Alternative fall-of-potential method for grounding grids impedance measurements and inductive coupling between leads

The classic fall-of-potential method (potential electrode is between grounding grid and current electrode) is universally used for measurement of grounding grid impedance for many decades. The inductive coupling between the current electrode and potential electrode leads is analyzed for different homogeneous earths, operating frequency and separation between leads. Also, in urbanized area very often the potential probe can not be located at the proper position, because of the presence of buildings, paved lots, underground metallic pipes, etc. In those cases the direction of the potential probe needs to be placed under angle a = 90deg-270deg towards the direction of grounding grid-current electrode, method known as alternative fall-of-potential method. The purpose of this paper is to calculate errors of grounding resistance for different types of grids buried in two-layer earth models, when the potential probe is under some angle to the straight line grounding grid-current electrode. The obtained results of the errors can be shown as family of curves, which can be used in practice for correction of measured grounding grids resistance values