Decision on Insulation and Interruption Gas Exceptional Event Claim for Scottish and Southern Electricity Networks (SSEN) at Blackhillock

Ofgem received a notification from SSEN Transmission on 1 November 2024 regarding a leakage event of 6.115kg of Sulphur Hexafluoride gas (SF6) at its Blackhillock substation, which occurred on 19 October 2024.  

Companies are financially incentivised to reduce the leakage of Insulation and Interruption Gases (IIG), such as SF6, which are used in some transmission equipment. If an IIG leak occurs on a company's network due to an event that it believes was beyond its reasonable control then the company may make a case to the Authority to designate it an Exceptional Event for all or some of the quantity of IIG leaked during the event; and for it to be excluded from the calculation of the company's revenue reward or penalty.

This letter sets out the Authority’s decision to reject SSEN Transmission’s claim for an IIG Exceptional Event that occurred on its network on 19 October 2024.