A study of grounding arrangements composed by vertical electrodes for two layered stratified soil models

This paper presents a study of a grounding arrangement proposed for transmission line (TL) towers, particularly for conditions of a stratified soil where the electric resistivity of the first layer is higher than the second medium. Techniques based on TL-theory are presented to estimate the harmonic grounding impedance of such configurations and are compared to the solution obtained with a rigorous electromagnetic (EM) method. The results show that the grounding resistance, important to low frequency frequency phenomena, and the impulse impedance, to fast transients, decrease significantly with the use of vertical electrodes. For a 230 kV TL, the critical towers can be improved by the proposed arrangement, which includes a significant economy of the conductor material applied to the grounding.