Topology has a significant effect on the reliability performance of an electrical collector system (ECS) of wind farms. Novel indices for the reliability of wind farm ECS are presented based on topological features of wind farm ECS in this paper. The concept of the section for a wind farm ECS is defined. The probability table of multistate capacity (PTMC) for a wind turbine generator (WTG) and the Probability Table of the Number of WTG in Up-state (PTNU) for a section can be created. Based on the PTMC and PTNU, PTMC of a wind farm can be established using the state enumeration algorithm and the matrix operations. Therefore, the reliability evaluation model considering effects of wind speed and component failures can be built. The proposed model not only considers the multi-failures of ECS components including failures of cable feeder, WTG, and wind turbine transformer (WTT) but also states of switching devices in failure, disconnection, and switching processes. Four wind farm ECS topologies, i.e., radial topology, single-sided ring topology, double-sided ring topology, and star topology, are implemented. Case studies on the reliability evaluation of wind farm ECS are used to verify the feasibility and validity of the proposed technique. V C 2013 AIP Publishing LLC. [http://dx.NOMENCLATURE U i unavailability of the ith component A j availability of the jth component v t wind speed at the tth hour P(v t )power output of a WTG at the tth hour P r rated power output of a WTG v ci , v r , v co cut-in, rated, and cut-out wind speeds of a WTG, respectively N s-wf number of sections in a wind farm ECS N w-s number of total WTGs in a section N w-wf number of total WTGs in a wind farm N ts-w number of total states for PTMC of a WTG N ts-wf number of total states for PTMC of a wind farm t re repair time of a failed component, which equals the time interval from the moment of the occurrence of component failure to the moment of the failed component being repaired t ds disconnection time, which equals the time interval from the moment of the occurrence of component failure to the moment of the failed component being isolated a) Electronic