Abstract
Recently the request for the compactness of rotating machines such as traction motors has been increasing and thus the rotating machines should be of high power density. This makes the magnetic saturation of the rotor-yoke more excessive and the heat generation per unit volume increasing To prevent the temperature rise, ventilation holes are provided in the rotor-yoke. Ventilation holes have not only the direct radiating effect but also the ventilation effect in the air-gap by reducing air-flow resistance. Moreover, ventilation holes have the role that lightens the weight of rotating machines. If we make the cross-area of ventilation hole larger for cooling however, the effective magnetic area becomes smaller, which causes in the further magnetic saturation. The magnetic saturation gives significant influence on the fundamental component of the air-gap flux density, which increases the magnetizing current and thus temperature. Hence, it can be said that the compactness of motors makes the problem of the magnetic saturation more serious.
With this background, this paper describes the design optimization of ventilation holes in induction motors. By investigating the relationship between the rotor-yoke configuration with ventilation holes and the magnetic flux density in the air-gap, we determine the desirable ventilation holes arrangement. Some numerical results, which demonstrate the validity of the proposed approach, are also presented.
