Application of order cyclostationary demodulation to damage detection in a direct-driven wind turbine bearing

This paper presents a method of fault detection and isolation for a direct-driven wind turbine (DWT) bearing. Computed order tracking is employed to convert the non-stationary envelope signal in the time domain into a quasi-stationary signal in the angular domain by even-angle resampling. Cyclostationary demodulation is then utilized to expose the orders related to fault characteristics in the demodulation spectrum. In order to realize the automatic fault diagnosis and emit a stable alarm about bearing damage, the peak value of the demodulation spectrum is scaled and compared to a defined threshold. The significant advantage of the proposed method is the implementation of an automatic algorithm for DWT bearing diagnostics under randomly varying speed and highly alternating load. Practical applications are provided to show that the proposed approach is able to achieve reliable failure warning in the bearing condition monitoring of a DWT.