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What is Gas insulated switchgear?

Gas insulated switchgears are metal enclosed types of switchgear with sulfur hexafluoride (SF6) gas acting as an insulation between the live parts and the earthed metal enclosure. The high voltage equipment is contained in a gas tight container filled with the insolent gas, SF6.


What is The Use of Gas Insulated Substation?

This type of equipment is available in the voltage range from 12 kV to 800 kV class. Medium voltage GISs up to 52 kV class are generally filled with SF6 gas at pressure below 2.5 bar. This range of GIS is covered in standard IEC 60298 /TEC 62271-100, applicable for metal enclosed switchgear. 

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Gas Insulated Switchgear

GIS for voltage class 72.5 kV and above are covered in standard IEC 60517 /TIEC 62271-2038. Gas insulated switchgear is a major component of gas insulated sub-stations. The principal gas insulated modules for a sub-station are bus-bar, disconnector or isolator, circuit breaker, current transformer, and earth switch.

Study About Different Types Of Circuit Breakers


The auxiliary gas insulated module or accessories required for a sub-station are terminations, voltage transformer, and surge and lighting arrester. The assembly of such equipment at a substation is defined as a gas insulated metal enclosed substation (GIMES) by the International Electrotechnical Commission. This technology has now been well established for almost thirty years.

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Percentage market share trend for various technologies in medium voltage switchgear

Medium voltage GIS equipment features vacuum circuit breaker as the interrupting medium and SF6 gas as the main insulation. Designs using the SF6 medium for both insulation and interruption are also available in medium voltage. Two operating pressures are specified for such equipment, one for insulation and the other for interruption. 

The high voltage GIS for voltages of 725 kV and above are essentially two pressure systems for non-availability of vacuum interrupters in this high voltage range. In gas insulated substations, modular components are assembled together to form the desired arrangement for a section or a bay.

Gas Insulated Switchgear Constructional Arrangements

Gas insulated metal enclosed switchgears, which are developed in various constructional arrangements, are explained below:

The isolated-phase GIS module consists of an assembly of individual circuit elements, like a pole of a circuit breaker, a single pole disconnector, one-phase assembly of a current transformer, etc. Three such circuits, arranged side by side, form a complete three-phase GIS bay. The circuits require larger bay width as compared to the other GIS configurations.

Some of the designs encapsulate all the three-phase elements of individual modules, like three poles of a circuit breaker, three poles (isolations) in a disconnector or three-phase current transformer assemblies, in an individual enclosure, thereby forming a three-phase module for the element. The total number of the enclosures is thus, reduced to one-third of the Isolated Phase GIS.

In another configuration called hybrid systems, a suitable combination of isolated-phase and three-phase common elements is used, like three-phase bus bar and single-phase elements, to achieve an optimal techno-commercial solution. While the three-phase common bus bar system simplifies the connections from the bus bar, the isolated-phase equipment prevents phase-to-phase faults in active modules, like the circuit breaker. The savings in space vary with the design and configuration of the section. Hybrid GIS technology has gained popularity, specifically in the medium and high voltage range, wherein the technology has helped to reduce the substation size.

Compact GIS systems are essentially three-phase common systems, with more than one functional element in one enclosure. A single enclosure housing a three-phase circuit breaker, current transformer, and earth switches, supports the bus bar and the other feeder elements. The depth of the section is considerably reduced in this configuration as compared to the three-phase modules.

The Highly Integrated Systems (HIS), introduced in 2000, are single unit metal encapsulated and gas insulated substations, and are gaining user appreciation as this equipment provides a total substation solution for outdoor/yard substations. The foundation work is limited to just one equipment, which helps to substantially save installation time.

Final Word

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