The analysis and simulation of the ground path of powertransmission systems depending on the environmental factors

Abstract

Electric energy is considered in three sections as generation, transmission and distribution.High voltage such as 154 kV and 380 kV is required to transmit the electrical power. For thepower transmission systems, steel galvanized towers are used. Based on the number ofcircuits of the transmission line, tower models differ. To prevent the transmission lines fromthe atmospheric discharge, ground wires are used. The towers must be grounded againstpossible high current flows caused from a lightning stroke or short-circuits.In this study, the analysis and simulation of a 100 MVA / 154 kV ground path of a 50 kmsingle-circuit transmission line having 163 towers with double ground wire are carried out.String isolators are used to insulate phase conductors against the tower / ground in the powertransmission lines. Because of the ambient conditions, isolators are contaminated and becomeconductive. Thus, leakage currents flow from the surface of isolators to the tower. On theother hand, because of the mutual coupling between phase conductors and ground wires, thevoltage / current is induced on the ground wires.In this study, the analysis and simulations of the ground path for different soil structures andfor all conditions of steady-state operation of power transmission lines have been performed.Tower footing voltages are obtained along the transmission line. In addition, tower footingvoltages in case of single line to ground fault, which frequently occurs in power system areanalyzed for different soil structures and fault points, namely at sending-end, mid-point andreceiving-end of the transmission line.The change of tower footing voltages for different spans (300 m, 400 m) and for differentvalue of electrode has been studied. On the other hand, magnetic fields for different weatherconditions, electrodynamic forces, asymmetry ratio, power losses and step voltages becauseof current flowing through the towers have been studied.In addition to these, the comparison between the ground path models in the literature and theproposed Matlab/Simulink model has been evaluated. It is shown that both numerical resultsmatch each other.