Multi-terminal multi vendor HVDC grid design studies - Part III: transient study

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 refine, and eventually instantiate, project-specific technical requirements at subsystem DC point-of-connection. This third part focuses on transient studies, quantifying maximum DC short-circuit currents and overvoltages induced by pole-to-ground faults throughout the fault separation process. The variability of system-level electrical stress is assessed as a function of two key design parameters: AC/DC converter reactor sizes and DC circuit breaker’s maximum fault neutralisation times. Broader discussions on insulation coordination considerations and DC fault ride-through requirements are also provided.