Anomalous Eddy Current Loss Research Articles

Loss Analysis of a Reactor under Inverter Power Supply Taking Account of Anomalous Eddy Current Loss

To reduce the iron losses of reactors under inverter power supply, the loss was calculated by using magnetic field analysis, which models a laminated core by combining a 3D solid-core model with a 1D steel plate model, using the finite element method (FEM). In this method, the structure of the laminations and the eddy currents in the steel plates can be taken into account. However, for reactors driven by inverter power supply, the calculated iron losses are much smaller than the measured results, because the anomalous eddy current loss induced by domain wall motion in the steel plates is neglected in the loss calculation. Therefore, this paper investigates a simple numeric modelling method that takes account of the anomalous eddy current loss by modifying the conductivity of the steel plates. First, the method is verified by comparing the calculated iron loss of one sheet of steel plate with the measured data. The method is then applied to the loss calculation of reactors under inverter power supply. The differences between the calculated and measured results become smaller when the anomalous eddy current loss in the steel plates is taken into account.

Loss Calculation of Reactor Under Inverter Power Supply Taking into Account Anomalous Eddy Current Loss in Laminated Core

Loss Calculation of Reactor Under Inverter Power Supply Taking into Account Anomalous Eddy Current Loss in Laminated Core

Ｆｅ‐Ｓｉ系圧粉磁心の粉末粒径および結晶粒径と磁心損失との関係

Compressed cores made with Fe-Si alloys are expected for smoothing and boost choke coils of switching regulators and DC-DC converters. In this study, compressed cores were made with atomized Fe-3mass%Si, and the relationships between particle size, crystal grain size and core loss were investigated. The crystal grain sizes were changed by heat treatment temperature. The following conclusions were obtained. (1) Hysteresis loss decreases with increase in crystal grain size. (2) Both contributions of classical eddy current loss assuming uniform magnetization and localized eddy current loss by domain wall movements were confirmed. It was found that anomalous eddy current loss is proportional to square root of the crystal grain size. As particle size decreases, anomalous eddy current loss becomes dominant relative to classical eddy current loss, because classical eddy current loss decreases.

Bulk Fe-Based Metallic Glass with Extremely Soft Ferromagnetic Properties

The authors have investigated the DC and AC magnetic properties of a bulk glassy Fe{sub 65.5}Cr{sub 4}Mo{sub 4}Ga{sub 4}P{sub 12}B{sub 5.5}C{sub 5} alloy. In the annealed state the alloy has coercivity H{sub C} and maximum DC permeability {mu}{sub m} of approximately 0.4 A/m (5 mOe) and 2.8 x 10{sup 5}, comparable to those found in annealed zero-magnetostriction Co-based alloys. The low H{sub C} found in the bulk glassy alloy is attributed to the low ratio of surface-roughness to sample thickness, and low residual internal-stress. The total power loss in the annealed bulk glass is about one order of magnitude lower than that of rapidly quenched Fe-based glassy ribbons. This is attributed to a low anomalous eddy-current loss.

Bulk Fe-Based Metallic Glass with Extremely Soft Ferromagnetic Properties

The authors have investigated the DC and AC magnetic properties of a bulk glassy Fe{sub 65.5}Cr{sub 4}Mo{sub 4}Ga{sub 4}P{sub 12}B{sub 5.5}C{sub 5} alloy. In the annealed state the alloy has coercivity H{sub C} and maximum DC permeability {mu}{sub m} of approximately 0.4 A/m (5 mOe) and 2.8 x 10{sup 5}, comparable to those found in annealed zero-magnetostriction Co-based alloys. The low H{sub C} found in the bulk glassy alloy is attributed to the low ratio of surface-roughness to sample thickness, and low residual internal-stress. The total power loss in the annealed bulk glass is about one order of magnitude lower than that of rapidly quenched Fe-based glassy ribbons. This is attributed to a low anomalous eddy-current loss.

