Power losses in thick steel laminations with hysteresis

Magnetic power losses have been experimentally investigated and theoretically predicted over a range of frequencies (direct current—1.5 kHz) and peak inductions (0.5-1.5 T) in 1‐mm‐thick FeSi 2 wt. % laminations. The direct current hysteresis properties of the system are described by the Preisach model, with the Preisach distribution function reconstructed from the measurement of the recoil magnetization curve (Bp=1.7 T). On this basis, the time behavior of the magnetic induction vs frequency at different lamination depths is calculated by a finite element method numerical solution of Maxwell equations, which takes explicitly into account the Preisach model hysteretic B(H) relationship. The computed loop shapes are, in general, in good agreement with the measured ones. The power loss dependence on frequency is predicted and experimentally found to change from a ∼f3/2 to a ∼f2 law with increasing peak induction

INFLUENCE OF THE DIFFUSION OF OXYGEN ON THE AGING OF ZINC OXIDE-BASED VARISTORS

L'étude de la cinétique de réduction de varistances à base d'oxyde de Zinc 650°C et sous atmosphère CO-CO2 a permis de relier la dégradation des caractéristiques électriques, observée lors du vieillissement sous champ électrique, à un transfert d'oxygène des grains d'oxyde de zinc vers les phases intergranulaires.The kinetics of reduction of zinc oxide-based varistors has been studied at 650°C in CO-CO2 mixtures in order to correlate ageing under electrical stress to diffusion phenomena. The experimental results indicate that the main cause of the ageing is a migration of oxygen from the outer core of the ZnO grains toward the intergranular phases

Aimants permanents FeNdB, obtenus à partir de la solidification rapide influencé du vanadium

L'influence d'ajouts de vanadium (1; 1,6; 2,1; 2,3 % at) sur les propriétés des matériaux rapidement solidifiés est étudiée ici. Ces additions provoquent une diminution de la température de Curie, tandis que la cristallisation de la phase amorphe contenue dans les rubans est retardée. Pour l'instant aucune évolution microstructurale n'a pu être décelée. La coercitivité des aimants de type I est maximale pour 1 % d'ajout. Pour les aimants de type II et au delà de 1.6 %, l'ajout de vanadium s'accompagne d'un accroissement de la coercitivité et d'une modification des mécanismes d'aimantation.The influence of vanadium additions (1; 1,6; 2.1; 2.3 % at) on the properties of melt spun materials is studied. These additions lower the Curie température, while the cristallisation of the amorphous phase present in ribbons is delayed. No evolution of the microstructure was observed at this time. For type I magnets, coercivity is maximum for a 1 % addition, for type II and above 1,6%, vanadium addition induces an increase in coercivity and a change in magnetisation mechanisms

Des materiaux magnetiques au coeur de l'electrotechnique

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : 26165 B, issue : a.1997 n.7 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc