HVDC Italy–Corsica–Sardinia

(Redirected from HVDC Italy-Corsica-Sardinia) Power transmission line between Corsica, Sardinia and mainland Italy

HVDC Italy–Corsica–Sardinia
Pylon of the HVDC Italy–Corsica–Sardinia
Map of HVDC Italy–Corsica–Sardinia
Location
Country	Italy France
From	Suvereto 43°03′10″N 10°41′42″E / 43.05278°N 10.69500°E / 43.05278; 10.69500 (Suvereto HVDC converter station)
Passes through	Lucciana, Corsica 42°31′40″N 9°26′59″E / 42.52778°N 9.44972°E / 42.52778; 9.44972 (Lucciana HVDC converter station)
To	Codrongianos, Sardinia 40°39′07″N 8°42′48″E / 40.65194°N 8.71333°E / 40.65194; 8.71333 (Codrongianus HVDC converter station (Sardinia))
Ownership information
Operator	Terna
Construction information
Manufacturer of substations	Ansaldo English Electric Alstom
Commissioned	1967, 1988, 1992
Technical information
Type	overhead lines submarine cables
Type of current	HVDC
Total length	385 km (239 mi)
Power rating	300 MW
DC voltage	200 kV
No. of poles	1

The HVDC Italy–Corsica–Sardinia (also called SACOI; Sardinia–Corsica–Italy) is an HVDC interconnection used for the exchange of electric energy between the Italian mainland, Corsica and Sardinia. 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 in Canada).

The scheme is a monopole using a mixture of overhead line 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.

The scheme was constructed in three phases.

SACOI 1 - Mercury arc system (1968)

Converter stations

When originally completed in 1968 by English Electric, the scheme comprised two converter stations, at San Dalmazio in Tuscany 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 valves 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 22 kilometres (14 mi), one on Corsica with a length of 156 kilometres (97 mi) and one on Sardinia with a length of 86 kilometres (53 mi). 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 mm in Sardinia and Italy, and 755 mm on Corsica.

In addition to this, there are two submarine cable sections: 105 kilometres (65 mi) between Italy and Corsica and 16 kilometres (9.9 mi) between Corsica and Sardinia. The conductor cross-sections are 1080 mm on land and 420 mm 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) and leaves the sea at the mainland end (cathode). 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 on Corsica, 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 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, 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

This section needs to be updated. Please help update this article to reflect recent events or newly available information. (February 2019)

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

List of waypoints

Italy Mainland

Electrode Line on Italian Mainland

Corsica

Electrode Line in Corsica

Sardinia

Electrode Line in Sardinia

References

^ Natale, M., Lane, F.J., Calverley, T.E., The Sardinian–Italian Mainland HVDC interconnection, IEE Conf. Pub No. 22, p42 - Sept 1966.
Ciallella, V., Grattarola, P., Taschini, A., Martin, C.J.B., Willis, D.B., Testing and operating experience of the Sardinia–Italian Mainland D.C. link, CIGRÉ session, Paris, 1968, paper reference 43-09.
Compendium of HVDC Schemes, CIGRÉ Technical Brochure No. 003, 1987, pp44–50.
Mazzoldi, F., Taisne, J.P., Martin, C.J.B., Rowe, B.A., Adaptation of the control equipment to permit 3-terminal operation of the HVDC link between Sardinia, Corsica and mainland Italy, IEEE Summer power meeting, 1988
Collet-Billon, V. Taisne, J.P., Charles, P., The SACOI (Sardinai-Corsica-Italy) multiterminal link: commissioning tests of the Corsican station Lucciana, CIGRÉ session, Paris, 1988, paper reference 14-12.
Arcidiacono, V., Corsi, S., Pincella, C., Gasparini, E., Piffer, A., Toffolo, G., Ricci, P., Vascellari, S., Zafferani, G., System commissioning tests for the SACOI-2 HVDc three-terminal link, CIGRÉ session, Paris, 1994, paper reference 14-107.
"SA.CO.I. 3: the important work on renewing the historical electrical connection between Tuscany, Corsica and Sardinia - Terna spa". www.terna.it. Retrieved 2023-08-09.

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