HVDC Italy–Corsica–Sardinia
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The HVDC Italy–Corsica–Sardinia (also called SACOI; Sardinia–Corsica–Italy) is an
HVDC 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. Most HVDC links use voltages betwe ...
interconnection used for the exchange of
electric Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...
energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...
between the Italian mainland,
Corsica Corsica ( , , ; ; ) is an island in the Mediterranean Sea and one of the Regions of France, 18 regions of France. It is the List of islands in the Mediterranean#By area, fourth-largest island in the Mediterranean and lies southeast of the Metro ...
and
Sardinia Sardinia ( ; ; ) is the Mediterranean islands#By area, second-largest island in the Mediterranean Sea, after Sicily, and one of the Regions of Italy, twenty regions of Italy. It is located west of the Italian Peninsula, north of Tunisia an ...
. It is unusual, having more than two converter stations as part of a single HVDC system, and (as of 2012) is one of only two ''multi-terminal'' HVDC systems in operation in the world (the other multi-terminal scheme being the Quebec – New England Transmission system linking northeastern United States with
Quebec Quebec is Canada's List of Canadian provinces and territories by area, largest province by area. Located in Central Canada, the province shares borders with the provinces of Ontario to the west, Newfoundland and Labrador to the northeast, ...
in Canada). The scheme is a monopole using a mixture of
overhead line An overhead line or overhead wire is an electrical cable that is used to transmit electrical energy to electric locomotives, Electric multiple unit, electric multiple units, trolleybuses or trams. The generic term used by the International Union ...
and submarine cable for the 200 kV high voltage conductor, and sea return for the neutral current. The overhead lines and submarine cables are duplicated, with both circuits being installed on the same towers.Natale, M., Lane, F.J., Calverley, T.E., The Sardinian–Italian Mainland HVDC interconnection, IEE Conf. Pub No. 22, p42 - Sept 1966. The scheme was constructed in three phases.


SACOI 1 - Mercury arc system (1968)


Converter stations

When originally completed in 1968 by
English Electric The English Electric Company Limited (EE) was a British industrial manufacturer formed after World War I by amalgamating five businesses which, during the war, made munitions, armaments and aeroplanes. It initially specialised in industrial el ...
, the scheme comprised two converter stations, at San Dalmazio in
Tuscany Tuscany ( ; ) is a Regions of Italy, region in central Italy with an area of about and a population of 3,660,834 inhabitants as of 2025. The capital city is Florence. Tuscany is known for its landscapes, history, artistic legacy, and its in ...
on the Italian mainland, which was situated close to a production area and offered a connection to two 220 kV lines, and Codrongianos on Sardinia. Each converter station was rated at 200 kV, 200 MW and consisted of two 6-pulse converter bridges in series. Normal operation was with both bridges in service but the scheme could be operated at 50% of rated voltage and power by bypassing one converter group at each end, to allow maintenance to be carried out. Each 6-pulse converter bridge consisted of 6 main
mercury-arc valve A mercury-arc valve or mercury-vapor rectifier or (UK) mercury-arc rectifier is a type of electrical rectifier used for converting high-voltage or high- current alternating current (AC) into direct current (DC). It is a type of cold cathode gas-f ...
s plus a 7th for high-speed bypass operations. Each valve was rated at 1000 A dc and had four anode columns in parallel, with air cooling used for both the anodes and cathodes of the valve. The original scheme was commissioned during 1967 and put into commercial operation in January 1968. The mercury arc valves were as well in San Dalmazio as in Codrongianos situated in a hall with a length of 60 metres, a width of 20 metres and a height of 15 metres. The valves are still in these halls, however the mercury was removed, after the decommissioning of the mercury arc system in 1992.


Transmission lines and cables

The scheme consists of three overhead line sections: one on the Italian mainland with a length of , one on Corsica with a length of and one on Sardinia with a length of . The overhead line sections use twin conductors (each rated at 1000 A dc) connected in parallel. Each aluminium conductor has a cross section of 628 mm2 in Sardinia and Italy, and 755 mm2 on Corsica. In addition to this, there are two submarine
cable Cable may refer to: Mechanical * Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof * Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
sections: between Italy and Corsica and between Corsica and Sardinia. The conductor cross-sections are 1080 mm2 on land and 420 mm2 for the submarine lengths.


