Low frequency AC for offshore wind power transmission - prospects and challenges

This paper deals with the technical feasibility of low frequency alternating current (LFAC) for offshore wind power transmission. As is well-known, the charging current presents itself as the main limitation for ac power transmission using 50/60Hz. By using LFAC, the reach of ac transmission can be extended and the investment cost that would have been necessary for VSC HVDC based transmission reduced. The paper starts by providing an overview of the technology of LFAC transmission on the basis of 16 2/3 Hz which is used for rail track electrification in some European countries. This is followed by a discussion on the availability of equipment for use in LFAC transmission and the possible areas where new development or major modifications are required. Finally the overall technical and economic viability of such a transmission for use in offshore wind power transmission evaluated. It is demonstrated that more than 600 MW can be transmitted with a single three-phase 245 kV cable over a distance of approximately 400-500 km. This means that the whole wind power expected from wind farms in the North Sea could be collected and transmitted to the onshore grid at 162/3 Hz frequency using 245-kV cables without HVDC lines and the need for offshore converter stations.