Lightning Performance of Transmission Lines: Methodology to Design Grounding Electrodes to Ensure an Expected Outage Rate

A novel methodology to be applied in the design of tower-footing electrodes to ensure a defined outage rate of transmission lines is proposed. It uses the critical peak currents (obtained from a first stroke distribution and from the application of the Disruptive Effect model on the waveforms of first-stroke overvoltages of direct strikes to the line simulated using an electromagnetic model) to determine the minimum electrode length required to ensure the defined outage rate for any given electrode arrangement and soil resistivity. This methodology is applicable to lines and soils in general, including the 138- and 230-kV lines tested in this paper.