Frequency dependence of the transverse biased permeability in thin permalloy films

The frequency dependence of the transverse biased permeability μ′t(f ) has been measured up to 250 MHz in thin (0.044 μm) and thick (2.1 μm) unpatterned sputtered permalloy films with uniaxial anisotropy. In these films, the initial permeability along the hard axis can be described by the classical eddy current damping model assuming uniform rotation. For both films, μ′t at low frequency agrees reasonably well with Hoffman’s ripple model assuming appropriate values for the structure factor. In the thin film, μ′t(f ) is independent of frequency within experimental error up to at least 250 MHz. However, in the thick film μ′t(f ) decreases more rapidly with frequency than can be explained by classical eddy currents, when the transverse bias field HB is not very large compared to the net anisotropy field. The value of HB at which μ′t(f ) reaches a maximum amplitude is also found to increase monotonically with increasing frequency, also inconsistent with simple eddy current predictions. It is suggested that the formation of ripple walls leads to anomalous eddy current losses similar to that observed in bulk materials.

AC loss analysis and domain structure in magnetostrictive amorphous wires

Low-field ac susceptibilities of rotating water quenched amorphous Fe 77.5Si 7.5B 15 wires have been measured as functions of frequency and position. Anomalous eddy-current losses have been detected for different positions at the remanence state of samples with different lengths, related to the domain structures. An eddy-current loss model has been developed which combines the effects of magnetization rotations in a tubular shell, the displacements of a tubular domain wall in the core region, and the displacements of the shell-core boundary. Using this model, the ac losses have been analyzed, concluding that the radius of the boundary is 83% of the wire radius and the domain division makes a roughly parabolic axial position dependence of the average magnetization in the core, no matter if the wire is in the stable state or during magnetization reversal. Thus, the magnetization reversal should be controlled by domain wall pinning. In addition, magnetic relaxation and magnetomechanical coupling play important roles in the technical magnetization of such wires.

Problems of loss separation for crystalline and consolidated amorphous soft magnetic materials

Losses were measured as a function of magnetization frequency f/sub d/ for two advanced soft magnetic alloys: laser-scribed 0.23-mm HI-B steel ZDKH (designated HB) and consolidated amorphous Powercore (designated PC). Although domain observations on HB yielded distinct domain refinements due to the laser treatment, anomalous losses W/sub a/ still proved to be higher than the classical ones. A further refinement resulted from increasing f/sub d/. Thus, anomalous eddy current losses were reduced while hysteresis losses were increased. As a consequence, it is suggested to separate W/sub a/ into an eddy current component and a hysteresis component, which arises in addition to the classical hysteresis loss. With increasing f/sub d/, especially wide domains were refined. Results of loss measurements performed at high f after demagnetization with low f/sub d/ indicated similar bar-type domain structures in HB and PC, the domain widths of the latter exceeding those of HB, however, by one order of magnitude. A Kerr-effect scanning technique confirmed the existence of an inner bar-type domain structure with domain widths of some millimeters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The stray-field structure of a HI-B sheet in the vicinity of laser scratches

The stray-field behaviour of laser scratches which are burned into the surface of HI-B sheets in order to reduce the domain-spacing and thus the anomalous eddy-current loss has been measured. The influence of the external applied field on the stray-field structure is shown and one possible mechanism for the observed loss reduction is favoured. Besides the influence of the charges at the laser scratches on the magnetization reversal of the single sheet the possibility of an interaction between several stacked sheets due to the stray field at laser scratches is discussed.

Low core loss rotating flux transformer

A rotating magnetic induction at saturation generates no hysteresis losses. In addition, because domain walls are absent, there are no anomalous eddy current losses. Thus, only classical eddy current losses are present. In materials with high resistivity such as ferrites or materials fabricated into thin sheets such as amorphous metals, these classical losses are small. A transformer has been designed which utilizes this principle. It consists of a hollow toroidal core with toroidal windings wrapped outside the core and poloidal windings wrapped through the interior channel. When these windings are energized by currents 90 electrical degrees apart or, with suitable winding schemes, by three-phase currents, rotating flux is generated throughout the core volume.

