Towards a Standardised Approach of Deriving Thermal Parameters in the Design of Electrical Machines

This paper describes a methodology for experimentally deriving thermal parameters in the design of electrical machines, with a focus on, but not limited to, short-duty transient operation. Here, all key stator-winding thermal resistances and capacitances, which can be directly derived from thermal tests, are considered. The proposed approach is based on the transient thermal step-change response for a specimen /mottorete under test, where the heat transfer is well-defined and limited to a single path, e.g. a heat source (stator-winding body) to a heat sink (machine housing). Any imperfections like the heat flux leakage from the motorette body/test rig are considered and experimentally compensated for. A detailed description of the underpinning assumptions, test procedure, required instrumentation, and measured data post-processing is provided and supplemented with several examples from hardware tests. Applicability and limitations of the methodology are also discussed. The presented approach provides a novel standardised testing method, where the measured data can be simply shared across different electrical machine designs to bring a means for an accurate, time- and resource-effective design/assessment process. This expanded work elaborates more on the existing figures of merit, highlighting their deficiencies when thermally sizing electrical machines. Further to this, a more detailed discussion of the methodology, supplemented with new examples, is provided.