Offshore wind farm faces challenges such as large capital investments in construction

high failure rate and low accessibility for operation and maintenance (O&M) because of the severe climate conditions compared with onshore wind farm. Aiming to achieve balance between cost of investment and reliability of power generation in the process of construction and operation

four types of redundancy configurations of power transmission system for offshore wind farm have been proposed. Based on the theory of life cycle cost (LCC)

a modified model according to offshore situation was established and applied to overall economic analysis of the main transformer at the substation in Laizhou Bay offshore wind farm project. The calculation of various stages in main transformers life cycle cost has been studied. Overall economic costs of main transformers under four redundancy configurations were calculated for comparison. The sensitivity analysis has been conducted in regard to the key factors including discount rate

feed-in tariff and failure rate. Then the optimal redundancy configuration considering these key factors will be selected. The analysis provides the theoretical basis for the optimal choice of redundancy scheme offshore wind farm power transmission system. This work is supported by National High Technology Research and Development Program of China (863 Program) (No. 2012AA051704).