TWENTIES : conclusions of a major R&D and demonstration project on offshore DC grids

TLDR: The TWENTIES European project as discussed by the authors has developed a DC Circuit Breaker (DCCB) prototype to overcome a strong technological barrier: this new equipment was successfully tested in presence of an independent expert to establish the qualification of this technology in the HV domain.

Abstract: European governments’ targets for renewable energy by 2020 will lead to large offshore wind power integration in the existing Power System. High-Voltage Direct Current (HVDC) provides the most suitable technology to enable massive integration of offshore wind farms into AC onshore grids over long distances, with great control on transmitted power. More specifically, DC Grids (DCG) based on Voltage Source Converters (VSC) are being widely investigated to integrate multiple offshore wind farms dispersed over wide areas into AC onshore networks.  For three and a half years, the « DC GRID » demo within the TWENTIES European project was focussed on a wide range of challenging issues related to the DC grid benefits for connecting offshore intermittent power: offshore DCGs economic assessment and likely layouts; DCG control and protection; ancillary services provided by such grids to the mainland AC network. This paper presents major achievements of the TWENTIES project in these domains.  In addition, two major outcomes of the « DC GRID » demo are physical demonstrators. One of them is a low scale DCG mock-up, on which some of the above controls, as well as DC grid protection algorithms were successfully tested. Last, a highly innovative DC Circuit Breaker (DCCB) prototype was developed to overcome a strong technological barrier: this new equipment was successfully tested in presence of an independent expert to establish the qualification of this technology in the HV domain.