Lightning Performance of Multiple Horizontal, Vertical and Inclined Grounding Electrodes

Single horizontal and vertical grounding electrodes are often used for an earth connection of the lightning protection system. However, there are many practical situations when such electrodes have to be enhanced for better efficiency and replaced by multiple horizontal, vertical and/or inclined electrodes. This paper presents a systematic approach to evaluating and comparing the lightning performance of such grounding arrangements based on simple formulas. The contributions of this paper are: It is shown that impulse impedance Z may be derived from known formulas for low-frequency grounding resistance R ; a new definition of effective length is introduced that allows for such a derivation; a collection of accurate formulas for R of all considered grounding electrode arrangements is presented; and a new concept of "effective volume" is described that enables a simple procedure to increase electrodes' effective length. The new formulas for R , Z , and effective length of the different electrode arrangements allow an analysis that might help search for a choice of cost-effective configuration and dimensions of the grounding systems in the early design stage.