Effect of Nonuniform Flux Distribution on Iron Loss in Amorphous Toroidal Core

Nonuniform flux distributions in amorphous toroidal cores can result in anomalous eddy current losses. Amorphous toroidal cores were excited (by a sinusoidal magnetic flux) and the resulting core losses and local flux distributions measured. Though the overall core flux was sinusoidal, the local flux distribution was distorted, and the distortion is thought to cause the 1.5 times greater eddy current loss than for sinusoidal flux at 50 Hz. This would explain the large anomaly factor in part using Pry and Bean's model, assuming domain widths in agreement with measured values.

方向性けい素鋼板の磁気特性におよぼす板厚と張力の影響

In general, decrease in sheet thickness decreases the core loss due to the decreased classical eddy current loss. However, at small thickness, surface pinning effects on the domain wall movement become dominant. The proportion of anomalous eddy-current loss arising from the domain wall movement is as much as about 45% of the total loss at the commercial frequencies, 50 and 60 Hz, but the relationship between the anomalous loss and the sheet thickness has not been clarified yet. The tensile stress imparted by the inorganic coating decreases the core loss, but there is no evaluation of the effect of thickness with tensile stress on the core loss.The systematic investigation has been made on specimens with various sheet thickness, for which the chemical polishing technique has been used.The decrease in core loss with tensile stress was greater for smaller thickness. Especially, for B8=1.77 T, the applied tensile stress increased the core loss for larger thickness and decreased the core loss for smaller thickness. The greater tensile stress decreases the domain wall spacing. The decrease in domain wall spacing with tensile stress was greater for larger thickness than for smaller thickness.The magnetostriction measurements indicated that the 90° domain volume at a demagnetized state was smaller for smaller thickness, and the volume of new 90° domains created at intermediate inductions due to the need of reducing magnetostatic energy was smaller for smaller thickness. The applied stress decreased the 90° domain volume at a demagnetized state and suppressed the formation of 90° domains at intermediate inductions. The magnetostatic energy due to free poles appearing on the surface was less effective in reducing the domain wall spacing and creating 90° domains for smaller thickness.The decrease in core loss with stress was due mainly to the decreasing supplementaly domains, especially 90° domain volume. The behavior of magnetization for a smaller thickness sheet was similar to that for a larger thickness sheet with larger B8.

Improvement of magnetic properties in thinner HI-B with domain-refinement

The domain-refinement technique which was developed to decrease anomalous eddy-current loss showed remarkable effect. The LASER-scribing method enabled the development of industrial products. Moreover, when this domain-refinement was applied to thinner gaged core material, the effect appeared in a marked degree. In this paper, the improvement of magnetic Properties of 0.23mm thick domain-refined core material is emphasized, because it has been used widely. It was clarifyed that the effect of domain-refinement depended on the thickness of core materials and the induction at 1000A/m strongly. The core losses, 0.80W/kg at 1.7T, 50Hz and 0.59W/kg at 1.5T, 50Hz were successfully obtained for an industrial product, 0.23mm HI-B. When the LASER-scribing was applied to very high permeability HI-B, the hysteresis loss was little changed, but the eddy-current loss decreased sharply. Further, by the numerical analysis with actually measured data, the Building Factor was also improved by the patterns of the LASER-scribing.

Anomalous rotational eddy current loss in electrical steel sheets

The rotational eddy current loss of different qualities of electrical steel sheets has been determined with a dynamical torque magnetometer. The measured values of the losses are higher than the losses calculated with a classical formula. The difference grows with increasing ratio of grain size to sheet thickness. In alternating fields this phenomenon has been explained theoretically by the Pry and Bean model.

