Asymmetric Thermal Model for Totally Enclosed Fan-Cooled Induction Motors

摘要

The report deals with the design of a thermal model for totally enclosed fan-cooled (TEFC) induction motors. The calculation of the temperature distribution is based on the thermal network method. The power losses are provided by the finite element (FEM) analysis of the motor. In the research a 15 kW cage-induction motor was used as a test motor in defining the accuracy of the designed thermal network. Heat conduction, convection and radiation take place in electrical motors and several formulas have been designed in order to model these heat transfer mechanisms. By help of these formulas and the analogy between electrical and thermal quantities a thermal network for TEFC induction motors has been designed. The complete thermal model consists of 12 thermal networks which are based on the thermal network of a regtangular prism or a general cylinder component. The ribbed frame of the motor has been considered as several straight fins parellel to each other. In a TEFC induction motor the asymmetric temperature distribution is due to the centrifugal fan in the non-drive end. Based on the thermal resistance of a straight fin and the heat transfer coefficients for a flat plate the frame is implemented to the thermal network. The formulas for convective heat transfer in the airgap, endwindings, endrings and endcaps have been found from the literature.