This paper studies the electrical network topology of two types of offshore wind farm power collection systems. The cost model of wind farm power collection system is established from the point of view of the whole life cycle. The topology of the radial structure is complex and variable

and the ring structure is operating in various ways

under these conditions

a unified model of the operating and maintenance cost of the collector system is built. This paper takes a typical offshore wind farm as an example

optimizes the power collection system from the life cycle cost perspective. The results show that at the present cost of the power cable

the ring structure displays some advantages after 16 years operation. A set of sensitivity analysis is done using different fault rates

repair times and maintenance costs of submarine cable to show their impacts on the life cycle cost of power collection system

which can provide guidance for the future design of power collection system. This work is supported by Shanghai Innovation Action Plan(No. 16DZ1203504).