Parametric Effects on the Induced Voltages on Overhead Lines by Lightning Strokes to Nearby Ground

Outages of low-voltage overhead lines are caused primarily by lightning strokes to nearby ground. These lightning strokes are generally known as indirect lightning strokes. Because of the complex interaction among the various line and lightning parameters, predicting the worst possible severity of indirect lightning strokes on an overhead line is difficult. The paper discusses the effects of some of these parameters, based on the work previously presented. [1,2] The effects of the following parameters on the induced voltage are discussed: 1. Line parameters a. Height of the line above ground, and b. Distance along the line from the struck point. 2. Lightning-stroke parameters a. Return-stroke current, b. Return-stroke velocity, c. Perpendicular distance of lightning stroke from overhead line, and d. Height of cloud charge center. The magnitude of the induced voltage will be directly proportional to the height of the overhead line above ground. In general, the severity of an indirect lightning stroke is not a strong function of the height of the cloud charge center; however, the waveshape of the induced voltage changes considerably for low cloud heights. The analysis shows that the highest induced voltage on an overhead line by a nearby lightning strike to ground may not appear at the point directly opposite the stroke. This phenomenon has also been observed indirectly during field investigations where distribution transformers were damaged at points on the line away from the location of the lightning stroke to ground.