Qualification and Sea Trial Tests for the 500 kV Tyrrhenian Link HVDC Cable System

The HVDC VSC Tyrrhenian Link consists in a Double Bipolar Interconnection with rated voltage of 500kV: 2 × 500 MW for East Bipole (between Italy Mainland and Sicily), and 2 × 500 MW for West Bipole (between Sicily and Sardinia), whose marine cable will reach the worldwide record laying depth of 2150m. The link owner is Terna, the Italian Transmission System Operator (TSO). Prysmian is in charge for engineering and construction for both cables of the East Bipole, one pole cable of West Bipole and the electrode system, while Nexans is in charge for engineering and construction of the other pole cable of West Bipole. This paper describes the design of the Prysmian power cable system and the qualification test program that will be carried out on all cable types and accessories, taking into account CIGRE recommendations and Terna prescriptions. Dedicated tests will be performed to verify the withstand to Temporary Over-Voltages (TOV) and fast grounding characteristics of the VSC converter. The paper also focuses on the challenging sea trials in high deep, deep and shallow water, and the burial machines; the results of some of these tests - already carried out by Prysmian - are also reported.