National Grid has completed work to upgrade overhead electricity transmission lines north of its Harker substation near Carlisle, strengthening a key cross‑border link that powers homes and businesses in England and Scotland.

Delivered in partnership with principal contractor Morgan Sindall Infrastructure, the work forms part of National Grid’s wider Harker upgrade project. This includes building new 400kV and 132kV indoor substations adjacent to its existing site, enabling new connections and helping to future-proof the network in the region.

The overhead line (OHL) works replaced existing circuits on two separate routes between Harker and the Scottish border with higher capacity wires, with an additional 12km OHL circuit also installed on existing pylons to help improve power flow and reduce congestion.

More than 90km of overhead line has been replaced or installed in total – enough to stretch from Carlisle to Newcastle.

To support the upgraded lines, existing pylons along each route have been refurbished and strengthened, with three new towers added and two older towers set to be removed which are no longer needed.

As part of the substation works, six 184-tonne supergrid transformers are being installed to improve resilience and support the distribution of power to homes and businesses in the area. Five transformer deliveries have already safely taken place, with the final unit scheduled in March.

The new 400kV and 132kV facilities will use gas-insulated switchgear (GIS) technology that is free from sulphur hexafluoride (SF6) – marking another step in National Grid’s commitment to cut emissions of the greenhouse gas from its network by 50% by 2030.

The substation and overhead line upgrades, together with other projects in the region, will help increase the amount of power that can be carried between England and Scotland in future – an increasingly important link as more renewable generation connects to the grid.

Mark Brindley, construction director at National Grid Electricity Transmission, said: “This overhead line upgrade is a significant step in strengthening this crucial part of the network between Harker and the Scottish border. By working closely with our supply chain and minimising disruption to the local community, we’ve delivered a complex engineering project that improves reliability today and creates capacity for cleaner energy in the future.”

The Harker substation and OHL works are separate from National Grid’s Cross Border Connection project, which proposes a new electricity connection between a location near Lauder in the Scottish Borders and the Carlisle area.