Magnetic wedge failures in wind turbine generators

Magnetic wedges (containing a high percentage of ferrite material) have been used successfully to improve the operating performance and optimize the physical size of motors and generators by reducing heating and improving efficiency. They contribute to the overall performance by smoothing the electrical flux characteristics and are utilized primarily in stator applications. In large generators utilizing fully cured coil systems, these wedges are readily inspected and replaced as needed during times where maintenance or reconditioning requires that the rotor be removed. Specialized equipment and techniques have been developed and this process is well implemented in the electrical generation industry. When global vacuum pressure impregnation systems are utilized, replacing loose wedges is very difficult. Reviewed in this paper will be several wind turbine generator applications where this is a common failure mode, some possible weaknesses in the design of the coil/slot configurations and some possible solutions to avoid a repeat failure after repair. Also, some identified but not confirmed causal forces will be discussed.