A conductor arrangement that overcomes the effective length issue in transmission line grounding

The reliability and availability of the electric power transmission system is severely influenced by lightning. In Brazil, roughly 65% of the overhead transmission lines outages are due to lightning, whereas the backflashover is the predominant phenomenon compared to shielding failure. Hence, obtaining a low value for the transmission line grounding impedance is an important issue when dealing with transmission lines backflashover performance. Usually, for high resistivity soils, increasing the grounding grid dimensions does not lead to low impedance due to the effective length issue. In this work, a special arrangement of ground electrodes is proposed in order to overcome the effective length problem in high resistivity soil. The transient voltage response of this low impedance ground arrangement is evaluated numerically using parametric modeling approach. Comparisons of numerical simulations results and measurements from a reduced model study are presented for validation purpose. Additionally, the quality of the results obtained using the reduced model elects it as a valuable tool for studies of electromagnetic transients involving interaction of lightning and grounding grids.