Excess Eddy Current Loss Research Articles

Emulating Full-Load Testing of Air-Cooled Nanocrystalline IHT at Zero Power

High-power high-frequency air-cooled induction heating transformers, mostly used as current multiplier and isolation purposes, are custom designed. For their reliable performance and long life, the thermal evaluation at rated load is necessary. Creating an equivalent load as a test facility for reliability testing of such type of transformer is difficult. Characteristics of such loads drastically change after Curie temperature. Moreover, prolonged heating could increase the nearby ambient temperature and, more importantly, the traditional heat run test wastes large amount of energy. Whenever the coil is energized, windings of transformer draw respective rated current; even at no-load condition, the copper loss is at rated value. While both windings drawing rated current at a desired frequency, using the concept of localized eddy current loss as well as excess eddy current loss, this article proposes a novel method to inject requisite core loss to the magnetic circuit to emulate the characteristics of full-load condition but the power drawn from the transformer would be zero. The proposed idea would be validated where only a 200-W resonant inverter would be used to inject power loss equivalent to full-load condition of 30-kW transformer to emulate the heat run test.

Influence of excess eddy current core losses of saturable reactor on the process of semiconductor valve turn-on

In this article the transient process was analyzed when the semiconductor valve turn-on with a new modernized equipment of the Vyborg HVDC scheme. It was found that transient processes occur at high frequencies of about 50-60 kHz. During high-frequency transients when the valve turn-on current can reach zero and negative values. This oscillation can lead to premature valve turn-off and even to its destruction, depending on the switching conditions. The paper deals with issue of damping of the turn-on high-frequency current oscillation witch can be achieved by effective eddy-current resistance due to excess eddy current magnetic core losses of the saturable reactors. Calculation energy losses in thin structures of laminated magnetic core of the saturable reactor were carried out using obtained data of transient process and Comsol Multiphysics modeling. This gave a numerical estimate of the effect of these losses on the transient process. In terms of obtaining data modificated equivalent electrical circuit was proposed. This modification allows to estimate the influence of excess eddy current core losses of saturable reactor on the semiconductor valve turn-on.

The Microstructural Characterization, Physical and Dynamic Magnetic Properties of (Ni49Fe51)100−xCrx (x = 0,3,7) Thin Sheets

In this work, the effects of Cr on the microstructure, physical, and AC magnetic properties of the Ni49Fe51 alloy was studied. In this respect, three series of thin sheets of (Ni49Fe51)100−xCrx (x = 0, 3, and 7 at. pct) alloys with a final thickness of 120 µm were prepared by means of severe cold rolling and an 1150 °C annealing process at H2 atmosphere. Optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), (200) X-ray pole figure, and magnetic force microscopy (MFM) were employed to study microstructure, texture, and magnetic domain structure of the alloys. The magnetic characteristics of the samples were evaluated using BH-hysteresis loop tracer at a frequency range of 0.5 to 300 Hz. Based on the results obtained, it was shown that the mean magnetic domain width was increased from 1.006 to 1.398 μm for 0 Cr and 7 Cr samples, respectively. Furthermore, the magnitude of the static hysteresis loss increased and the excess and classical eddy current loss decreased for the Cr-added thin sheets.

Dynamic hysteresis modeling of silicon steel sheet considering excess eddy-current loss

Dynamic hysteresis modeling of silicon steel sheet considering excess eddy-current loss

Development of Block Cores Comprising High-<inline-formula> <tex-math notation="LaTeX">$B_{s}$ </tex-math> </inline-formula> Nanocrystalline Alloy Ribbon

Soft magnetic properties of block cores comprising Febal.Cu1Mo0.2Si4B14 nanocrystalline alloy ribbons (HBN core) were investigated. The HBN core shows a magnetic flux density at 2000 A/m (B2000) of 1.73 T, which is about 0.2 T higher than that of the core comprising Fe-based amorphous alloy ribbons (Fe-AM core). The core loss at 200 mT and 10 kHz is 8.5 W/kg, two thirds of that of the Fe-AM core. The coefficient of the excess eddy current loss for the HBN core is one half of that of the Fe-AM core; the difference in core loss is prominent at higher frequencies.

