SCALE-MODEL EXPERIMENTAL-STUDY ON THE EFFECT OF LIGHTNING-STROKE INCLINATION ON THE OVERVOLTAGES ACROSS INSULATOR STRINGS

An experimental study on the overvoltages across insulator strings res ulting from inclined lightning strokes has been carried out on a 500 k V double-circuit vertical-suspension transmission line using a scale m odel. The effect of lightning stroke inclination on the insulator stri ng overvoltages has been investigated under different conditions of st roke current rise time, tower footing resistance, and strike location on the transmission line. The results show that, for an inclined light ing stroke, the overvoltages appearing across the insulator strings of the phases located at the same height are not the same. The differenc e between these overvoltages increases with increase in inclination. T he effect of lightning stroke inclination for practical values of towe r footing resistance and stroke current rise time has been verified. I t is also shown that direct strikes on the tower produce higher insula tor string overvoltages than midspan strikes.