QUADRATIC SPLINE FORMULATION OF LIGHTNING-STROKE INCLINATION EFFECTS ON INSULATOR STRING OVERVOLTAGES

Digital simulation is imperative for insulation coordination which nec essitates evaluation of the various overvoltages likely to be imposed on systems. In this paper the experimental results of the effects of l ighting stroke inclination on the insulator string overvoltages of a 5 00 kV transmission line have been represented as empirical formulas by quadratic splines. The overvoltages have been obtained as ratios of t he overvoltage peaks to the peaks of the stroke currents. The formulas have been derived for practical values of stroke current waveshapes a nd tower footing resistances. The insulator strings of the phases havi ng the same height may, according to the experimental results, be expo sed to equal or unequal overvoltages depending on the lightning strike characteristics. For the former case a single formula has been derive d, but for the latter distinctive formulas have been found. These form ulas will be useful in the analysis of lighting overvoltages and trans mission line outage prediction by digital simulation.