Work-package 2.1: From nominal core properties to in-service performance
The sheet materials used for electrical machine cores have magnetic properties that exhibit varying degree of sensitivity to the processes involved in the manufacture of a complete stator core from the starting sheets, notably the cutting of the lamination profile, the formation of a stack and the fitting of the stack into a casing. As a result, there is a general acceptance of some loss in performance of the core material, and hence some loss in overall performance in the final machine, compared to performance predictions based on manufacturer’s datasheet properties for the nominal grade of core material. It has been demonstrated, for example by Rasilo et al [RAS16], that edge effect can increase overall machine cores loss by up to 30%. This project will develop, principally through extensive experimental measurements on a range of materials, a comprehensive understanding of the various phenomena in play. This understanding will provide a basis for both developing new or variations on manufacturing processes and providing a well-founded methodology for accounting for manufacturing induced degradation of core properties.
This will include consideration of both remote laser cutting, stamping and any other methods that may emerge or be refined sufficiently during the course of the project, e.g. ultra-precision water jet cutting. A particular focus will be on developing processes and modelling for Cobalt Iron for which the published knowledge is scarce and rudimentary in comparison to Silicon Iron.
GC2.1A: Experimental characterisation. This will involve systematically preparing an array of samples of varying width and controlled cutting conditions. These samples will be characterised in terms of local edge profiles and magnetically, e.g. permeability and core loss measurements in a single-strip tester. This characterisation will focus on Cobalt Iron and the highest performance grades of non-oriented Silicon Iron. Samples will be produced systematically through a combination of stamping and remote laser cutting in terms of processes, although any material or processes that emerge during the course of the research programme will be factored in. The influence of post current heat-treatment will be evaluated.
GC2.1B: Development of models for accounting for edge damage and bulk compressive stress. The data from GC2.1A will be used to develop models – a particular feature will be the need to develop finite element models of complete machines which have localised modified properties to account for the edge damage and compressive stress effects.
GC2.1C: Process enhancements to reduce losses in electrical machines. This task, which links closely to GC2.1A will consider methods for alleviating any performance degradation caused by the cutting of the lamination profile and/or the fitting of a core in to casing.
[RAS16] P. Rasilo, U. Aydin, T. P. Holopainen and A. Arkkio, “Analysis of iron losses on the cutting edges of induction motor core laminations,” 2016 XXII International Conference on Electrical Machines (ICEM), 2016, pp. 1312-1317.