Very fast transient overvoltages (VFTOs) due to switching operations can appear between the gas-insulated substation (GIS) enclosures and the cable sheaths and between these grounding parts and the substation Earth structures. These VFTOs achieve hundreds of kilovolts, provoking hazardous disruptive discharges for human safety. This paper includes a sensitivity analysis of the different parameters in order to establish criteria to be adopted in the grounding system design of the GIS structures and the cable connection to mitigate transient overvoltages. The use of bypass surge voltage limiters (SVLs) between the GIS enclosure and the cable sheath is also needed to avoid uncontrolled discharges. The selection of these SVL according to insulation coordination rules is presented in this paper, ensuring electrical safety without affecting the current mode of exploitation of the 220-kV GIS or the cable.

The effect caused by ground fault current in a complex system of interacting electrodes is theoretically studied. The calculation applies to a specific case in which a set of interconnected electrodes, which are part of a grounding facility network, are activated by ground fault current. Transferred potentials to adjacent passive electrodes are calculated and the most relevant parameters of the electrode system are evaluated. Finally, the convenience of connecting the grounding electrodes is discussed.

The paper presents a model to include the internal resistance of the grounding electrodes in the calculation of its electrical features. The semi-analytical expressions for the calculation of the grounding resistance arising from the model are used to study the feasibility of the driven-rod method for the estimation of the soil resistivity profile since, unlike other methods, the internal resistance of the conductors can be of great influence for a correct estimate. From the grounding resistance profile an inverse problem based on the minimization of the quadratic differences between the resistance measured and that calculated from the model is posed. Several synthetic examples are used to assess the limitations of the method in conditions close to real situations. Finally, some real cases involving data measured in the field are analyzed. Whether in synthetic examples or in real soils it is found that the spatial frequency of the driven-rod resistance sampling is a determinant factor in order to study the feasibility of the driven–rod method.

The possibility of using a set of unequal electrodes, within limits, in a Wenner arrangement for the measurement of apparent resistivity at small depths is explored in this paper. A procedure in which only a simple preliminary calibration is necessary to obtain the best measurements of the apparent resistivity is proposed. On the basis of some case studies, a comparison with the usual procedures to obtain the apparent resistivity from resistance measurements is carried out. The results showed that when an unequal set of electrodes was used, the procedure proposed here was the only one that guaranteed the best apparent resistivity values for any value of electrode separation in the Wenner arrangement, especially for those associated with small depths.

The measurement of the grounding resistance of grounding grids in large installations as well as grounding electrodes in urban areas is addressed in this article. The resistance value is obtained using a three-pin array by measuring the fall-of-potential on the ground surface. The resistance measured by this method is adjusted to its true value using a correction factor that aligns the measured resistance with the actual value. The proposed measurement method obtains correct values of the grounding resistance even when the auxiliary and potential electrodes of the tree-pin array are close to the electrode to be measured. Thus, it can be applied to large electrodes as well as electrodes in urban areas. Several simulated examples are used to illustrate the method, and some real cases with field measurements are presented for a final validation of the method.