Various Aspects of Designing of Grounding System of Gas Insulated Substation (GIS)

This paper presents an accurate method cum procedure for designing the grounding system of gas-insulated substation (GIS). A grounding system design of the gas- insulated substation (GIS) is a complicated task to provide an adequate grounding system and meet specific criteria with regards to personnel safety and integrity of equipment during a fault condition. First, in the case of GIS, the GIS equipment has the metal enclosing gas-insulated switchgear and the inner high-voltage buses that are completely contained within the outer pipe type enclosures. Under fault conditions, especially when the fault is inside the enclosure, induction between faulted inner buses and associated enclosures can result in significant induced currents in the enclosures that may generate sufficient voltage drops along the enclosures. The same thing may happen between the enclosures and the ground conductors as well. Therefore, an additional internal fault within the gas-insulated bus system has to be examined when there is a flashover between the bus conductor and the inner wall of the enclosure.

Secondly, the aboveground bus bars are parallel to the ground conductors and there is indeed inductive coupling between aboveground bus bars and ground conductors when a grounding system has a rather large size. Moreover, when a large amount of circulating currents exists within the substation, they are also flowing along.

Finally, the GIS necessitates a fraction of the land area required for conventional substations. Because of this smaller area, it may be difficult to obtain adequate grounding since GIS is still subjected to the same magnitude of fault current as conventional substations. Frequent bonding and grounding of GIS enclosures will be needed to minimize hazardous touch and step voltages within the GIS area. This document contains information about the matters concerning Grounding systems of AC power networks in general and GIS (Gas insulated substation)