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 resulting strokes has been carried out on a 500 kV double-circuit vertical-suspension transmission line using a scale model. The effect of lightning stroke inclination on the insulator string overvoltages has been investigated under different conditions of stroke current rise time, tower footing resistance, and strike location on the transmission line. The results show that, for an inclined lightning stroke, the overvoltages appearing across the insulator strings of the phases located at the same height are not the same. The difference between these overvoltages increases with increase in inclination. The effect of lightning stroke inclination for practical values of tower footing resistance and stroke current rise time has been verified. It is also shown that direct strikes on the tower produce higher insulator string overvoltages than midspan strikes.