Jones Bros wins Carno 3 infrastructure contract

Jones Bros Civil Engineering UK has secured a £46.5 million contract covering major civil and electrical infrastructure for the 45MW Carno 3 wind farm in Powys, including approximately 20km of underground cable required to reinforce part of the existing mid-Wales 132kV network.

The ten-turbine development is owned by Carno 3 LLP, a joint venture between Amegni Renewables and Gresham House. Construction is under way and completion is expected in autumn 2027, adding another sizeable renewable generation project to a part of Wales where grid infrastructure is a central development constraint.

Jones Bros’ scope extends well beyond access roads and turbine foundations. The contractor will construct an on-site substation and control building, undertake electrical cabling, and install the underground circuit running from Welshpool substation to a connection point south of Abermule. The work will reinforce part of SP Energy Networks’ existing 132kV infrastructure while providing the electrical route needed for Carno 3’s output.

The package also includes turbine foundations, upgrades to more than 4.4km of existing access tracks, around 4.7km of new tracks, and highway works required for turbine and equipment deliveries. Up to 90 people are expected to work on the scheme, reflecting the mix of civil, electrical, logistical, and environmental work required before generation can begin.

The 20km connection is particularly significant because it demonstrates how far the enabling infrastructure of a wind farm can extend beyond the turbine site itself. Suitable wind resource and available land do not necessarily coincide with spare network capacity, and new generation can require reinforcement several kilometres away before an acceptable connection can be provided.

At 132kV, the interface involves more than cable capacity. Protection studies must coordinate the new circuit and project substation with the existing network, while circuit-breaker duties, fault levels, earthing, voltage control, metering, and communications all have to meet the network operator’s requirements.

The wind farm’s own electrical system then has to operate inside those limits. Turbine transformers and collection circuits feed power towards the project substation, where switchgear, protection, and control equipment manage the transition into the export system. Reactive-power behaviour and voltage regulation also need to remain within agreed parameters as generation changes with wind conditions.

Using underground cable changes both the civil and electrical design compared with an equivalent overhead route. Construction requires excavation, cable laying, joints, crossings, reinstatement, and coordination with roads, watercourses, utilities, and landowners. Thermal conditions around buried conductors have to be considered because cable rating depends partly on how effectively heat can be transferred into the surrounding ground.

Underground circuits also contribute different electrical characteristics from overhead lines, particularly capacitance. On longer high-voltage routes that can influence reactive-power requirements and has to be considered alongside the wind farm’s transformers and controls during system studies.

The connection work sits alongside a wider project investment exceeding £100 million. Carno 3 has already progressed through financing and turbine procurement, while the Jones Bros contract now puts the balance-of-plant and grid package firmly into construction. Separate turbine, electrical, and civil packages have to converge against the same commissioning programme if the project is to meet its autumn 2027 target.

Once built, the wind farm is expected to generate electricity equivalent to the annual consumption of roughly 46,000 homes. Actual output will vary with wind resource, turbine availability, network conditions, and any curtailment, which makes the reliability of the connection just as relevant to operating performance as the mechanical availability of the turbines.

The site also forms part of an existing generation cluster around Carno. Jones Bros previously worked on Carno II, while Amegni operates earlier wind developments in the area. Additional capacity can make use of regional renewable expertise, but concentrating generation also increases the importance of sufficient export infrastructure.

Commissioning will bring all of those systems together. The new substation and cable route will need to be energised, protection and communications tested, individual turbine circuits brought online, and the completed installation demonstrated against connection requirements. Civil completion is therefore only one milestone in a programme that ultimately has to deliver a functioning 45MW power station.

Carno 3’s ten turbines will remain the most visible part of the development, but the £46.5 million contract shows where much of the engineering effort sits. Twenty kilometres of underground cable, 132kV reinforcement, a new substation, protection, controls, foundations, and site infrastructure are what turn the turbine array into grid-connected generating capacity.