OS4-3 Transient grounding behavior: field vs. transmission line theories considering frequency-dependent soil parameters

This paper assesses the transient behavior of electrical groundings systems due to direct lightning strikes under the assumptions of constant and frequency-dependent soil parameters. It is known that this is a parameter that affects the overvoltages of the insulation rope and the increase of the soil potential (GPR). In this case, two configurations are analyzed and two different methodologies for modeling the transient ground response are considered, being: one based on field theory and another on transmission line theory. For the inclusion of the variation with frequency two formulations widely published in the literature are considered. The developed grounding system model was implemented in the EMTP-ATP program. A RLC synthetized network is used to synthesize ground responses in the frequency domain. The results illustrate that both frequency responses and GPR levels vary according to the methodology used and whether or not to consider the variation with frequency. However, the maximum differences between the GPR peak values reach approximately 13% (high resistivity), indicating that in practical analysis, transmission line theory can be used for initial estimates.

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