japan, these lines are vulnerable to double-circuit faults during the winter. Exhaustive effort has been made to trace the origin. The author examined statistical data on the lightning performance of transmission lines as well as results of various field investigations, and established a fault probability estimation theory, which may be utilized to formulate pertinent countermeasures.