Nowadays, under the background of global energy crisis and environment protection, the expansion of low-carbon generation is reshaping the traditional structure of power system. Many countries face the similar challenges in integrating the offshore wind power generation into the onshore power grid. HVAC, HVDC and LFAC (Low Frequency AC) technologies are regarded as the most promising solutions for the offshore wind farm transmission systems as shown in Figure.

xiang
Layouts of the offshore wind farms transmission systems

The cost analysis and comparison for these three transmission alternatives is the key factor to decide which alternative is the most cost-effective solution for a given offshore transmission distance. All of these three transmission alternatives consist of terminal cost and cable transmission cost. The terminal cost in lower frequency transmission alternative is much higher than that in higher frequency solution because of the expensive terminal converter stations, so when the transmission distance is short, the higher frequency solution is the cost-effective choice. However, the cable cost slope in higher frequency transmission system go much sharper than that in lower frequency alternative due to the larger charging current and lower transmission capability. When the transmission distance increases, the lower frequency transmission alternatives become the economical solution.  Meanwhile, with the transmission power rating increasing, the higher frequency transmission system will lose the advantage of lower terminal cost in shorter transmission distance due to the much higher cost in the cable cost when transmission power grows.

In order to locate the cost-effective range for HVAC, HVDC and LFAC respectively, a lot of factors, such as capital cost, maintenance cost, power losses, system reliability, all need be carefully compared and analysed. This research mainly take the capital cost and system power losses into consideration, and try to explore the cost break-even points for all of these three transmission alternatives with  the transmission distance and transmission power rating increasing.

 CAP People

  • Xin Xiang (x.xiang14@imperial.ac.uk)
  • Tim Green