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.
HVDC connections around Europe
Red=in operation
Green=decided/under construction
Blue=planned

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).[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.

Conductor

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.

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, 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.

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).

AC or DC

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 cables

Alternating current cables

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.

ConnectingConnectingVoltage (kV)Length(km)YearNotes
Peloponnese, GreeceCrete, Greece1501352021Two 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 CowichanVancouver Island138331956"The cable became operational on 25 September 1956" [6]
Mainland British Columbia to Texada Island to Nile Creek TerminalVancouver Island / Dunsmuir Substation525351985Twelve, separate, oil filled single-phase cables. Nominal rating 1200 MW.[7]
Tarifa, Spain
(Spain-Morocco interconnection)
Fardioua, Morocco
through the Strait of Gibraltar
400261998A second one from 2006[8] Maximum depth: 660 m (2,170 ft).[9]
Norwalk, CT, USA Northport, NY, USA 13818 A 3 core, XLPE insulated cable
SicilyMalta220952015The Malta–Sicily interconnector
Mainland SwedenBornholm Island, Denmark6043.5The Bornholm Cable
Mainland ItalySicily380381985Messina Strait submarine cable replacing the "Pylons of Messina". A second 380 kV cable began operation in 2016
GermanyHeligoland3053[10]
Negros IslandPanay Island, the Philippines138
Douglas Head, Isle of Man,Bispham, Blackpool, England901041999The Isle of Man to England Interconnector, a 3 core cable
Wolfe Island, Canada
for the Wolfe Island Wind Farm
Kingston, Canada2457.82008The first three-core XLPE submarine cable for 245 kV[11]
Cape Tormentine, New BrunswickBorden-Carleton, PEI7.82017Prince Edward Island Cables[12]
Taman Peninsula, Mainland RussiaKerch Peninsula, Crimea572015ru:Энергомост в Крым

Direct current cables

NameConnectingBody of waterConnectingkilovolts (kV)Undersea distanceNotes
Baltic CableGermanyBaltic SeaSweden450250 km (160 mi)
Basslinkmainland State of VictoriaBass Straitisland State of Tasmania, Australia500290 km (180 mi)[13]
BritNedNetherlandsNorth SeaGreat Britain450260 km (160 mi)
COBRAcableNetherlandsNorth SeaDenmark320325 km (202 mi)Commissioned September 2019
Cross Sound CableLong Island, New YorkLong Island SoundState of Connecticut150
East–West InterconnectorDublin, IrelandIrish SeaNorth Wales and thus the British grid200186 km (116 mi)Inaugurated 20 September 2012
Estlinknorthern EstoniaGulf of Finlandsouthern Finland330105 km (65 mi)
Fenno-SkanSwedenBaltic SeaFinland400233 km (145 mi)
HVDC Cross-ChannelFrench mainlandEnglish ChannelEngland27073 km (45 mi)very high power cable (2000 MW)
HVDC GotlandSwedish mainlandBaltic SeaSwedish island of Gotland15098 km (61 mi)1954, the first HVDC submarine power cable (non-experimental)[14] Gotland 2 and 3 installed in 1983 and 1987.
HVDC Inter-IslandSouth IslandCook StraitNorth Island35040 km (25 mi)between the power-rich South Island (much hydroelectric power) of New Zealand and the more-populous North Island. Commissioned in 1965.
HVDC Italy-Corsica-Sardinia (SACOI)Italian mainlandMediterranean Seathe Italian island of Sardinia, and its neighboring French island of Corsica200385 km (239 mi)3 cables, 1967, 1988, 1992[15]
HVDC Italy-GreeceItalian mainland - Galatina HVDC Static InverterAdriatic SeaGreek mainland - Arachthos HVDC Static Inverter400160 km (99 mi)Total length of the line is 313 km (194 mi)
HVDC Leyte - LuzonLeyte IslandPacific OceanLuzon in the Philippines
HVDC MoyleScotlandIrish SeaNorthern Ireland within the United Kingdom, and thence to the Republic of Ireland25063.5 km (39.5 mi)500MW
HVDC Vancouver IslandVancouver IslandStrait of Georgiamainland of the Province of British Columbia28033 kmIn operation in 1968 and was extended in 1977
Kii Channel HVDC systemHonshuKii ChannelShikoku25050 km (31 mi)in 2010 the world's highest-capacity long-distance submarine power cable (rated at 1400 megawatts). This power cable connects two large islands in the Japanese Home Islands
KontekGermanyBaltic SeaDenmark
Konti-Skan[16]SwedenKattegatDenmark400149 km (93 mi)
Maritime LinkNewfoundlandAtlantic OceanNova Scotia200170 km (110 mi)500 MW link went online in 2017 with two subsea HVdc cables spanning the Cabot Strait.[17]
Nemo-Link[18]BelgiumNorth SeaUnited Kingdom400140 km (87 mi)
Neptune CableState of New JerseyAtlantic OceanLong Island, New York500104.6 km (65.0 mi)[19]
NordBaltSwedenBaltic SeaLithuania300400 km (250 mi)Operations started on February 1, 2016 with an initial power transmission at 30 MW.[20]
NordLinkErtsmyra, NorwayNorth SeaBüsum, Germany500623 km (387 mi)Operational May 2021[21]
NorNedEemshaven, NetherlandsFeda, Norway450580 km (360 mi)700 MW in 2012 previously the longest undersea power cable[22]
North Sea LinkKvilldal, Suldal, in Norway, Cambois near BlythNorth SeaUnited Kingdom, Norway515720 km (450 mi)1.4 GW the longest undersea power cable
Skagerrak 1-4NorwaySkagerrakDenmark (Jutland)500240 km (150 mi)4 cables - 1700 MW in all[23]
SwePolPolandBaltic SeaSweden450
Western HVDC LinkScotlandIrish SeaWales600422 km (262 mi)Longest 2200 MW cable, first 600kV undersea cable[24]

