Magnetic Loss Measurements Research Articles

Structure, magnetic properties and hyperthermia of Fe3-xCoxO4 nanoparticles obtained by wet high-energy ball milling

In this work, the methods of X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), Mössbauer spectroscopy (MS), magnetic properties measurements and specific loss measurements (hyperthermia) were used for the investigation of the structure and properties of Fe3-xCoxO4 nanoparticles. The Fe3-xCoxO4 nanoparticles were synthesized by using high-energy ball milling of Fe and Co mixed with water and surfactant additives. Co substitution increased the coercivity of the samples and changed the kinetics of oxidation process. The presence of cobalt ferrite was verified by MS. TEM images of synthesized samples demonstrated 5–50 nm particle size. Specific loss related heating effect depended mostly on the ratio between the samples coercivity and the amplitude of the high-frequency field. Specific loss power (SLP) and intrinsic loss power (ILP) values reached 164 W/g and 1.57 nH·m2/kg, respectively.

Repeatability and reproducibility of physically consistent single sheet testing with H-coil

Measurements of magnetic losses of electric steel are usually performed by International Electrotechnical Commission standardized Epstein testers or Single Sheet Testers (SSTs). According to round robin tests, the corresponding levels of repeatability are of the order of 0.1%, and those of reproducibility are of the order of 1%. However, orders of absolute accuracy are unknown due to the applied “current method.” Here, we report corresponding tests for the so-called “physically consistent SST.” Consistency is achieved by a “giant” tangential field coil on a 50 cm long and 17 cm wide soft magnetic sample, using a thin amorphous yoke for magnetization. Tests were made in two labs with very different working conditions (sea levels of 200 and 1100 m, respectively), with very similarly built-up testers. Measurements were made for peak inductions between 1 and 1.9 T. For two distributed samples, the repeatability errors were lower than 0.3%, and the reproducibility errors were lower than 1%. This indicates that SSTs with an H-coil are not less reliable than current based ones. However, the absolute accuracy can be estimated to be much better, being close to 2%.

Improved Oscillation Method for High-Frequency Magnetic Core Loss Measurement

Improved Oscillation Method for High-Frequency Magnetic Core Loss Measurement

Magnetization Loss Measurement of Twisted Stacked Tape Cable and Comparison With CORC

High Temperature Superconducting (HTS) cables for large current capacity are being studied in several forms for power device applications. Currently, the cables are being developed for DC applications rather than AC applications. However, if a technology for reducing AC loss is developed, it will be possible to apply HTS cables to various AC devices. Twisted Stacked-Tape Cable (TSTC) is one of the large current HTS cables. It is made by stacking and twisting multiple HTS tapes for large current capacity. The HTS tapes in TSTC should be twisted for the uniformity of current distribution in each tape. Since the HTS tape has a wide thin film shape, it is very difficult to twist itself. In this paper, we measured the magnetization losses of TSTC samples without the striations under AC magnetic fields that had peak values below 0.1 T. Several molds for the TSTC samples were made by using a 3D printer. TSTC samples had several numbers of stacked tapes and two kinds of the tape width. The magnetization losses of the samples in the molds were measured under uniform AC magnetic fields. The experimental results were compared to those of the straight HTS stacked cables and conductor on round core (CORC) cables.

Non-Destructive Electromagnetic Evaluation of Material Degradation Due to Steel Cutting in a Fully Stacked Electrical Machine

Although it is well known that the magnetic properties of electrical steel can be deeply affected by the cutting process, it is still not clear how to accurately evaluate these effects on a prototyped machine on its final shape, especially at a high frequency or a high power rating. This research provides a more practical method for accurate measurement of magnetic losses in electrical steel with consideration of material degradation effects due to the cutting process. Unlike other similar studies, these investigations are conducted not only on a few laminations but also on a complete electrical machine core. For a fair comparison between both cases, backlack bonding is used for lamination stacking since it is the most non-damaging joining technique. Two different test setups are used to measure the steel performance at a wide range of frequency and input power. Furthermore, a full axial length stator of a switched reluctance machine (SRM) is used as a case study to identify the magnetic properties of NO20 electrical steel. Additionally, by comparing the results obtained from the individual laminations and the assembled stator, the extra losses due to the cutting process and material degradation are extracted accurately.

