Submarine power cable

A submarine power cable is a transmission cable for carrying electric power below the surface of the water.[1] These are called "submarine" because they usually carry electric power beneath salt water (arms of the ocean, seas, straits, etc.) but it is also possible to use submarine power cables beneath fresh water (large lakes and rivers). Examples of the latter exist that connect the mainland with large islands in the St. Lawrence River.

Cross section of the submarine power cable used in Wolfe Island Wind Farm.

Design technologiesEdit

The purpose of submarine power cables is the transport of electric current at high voltage. The electric core is a concentric assembly of inner conductor, electric insulation and protective layers (resembling the design of a coaxial cable).[2] Modern three-core cables (e.g. for the connection of offshore wind turbines) often carry optical fibers for data transmission or temperature measurement, in addition to the electrical conductors.


The conductor is made from copper or aluminum wires, the latter material having a small but increasing market share. Conductor sizes ≤ 1200 mm2 are most common, but sizes ≥ 2400 mm2 have been made occasionally. For voltages ≥ 12 kV the conductors are round, so that the insulation is exposed to a uniform electric field gradient. The conductor can be stranded from individual round wires, or can be a single solid wire. In some designs, profiled wires (keystone wires) are laid up to form a round conductor with very small interstices between the wires.


Three different types of electric insulation around the conductor are mainly used today. Cross-linked polyethylene (XLPE) is used up to 420 kV system voltage. It is produced by extrusion, with an insulation thickness of up to about 30 mm; 36 kV class cables have only 5.5 – 8 mm insulation thickness. Certain formulations of XLPE insulation can also be used for DC. Low-pressure oil-filled cables have an insulation lapped from paper strips. The entire cable core is impregnated with a low-viscosity insulation fluid (mineral oil or synthetic). A central oil channel in the conductor facilitates oil flow in cables up to 525 kV for when the cable gets warm but rarely used in submarine cables due to oil pollution risk with cable damage. Mass-impregnated cables have also a paper-lapped insulation but the impregnation compound is highly viscous and does not exit when the cable is damaged. Mass-impregnated insulation can be used for massive HVDC cables up to 525 kV.


Cables ≥ 52 kV are equipped with an extruded lead sheath to prevent water intrusion. No other materials have been accepted so far. The lead alloy is extruded onto the insulation in long lengths (over 50 km is possible). In this stage the product is called cable core. In single-core cables the core is surrounded by a concentric armoring. In three-core cables, three cable cores are laid-up in a spiral configuration before the armoring is applied. The armoring consists most often of steel wires, soaked in bitumen for corrosion protection. Since the alternating magnetic field in AC cables causes losses in the armoring those cables are sometimes equipped with non-magnetic metallic materials (stainless steel, copper, brass).

AC or DCEdit

Most electrical power transmission systems use alternating current (AC), because transformers can easily change voltages as needed. High-voltage direct current transmission requires a converter at each end of a direct current line to interface to an alternating current grid. A system using submarine power cables may be less costly overall if using high-voltage direct current transmission, especially on a long link where the capacitance of the cable would require too much additional charging current. The inner and outer conductors of a cable form the plates of a capacitor, and if the cable is long (on the order of tens of kilometres), the current that flows through this capacitance may be significant compared to the load current. This would require larger, therefore more costly, conductors for a given quantity of usable power to be transmitted.

Operational submarine power cablesEdit

Alternating current cablesEdit

Alternating-current (AC) submarine cable systems for transmitting lower amounts of three-phase electric power can be constructed with three-core cables in which all three insulated conductors are placed into a single underwater cable. Most offshore-to-shore wind-farm cables are constructed this way.

For larger amounts of transmitted power, the AC systems are composed of three separate single-core underwater cables, each containing just one insulated conductor and carrying one phase of the three phase electric current. A fourth identical cable is often added in parallel with the other three, simply as a spare in case one of the three primary cables is damaged and needs to be replaced. This damage can happen, for example, from a ship's anchor carelessly dropped onto it. The fourth cable can substitute for any one of the other three, given the proper electrical switching system.

