SF6 gas insulated switchgear (GIS) is a compact, reliable and safe electrical switching solution widely used in medium and high voltage power systems. Unlike conventional air-insulated switchgear, GIS encloses all live parts within a sealed tank filled with sulfur hexafluoride (SF6) gas, providing superior insulation and arc-quenching performance. This guide covers the main types of SF6 GIS, their key advantages, typical applications, and selection considerations for global buyers.
What is SF6 Gas Insulated Switchgear?
SF6 gas insulated switchgear is a metal-enclosed switchgear assembly in which all conductive components — including busbars, circuit breakers, disconnectors, earthing switches, current transformers, voltage transformers and surge arresters — are sealed inside earthed metal tanks filled with SF6 gas at a pressure typically between 0.4 and 0.7 MPa.
SF6 (sulfur hexafluoride) is an extremely stable, electronegative gas with excellent dielectric strength — roughly 2.5 to 3 times that of air at the same pressure. This allows GIS to achieve the same voltage rating in a footprint that is only 10–20% of an equivalent air-insulated substation (AIS).
Main Types of SF6 GIS
1. Medium Voltage GIS (12–36 kV)
- RMU-type GIS: Compact ring main units used in secondary distribution networks. Typical ratings: 630A–1250A, 16kA–25kA for 3 seconds.
- CB-type GIS: Full-featured switchgear with vacuum or SF6 circuit breakers, used in primary distribution substations and industrial plants.
- Extendable GIS: Modular designs that allow future expansion without shutting down the existing installation.
2. High Voltage GIS (72.5 kV–800 kV and above)
- Bay-type GIS: Standardized bays for transmission substations, available in single-phase or three-phase enclosure designs.
- Compact GIS: Reduced-footprint designs for urban substations, underground stations, and retrofits.
- Gas-insulated switchgear for special environments: Marine-rated, tropicalized, or seismic-qualified versions for harsh conditions.
Key Advantages of SF6 GIS
| Advantage | Description |
|---|---|
| Space Saving | Footprint is 10–20% of equivalent AIS; ideal for urban and indoor substations. |
| High Reliability | Sealed design eliminates contamination, moisture and animal-related faults. Typical service life exceeds 30 years. |
| Safety | Live parts are completely enclosed; no exposed conductors. Internal arc protection and pressure relief devices add further safety. |
| Low Maintenance | No routine cleaning of insulators; gas density monitors provide continuous condition monitoring. |
| Environmental Resistance | Suitable for coastal, desert, high-altitude and heavily polluted environments. |
Typical Applications
- Urban distribution substations: Where land is expensive and space is limited.
- Industrial plants: Steel mills, chemical plants, refineries and mining operations requiring high reliability.
- Renewable energy: Wind and solar farm collector substations, especially in remote or constrained sites.
- Commercial buildings and data centers: Critical power distribution where safety and uptime are paramount.
- Transportation: Railway traction substations, airports, and marine installations.
How to Select the Right SF6 GIS
Choosing the correct SF6 gas insulated switchgear requires careful evaluation of several technical and commercial factors:
- Voltage rating: Match to system nominal voltage (12 kV, 24 kV, 36 kV, 72.5 kV, 145 kV, etc.).
- Rated current: Busbar and feeder current ratings must exceed maximum continuous load, with adequate margin.
- Short-circuit breaking capacity: Select based on maximum fault current at the installation point, typically 16kA, 20kA, 25kA or 31.5kA for 3 seconds.
- Type of busbar: Single-phase vs. three-phase enclosure; three-phase is more compact but requires internal arc testing.
- Protection and control: Decide between conventional electromechanical relays, numerical protection relays, or IEC 61850 digital substations.
- Environmental conditions: Altitude, ambient temperature range, humidity, pollution level, and seismic requirements.
- Standards compliance: IEC 62271-1, IEC 62271-100, IEC 62271-200, GB, ANSI/IEEE as applicable.
Maintenance and Safety Considerations
Although SF6 GIS is low-maintenance, proper upkeep is essential:
- Gas density monitoring: All bays should be equipped with density monitors with alarm and lockout contacts. Refill only by certified personnel.
- Annual inspection: Check gas density readings, indicator lamps, heater operation, and control circuits.
- Every 3–6 years: Perform functional tests on interlocks, trip circuits, and anti-pumping relays.
- SF6 gas handling: Always use approved gas-recovery equipment. SF6 is a potent greenhouse gas — never vent to atmosphere.
- Safety gear: Use self-contained breathing apparatus (SCBA) when working near SF6 equipment in confined spaces, as leaked gas can displace oxygen.
Common FAQs About SF6 GIS
Is SF6 harmful to the environment?
SF6 has a high global warming potential (GWP = 23,500), which has led to regulations such as the EU F-Gas Regulation. Modern manufacturers use sealed pressure systems that minimize emissions, and alternative gases (such as vacuum interrupters with dry air or eco-efficient mixtures) are increasingly available for new installations.
How long does SF6 GIS last?
With proper maintenance, SF6 gas insulated switchgear has a typical design life of 30–40 years. The sealed tank does not need routine opening; most maintenance items are external (controls, accessories, gas density checks).
Can SF6 GIS be retrofitted into an existing AIS substation?
Yes. GIS is often chosen for substation retrofits because its compact footprint allows replacement of large AIS bays within the same switchbuilding footprint, or installation in spaces where no new land is available.
What is the difference between GIS and RMU?
An RMU (ring main unit) is a small, compact type of medium-voltage switchgear, typically used for secondary distribution. Many modern RMUs are SF6 gas-insulated. GIS is a broader term covering full switchgear assemblies from 12 kV up to very high voltages.
How much does SF6 GIS cost compared to AIS?
SF6 GIS has a higher upfront capital cost than conventional air-insulated switchgear (typically 1.5–2.5×), but the total cost of ownership is often lower due to reduced civil works, smaller land requirement, and lower maintenance over the equipment life.
About Electric-GS
Electric-GS is a professional electrical equipment manufacturer based in Yueqing, Zhejiang, China — the heart of China’s low-voltage and medium-voltage electrical industry. We design and manufacture a full range of SF6 gas insulated switchgear, ring main units, vacuum circuit breakers, disconnectors, and complete switchgear panels for global clients.
Our products are certified to IEC, CE, ISO and other international standards, with export experience to over 50 countries in Southeast Asia, the Middle East, Africa, Europe and South America. We provide OEM/ODM services, competitive factory-direct pricing, and comprehensive technical support.
Contact us at info@electric-gs.com or WhatsApp +86 135 8897 8050 for SF6 GIS inquiries, specifications and quotations. Visit our website at electricgs.com to explore our complete product lineup.
One thought