Subsea Cables

Copper technology is on the verge of a breakthrough that will allow deep-sea power cables to operate at higher voltages (beyond 170 kilovolts) and at greater depths than ever before.

Engineers and scientists have developed and are testing fatigue-resistant, compliant copper sheath that will replace the lead sheaths used in today’s subsea cables.

A copper sheath is expected to decrease the weight and diameter of the cable, producing lighter cables, with higher voltage and higher power transmission capacity.

The market for high voltage subsea power cables is expanding in offshore oil/gas production platforms, wind farms and power grid applications. There is industry pressure to move to 420 kV XLPE insulated power cable systems, and at depths up to more than 1,000 metres and spanning up to 200 km. The current lead sheath cannot be used for this application as it is not adequate to meet the 40-year lifetime requirement.

Higher voltage requires thicker electrical insulation, and this insulation expands and contracts with temperature changes created by variations in the cable loading and the enormous external pressure of water at hundreds of meters beneath the sea.

As the insulation heats and expands, it creates large mechanical stresses on the surrounding watertight metal sheath. When the cable cools, the insulation contracts and the external pressure compresses the sheath. The sheath will eventually crack as a result of fatigue and allow water to migrate into the insulation causing the cable to fail. These problems are intensified as the diameter of the cable and the depth of operation increase.


In addition, subsea cables are used increasingly to provide power to offshore platforms and floating production units. In these dynamic applications, the cable must withstand mechanical movements caused by ocean waves and currents. This also places increased demands on the fatigue resistance of the cable sheath.

The test of strength for the copper sheath will be whether it can keep water out of the insulation, as well as withstand many expansion/contraction cycles and mechanical movements.

Extensive prototype development and testing activity is currently underway, with the hopes of achieving commercialization of copper-sheathing in the near future.