Magnetization Loss Measurements of Spiral Copper-Plated Multifilament Coated Conductors With Various Filament and Conductor Widths

We can achieve both small magnetization loss and the robustness against local defect or local normal transition by winding copper-plated multifilament coated conductor spirally. The particular focus of this study is the impact of narrowing conductor (tape) width as well as filament width on magnetization losses. We measured the magnetization losses of various spiral copper-plated multifilament coated conductors, separated them into hysteresis losses and coupling losses, and examined the impact of narrowing filament width and conductor width. We demonstrated that the magnetization loss of the spiral 2 mm-wide coated conductor with 0.2 mm-wide filaments and 10 μm-thick copper was one-twentieth of that of a flat standard 4 mm-wide coated conductor in transverse ac magnetic fields of 65.44 Hz.

Consistent Measurement of Magnetic Energy Losses by a Low-Mass, High-Frequency Single Sheet Tester

Consistent Measurement of Magnetic Energy Losses by a Low-Mass, High-Frequency Single Sheet Tester

Giant Epstein Tester for Magnetic Energy Loss Measurements of Non-Annealed Domain-Refined Fe–Si

Since 100 years, the Epstein tester serves as a compact and simple apparatus for the measurement of magnetic energy losses, in particular for Fe&#x2013;Si steel. However, drawbacks result from time-consuming cutting and stacking of the high number of just <inline-formula> <tex-math notation="LaTeX">$W =3$ </tex-math></inline-formula> cm wide sample strips of the standard Epstein tester (SET). Furthermore, the effects of cutting result in increased losses. Needs of annealing impede tests of modern materials with domain refinement that may lose its effectiveness. Results of numerical modeling indicated that both problems can be reduced by a strong enlargement of the strip width. Here, we report a novel giant Epstein tester (GET) with <inline-formula> <tex-math notation="LaTeX">$W =10$ </tex-math></inline-formula> cm, in combination with increased strip length <inline-formula> <tex-math notation="LaTeX">$L = 65$ </tex-math></inline-formula> cm. Sufficient averaging over test material is attained with two layers, i.e., from just eight strips. The magnetic field strength is determined by four large 3-D-printed tangential field coils, excluding impact from the four corners of frame. Time-averaged loss <inline-formula> <tex-math notation="LaTeX">$P$ </tex-math></inline-formula> is computed from instantaneous magnetization power values <inline-formula> <tex-math notation="LaTeX">$p$ </tex-math></inline-formula>, offering also maximum loss and orientation power. Results of GET were compared to data from single-sheet tester (SST) data, proving close similarities, without needs of annealing which is significant for laser scribed steel, as tested here. Results from SET prove to be higher. Analysis of power <inline-formula> <tex-math notation="LaTeX">$p$ </tex-math></inline-formula> indicates the impact of supplementary domains in the magnetization process of the scribed material. Compared to SST, the drawbacks of the GET are the need of eight sample strips, as well as lower absolute accuracy, due to higher inhomogeneity. On the other hand, advantages are the absence of a yoke system and simplicity of test apparatus.

Impact of Copper Thickness, Conductor Width, and Number of Striations on Coupling Loss Characteristics of Copper-Plated Multifilament-Coated Conductors

This article investigates the coupling loss characteristics of multifilament-coated conductors that have been plated with copper to connect electrically all the filaments to enhance their stability. Short pieces of copper-plated multifilament-coated conductors were prepared, each of which simulated a half-pitch of the conductor wound spirally on a round core with respect to the loop of the coupling current, and their magnetization losses were measured. The measured magnetization loss was separated into the hysteresis and coupling losses. This article focused on the latter one, which is peculiar to copper-plated multifilament-coated conductors, and the reduction of which is important for their applications. The coupling time constants as well as the geometry factors of the coupling losses and the magnitudes of coupling losses were studied using copper-plated multifilament-coated conductors with various copper thicknesses, numbers of striations, and conductor widths. Numerical electromagnetic field analyses were conducted, and the numerical and measured results were compared.

