FDTD simulation of back-flashover at the transmission-line tower struck by lightning considering ground-wire corona and operating voltages

In this paper, we simulated transient voltages across insulators and back-flashover at the transmission line tower struck by lightning in the presence of corona on the ground wires. The FDTD method and simplified (engineering) model of corona discharge were used. Three two-circuit 60-m high towers, separated by 400 m, with two overhead ground wires, and six phase conductors (two three-phase circuits) were considered. Back-flashover was assumed to occur at the upper, middle, or lower phase. Operating voltages of phase conductors were modeled by using a voltage source inserted between each phase conductor and ground. It is observed that ground-wire corona serves to reduce voltage peaks and delay the occurrence of flashover. For the upper-phase back-flashover due to a positive 50-kA stroke, the peak voltages across the upper-, middle-, and lower-phase insulators are reduced by 11%, 12%, and 12% by the ground-wire corona, and for a negative 50-kA stroke they are reduced by 8%, 9%, and 9%. Influences of ground-wire corona on transient voltages were also studied for the back-flashover at the middle or lower phase. Presence of operating voltages can lead to either increase or decrease of the peak of transient voltage, with the change being less than 20%. To the best of our knowledge, this is the first FDTD simulation of back-flashover at a transmission-line tower considering both ground-wire corona and operating voltages.