This paper focuses on reviewing grid connection of large offshore wind farms (OWFs) employing current state-ofthe-art voltage source converter based high voltage direct current (VSC-HVDC) technologies. A brief review of the VSC-HVDC evolvement is given followed by an overview of the advantages of employing VSC-HVDC for grid connection of large OWFs located remote from shore. A detailed description of the topologies is given and simulation results are presented in order to illustrate some of the main features of the most popular multilevel VSC-HVDC topology.Based on the review it is found that there are currently three vendors of the VSC-HVDC. Furthermore, it is found that the VSC-HVDC is a promising technology for grid connection of remote located OWFs and is going to be the preferred choice for remote located OWF grid connection in e.g. the UK.

Switching overvoltages (SOV) are considered a possible source of component failures experienced in existing offshore wind farms (OWFs). The inclusion of sufficiently accurate and validated models of the main electrical components in the OWF in the simulation tool is therefore an important issue in order to ensure reliable switching operations. Transient measurement results in an OWF are compared with simulation results in PSCAD EMTDC and DigSILENT Power Factory. A user-defined model of the vacuum circuit breaker (VCB) is included in both tools, capable of simulating multiple prestrikes during the closing operation. An analysis of the switching transients that might occur in OWFs will be made on the basis of the validated model, and the importance of the inclusion of a sufficiently accurate representation of the VCB in the simulation tool will be described. The inclusion of the VCB model in PSCAD greatly improves the simulation results, whereas little improvement is found in DigSILENT. Based on the transient study it is found that the simulated SOV can be up to 60% higher at the sending end when using the detailed VCB representation compared to the built-in switch, which emphasises the need for accurate representation of the VCB for energisation studies.

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