HVDC submarine power cable systems-state of the art and future developments

The paper begins with an introduction on the reasons that lead to the use of HVDC submarine cable links. The main aspects for the choice of direct current are presented as well as the advantages deriving from the utilization of submarine cables. The second part is dedicated to a discussion on the various type of insulation that could be used in power cables and their possible application to HVDC submarine cables. There is a description of the main characteristics and technical details of two projects. The first is Spain-Morocco link, a 26 km long interconnection for the transmission, in a first phase, of 700 MW from Spain to Morocco at 400 kV AC by means of three cables, plus one spare, of the fluid filled type. The cables are designed for a future change to 450 kV DC, allowing a transmission of 500 MW each (i.e. 2 GW total). One of the peculiarities of the link is the maximum water depth of 615 m (world record for submarine power cables at the time of installation). The second is the Italy-Greece link, a 160 km long interconnection for the transmission of 500 MW (bi-directional) by means of one paper insulated mass impregnated cable having 1250 mm² conductor size and insulated for a rated voltage of 400 kV. This link will attain the world record for the maximum water depth for submarine power cables: 1000 m. The last part deals with the future development expected in this field, in terms of conductor size and voltage leading to an increase in transmissible capacity