Underwater transmission cables, such as submarine power cables, are used to transport electric power below the sea water’s surface. For this reason, they’re known as “submarine” power cables; however, it’s also conceivable to utilize these cables beneath freshwater (large lakes and rivers).
In 1811, the Isar River in Bavaria was crossed by the first undersea cable to deliver electricity. Through advances in technology and design, submarine power cables have grown in capacity and length over the years.
It has become increasingly important to use underwater power cables in recent years. In order to get the renewable energy generated offshore to the mainland, export cables from wind, wave, and tidal plants are required.
Submarine Power Cables Types
Submarine power cables can range in diameter from 70mm to more than 210mm and are available in AC or DC types. The route length, power, transmission capacity, and Grid synchronization all play a role in determining which type of cable to employ.
AC is often the most cost-effective system for a route shorter than 80 kilometers in length since it is the cheapest technology, but it is restricted by its range. On the other hand, DC technology is used for longer distances. In order to increase the cable length, greater system voltages are being used.
Submarine Power Cables Composition
Submarine power lines carry high-voltage electric currents under the sea. There are usually two types of power cables:
1- 3 Phase AC cable
2- Co-Axial High Voltage DC cable
Inner conductor, electric insulation, and protective layers form the core of the electric core, which is a concentric arrangement (resembling the design of a coaxial cable). In addition to electrical conductors, modern three-core cables sometimes contain optical fibers for data transfer or temperature measurement.
Copper or aluminum wires are used to make the conductor. Conductors with a surface area smaller than 1200 mm2 are the most frequent, while larger ones up to 2400 mm2 are less used. Strings of round wires can be used as the conductor, or it can be a solid wire.
Currently, three forms of electric insulation are employed around the conductor:
- Up to 420 kV, XLPE is used. It is extruded and has an insulation thickness of up to 30 mm. Certain XLPE insulating compositions can also be utilized for DC.
- Low-pressure oil-filled cables feature paper-wrapped insulation. This is a low-viscosity insulation fluid impregnated cable core. A central oil channel in the conductor improves oil flow in cables up to 525 kV but is rarely used in underwater cables because of the risk of oil contamination.
- This cable type has paper-lapped insulation, but the impregnation chemical is very viscous and does not leave when the cable is broken. It is possible to insulate huge HVDC cables using mass-impregnated insulation up to a voltage of 525 kV.
An extruded lead coating protects cables under 52 kV against water. Extruded in long lengths, the lead alloy is applied to the insulating material (over 50 km is possible).
The product at this point is known as cable core. A concentric armoring surrounds the core of single-core wires. Before the armoring is applied to three-core cables, the cable cores are arranged in a spiral pattern.
In AC cables, the alternating magnetic field causes losses in the armoring hence non-magnetic metallic materials are sometimes used (stainless steel, copper, brass).
Submarine Power Cables Around the World
When Gotland 1 was installed in 1954, it was the first subsea HVDC cable in the world. This 98-kilometer-long cable, which connected Gotland Island to Sweden’s mainland, could produce 20 megawatts of power.
Since previously unreachable nations may now be connected, this revolutionized the way the world views undersea power transmission.
The NorNed cable, which connects Norway and the Netherlands, is currently the longest interconnector. It is the world’s longest submarine power cable, stretching 580 kilometers and carrying 700 megawatts of power.
The most recent cable technology, on the other hand, has a potential range of 1,500 kilometers. Many power cables are now connecting the world together, and you could easily browse the world map and find out how many cables is connecting your country with the world using this website: