National Grid has energised the second of three new high-voltage electricity circuits linking the Dinorwig hydroelectric station to the transmission network in North Wales, marking a further milestone in strengthening a key part of Britain's grid.

The switch-on follows the first new circuit coming online in January last year and sits within a wider programme to replace equipment first installed in the 1970s between Dinorwig and the Pentir substation. The Dinorwig pumped storage facility, located within Elidir Fawr mountain in Gwynedd, provides rapid-response generation that helps stabilise the system. It is owned and operated by First Hydro, a company 75% owned by ENGIE.

Since autumn 2021, National Grid and its delivery partners Morgan Sindall Infrastructure and Siemens Energy have been overhauling the station’s connection to ensure clean power from Dinorwig continues to be delivered reliably for decades ahead.

Reinforcement works are also advancing at the Dinorwig substation, which sits inside the mountain alongside the pumped storage plant, tying its output into the grid through the new circuits.

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The upgraded substation includes a hybrid arrangement of SF6 and ‘clean air’ gas-insulated switchgear (GIS), supporting National Grid’s objective to halve SF6 emissions from its network by 2030.

With the second circuit now operational, attention shifts to completing the final new circuit and continuing works at both Pentir and Dinorwig substations to further bolster the regional network.

During these works, a temporary road closure remains in place on the lane between Brynrefail and Fach-wen to protect residents and construction teams while activity continues. A diversion via Deiniolen – agreed with Cyngor Gwynedd – is signposted, and alternative footpath routes are marked on affected sections of the Llyn Padarn circular walk. National Grid is providing regular updates to local residents and businesses about the diversions.

Mark Brindley, construction director at National Grid, said: "Switching on the second new circuit is a major step forward for this project. We're strengthening a vital clean energy link in North Wales and ensuring Dinorwig can continue to power homes, businesses and communities for years to come. We're immensely grateful for the continued patience and understanding of local communities as we push ahead with the final phase of this complex once-in-a-generation project."

Peter Kirk, managing director – energy at Morgan Sindall Infrastructure, added: "We're proud to be delivering this important work in North Wales, helping to bring cleaner energy onto the UK national grid and strengthen the resilience of the network. Energising the second circuit is the latest success story of strong collaboration, as we apply an innovative approach to upgrading existing circuits and boosting capacity between the Dinorwig and Pentir substations in a challenging environment."