IN Brief:
- National Grid has switched on the second of three new high-voltage circuits linking Dinorwig to Pentir in North Wales.
- The work replaces 1970s-era infrastructure and includes reinforcement at the substation inside the mountain alongside the pumped storage station.
- The upgraded installation uses a hybrid combination of SF6 and clean-air GIS technology as the final circuit moves toward completion.
National Grid has energised the second of three new high-voltage electricity circuits connecting Dinorwig hydroelectric power station to the transmission network in North Wales, marking another stage in the replacement of infrastructure installed between Dinorwig and Pentir substation in the 1970s.
The latest circuit follows the first new connection, which entered service in January 2025. Work has been under way since autumn 2021, with Morgan Sindall Infrastructure and Siemens Energy delivering the upgrade programme. The scheme is designed to maintain the long-term connection between the Dinorwig pumped storage station and the wider transmission network as reinforcement work continues on both the cable route and the substations at either end.
Dinorwig remains one of the UK’s most important sources of fast-response generation, providing flexible output that can be brought online rapidly to support grid stability. National Grid said reinforcement work is continuing at Dinorwig substation, which sits within Elidir Fawr mountain alongside the power station and connects its output to the transmission system through the new circuits.
The upgraded substation includes a hybrid arrangement using SF6 and clean-air gas insulated switchgear technology. That forms part of National Grid’s wider programme to reduce SF6 emissions across its network while modernising critical transmission assets. With the second circuit now in service, attention turns to completing the third new circuit and continuing the remaining works at Pentir and Dinorwig.
The cable replacement scheme sits alongside broader network investment in North Wales, where National Grid is also progressing the separate Pentir to Trawsfynydd reinforcement project. Together, the works reflect the growing need to strengthen transmission infrastructure in areas expected to play a larger role in balancing demand, integrating cleaner generation, and maintaining system resilience.
