HVDC submarine power cables in the world: state-of-the-art knowledge

This science-for-policy report is the first deliverable of the OTG project. It provides an extensive study on the availability of the technologies required for the realisation of a High Voltage Direct Current (HVDC) interconnection between the European and North American Alternating Current (AC) transmission grids. An introduction on HVDC transmission systems is given. This implies a discussion on the monopolar, bipolar and back-to-back configurations. Also the connection with AC grids, i.e. the converter station, is treated. Further, attention is paid to the spatial context of laying a HVDC submarine power cable. Information is provided regarding geological and path surveys, subsea bed topography, geological structure and lithology. Geodynamic processes, sea currents, waves as well as temperature and salinity are also discussed. Technologies and materials used to produce HVDC submarine cables are presented. Different cable types are shown. Special attention is given to the installation of HVDC submarine cables. Techniques for laying a cable are discussed. Also issues such as protection measures and maintenance aspects are dealt with. The operation of HVDC submarine cable is treated as well. Reliability and accident risk issues are discussed in a dedicated paragraph as well as environmental aspects. A complete, comprehensive chapter is spent on existing and planned HVDC submarine interconnectors. Emphasis is given the longest and deepest examples. An extensive list of these cables with relevant data is given in Annex 1. The report ends with a set of conclusions, primarily pointing at the following steps of the OTG project. Shortly, they are as follows: - the HVDC submarine power cable technology is now mature; - the experience in laying the cable on the seafloor is inherited and adapted from the much older technology of telecommunication submarine cables; 8 - Europe is the leading region in both the length and number of cables having the longest one, the deepest one and one of the most powerful cables; the majority of manufacturers and sea-laying cable operators originate here; - mass-impregnated cables are the most used but a new generation of extruded cables are gaining field; - first submarine power cables used a monopolar configuration but the newly built ones are predominantly bipolar.