Summary of Merits of SF6 GIS

Safe

Operating personnel are protected by the earthed metal enclosures

Reliable

The complete enclosure of all live parts guards against any Impairment of the insulation system.

Space saving

SF6 Switchgear installations take up only 1/10 of the space Required for conventional installations.

Economical

High flexibility and application versatility provide novel, and economic overall concepts.

Maintenance free

An extremely careful selection of materials. an expedient design and a high standard of manufacturing quality assure Long service life with practically no maintenance requirement.

Low weight

Low weight due to aluminum enclosure, correspondingly

Low cost foundations and buildings.

Shop assembled

Quick site assembly ensured by extensive preassembly and Testing of complete feeders or large units in the factory.

Disadvantages of GIS: 

1- High cost compared to conventional outdoor substation.

2 - Excessive damage in case of internal fault. Long outage periods as
     Repair of damaged part at site may be difficult.

3 - Requirement of cleanliness is very stringent. Dust or moisture can cause
      internal flashovers.
 

4 - Such substations are generally in door. They need a separate building.
     This is generally not required for conventional outdoor substations.

5 - Procurement of gas and supply of gas to site is problematic.
     Adequate stock of gas must be maintained.

6 - Project needs almost total imports including SF6 Gas. Spares conventional
      substation is totally indigenous up to 400 kV.

Configuration of GIS: 

The GIS installations are assembled from a variety of standard modules.

Which are joined together by flange connections and plug contacts on the

Conductors. So as to easily permit subsequent disassembly of individual  components. Gas-tight barrier insulators in the Switchgear sections prevent neighboring Switchgear parts from being affected by overhauls.

Any maintenance and overhaul work on Switch contacts can be done without removing the enclosure.

With GIS installations, all basic substation Bus-Bar schemes used, in

conventional plant constructions can be realized. Installations with single or

multiple Bus-Bar-also alternatively with a bypass bus-can be made with the

standard modules, including Bus-Bar sectionalizing with disconnects and

 Breakers, and Bus-Bar coupling. The two-breaker. One and-a-half circuit

breaker and ring-bus systems can also be realized economically.

 

    The essential parts of a GIS are: -

1 - Conductors which conduct the main circuit current and transfer power
      these are of copper
or aluminum tubes. 

2 - Conductors need insulation above grounded enclosures. Conductors also
      need phase to phase insulation, In SF6 GIS these insulation requirements
     are met by cast resin insulators and SF6
gas insulation.

3 - Gas filled modules have nonmagnetic enclosures. Enclosures are of aluminum
      alloy or stainless steel.
Adjacent modules are joined by means of multi-bolts
      tightened on flanges. Suitable neoprene rubber O ring gaskets are provided
      for ensuring Gas-tight sealing joints.
 

 4 - Various circuit components in main circuit are: CB, Isolator, Earthing Switches
       for conductors, CTs, VTs, cable-ends, Bushing-ends and Bus-Bars.
      Each of these main components has its own gas -filled metal enclosed module.

5 - Gas filling, monitoring system. 

6 - Auxiliary LV DC and LV AC supply system, control, protection and Monitoring
     system. This is air-insulated like in conventional sub-station.

  The Bus-Bars are conducting bars to which various incoming and
  outgoing bays are connected. In
SF6 GIS the Bus-Bars are laid l
  longitudinally in GIS hall.
 

  The bays are connected to Bus-Bars cross-wise. Bus-Bars are either

  with  a three-phase enclosure or single phase enclosure.