Direction on Scottish Hydro Electric Transmission's Insulation and Interruption Exceptional Event claim


Publication date


Industry sector

Transmission Network

Licence type

Electricity Transmission Licence

Electricity transmission companies are financially incentivised to reduce the leakage of Insulation and Interruption Gases (IIG), which are used in some transmission equipment. Some IIG, such as sulphur hexafluoride (SF6), are potent greenhouse gases. Some leakage of SF6 is expected from normal operating assets, therefore a target quantity of IIG (measured in kg) leaking from all network assets is set for each company. Each company is then rewarded or penalised through a revenue adjustment based on how it performs each year against the target.

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 and for all or some of the quantity of IIG leaked during the event to be excluded when we calculate the company's revenue reward or penalty.

On 5 July 2022 we issued a notice of our intention to direct that, for the purpose of calculating its volume IIG leakage for 2021/22, Scottish Hydro Electric Transmission should exclude 34 kg related to an Exceptional Event on its network which occurred on 12 to 13 December 2021. After allowing 28 days in which representations could be made, the Authority directs that for the purpose of calculating the licensee’s IIG leakage, 33.92 kg related to this Exceptional Event shall be excluded for the 2021/22 regulatory year.