Analysis of the endwinding cooling effects in TEFC induction motors

This paper deals with the endwinding cooling problems of totally enclosed fan-cooled (TEFC) induction motors. In order to obtain information about the phenomena involved in the motor end space, three "ad hoc" prototypes have been build. The complete test-bench setup, together with the followed test procedures, is reported in detail. The measurement results have shown that all the motor-part overtemperatures (winding, endwindings, stator lamination, and external motor frame) decreasing, with the inner air speed increasing. The measured motor overtemperatures and losses allow the thermal-resistance identification of a simplified thermal model suitable to describe the thermal behaviors of the prototypes. By the endwinding-to-motor frame thermal resistance, the related heat-exchange coefficients have been evaluated as a function of the rotor speed. The proposed procedure allows separating the forced-convection contribution by the other thermal-exchange phenomena that occur in the end-space regions. The obtained heat-transfer coefficients are in agreement with the results reported in the past literature.