Wolfe Island Wind Project Submarine Power Cable

A submarine power cable is a transmission cable for carrying

electric power Electric power is the rate of transfer of electrical energy within a electric circuit, circuit. Its SI unit is the watt, the general unit of power (physics), power, defined as one joule per second. Standard prefixes apply to watts as with oth ...

below the surface of the water.Underwater Cable an Alternative to Electrical Towers
Matthew L. Wald, ''

New York Times ''The New York Times'' (''NYT'') is an American daily newspaper based in New York City. ''The New York Times'' covers domestic, national, and international news, and publishes opinion pieces, investigative reports, and reviews. As one of ...

'', 2010-03-16, accessed 2010-03-18. These are called "submarine" because they usually carry electric power beneath salt water (arms of the

ocean The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...

sea A sea is a large body of salt water. There are particular seas and the sea. The sea commonly refers to the ocean, the interconnected body of seawaters that spans most of Earth. Particular seas are either marginal seas, second-order section ...

s, straits, etc.) but it is also possible to use submarine power cables beneath

fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salt (chemistry), salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include ...

(large

lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...

s and

river A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...

s). Examples of the latter exist that connect the mainland with large islands in the St. Lawrence River.

Design technologies

As key tools in bulk power transmission, submarine power tables tend to operate at high voltage in order to minimize resistive losses between the endpoints. Unlike overhead powerlines, many submarine power cables tend to operate with DC current.

Electrical phase A polyphase system (the term coined by Silvanus Thompson) is a means of distributing alternating-current (AC) electrical power that utilizes more than one AC phase, which refers to the phase offset value (in degrees) between AC in multiple c ...

s must endure close proximity inside the cable, increasing

parasitic capacitance Parasitic capacitance or stray capacitance is the unavoidable and usually unwanted capacitance that exists between the parts of an electronic component or circuit simply because of their proximity to each other. When two electrical conductors a ...

. It is more economical to use AC only with lines shorter than 100 km in length, in which case losses at the landing point grid interfaces dominate.Ardelean, M.; Minnebo, P. The suitability of seas and shores for building submarine power interconnections. Renewable Sustainable Energy Rev 2023, 176, 10.1016/j.rser.2023.113210. When the reasons for high voltage transmission, the preference for AC, and for capacitive currents are combined, one can understand why there are no underwater high electric power cables longer than 1000 km (see the table in "Operational submarine power cables" section below).

Conductor

As indicated above, submarine power cables transport

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

high voltage High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, ''high voltage'' refers to voltage above a certain threshold. Equipment and conductors that carry high voltage warrant sp ...

. The electric core is a concentric assembly of inner conductor, electric insulation, and protective layers (resembling the design of a

coaxial cable Coaxial cable, or coax (pronounced ), is a type of electrical cable consisting of an inner Electrical conductor, conductor surrounded by a concentric conducting Electromagnetic shielding, shield, with the two separated by a dielectric (Insulat ...

). Modern three-core cables (e.g. for the connection of offshore wind turbines) often carry

optical fiber An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...

s for data transmission or temperature measurement, in addition to the electrical conductors. The conductor is made from

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

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.

Insulation

Three different types of electric insulation around the conductor are mainly used today.

Cross-linked polyethylene Cross-linked polyethylene, commonly abbreviated PEX, XPE or XLPE, is a form of polyethylene with cross-links. It is used predominantly in building services pipework systems, hydronic radiant heating and cooling systems, domestic water piping, in ...

(XLPE) is used up to 420 kV system voltage. It is produced by

extrusion Extrusion is a process used to create objects of a fixed cross section (geometry), cross-sectional profile by pushing material through a Die (manufacturing), die of the desired cross-section. Its two main advantages over other manufacturing pro ...

, 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 Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...

insulation fluid (

mineral oil Mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum, as distinct from usually edible vegetable oils. The name 'mineral oil' by itself is imprecise, ...

