Gwynt-y-Môr OFTO plc cannot claim that a series of planned outages to fix SF6 leaks were an ‘exceptional event’ out of its control, Ofgem has decided.
The OFTO, which owns and operates the transmission link that connects the Gwynt-y-Môr wind farm to the onshore grid under licence, had to undertake a series of planned outages between 10 December 2020 and 26 April 2021 in connection with a leak in sulphur hexafluoride (SF6), an insulating gas used in switchgear that represents a large greenhouse gas risk (24,000 times that of carbon dioxide). The SF6 gas was leaking at a pipework joint on a transformer on an offshore platform.
The OFTO used the outages to conduct investigations, top up the SF6 gas and to carry out a permanent repair.
The OFTO said the SF6 gas leak cannot be considered as‘wear and tear’ as the asset had been maintained in accordance with the Original Equipment Manufacturer instructions. It assumed that the root cause of the event occurred before the OFTO took over the project but it did not persuade Ofgem of that.
An independent technical report carried out by RINA Tech (UK) Limited found differing levels of corrosion on the fasteners, which it said may indicate a difference in the level to which they were torqued and a lack of paint on some of the fastener heads suggesting that they were not all from the original installation. It said “the root cause of the leak was a combination of factors associated with the joint design, variability in the joint assembly and inadequate corrosion resistance, due to either the material selected for use in the equipment or the protection/coating methods used”. Ofgem said poor equipment maintenance was never considered in the RIMA report.
The global warming potential of SF6 means it is tightly controlled in onshore networks and research is ongoing into less damaging replacements.

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