Modeling of transmission line exposure to direct lightning strokes

A new model for assessing the exposure of free-standing structures and horizontal conductors above flat ground to direct lightning strokes is introduced. A recently developed criterion for positive leader inception modified to account for positive leaders initiated under the influence of a negative descending lightning stroke, is discussed. Subsequent propagation of the positive leader is analyzed to define the point of encounter of the two leaders which determines the attractive radius of a structure or the attractive lateral distance of a conductor. These parameters are investigated for a wide range of heights and return-stroke currents. A method for analyzing shielding failure and determining the critical shielding angle is also described. The predictions of the model are compared with field observations and previously developed models