Submarine power cables under construction

  • 500 MW capacity, 165 km DC Maritime Transmission Link between the Canadian province of Newfoundland and Labrador and the province of Nova Scotia.[25]
  • 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.[26][27]
  • 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.[28]

Proposed submarine power cables

See also

References

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  2. "Submarine Power Cables - Design, Installation, Repair, Environmental aspects", by T Worzyk, Springer, Berlin Heidelberg 2009
  3. "Crete-Peloponnese: The record-breaking interconnection is completed". IPTO.
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  5. "Crete – Peloponnese 150kV AC Interconnection" via www.researchgate.net.
  6. "The 132,000 volt submarine cable in the Mainland - Vancouver Island interconnection : part 3, cable laying - RBCM Archives". search-bcarchives.royalbcmuseum.bc.ca.
  7. "British Columbia Transmission Corporation Application for Certificate of Public Convenience and Necessity For Vancouver Island Transmission Reinforcement Project" (PDF). Archived (PDF) from the original on 2021-05-26.
  8. "A Bridge Between Two Continents", Ramón Granadino and Fatima Mansouri, Transmission & Distribution World, May 1, 2007. Consulted March 28, 2014.
  9. "Energy Infrastructures in the Mediterranean: Fine Accomplishments but No Global Vision", Abdelnour Keramane, IEMed Yearbook Archived 2020-10-20 at the Wayback Machine 2014 (European Institute of the Mediterranean), under publication. Consulted 28 March 2014.
  10. "Mit der Zukunft Geschichte schreiben". Dithmarscher Kreiszeitung (in German). Archived from the original on 19 July 2011.
  11. "Wolfe Island Wind Project" (PDF). Canadian Copper CCBDA (156). 2008. Retrieved 3 September 2013.
  12. "P.E.I.'s underwater electric cable project officially plugged in - New underwater cables supply about 75% of the Island's electricity". CBC News. Aug 29, 2017. Retrieved 1 August 2020.
  13. "Basslink - About". www.basslink.com.au. Retrieved 11 February 2018.
  14. "European Subsea Cables Association - Submarine Power Cables". www.escaeu.org.
  15. "Sardinia's electricity transmission network". 2009.
  16. "THE KONTI-SKAN HVDC SCHEME". www.transmission.bpa.gov. Archived from the original on 2005-09-02.
  17. "Maritime Link Infrastructure". Emera Newfoundland and Labrador.
  18. Chestney, Nina (January 14, 2019). "New UK-Belgium power link to start operating on Jan. 31". Reuters via www.reuters.com.
  19. "Home". Neptune Regional Transmission System.
  20. "Power successfully transmitted through NordBalt cable". litgrid.eu. 2016-02-01. Retrieved 2016-02-02.
  21. "NordLink - TenneT". www.tennet.eu. Retrieved 2021-10-17.
  22. "The Norned HVDC Cable Link" (PDF). www05.abb.com.
  23. "Skagerrak An excellent example of the benefits that can be achieved through interconnections". new.abb.com. Archived from the original on 2016-01-20. Retrieved 2016-01-21.
  24. "None". www.westernhvdclink.co.uk.
  25. "Lower Churchill Project". Nalcor Energy. Archived from the original on 2016-11-29. Retrieved 2013-06-08.
  26. "Kabel til England - Viking Link". energinet.dk. Archived from the original on 2017-03-23. Retrieved 2015-11-12.
  27. "Denmark - National Grid". nationalgrid.com. Archived from the original on 2016-03-03. Retrieved 2016-02-03.
  28. "Quadrilateral agreement inked on Black Sea electric cable Link". Archived from the original on 2022-12-17. Retrieved 2022-12-17.
  29. "Australia Fast Tracks Approval Process for $16 Billion Solar Power Export Project". Reuters. 2020-07-30. ISSN 0362-4331. Retrieved 2020-11-03.
  30. The EuroAsia Interconnector document, www.euroasia-interconnector.com October 2017.
  31. "ENERGY: End to electricity isolation a step closer". Financial Mirror. 2017-10-19. Retrieved 2017-01-04.
  32. "Cyprus group plans Greece-Israel electricity link". Reuters. 2012-01-23. Archived from the original on 2012-01-26.
  33. Transmission Developers Inc. (2010-05-03), Application for Authority to Sell Transmission Rights at Negotiated Rates and Request for Expedited Action, Federal Energy Regulatory Commission, p. 7, retrieved 2010-08-02
  34. "Territory to Study Linking Power Grid to Puerto Rico". stcroixsource.com. June 29, 2010. Archived from the original on July 16, 2011.
  35. HVDC Transmission & India-Sri Lanka Power Link www.geni.org 2010
  36. "Malta signs €182 million interconnector contract". Times of Malta.
  37. "Taiwan power company-Taipower Events". www.taipower.com.tw. Archived from the original on 2014-05-17.
  38. Carrington, Damian (2012-04-11). "Iceland's volcanoes may power UK". The Guardian. London.
  39. FAB website fablink.net, as well as (fr) Interconnexion France Aurigny Grand-Bretagne website rte-france.com, site of Réseau de Transport d'Électricité.
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  41. Electricity Cable Aims to Link Cyprus, Egypt, Greece Bloomberg, February 8, 2017
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