Lightning induced overvoltages on overhead lines shielded by nearby buildings

In urban areas the presence of buildings is expected to reduce the amplitude of lightning induced voltages on overhead lines with respect to the case of open terrain. This paper presents a method for estimating such a reduction effect. For this purpose weighting functions are applied to the electrostatic, induction and radiation terms of the expressions adopted for the lightning electromagnetic field calculation assuming open terrain. The parameters of the weighting functions are identified by means of a least square fitting procedure using a finite element method model as benchmark for the field calculation. These functions are shown to be rather independent of the lightning return stroke current waveform and of the distance between the line and the stroke location. Although this paper presents only results obtained for the case of a single line, the method is conceived in order to be applicable for the lightning performance assessment of more complex power distribution networks.