Submarine power cable

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Cross section of the submarine power cable used in Wolfe Island Wind Farm. Wolfe Island Wind Project Submarine Power Cable.jpg
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 HVDC Europe.svg
HVDC connections around Europe
Red=in operation
Green=decided/under construction
Blue=planned

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.

Contents

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, Greece Crete, Greece 1501352021Two 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 Cowichan Vancouver Island 138331956"The cable became operational on 25 September 1956" [6]
Mainland British Columbia to Texada Island to Nile Creek Terminal Vancouver 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, USA13818A 3 core, XLPE insulated cable
Sicily Malta 220952015The Malta–Sicily interconnector
Mainland Sweden Bornholm Island, Denmark 6043.5The Bornholm Cable
Mainland Italy Sicily 380381985 Messina Strait submarine cable replacing the "Pylons of Messina". A second 380 kV cable began operation in 2016
Germany Heligoland 3053 [10]
Negros Island Panay 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, Canada 2457.82008The first three-core XLPE submarine cable for 245 kV [11]
Cape Tormentine, New Brunswick Borden-Carleton, PEI 138172017 Prince Edward Island Cables [12]
Taman Peninsula, Mainland Russia Kerch Peninsula, Crimea 572015 ru:Энергомост в Крым

Direct current cables

NameConnectingBody of waterConnecting kilovolts (kV)Undersea distanceNotes
Baltic Cable Germany Baltic Sea Sweden 450250 km (160 mi)
Basslink mainland State of Victoria Bass Strait island State of Tasmania, Australia 500290 km (180 mi) [13]
BritNed Netherlands North Sea Great Britain 450260 km (160 mi)
COBRAcable Netherlands North Sea Denmark 320325 km (202 mi)Commissioned September 2019
Cross Sound Cable Long Island, New York Long Island Sound State of Connecticut 150[ citation needed ]
East–West Interconnector Dublin, Ireland Irish Sea North Wales and thus the British grid200186 km (116 mi)Inaugurated 20 September 2012
Estlink northern Estonia Gulf of Finland southern Finland 330105 km (65 mi)
Fenno-Skan SwedenBaltic SeaFinland400233 km (145 mi)
HVDC Cross-Channel French mainland English Channel England 27073 km (45 mi)very high power cable (2000 MW)[ citation needed ]
HVDC Gotland Swedish mainland Baltic SeaSwedish island of Gotland 15098 km (61 mi)1954, the first HVDC submarine power cable (non-experimental) [14] Gotland 2 and 3 installed in 1983 and 1987.
HVDC Inter-Island South Island Cook Strait North Island 35040 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 mainland Mediterranean Sea the Italian island of Sardinia, and its neighboring French island of Corsica 200385 km (239 mi)3 cables, 1967, 1988, 1992 [15]
HVDC Italy-Greece Italian mainland - Galatina HVDC Static Inverter Adriatic Sea Greek mainland - Arachthos HVDC Static Inverter400160 km (99 mi)Total length of the line is 313 km (194 mi)
HVDC Leyte - Luzon Leyte Island Pacific Ocean Luzon in the Philippines [ citation needed ]
HVDC Moyle Scotland Irish Sea Northern Ireland within the United Kingdom, and thence to the Republic of Ireland 25063.5 km (39.5 mi)500MW
HVDC Vancouver Island Vancouver Island Strait of Georgia mainland of the Province of British Columbia 28033 kmIn operation in 1968 and was extended in 1977
Kii Channel HVDC system Honshu Kii Channel Shikoku 25050 km (31 mi)in 2010 the world's highest-capacity[ citation needed ] long-distance submarine power cable[ inconsistent ] (rated at 1400 megawatts). This power cable connects two large islands in the Japanese Home Islands
Kontek GermanyBaltic SeaDenmark
Konti-Skan [16] Sweden Kattegat Denmark 400149 km (93 mi)
Maritime Link Newfoundland Atlantic Ocean Nova Scotia 200170 km (110 mi)500 MW link went online in 2017 with two subsea HVdc cables spanning the Cabot Strait. [17]
Nemo-Link [18] Belgium North SeaUnited Kingdom400140 km (87 mi)
Neptune Cable State of New Jersey Atlantic Ocean Long Island, New York 500104.6 km (65.0 mi) [19]
NordBalt SwedenBaltic Sea Lithuania 300400 km (250 mi)Operations started on February 1, 2016 with an initial power transmission at 30 MW. [20]
NordLink Ertsmyra, NorwayNorth Sea Büsum, Germany500623 km (387 mi)Operational May 2021 [21]
NorNed Eemshaven, Netherlands Feda, Norway450580 km (360 mi)700 MW in 2012 previously the longest undersea power cable [22]
North Sea Link Kvilldal, Suldal, in Norway, Cambois near Blyth North SeaUnited Kingdom, Norway515720 km (450 mi)1.4 GW the longest undersea power cable
Skagerrak 1-4 Norway Skagerrak Denmark (Jutland)500240 km (150 mi)4 cables - 1700 MW in all [23]
SwePol Poland Baltic SeaSweden450
Western HVDC Link Scotland Irish SeaWales600422 km (262 mi)Longest 2200 MW cable, first 600kV undersea cable [24]

