Coupling effect in substation ground measurements

A method to measure ground impedance in various soil structures is described, which takes into account inductive coupling between current and potential wires. For this purpose, a family of coupling effect curves versus the potential wire length was calculated. It was found that these curves are not dependent on the current wire length and are practically identical to the same soil resistivity. The true resistance of the substation grounding is determined using received coupling effect curves, and a simple formula which subtracts the coupling effect from the measured substation grounding resistance. Practical comparative measurements were performed to validate the method.