New SF6 Insulating Gas Alternatives

One alternative insulating gas to SF6 is a synthetic gas called Perfluoroisobutyronitrile. For ease of use and recognition, this gas is recognised within the industry by its shortened name C4-FN or C4-F7N. Previously it was branded by its inventor (3M) as Novec 4710^TM 

A Nitrile based hydrocarbon; C4-FN offers positive environmental advantages over the use of SF6.

In its raw state C4-FN’s GWP of 2750 offers a near 90% reduction in GWP in addition to only an approximate 35-year life span in the environment compared to SF6. Its di-electric properties allow the C4-FN to be used in similar sized GIE to SF6, and across all voltage ranges making it an ideal replacement for SF6.

However, with a boiling point of just -4.7C, C4-FN on its own would ready liquefy back from gaseous phase reducing the capability to quench arcs; and so The C4-FN is mixed with Carbon Dioxide (CO2), and/or Nitrogen (N2) to reduce the boiling rate down allowing the C4-FN to remain in a gaseous phase.

This blending with CO2 means the actual GWP of the final installed gas within the gas compartment is in the range of 300-500GWP; a significant reduction in GWP from the 23000+ GWP of SF6.

Carbon Dioxide is used in most new build applications, with C4-FN in Nitrogen (N2) mixtures becoming more popular for direct replacement of SF6 gas from GIE; but this is only possible in certain situations/applications.

Oxygen is used as a Carbon “getter” to prevent the creation of Carbon particulate during the breakdown of C4-FN when arcing occurs; typically, it offers no direct di-electric properties or influence on the system as a whole.

Some GIE OEM’s have branded their mixtures and so brand names such as G3^TM  from GE or Econiq^TM from Hitachi are more widely known names for this gaseous mixture.

OEM mixtures can vary quite widely depending on the voltage, current load, GIE design and environmental conditions the equipment will be installed within; some example blends are below:

13% C4-FN, 87% CO2                          10% C4-FN, 5% O2, 85% N2

5% C4-FN, 95% CO2                             4% C4-FN, 5% O2, 91% N2

5% C4-FN, 3% O2, 92% O2

3.5% C4-FN, 10% O2, 86.5% CO2

2% C4-FN, 3% O2, 95% CO2

C4-FN mixtures will require users to work with the gas differently to procedures that may have been used for SF6:

C4-FN Gas Analysis

IEC standards for the measurement of Technical Grade or Re-use grade C4-FN mixtures are in development with the IEC63360 released in January 2025.

• IEC63359 Fluids for electrotechnical application: Specifications for the re-use of mixtures of gases alternative to SF6
• IEC63360:2025 Fluids for electrotechnical application – Specification of gases alternative to SF6 to be used in electrical power equipment

These standards will give the guidance on whether the constituent gases are of sufficient quality to be mixed and then when in use if the blend quality and/or breakdown gases are at concentrations that merit intervention to ensure good working order of the GIE.

As with SF6 gas, the moisture (H2O) content in the gas is critical to ensure the gas works efficiently where it is being used. Unlike SF6, C4-FN does not “self-heal” after arcing events and so regular testing as part of a maintenance program should be considered to find faults early.

During arcing or quenching events, the C4-FN is broken down into many by-products. Similarly to SF6 we look to detect and measure these by-products as an indication of the extent of breakdown; for C4-FN mixture we look for Carbon Monoxide (CO) as this indicator.

The EMT Zerowaste Eco+ has the capability of measuring all these gases including the Carbon Monoxide by-product within 2 minutes, providing a fast and reliable analysis result for fault and quality determination. With unique multi-gas measurement capability and lifetime warranty on sensors the Zerowaste Eco+ is the perfect tool for SF6 alternative gas analysis.

C4-FN Gas Handling & Safety

For C4-FN gas handling, specialist equipment needs to be utilised, existing SF6 handling equipment in most cases cannot be used due to differing chemical and physical characteristics.

In the first instance the decision on using pre-mixed gas cylinders or mixing your own gas blends onsite/within depot needs to be determined. Dedicated C4-FN mixing systems such as the EMT Smartmix can be purchased that allows utilities to make their own gas blends for the filling and topping up requirements they may have.

Once mixed the gases then need to be moved on site and so dedicated C4-FN gas carts are required for filling, recovery and filtration of the gas blend. These carts are typically specifically for C4-FN in CO2 so that compression rates and chemical compatibility is best suited.

Within IEC 62271-4 guidance on the procedures for handling C4-FN are detailed to support operators and users of the gas.

As with most insulating gas filled compartments, over time they will leak. Dedicated leak detectors such as the EMT Leak Hunter can be used to find the source of the leak and enable repairs. With typically >80% Vol CO2 being emitted from the leak source, leaks from C4-FN filled system are relatively easy to locate.

With new gases comes new safety challenges with CO2 and CO both being toxic and having occupational exposure limits assigned to them. EMT’s range of personal (and fixed system) safety monitors allows early detection and warning of these toxic gases in the environment.

C4-FN Resources

An excellent guide written by GE and Hitachi to increase knowledge and understanding of this technology can be found here:

The term “Natural Origin Gases” or N.O.G, is the broad name used for gas mixtures containing Carbon Dioxide (CO2), Nitrogen (N2) and Oxygen (O2).

Typically, three insulating gas variations appear on the marketplace for these gases:

1. 80% Vol N2, 20% Vol O2 (Dry Air, Clean Air, Pure Air, Synthetic Air)
2. 80% Vol CO2, 20% Vol O2
3. 100 Vol CO2

As gases found in nature, these gases offer substantial advantages over SF6 usage:

With extremely low boiling points there is no chance of the gases liquefying with in the gas compartment and atmospheric life is effectively not applicable for the N2/O2 mixture. For CO2 and CO2/O2 mixtures there is a GWP associated to these due to the CO2 content, however this will always be GWP 1 or less depending on the mixture.

