Effect of Earth Wire Connections on Hazard Limitation at ´Often Frequented Towers´

This paper investigates the effects of earth wire isolation on tower base voltages at a single tower of an overhead transmission line. Computation studies on a generic tower line were carried out. Various models developed to represent transmission lines including earth wires, phase conductors with different scenarios of fault locations were simulated using ´CDEGS´ for direct lightning strikes to earth wire and phase-to-earth fault conditions. The line termination and earthing grid effects on the current distribution along the tower route were also analysed. It was found that the higher earth potential rise (EPR) always appears at the point of current injection. The effect of the isolation of earth wire resulted in higher EPR at the adjacent towers by some 6%, compared with the case when the earth wire was connected. At the disconnected earth wire tower, the computed EPR is reduced up to 92% for all cases depending on the soil resistivity of the tower locations