The distribution of lightning strokes to towers and along the span of shielded and unshielded power lines

A knowledge of the distribution of lightning strokes to towers and along the span of shielded power lines is needed to refine the outage rate calculation method. Such information is also needed for unshielded lines because the outage mechanism differs depending on whether the stroke terminates on a tower or on a live wire. This paper provides the needed information based on a 3-D representation of the line and on a validated revised electrogeometric model. The effects of height, span and width of tower are studied and the span is found to be the most important governing parameter. Unshielded lines are found to have similar characteristics except that the tower collects a larger percentage of the total strokes and its shielding influence on adjacent wire segments is more pronounced. The effects of the form of striking distance equation and the coefficient of striking distance to the tower are also investigated.