Multi-terminal multi vendor HVDC grid design studies – Part I: load flow study and contingency analysis

Multi-Terminal (MT) HVDC networks have been studied for over a decade, with recent efforts increasingly focusing on enabling multi-vendor interoperability to support a competitive and scalable deployment framework. Concurrently, protection selectivity is receiving renewed attention in the context of large-scale offshore connections based on 2 GW bipolar building blocks, where the maximum loss of infeed has become a critical planning constraint. This three-part series addresses early-stage system-level studies of MT HVDC grids using generic models, which are essential to support primary design. As part of the InterOPERA project, involving HVDC vendors traditionally responsible for DC-side design in point-to-point schemes, a methodology is proposed to instantiate project-specific technical requirements at subsystem DC point-of-connection. This first part focuses on steady-state studies to determinesecureDC voltage ranges and primary control settings, ensuring N-1 compliance. For the considered three-terminal topology, different configurations of converter station connections (to onshore grids and offshore wind farms) are analysed. The case with two onshore and one offshore station exhibited the narrowest margins, prompting the definition of configuration-specific settings for the InterOPERA demonstrator. The same approach is shown to be relevant for degraded modes arising from permanent asset unavailability, with particular attention to pole-to-ground voltages under asymmetrical operation.