The Use of Electrical Models in Cooling Studies of Electrical Machines

The electrical analogy of heat transfer is a well-established experimental approach to complex heat transfer problems. In this paper the theory of the analogy is summarized and the results of applying the analogy to cooling studies of traction motor armatures are discussed. Electrical models, simulating two- and three-dimensional heat flow in 375-kW traction motor armatures were constructed, and temperatures in the armature conductors, core, and teeth were predicted for varying speed conditions. An axially varying surface heat transfer coefficient was found to give considerable axial temperature variation, due to the low thermal conductivity of the armature core in that direction. Values of surface heat transfer coefficient were obtained which gave predicted temperatures in agreement with measurement. The effects of increasing the axial cooling duct area were investigated.