If transformers are the muscles of a battery energy storage plant, switchgear is its reflex system.
Switchgear connects and disconnects equipment during normal operation, isolates circuits for maintenance, and—during the worst milliseconds of the plant’s operating life—interrupts fault current before damage spreads.
Battery storage engineers inherit much of this equipment from conventional substations and industrial power systems. However, one important part of the technology is changing quickly: sulfur hexafluoride, or SF₆, is being phased out of new switchgear in several markets.
For BESS developers, owners, and engineers, this is no longer only an environmental consideration. It is becoming a procurement, commissioning, and long-term asset-management issue.
What switchgear actually does in a BESS
Switchgear performs three main functions.
1. Routine switching and isolation
Switchgear connects and disconnects battery blocks, PCS feeders, transformers, auxiliary systems, and the grid interconnection.
It also provides defined isolation and grounding functions so maintenance personnel can safely work on de-energized equipment.
In a large BESS, routine switching may be required to:
Remove one battery or PCS block from service
Isolate a transformer
Perform cable maintenance
Sectionalize the medium-voltage collection system
Reconfigure the plant following equipment failure
Maintain part of the plant while the remaining blocks continue operating
The ability to isolate one section without shutting down the entire facility can have a direct effect on project availability.
2. Protection coordination
Protection relays monitor currents, voltages, frequency, differential quantities, and other electrical conditions. When the protection system determines that a fault has occurred, it sends a trip command to the appropriate breaker.
Protection coordination in a BESS extends through an unusual chain of equipment:
Battery rack fuses and DC protection
Battery disconnects and contactors
PCS internal protection
Low-voltage or medium-voltage breakers
Medium-voltage feeder protection
Main transformer protection
Substation and grid-intertie protection
All of these devices must agree about which device should operate first.
A fault inside one BESS block should normally disconnect that block without unnecessarily tripping the entire plant. A transformer differential fault, by contrast, may require multiple breakers to open almost simultaneously.
The fact that an inverter may limit its own fault-current contribution does not eliminate the need for high-performance switchgear. The breaker may still need to interrupt current contributed by the grid, transformers, parallel feeders, or other energized sections of the plant.
3. Fault interruption
When breaker contacts separate under fault current, an electrical arc forms between them. The interrupter must extinguish that arc and prevent the current from restriking.
At alternating current, interruption is normally achieved around a natural current zero. The breaker must cool and de-ionize the arc path quickly enough that the system voltage does not re-establish the arc immediately after the zero crossing.
This is the difficult physics hidden inside what appears, from the outside, to be a simple switching operation.
AIS versus GIS
Medium- and high-voltage switchgear is generally divided into two very broad categories.
Air-insulated switchgear
Air-insulated switchgear, or AIS, relies mainly on atmospheric air and physical clearance for insulation.
Its main advantages are:
Straightforward construction
Easier visual inspection and access
Established service practices
Competitive equipment cost
No insulating-gas management
The main disadvantage is footprint. Sufficient electrical clearance must be maintained between phases and between energized parts and ground.
For many outdoor BESS substations, this additional space may be acceptable. Inside compact power stations, urban projects, or constrained sites, it can become a significant limitation.
Gas-insulated switchgear
Gas-insulated switchgear, or GIS, places energized components inside sealed compartments filled with an insulating gas.
GIS is compact, protected from dust and weather, and attractive where land or building space is limited.
This is the major type of RMU used in BESS projects around the globe especially in European installations
Historically, the gas that made compact GIS practical was SF₆. Depending on the switchgear design, SF₆ may be used for insulation, switching, or both. Many modern medium-voltage GIS products already use vacuum interrupters for current interruption but still rely on SF₆ for insulation around the live components.
That distinction matters: a vacuum circuit breaker is not automatically an SF₆-free switchgear solution.
Why SF₆ is being phased out
SF₆ is an exceptionally effective electrical insulator, but it is also an extremely powerful greenhouse gas.
The European Commission assigns SF₆ a 100-year global warming potential of 24,300. In practical terms, releasing one kilogram of SF₆ has the same calculated 100-year warming effect as releasing approximately 24.3 metric tonnes of carbon dioxide.
