Estimation of step and touch voltage at 275/132 kV transmission line due to lightning stroke

Abstract

Electrical transmission tower remains one of the important elements of today’s electrical power system. Transmission tower is designed to support conductors and ground wires of electrical power lines. Transmission line system deliver power from generating plant to the industrial sites and from substation for which distribution system supply to residential for commercial purposed. A significant number of faults in overhead transmission lines are due to lightning strikes which cause back flashovers and hence single or double circuit outage. The continuity and quality of the power supply is therefore can be severely affected by the outages, especially in Malaysia where the isokeraunic level is rather high. In Malaysia, the TNB’s transmission lines consist of 500 kV or 275 kV double circuits, and 275/132 kV quadruple circuits. It is known that the lower portion of the 132 kV line apparently has the lowest lightning performance. The transmission tower foot is modeled as hemisphere electrode impeded in the ground with specific conductivity and permittivity (dielectric constant). The step and touch voltages are estimated for different towers length and different ground parameters. In this project, 275/132 kV quadruple transmission tower model has been used for simulation of step and touch voltages. The step and touch voltages are determine according to the ground resistivity at tower foot of the transmission tower and the transmission tower height. Therefore the varying of permittivity has no effect on both voltages. As the ground resistivity increases, the touch voltage increases. The soil permittivity has no significance effect to ground impedance of tower foot in case of hemisphere presentation.