Green light for National Grid’s £252m ‘SF6-free’ site upgrade

Ofgem has approved the final needs case for National Grid Electricity Transmission’s (NGET) planned £252.6 million upgrade of its Harker site in Cumbria.

The plans consist of an offline rebuild of 132kV and 400kV substations, along with the rationalisation of the 275kV substation.

The proposal also includes the implementation of SF₆-free solutions across the site.

Sulphur hexafluoride, known as SF₆, is the most potent greenhouse gas in existence but it plays a vital, and often irreplaceable, role in insulating switchgear on the electricity network.

In approving the final needs case for the Harker project, Ofgem said that it expects NGET “will do everything reasonably practicable to deliver a sulphur hexafluoride (SF6) free solution”.

However, it concedes that SF₆-free solutions do not yet exist for parts of the project’s scope.

In particular, consultation responses raised a number of concerns about the proposals for an SF₆-free solution, including:

• A type-registered SF6-free solution does not yet exist for the 400kV equipment required for Harker, and the current expectation for completion of type testing is March 2024. The success of such type testing is outside of the control of both NGET and its delivery contractor.
• There are certain instances where individual circuit breaker(s) may need to be of an SF6 variant as at present SF6 free technologies will not be adequate for the duties required, namely in limited reactive control instances.

Consequently, Ofgem accepts that SF₆-free “innovation […] carries a risk of delay to the delivery programme and the potential for higher costs due to delays and early adoption risk”.

The regulator does however point out that the Harker scheme is not be the first GIS switchgear in the UK to attempt to minimise SF₆.

It adds: “NGET are in the process of delivering 400kV gas insulated switchgear at Bengeworth Road Substation, where SF₆ will only be present in the interruption components. SF₆-free insulation mediums will be in use for the remaining switchgear.

“We expect NGET to lean on this experience in their solution for Harker and adopt a similar approach if reasonably practicable.”

The total scope of works at the Harker site includes:

• Construction of new 132kV and 400kV substations, incorporating any extension and up ratings required for new circuits and additional supergrid transformers.
• Tendering for SF6-free solutions across the site.
• Addition of six 400/132kV 240MVA transformers to replace existing transformers, providing capacity required for present and future load drivers.
• The removal of the 275kV substation as it is no longer needed, but maintaining existing connection to Stella West and Fourstones connected to the 400kV substation.

The need for the upgrades has been “triggered by several interfacing drivers which include asset health, several new customer connections, proceed signals under the Network Options Assessment (NOA) and environmental concerns”.

The project is slated for delivery by 2026 under the LOTI mechanism as part of the RIIO-2 price control.

NGET’s description of the project adds: “Our plans allow us to provide the improvements required to maintain the existing electricity transmission system. They will also ensure the substation is prepared for future demand so it can continue to serve as a critical point of intersection on the UK energy network, connecting supplies between Scotland to England.

“This work is part of National Grid’s contribution to the government’s target to achieve net zero carbon emissions by 2050. To meet these targets, more generation from renewable energy sources such as wind needs to be connected to the electricity network. Our proposed work will provide additional network capacity to accommodate this generation.”

The plans have also been approved by Cumberland Council.

Earlier this year, Utility Week looked at the work that was being done to reduce SF_6, and asked industry experts if electricity networks are doing enough.