Figure 32 Dynamic array cable. Image courtesy of JDR. All rights reserved.
Function
The network of array cables transfers power from the wind turbines to the offshore substation. It also provides auxiliary power to the turbines when they are not generating and provides fibre communications.
What it costs*
About £76 million for a 1 GW wind farm.
Who supplies them
Array cable manufacturers include Hellenic Cables, JDR Cable Systems, LS Cable & System, Nexans, NKT, Oceaneering, Prysmian, Sumitomo Electric and TKF.
There are other cable manufacturers based in China and Japan, but they have yet to be used widely for UK projects.
Key facts
Array networks are most often designed as “strings” which connect several turbines to the substation. They can also be designed in loops to increase redundancy.
Each turbine is linked to the next with at least 1.5 km of array cable, assuming a 15 MW turbine with 224 m rotor diameter and seven times diameter spacing between turbines.
Array cables are typically rated at 66 kV. In the next few years, array cable voltages are expected to increase to 132 kV. This is to accommodate more efficiently turbines rated at and above 16 MW and to reduce the number of array cable strings required.
Array cables are typically supplied with cable accessories, although the manufacture of accessories may be outsourced. Cable protection may also be included in the supply scope but it is more often part of the installer’s scope.
Cables may be supplied as pre-cut lengths or as a continuous length, depending on the project’s requirements.
Some larger cable manufacturers have cable installation equipment and vessels (see I.5 for further information), but EPCI array cable packages have typically been led by marine contractors.
What’s in it
- Conductor
- Insulator
- Electrical screen
- Optical fibre cable
- Mechanical and chemical protection