Closed-Form Approximation for Grounding Grids Transient Analysis

Traditionally, wideband modeling of grounding system demands the usage of the method of moments (MoM) which implies a large number of segments to represent the conductors involved and the solution of a double integral for each and every one of these segments. Approaches presented in the literature as PEEC (partial element equivalent circuit) and HEM (hybrid electromagnetic model) are based on these assumptions. In either of these approaches, a heavy computational burden occurs, leading to a very time-consuming simulation. This paper proposes to use a two-term series expansion to allow a closed-form solution to the double integral found in HEM and thus is named as sHEM. The proposed approach, sHEM, is compared with HEM with respect to the harmonic impedance and the time responses associated with impulse currents. The results indicate only a small loss of accuracy with respect to the peak value of the overvoltage with a significant gain in the computational time. Finally, a comparison with actual measurement results is provided to evaluate the adequacy of using sHEM in the analysis of grounding grids.