Analysis of bipolar-6-phase-transmission system with option of 4-phase-operation for large scale wind farms

This Paper presents the power system behavior of a bipolar 6-phase system. It is designed for connecting large scale offshore wind farms (OWFs) to the onshore grid. The 6-phase bipolar system fulfills the strict German environmental requirements concerning the surrounding magnetic field on high voltage transmission links through the North Sea. Further befit results from the option of switching the six phase system following cable faults to a symmetrical four phase system. It offers a continuous transmission capacity of 67 % of the design value if only one string is affected. Unbalanced interim states are, as shown in the paper, acceptable for the connected wind farm as well as the high voltage grid for a limited time duration.