The essential characteristics and the steps followed in the realization process of the new ±500 kV 1000MW HVDC link Sardinia Island – Italian Peninsula (SAPEI), whose completion was achieved at theend of 2010, are presented in this paper.
Notwithstanding the growing application of HVDC links around the world and the acquiredexperience in the area of DC energy transmission, any new HVDC link requires substantialengineering efforts because of the peculiarities of the networks to be interconnected and the quickevolution of the technology, that involve a continuous updating of system design.
In the case of SAPEI, the highest levels of availability and reliability of the link, together with thepossibility to restart from emergency conditions so as to cope with the peculiar needs of the Sardiniannetwork, were the drivers throughout any stage of the project, from the early localization of the plantsto the final commissioning.
Converters, converter transformers, AC filters, smoothing reactors, AC and DC yard switchingequipment as well as the control and protection system were designed, tested and realized with qualitystandards at the top of the state of art. At the same time, redundancies were adopted for all majorfunctionalities, and a particular flexibility of the circuit configurations was realized so as to permit aquick passage from bipolar to monopolar operation, avoiding the interruption of the entireinterconnection in case of failure of either one converter unit or one pole cable.
As far as the HVDC cables are concerned, the main challenges were the very high voltage, the lengthof the route, and above all the sea bottom depth, reaching the maximum of 1,620 m, an unprecedentedrecord for submarine cables, that confirms the high technology needed to achieve this kind of works.Mass impregnated paper insulated cables together with different sizes and conductor material (Cu andAl), were the solution to cope with the different installation and ambient conditions along the route.
The laying activities of submarine cables, that had been preceded by an extensive sea-trial campaign,were all performed by the Prysmian owned ship "Giulio Verne”. Following the laying, the cables wereprotected by burial on the seabed at a depth of up to 600m.
Finally, the commissioning tests were not only aimed at verifying the design performances, but werethemselves a fundamental part of the project, as they also gave the opportunity to make the finaltuning of the system performances and operations possibilities. To this end, even very rare conditionswere reproduced so that operators be ready to tackle any events.
But the challenges that the new realization went across were not of technical nature only.
Today developing and reinforcing the electric networks doesn’t only mean solving high-techproblems. Environmental sustainability is also a fundamental issue to be faced at any stage of any newrealization. This particularly applies to SAPEI link, that due to its nature, dimension and variety of thecrossed land or water stretches, has required a special care in the adoption of the most environmentallyfriendly solutions.