Ladder Circuit Modeling of Dynamic Hysteretic Property Representing Excess Eddy-Current Loss

Bertotti’s model for excess eddy-current (EC) loss is combined with the dynamic hysteresis model represented by a Cauer circuit and the play model. The excess EC field of the Cauer circuit is represented by nonlinear resistors. A formulation of excess EC field based on nonlinear current conduction is developed for the finite-element EC analysis, which is applied to the physical Cauer circuit. The proposed models improve the ac iron-loss evaluation under sinusoidal excitation of frequencies up to 20 kHz and achieve an accurate $B$ – $H$ loop representation under pulse-width modulation excitations.

Effect of Silicon Content on Iron Loss and Magnetic Domain Structure of Grain-Oriented Electrical Steel Sheet

Increasing the silicon content in non-grain-oriented (NO) electrical steel sheets is known to decrease iron loss by changing electrical resistivity and magnetostriction behavior. However, few studies on the effect of high silicon contents in grain-oriented (GO) electrical steel have been reported. One of the major differences in the iron loss of GO and NO is that excess eddy current loss, which has a strong relationship with the magnetic domain structure, is more dominant in total iron loss in GO. In this paper, high silicon GO was prepared by the CVD siliconizing method, which has the advantage that the silicon content can be changed without changing the crystal grain size and crystallographic texture of the specimen. It was found that iron loss was reduced as the silicon content was increased, and 6.5 mass% silicon steel showed about half the hysteresis loss of conventional 3 mass% silicon steel, but the eddy current loss in 6.5 mass% silicon steel was equivalent to or slightly larger than that in 3 mass% silicon steel. Magnetic domain observation and calculations suggested that this difference was a result of coarsening of the magnetic domains in the high silicon steel.

Core loss analysis of Finemet type nanocrystalline alloy ribbon with different thickness

Nanocrystalline soft magnetic materials are widely used in power electronic applications due to their high permeability, magnetization and low core loss. In this paper, Fe73.5Cu1Nb3Si15.5B7 (at%) nanocrystalline alloy ribbons, with ultra-thin thickness of 14µm, and also 18 and 22µm, were prepared by a planar flow casting method with a single roller device. Soft magnetic properties of these ribbons were analyzed after nanocrystallization annealing. The experiments were conducted on toroidal samples using IWATSU B-H Analyzer over a frequency range of 10–100kHz, at induction amplitudes of 100–500mT, at room temperature. It was found that the excess eddy current loss Pex was the dominant factor in the overall core loss above 10kHz. The toroidal samples made of the 14µm thickness ribbon exhibit very low total core loss of 48W/kg at a frequency of 100kHz and magnetic flux density of 300 mT. The ratio of the Pex was up to 89% at 100kHz. The ribbon with lower thickness exhibits lower Pex and therefore lower total core loss. The domain structure evidences were found. It indicates that the ribbons with small thickness are preferable for application in high frequency condition.

Low power loss in Fe65.5Cr4Mo4Ga4P12B5.5C5 bulk metallic glasses

Power loss – one of the important application-oriented magnetic properties of ferromagnetic metallic glasses – has been well studied in glassy ribbons rather than bulk metallic glasses. This paper studies the influence of frequency, induction, annealing, and specimen thickness on the total power loss – which is divided into hysteresis loss, classical eddy current loss, and excess eddy current loss – of bulk ferromagnetic Fe65.5Cr4Mo4Ga4P12B5.5C5 glasses. The total power loss of bulk glasses increases with frequency and peak induction and follows a power relation, similar to what has been observed in glassy ribbons. Annealing decreases both the hysteresis loss and the classical eddy current loss, resulting in a lower total power loss. The ratio of excess eddy current loss to classical eddy current loss deceases with increasing specimen thickness. The excess eddy current loss is negligible for our thickest glass and comparable to the classical eddy current loss for our thinner glasses. In contrast, the excess eddy current loss is often at least one to two orders of magnitude greater than the classical eddy current loss in glassy ribbons. The low total power loss achieved in bulk ferromagnetic glasses should be beneficial to their practical applications in energy conversion devices.

Core Loss in Toroidal Cores Based on Fe-Based Amorphous Metglas 2605HB1 Alloy

Amorphous ribbon exhibits low power loss. However, core loss of amorphous ribbon based toroidal cores is about twice as large as that of the ribbon even after field annealing under an optimum condition. In the present work, effects of residual strain and inter-laminar eddy-current loss on loss increase were examined for toroidal cores based on recently developed Metglas 2605 HB1 alloy which has a high saturation induction B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> of 1.64 T. The results show that: 1) with increase in residual strain, core loss and hysteresis loss are increased and no significant change in excess eddy-current loss was observed, and 2) there is no significant difference for frequency dependence of eddy-current loss by varying packing factor from 83% to 87%. This implies that there is no loss increase due to inter-laminar eddy current.