Effects of field annealing on the magnetic characteristics and magnetic losses of amorphous ribbons Fe78Si10B12

The effects of magnetic annealing on the magnetic characteristics and magnetic losses of amorphous ribbons Fe78Si10B12 were studied. The annealing temperature was chosen at 400°C, being lower than the Curie temperature 440°C. A magnetic field of 30 Oe was applied during the heat treatment, in a direction at an angle θ to the length of the ribbon, with θ = 0°, 45°, 60°, 90°. The magnetic characteristics in ac fields were measured with the frequencies from 50 Hz to 10 kHz. The total losses W were measured and resolved into the hysteresis loss Wh, the classical eddy current loss We, and the anomalous eddy current loss Wea. In general, at a given frequency and a given maximum induction, Wea decreases and Wh increases with the direction θ. So the optimum annealing conditions for lowest total loss are different for different frequency and maximum induction.

Domain interactions between stacked HI-B SiFe sheets

Attempts to reduce anomalous eddy current losses by means of domain refinement are usually performed on single crystals or polycrystalline single sheets. However, studies on stacked sheets reported in this paper showed that arranging the single sheet into a stack may result in a refinement of large 180 degree domains without additional treatments such as scratching. On the other hand, an example is shown which demonstrates that stacking of scratched sheets may result in a distinct widening of domains previously refined by scratches. It can be concluded that single sheet investigations concerning the ac demagnetized domain patterns are of restricted practical relevance.

Anomalous eddy current loss and amorphous magnetic materials with low core loss (invited)

Heat-treatment methods for obtaining low core loss in Fe rich amorphous alloys with high magnetic induction and the physical mechanism concerned will be discussed. Field annealing is necessary to avoid inducing local magnetic anisotropies or magnetic domain wall fixing, and then to make stress relieving effective. Consequently, field annealing can reduce hysteresis energy loss. However, core loss at high frequencies involves a fairly large anomalous eddy current loss. This is due to a large size of 180° magnetic domains resulting from field annealing. Oblique field annealing is, on the other hand, effective to reduce anomalous eddy current loss, because of increase in the number of 180° domain walls. The experimental relation between core loss and domain structure obtained on Fe(72)Co(8)Si(5)B(15) has satisfactorily been explained by the simple model on the basis of bar-like 180° wall motion. Magnetic properties of Fe(81)-(B, C, Si) (19) amorphous alloys suitable for transformer materials will also be reported. In Fe(81)B(13)C(2)Si(4), for example, core loss at 50 Hz is 1.3 mw⋅sec/kg at 15 KG and 25°C (2.2 mw⋅sec/kg at 15 KG and 80°C).

Anomalous eddy current loss in amorphous magnetic thin sheets and its improvement

Soft magnetic properties of amorphous metals are interesting for application in transformers and other devices. So far, annealing in a field applied parallel to the amorphous ribbon axis was necessary to obtain the desirable magnetic properties. However, the amorphous cores made by this annealing method exhibit large eddy current losses. In order to reduce such large anomalous losses, we have improved the field annealing method, by applying the field oblique to the ribbon axis. In Fe-rich amorphous alloys, the core losses have been reduced by about 30-40 % by this method. Relation between the core losses and the magnetic domain structure has been investigated by comparing with the theory of Pry and Bean.

A factor contributing to domain-wall damping in magnetic tape-wound cores

Discusses a factor beta r which contributes to the damping coefficient for domain wall movement in tape-wound 3% Si-Fe and Supermalloy cores. The factor is a constant independent of the domain wall geometry and the dimension of tape. It is similar to the spin relaxation damping but far larger. The study on the eddy current loss equation including beta r shows that the loss caused by beta r becomes comparable with that based on the macroscopic eddy current in tape thickness as great as 50 mu m in 3 % Si-Fe. The result will help to clarify anomalous eddy current loss in thin-sheet materials.

LOSSES IN THE MAGNETIC CORES OF IRON-NICKEL-COBALT ALLOY HAVING RECTANGULAR HYSTERESIS LOOP

Investigation has been made on the losses in magnetic cores consisting of strips of iron-nickel-cobalt alloy after annealment in a longitudinal magnetic field. It has been found that the p/f-f curve shows obvious anomalous behaviour. Explanation is given for this behaviour with a Theoretical model of the anomalous eddy current loss caused by the wall displacement in the 180?domains. Possible ways of minimizing the loss are suggested.