Accelerating the decarbonisation of electricity networks through retrofill replacement of sulphur hexafluoride

Manchester experts have demonstrated a viable retrofill solution to replace Sulphur Hexafluoride (SF6), a potent greenhouse gas, used to provide electrical insulation to power equipment, without having to replace or significantly modify existing equipment.

Finding an alternative for insulating switchgear

As the UK transitions towards net zero, demand for electricity is set to quadruple. Keeping the existing network safe, reliable and functioning well for as long as possible is key.

SF₆ is a gas commonly used to provide insulation in gas-insulated switchgear. It is, however, a potent greenhouse gas and the largest controllable direct emission for National Grid Electricity Transmission (NGET), with ~244,516 tonnes CO2 equivalent reported in 2021/22. It has therefore the primary target of NGET for emission footprint reduction by 2050.

Designing a cost effective SF₆ replacement

Decommissioning the existing system with a new approach at all GIS sites would cost billions of pounds, levied directly on UK electricity consumers. To avoid this, the researchers needed to find an environmentally sound SF₆ replacement that did not require the complete replacement of the existing SF₆-deisgned equipment.
Aspiring to eliminate the use of SF₆ from its network by 2050, NGET teamed up with Manchester researchers to devise a transformational solution to achieve wide-scale decarbonisation across the UK transmission network with a retrofill solution.

Optimising an environmentally sound solution

The Manchester team, led by Dr Tony Chen, working from the High Voltage Laboratory, the biggest high voltage research laboratory in UK academia, assembled a gas insulated busbar demonstrator using equipment components designed for SF₆.
A fine balancing act was undertaken between identifying the suitable gas mixture and finding the right operating conditions at which its properties most closely mirror those of SF₆.

Working with C3F7CN, a gas identified as being a good SF₆ alternative for new equipment that’s been optimised by manufacturers, the team were able to identify, optimise and retrofill a suitable C3F7CN mixture within existing busbar and bushing equipment.

As part of this process, the team addressed additional technical challenges such as International Electrotechnical Commission (IEC) type test using full-scale equipment.

Consolidating the results

By taking this approach, Manchester researchers were able to both prove the technical viability of retrofilling existing assets using a C3F7CN based mixture, plus optimise and validate a C3F7CN gas mixture and show - through rigorous type testing - the equivalent electrical performance and more than a 99% reduction in carbon footprint when compared to SF₆ (the carbon footprint reduction takes into account the different densities of C3F7CN mixture and SF₆ at the same pressure).

This demonstration gave NGET the confidence to accelerate retrofill projects on their transmission networks.

A net zero future for electricity

NGET has since awarded Manchester a £1.2 million 4-year project to test at scale how the UK can retrofill SF₆ across its network and assess the long-term gas stability of SF₆ alternatives when operated in a representative outdoor substation environment at Deeside, North Wales.

This breakthrough unlocks the potential of replacing SF₆, without having to replace the equipment completely – resolving a huge environmental and economic challenge and accelerating the UK’s progress towards a net zero future.
Retrofill is now considered a viable intervention option and part of the NGET’s strategic plan to achieve SF₆-free by 2050. The world’s first retrofilled SF₆-free substation equipment now exists in Richborough, successful removing 755 kg of SF₆ from service. This breakthrough work has also won the Best Innovation in Net Zero and Sustainability at the IET E&T Annual Innovation Awards Ceremony in London.