Figure 54 Offshore cable installation works, © Seaway Offshore Cables.
Function
The installation of array cables enables the connection of the wind turbines to the offshore substation whilst the installation of the export cable enables the connection between the offshore and onshore substations.
What it costs*
About £193 million for a 1 GW wind farm. This includes cable-laying vessel, cable burial, cable pull-in and electrical testing and termination. It also includes survey works, route clearance and cable protection systems (not itemised in sections below).
Who supplies them
Marine contractors: Aquatic Engineering and Construction, Boskalis, DEME, DeepOcean, Global Marine, Global Offshore, Huisman, IKM Testing, Jan de Nul, Oceanteam, Seaway 7 and Van Oord.
Cable manufacturers with installation capabilities: Nexans, NKT and Prysmian.
Key facts
All offshore cable installation activities are preceded with a survey to define the route and identify any unexploded ordnance (UXO). This is followed by a pre-lay grapnel run (or alternative method) to clear debris from the cable route.
Offshore cable installation involves cable laying, and in some cases cable burial and trenching. This typically involves one or two runs depending on the ground conditions, the equipment available and the preferences of the developer and contractor.
Test and inspection typically include independent observation of all cable handing and laying operations, often with subsea video recording.
To avoid unnecessary handling, it is preferred that subsea cables are loaded directly onto an installation vessel from the factory. Lengths may be pre-cut.
Cable protection typically falls within the installer’s scope of work (B.1.3 Cable protection). Other techniques like rock dumping and mattresses are also used to ensure burial and protection on cable crossings.