Prompt calculation of tower-footing impulse impedance considering different levels of conservativeness for the frequency dependence of soil parameters

Abstract

This paper assesses the influence of the frequency dependence of soil parameters on tower-footing grounding systems, according to different levels of conservativeness. Practical formulas are proposed for immediate estimation of the tower-footing grounding impedance from the low-frequency grounding resistance. The quality of the proposed formulas is verified by comparing the results they provide with that obtained from a numerical electromagnetic approach. It is shown that the frequency dependence of soil parameters leads to a decrease of the tower-footing impedance, in comparison with the low-frequency resistance, and that the adopted level of conservativeness is relevant to quantify such decrease. It is also shown that, even considering a conservative approach, the frequency dependence of soil parameters leads to decreases of the impulse impedance higher than 15% in the case of high-resistivity soils.