High Resolution Lumped Parameter Thermal Network for Load Cycle Analysis of Electrical Machines

In electrical machine design, the winding temperatures arising during machine operation are of crucial interest, as they are closely related to a maximum permissible current density. Moreover, under varying load conditions also the operation trajectory, i.e. the temporal sequence of operating points, needs to be considered to ensure compliance of maximum winding temperatures and thus a safe operation. However, the temperature distribution among the winding conductors inside the slot is usually considered, if at all, by means of a single object with a uniformly distributed equivalent thermal conductivity incorporating conductors, insulation material, air and further impurities. This approach lacks accuracy and may not regard possible hotspot temperatures. Therefore, this paper proposes a thermal network model of a slot with single conductor resolution based on triangular elements, making it possible to identify each conductor’s temperature individually. Furthermore, this approach also allows the consideration of additional AC losses apparent in the winding on a single conductor basis and their influence on the temperature distribution inside the slot. Altogether, the proposed thermal model offers a computationally efficient method to calculate the expectable evolution of chosen machine temperatures during load cycle operation, giving the machine designer a tool to tailor an electrical machine for a demanded load profile.