Offshore construction
Offshore cabling
Specialist offshore cable laying vessels were used to install the offshore subsea electricity cables. There are two types of subsea cables - 'export cables' and 'inter-array cables'.
The export cables take the electricity from the offshore substation to the landfall point at Carnoustie.
The inter-array cables form a network within the wind farm site and take the electricity generated by the wind turbines to the offshore substation.
In both cases, the cables were installed by the specialist vessels following careful survey and route clearance. The aim is for cables to be buried wherever possible, however, where this is not possible due to seabed conditions, cables will be protected using rock placement.
The manufacture and installation of the offshore cabling provided significant employment and business opportunity.
The image below (© Nexans) shows the cable laying vessel 'Nexans Aurora' within the Seagreen site laying export cables from the offshore platform (shown to the right of the image) and landfall at Carnoustie.
Offshore substation
The offshore substation is essentially the backbone of the wind farm, taking the electricity generated by the turbines and converting it to the voltage required for onward transmission to the onshore substation at Tealing.
The substation (installed in January 2022) is secured to the seabed via a 5,100t jacket substructure, which will play a critical role in safely supporting the substation topside above the sea during Seagreen's 25-year operational lifespan.
With a 43m x 43m footprint, the jacket has built in tubing designed to guide the incoming 15 inter-array cables bringing the electricity generated by the turbines to the substation. There is additional tubing which guides the three outgoing export cables from the substation to the seabed.
The 4,800t topside was installed in March 2022, measuring in at 40m long, 45m wide and 15m high. The complete structure of topside and jacket foundation sits in water depths of around 55m and will be one of the largest AC platforms in UK waters.
The image below shows the offshore platform (yellow) with a jack up commissioning vessel alongside (grey) and another support vessel.
Turbine installation
The installation of the turbines was undertaken by the specialist heavy lifting vessel 'Wind Osprey' and other support vessels. Such support vessels include local fishing vessels who are employed as guard vessels throughout the offshore construction phase ensuring a safe construction zone for all marine traffic.
The 'Wind Osprey' would jack-up at each turbine location, as shown in the image below, before carefully installing a turbine tower, nacelle and three blades before lowering back in to the water and moving on to the next location.
The vessel could carry enough components for up to five wind turbines on each sailing and, in optimal conditions, a turbine could be installed in fewer than 36 hours,
