Sulphur Hexafluoride (SF6) is a potent and persistent greenhouse gas which has been used in electrical switchgear for many years, due to its excellent electrical insulation and arc-quenching properties. Work is underway to find a suitable replacement for SF6, but until alternative solutions are found and successfully deployed, some ageing assets continue to leak and need to be managed. The overall aim of this project was to reduce Sf6 emissions from leaking plant and equipment on electricity networks.
THE SOLUTION
Following a call for innovation facilitated by the EIC in 2021, National Grid Electricity Transmission selected a proposal from Rawwater Applied Technology Limited. Part of the proposed solution involves the use of the M3CollarCast process, which entails the injection of the novel low-melting point alloy, currently used for the sealing of oil leaks, to adapt it for the sealing of gas leaks in electrical transmission switchgear.
Rawwater had previously proven the feasibility of using their M3CollarCast process to heavily mitigate leaks on small bore pipework. The challenge remained to develop this into a cost effective and flexible process, specifically targeting SF6 leaks on a wide range of small-bore pipework connectors.
APPROACH
The TST(E) is a development project resulting from an original call to innovation launched in 2017, which led to the development of the mk2 TST Pole Current indicator.
This unit was subsequently trialed by UKPN and SSEN, successfully confirming the unit had the capabilities to detect earth leakage on un-earthed installations, but required further development.
The EIC facilitated a subsequent development project, coupled with a further call to innovation issued in June 2020, which is due to complete in Q4 2024 after extensive fi eld testing of the final design through summer 2024. This will deliver a unique BAU ready device.
PARTNERS
This collaborative Network Innovation Allowance (NIA) project led by National Grid Electricity Transmission was delivered by Rawwater Applied Technology Ltd, with the support of SSEN Transmission and SP Transmission. The EIC facilitated project plan development and legal contract discussions. The EIC also supported the delivery of the project to ensure completion on time and budget.
The project has successfully progressed the solution from TRL 4 to 8, which can now be adopted into business as usual. This technology will both reduce the volume of harmful emissions of SF6 gas to the environment and deliver significant financial benefits.
THE PROJECT
The first step was for the network partners to investigate all SF6 -filled equipment at substations across their networks and identify the different configurations of pipework and joints causing problems. Rawwater analysed these to identify the ‘top ten’ problem areas, which were reviewed by the networks to prioritise their top three areas.
Sealing of each leak at these sites, required a mould to be fitted around the leaking component, into which the molten metal alloy is poured and allowed to cool and solidify. Raw water considered several options for creating these modular moulds, before selecting the most suitable option to apply the M3CollarCast process.
The project involved many iterations of mould modification and in-house testing before performing trials using the final design at selected substation sites.
- The concept of a cost-effective, reversible and non-destructive leak sealing system was
demonstrated - Leaks of SF6 gas were sealed on live equipment without the need for an outage or to de-gas the
switchgear - The new approach to producing bespoke moulds for similar geometries enabled leaks to be
sealed in much shorter timescales than was possible previously, in a matter of weeks rather than
months.
NEXT STEPS
Following the success of the pilot trials, the transmission networks are working on incorporating this
technology into their business-as-usual leak repair processes.
The solution also has the potential for repairing leaks on the distribution networks.