Submarine power cable
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A submarine power cable is a transmission cable for carrying electric power below the surface of the water. 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.
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. 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 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 in 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 DC
Most electrical power transmission systems use alternating current (AC), because transformers can easily change voltages as needed. 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.
|Mainland British Columbia to Texada Island to Nile Creek Terminal||Vancouver Island / Dunsmuir Substation||525||Reactor station at overhead crossing of Texada Island. Two three-phase circuits using twelve, separate, oil filled single-phase cables. Shore section cooling facilities. Nominal rating 1200 MW (1600 MW - 2hr overload)|
through the Strait of Gibraltar
|400||The Spain-Morocco Interconnection consists of two 400-kV, AC submarine cables operated jointly by Red Eléctrica de España (Spain) and Office National de l'Électricité (Morocco); the first, 28 km (17 mi) cable, began operating in 1998, the second, of length 31 km (19 mi) began operation in 2006 . The total underwater length of the cables through the Strait of Gibraltar is 26 km (16 mi) and the maximum depth is 660 m (2,170 ft).|
|Sicily||Malta||220||The Malta–Sicily interconnector, a 95-kilometre (59 mi) long subsea cable starts at Magħtab, Qalet Marku in Malta and runs to Marina di Ragusa in Sicily, Italy.|
|Mainland Sweden||Bornholm Island, Denmark||60||The Bornholm Cable|
|Mainland Italy||Sicily||380||Under the Strait of Messina, this submarine cable replaced an earlier, and very long overhead line crossing (the "Pylons of Messina")|
|Negros Island||Panay Island, the Philippines||138|
|Douglas Head, Isle of Man,||Bispham, Blackpool, England||90||The Isle of Man to England Interconnector, a 3 core cable over a distance of 104 km (65 mi)|
|Wolfe Island, Canada||Kingston, Canada||245||The 7.8 km (4.8 mi) cable installed in 2008 for the Wolfe Island Wind Farm was the world's first three-core XLPE submarine cable to achieve a 245 kV voltage rating.|
Direct current cables
|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)|
|BritNed||Netherlands||North Sea||Great Britain||450||260 km (160 mi)|
|Cross Sound Cable||Long Island, New York||Long Island Sound||State of Connecticut|||
|East–West Interconnector||Ireland||Irish Sea||Wales/England 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||very high power cable (2000 MW)|
|HVDC Gotland||Swedish mainland||Baltic Sea||Swedish island of Gotland||the first HVDC submarine power cable (non-experimental)|
|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|
|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|
|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|
|Kii Channel HVDC system||Honshu||Kii Channel||Shikoku||250||50 km (31 mi)||in 2010 the world's highest-capacity long-distance submarine power cable[inconsistent] (rated at 1400 megawatts). This power cable connects two large islands in the Japanese Home Islands|
|Konti-Skan||Sweden||Baltic Sea||Denmark||400||149 km (93 mi)|
|Nemo-Link||Belgium||North Sea||United Kingdom||400||140 km (87 mi)|
|Neptune Cable||State of New Jersey||Atlantic Ocean||Long Island, New York||345||103 km (64 mi)|
|NordBalt||Sweden||Baltic Sea||Lithuania||300||400 km (250 mi)||Operations started on February 1, 2016 with an initial power transmission at 30 MW.|
|NorNed||Eemshaven, Netherlands||Feda, Norway||450||580 km (360 mi)||700 MW in 2012 the longest undersea power cable|
|Skagerrak 1-4||Norway||Skagerrak||Denmark (Jutland)||500||240 km (150 mi)||4 cables - 1700 MW in all|
|Western HVDC Link||Scotland||Irish Sea||Wales||600||422 km (262 mi)||Longest 2200 MW cable, first 600kV undersea cable|
Submarine power cables under construction
- Atlantic Wind Connection between Delaware and New Jersey, potentially between Virginia and New York
- 500 MW capacity, 165 km DC Maritime Transmission Link between the Canadian province of Newfoundland and Labrador 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.
Proposed submarine power cables
- EuroAsia Interconnector, a 1,520 km submarine power cable, reaching depths of up to 3 km (1.9 mi) under sea level, with the capacity to transmit 2,000 megawatts of electricity connecting Asia and Europe (Israel-Cyprus-Greece)
- Champlain Hudson Power Express, 335-mile line. The Transmission Developers Company of Toronto, Ontario, is proposing "to use the Hudson River for the most ambitious underwater transmission project yet. Beginning south of Montreal, a 335-mile line would run along the bottom of Lake Champlain, and then down the bed of the Hudson all the way to New York City."
- Power Bridge, Hawaii
- Power Bridge, State of Maine
- Puerto Rico to the Virgin Islands
- 400 kV HVDC India to Ceylon
- 220 kV HVAC, 225 megawatts, 117 km Malta–Sicily interconnector between Magħtab, Malta, and Ragusa, Sicily.
