Diagnosis of induction motor faults using the full spectrum of direct and quadrature currents

In this work, it is proposed to use a new reference frame in dq variables fixed to the stator fluxes to discriminate faults such as broken rotor bars in induction motors from low frequency load oscillations. In this new reference frame, only the stator current q contributes to the electromagnetic torque. This makes it sensitive to load faults, such as oscillations, while the current d is sensitive to motor faults, such as broken bars. Also, the steady state currents in dq variables are constant. Finally, it is possible to obtain two three-phase currents, one load-sensitive and the other motor-sensitive, which can be analyzed with classical signal analysis techniques. The proposal is validated through simulations, analyzing the full spectrum of the two three-phase currents. It is shown that with this new reference frame it is possible to discriminate between broken rotor bars in induction motors and low-frequency load oscillations.