Selection of the rated frequency for fractional frequency offshore wind power system

Nowadays the exploitation and utilization of the offshore wind power has won global attention. The application of fractional frequency transmission system (FFTS) in the integration of offshore wind power forms fractional frequency offshore wind power system (FFOWPS), which provides an efficient solution for large-scale offshore wind power integration. To achieve the standardized production of transmission equipment and boost the economies of scale equipment manufacturing, FFOWPS is supposed to operate at its own rated frequency, like traditional AC transmission system. Taking all the factors such as the influence of frequency on critical equipment in the system, operating experience of low frequency system from home and abroad, economic efficiency and technicality into account, this paper puts forward 50/3 Hz as the rated frequency of FFOWPS. Then an offshore wind farm case is analyzed to compare the transmission capacity of the cable and the voltage fluctuation of the integration point at 50 Hz and 50/3 Hz. The result shows that the technical performance of 50/3 Hz is much superior to that of 50 Hz. Even without shunt reactor, FFOWPS with 50/3 Hz as the rated frequency can transmit 467.6MW wind power to a distance of 364.2 km. Besides, the voltage fluctuation of integration point in the system can also meet the relevant regulations.