Use of high order harmonics for diagnosis of simultaneous faults via Wigner-Ville distributions

In this paper, high-order fault-related current harmonics are used for the diagnosis and discrimination between two different faults in induction machines: rotor asymmetries and mixed eccentricities, both when only these faults are simultaneously present in the machine and when they are combined with other non-fault related phenomena. The idea is to track the evolutions of both the high-order fault-related harmonics and the low-frequency ones during the startup transient, making use of suitable time-frequency decomposition tools. In this work, a Wigner-Ville Distribution (WVD)-based method is proposed, since this is a tool showing a good trade-off between frequency resolutions at high and low frequencies, despite other Time Frequency Decomposition (TFD) tools could be also valid. As stated by several authors, use of high-order harmonics can provide very useful information for the diagnosis, mainly in those cases in which the only identification of low-frequency fault-related components might be not enough conclusive (presence of inter-bar currents, effect of load torque oscillations, etc...). In the paper, several cases corresponding to single and combined faults are presented. Simulated and experimental results show the ability of the tool for tracking those fault-related components, enabling the diagnosis of the aforementioned faults, even when these faults are combined or coexist with other phenomena which could interfere the diagnosis, such as pulsating load torques.