Investigation of equivalent stator-winding thermal resistance during insulation system ageing

Sam Williamson, Rafal Wrobel, Jason Yon, Julian Booker, Phil Mellor

Research output: Chapter in Book/Report/Conference proceedingConference Contribution (Conference Proceeding)

11 Citations (Scopus)
569 Downloads (Pure)


High performance electrical machine operation is limited by the losses generated in the machine and how well the heat developed by these losses is extracted. For conductive heat transfer from the main winding body, the insulation materials provide the main heat transfer pathway. As a machine ages through its lifetime, these materials will change their properties, and therefore these heat transfer characteristics will also alter. This paper describes the methodology and measurements on a set of motorettes undergoing an insulation ageing process to identify the change in heat transfer characteristics. The motorettes are subjected to a combination of thermal, electrical, mechanical and humidity stresses, before their thermal performance is measured. It has been found that the equivalent thermal resistance of the motorettes over the nominal lifetime of the insulation increases by over 100%, with the current carrying capability of the machine reducing by over 30% across the machine’s lifetime. It is therefore recommended that this is taken into account during the initial thermal design of the machine to ensure it remains fit for purpose during its complete life.
Original languageEnglish
Title of host publication11th IEEE International Symposium on Diagnostics for Electric Machines, Power Electronics and Drives (SDEMPED 2017)
Subtitle of host publicationProceedings of a meeting held 29 August - 1 September 2017, Tinos, Greece
PublisherInstitute of Electrical and Electronics Engineers (IEEE)
Number of pages7
ISBN (Electronic)9781509004096
ISBN (Print)9781509004102
Publication statusPublished - Oct 2017


  • Insulation ageing
  • heat transfer
  • motorette testing
  • insulation stress


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