Connecting Connecting Voltage (kV) Length(km) Year Notes
Peloponnese, Greece Crete, Greece 150 135 2021 Two 3-core XLPE cables with total capacity of 2x200MVA. 174 km total length including the underground segments. Maximum depth 1000m. Total cost 380 million EUR. It is the longest submarine/underground AC cable interconnection in the world.[3][4][5]
Mainland British Columbia to Gulf Islands Galiano Island, Parker Island, and Saltspring Island thence to North Cowichan Vancouver Island 138 33 1956 "The cable became operational on 25 September 1956" [6]
Mainland British Columbia to Texada Island to Nile Creek Terminal Vancouver Island / Dunsmuir Substation 525 35 1985 Twelve, separate, oil filled single-phase cables. Nominal rating 1200 MW.[7]
Tarifa, Spain
(Spain-Morocco Interconnection)
Fardioua, Morocco
through the Strait of Gibraltar
400 26 1998 A second one from 2006[8] Maximum depth: 660 m (2,170 ft).[9]
Norwalk, CT, USA Northport, NY, USA 138 18 A 3 core, XLPE insulated cable
Sicily Malta 220 95 2015 The Malta–Sicily interconnector
Mainland Sweden Bornholm Island, Denmark 60 43.5 The Bornholm Cable
Mainland Italy Sicily 380 38 1985 replacing the "Pylons of Messina"
Germany Heligoland 30 53 [10]
Negros Island Panay Island, the Philippines 138
Douglas Head, Isle of Man, Bispham, Blackpool, England 90 104 1999 The Isle of Man to England Interconnector, a 3 core cable
Wolfe Island, Canada
for the Wolfe Island Wind Farm
Kingston, Canada 245 7.8 2008 The first three-core XLPE submarine cable for 245 kV[11]
Cape Tormentine, New Brunswick Borden-Carleton, PEI 7.8 2017 Prince Edward Island Cables[12]
Taman Peninsula, Mainland Russia Kerch Peninsula, Crimea 57 2015 ru:Энергомост в Крым

Direct current cablesEdit

Name Connecting Body of water Connecting kilovolts (kV) Undersea distance Notes
Baltic Cable Germany Baltic Sea Sweden 450 250 km (160 mi)
Basslink mainland State of Victoria Bass Strait island State of Tasmania, Australia 500 290 km (180 mi)[13]
BritNed Netherlands North Sea Great Britain 450 260 km (160 mi)
Cross Sound Cable Long Island, New York Long Island Sound State of Connecticut [citation needed]
East–West Interconnector Dublin, Ireland Irish Sea North Wales and thus the British grid 186 km (116 mi) Inaugurated 20 September 2012
Estlink northern Estonia Gulf of Finland southern Finland 330 105 km (65 mi)
Fenno-Skan Sweden Baltic Sea Finland 400 233 km (145 mi)
HVDC Cross-Channel French mainland English Channel England 73 km (45 mi) very high power cable (2000 MW)[citation needed]
HVDC Gotland Swedish mainland Baltic Sea Swedish island of Gotland the first HVDC submarine power cable (non-experimental)[14]
HVDC Inter-Island South Island Cook Strait North Island 40 km (25 mi) between the power-rich South Island (much hydroelectric power) of New Zealand and the more-populous North Island
HVDC Italy-Corsica-Sardinia (SACOI) Italian mainland Mediterranean Sea the Italian island of Sardinia, and its neighboring French island of Corsica[citation needed]
HVDC Italy-Greece Italian mainland - Galatina HVDC Static Inverter Adriatic Sea Greek mainland - Arachthos HVDC Static Inverter 400 160 km (99 mi) Total length of the line is 313 km (194 mi)
HVDC Leyte - Luzon Leyte Island Pacific Ocean Luzon in the Philippines[citation needed]
HVDC Moyle Scotland Irish Sea Northern Ireland within the United Kingdom, and thence to the Republic of Ireland 250 63.5 km (39.5 mi) 500MW
HVDC Vancouver Island Vancouver Island Strait of Georgia mainland of the Province of British Columbia 33 km In operation in 1968 and was extended in 1977
Kii Channel HVDC system Honshu Kii Channel Shikoku 250 50 km (31 mi) in 2010 the world's highest-capacity[citation needed] long-distance submarine power cable[inconsistent] (rated at 1400 megawatts). This power cable connects two large islands in the Japanese Home Islands
Kontek Germany Baltic Sea Denmark
Konti-Skan[15] Sweden Kattegat Denmark 400 149 km (93 mi)
Maritime Link Newfoundland Atlantic Ocean Nova Scotia 200 170 km (110 mi) 500 MW link went online in 2017 with two subsea HVdc cables spanning the Cabot Strait.[16]
Nemo-Link[17] Belgium North Sea United Kingdom 400 140 km (87 mi)
Neptune Cable State of New Jersey Atlantic Ocean Long Island, New York 500 104.6 km (65.0 mi)[18]
NordBalt Sweden Baltic Sea Lithuania 300 400 km (250 mi) Operations started on February 1, 2016 with an initial power transmission at 30 MW.[19]
NorNed Eemshaven, Netherlands Feda, Norway 450 580 km (360 mi) 700 MW in 2012 previously the longest undersea power cable[20]
North Sea Link Kvilldal, Suldal, in Norway, Cambois near Blyth North Sea United Kingdom, Norway 515 720 km (450 mi) 1.4 GW the longest undersea power cable
Skagerrak 1-4 Norway Skagerrak Denmark (Jutland) 500 240 km (150 mi) 4 cables - 1700 MW in all[21]
SwePol Poland Baltic Sea Sweden 450
Western HVDC Link Scotland Irish Sea Wales 600 422 km (262 mi) Longest 2200 MW cable, first 600kV undersea cable[22]

Submarine power cables under constructionEdit

Proposed submarine power cablesEdit

See alsoEdit


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External linksEdit