There are currently some disadvantages to systems containing these gases in that they are typically larger in size and have a lower voltage/current rating compared with SF6; however, technology is rapidly advancing in this area.

Various OEMs have branded their new SF6 free alternatives such as Clean Air^TM by Siemens or AirSeT^TM by Schneider.

Air and/or CO2 containing compartments will require users to work with the gas differently to procedures that may have been used for SF6:

Natural Origin Gas Analysis

IEC standards for the measurement of Technical Grade or Re-use grade of Natural Origin Gas mixtures are in development with the IEC63360 released in January 2025.

• IEC63359 Fluids for electrotechnical application: Specifications for the re-use of mixtures of gases alternative to SF6
• IEC63360:2025 Fluids for electrotechnical application – Specification of gases alternative to SF6 to be used in electrical power equipment

These standards will give the guidance on whether the constituent gases are of sufficient quality to be mixed and then when in use if the blend quality and/or breakdown gases are at concentrations that merit intervention to ensure good working order of the GIE.

As with SF6 gas, the moisture (H2O) content in the gas is critical to ensure the gas works efficiently where it is being used. The blend rations for Natural Origin Gas systems are important like C4-FN systems, however the gases are harder to breakdown into by-products and so the blend generally is stable.

During arcing or quenching events, it is possible for the CO2, N2 and O2 to breakdown into by-products. Similarly to SF6 we look to detect and measure these by-products as an indication of the extent of breakdown; for N.O.G gas mixtures we typically look for Carbon Monoxide (CO) or Nitrogen Dioxide as this indicator.

The EMT Zerowaste Eco+ has the capability of measuring all of these gases including the by-products within 2 minutes, providing a fast and reliable analysis result for fault and quality determination. With unique multi-gas measurement capability and life time warranty on sensors the Zerowaste Eco+ is the perfect tool for SF6 alternative gas analysis.

Natural Origin Gas Handling & Safety

For Natural Origin Gas gas handling, specialist equipment needs to be utilised, existing SF6 handling equipment in most cases cannot be used due to differing chemical and physical characteristics.

As with C4-FN blends, in the first instance the decision on using pre-mixed gas cylinders or mixing your own gas blends onsite/within depot needs to be determined. This can be done using dedicated mixing systems such as the EMT Smartmix can be purchased that allows utilities to make their own gas blends for the filling and topping up requirements they may have. Typically, N.O.G mixtures are easy to source, low cost and with quick delivery, as such utility onsite mixing is not required.

The benefit of using N2/O2 mixtures is that removing the gas from compartments can be done straight to air using either a release valve or vacuum pump. It should be noted that prior to doing this the gas should be tested to ensure there are no toxic by-products in the compartment that releasing to the environment could cause harm.

For blends containing Carbon Dioxide (80/20 or 100%), the direct release of this gas to atmosphere needs to be determined by company policy and safety awareness. Primarily for indoor based equipment, the release of large quantities of CO2 could lead to over exposure of operators to this toxic gas or in some scenario’s asphyxiation.

In an outdoor environment this is not so much of a risk, however CO2 is a greenhouse gas and so each utility or operating company may have their own policy on the release of CO2 to atmosphere as it will contribute to global warming and so the recovery of CO2 (as per SF6) maybe required.

Dedicated N.O.G carts and vacuum systems are available for filling, recovery and filtration of the gas blend. These carts are typically specifically for either air or CO2 so that compression rates and chemical compatibility is best suited.

The EMT Smartfill Eco+ can also be used as a more portable filling, topping up and leak management system for N.O.G GIE. Simple, lightweight and easy to use the Smartfill Eco+ provides reliable, repeatable and auditable fills and top-ups ensuring safety and minimal downtime.

Within IEC 62271-4 guidance on the procedures for handling Natural Origin Gases are detailed to support operators and users of the gas.

As with most insulating gas filled compartments, over time they will leak. Dedicated leak detectors such as the EMT Leak Hunter can be used to find the source of the leak and enable repairs. With typically >80% Vol CO2 being emitted from the leak source, leaks from CO2 filled system are relatively easy to locate.

Locating leaks from N2/O2 based systems is more challenging as you are leaking “air into air” and so EMT’s Smartfill Eco+ with its Leak Dose technology coupled with the Leak Hunter leak detector can be used to detect these small leaks in air systems, quickly and easily.

With new gases comes new safety challenges with CO2, CO and NO2 by-products being toxic and having occupational exposure limits assigned to them. EMT’s range of personal (and fixed system) safety monitors allows early detection and warning of these toxic gases in the environment.

EU F-Gas Regulations 2014 (517/2014)

EU F-Gas Regulations 2024 (2024/573)

IEC 62271-4:2022 Handling procedures for gases for insulation and/or switching.

IEC 60376:2018 Specification of technical grade Sulphur Hexafluoride (SF6) and complementary gases to be used in its mixtures for use in electrical equipment.

IEC 60480:2019 Specifications for the re-use of Sulphur Hexafluoride (SF6) and its mixtures in electrical equipment.

IEC 63360:2025 Fluids for electrotechnical application – Specification of gases alternative to SF6 to be used in electrical power equipment.

CIGRE Technical Brochure 871: Current Interruption in SF6-Free Switchgear.

CIGRE Technical Brochure 849: Electric Performance of new Non-SF6 gases & gas mixtures for gas insulated systems.

CIGRE Technical Brochure 802: Application of Non-SF6 Gases or Gas Mixtures in Medium & High Voltage GIS gas-insulated switchgear.

CIGRE Technical Brochure 730: Dry Air, N2, CO2 & N2/SF6 Mixtures for Gas Insulated Systems.