Analysis And Calculation Of A Canned Motor With Solid And Cage Rotor By Finite Element Method

Canned motor with solid and cage rotor has the same operating characteristic with ordinary canned motor, while ferromagnetic solid rotor embedded with rotor bars is adopted, it makes this special kind of motor has not only the high mechanical reliability as the solid rotor motor, but high power factor and efficiency when running with small slip as the ordinary induction motor, and therefore, it is widely applied in many drive systems.Induced eddy currents in stator can, rotor can and solid rotor body influence on the distribution of air gap field when motor runs, on the other hand, losses caused by eddy currents make the motor's temperature rise as well as efficiency lower. Electromagnetic design and performance analysis to the motor with traditional magnetic circuit method couldn't precisely take the saturation and eddy current into account, the calculated values often have greater errors compared with test results. When finite element method (FEM) is introduced, it is easy to consider the impacts of these factors on motor's performances, analyze the distribution of magnetic field and eddy currents and offer the reliable theoretical references on analysis of running performances as well as the optimization design for the motor.Firstly, equivalent circuit is set up according to the structural characteristic of this kind of motor, the method to calculate the parameters by using FEM is presented. The calculated formula for eddy current losses in stator can is derived under certain assumed conditions, all main factors related with eddy current losses are analyzed and the measures to reducing the losses are also given. Then, the paper presents the principles and computational methods of numerical calculation to the electromagnetic field, summarizes all kinds of motor's two-dimensional (2D) finite element models and illustrates the scopes of application, advantages and disadvantages of each model respectively. Magnetic saturation and skin effect of rotor's eddy current of an induction motor with solid and cage rotor when starting are analyzed using 2D nonlinear time-harmonic FEM. Finally, modeling and calculation to a canned motor with solid and cage rotor are implemented using 2D transient FEM, operating performances for no-load starting and rated load conditions are also analyzed. Eddy current losses in stator can are calculated and the results are also compared with values calculated by analytical formula to validate the reliability and accuracy of FEM when analyzing motor's eddy current field.