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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.

Mastering GIS control circuits – AC/DC auxiliary circuits and circuit breaker closing circuit
Mastering GIS control circuits – AC/DC auxiliary circuits and circuit breaker closing circuit

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.

Table of Contents:

  1. High Voltage GIS Control Circuits
  2. GIS Components
  3. GIS Single-Line Diagram
  4. Keys for Drawing Reading
  5. Substation Control Systems
    1. AC/DC Circuits
    2. Circuit Breaker Closing Circuit
      1. Motor Drive Circuit
      2. Closing Circuit

1. High Voltage GIS Control Circuits

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.

The choice depends on the functionality required and the cost factor. A local control cabinet (LCC) is often provided for each bay position to house the GIS bay wires and interface it to the substation control room. The LCC consists of a mimic diagram, switches/indicators, and annunciator/interlocks.

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:

  1. Mastering switchgear control circuits: AC/DC circuits & circuit breaker closing circuit
  2. Mastering switchgear control circuits: trip, BCPU & alarm, indication & interlock circuits.

Figure 1 – GIS Modules

GIS Modules
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.

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Salem Alshahrani

Electrical engineer (BEE & Meng). Specialized in substation design, especially in LV/MV switchgears and transformers. Passionate in power system planning, analysis, and stability studies.

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