Sardinia-Corsia-Italy (SACOI)

The SACOI (Sardinia-Corsica-Italy) HVDC project is a power transmission system connecting the Italian mainland, Corsica, and Sardinia. This multi-terminal high-voltage direct current link helps to ensure power supply and grid stability across these regions.

Historical Context

The original SACOI HVDC link, known as SACOI 2, was established between 1964 and 1967. It was a pioneering project that utilized mercury-arc valves and HVDC control systems supplied by Hitachi Energy. This initial link had a capacity of 200 MW and operated at 200 kV, connecting Codrongianos in Sardinia to San Dalmazio in Tuscany, south of Florence, with an intermediate connection in Corsica.

Technical Specifications

SACOI is a bipolar HVDC system with a transmission capacity of 300 MW, operating at ±200 kV. The project involves approximately 400 km of HVDC link, with about 50% in Italy and 50% in Corsica. It includes overhead lines, underground cables, and marine cables.

Infrastructure

The SACOI project encompasses several key components. The overhead line sections consist of 22 km on the Italian mainland, 156 km on Corsica, and 86 km on Sardinia. The submarine cable sections span 105 km between Italy and Corsica, and 16 km between Corsica and Sardinia. The overhead lines use twin conductors connected in parallel, each rated at 1000 A DC. The conductor cross-sections are 628 mm² in Sardinia and Italy, and 755 mm² on Corsica.

Key Locations

The HVDC converter stations are located at Codrongianos in Sardinia (Italy), Lucciana in Corsica (France), and Suvereto in Tuscany (Italy).

Significance and Benefits

SACOI is recognized as a Project of Common Interest by the European Union, highlighting its importance for regional energy security and integration. It allows the supply of Corsican demand using more efficient, low CO2 emission generation sources located in Italy and other European countries. The project is essential for maintaining Corsica's connection to the European grid. It also enhances the security of supply and resilience of the Sardinian system, which relies on aging power plants.

Technological Advancements

In 1992, SACOI underwent a significant upgrade. The mercury arc converters at Codrongianos and San Dalmazio were decommissioned and replaced with new converter stations using air-cooled, air-insulated thyristor valves. This upgrade increased the scheme's rating to 300 MW while maintaining the 200 kV voltage.

World Record

SACOI holds the world record for the longest in-service HVDC submarine cable link. After 50 years of operation, it continues to be a crucial energy interconnection between Sardinia and the Italian mainland.

SACOI 3 upgrade

SACOI 3 is a planned upgrade to the existing SACOI (Sardinia-Corsica-Italy) HVDC interconnection. This project aims to replace the aging SACOI 2 link with a new bipolar multi-terminal HVDC system, increasing the transmission capacity to 400 MW at ±200 kV. The upgrade involves revamping approximately 400 km of HVDC link, including overhead lines, underground cables, and submarine cables, as well as constructing new 200 kV DC/AC converter stations in Corsica, Tuscany, and Sardinia. SACOI 3 is recognized as a Project of Common Interest by the European Union and is designed to enhance power supply security, improve system efficiency, and support renewable energy integration for the Mediterranean islands and Tuscany. The project, led by Terna and EDF, is scheduled to begin preliminary works in 2024 and is expected to take five years to complete.