Measurement of earth surface potential using scale model

Determination of the earth surface potential distribution due to discharging impulse current into grounding grids is difficult by using numerical methods. One way to measure the earth surface potential (ESP) and to study the transient performance of grounding grids subjected to impulse lightning current is using a scale model of the grounding grids with an electrolytic tank, because if all dimensions of the grid is reduced by the same factor, the percentage of the mesh voltage is unchanged and also the shape of current and equipotential surfaces is unaltered. Therefore, it is possible to simulate the actual grounding grids with the help of scale models and the potential profiles measured on a model may be used to determine the corresponding potentials on a full scale grid. The discharging impulse current is injected at the corner of the grid and the potential at different points along different profiles on the surface of the water filled the electrolytic tank is measured. The results obtained from the experimental work provide guidelines for safe design of the grounding systems.