Italy-Greece (GRITA)

The GRITA HVDC project, also known as the Italy-Greece HVDC link, is a significant power transmission infrastructure connecting the electrical grids of Italy and Greece. Commissioned in 2001, this bi-directional 500 MW HVDC link was the first energy project implemented under the European Union's Trans-European Networks (TEN) initiative.

Technical Specifications

The GRITA link consists of a monopolar cable system operating at a DC voltage of 400 kV. It connects the Galatina converter station in the Puglia region of southeast Italy to the Arachthos converter station in the northwestern Greek region of Epirus. The total length of the transmission system is approximately 313 km, comprising three main sections:

A 43 km underground cable in ItalyA 160 km submarine cable crossing the Ionian SeaA 110 km overhead line in Greece

The submarine portion of the cable reaches a maximum depth of 1,000 meters, making it the world's deepest submarine power cable at the time of its commissioning. This achievement represented a significant milestone in subsea cable technology.

Technical Features

The GRITA link employs a mono-polar cable utilizing a sea return, based on a grid-commuted twelve-pulse thyristor bridge. The design anticipates a possible future upgrade to a 1000 MW bipolar extension. The system incorporates state-of-the-art components at the converter stations, including DC cables, thyristor valves, converter transformers, AC and DC filters, smoothing reactors, and AC and DC yard switching equipment.

The link features a modern control and protection system, which includes converter firing, pole power control, frequency regulation, inter-station telecommunication, and station control and monitoring. Both converter stations are connected to two 400 kV lines, with interconnection to the 150 kV distribution network. The AC networks at each end can supply 140 MVAr and absorb 100 MVAr, with a maximum single bank operation of 100 MVAr.

Performance and Testing

The GRITA link underwent rigorous testing during its development and installation phases. Factory system tests were conducted to ensure the link could withstand stresses caused by large perturbations, such as short circuits on the AC or DC side, and energisation and de-energisation of line components. On-site testing included an HVDC integrity test at 500 kV for 15 minutes, as well as full-scale tests of all equipment under normal operating conditions.

The link demonstrated several advanced features, including frequency regulation of the islanded AC network, automatic power fast reversal procedure, and a new protection mechanism for quickly recognizing total loss of the AC network.

Significance and Impact

The GRITA HVDC link plays a crucial role in connecting the EU grid to Greece, and through Greece, to producers in Albania and Turkey. This connection reinforces the Mediterranean ring and fosters east-west energy trading. The project has reduced grid operational costs, improved emergency response capabilities, and increased flexibility and reliability through active power reserve sharing between the Italian and Greek power systems.

Financially supported by European Commission grants and loans from the European Investment Bank, the GRITA project exemplifies the EU's commitment to developing integrated energy infrastructure. It enables Italy and Greece to use their installed power generation capacity more efficiently, contributing to the creation of a single European energy market capable of handling cross-border power flows.