Analysis of electromagnetic and thermal fields for induction motors during starting

In order to improve the starting performance of squirrel-cage induction motors, the so-called "skin effect" becomes very serious, which causes a highly uneven distribution of rotor-bar currents. The corresponding conduction losses of the upper and lower portions of rotor bars create high thermal stress, which may damage the rotor bars, particularly at the junction of rotor bars and end-rings. Hence, it is important to predict the starting and operating characteristics of induction motors more accurately for the purpose of ensuring the reliability of motor operation. This paper employs a visual-aided finite-element method to analyze the electromagnetic and thermal fields of induction motors during starting. By using visual and interactive pre- and post-processing techniques, the analysis can be applied to squirrel-cage induction motors with any physical dimensions, material properties, and system parameters. The starting performance, including the distributions of magnetic flux density, current density, loss density and temperature rise, are presented dynamically by computer animation, which are convenient and powerful for the evaluation and design optimization of induction motors. The theoretical predictions are verified by direct comparison with experimental results.<
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