Unified Modeling Technique for Axially Uniform and Nonuniform Eccentricity Faults in Three-Phase Squirrel Cage Induction Motors

Many mechanical faults cause eccentricity in squirrel cage induction motors (SCIMs), so it is reasonable to design and implement reliable eccentricity fault diagnosis systems for the SCIMs. Accurate modeling and simulation techniques help to reach this aim more easily. It is common to assume that the eccentricity fault is uniform along the motor length when modeling and simulation that is often far from real situation. In this paper, experimental inspection is performed first to show that having the same severity of eccentricity at one end of the motor, the axially nonuniform eccentricity may produce lower fault indices than the axially uniform eccentricity. Then, the two-dimensional (2-D) modified winding function theory is presented and used to obtain analytic expressions for various self-/mutual inductances of the stator windings and the rotor meshes and their derivatives versus the rotor position. The expressions are applicable under various axially uniform and nonuniform eccentricities as well as the healthy condition. Multiple coupled circuit model is used along with these expressions to develop a comprehensive analytic model for the SCIMs. Simulation results obtained by this model are in good agreement with corresponding experimental results and confirm accuracy of the attained modeling and simulation technique.