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

Abstract

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 o C lower winding temperature or an 11% increase in torque at the intended machine operation point.

Characterizing the in situ Thermal Behavior of Selected Electrical Machine Insulation and Impregnation Materials

“…The coil insertion stage requires particular attention due to tight tolerance between the stator and winding assemblies. This has been chosen to provide 'good' heat transfer from the winding body into the machine periphery, fully utilising the attributes of the open-slot machine topology [23]. Finally, the coil is mechanically secured within the stator slots using suitable glass-fibre based wedges.…”

“…Some of the machine characteristics include: radial-flux topology, surface mounted PM rotor assembly, forced aircooled housing and high torque-density with targeted continuous specific torque capability of the machine exceeding 20Nm/kg, based on the weight of the active stator and rotor elements. A more detailed machine specification is provided in [23]. The relatively 'high' transient overload capability requirement for the machine with air-cooled housing imposes the use of particular insulating and impregnating materials.…”

Design of a brushless PM starter-generator for low-cost manufacture and a high-aspect-ratio mechanical space envelope

“…The experimental approach comprises tests on machine hardware subassemblies (motoretts). The stator winding subassembly has been found to be particularly useful in assessing various manufacture and assembly nuances affecting the power loss and heat transfer from the winding body into the machine periphery, which are notoriously difficult to derive accurately using theoretical techniques [14], [23], [24], [26]. A detailed description of the design process supplemented with experimental and theoretical data has been provided in consecutive sections of the paper.…”

Experiment informed methodology for thermal design of PM machines

“…Motorettes have also been used to evaluate impact of different winding arrangements [20]- [28] and stator slot shapes [16] on the heat transfer effects. The motorette informed thermal design process has been found particularly useful when developing less common machine designs, where several design iterations are usually required to satisfy all the design requirements [18], [30].…”