Wolfe Island Wind Project Submarine Power Cable

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 wat ...

(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 wo ...

, seas, straits, etc.) but it is also possible to use submarine power cables beneath fresh water (large

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

s 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 w ...

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 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). 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. Optical fibers are used most often as a mea ...

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 pinkis ...

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, ins ...

(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 ...

, 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 inte ...

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.

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 A high-voltage direct current (HVDC) electric power transmission system (also called a power superhighway or an electrical superhighway) uses direct current (DC) for electric power transmission, in contrast with the more common alternating curre ...

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 ar ...

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 (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 used in electricity generation, transmission, and distribution. It is a type of polyphase system employing three wires (or four including an optional neutral ...

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 ἄ� ...

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

electrical switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...

ing 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 Del ...

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 Delaware ...

, 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 ar ...

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 d ...

'' 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 provinces and territories of Canada, province of Canada, in the country's Atlantic Canada, Atlantic region. The province comprises t ...

and the province of

Nova Scotia Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland". Most of the population are native Eng ...

. * On February 1, 2016 Danish and Dutch operators (Energinet.dk and

TenneT TenneT is a transmission system operator in the Netherlands and in a large part of Germany. ''TenneT B.V.'' is the national electricity transmission system operator of the Netherlands, headquartered in Arnhem. Controlled and owned by the Dutch ...

) 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 Norwegian, Norwayan, or Norsk may refer to: *Something of, from, or related to Norway, a country in northwestern Europe * Norwegians, both a nation and an ethnic group native to Norway * Demographics of Norway *The Norwegian language, including ...

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, 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, 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, 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 N ...

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 Lake Champlain ( ; french: Lac Champlain) is a natural freshwater lake in North America. It mostly lies between the US states of New York and Vermont, but also extends north into the Canada, Canadian province of Quebec. The New York portion of t ...

, 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 most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the most densely populated major city in the Un ...

." * 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 state ...

* Power Bridge, State of Maine *

Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and unincorporated ...

to the

Virgin Islands The Virgin Islands ( es, Islas Vírgenes) are an archipelago in the Caribbean Sea. They are geologically and biogeographically the easternmost part of the Greater Antilles, the northern islands belonging to the Puerto Rico Trench and St. Cro ...

* 400 kV HVDC

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

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

Ragusa, Sicily Ragusa (; scn, Rausa ; la, Ragusia) is a city and ''comune'' in southern Italy. It is the capital of the province of Ragusa, on the island of Sicily, with 73,288 inhabitants in 2016. It is built on a wide limestone hill between two deep valley ...

. * 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 nort ...

Island to the

Penghu Islands The Penghu (, Hokkien POJ: ''Phîⁿ-ô͘'' or ''Phêⁿ-ô͘'' ) or Pescadores Islands are an archipelago of 90 islands and islets in the Taiwan Strait, located approximately west from the main island of Taiwan, covering an are ...

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 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 1919 ...

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 Icelink is a proposed electricity interconnector between Iceland and the United Kingdom via Great Britain. At , the 8001,200MW high-voltage direct current (HVDC) link would be the longest sub-sea power interconnector in the world. The project pa ...

) between

Scotland Scotland (, ) is a Countries of the United Kingdom, country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a Anglo-Scottish border, border with England to the southeast ...

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 s ...

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 i ...

and

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...

via Alderney Island in the

Channel Islands The Channel Islands ( nrf, Îles d'la Manche; french: îles Anglo-Normandes or ''îles de la Manche'') are an archipelago in the English Channel, off the French coast of Normandy. They include two Crown Dependencies: the Bailiwick of Jersey, ...

. * 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 Kat O () also named Crooked Island, is an island in Northeast Hong Kong. Administration Administratively, Kat O is part of North District. It is a recognized village under the New Territories Small House Policy. Geography Kat O is located in ...

, 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