Италия-Корсика-Сардиния: Желілік жүйесі

Power transmission line between Corsica, Sardinia and mainland Italy

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.

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.

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 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.

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.