Hybrid and pi-circuit approaches for grounding system lightning response

Prediction of the potential threats due to direct lightning strokes of sensitive targets, e.g., overhead power-line towers, substations or buildings, requires accurate modeling of the transient impedance of grounding systems. When large-scale simulations are needed, detailed and computationally intensive models are hardly viable, although they usually offer great accuracies. In this work we investigate the suitability and compare the accuracies of two different approaches. In the first we adopt a hybrid circuit-field approach to predict the behavior of grounding systems at any frequency of interest. This approach is based on circuit theory and Method of Moments, and is capable to fully account for resistive, inductive and capacitive couplings between elements of the grounding system. Since the analysis is carried out in the frequency domain, the actual transient behavior can be obtained by means of an Inverse Fourier Transform. In the second approach we consider a fully circuital approach. It is a genetic algorithm-based procedure able to synthesize a generalized equivalent pi-circuit model that is used to simulate the impulse response of complex grounding systems, including possible nonlinear soil ionization, working directly in the time domain.