National Grid SF6 loses are in the region of 12,000kg per annum from Air Insulated and Gas Insulated Switchgear (AIS and GIS). Given that SF6 has a global warming potential 24,000 times worse than CO2 this results in ~ 306k tonnes CO2eq per annum or circa 30% of National Grid's UK carbon emissions. The majority of these losses come from a few of our largest leakers, often where it is difficult to gain an outage or where our various repair techniques prove ineffective - for example leaks from Littlebrook 400kV substation represents 10% of our UK losses alone.

Objectives

The immediate challenge is for a team from across National Grid and external suppliers to review the current leak repair methodology and implement changes to attempt to ensure leak repairs are 100% efficient. Previous experience has identified that this has not always achievable due to a number of influencing factors.

Where a leak repair, going forward, is not successful a means of capturing the fugitive emissions is required. A methodology has been trialled around a leaking SF6 gas insulated switchgear flange to prove its effectiveness during the latter part of 2012. This method utilised diverting the fugitive emission through an adsorbent material (activated carbon) which once saturated would allow the gas to reclaimed by further processing. Although this trial was successful its future sustainability is questionable therefore design changes have been made which enable the gas to be collected and pumped into a storage vessel.

Both designs are based around, ideally, not needing an outage to install it, but if an outage is required because the leak infringes safety distances, it should be able to be installed within 2 days to enable installation within a weekend outage. The bottle reclamation principle is being carried forward and a prototype system is currently being designed.

In addition work is being conducted with the University of Liverpool to analyse the carbon captured SF6 to assess its suitability for re-use after reprocessing.