Influences on the electromagnetic torque and rotor force of different faults in squirrel-cage induction motors

Based on the scalar 3D formulation and the step by step in time domain finite element solution of the electromagnetic field in a squirrel-cage induction motor, the time dependence and harmonics of the electromagnetic torque and rotor unbalanced force are computed. The results for different faulty states of motor operation are compared with those for the healthy motor. In comparison with the healthy state, when the imposed speed motion model for loaded motor operation is considered, only the broken bar fault has a consistent influence on the mean value of the motor torque. Important influences on the mean values of the rotor unbalanced force are in decreased order the broken bar fault, the rotor eccentricity fault and the stator short-circuit fault. All the three faults generate specific harmonics of the motor torque and of the rotor force.