| The squirrel-cage induction motor has been widely used in engineering, broken bars fault has been a common form of the fault of motor. Cage is easy to be broken by the joint action of electromagnetic force, thermal stress, rotor dynamic stresses and residual stresses of cast aluminum and other forces, especially in the frequent starting process. In this paper, taking a squirrel-cage induction motor Y802-2 as an example, the electromagnetic force, structural mechanics and fatigue life are analyzed when motor is running at broken bars fault state. Based on the results of analysis, the process of rotor broken bars in squirrel-cage motor, and the evolution trend of broken bars are explained and discussed. Furthermore, it can provide ideas for analyzing the affect result from a variety of forces, and laying the foundation for the study of fault stress field.First, the magnetic field distribution are calculated with the case of healthy rotor,one broken bar fault and two broken bars fault in the squirrel-cage motor. Based on the results of magnetic field and combined with the Maxwell stress method and the principle of the Lorentz force, the electromagnetic force of rotor are calculated. In order to ensure the accuracy of the results of calculation process, local subdivision mesh, the weighted average and other methods are adopted. Rotor electromagnetic stress changes over time are obtained with the rated load operation and starting process by calculation, and the distribution characteristics and variation of the electromagnetic force are observed. The main action position of the magnetic force and the influence of the broken bar on the stress are summarized. In addition, the accuracy of the magnetic stress results is verified through comparing the calculated torque values of the method in this article and local Jacobian derivative method with the experimental ones.Secondly, the structural mechanics of rotor is studied, taking the electromagnetic force calculated by transient magnetic field as a load for the structural mechanics calculations. The mechanical process at a certain moment is approximately regardedas a static force, the moment of the rotor structure statics is analyzed. The distribution of rotor deformation with broken bar fault are gotten in the rated load steady and start state of the motor, and the large deformation of the position on the rotor are found. Based on the Von Mises stress by static calculated, the structure strength of the rotor is analyzed, and the rationality of the rotor structure and material is judged. The transient dynamics of the rotor is calculated according to the magnetic stress which varies with time, the time variation of displacement component curves of all direction and Von Mises stress curve changes are achieved.Finally, using ANSYS/FE-SAFE software, fatigue life distribution is carried out on three cases before and after the rotor broken bar. Rotor transient dynamic calculation results are taken as the load, combined with the S-N curve and the fatigue cumulative damage theory of the material, the degree and the effect of electromagnetic force are analyzed. Moreover, by changing the scaling factor in order to achieve the effect of a variety of forces, the fatigue damage degree of the rotor is analyzed in three cases, and the effect of the electromagnetic force on the fatigue life of the rotor is explained. |
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