Submarine power cables under construction

Proposed submarine power cables

See also

Related Research Articles

<span class="mw-page-title-main">Electric power transmission</span> Bulk movement of electrical energy

Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines that facilitate this movement form a transmission network. This is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution. The combined transmission and distribution network is part of electricity delivery, known as the electrical grid.

<span class="mw-page-title-main">High-voltage direct current</span> Electric power transmission system

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.

<span class="mw-page-title-main">HVDC Cross-Channel</span> Electrical interconnector between the UK and France

The HVDC Cross-Channel is the 73-kilometre-long (45 mi) high-voltage direct current (HVDC) interconnector that has operated since 1986 under the English Channel between the continental European grid at Bonningues-lès-Calais and the British electricity grid at Sellindge. The cable is also known as IFA, and should not be confused with the new IFA-2, another interconnect with France that is three times as long but only half as powerful.

The HVDC Inter-Island link is a 610 km (380 mi) long, 1200 MW high-voltage direct current (HVDC) transmission system connecting the electricity networks of the North Island and South Island of New Zealand together. It is commonly referred to as the Cook Strait cable in the media and in press releases, although the link is much longer than its Cook Strait section. The link is owned and operated by state-owned transmission company Transpower New Zealand.

Directlink (Terranora)Interconnector is a mixed buried and above ground 59 kilometre (37 mi) High Voltage Direct Current (HVDC) electricity transmission cable route from near Lavertys Gap (28°34′15″S153°27′8″E), 5 kilometres (3.1 mi) Southwest of Mullumbimby, New South Wales and Bungalora (28°15′20″S153°28′20″E) & connected via a 3.5km (2.2mi) AC Overhead Transmission Line to the NorthEast to the Terranora Electrical Substation (28°14′28.3″S153°30′12.7″E) @ Terranora, New South Wales New South Wales in Eastern Australia. The DC cables alternate between above ground in a galvanised steel trough and below ground with depths up to 1m.

The East–West Interconnector is a 500 MW high-voltage direct current submarine and subsoil power cable which connects the Irish and British electricity markets. The project was developed by the Irish national grid operator EirGrid.

NordBalt is a submarine power cable between Klaipėda in Lithuania and Nybro in Sweden. The purpose of the cable is to facilitate the trading of power between the Baltic and Nordic electricity markets, and to increase the supply and energy security in both markets.

<span class="mw-page-title-main">Synchronous grid of Continental Europe</span> Worlds largest single electric network

The synchronous grid of Continental Europe is the largest synchronous electrical grid in the world. It is interconnected as a single phase-locked 50 Hz mains frequency electricity grid that supplies over 400 million customers in 24 countries, including most of the European Union. In 2009, 667 GW of production capacity was connected to the grid, providing approximately 80 GW of operating reserve margin. The transmission system operators operating this grid formed the Union for the Coordination of Transmission of Electricity (UCTE), now part of the European Network of Transmission System Operators for Electricity (ENTSO-E).

