Validation of a Faulted Rotor Induction Machine Model With an Insightful Geometrical Interpretation of Physical Quantities

Many proposals about induction-machine broken-bar detection can be found in the literature. Disturbances that affect phase currents, current space vector, power, fluxes, torque, and speed have been utilized to diagnose mains-supplied machines. Nevertheless, there is still disagreement about how the fault signatures of the different variables correlate with the actual fault and how they depend on the operating conditions. This paper presents a simple but effective analytical representation of induction machines with rotor faults, based on a synchronous reference frame and on Steinmetz's phasors. The developed relationships can be visualized through equivalent circuits, feedback loop block diagrams, or geometrical loci, allowing a deep understanding of the underlying physical phenomena, particularly as functions of inertia and of the machine parameters. The insight thus gained helps to enhance the quantification of fault severity with respect to the usual diagnostic technique based on the sum of the sidebands, clearly defining for the first time the field of validity of such technique. The analytical results are verified through simulations and experiments.