- The 58.9-km, 161-kV Taiwan 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 in Taiwan Island to the Penghu Islands of the Republic of China(ROC).
- The British and Icelandic Governments are supposedly in "active discussion" to build a cable (Icelink) between Scotland and Iceland to carry geothermal power to Scotland.
- Norwegian and German power companies have agreed to build NORD.LINK, a submarine cable transmitting up to 1,400 MW between the two countries by 2018. 
- British and Danish power companies (National Grid and Energinet.dk, respectively) have agreed to study a Viking Link, a 740 km cable to provide the two countries with 1,400 MW transmission by 2022.
- British and Norwegian power companies (National Grid and Statnett) have agreed to jointly construct NSN Link, a 730 km cable to provide the two countries with 1,400 MW transmission by 2021. Such a cable would be one of the longest in the world and cost between 1 1/2 and two billion euros.
- FAB between Great Britain and France via Alderney Island in the Channel Islands..
- EuroAfrica Interconnector, a 1,707 km submarine power cable, reaching depths of up to 3 km (1.9 mi) under sea level, with the capacity to transmit 2,000 megawatts of electricity connecting Africa and Europe (Egypt-Cyprus-Greece)
- High-voltage direct current
- Electric power transmission
- Single-wire earth return
- List of HVDC projects
- List of high voltage underground and submarine cables
- Electrical interconnector, eg between grids
- Underwater Cable an Alternative to Electrical Towers, Matthew L. Wald, New York Times, 2010-03-16, accessed 2010-03-18.
- "Submarine Power Cables - Design, Installation, Repair, Environmental aspects", by T Worzyk, Springer, Berlin Heidelberg 2009
- "A Bridge Between Two Continents", Ramón Granadino and Fatima Mansouri, Transmission & Distribution World, May 1, 2007. Consulted March 28, 2014.
- "Energy Infrastructures in the Mediterranean: Fine Accomplishments but No Global Vision", Abdelnour Keramane, IEMed Yearbook 2014 (European Institute of the Mediterranean), under publication. Consulted 28 March 2014.
- "Mit der Zukunft Geschichte schreiben". Dithmarscher Kreiszeitung (in German). Archived from the original on 2011-07-19.
- "Wolfe Island Wind Project" (PDF). Canadian Copper CCBDA (156). 2008. Retrieved 3 September 2013.
- "Basslink - About". Retrieved 11 February 2018.
- Bright Future for Long Island
- "Power successfully transmitted through NordBalt cable". litgrid.eu. 2016-02-01. Retrieved 2016-02-02.
- The Norned HVDC Cable Link
- "Offshore Wind Power Line Wins Praise, and Backing" article by Matthew L. Wald in The New York Times October 12, 2010, Accessed October 12, 2010
- Loyd, Linda (April 13, 2012). "Construction under way at new Paulsboro port". Philadelphia Inquirer. Retrieved 2013-07-08.
- "Lower Churchill Project". Nalcor Energy.
- "Cable to the Netherlands - COBRAcable". energinet.dk. 2015-06-10. Archived from the original on 2016-01-20. Retrieved 2016-01-28.
- "Siemens and Prysmian will build the COBRA interconnection between Denmark and the Netherlands". Energinet.dk. 2016-02-01. Archived from the original on 2016-02-02. Retrieved 2016-02-02.
- The EuroAsia Interconnector document
- "ENERGY: End to electricity isolation a step closer". Financial Mirror. 2017-10-19. Retrieved 2017-01-04.
- "Cyprus group plans Greece-Israel electricity link". Reuters. 2012-01-23.
- 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
- Territory study linking power grid between Puerto Rico and Virgin Islands Archived 2011-07-16 at the Wayback Machine
- HVDC Transmission & India-Sri Lanka Power Link 2010
- "Taiwan power company-Taipower Events". Archived from the original on 2014-05-17.
- Carrington, Damian (2012-04-11). "Iceland's volcanoes may power UK". The Guardian. London.
- "Agreement to realize electricity interconnector between Germany and Norway", Statnett 21 June 2012. Retrieved: 22 June 2012.
- "Kabel til England - Viking Link". energinet.dk. Retrieved 2015-11-12.
- "Denmark - National Grid". nationalgrid.com. Archived from the original on 2016-03-03. Retrieved 2016-02-03.
- "The world's longest interconnector gets underway". statnett.no. Retrieved 2016-02-03.
- FAB website fablink.net, as well as (fr) Interconnexion France Aurigny Grand-Bretagne website rte-france.com, site of Réseau de Transport d'Électricité.
- The EuroAfrica Interconnector
- Electricity Cable Aims to Link Cyprus, Egypt, Greece, Bloomberg, February 8, 2017
- EuroAfrica 2,000MW cable boosts Egypt-Cyprus ties, Financial Mirror February 8, 2017
- EEHC, Euro Africa Company sign MoU to conduct a feasibility study to link up Egypt, Cyprus, and Greece, Daily News Egypt,February 6, 2017
- 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