Detection of Eccentricity Faults in air-cored C-GEN PM Machines for Wind Turbine

Eccentricity faults in air-cored Permanent Magnet (PM) machines may go undetected when MCSA is applied, due to harmonic cancellation between different coil induced voltages. This condition may lead to false negative diagnostic alarms when the stator current is used. However, when the fault happens, the current density in specific coils could increase significantly and depending on the eccentricity fault severity level, leading to increased thermal stress and therefore accelerated insulation degradation. Moreover, the overall generator efficiency will be negatively affected. In this work, the stator current, stray flux, and torque have all been thoroughly investigated, with the torque proving to have significant advantages and increased diagnostic sensitivity under static, dynamic, and mixed eccentricity situations and various fault severity scenarios.