Magnetic domains and magnetization process of amorphous granular (CoFeB)–SiO2 thin films

The domain structure and magnetization process of a granular film were explored using a Kerr microscope. Narrow line-shaped reversal domains were observed in a granular (Co25Fe66B9)75–(SiO2)25 film, and no increase in the width of the domains was observed during the magnetization reversal process by applying a dc field along the easy axis. In addition, no wall displacement was observed in an ac field along the hard axis because only magnetization rotation occurs due to wall pinning. It was found that wall motion that causes excess eddy current losses at high frequencies is hard to occur by the granular structure.

Iron Loss Model for Permanent-Magnet Synchronous Motors

Iron losses in permanent-magnet synchronous machines form a larger portion of the total losses than in induction machines and, hence, more importance should be given to the iron losses. Previously, models have been presented for the calculations of these losses, but these models still rely on finite-element simulations to obtain correction factors, which are substantial, to apply to the theoretically derived formulas in order to obtain good agreement with the experimental data. This paper points out the source of this correction factor: the neglect of the excess eddy-current loss component. In many cases, this loss component dominates the total iron losses and needs to be incorporated in the theoretical considerations. The paper also provides a more complete model of iron loss, which greatly reduces the need for calculating the correction factors using the finite-element method (FEM). This more complete model reduces design time, especially when a number of candidate designs need to be analyzed. Otherwise, the calculation of the correction factors using FEM would be cumbersome, as the correction factors tend to be nonlinear.

High-Frequency Tunneling Magnetic Loss in Soft Ferrites

This paper considers high-frequency (200 kHz-1.0 MHz) losses in MnZn power ferrites and shows that none of the three well-known magnetic loss mechanisms (namely, hysteresis, classical eddy-current loss, and excess eddy-current loss) can account for the experimentally observed dependence of the loss on the frequency and flux density. In order to investigate the origin of this discrepancy, the electric field that is induced in the typical core when the material is driven at high frequencies and flux densities was estimated. The estimates show that these electric fields can be quite large. The paper presents experimental data on the electrical conductivity for such large electric fields, which shows a highly nonlinear behavior that can give rise to a modified eddy-current loss mechanism. By a simple curve fit to the nonlinear conductivity, the experimentally observed flux density dependence of the high-frequency loss, which previously could not be explained, can be reproduced by using this modified eddy-current loss mechanism. A modified ferrite structure can eliminate most of these extra losses by reducing the electric field generated at the grain boundaries due to high frequencies and flux densities

Magnetic losses for non-sinusoidal waveforms found in AC motors

Both high-power and low-power ac motors are in common use in a wide range of applications. However, it is currently very difficult to predict the efficiency of ac motors because the magnetic losses are difficult to calculate under the non-sinusoidal voltage waveforms that are applied to the ac motors by the inverters. The manufacturers of the magnetic materials usually supply loss data for sinusoidal waveforms only. As a result, a power de-rating factor has to be applied to the design in order to avoid thermal problems. In this letter, a model is provided for calculating magnetic losses under non-sinusoidal voltage waveforms. It is shown that the magnetic losses for non-sinusoidal voltage waveforms can far exceed the magnetic losses for sinusoidal voltage waveforms if either the eddy current loss or excess eddy current loss dominates the total magnetic loss, even when the peak flux density and the frequency are kept the same for both waveforms. The model is applied to experimental data on two different materials and to two common voltage inverter waveforms. Very good agreement with experimental data is found.

