Grounding of gas insulated substations

The Grounding of Gas Insulated Substations (GIS) presents several unique problems not encountered in the grounding, of conventional substations. For the purposes of this paper, Gas Insulated Substations are defined as high-voltage, compact, metal-enclosed minisubstations which are compressed gas insulated at maximum rated voltages of 72.5 kV and above. The metal enclosure is grounded and consists of the outer sheath for the substation equipment and the coaxial gas insulated bus. The maximum voltage developed on the grounded outer sheath during fault conditions is calculated using coupling techniques and a transformer equivalent circuit. By setting limits on the maximum outer sheath voltage to station ground, the maximum distance between grounding points can be determined for the safety of personnel in a Gas Insulated Substation.