The first Belgian HVDC Link - NEMO - technical choices, obstacles and future

A major focus of the Western European Transmission System Operators (TSO's) is reinforcing their crossborder power capacity for mutual support in case of emergencies and also as an beneficial good that can be traded on specialised energy markets. The Belgian TSO, Elia, is studying the use of new and emerging technologies, together with their advantages and disadvantages, for further development of the interconnections with the neighbouring countries. High Voltage Direct Current (HVDC) technology, and especially the promising Multilevel Modular Converters (MMC) for the Voltage Sources Converters (VSC) opened a wide range of new opportunities. The NEMO project, a 1000MW undersea link with the United Kingdom, is the object of interest for this paper. A quite similar link, technology-wise, but with other motivations and challenges, is the ALEGRO-link, with a rating of 1000MW as well. Both installations will be connected to the meshed 400kV-grid. The paper gives an overview of the technical choices and obstacles that are made, their motivations both for the AC/DC converter and the subsea cable. For the converter and its connection to the main grid, specifically the Belgian side, the main focus will lay on the choice of converter technology between the two concurring state-of-the-art technologies based on thyristor and IGBT topologies. The drastic reduction of the operation losses over the years, lesser footprint, absence for the need of reactive power and additional filtering, grid support in voltage and frequency, the possibility for blackstarting, and by nature the most adapted technology for meshed DC grids, made the technology decision sway in the direction of the MMC VSC configuration. The subsea power link side of the project contains a set of particular obstacles as well. First of all: the cable routing. This part of the North Sea, close to the harbours of Zeebruges, Antwerp and Rotterdam, is one of the world's most used sea routes. The selection of the cable route needed to be chose for minimal interaction with the present maritime transport (e.g. anchor dragging, compass deviations), with existing pipe line and telecom routes, detected ship wrecks, environmental protected zones (onshore as well as offshore) and future possible development of the HV network in the sea. The paper will present the major outcomes for the cable routing: offshore route on the seabed, the necessary landfalls and the onshore route to the HVDC substation on the Belgian side. In