Rockwill RGIS Switchgear — Gas Selection Considerations for 12 kV, 24 kV, and 40.5 kV Applications

Rockwill RGIS uses differentiated insulation gases across voltage classes (N2/dry air for 12/24 kV, SF6 for 40.5 kV, with g3being introduced as an eco-friendly alternative). This selection is fundamentally an engineering decision that balances insulation performance, equipment compactness, cost-effectiveness, and environmental regulations. Understanding this logic first requires a thorough comparison of the insulation and arc-quenching properties of N2, dry air, SF6, and g3.

Core Differences in Insulation and Arc-Quenching Performance

1. Main Composition

2. Dielectric Strength (relative to SF₆)

3. Electron Capture Mechanism

4. Arc-Quenching Ability (relative to air)

5. Global Warming Potential (GWP)

6. Environmental and Toxicity Considerations

7. Liquefaction Temperature (at operating pressure)

8. Sensitivity to Impurities

Key Takeaways

• First, the insulation performance gradient. SF6 and g3 belong to the top tier, with dielectric strength more than 2.5× that of N₂2/dry air. This means at the same voltage and clearances, SF6 or g3 can reduce equipment volume to 1/3 or less of an air-insulated cabinet. Through careful blending of fluoronitrile and CO2, g3 can achieve nearly equivalent insulation performance to SF6 at design pressure — removing the biggest obstacle to compact 40.5 kV eco-friendly switchgear.
• Second, the arc-quenching capability gap. SF6's unique thermochemical arc-quenching properties allow it to independently interrupt high currents. N2, dry air, and g3 all lack this capability. Therefore, any switchgear using these three gases — regardless of voltage level — must rely entirely on a vacuum interrupter for current interruption, with the gas serving only as an insulating medium. This is why the "vacuum interruption + eco-friendly gas insulation" combination has become the industry mainstream.
• Third, the g³ trade-off. g3 offers insulation performance comparable to SF6 with extremely low GWP — making it an ideal substitute. However, its weakness is higher liquefaction temperature at operating pressure, making it unsuitable for direct use in extreme cold regions without blending more CO2 (which slightly reduces insulation) or adding heating/insulation. Its weak arc-quenching ability is perfectly compensated by the vacuum interrupter, allowing g3 to focus on its insulation strengths.

With the above differences in mind, Rockwill's gas selection logic for RGIS across voltage classes becomes clear.

High Reliability RGIS Type C-GIS Switchgear 

For 12 kV / 24 kV — N₂ or Dry Air + Vacuum Interrupter

At these voltage levels, insulation requirements are moderate. By slightly increasing gas pressure (e.g., 0.1–0.15 MPa relative pressure), N2 or dry air can provide sufficient dielectric strength for a compact design without introducing any greenhouse gas. Using the cheapest, most environmentally friendly, and easiest-to-maintain N2 or dry air — paired with a mature vacuum interrupter — perfectly delivers on the product promise of "high cost-effectiveness and zero lifecycle greenhouse emissions." Additionally, the trace oxygen in dry air helps decompose carbon deposits from partial discharge, further improving operational reliability.

For 40.5 kV — SF₆ + Vacuum Interrupter, or g³ as an Alternative

At 40.5 kV, insulation clearance becomes critically sensitive. If N2 or dry air were used, even at maximum allowable pressure, the equipment volume would multiply — losing the compactness that defines RGIS. A top-tier insulation gas must be introduced.

The conventional solution uses SF6, with its 2.5–3× higher dielectric strength than air, ensuring minimal electrical clearances at low pressure (e.g., 0.15 MPa) for high reliability and compactness. The "SF6 for insulation only, vacuum interrupter for interruption" strategy fundamentally eliminates large quantities of toxic arc decomposition byproducts and simplifies maintenance.

The future-ready upgrade introduces g3 Within the same compact footprint, g3 blends deliver nearly equivalent insulation to SF6 while reducing GWP to below 500 — fully aligned with increasingly stringent global F-gas regulations. The current barriers to large-scale g3 deployment at 40.5 kV are low-temperature adaptability and initial cost. As formulations improve and the supply chain matures, g3will become the definite direction for eco-friendly 40.5 kV RGIS evolution.

Summary

RGIS gas selection philosophy — grounded in a clear understanding of the fundamental physical boundaries of N2, dry air, SF6, and g3 in insulation and arc-quenching performance — uses the most appropriate tool to solve the primary challenge at each voltage tier:

• Low and medium voltage (12/24 kV): Use the "green gas + vacuum" combination — eco-friendly, economical, and fully SF6-free.
• High voltage (40.5 kV): Deploy SF6 first to maintain compactness and reliability as lifelines, while positioning g3 as a technology reserve — continuously approaching a new Pareto optimum between performance and environmental responsibility.

Rockwill RGIS Case Study and Gas Insulated Switchgear Project in Ghana

Edited From：Garca