Core-loss analysis of an (Fe, Co, Ni)-based nanocrystalline soft magnetic alloy

Nanocrystalline soft magnetic materials possess higher magnetization and operation temperatures than amorphous alloys with similar compositions. For these reasons, they are good candidate materials for power electronics applications. As an indication of their performance, core losses have been measured for a nanocrystalline alloy with the composition Fe64.08Co10.68Ni10.68Zr8.49B4.86Cu1.2 synthesized by a melt-spinning process with subsequent isothermal anneal at 550°C for 1h. The experiments were conducted on toroidal samples using a Walker ac permeameter over a frequency range of 100Hz–500kHz, at induction amplitudes of 100 and 1100mT, at room temperature. A measured toroidal sample possessed a saturation magnetization of 1.529T and core loss of 17.5W∕kg at a frequency of 10kHz and magnetic flux density of 100mT. The Steinmetz analysis of the static hysteresis losses yielded a power-law coefficient of 1.475. A statistical model for excess eddy current losses showed good agreement with experimental results. Excess eddy current losses were found to be the dominant factor in losses above 10kHz for these alloys.

Representation of AC hysteretic Characteristics of silicon steel sheet using simple excess eddy-current loss approximation

A stop model is combined with a one-dimensional finite-difference method or a homogenization method to represent ac hysteretic characteristics of a silicon steel sheet. Eddy-current analysis without excess eddy-current loss fails to give an accurate eddy-current field. Representation of ac B--H loops is improved by increased conductivity that is obtained from an excess loss evaluation by the Pry and Bean model.

Design of a 100 kVA high temperature superconducting demonstration synchronous generator

The paper presents the main features of a 100 kVA high temperature superconducting (HTS) demonstrator generator, which is designed and being built at the University of Southampton. The generator is a 2-pole synchronous machine with a conventional 3-phase stator and a HTS rotor operating in the temperature range 57–77 K using either liquid nitrogen down to 65 K or liquid air down to 57 K. Liquid air has not been used before in the refrigeration of HTS devices but has recently been commercialised by BOC as a safe alternative to nitrogen for use in freezing of food. The generator will use an existing stator with a bore of 330 mm. The rotor is designed with a magnetic core (invar) to reduce the magnetising current and the field in the coils. For ease of manufacture, a hybrid salient pole construction is used, and the superconducting winding consists of twelve 50-turn identical flat coils. Magnetic invar rings will be used between adjacent HTS coils of the winding to divert the normal component of the magnetic field away from the Bi2223 superconducting tapes. To avoid excessive eddy-current losses in the rotor pole faces, a cold copper screen will be placed around the rotor core to exclude ac magnetic fields.

Eddy current losses in ferromagnetic laminations

It is demonstrated through the comparison of analytical, numerical, and experimental results that the existence of excess eddy current losses can be explained by the peculiar nature of the nonlinear diffusion of electromagnetic fields in magnetically nonlinear laminations. The essence of this peculiar nature is that nonlinear diffusion occurs as inward progress of almost rectangular profiles of magnetic flux density of variable height. Approximating actual profiles of magnetic flux density by rectangular ones, the problem of nonlinear diffusion can be treated analytically by using a simple model. The accuracy and the limit of applicability of the rectangular profile model are discussed by comparing its predictions with finite elements numerical solutions of nonlinear diffusion equation as well as with experimental results.

Nonlinear diffusion of electromagnetic fields and excess eddy current losses

The purpose of the paper is to demonstrate through analytical calculations that excess eddy current losses can be (at least in part) explained by the peculiar nature of nonlinear diffusion of electromagnetic fields in magnetically nonlinear conducting laminations. This peculiar nature of nonlinear diffusion leads to the breakdown of the classical “uniformity assumption” for distribution of magnetic flux density even for low frequencies, and this results in the appearance of excess eddy current losses.

Magnetomechanical damping in amorphous ribbons with uniaxial anisotropy

We have investigated the magnetomechanical damping and the resonant amplitude of the longitudinal vibrations of amorphous ribbons with a uniaxial anisotropy induced transverse to the ribbon axis by magnetic field annealing. The damping and herewith the resonant amplitude are governed by eddy current losses. Yet, classical eddy current theory fails to describe the experimental results, in particular, when the sample is biased by a constant magnetic field. This failure ultimately originates in the commonly used assumption of an isotropic permeability tensor. This is not true in uniaxial ferromagnets where magnetization changes by rotation. Thus, within a domain, a change of magnetization along the ribbon axis is inevitably accompanied by a change of magnetization transverse to the ribbon axis. The latter produces excess eddy current losses which become increasingly important the more the equilibrium position of the magnetization vector is declined towards the ribbon axis by the bias field. Taking this into account, a straight forward calculation ends up in analytic expressions capable to describe correctly the experimental findings starting from the basic material parameters.