ABSTRACT
This chapter concentrates on comparing geared generator and direct-drive concept wind turbines (WTs), and so focuses on the following sub-assemblies: blade, gearbox, generator, converter, pitch and yaw system. The reliability of WTs as a part of a large power system is assessed in many references. The main reason for using the direct-drive concept rather than the geared generator variable-speed system is to eliminate gearbox failure and downtime effects. A reliability comparison between geared- and direct-drive concepts WT could verify this reason. ‘Sub-assembly Reliability Models’ reviews related concepts of reliability modelling theory, and shows the subdivision considered for WT. The first generation of variable-speed WT systems used a multistage gearbox, a relatively low-cost standard doubly fed induction generator and a power electronic converter feeding the rotor winding with a power rating of approximately 30 per cent of the rated power of the turbine.
