Impact of compressive mechanical stress from shrink fitting of a casing on the core loss in a Cobalt Iron stator core of a permanent magnet synchronous machine

Shrink fitting of stator housings (casings) introduces a compressive mechanical stress into the stator core of an electrical machine, and consequently tends to increase the core loss. The calculation of stress distributions within the stator core is a pre-requisite for accounting for mechanical stress effects in the prediction of core loss or for adapting the shrink-sitting process to manage the resulting core loss. This paper investigates the mechanical stress distribution in a representative stator core with models of increasing fidelity, starting from the basic analytical hoop stress model with a simplified back-iron ring to a machine level stress model with stator teeth, windings, slot liners, winding insulations and slot wedges. The impact of windings and stator teeth on the accuracy of the mechanical stress model is quantified. Compared to the existing literature, this paper highlights the importance of the windings and the associated insulations, slot liners and wedges for an accurate prediction of mechanical stress in the stator core. It is shown, for the machine used in the case study, that the core loss in the stator core can be underestimated by ∼10–20% if the mechanical stress caused by shrink fit process is neglected.