Influence of the Radial Electric Field Appraisal on Lightning-Induced Overvoltages Statistical Assessment

This paper analyzes the influence of the radial electric field radiated by return strokes on the lightning performance of an overhead distribution line. The calculation of the lightning electromagnetic pulse (LEMP) over a finitely conducting ground is performed by solving the Sommerfeld integral for the radial component of the electric field. The proposed method uses a trapezoidal scheme in which nodes are equidistant in logarithmic scale. The method is implemented in the LIOV-EMTP (lightning induced overvoltages-electromagnetic transient program) code that solves the field-to-multiconductor line coupling equations and calculates the lightning induced voltages in distribution networks having complex and realistic configuration. The results obtained by the proposed method for the LEMP calculation are compared with those obtained by using the Cooray-Rubinstein formula, which is the most commonly adopted approximation. Finally, the peak-amplitude probability distributions of the induced voltages obtained by using the two approaches are presented. It is shown that for ground conductivity values larger than 0.001 S/m, the Cooray-Rubinstein formula provides results in agreement with the accurate solution, while it significantly underestimates the lightning performance for lower conductivities and for lines with a high insulation level.