Sea electrodes

The scheme was designed to export power from coal-fired power stations on Sardinia to the Italian mainland, and thus was only required to operate in one direction. Although the converter stations are inherently capable of operating in either direction of power transmission, advantage was taken of the unidirectional power-flow requirement to economise on the design of the sea electrodes. The sea return current enters the sea at the Sardinian end (
anode An anode usually is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, which is usually an electrode of the device through which conventional current leaves the devic ...
) and leaves the sea at the mainland end (
cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device such as a lead-acid battery. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. Conventional curren ...
). The mainland electrode consists of bare copper (a section of insulated copper cable with the insulation stripped off), which would corrode rapidly if used as an anode but suffers no degradation when used as a cathode. However, the anode electrode on Sardinia required a more sophisticated design using platinum-coated titanium pipe, subdivided into 30 sub-electrodes, in order to prevent corrosion.


Corsica tap (1988)

In 1988 a third converter station, rated at 50 MW, along with a reversible ground electrode, was installed at
Lucciana Lucciana (, , ) is a French communes of France, commune in the departments of France, department of Haute-Corse, Upper Corsica, collectivity and island of Corsica. Geography Situated on the eastern coast of Corsica nearly to the south of Basti ...
on
Corsica Corsica ( , , ; ; ) is an island in the Mediterranean Sea and one of the Regions of France, 18 regions of France. It is the List of islands in the Mediterranean#By area, fourth-largest island in the Mediterranean and lies southeast of the Metro ...
, making the scheme into a multi-terminal scheme for the first time. In order to allow power to be either imported into or exported from Corsica (even though the direction of power flow is always from Sardinia to Italy), the Lucciana converter station was equipped with high-speed changeover switchgear. Unlike the two original converters, the Lucciana converter station was built with air-insulated, air-cooled
thyristor A thyristor (, from a combination of Greek language ''θύρα'', meaning "door" or "valve", and ''transistor'' ) is a solid-state semiconductor device which can be thought of as being a highly robust and switchable diode, allowing the passage ...
valves, supplied by CGE Alstom


SACOI 2 - 1992 upgrade

In 1992 the mercury arc converters at Codrongianos and San Dalmazio were decommissioned and two new converters stations were built, using air-cooled, air-insulated thyristor valves similar to those supplied for the connection at Lucciana. At the Sardinian end, the new converter station was built next to the existing station but at the mainland end a new converter station was built at
Suvereto Suvereto () is a ''comune'' (municipality) in the Province of Livorno in the Italian region Tuscany, located about southwest of Florence and about southeast of Livorno. It is one of ("The most beautiful villages of Italy"). Government ;''Frazi ...
, as this site offered in opposite to San Dalmazio an interconnection to the 380 kV grid. At the same time, the rating of the scheme was increased to 300 MW, keeping the same voltage of 200 kV. As well as in Suvereto as in Codrongianos, the converters are situated in halls with a length of 38 metres, a width of 15 metres and a height of 11 metres.


SACOI 3

It is planned to replace the existing scheme with a bipolar system with a transmission rate of 400 MW called SACOI 3. It will also operate with a voltage of 200 kV. While the overhead lines can be used without modification, the underground and underwater cables have to be replaced for the higher transmission rate. Two new converters will also be built at the existing sites in Suvereto and Codrongianos. Public consultation for the project took place in 2023.


Sites


Waypoints

;Italy Mainland * * * * * * * * * * * * * * ;Electrode Line on Italian Mainland * * * * * * ;Corsica * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ;Electrode Line in Corsica * * ( Start of underground cable) * ( End of underground cable) * * * * * * * * * * * * ( Start of underground cable) * ( End of underground cable) * * ;Sardinia * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ;Electrode Line in Sardinia * * * * * * * * * *


See also

* SAPEI, the new HVDC interconnection between Sardinia and the Italian mainland.


References


External links

* https://web.archive.org/web/20041118012809/http://www.jce.it/newjce/contents/elettronica/cinescopio/200206/CIN6%20Chiama.pdf * https://web.archive.org/web/20051115115248/http://www.transmission.bpa.gov/cigresc14/Compendium/SACOI.htm * https://web.archive.org/web/20051115133446/http://www.transmission.bpa.gov/cigresc14/Compendium/Sacoi+Pictures.pdf * http://www.openstreetmap.org/relation/3391794 * https://www.progettodighe.it/gallery/albums/userpics/10156/SACOI.pdf * https://www.terna.it/en-gb/sistemaelettrico/dialogoconicittadini/sacoi3ternaincontratoscanaesardegna.aspx#!#tab-2
SACOI 3 project ( in Italian)

Video on construction of SACOI 1
{{DEFAULTSORT:HVDC Italy-Corsica-Sardinia Italy-Corsica-Sardinia Electric power infrastructure in Italy Electric power infrastructure in France Economy of Sardinia Corsica HVDC transmission lines France–Italy relations Energy infrastructure completed in 1968 Energy infrastructure completed in 1988 1968 establishments in Italy 1988 establishments in France