Torque and field currents peculiarities under different induction machine troubles

Motor current signature analysis (MCSA) is a method usually adopted to detect troubles in induction machines. However misunderstandings can be found about the mechanisms linking the anomalies to the current spectrum components. To improve the comprehension of these mechanisms a rotor flux observer to compute field current and torque current is proposed. Input currents and voltages and mechanical speed are the signals taken into account for the computation. The effects of mechanical unbalance and of mixed eccentricity and then the effect of a rotor asymmetry are considered. For the experiments a machine presenting an intrinsic rotor asymmetry and an intrinsic mixed eccentricity is utilized. A mechanical unbalance and an artificial increment of mixed eccentricity are introduced. The peculiarities of the considered variables due to the different troubles and their dependence on machine load are evidenced.