Evaluation of ground grid resistance for inservice substations

Ground grids are installed in substations for proper equipment operation and personnel safety. With passage of time, the grid conductors are subjected to corrosion and vandalism. The best way to identify ground grid degradation problem is by frequently inspecting the station equipment ground connections and by measuring the ground grid resistance. For the purpose of this paper, the focus will be on measuring the grid resistance. Fall of potentials test method is used to measure ground grid resistance. But the method requires disconnecting the static wire and distribution neutral connections for accurate results. This is not a practical method for energized substations. This paper demonstrates a method of estimating the ground grid resistance from the overall ground resistance measured without disconnecting the static wire and/or distribution neutral connections.