COOLING AND COOLING CIRCUITS FOR ELECTRIC MOTORS.

The superior dissipation obtained by blowing air over a surface rather than relying on natural convection and radiation results in all but the smallest motors relying on some form of forced cooling, in which cooling air is blown over the surfaces to be cooled by shaft-driven fans. Though the cooling-air paths of electric motors are often complicated by the need to cool all the many component parts of the machine in which losses occur and therefore in which heat is generated, nevertheless an application of quite simple considerations of fluid flow yield acceptable methods of estimating the resistance of the air paths. Similarly, the behavior of the common types of fans used on electrical machines is developed, and, by way of illustration, graphical solutions are indicated for a few typical motor cooling circuits.