🟢 A New Era in Load Break Switch Design for Eco-Friendly MV RMUs: Vacuum interrupter or Puffer interrupter?

As sustainability goals and regulations accelerate the transition away from SF₆-based insulation, the medium-voltage (MV) switchgear industry is entering a new era. Utilities, cities, and industries are actively seeking eco-friendly RMU solutions that maintain reliability and performance while aligning with carbon neutrality targets.

The core technology question:

Which load break switch (LBS) approach will define the next generation of 24kV and below RMUs?

Two dominant paths have emerged among leading manufacturers like Siemens, ABB, Schneider Electric, and Eaton:

🔌 1. Vacuum Interrupter-Based Designs

·       A vacuum interrupter (VI) is placed in parallel with a mechanical disconnector.

·       The VI operates exclusively during the breaking phase and must withstand transient recovery voltage (TRV), but not short-circuit making or continuous current.

·       Short-circuit making is ensured mechanically by the blades.

·       Advantage: Compact, cost-effective VI design suited for modern RMUs.

🌬 2. Puffer Principle Designs

·       Arc extinction is achieved through mechanically compressed gas without the need for a separate vacuum interrupter.

·       Separation of contacts creates a visible, natural disconnector gap.

·       No involvement of metal vapor or vacuum, ensuring robust performance even under high TRV conditions like capacitive switching and fuse transfer duties.

💡 Where Siemens Stands

    "The 8DJH 24-blue GIS is a load-break switchgear for secondary distribution networks. All products are free of fluorinated gases and use climate-neutral Clean Air insulation as well as vacuum technology. The ring-main feeder is equipped with a three-position switch, integrating the functions of a switch-disconnector and a make-proof earthing switch."

With Clean Air insulation and vacuum switching, Siemens' blue GIS family delivers a sealed, maintenance-free alternative to SF₆ switchgear — while maintaining the same compact footprint and operational principles familiar to utility operators.

🌱 Looking Ahead

Although air has lower dielectric strength compared to synthetic gases, it brings undeniable advantages: safety, simplicity, zero GWP (Global Warming Potential), and full end-of-life recyclability.

With continuous technical evolution, SF₆-free RMUs are no longer an aspiration — they are today’s reality, paving the way toward carbon-neutral power distribution systems.

🔍 What’s your view?

Which switching technology do you believe offers the best balance between performance, reliability, and sustainability for future grids?

Let’s discuss!