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This paper deals with the temperature-dependent modelling of iron losses in the context of magnetic ageing of electricals steel used in high power electrical machines. First, two electrical steel sheet grades were heat treated at three temperatures in order to study the ageing effect evolution as a function of temperature. Results show a significant increase in iron losses for both steel grades. Then, considering the link between the macroscopic magnetic properties evolution (effect) and the microscopic precipitation (cause), the Johnson – Mehl – Avrami – Kolmogorov (JMAK) law describing the kinetics of precipitation was applied to model the time evolution of magnetic ageing. By coupling this model with the Arrhenius’ law, a model is developed to be able to predict the ageing for several temperature levels.

This paper deals with the analysis of the magnetic properties degradation following an industrial impregnation process of electrical steels employed in stators of large generators. First, the impregnation process is studied directly on industrial stators to emphasize the significance of the process effect. Then, to have a controlled approach of the impregnation conditions, laminated ring cores were subjected to the same process but for different configurations. The ring cores were magnetically characterized to highlight the influence of the resin on the magnetic properties. Also, in order to distinguish the effect of the resin from potential other phenomena during the curing phase (i.e. the ageing effect), an experimental protocol is proposed: the results allow to emphasize the impact of such process on the magnetic properties.

The manufacturing processes of electrical machines may lead to significant degradation of the magnetic properties of their magnetic core (stator, rotor) performances and, as a consequence, to a decrease of their energy efficiency. While the effects of some processes (cutting, welding …) are widely discussed in the literature, this is not the case with the compaction process although it is systematically used to maintain the assembly of electrical steel sheets that compose the magnetic circuits. In addition to the conventional one, a specific compaction process exists for high-power electrical machines. After an introduction, the paper firstly deals with the two studied processes (conventional, specific). Then, an experimental mock-up to study the impact of the two configurations on the magnetic properties (iron losses, normal magnetization curve) is presented. This mock-up is the first, in the literature, that allows to study the effect of a controlled compaction mechanical stress on magnetic properties. Obtained results in both configurations highlight a magneto-mechanical effect that is not reported in the literature where these effects are commonly considered following in-plane mechanical stresses. This paper presents a magneto-mechanical model, taking into account the compaction stress effect, as well as a modelling protocol to model the effect of 3D mechanical stress on magnetic properties, which has never been done in the literature.

This paper deals with the experimental investigation of the effect of impregnation process on the normal magnetization curve and iron losses of electrical steels. To address this issue, several laminated toroidal magnetic circuits have been designed to characterize the magnetic properties with the flux metric method. The first configuration considers magnetic circuits wrapped with adhesive tape so that the dielectric resin will be deposited only on the outer surface of the magnetic circuit. In the second configuration, the magnetic circuits are unwrapped, which will allow the resin to diffuse within the inter-laminar spaces of the magnetic circuit. The obtained experimental results show significant effects on the magnetic properties in both cases. However, depending on the considered configuration, the resin diffusion also has an influence on the changes in magnetic properties.

The manufacturing processes of electrical machines may lead to significant degradation of magnetic core properties and therefore of the machine performance. Laminations are usually stacked and pressed which affects the magnetic properties and the iron losses. However, the influence of this step must be still investigated when large generators are considered. Indeed, in that case, the stator and rotor stacking process consists in assembling several stacks of electrical steel sheets separated by airvents. The surface of the airvent spacers represents about ten percent of the lamination surface of the magnetic circuit, implying, during the compaction process, an inhomogeneous stress distribution with significant local stresses. The present work deals with the experimental characterization of a lamination stack, including airvents, under compressive stress in the thickness direction. A mock-up has been designed and built-up to study magnetic properties of lamination stacks under pressing conditions corresponding to the industrial process.

For some specific industrial applications, such as large generators, once the magnetic circuits are built and wound, they are usually impregnated with a dielectric resin, which is polymerized under heat treatment, to ensure insulation, thermal and mechanical properties. This talk is about the experimental study of the effect of such impregnation process on the magnetic properties of electrical steels used for the manufacture large generator stators.

During the operation of electrical machines, the increase in temperature up to about 200 °C promotes, in some electrical steels, basically Fe-Si alloys, the formation of precipitates (carbides, nitrides…). This precipitation causes a deterioration of the magnetic properties, in particular an increase in iron losses, a phenomenon known as magnetic ageing [1]. The aim of this study is to develop a preliminary multi-physical and multi-scale modelling approach coupling precipitation kinetics and the evolution of magnetic losses due to magnetic ageing.

In this work, we propose to characterize and analyze the phenomena involved by an industrial impregnation process that degrades the magnetic properties (B-H curve, iron losses) of electrical steels. Two main aspects are considered: the thermal effect as well as the dielectric resin deposition and diffusion within the magnetic circuit.

This paper presents a combined experimental/numerical approach to identify the degradation profile of the magnetic characteristics regarding the distance from the cut edge of punched electrical steels. Using a dedicated magnetic measurement device and mechanical hardness measurements, the impacted cutting-edge (I.C-E) distance has been experimentally identified. In association with a magneto-plastic model, the numerical model allows to determine the I.C-E distance and its associated degradation profile by an inverse optimization method.

Dans le contexte de l'accroissement de l’efficacité énergétique des machines électriques de fortes puissances, la réduction des pertes fer constitue évidemment un des points clés. Or, il subsiste encore aujourd'hui des écarts entre les pertes estimées lors de la phase de conception et celles mesurées sur les machines réelles. Ces écarts sont, entre autres, liés aux conditions de fabrication du circuit magnétique (découpe, assemblage, imprégnation...) qui peuvent conduire à une modification des propriétés des aciers électriques, notamment par une dégradation des performances magnétiques et une augmentation des pertes fer. Afin d’améliorer les outils de conception, il est alors nécessaire d’analyser et de quantifier les phénomènes et mécanismes physiques qui conduisent à la dégradation des propriétés magnétiques tout en faisant le lien avec les procédés de fabrication. L’objectif de ces travaux de thèse est d’avoir, à terme, une meilleure connaissance de l’évolution des différents postes de pertes fer en lien avec les procédés dégradant les propriétés magnétiques pour une chaîne de fabrication type des machines électriques de fortes puissances. La démarche proposée repose sur la quantification expérimentale des effets de ces procédés sur les performances magnétiques. Pour cela, des maquettes expérimentales dédiées et représentatives de trois procédés industriels identifiés (procédé de compactage, procédé d’imprégnation et procédé de découpe) ont été développées. Dans le cas du procédé d’imprégnation, son effet sera même directement étudié sur les performances magnétiques de stators industriels. Les résultats expérimentaux obtenus sont analysés et discutés en s’appuyant sur les connaissances théoriques de l’état de l’art et sont exploités pour le développement de modèles magnéto-mécaniques et magnéto-thermiques permettant de prendre en compte l’effet desdits procédés sur les propriétés des aciers électriques.