Evaluation of a Methodology for Estimating the Symmetrical Ground Current in Substations: a Study Considering the Influence of Transmission Lines Guard Wire

The performance of a substation grounding grid needs to be evaluated periodically. Considering the increase in short-circuit currents in the electrical power system, ground grid tests of substations where the overhead ground wires (guard wire) of the transmission lines are connected to the grid may indicate that the ground grids are not safe (touch and step potentials tolerable by the human beings), due to the impossibility of measuring the portion of the total fault current flowing through the ground. In this context, the paper deals with the determination of a formulation for estimating the ground current. The solution is characterized by solving the equations that govern the phenomenon using an optimization method subject to adequate constrains. The determination of the substation grid resistance and the equivalent impedance of the overhead ground wires allow determining the most important parameter: the portion of the total ground fault current that leads touch and step voltages.