The Influence of the Frequency-Dependent Behavior of Ground Electrical Parameters on the Lightning Performance of Transmission Lines

This study assesses the lightning performance of a 138 kV transmission line with constant and frequency-dependent soil electrical parameters. A transmission line theory based wideband model was used to include the frequency-dependent impedance behavior of the tower grounding system. The overvoltages developed across the insulator strings were simulated using ATP and considering representative first stroke current waveforms. The Disruptive Effect (DE) method was used to compute the backflashover rates of the studied lines. It was found that the decrease of soil resistivity and relative permittivity resulting from the frequency dependence effect is responsible for the significant decrease of the expected outage rates of the tested lines in a range of 29-55% for realistic distributions of soil resistivity along the line, and a consequent relevant improvement of the lightning performance of the line.