Effects on the results of the fall of potential test when using sky wires for the remote current probe

As specified in the electrical codes, a solar farm grounding system must be measured to determine if its resistance is equal to or lower than the resistance predicted by the design. The methods of choice for this measurement are the fall of potential test and the slope test. As described in IEEE 81-2012, in order for these two methods to give meaningful results, the remote current probe must be located at a distance of at least five times the largest dimension of the solar farm footprint. To comply with this requirement, some contractors have recently introduced the use sky wires of nearby sub transmission lines to inject the test current at a remote location. This paper presents the analysis of the errors introduced by the use of sky wires in the fall of potential test.