Abstract: In order to select a suitable way for submarine power transmission system with cables, discounted cash flow model was used to compare DC system and AC system from an economic perspective. The costs of DC/AC submarine transmission system were analyzed from three aspects： investment cost, maintenance cost and loss cost, and the calculation methods of each kind of cost were presented. In the case of submarine cable system connecting an offshore wind farm and onshore grid, the economies of DC/AC submarine transmission systems with different transmission distances were compared, and the comparison results were obtained. The results indicate that the cost of DC submarine transmission system is higher than AC submarine transmission system when transmission distance is short, while in the case that the distance is beyond a certain level, DC submarine transmission system will have economic advantage.

Key words: economy, AC power transmission, DC power transmission, submarine cable