Backflashovers of Transmission Lines Due to Subsequent Lightning Strokes

Lightning overvoltages across insulator strings of existing 138- and 69-kV transmission lines were simulated using the hybrid electromagnetic model. It was found that, though the reduction of tower-footing grounding resistance is very effective to decrease lightning overvoltages caused by first strokes, this reduction is saturated around 750-600 kV for typical currents of subsequent strokes. The lightning performance of these lines was estimated and subsequent strokes were found to be relevant cause of backflashovers in 69-kV lines.