Onshore cable route
The onshore infrastructure required to bring the electricity from the export cable landfall site at Carnoustie on to the national electricity network includes:
approximately 19km of underground electricity transmission cables from Carnoustie to Tealing (near Dundee)
a new dedicated Seagreen substation at Tealing with Petrofac being the Tier 1 Contractor for these works
an extension to the footprint of the existing SSEN substation at Tealing to facilitate connecting Seagreen to the national electricity network.
Construction on the extension to the existing substation at Tealing began at the start of 2020 and is being managed by SSEN Transmission.
Construction of the new Seagreen substation began in March 2020 and is being managed by Seagreen Wind Energy Ltd (SWEL).
The construction of the underground cable route began in August 2020 and is being managed by SWEL.
The onshore element of the export cable installation works began in August 2020 and is being undertaken by Nexans as Principal Contractor. Nexans are responsible for the design, supply and installation of the offshore and onshore cabling.
The activities being undertaken during cable installation include:
Creation of temporary haul and access roads
Creation of temporary compounds and storage areas
Excavation of trenches and installation of cable ducting
Excavation of cable 'pits'
Installation of 'joint bays'
Laying of cable through installed ducting
Reinstatement of the ground once work is complete
The cable route includes the requirement to cross roads, railways and watercourses. These are being crossed either by using Horizontal Directional Drilling (HDD) underneath where appropriate or the use of 'open cut' techniques where roads are trenched, ducting installed and the road reinstated again. Where open cut is used, vehicular access will be maintained through the use of traffic management.
Seagreen will have a three circuit 220kv High Voltage Alternative Current (HVAC) connection which means that there will be three sets of cables installed, side by side, along the entire cable route.
The majority of the cables are being directly installed in conventional open cut trenches or in ducts laid within trenches. There will be three cable trenches within the working corridor.
Joint bays are needed to join the lengths of cable together along the route as cable lengths are restricted to allow them to be safely delivered by road. Joint bays are simple underground concrete chambers which enclose and protect the cable joints.
Pulling pits are temporary excavations which are required for the pulling operations - when the cables are pulled through the installed ducting. This short video shows the cable pulling process:
Once the pulling is complete, the pits will be reinstated back to existing ground levels.
We've made a short video which shows how the cables are pulled:
A variety of best practice and mitigation measures will ensure that construction of the onshore infrastructure does not result in unacceptable environmental effects. Construction work has been preceded by extensive surveys and studies and is subject to ongoing assessment.
Potential impacts such as noise, dust and air quality and traffic will be controlled through conditions attached to the planning permissions.
A suitably qualified and experienced Ecological Clerk of Works (ECoW) is employed for the duration of the works. The ECoW works to ensure compliance with the Construction Environment Management Plan (CEMP) and wider environmental protection legislation and best practice.