Synthesis, characterization, and magnetic properties of ZnO-ZnFe 2 O 4 nanoparticles with high photocatalytic activity

The efficiency and performance of an electrical machine depend on the magnetic properties of its magnetic core, i.e., the rotor and stator core made of stacked and processed electrical steel laminations. Especially a mechanical cutting, also known as punching or blanking, deteriorates the magnetic material properties next to the cutting line due to induced residual stress. The extent of the deterioration depends on the amount of induced stress, which is affected by the mechanical material properties and the process parameters used during punching. For this reason, in this paper, the effect of punching parameter variations on the magnetic properties of eight different nongrain-oriented electrical steels is investigated by using a single-sheet tester. The magnetic property deterioration is discussed based on the specific loss and the maximum field strength increase. In addition, the impact of punching parameter variations on the efficiency and the local flux and loss distribution of a permanent-magnet synchronous machine is shown based on a finite-element analysis. This allows one to tailor the punching parameters toward energy-loss minimization.

Impact of Punching Parameter Variations on Magnetic Properties of Nongrain-Oriented Electrical Steel

The development of energy-efficient electrical machines requires an accurate knowledge of the soft- and hard-magnetic material behavior already in the design stage Accurate numerical models are required which offer the ability of better understanding and modelling in an appropriate accuracy With such model properties on the one hand accurate simulations can be performed and on the other hand the best possible material choice for a particular application, ie for an electrical machine, can be done The soft-magnetic material constitutes the magnetic core of an electrical machine and its properties On that account, the accurate prediction of iron losses of soft-magnetic materials for various frequencies and magnetic flux densities, ie, arbitrary magnetic field waveforms, is eminent for the design of electrical machines [1] For this purpose different phenomenological iron-loss models were proposed, which describe the loss-generating effects, ie, hysteresis, non-local eddy currents and anomalous eddy currents Most of these suffer from poor accuracy for not considering the effect of high frequencies and high material utilization as well as the material degradation due to the magneto-elastic coupling [2, 3, 5] This paper presents a comparison of common iron-loss models The IEM-formula used, resolves the limitation by introducing a high-order term of the magnetic flux density and considers the alteration of material-dependent loss-parameters due to the magneto-elastic coupling [3] The knowledge of the magnetic property deterioration due to induced residual stress occurring during the manufacturing or operation of the electrical machine is indispensable for the contemporary design It has been widely ascertained that processing of electrical steel laminations significantly alters the magnetic properties of the electrical steel [2–6] Cutting induces plastic deformation and residual stress in the laminations Due to their strong sensitivity to mechanical stress, the magnetic properties are locally degraded near the cut edge The extent of the degradation depends substantially on the process characteristics, ie, the cutting procedure and cutting parameters in combination with material properties, such as mechanical strength and grain size [4–6] In [7] a continuous material model for an efficient numerical model of the local magnetization was introduced By replacing numerically expensive sliced models, the continuous model (CM) is independent of the discretization and converges in the case of coarse meshes to the sliced model [7] Measured single-sheet specimens are used to identify the different model parameters In Fig 1 results on hysteresis loss distribution are presented The vital advantage of the proposed CM is that properties depend only on the distance to the cut edge For improved estimation of penetration depth and mechanical stress distribution, novel experimental procedures are utilized [8] and mechanical simulations are evaluated [6] to further advance the cut-edge model Permanent magnets are central to the electromagnetic energy conversion process in permanent-magnet synchronous and flux-switching machines In order to design the magnetic circuit and a magnetizing circuit for post-assembly magnetization as well as to analyze the resistance to being demagnetized during the simulation of electrical machines, it is indispensable to describe the magnetization behavior of the permanent magnets accurately However, due to the complex interplay of the non-linear and hysteretic magnetization behavior and the magnetic anisotropy, it is a complex problem Commonly, simplified models are used, which are based on empirical and phenomenological approaches These describe the major loop of the permanent magnets only However, the magnetization state of the permanent magnet depends on the magnetic and thermic history, ie, it is indispensable to account for minor loops or incompletely magnetized permanent magnets In this paper, a pragmatic methodology to replicate the hysteresis of permanent magnets is presented, which uses first-order return curves and the magnetization behavior starting from the virgin state for model-parameter identification [10] Efficient parametric models with low additional computational effort are perfectly suited for the finite-element analysis Starting from these advanced models of soft- and hard-magnetic materials, a methodology for selecting the optimal steel grade during the design-stage of electrical machines in due consideration of the application-specific requirements on torque-speed operating points, ie, all have to meet the requirements of the same driving cycle, is presented [1] This allows one to study the effect of different electrical steel grades on the operational characteristics along the torque-speed map [11] In order to determine the efficiency of each combination of machine topology and lamination type, the iron-loss model with material degradation is used in combination with a machine simulation scheme of the entire operating range of the machine In the light of this, this paper will give an overview on the current modeling approaches applied at the Institute of Electrical Machines (IEM) for soft- and hard-magnetic materials in the simulation of rotating electrical machines

Advanced Soft- and Hard-Magnetic Material Models for the Numerical Simulation of Electrical Machines

Neutron grating interferometry (nGI) is a unique technique allowing to probe magnetic and nuclear properties of materials not accessible in standard neutron imaging. The signal-to-noise ratio of an nGI setup is strongly dependent on the achievable visibility. Hence, for analysis of weak signals or short measurement times a high visibility is desired. We developed a new Talbot-Lau interferometer using the third Talbot order with an unprecedented visibility (0.74) over a large field of view. Using the third Talbot order and the resulting decreased asymmetry allows to access a wide correlation length range. Moreover, we have used a novel technique for the production of the absorption gratings which provides nearly binary gratings even for thermal neutrons. The performance of the new interferometer is demonstrated by visualizing the local magnetic domain wall density in electrical steel sheets when influenced by residual stress induced by embossing. We demonstrate that it is possible to affect the density of the magnetic domain walls by embossing and therefore to engineer the guiding of magnetic fields in electrical steel sheets. The excellent performance of our new setup will also facilitate future studies of dynamic effects in electric steels and other systems.

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S. Jenner

Papers

Influence of shear cutting parameters on the electromagnetic properties of non-oriented electrical steel sheets