Experimental Derivation of Thermal Parameters of the Stator- Winding Region in Thermal Analysis of PM Electrical Machines

The majority of heat generated in a permanent magnet (PM)electrical machine is usually attributed to the stator-winding assembly. Here, the main dissipative heat flow from the winding body is typically through the stator core pack to the machine housing. A good understanding of the machine dominant heat transfer mechanisms is therefore crucial in thermal design-analysis. There are two main experimental techniques available in the literature to inform the stator-winding heat transfer, the short-transient and steady-state DC thermal tests. Both tests allow deriving thermal parameters of the stator-winding region, including the winding-to-stator thermal resistance. The `short-transient' technique has been developed specifically for rapid thermal evaluation of complete machine assembly, e.g. in-production machine quality assessment. In contrast, the `steady-state' method is frequently time intensive, requiring for the tested hardware to reach thermal equilibrium. This drawback of the considerable testing time is particularly prominent for large machines with high thermal time constant. Both techniques can be applied to the complete machine as well as to a variety of the stator-winding sub-assemblies (motorette testing). Motorette testing enables a more controlled and repeatable testing environment with reduced time and resources required. This paper aims to connect both experimental techniques by comparing thermal parameters obtained from both complete stator and motorette thermal testing. The experimental work has been supplemented with theoretical analyses to identify applicability and limitations of both experimental methods.