Lightning strikes to elevated structures: influence grounding conditions on currents and electromagnetic fields

This paper presents an analysis of lightning return strokes to tall structures. The interaction of lightning with a tall structure is modeled using the antenna theory. The finite ground conductivity as well as the buried grounding system of the tall structure are taken into account in the analysis. It is shown that the current waveform, in sections of the tower close to ground, is somewhat affected by a finite ground conductivity. However, for sections further up the tower, it is not significantly influenced. Furthermore, our simulations show that some fine structure associated with current waveforms measured on the Toronto CN tower can be attributed to the finite ground conductivity. It is also shown that the current path down the tower structure is notably subjected to the skin effect. The current distribution along the buried grounding structure of the tower is also presented, illustrating the dispersion effect as a function of the ground conductivity. Finally, the lightning return-stroke generated electric and magnetic fields computed at a distance of 2 km from the tower are presented. It is shown that some late-time subsidiary peaks are smoothed out by the effect of the propagation along a finitely-conducting ground.