On the use of homogeneous ground model for lightning-induced voltage calculation

Lightning induced voltages on aerial and underground lines depend on the ground resistivity. Most calculating methodologies were developed considering the ground as a homogeneous medium. However, actual ground is better represented if stratified into horizontal layers of different resistivity values. This paper proposes the use of a simplified expression for the calculation of the equivalent resistivity of a uniform ground that can represent a two-layer stratified ground in lightning induced voltage calculations. The analysis is made by comparing the results from a homogeneous ground having the equivalent resistivity value with results from two-layer ground. It is shown that, for the range of parameters considered, the absolute average and maximum errors on the induced voltage peak values are 2.9% and 8.2%, respectively. It is also shown that, with the equivalent resistivity, a peak-value formula developed for uniform ground could be used for the calculation of lightning induced voltages on lines above two-layer ground.