Transient performance of grounding grids

An analytical method to determine the transient performance of grounding grids is presented. In the proposed method, the leakage current to ground of each element of the grounding grid is represented more realistically than by considering the grid as an equivalent circular plate. Vertical ground rods of the grid are also considered. The maximum voltage to which a station grounding grid is raised due to incident impulse current can be determined. This is an important criterion in evaluating the transient performance of substation grounding grids which are generally designed from the point of view of power frequency fault currents. It has been found from both analytical and field studies that, in cases where impulse current injection is at the corner of the grid, the voltage induced and hence the impulse impedance are the highest. If the impulse current is incident at any other location within the grid, the grid exhibits a lower value of impulse impedance. Comparison of analytical results and field results shows good correlation for maximum induced voltages and impulse impedances