DC Fault Protection Assessment of Medium Voltage DC (MVDC) Systems for Offshore Wind Energy Transmission

Medium voltage DC (MVDC) systems have the advantages of fewer conversion stages and lower power losses in the MVDC collector for offshore wind energy transmission and can avoid the need of costly offshore platforms, leading to significant reduction of the capital cost. In this paper, DC fault protection of MVDC systems is assessed considering both parallel and series connection arrangements of wind turbine converters. Typical DC fault protection strategies considering selective, non-selective, and partially selective fault clearing will be assessed and their impact on fault currents and voltages and the AC onshore and MVDC offshore network will be studied. The use of different DC protection devices including fast acting DC circuit breakers (DCCBs) and DC switches/disconnectors (DCSWs), and their locations on protection and system recovery will be highlighted.