Non-Steady State Thermal Performance of Electrical Machines

Abstract

Because the ratings of electrical machines continue to increase, there is a growing need to be able to predict their thermal performance under the transient conditions caused by overloading or stop-start operation. The design of electrical machines is often too complex to make an analytic solution feasible, but a general numerical method has been developed to predict component temperatures at the drawing-board stage. The problem to be solved is represented by a thermal resistance-capacitance network, the resulting set of simultaneous equations being solved by a digital computer employing a step-by-step procedure. The number of network nodal points at which the temperature can be calculated is at present restricted by computer storage space to 150, therefore the fully three-dimensional problems which can be solved are of limited complexity. However, the majority of electrical machines can be simplified by assuming axial symmetry, which permits a large variety of problems to fall within the capabilities of this technique.