Gas-insulated substation (GIS)
A gas-insulated substation (GIS) is usually utilized in high voltage applications in which all conductive parts are encapsulated in sealed cylinders with SF6 as the insulating medium. The air-insulated substation (AIS), on the other hand, has air as an insulating medium, and this substation type is almost always an outdoor type.
Historically, GIS was established in Japan in the ’60s due to the urgent need for small footprint substations. Therefore, GIS is not always feasible if space availability is not an issue. The GIS enclosure is designed to accommodate three-phase equipment normally up to 170 kV level and a single-phase equipment beyond that.
GIS is the same as air-insulated substation (AIS) in terms of functionality, but they differ in many other ways. The substation components’ specifications, mounting, and otherwise.
- High Voltage GIS Control Circuits
- GIS Components
- GIS Single-Line Diagram
- Keys for Drawing Reading
- Substation Control Systems
SF6 circuit breaker, for example, is used in both AIS and GIS with only one difference which is that the breaker in the GIS has no SF6-to-air bushing. It is directly connected to the GIS module. In the same manner, all components experience such changes to fit in the GIS.
There are several variations to the GIS module ranging from enclosing breaker only to integrating all the components as shown in Figure 1 below.
Although the LCC is not considered as a GIS component, it controls its operation. The LCC is the control cabinet that has the GIS control circuits. These control circuits are similar to what has been discussed in the MV switchgear control circuits two articles:
- Mastering switchgear control circuits: AC/DC circuits & circuit breaker closing circuit
- Mastering switchgear control circuits: trip, BCPU & alarm, indication & interlock circuits.
Figure 1 – GIS Modules
The same principles explained already still apply to these circuits. The exception is that there are additional functions to account for the GIS system size and associated hazards. Thus, it is highly recommended to go through these two articles before proceeding to the GIS control circuits since the basic principles are the same and they are not discussed elaborately here as in the two mentioned articles.