Gas Insulated Switchgear (GIS) systems used in high-voltage infrastructure

Gas Insulated Switchgear (GIS) is a type of high-voltage electrical switchgear that uses sulphur hexafluoride (SF₆) gas to insulate and quench arcs within a compact, sealed unit. It is commonly used in urban, industrial, and space-constrained applications.

🔧 Key Components of GIS 

1. Circuit Breaker – Interrupts fault currents and switches the circuit on/off.

2. Disconnector (Isolator) – Provides a visible isolation point.

3. Earthing Switch – Grounds the circuit for safety during maintenance.

4. Current Transformer (CT) – Measures current for protection and metering.

5. Voltage Transformer (VT) – Measures voltage.

6. Busbar – Conducts electricity within the GIS unit.

7. Enclosure – Airtight metallic casing filled with SF₆ gas.

⚡ How GIS Works

• Electrical components are enclosed in metal and insulated by pressurized SF₆ gas, which has excellent dielectric and arc-quenching properties.

• When a fault occurs, the circuit breaker interrupts the flow, and the SF₆ gas cools and quenches the arc.

• All components are assembled in a modular, sealed design, allowing safe and reliable operation even in harsh or limited-space environments.

🏗️ Applications

• Urban substations (where space is limited)

• Underground substations

• Hydropower and thermal power plants

• Offshore platforms and industrial zones

✅ Advantages

• Compact size (up to 10× smaller than Air-Insulated Switchgear)

• High reliability and safety

• Low maintenance (sealed design prevents dust, humidity intrusion)

• Better performance in harsh environments

❌ Disadvantages

• High initial cost

• SF₆ gas is a potent greenhouse gas (with a global warming potential ~23,500 times that of CO₂)

• Specialized handling and equipment required for maintenance and gas recovery

🌍 Environmental Considerations

Due to the environmental impact of SF₆ gas, modern GIS manufacturers are:

• Reducing SF₆ content

• Developing alternative gases (e.g., g³ by GE, AirPlus by ABB)

• Improving gas recycling techniques

🌍 Case Studies of GIS Implementation

✅ 1. Nepal: GIS in Khimti-Dhalkebar Transmission Line (NEA Project)

• Location: Dhalkebar, Dhanusha District, Nepal

• Implemented by: Nepal Electricity Authority (NEA) and funded by JICA/World Bank

• Voltage Level: 220/132/33 kV GIS Substation

• Purpose: Key node in east-to-central transmission; part of strengthening cross-border electricity trade with India

• Why GIS?:

  • Space-constrained substation site

  • Need for enhanced reliability during monsoon conditions

  • Reduction in maintenance in remote locations

🔍 Result:

• Significantly improved load flow and voltage stability across eastern Nepal.

• Minimization of outages and flashovers during stormy seasons.

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✅ 2. India: Bina GIS Substation (MP)

• Voltage Level: 765 kV GIS (Ultra High Voltage)

• Developer: Power Grid Corporation of India (PGCIL)

• Application: Part of India’s National Grid backbone

• Key Points:

  • Operates in hot, dusty conditions with minimal issues

  • Compact footprint allowed installation near sensitive ecological zones

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✅ 3. Switzerland: Zurich Unterwerk Selnau Underground GIS Substation

• Developer: ABB Switzerland

• Design: Built underground to preserve historical city architecture

• Voltage: 110 kV GIS

• Application: Urban power supply with high reliability

• Why GIS?:

• Limited surface space

• High population density

• Need for aesthetic/architectural preservation

📊 GIS vs AIS Quick Comparison

Feature	GIS	AIS
Size	Compact	Requires large open space
Maintenance	Low	High (exposed to weather/dust)
Installation Cost	High	Lower
Arc Quenching	SF₆ gas (excellent)	Air (lower dielectric strength)
Environmental Risk	SF₆ – GHG, regulated	Less impactful
Lifespan	Long (~30–40 years)	Slightly lower (~25–30 years)

- Upendra Bhattarai, second year Civil Engineering student at Tribhuvan University Institute of Engineering Purwanchal Campus, Dharan, Sunsari, Nepal