Diagnosis of Rotor and Stator Asymmetries in Wound-Rotor Induction Machines Under Nonstationary Operation Through the Instantaneous Frequency

This paper proposes a methodology to improve the reliability of diagnosis of different types of faults in wound-rotor induction generators which work under variable load conditions, as in wind turbine applications; the method is based on the extraction of the instantaneous frequency (IF) of the fault-related components of stator and rotor currents during speed changes caused by nonstationary functioning. It is shown that, under these conditions, the IF versus slip plots of the fault components are straight lines with a specific slope and y-intercept for each kind of fault. In addition, neither of these patterns are dependent on the machine features or the way that the load changes. The practical methodology of this technique is introduced for diagnosing two different anomalies: stator winding asymmetry and rotor winding asymmetry. The approach is validated by laboratory tests for both types of faults in two different kinds of machines.