Are subsequent strokes relevant to transmission lines lightning-related outages?

The relevance of subsequent strokes as source of backflashovers is assessed from simulations using the hybrid electromagnetic model for transmission lines with distinct voltage levels. It was found that, in spite of the effectiveness of the usual practice of reducing tower-footing grounding resistance to decrease the lightning overvoltage developed across insulator strings for first-stroke currents, it does not work in the same way for subsequent-stroke currents. The finding of a significant contribution of subsequent strokes to the outage rate of 69-kV lines suggests the need to include such event on lightning performance evaluations of lines.