Detection and Identification of Demagnetization in PM Generators During Transient Conditions

Direct drive permanent magnet machines used in renewables typically have high numbers of poles leading to low speeds. This poses a challenge for detection of faults during transients, while few periods of the operating waveforms can be captured. In this paper, the authors will demonstrate that the demagnetization harmonics are directly related to the number of stator coils and the number of poles leading to different signatures in every machine. Moreover, the traditional signatures may not be clear in the spectrograms due to the low rotor speed. Under such conditions, the monitoring of specific higher harmonics can lead to reliable detection and identification of the demagnetization fault. The fault can be reliably distinguished from other rotor-related faulty conditions. This paper demonstrates results from a double rotor axial flux PM generator.