Case Study: Journey to SF6-free HV Substations

Source: GE Grid Solutions


National Grid Begins Journey to SF6-free HV Substations

The entire electrical transmission industry is buzzing over the technical achievement of energizing the first high voltage gas-insulated line (GIL) using an environmentally friendly alternative to SF6. This SF6 alternative insulation medium is called g3. To date, there has been no alternative to SF6 technology since its inception in the 1970’s, when it was introduced as an insulation medium in high voltage (HV) switchgear. 

Indeed, on April 13 2017, National Grid achieved a huge industry milestone with the energization of the first SF6- free 420 kV gas-insulated line in their Southeast England network. The new Sellindge substation was deployed in an operationally critical part of the UK’s transmission network to help ensure the region would continue to benefit from a safe and reliable supply of electricity. It plays a vital role in the ElecLink project, which will increase the UK’s energy security, reliability and capacity by connecting with the French electricity transmission network. 

We are very pleased to collaborate with National Grid on this project, the first in the world to use a g3 solution. Utilities wanting to take the step to reduce their global warming potential now have an alternative to SF6. - Giuseppe Sottero, General Manager GE Gas-Insulated Substations

National Grid at the Forefront of Green Technology Implementation 

With strong commitments to their regulator and stakeholders regarding the ongoing reduction of SF6 gases released into the atmosphere, National Grid has set voluntary targets to reduce greenhouse gas (GHG) emissions across their UK and US businesses by 45% by 2020 (baseline: 1990). This corporate philosophy led National Grid to select g3 technology in 2015 for a new project as part of their Network Reinforcement Program.

The introduction of GE’s g3 solution provides an opportunity for National Grid to be at the forefront of new technology development, and obtain an early understanding of the performance of the equipment. In addition to its negligible environmental impact, this new gas checked all the boxes for National Grid's health and safety pre-requisites and stringent performance specifications.

The Impact of SF6 is Significant

Replacing 1 kg of SF6 with the corresponding mass of g3 is the carbon equivalent of removing 16 cars running one year off the road.*** The potential for global warming reduction is further underscored when you look at the sheer quantity of SF6 installed worldwide. Specifically, studies indicate 10,000 tons of SF6 are installed each year, with 80% concentrated in the transmission industry alone.

Benefits of SF6 Replacement | Source: GE Grid Solutions

About g^3 Technology

  • g3 (pronounced “g cubed”) is GE ‘s alternative to SF6 developed in collaboration with 3MTM. 
  • g3 is a proven and ready-to-go alternative insulating gas mixture for high voltage electrical transmission equipment, which provides the same technical performance as SF6 with a drastically reduced environmental impact - g3’s impact is a whopping 99% less than SF6. 
  • The g3 gas mixture is blended using 3M™ Novec™ 4710 of the Fluoronitrile based insulating fluid family with a balanced percentage of Carbon Dioxide and Oxygen to optimise performance.
  • The gas mixture offers an efficient combination of low global warming potential (GWP) with high dielectric performance and minimum operating temperatures in accordance with the typical Transmission System Operators’ (TSO) needs.

g^3 Benefits


  • g3 is fully type-tested and commercially available for GIS up to 145 kV, GIL up to 420 kV, live tank circuit breakers up to 145 kV. 
  • g3 is applicable in the same environmental conditions and at the same ambient temperature ranges as SF6. 
  • g3 high-voltage equipment feature the same dimensional footprint as state-of the-art SF6 equipment. 
  • g3 is non toxic and falls in the same safety class as SF6. 


  • g3 Global Warming Potential represents less than 1% of that of SF6. 


  • Utilities can qualify for tax reductions or incentives related to greenhouse gas emissions reduction.


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