Design considerations for the COBRAcable HVDC interconnector

TenneT and Energinet.dk - TSO's of the Netherlands and Denmark respectively - are currently in the construction phase of a HVDC cable connection that will interconnect the electricity grids of the two countries. The new interconnector will run between two onshore converter stations; from Eemshaven station in the Netherlands to Endrup station in Denmark [1]. The COBRAcable interconnector links the two AC networks via a HVDC symmetrical monopole configuration connected by submarine and land cables of ±320 kV. Bi-directional power transmission capability is foreseen. The nominal transmission power capacity of the link is 700 MW, as referred to the AC side of the sending end. The reactive power exchange capacity is ±230 MVAr at each end. The COBRAcable project is currently in the detailed design phase and this paper's work was prepared during the development and early stages of the design phase. The work presented here has been part of TSO's overall responsibility task to ensure and check the smooth technical integration of the converters with the cable and of the HVDC system into the AC network. Therefore, certain design aspects were studied in more detail; two of those are presented in this paper: the energization process (in chapter 3) and, ; the HVDC system compatibility with the DC cable (in chapter 4).