Operating Experience With Wood Utilized As Lightning Insulation

Operating experience with a large number of lines of various types, utilizing wood as lightning insulation, has demonstrated that ordinary woods have considerable insulation strength for lightning voltages, and that wood can be used to advantage in combination with other measures for improving the lightning performance of lines. The analyses have contributed materially to the present general conclusion that lightning strokes terminating on conductors and structures are responsible for the majority of lightning flashovers, at least on the higher-voltage lines; also that direct strokes must and can be coped with. The methods offering the greatest promise at present are; (1) diverting the lightning strokes from the conductors and conducting the lightning currents to earth without permitting flashover to the power conductors; (2) draining the lightning from the power conductors through fast operating dynamic follow current interrupting devices, thus avoiding insulator flashovers; and (3), a combination of these two methods. High lightning insulations alone are not generally effective in reducing the number of lightning tripouts of lines, though in the lower-voltage ranges, some decrease in the probability of dynamic current following the lightning arcs may be realized.