A practical approach to estimate grounding impedance of a vertical rod in a two-layer soil

•A procedure based on transmission line theory for computing the ground impedance of a vertical rod in a two-layered soil is proposed.•Tagg’s formula is incorporated into the method to increase the accuracy of the ground impedance estimation.•The proposed procedure shows consistent results for the evaluated cases, which includes a practical condition. This paper shows a simple procedure to compute the grounding impedance of a vertical rod that penetrates a two-layer soil. The technique considers grounding resistance as a two-parallel resistor located in each layer of the soil. A correction factor that needs to be multiplied to the resistive element related to the first or second layer is derived to consider the images due to the reflections at the discontinuity along the soil. The solution using this procedure, which is based on transmission line (TL) approach, is compared to a software reasoned on a rigorous electromagnetic model (EM) and another technique report by literature with the same fundaments. The solutions provided by the proposed method are very similar to those obtained from EM model, especially the voltage waves resulting from current waveforms analogue to lightning. Furthermore, the TL procedure results in consistent solutions for some practical conditions of grounding analysis and presents a low computational cost.