Estimation of the statistical distributions of lightning current parameters at ground level from the data recorded by instrumented towers

This paper describes a procedure based on the Monte Carlo method to obtain the statistical distributions of lightning current parameters at ground level starting from those inferred from experimental data recorded by means of tall instrumented towers. As a matter of fact, it is generally accepted that these distributions are affected by the presence of the tower; lightning current amplitudes, in particular, are "biased" toward higher values, as the tower ability to attract lightning flashes tends to increase for flashes with larger currents. Concerning the current peak distribution, the obtained results match with those presented in previous studies on the subject; for instance, for the Berger et al. distribution, they provide a median value decrease ranging from 20%-40%, depending on the attractive radius expression adopted in the calculation. The proposed procedure is more general than others presented in the literature for the same purpose. It can be applied, indeed, to whatever model is adopted to represent the exposure of the tower to direct strokes and, further, it allows to quantify the tower effect on the statistical distributions of all lightning current parameters of interest, and not only of the peak value one. The statistical distributions at ground, calculated with the proposed procedure, should be considered for power system insulation coordination studies, chiefly for a more representative and significant evaluation of the indirect lightning performance of distribution lines. The obtained results can also be used to assess the performance of lightning location systems concerning the relevant current statistical distributions.