Calculation And Analysis Of The Force On The Rotor In Squirrel Cage Induction Motor With Broken Bar Fault

Broken bar fault is a common fault in a squirrel cage induction motor. One orsome combinations of the factors such as the thermal stress of the rotor, the magneticforce on rotor, the residual stress on cast aluminum, the dynamic stress of the rotormay lead to the broken bar fault. According to the literatures, there is no quantitativeanalysis on how much the factors affect the faults.The physical fields changing of the motor before and after the fault are studied inthis dissertation, the magnetic field of the motor, the thermal field, magnetic forcedistribution, and the thermal stress of the rotor with healthy, one broken bar and twobroken bars fault are calculated by finite element method, respectively.Firstly, the magnetic fields when the motor operates in different fault levels arecalculated, and the losses in the rotor are solved due to the magnetic results, so thethermal fields of the rotor could be obtained, and the temperature results are verifiedby the experimental value. Secondly, combining the Maxwell stress tensor methodand the Lorentz theory, we calculate the magnetic force on the rotor based on themagnetic results. In the procedure of the force calculation, the accuracy problem isconsidered. The characteristics of the three kinds of magnetic force are analyzed inthree cases, the stress concentration positions are also summarized, and the furtherbar breakage is predicted. Finally, on the basis of the thermal results, the von-Misesstress, the stress vector and the displacement of the rotor in three cases are solved, wecalculate the safety factor of the squirrel cage based on the thermal stress distribution,and one brittle failure criterion is recommended, the most probably broken locationdue to the thermal load is also proposed.The aim of this dissertation is to provide the references for proposing thediagnostic characteristics, and the reports about the effect of the magnetic force andthermal stress on the fault could guide the further investigation on the failure causes and development.