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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.

✅ 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

✅ 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

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Location: Tinkune Gangalal Marg, Dharan 56700, Nepal

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