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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 article deals with the modelling of iron losses due to the magnetic ageing of electrical steels used in energy conversion devices. This phenomenon is the consequence of irreversible mechanisms in the material which can be triggered by the operating temperature of electrical devices. At first, an experimental study is carried out at 180◦ C in order to assess the effect of isothermal ageing on electromagnetic properties of a magnetic steel sample. The results show that, during the thermal ageing, the hysteresis losses and the coercive field increase. These experimental observations, mainly caused by the formation of precipitates at the material microstructural scale, are then discussed. Considering the link between the effect of magnetic ageing on macroscopic magnetic properties (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. Once this approach was validated, it is proposed to integrate the JMAK law in the Steinmetz iron loss model.

In this paper, the magnetic ageing of a bulk forged non-annealed magnetic core, used in claw pole synchronous machine, is investigated. The study is carried out by characterizing the material properties of two groups of samples subjected to a thermal ageing at 180 °C that corresponds to the maximum operating temperature of the claw pole rotor. The investigated characteristics are the electrical conductivity, the magnetic properties, the material microstructure and the Vickers hardness. They were characterized along with the ageing time. The results show that, during the thermal ageing, the hysteresis losses and the Vickers hardness have been affected by the magnetic ageing, whereas the electric conductivity and the normal B-H curve have not been modified. The microstructure analyses showed that carbides precipitates were the main cause behind the magnetic ageing. Moreover, the comparison between the results of two groups of samples revealed the possibility that the magnetic ageing of the material could have started during the manufacturing process of the magnetic core.

During the operation of Claw Pole (CP) machines, and for some operating loads, the magnetic core temperature can reach 180°C in some hot spots. As a consequence, the core electromagnetic properties may considerably change, impacting the machine performances. In such a case, a deep knowledge of the electromagnetic behavior as a function of the temperature is required. In this paper, we present a dedicated study of the CP rotor made from a forged magnetic steel. In fact, the CP magnetic properties heterogeneity and the claw shape made it necessary to extract specific samples that are characterized with a miniaturized Single Sheet Tester (SST). To that end, this work proposes a specific methodology to characterize the electromagnetic properties of the CP rotor material as a function of the temperature in order to better predict the machine electrical performances, especially regarding the iron losses.

Claw pole machine performances are strongly related to the electromagnetic properties of ferromagnetic materials. These properties are impacted by the manufacturing processes, in a heterogeneous way, as well as by the thermal behavior of the machine and the mechanical stress distribution. Due to the complexity of CP geometry, extracted samples cannot respect the dimensions prescribed in international standards of electric and magnetic measurements. This paper proposes a specific methodology to characterize the electrical conductivity and the magnetic behavior of massive parallelepiped specimens extracted from different locations of a CP rotor.

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.

La réduction des pertes fer dues au vieillissement magnétique des aciers doux est une voie d’optimisation de l’efficacité énergétique des machines électriques telle que recommandée par l’union européenne. Le vieillissement magnétique se traduit par une détérioration des propriétés magnétiques lors du fonctionnement de la machine électrique, ce vieillissement est lié à la formation de précipités de carbures ou nitrures à la température de fonctionnement (inférieure à 180°C). Cette étude propose un travail préliminaire dans le développement d’un modèle multi-physique et multi-échelles afin d’évaluer l’évolution des pertes fer pendant les cycles d’utilisation des machines électriques.

En fonctionnement, la température au sein d’une machine électrique peut être élevée. En conséquence, les propriétés électromagnétiques de ses composants sont affectées modifiant ainsi les performances de la machine. Cette modification peut être réversible, c’est-à-dire que le matériau retrouve ses propriétés initiales avec la diminution de la température, comme elle peut être irréversible et on parle alors de vieillissement magnétique du matériau. Dans ces travaux, nous nous intéressons aux effets de la température de fonctionnement sur les caractéristiques électromagnétiques du matériau roue polaire (RP) de la machine à griffes. Cette pièce massive possède une géométrie complexe, une composition chimique ainsi qu’un procédé d’élaboration différents de ceux des noyaux magnétiques feuilletés majoritairement utilisés. Afin de s’adapter aux contraintes imposées, nous proposons une méthodologie spécifique de caractérisation des propriétés électromagnétiques à différentes températures, basée sur une miniaturisation du cadre à bande unique (SST). Les résultats de l’étude de l’effet de la température montrent une nette dépendance en température des propriétés électromagnétiques, principalement de la conductivité électrique, ce qui se traduit par une diminution des pertes par courants induits au rotor. Par ailleurs, au cours du temps, le matériau RP sous contrainte thermique, vieillit et ses pertes par hystérésis augmentent. Ce phénomène est dû à la précipitation des carbures. Par suite, un lien entre la cinétique du vieillissement et celle de la précipitation est souligné et une approche de modélisation de la cinétique du vieillissement, en condition isotherme est proposée.