Improved thermal model of forced air-cooled motors considering heat transfer in wirewound winding and end region

Abstract

This study introduces an innovative thermal model to accurately consider the heat transfer in the winding and end region of forced air-cooled motors, which is an attractive supplement of classical lumped parameter thermal network approaches. Through coupling of the analytical method and local numerical calculations, the effective length of the winding heat path and the air convection of the end region can be exactly considered. An improved analytical derivation of the equivalent thermal conductivity of the winding is applied. To reduce the errors caused by the irregular slot type, the winding thermal resistance is calculated by the 2D numerical calculations. After that, the 3D model of the end region is built to accurately calculate the end air velocity and end convection resistance. The unknown boundaries of the 3D end model are determined by a coupling iteration. The errors of the winding thermal resistance and end convection resistance are less than 3.12 and 11%, respectively, verified by simulations and temperature tests of the prototype. Finally, the mechanism of the end region convection and its influence on the temperature rise of the entire motor are discussed in detail.