Towy-Usk grid connection proposal

132kV transmission line, approximately 355 pylons and 94 wood poles, over about 60 miles.

This was announced early 2023, with initial public consultations in March. Significant revisions to the proposals were made in spring 2024, with more detail about pylon locations. Further revisions to the route were made in March 2026 and again in October with another round of public consultations scheduled for Autumn 2026.

The original proposal was for standard steel pylons, probably L7 type, average height 27 metres, variable depending on terrain up to 36 metres, typical span between pylons 250 metres. They would carry dual circuit conductors with a quoted power capacity of around 800MW. A revision for Autumn 2026 proposes the use of a monopole pylon type in place of the lattice towers. The monopole pylons would be of a completely new design, at this time only seen as a computer generated image, and said to be of lower height than the lattice pylons at an average of 22 metres. At the moment it is not finalised if they will be single-circuit or dual-circuit. The proposal involves the use of a newly developed conductor cable known as ACCC-Cardiff, enabling a single circuit capacity of approximately 575MW. ACCC-Cardiff is a variation of ACCC, Aluminum Conductor Composite Core, cable that has a higher current capacity than traditional cables. The span between monopoles is the same at 250 metres, which is reflected by the newly revised detail plans of the route. Both pylon design types would include variation options for straight-line, direction change and terminal locations.

Route is from Nant Mithil Energy Park, Radnor Forest, to Llandyfaelog south of Carmarthen. Originally all overhead lines on pylons, the route has had several revisions. First section from the Nant Mithil substation to Hundred House is now single circuit on wood poles and there is an underground section near Llanarthne. The remaining route is overhead cables on steel pylons, now specified as monopole towers.

From Hundred House the route goes across the River Wye and around the south of Builth Wells, then through the Irfon and Towy valleys. Despite the project name, it does not run directly near the Usk. A large part of the route roughly follows the Heart of Wales railway line, which is strongly promoted as a tourist attraction. Internationally known for the striking beauty of its surrounding landscape, the railway line was named as one of the best train journeys in the world by National Geographic magazine. The pylon route and Heart of Wales rail line can be seen together on the Re-Think edition of our interactive map.

The purpose of the Towy-Usk pylon line on its initial announcement was connection of the proposed Nant Mithil Energy Park at Radnor Forest. Two other nearby wind farms were added soon after, Aberedw and Bryn Gilwern. In the latest planning revisions, Aberedw Energy Park extends to the A481 with its substation located adjacent to the start of the Towy-Usk pylons section. Bryn Gilwern Energy Park has its own wood pole overhead line connecting the wind farm substation to the same location. This is a separate Green GEN Cymru planning project.

The latest Towy-Usk revision includes a switching station near Llanwrda, at an approximately half-way position along the line, enabling compensation for voltage drop over the long cable runs. It replaces the previous switching station location near Hundred House, where smaller, simpler junction infrastructure will connect the Bryn Gilwern wood pole line and Aberedw Energy Park substation in addition to Nant Mithil.

The more recently proposed Garreg Fawr Energy Park, to the north of Sennybridge (which is on the River Usk), will also connect to the Towy-Usk line. This is another separate Green GEN Cymru project for a 132kV wood pole overhead line. At this time there is no published route although we understand it will most likely connect to the Towy-Usk line south-east of Builth Wells at monopole number T023.

A further large wind farm, Banc y Ceyn, is proposed south of Builth Wells by the Wind 2 Limited. The proposal documentation is evasive regarding the grid connection, however some kind of link to the Towy-Usk line might be a logical possibility.

References (external, open in new tab):

Green GEN Cymru Towy-Usk project website

PEDW planning casework: Green GEN Towy-Usk Project

PEDW planning casework: Nant Mithil Energy Park

Green GEN Cymru Bryn Gilwern project

PEDW planning casework: Bryn Gilwern Overhead Line

Green GEN Cymru Garreg Fawr project

PEDW planning casework: Banc Y Celyn Energy Park

National Geographic: Best train trips in the world (No.11)