Diagnosis-oriented sequence circuit-based modeling of eccentric rotor traction induction motors accounting for cage damping and split-phase currents

A 1130kW squirrel-cage induction motor used for railway traction is analyzed in this paper in case of eccentric rotor. Since the motor has parallel-connected windings, the air-gap unbalance makes rise unbalanced currents in the stator branches, and the split-phase current signature analysis can be attempted for fault detection. The split-phase currents are better analyzed when transposed in the complex domain, by using symmetrical components. Moreover, the rotor cage currents must be carefully taken in account in the model, since they develop a powerful damping effect on the signature of static eccentricity. This paper shows that the faulted machine can be represented by the superimposition of five equivalent circuits corresponding to five centered-rotor virtual machines, useful for fault-related split-phase current calculation. The mathematical modeling shown in this paper is useful to carry out a diagnostic method, as shown in a companion paper. The latter also reports confirmatory simulations of the faulted 1130kW motor, based on winding function approach.