Impact of slot shape on loss and thermal behaviour of open-slot modular stator windings

This paper presents results from an investigation into the optimal design of an open-slot, modular stator winding. The impact of the stator slot shape on the winding temperature rise is explored, taking account the distribution of loss that occurs in the open slot winding, including ac effects, and the heat transfer characteristics from the winding assembly into the stator core pack. The application focus is a single-layer, concentrated wound brushless PM machine, however the work is applicable to other machine formats. Alternative stator lamination profiles are compared; the commonly used parallel sided tooth with a trapezoidal slot, and a parallel sided slot with a trapezoidal tooth. The investigation includes the development of a reduced order thermal model representation of the stator. This model is employed to undertake coupled loss and thermal analyses to provide more accurate comparisons of the designs accounting for ac and temperature effects. The experimental and theoretical findings indicate the parallel sided slot design will result in a 37°C lower winding temperature or an 11% increase in torque at the intended machine operation point.