Function
The cable core contains the conductor through which power is transferred. The rest of the core consists of screens, insulation, and sheathing to protect the conductor and prevent short circuits.
Who supplies them
Cable cores are typically manufactured by the cable manufacturer such as JDR Cables. Usually, complete cable cores are manufactured and assembled at the same site to reduce the transportation costs of the different components.
Key facts
The core is typically made up of the conductor, a screen, insulation and a protective sheath.
The conductor may be stranded copper or aluminium. Both have low resistance, excellent conductivity, are ductile, and are relatively resistant to corrosion. Copper has a higher conductivity, 60% greater than aluminium for the same cross section, but is more expensive and the price is more volatile. Aluminium is lighter, and therefore easier to handle. The cable should at least have a conductor cross-section adequate to meet the system requirements for power transmission capacity. Energy losses can be reduced by using a larger conductor with a greater current carrying capacity but at a greater capital cost.
The conductor screen is a semiconducting tape that surrounds the conductor, maintains a uniform electric field, and minimises electrostatic stresses on the cables.
Most subsea cables used in offshore wind are insulated with cross-linked polyethylene (XLPE). This is due to its excellent strength and rigidity. HVDC systems have traditionally used mass impregnated cables with paper-based insulation as they can be manufactured and installed in long lengths and are available at higher voltages. Modern HVDC cables mostly now use XLPE insulation as it can operate at a higher temperature and are lighter so easier to handle during installation. Surrounding the insulation is a further screen, similar to the conductor screen.
The sheath has historically been lead but alternatives are being developed on environmental grounds.
A 220 kV AC subsea cable conductor typically has a cross-sectional area of between 800 mm2 and 1,600 mm2 with 23 mm of insulation.
A 320 kV DC cable conductor typically has a cross-sectional area of between 1,000 mm2 and 2,500 mm2 with 25 mm of insulation.
What’s in it
- Conductor
- Conductor screen
- XLPE insulation
- Insulation screen
- Lead sheath