GIS or Gas Insulated Switchgear
It is very much required to establish an electrical substation at load center. Since, establishing a substation at load center is quite economical and profitable in many aspects. As it reduces length of feeders and due to short length feeders, the quality of voltage regulation improves. But the main obstruction of establishing a substation at load center is space. Generally main load center of any place is situated at very congested place where, sufficient land for establishing conventional electrical substation is very hardly available.
This problem can be solved by using gas insulated switchgear technology. In this type of switchgear, all the necessary components of switchgear can be assembled in very limited space. GIS is a kind of metal enclosed switchgear.
That means, all the equipments of the electrical switchgear are enclosed by gas tight metal enclosure and SF6 gas is used as insulation between live parts of the equipments and earthed metal enclosure. This type of switchgear, means, and gas insulated switchgear is available from 12 KV systems to 800 KV system. For establishing electrical substation in very limited place this type of SF6 insulated electrical switchgear plays the major role.
Gas insulated components of substation are generally,
- Electrical bus bars.
- Electrical isolators or disconnectors.
- Circuit breakers.
- Current transformers.
- Voltage transformers.
- Earth switches.
- Surge arrestors or lightning arresters.
The substation, assembled by gas insulated switchgear, is popularly known as gas insulated metal enclosed substation (GIMES). GIMES technology is not very recent invention, it is successfully running for over thirty years. In gas insulated medium voltage switchgear, vacuum technology is used as interrupting purpose and SF6 gas is used as insulation material. Although for both interruption and insulation, SF6 gas is used in many medium voltage GIS system. But for such equipments rated SF6 gas pressures are different for interruption and insulation. SF6 gas pressure for insulating purpose is generally kept below 2.5 bar whereas SF6 gas pressure for interrupting purpose is ranged from 5 bar to 7 bar. As vacuum technology is not available for high voltage, so for GIS or gas insulated switchgear system above 72.5 KV, only SF6 is used both for interruption medium and insulation. There are different types of gas insulated metal enclosed switchgears available depending upon their constructional feature.