What Are Power Cables?

Power cables are insulated electrical conductors used to transmit and distribute electrical energy between generating stations, substations, and end-use loads. Unlike bare overhead conductors, power cables enclose the current-carrying conductor within layers of insulation and protective sheathing, allowing installation underground, through conduits, underwater, and in locations where open conductors would present safety or space constraints. Power cables operate across a broad voltage spectrum, from low-voltage distribution below 1 kV through medium-voltage feeder circuits at 11 to 35 kV, up to extra-high-voltage transmission systems operating at 400 kV AC or higher for HVDC links.

The engineering of power cables draws on conductor materials technology, polymer and paper dielectrics, thermal management, and civil or marine installation practice. Standards governing power cable design, testing, and installation are produced by IEC, IEEE, and CIGRE, with the IEC 60228 series covering conductor requirements, the IEC 60840 and 62067 series governing extruded insulation cables at high voltage, and IEEE 400 addressing field testing of shielded cable systems.

Conductor and Insulation Design

The conductor is the central element, typically made from stranded copper or aluminum wire laid up in concentric layers. Aluminum is preferred for large transmission cables because its lower density reduces weight and mechanical tension in submarine and underground installations, while copper offers higher conductivity per unit cross-section and is favored where space is constrained. The conductor is surrounded by a semiconducting conductor shield, which smooths surface irregularities that would otherwise concentrate the electric field at the insulation boundary. Cross-linked polyethylene (XLPE) is the dominant insulating material for medium-voltage and high-voltage cables, valued for its high dielectric strength, low dielectric loss, and resistance to the thermal and electrical stresses of continuous operation. Research collected in PMC on XLPE nanocomposite insulation for high-voltage cables examines how nano-filler additives can reduce space charge accumulation and extend dielectric life. Over the insulation sits a semiconducting insulation shield and a metallic screen, typically concentric copper wires or a corrugated aluminum sheath, which carries fault current and provides electrostatic shielding.

Shielded and Submarine Cable Systems

Shielded power cable systems use the metallic screen as a functional part of the insulation system, maintaining a defined ground reference around the insulation and intercepting any fault current before it can cause injury or damage to adjacent infrastructure. Screen bonding arrangements, including single-point bonding and cross-bonding of the screens in sections, manage induced circulating currents and sheath voltage rise under normal load. Submarine power cable systems carry power across bodies of water, serving offshore wind farm export connections, island power supply, and international grid interconnection. Submarine cables add armoring, typically one or two layers of galvanized steel wire, to resist mechanical damage from anchors, fishing gear, and the stresses of installation and seabed movement. The JRC technical survey of HVDC submarine power cables documents installed links at voltages up to 450 kV with route lengths exceeding 500 km, using both mass-impregnated and extruded polymer insulation technologies. IEC 60287 provides the thermal rating methodology used to determine the maximum sustained current that a buried or submerged cable can carry without exceeding conductor or insulation temperature limits.

Installation and Current Rating

Underground cable installation uses direct burial in a prepared trench, installation in buried ducts, or placement in cable tunnels. The installation method affects the thermal environment of the cable, which determines the current-carrying capacity: cables in air tunnels dissipate heat more readily than direct-buried cables surrounded by soil, allowing higher continuous ratings. Joints and terminations are installed at intervals wherever cable drum lengths end or where the cable connects to an overhead line or apparatus. These accessories must be factory-tested and field-installed by qualified technicians because they are the most common points of cable system failure. The IET study on failure mechanisms in submarine high-voltage cables identifies accessory failures, corrosion of metallic sheaths, and mechanical damage as the dominant failure categories in offshore cable systems, findings that shape both design standards and maintenance practice.

Applications

Power cables have applications in a wide range of disciplines, including:

• Underground urban distribution networks where overhead lines are restricted
• Offshore wind farm array and export cabling connecting turbines to substations
• HVDC bulk transmission links between regional or national grids
• Industrial and commercial building power distribution systems
• Railway traction power supply and transit system electrification