TenneT is a transmission system operator in the Netherlands and in a large part of Germany.

<span class="mw-page-title-main">National Grid (New Zealand)</span> Overview of the electrical grid in New Zealand

The National Grid is the nationwide system of electric power transmission in New Zealand. The grid is owned, operated and maintained by Transpower New Zealand, a state-owned enterprise, although some lines are owned by local distribution companies and leased to Transpower. In total, the national grid contains 11,803 kilometres (7,334 mi) of high-voltage lines and 178 substations.

BritNed is a 1,000 MW high-voltage direct-current (HVDC) submarine power cable between the Isle of Grain in Kent, the United Kingdom; and Maasvlakte in Rotterdam, the Netherlands.

COMETA is an undersea electric power transmission system between mainland Spain and the island of Majorca. It connects Morvedre near Valencia and Santa Ponsa near Palma de Mallorca. The project was developed by Red Electrica de España. The project aims were to connect the Balearic Islands with the Spanish peninsular grid, providing a better electrical supply to the two isolated Balearic grids.

<span class="mw-page-title-main">North Sea Link</span> Subsea electricity transmission line

The North Sea Link is a 1,400 MW high-voltage direct current submarine power cable between Norway and the United Kingdom.

<span class="mw-page-title-main">EuroAsia Interconnector</span> Planned submarine electricity cable

The EuroAsia Interconnector is a planned HVDC interconnector between the Greek, Cypriot, and Israeli power grids via the world's longest submarine power cable, with a length of 310 kilometres (190 mi) from Israel to Cyprus and 898 kilometres (558 mi) from Cyprus to Greece for a total of 1,208 kilometres (751 mi). Connecting Kofinou, Cyprus to Hadera, Israel and Korakias, Crete, Greece, the EuroAsia Interconnector is a major Project of Common Interest (PCI) of the European Union and a priority Electricity Highway Interconnector Project as an energy highway bridging Asia and Europe. Regulatory approval of electricity interconnection between Cyprus and Greece was completed on October 10, 2017.

Shetland HVDC Connection is a high-voltage direct current submarine power cable under construction to connect Shetland to the British mainland.

An interconnector 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 synchronous grids. They can be formed of submarine power cables or underground power cables or overhead power lines.

Viking Link is a 1,400 MW HVDC submarine power cable nearing completion between the United Kingdom and Denmark.

FAB Link is a proposed HVDC Interconnector, spanning the 220 kilometres (140 mi) between France and Great Britain, running close to the island of Alderney.

<span class="mw-page-title-main">EuroAfrica Interconnector</span>

EuroAfrica Interconnector is a planned HVDC interconnector and submarine power cable between the Greek, Cypriot, and Egypt power grids. The Interconnector is an energy highway bridging Africa and Europe. It will have a capacity to transmit 2,000 megawatts of electricity in either direction. Annual transmission capacity will be rated at 17.5 TWh, much more than the annual production at the Aswan Dam power stations. President of Egypt Abdel Fattah el-Sisi, President of Cyprus Nicos Anastasiades and Prime Minister of Greece Kyriakos Mitsotakis, issued a joint declaration at the conclusion of the 7th Trilateral Summit, held in Cairo on October 8, 2019, in which they expressed their desire to continue strengthening their cooperation in matters of energy. In particular, the joint declaration by the three leaders stated they recognised the importance of establishing an electrical grid between Egypt, Cyprus and Greece, building on the framework agreement between the Egyptian Electricity Holding Company and the Euro Africa Interconnector Company on 22 May 2019.

References

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  3. ↑ "Crete-Peloponnese: The record-breaking interconnection is completed". IPTO.
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  6. ↑ "The 132,000 volt submarine cable in the Mainland - Vancouver Island interconnection : part 3, cable laying - RBCM Archives". search-bcarchives.royalbcmuseum.bc.ca.
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  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.
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  14. ↑ "European Subsea Cables Association - Submarine Power Cables". www.escaeu.org.
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  17. ↑ "Maritime Link Infrastructure". Emera Newfoundland and Labrador.
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  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.
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