Effect of shield wires on GICs: Equivalent resistance and induced voltage sources

In transmission power networks and during geomagnetic storms, shield wires can carry induced currents in the same way as phase conductors. Shield wires are not usually considered in the transmission line models used in the study of the impact of geoelectric phenomena in power systems. In this study, the influence of shield wires on GICs in power systems is made clearer. The most simple power system, with one single transmission line connecting two substations and one shield wire, is considered. An analytical expression for the Thevenin equivalent circuit that, in parallel with the substations grounding resistances, produces the same effects on GICs as the complete circuit, is derived. Our model extends the results from previous studies by including the induced voltage along the shield wires. Differences can be relevant in relatively short transmission lines with only some tens of towers, where nevertheless the more simple asymptotic derived expressions may be used. Tests were done using realistic values for the circuit parameters and applied to real transmission lines.