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 A high-voltage direct current (HVDC) electric power transmission system uses direct current (DC) for electric power transmission, in contrast with the more common alternating current (AC) transmission systems. Most HVDC links use voltages betwe ...

cables up to 525 kV.

Armoring

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 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).

Operational submarine power cables

Alternating current cables

Alternating-current (AC) submarine cable systems for transmitting lower amounts of

three-phase electric power Three-phase electric power (abbreviated 3ϕ) is a common type of alternating current (AC) used in electricity generation, transmission, and distribution. It is a type of polyphase system employing three wires (or four including an optional n ...

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 An anchor is a device, normally made of metal, used to secure a vessel to the bed of a body of water to prevent the craft from drifting due to wind or current. The word derives from Latin ', which itself comes from the Greek (). Anch ...

carelessly dropped onto it. The fourth cable can substitute for any one of the other three, given the proper electrical switching system.

Direct current cables

Submarine power cables under construction

* 500 MW capacity, 165 km DC Maritime Transmission Link between the Canadian province of

Newfoundland and Labrador Newfoundland and Labrador is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region of Labrador, having a total size of . As of 2025 the populatio ...

and the province of

Nova Scotia Nova Scotia is a Provinces and territories of Canada, province of Canada, located on its east coast. It is one of the three Maritime Canada, Maritime provinces and Population of Canada by province and territory, most populous province in Atlan ...

. * British and Danish power companies ( National Grid and Energinet.dk, respectively) are building

Viking Link Viking Link is a 1,400 megawatt, MW high-voltage direct current, HVDC submarine power cable between the United Kingdom and Denmark, which was completed in 2023. , it is the longest land and subsea HVDC interconnector in the world. The project is ...

, a 740 km cable to provide the two countries with 1,400 MW transmission by 2022. *Black Sea submarine electric cable with a capacity of 1 GW and voltage of 500 kV will transfer green electricity from Azerbaijan through Georgia, Romania, Moldova to the EU. It is estimated to be approximately 1100 km in length and to be built in late 2029.

Proposed submarine power cables

Australia–ASEAN Power Link The Australia–Asia Power Link (AAPowerLink) is a proposed electricity infrastructure project that is planned to include the List of photovoltaic power stations, world's largest solar plant, the world's largest battery, and the world's longest ...

(AAPL), or the Australia–Singapore Power Link (ASPL), is a proposed electricity infrastructure project that is planned to include the world's longest submarine power cable. A solar farm in Northern Territory, Australia, will produce 10 gigawatts of electricity, most of which will be exported to Singapore by a 4,500 km (2,800 mi) 3 GW HVDC transmission line. * EuroAsia Interconnector, a 1,520 km submarine power cable, reaching depths of up to under sea level, with the capacity to transmit 2,000 megawatts of electricity connecting Asia and Europe (Israel–Cyprus–Greece)The EuroAsia Interconnector document
''www.euroasia-interconnector.com'' October 2017. * Champlain Hudson Power Express, 335-mile line. The Transmission Developers Company of

Toronto, Ontario Toronto ( , locally pronounced or ) is the List of the largest municipalities in Canada by population, most populous city in Canada. It is the capital city of the Provinces and territories of Canada, Canadian province of Ontario. With a p ...

, is proposing "to use the

Hudson River The Hudson River, historically the North River, is a river that flows from north to south largely through eastern New York (state), New York state. It originates in the Adirondack Mountains at Henderson Lake (New York), Henderson Lake in the ...

for the most ambitious underwater transmission project yet. Beginning south of

Montreal Montreal is the List of towns in Quebec, largest city in the Provinces and territories of Canada, province of Quebec, the List of the largest municipalities in Canada by population, second-largest in Canada, and the List of North American cit ...

, a 335-mile line would run along the bottom of

Lake Champlain Lake Champlain ( ; , ) is a natural freshwater lake in North America. It mostly lies between the U.S. states of New York (state), New York and Vermont, but also extends north into the Canadian province of Quebec. The cities of Burlington, Ve ...

