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A submarine power cable is a transmission cable for carrying electric power below the surface of the water.Underwater Cable an Alternative to Electrical Towers
Matthew L. Wald, ''
New York Times ''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid ...
'', 2010-03-16, accessed 2010-03-18.
These are called "submarine" because they usually carry electric power beneath
salt water Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish w ...
(arms of the
ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wor ...
,
sea The sea, connected as the world ocean or simply the ocean, is the body of salty water that covers approximately 71% of the Earth's surface. The word sea is also used to denote second-order sections of the sea, such as the Mediterranean Sea, ...
s,
strait A strait is an oceanic landform connecting two seas or two other large areas of water. The surface water generally flows at the same elevation on both sides and through the strait in either direction. Most commonly, it is a narrow ocean chan ...
s, etc.) but it is also possible to use submarine power cables beneath fresh water (large lakes and
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of ...
s). Examples of the latter exist that connect the mainland with large islands in the St. Lawrence River.


Design technologies

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). Modern three-core cables (e.g. for the connection of offshore wind turbines) often carry
optical fiber An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass ( silica) or plastic to a diameter slightly thicker than that of a human hair Hair is a protein filament that grows ...
s for data transmission or temperature measurement, in addition to the electrical conductors.


Conductor

The conductor is made from
copper Copper is a chemical element with the symbol Cu (from la, cuprum) 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 pink ...
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 (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-sectional profile by pushing material through a die of the desired cross-section. Its two main advantages over other manufacturing processes are its ability to create very complex c ...
, 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 The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the int ...
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 An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into t ...
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.


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 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 DC

Most electrical power transmission systems use alternating current (AC), because
transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
s 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 Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are ...
of the cable would require too much additional charging current. The inner and outer conductors of a cable form the plates of a
capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...
, 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 cables


Alternating current cables

Alternating-current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in which ...
(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 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 ''ancora'', which itself comes from the Greek � ...
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

* Atlantic Wind Connection between
Delaware Delaware ( ) is a state in the Mid-Atlantic region of the United States, bordering Maryland to its south and west; Pennsylvania to its north; and New Jersey and the Atlantic Ocean to its east. The state takes its name from the adjacent ...
and
New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delawa ...
, potentially between
Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth are ...
and New York"Offshore Wind Power Line Wins Praise, and Backing"
article by Matthew L. Wald in ''
The New York Times ''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid ...
'' October 12, 2010, Accessed October 12, 2010
* 500 MW capacity, 165 km DC Maritime Transmission Link between the Canadian province of
Newfoundland and Labrador Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...
and the province of Nova Scotia. * On February 1, 2016 Danish and Dutch operators (Energinet.dk and TenneT) awarded construction contracts to Siemens and Prysmian for COBRAcable, a 294 km submarine cable to provide the two countries with 700 MW transmission at 320 kV DC starting in 2019. * Norwegian and German power companies have built NORD.LINK, a submarine cable transmitting up to 1,400 MW between the two countries by 2018. As of 2021, it is in testing. * British and Danish power companies ( National Grid and Energinet.dk, respectively) are building
Viking Link Viking Link is a 1,400 MW HVDC submarine power cable under construction between the United Kingdom and Denmark. Current status Land cables and submarine cables are being installed since 2020 and expected to finish in 2023. As of August 2022 Den ...
, a 740 km cable to provide the two countries with 1,400 MW transmission by 2022. *Black Sea submarine electric cable with 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 (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 The EuroAsia Interconnector is a HVDC interconnector between the Greek, Cypriot, and Israeli power grids via the world's longest submarine power cable ( from Israel to Cyprus and from Cyprus to Greece, for a total of ). Connecting Kofinou, Cy ...
, 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 The Champlain Hudson Power Express (CHPE) is a proposed high-voltage direct current (HVDC) underwater and underground power cable project project linking the Quebec area to the New York City neighborhood of Astoria, Queens. Following completion of ...
, 335-mile line. The Transmission Developers Company of Toronto, Ontario, is proposing "to use the
Hudson River The Hudson River is a river that flows from north to south primarily through eastern New York. It originates in the Adirondack Mountains of Upstate New York and flows southward through the Hudson Valley to the New York Harbor between Ne ...
for the most ambitious underwater transmission project yet. Beginning south of
Montreal Montreal ( ; officially Montréal, ) is the second-most populous city in Canada and most populous city in the Canadian province of Quebec. Founded in 1642 as '' Ville-Marie'', or "City of Mary", it is named after Mount Royal, the triple- ...
, a 335-mile line would run along the bottom of
Lake Champlain , native_name_lang = , image = Champlainmap.svg , caption = Lake Champlain-River Richelieu watershed , image_bathymetry = , caption_bathymetry = , location = New York/ Vermont in the United States; and Quebec in Canada , coords = , type ...
, and then down the bed of the Hudson all the way to
New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
." * Power Bridge,
Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
* Power Bridge, State of Maine * Puerto Rico to the Virgin Islands * 400 kV HVDC
India India, officially the Republic of India (Hindi: ), 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 and dependencies by population, second-most populous ...
to
Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
* 220 kV HVAC, 225 megawatts, 117 km Malta–Sicily interconnector between Magħtab, Malta, and Ragusa, Sicily. * The 58.9-km, 161-kV
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the no ...
Island to the Penghu Islands submarine power cable system (T–P-cable), the first submarine project of the
Taiwan Power Company The Taiwan Power Company (, Taipower; ) is a state-owned electric power industry providing electricity to Taiwan and off-shore islands of the Republic of China. History Taipower was established on 1 May 1946. Its origins can be traced to 19 ...
(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 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 country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to ...
and
Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its ...
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 northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It ...
and
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
via Alderney Island in the Channel Islands. *
EuroAfrica Interconnector EuroAfrica Interconnector is a HVDC interconnector and submarine power cable between the Greek, Cypriot, and Egypt power grids.Liu Ko Ngam and
Pak Sha Tau Tsui Pak or PAK may refer to: Places * Pakistan (country code PAK) * Pak, Afghanistan * Pak Island, in the Admiralty Islands group of Papua New Guinea * Pak Tea House, a café in Lahore, Punjab, Pakistan Arts and entertainment * PAK (band), an Am ...
at Kat O, Northeast Hong Kong, approximately 880 m in length.


See also

* Cable landing point * Electric power transmission * Single-wire earth return *
List of HVDC projects This is a list of notable high-voltage direct-current power transmission projects. HVDC projects for long-distance transmission have two (or rarely, more) converter stations and a transmission line interconnecting them. Generally overhead lines ...
* List of high voltage underground and submarine cables *
Electrical interconnector An interconnector (also known as a DC tie in the USA) is a structure which enables high voltage DC electricity to flow between electrical grids. An electrical interconnector allows electricity to flow between separate AC networks, or to link sy ...
, e.g. between grids


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