Switchgear is designed to be sealed, but leakage can occur during:
Equipment operation
Installation and commissioning
Maintenance
Gas recovery
Repair after a failure
Decommissioning and disposal
The environmental impact is therefore not limited to the normal operating leakage rate. The full lifecycle must be considered.
The EU regulatory schedule for medium-voltage switchgear
The European Union’s revised F-gas Regulation, Regulation (EU) 2024/573, establishes specific dates based on switchgear voltage.
A particularly important detail is that the medium-voltage restrictions apply to switchgear using fluorinated greenhouse gases, not only to equipment using SF₆. Therefore, replacing SF₆ with another fluorinated gas does not automatically provide a permanent compliance solution.
Switchgear rated voltage
EU prohibition date
Typical BESS application
Up to and including 24 kV
January 1, 2026
11 kV, 13.8 kV, 20 kV, 22 kV and 24 kV collection systems
More than 24 kV and up to and including 52 kV
January 1, 2030
Common 33 kV and 34.5 kV BESS collection systems and associated 36 kV or 40.5 kV-class equipment
The regulation prohibits the putting into operation of affected new switchgear after the relevant date. It is not a requirement to immediately remove all existing SF₆ equipment from service.
This means that, as of July 2026:
The EU deadline for new F-gas-based switchgear rated up to and including 24 kV has already passed.
Switchgear above 24 kV and up to and including 52 kV is scheduled to follow on January 1, 2030.
A typical European 33 kV BESS collection system falls into the second category.
The regulation contains specific grandfathering provisions and derogations. For example, the main prohibition does not apply when the operator can demonstrate that the switchgear order was placed before March 11, 2024. Procurement-based and certain technical derogations may also apply, but they require documentation and should not be treated as the normal design path for a new project.
For existing equipment, another milestone arrives on January 1, 2035. From that date, SF₆ used for maintenance or servicing of electrical switchgear must generally be reclaimed or recycled. Limited technical and emergency-repair exceptions remain.
These dates apply to the European Union. Other jurisdictions, utilities, and grid operators may use different schedules or equipment-acceptance rules.
What are the alternatives?
The transition away from SF₆ does not mean abandoning GIS or returning every project to large outdoor AIS substations. Several alternative architectures are already commercially available.
Vacuum interruption with dry-air insulation
This is becoming one of the most important solutions for medium-voltage switchgear.
The vacuum interrupter extinguishes the switching arc, while dry air or another non-fluorinated air-based mixture provides insulation around the energized components.
The main advantages are:
No SF₆
No fluorinated insulating gas
Mature vacuum-interruption technology
Lower regulatory exposure
Simpler end-of-life gas management
The design may require different internal clearances or enclosure geometry compared with traditional SF₆ equipment, so the footprint should still be checked carefully.
Vacuum interruption with solid insulation
Some switchgear uses solid dielectric materials around energized components, sometimes combined with air insulation.
This can reduce or eliminate the need for insulating gas and can produce compact designs. However, engineers should examine:
Partial-discharge performance
Long-term ageing of insulating materials
Repairability
Replaceability of individual components
End-of-life treatment
Performance under the project’s temperature and humidity conditions
Air-insulated switchgear with vacuum circuit breakers
Conventional AIS combined with vacuum circuit breakers remains one of the most straightforward SF₆-free solutions.
Where space is available, it can offer:
Familiar maintenance practices
Easy access to components
No insulating-gas system
A broad supplier base
Clear separation between functional compartments
For many BESS projects, the largest trade-off is simply the additional footprint.
What is next?
For new European medium-voltage projects, the direction is now clear:
Up to and including 24 kV: affected F-gas switchgear has been prohibited from being put into operation since January 1, 2026. BESS operators have to use SF6-free RMUs, or they won't be able to operate the site.
More than 24 kV and up to and including 52 kV: the corresponding prohibition begins January 1, 2030.
Common 33 kV and 34.5 kV BESS collection systems fall into the second group.
Existing SF₆ equipment is not automatically required to be removed, but servicing, gas sourcing, reporting, and end-of-life obligations will become increasingly important.
Vacuum interruption combined with dry air, air, solid insulation, or a hybrid F-gas-free system is becoming the most future-resistant approach for new medium-voltage BESS projects.