Improved Cable Connection to Mitigate Transient Enclosure Voltages in 220-kV Gas-Insulated Substations

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.