Diagnostics of a double-cage induction motor under steady state with the rotor asymmetry

This article presents a method of diagnosing the rotor circuits of a double-cage induction motor operating under a steady state at a constant angular velocity. A circuit model of the motor is formulated, considering an infinite spectrum of spatial harmonics in the airgap under the parametric asymmetry of the rotor cages. This facilitates the qualitative determination of diagnostic signals in the phase current of the stator circuit. The proposed method can effectively recognize the location and level of damage. The harmonic balance method is used to solve the model. Example calculations are provided for a medium power motor, associated in a star without a neutral conductor and a rotor shorted using separate rings.