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Theme of the month: Power engineeringSF₆-free switchgear: what changed on 1 January 2026
The most common insulating gas in medium-voltage switchgear can no longer be used in new equipment up to 24 kV. What the alternatives are, what they give up, and what the designer of a transformer substation needs to know.
Sulphur hexafluoride — SF₆ — has been in medium-voltage switchgear since the late 1960s and for almost half a century had no competitor. The reason is physical: at atmospheric pressure its dielectric strength is roughly two and a half times that of air, and its arc-quenching capability many times greater. That made possible the compact gas-insulated switchgear and cabinet-sized substations we know today.
The problem is also physical. SF₆ is the most potent greenhouse gas humanity produces: its global warming potential is around 25,000 times that of CO₂ by the latest IPCC assessment, and it persists in the atmosphere for over a thousand years. One kilogram of leaked SF₆ equals roughly 25 tonnes of CO₂. The annual leakage from a sealed unit is small — under 0.1 % — but fleets of millions of units worldwide turn it into a measurable contribution.
What the regulation says
Regulation (EU) 2024/573 on fluorinated greenhouse gases, in force since March 2024, prohibits placing new switchgear using fluorinated gases on the market in stages by voltage. Two dates matter for practice in Bulgaria:
- 1 January 2026 — medium-voltage switchgear up to and including 24 kV. That is almost every transformer substation for industrial and public sites in the country, since the distribution network is 20 kV.
- 1 January 2030 — switchgear from 24 to 52 kV.
- For high voltage the dates are 2028 and 2032 depending on class.
The ban applies to placing on the market of new equipment. Existing SF₆ switchgear may operate to the end of its life, be maintained and, where needed, topped up. Replacement is not required. However, the gas must be recovered at decommissioning, and handling must be carried out by certified personnel.
The regulation provides an exception: if a specific tender receives no offer for fluorinated-gas-free switchgear, equipment with a gas of GWP below 1000 may be accepted — which opens the door to some of the intermediate mixtures described below.
Three routes without SF₆
Manufacturers went in three directions. What they share is that arc quenching and insulation are separated — the arc is extinguished in a vacuum interrupter, while the gas or solid insulation only holds the voltage.
Clean air and vacuum. The switchgear is sealed and filled with dry air or a nitrogen–oxygen mixture at slightly elevated pressure, with current interruption in a vacuum breaker. This is the route taken by Siemens (blue GIS), Schneider Electric (SM AirSeT, RM AirSeT) and ABB. The advantage is that the gas has neither warming potential nor toxic decomposition products, and maintenance needs no certification. The drawback is the dielectric strength of air — about a third of SF₆. It is compensated by pressure, larger clearances or epoxy barriers, which in some designs means 10–30 % more volume.
Fluoronitrile mixtures. A mixture of fluoronitrile (C4-FN) with CO₂ and oxygen, commercially known as g³ from GE Vernova. Dielectrically it is close to SF₆, so dimensions are preserved, and the warming potential is under 1 % of SF₆. The trade-off is that the gas is still fluorinated, requires similar handling procedures and has condensation limits at very low temperatures. Fluoroketone (C5-FK) mixtures, developed by ABB as AirPlus, remained mainly in high voltage.
Solid insulation. Live parts and vacuum interrupters are cast in epoxy resin, with no gas at all. Eaton Xiria is the best-known example. The switchgear is entirely maintenance-free, but the geometry is fixed and extending an existing installation is harder.
What changes for the designer
At first sight nothing — a 20 kV unit with a breaker, a disconnector and protection. In practice there are four things to check at an early stage.
- Room dimensions. Clean-air switchgear may be deeper or taller than its SF₆ equivalent. In the refurbishment of an existing substation this decides whether it fits at all. Check with real dimensions from the current catalogue, not the typical ones from five years ago.
- The specification. The phrase “SF₆-free” is not enough — the g³ mixture is also “SF₆-free” yet fluorinated. If the aim is zero warming potential, write it explicitly: “insulating medium with GWP < 1” or “clean air / vacuum”. The standard remains IEC 62271-200 and the type tests are the same.
- Lead times. Demand turned around in two years and some series are produced to a waiting list. The switchgear is ordered earlier in the programme than used to be usual.
- Maintenance. With clean air, the fluorinated-gas handling certificate and quantity reporting disappear. With fluoronitrile mixtures they do not. That is a real cost over the life of the equipment and belongs in the comparison.
If the site already has SF₆ switchgear, it stays. It is replaced when its condition requires it, not the regulation. But for a new connection or a substation replacement in 2026, the question “with or without SF₆” no longer exists — the law has answered it.
Cost and direction
At present SF₆-free switchgear costs more — the difference varies between manufacturers and series and is usually in the range of 10–30 % for the unit itself. It is shrinking as volumes grow and as gas-handling costs disappear. More importantly, the difference is no longer a choice: for a 20 kV substation commissioned this year, there is no alternative.
Coming up in this series: silicon-carbide solid-state circuit breakers, IEC 61850 in industrial substations, and grid-forming inverters for battery systems.