SACOI (Sardinia–Corsica–Italy)

The first power flowed in 1967, and commercial operation began in January 1968. That makes SACOI one of the oldest HVDC links in Europe still in use. Its job then was to carry electricity from coal-fired power stations on Sardinia to the Italian mainland.

The route is unusual because it crosses an island in the middle. From the converter station at Codrongianos in northern Sardinia, an 86 km overhead line runs to the coast. A 16 km cable crosses the Strait of Bonifacio to Corsica, where a 156 km overhead line runs the length of the island. A 105 km cable then crosses to Tuscany, and a short 22 km overhead line reaches the mainland station. The SACOI article on Wikipedia sets out each section.

The original converters used mercury-arc valves, each rated at 1,000 A, with air cooling for anodes and cathodes. The mainland terminal was at San Dalmazio, and both ends were rated at 200 MW.

Two changes turned it into something new. In 1988 a third converter station, rated at 50 MW, was installed at Lucciana on Corsica, tapping the line so the island could draw power from it. That made SACOI the first multi-terminal HVDC system in operation, decades before the idea became a research topic for offshore grids. Then in 1992 the mercury-arc converters were taken out and replaced with thyristor valves, the mainland end moved to Suvereto with its stronger 380 kV connection, and the rating rose to 300 MW at 200 kV. That second version is often called SACOI 2.

The line also had a place in European research. The BEST PATHS project chose SACOI as the Italian case study for its third demonstration, led by Terna, which tested new components (cables, conductors and insulators) for upgrading multi-terminal links. The project’s own news coverage from 2017 pointed out that the initial scheme was built to export Sardinian coal power.

It will not run forever. The whole system is being replaced by SACOI 3, with new converters at the same three sites. When that is done, the oldest active multi-terminal HVDC line in the world will be switched off after about sixty years.