What Is Gas Insulated Switchgear (GIS)?

This article explores what gas insulated switchgear (GIS) is, how it operates, and the typical voltage levels used in the industry.

1. Introduction to Switchgear

Switchgear is a collection of electrical devices designed to switch, carry, and break circuits within a power system. It includes components such as circuit breakers, fuses, contactors, relays, voltage transformers, and current transformers. Switchgear is classified by voltage level into low voltage (below 1,000 V AC), medium voltage (1,000 to 36,000 V AC), and high voltage (above 36,000 V AC). It is also categorized by insulation type: air, oil, or gas insulated. Our focus here is on gas insulated switchgear.

2. What Is Gas Insulated Switchgear?

Gas Insulated Switchgear encloses most of its components inside a sealed metal housing filled with sulfur hexafluoride (SF6) gas. SF6 offers excellent electrical insulation and arc-extinguishing properties, making GIS much more compact and lighter compared to air-insulated switchgear. This makes GIS ideal for confined indoor or underground spaces where high voltages are handled.

Design Features

Gas Insulated Switchgear uses SF6 gas, typically at 400-600 kPa pressure, to insulate and separate energized parts inside grounded metal enclosures. SF6 is a colorless, inert gas with a density about five times that of air, providing 2 to 3 times higher dielectric strength and roughly 100 times better arc-quenching capability than air.

How It Works

Gas Insulated Switchgear isolates live components with SF6 gas and vacuum technology to efficiently interrupt circuits. While SF6 decomposes during arc extinction, its decomposition products recombine back into SF6, ensuring long-term usability.

3. Why Use SF6?

SF6 is the preferred insulating gas for high-voltage equipment due to its excellent dielectric strength, chemical stability, and non-flammable nature. It fully encloses critical components like circuit breakers, transformers, and current transformers inside a pressurized casing, preventing electrical faults and reducing sound from switching operations. SF6 also allows for smaller and safer equipment designs.

4. Key Components of GIS

• Busbar: Conductive strips (copper or aluminum) that connect power sources and loads within the switchgear.
• Circuit Breaker: Mechanical switch that protects circuits by interrupting current during overloads or faults.
• Current Transformer: Steps down high current to measurable levels for monitoring and protection.
• Potential Transformer: Reduces voltage to safe levels for measurement and control devices.
• Cables: Transmit power from substations to load points, either overhead or underground.

5. Advantages of GIS

• Compact and modular design saves space.
• High reliability and low maintenance requirements.
• Suitable for indoor and underground installations.
• Offers protection against environmental hazards and natural disasters.
• Flexible configurations support various busbar arrangements.

6. Disadvantages of GIS

• Higher initial cost compared to air-insulated switchgear (AIS).
• Handling and transportation of SF6 gas require care.
• Maintenance and cleaning demand specialized procedures to avoid contamination.
• Repairs may be complex and cause longer outages.

7. GIS vs. AIS

GIS uses SF6 gas for insulation, making it more compact, reliable, and low-maintenance compared to AIS, which uses air. However, GIS has higher upfront costs but shorter installation times, while AIS is generally less expensive and easier to maintain in open environments.

8. Applications

GIS is widely used in urban areas with space constraints, hydroelectric plants, offshore substations, polluted industrial environments, and wherever compact, reliable switchgear is needed.

9. Installation and Maintenance

Proper installation and commissioning by certified specialists ensure optimal reliability and performance. Maintenance includes testing insulation, verifying connections, monitoring communication systems, and scheduled servicing to prevent faults.

10. Conclusion

Gas-insulated switchgear represents a significant advancement in power distribution technology, combining compact design, high reliability, and minimal maintenance. It plays a crucial role in modern power grids and smart infrastructure development.

 

Professiona Switchgear supplier and manufacturer 

1. Zhejiang GONGSHUN Electrical Co.,Ltd (electricgs.com), Our company was founded in the late 1990s, specializing in the production of inflatable cabinets, SF6 inflatable cabinets, and various high and low voltage complete sets of electrical equipment. It has multiple subsidiaries under its jurisdiction, including high-voltage load switch branch, high-voltage circuit breaker branch, high-voltage fuse branch, and technology development branch.Our technical expertise, comprehensive product portfolio and long-term rich experience are helping many customers in need to solve their power problems. We’re happy to help at any time.  Whether you need application product advice or technical assistance, our global service team is committed to providing you with the right support. For more technical information about medium voltage earthing switch, feel free to contact us, send an email to gongshun@electric-cn.com 
2. Our company specializes in producing 12KV-40.5KV series high-voltage electrical products: FZN58, FLN48, FLN36, FZRN25, FZN21, FN18, ZFN16, FN12, FN8, FN7, FN5, XRNT, XRNP, VS1, ZN28, ZW8, ZW32, JN15, GN19, GN22, GN24, GN30, CLXGN15-12, HXGN □ -12, DXG-12 (L), DFW □ -12 high-voltage cable branch box, CLXGN □ -12 (SF6) series inflatable cabinet 12KV and 35KV cable accessories, etc; CLVXP-12 indoor AC high voltage fixed switchgear, CL-SIS-12 compact solid insulated ring main unit, professional assembly Schneider SC6 (SF6) series load switchgear, ABB produced SFG (SF6) series load switchgear and other series products; Distribution and agency of high-voltage load switches and inflatable cabinets produced by Schneider Electric and ABB; Siemens produces the 3AJ1 series of indoor medium voltage vacuum circuit breakers and other related products. The company has a complete range of products and has been operating safely on domestic and international power grids for a long time, receiving unanimous praise from both new and old users. Among them, multiple products such as FZRN25, FN12, FLN36-12, XRNT-12 have been exported to various countries and regions in East Asia, South Asia, Southeast Asia, Africa, and the United States.