Computing grounding resistance and impulse impedance of horizontal electrodes parallel or perpendicular to the interface of a vertically stratified soil using transmission line theory

This work shows a procedure to compute the resistance and harmonic impedance of horizontal grounding electrodes buried in a vertically stratified soil. Such electrodes can be parallel or perpendicular to the interface of the vertically stratified soil. An additional resistive element is developed for such condition of soil. A procedure based on transmission line (TL) theory is applied using the developed expressions for grounding harmonic impedance, including different dielectric permittivities for each soil layer. Solutions obtained for slow and fast transients, similar to that from lightning currents, are compared to a rigorous electromagnetic (EM) model. The cases evaluated show a good agreement compared to EM technique, which supports the suitability of the developed procedure, when the procedure premises are a good approximation for the problem. Furthermore, the results for TL procedure agree with the overestimation commonly reported by literature and, for this peculiar soil model, indicate the conditions that are capable to modify significantly the whole behavior of the grounding, i.e., the values of grounding resistance and impulse impedance, for a condition where the interface is parallel or perpendicular to the conductors. The conclusions are supported by the analysis of practical and similar real world conditions.