Observation and analysis of multiphase back flashover on the Okushishiku Test Transmission Line caused by winter lightning

This paper describes observation and analysis of multiphase back flashover phenomena on the Okushishiku Test Transmission Line in the winter lightning season. Observation of lightning surges caused by natural lightning and rocket-triggered lightning strokes has been carried out on the test transmission line since 1987. From 1993 to 1996, lightning currents and voltages at the test transmission line were measured simultaneously for ten times. Especially, a four-phase back flashover was observed in 1994. A new calculation method of multiphase back flashover, which is based on the leader developing model, is proposed. Calculated results by the proposed method show good agreements with the observations.