, and then down the bed of the Hudson all the way to

New York City New York, often called New York City (NYC), is the most populous city in the United States, located at the southern tip of New York State on one of the world's largest natural harbors. The city comprises five boroughs, each coextensive w ...

." * Power Bridge,

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

* Power Bridge,

State of Maine Maine ( ) is a U.S. state, state in the New England region of the United States, and the northeasternmost state in the Contiguous United States. It borders New Hampshire to the west, the Gulf of Maine to the southeast, and the Provinces and ...

Puerto Rico ; abbreviated PR), officially the Commonwealth of Puerto Rico, is a Government of Puerto Rico, self-governing Caribbean Geography of Puerto Rico, archipelago and island organized as an Territories of the United States, unincorporated territo ...

to the

Virgin Islands The Virgin Islands () are an archipelago between the Atlantic Ocean, North Atlantic Ocean and northeastern Caribbean Sea, geographically forming part of the Leeward Islands of the Lesser Antilles in the Caribbean, Caribbean islands or West Indie ...

* 400 kV HVDC

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

Sri Lanka Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, also known historically as Ceylon, is an island country in South Asia. It lies in the Indian Ocean, southwest of the Bay of Bengal, separated from the Indian subcontinent, ...

* 220 kV HVAC, 225 megawatts, 117 km Malta–Sicily interconnector between Magħtab, Malta, and

Ragusa, Sicily Ragusa (; ; ) is a city and ''comune'' in southern Italy. It is the capital of the province of Ragusa, on the island of Sicily, with 73,778 inhabitants as of 2025. It is built on a wide limestone hill between two deep valleys, Cava San Leonardo ...

. * The 3,500-km, 6-GW North Atlantic Transmission One Link between Newfoundland and Ireland was proposed in 2024 by three investment bankers to ensure secure coordination between the North American and Western European power grids. * The 58.9-km, 161-kV

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...

Island to the Penghu Islands submarine power cable system (T–P-cable), the first submarine project of the Taiwan Power Company (Taipower) at this level, scheduled for completion in 2014. On 24 December 2010, the '' Taiwan-Penghu Undersea Cable Project'' of Taipower was approved to connect the

electrical grid An electrical grid (or electricity network) is an interconnected network for electricity delivery from producers to consumers. Electrical grids consist of power stations, electrical substations to step voltage up or down, electric power tran ...

in Taiwan Island to the Penghu Islands. * The British and Icelandic Governments are supposedly in "active discussion" to build a cable ( Icelink) between

Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...

and

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

to carry geothermal power to Scotland. It would be 1,000 to 1,500 km long "and by far the longest in the world." assuming a longer cable not yet built like the proposed 4,200 km Australia–Singapore cable * FAB between

Great Britain Great Britain is an island in the North Atlantic Ocean off the north-west coast of continental Europe, consisting of the countries England, Scotland, and Wales. With an area of , it is the largest of the British Isles, the List of European ...

and

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

via Alderney Island in the

Channel Islands The Channel Islands are an archipelago in the English Channel, off the French coast of Normandy. They are divided into two Crown Dependencies: the Jersey, Bailiwick of Jersey, which is the largest of the islands; and the Bailiwick of Guernsey, ...

. * EuroAfrica Interconnector, a 1,707 km submarine power cable, reaching depths of up to under sea level, with the capacity to transmit 2,000 megawatts of electricity connecting Africa and Europe (Egypt–Cyprus–Greece) * 11 kV submarine replacement cables connecting Liu Ko Ngam and Pak Sha Tau Tsui at Kat O, Northeast Hong Kong, approximately 880 m in length.

References

External links

Subsea Cables UK - An organisation of submarine cable owners, operators and suppliers aimed at promoting marine safety and protecting cable installations on the UK continental shelf

The International Cable Protection Committee

Subsea Cables UK article on Submarine Power Cables

Export cables from Offshore Wind farms to Offshore substations

Transmission cables from Offshore converter to shore

(Cross sections of historic power cables) {{DEFAULTSORT:Submarine Power Cable Electric power transmission de:Seekabel#Gleichstromkabel