Dynamic resistance and total loss in a three-tape REBCO stack carrying DC currents in perpendicular AC magnetic fields at 77 K

In many high-temperature superconducting (HTS) applications, HTS-coated conductors carry a DC current under an external AC magnetic field. In such operating conditions, dynamic resistance will occur when the traversing magnetic flux across the HTS conductors. Consequently, AC loss within the superconductors is composed of the dynamic loss component arising from dynamic resistance and the magnetization loss component due to the AC external magnetic field. This AC loss is one of the critical issues for HTS applications, such as persistent current switches, flux pumps, and rotating machines. In this work, the dynamic resistance and the total loss in a three-tape HTS coated conductor stack were measured at 77 K under perpendicular AC magnetic fields up to 80 mT and DC currents (I dc) up to the critical current (I c). The stack was assembled from three serial-connected 4 mm wide Superpower wires. The measured dynamic resistance results for the stack were well supported by the results from 2D H-formulation finite element modelling (FEM) and broadly agree with the analytical values for stacks. The FEM analysis shows asymmetric transport DC current profiles in the central region of the superconductor. We attribute the result to the superposition of DC currents and the induced subcritical currents which explains why the measured magnetization loss values increase with DC current levels at low magnetic field. The onset of dynamic loss for the stack for low i (I dc/I c) values is much slower when compared to that of the single tape and hence the contribution of the dynamic loss component to the total loss in the stack is much smaller than that of the single tape. Dynamic loss in the stack becomes comparable to the magnetization loss at i = 0.5 and becomes greater than the magnetization loss at i = 0.7. Both magnetization loss and dynamic loss in the stack are smaller than those of the single tape due to shielding effects. The difference between the Q total behaviours in the stack and single tape is due to the variation of the penetration depths of the stack and single tape at the different magnetic field amplitudes.

In Situ Direct Magnetic Loss Measurement With Improved Accuracy for Lossier Magnetics

Magnetic loss often tops the power converter’s loss breakdown chart. The optimization of a magnetic component is, therefore, crucial in developing an efficient power converter. However, it is difficult to verify the design of magnetic components <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>in situ</i></b> , while they operate in the desired condition. The accurate, direct magnetic loss measurement is severely hindered by an uncertain timing skew between the measurement channels. This unknown timing skew could introduce an intolerable error in the measured magnetic loss. This article presents a novel method that avails the accurate, direct, and <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>in situ</i></b> magnetic loss measurement. An improved mathematical model of the measured magnetic loss in a power converter is developed with respect to the timing skew. Nonidealities in a practical magnetic component are also incorporated in the model for improved accuracy. The new method termed as triple-curve derivative (TCD) method is introduced and analyzed in detail to determine the actual timing skew and real magnetic loss with an enhanced accuracy, compared to the known methods. The TCD method is validated in simulation and verified in the experiment under various circuit design parameters based on a dc–dc step-down buck converter.

Numerical modeling of magnetic induction in standard and triple Epstein frames considering cutting and staggering of sensor strips

For magnetic energy loss measurements on electric steel sheets, the Epstein tester (ET) is applied for 100 years. However, it suffers from unsolved problems, such as inhomogeneity of flux in the corners and even more of impact of sample cutting. As a matter of fact, a detailed study of flux distributions—as a pre-condition for improvements—has not been performed so far. In this work, we present the results of an advanced numerical 3D-magnetic anisotropic circuit calculation modeling. It considers most relevant impacts such as anisotropy, non-linearity, method of staggering, and in particular, consequences of sample cutting. According to the literature, the latter may yield material deterioration for edge zones of high width WDET. Here, we set WDET to 2.5 mm as a “coarse-cut” convention for practice, and we compare it with perfect “fine-cut” (W = 0). As a main result, deteriorated edge zones of standard ET strips of low width W = 30 mm yield a distinct concentration of flux along inner axial strip regions as a reason for strong local flux inhomogeneity and distortion. Consistent numerical comparisons predict that higher grades of magnetic homogeneity can be expected from wider sample strips, e.g., from a “Triple ET” with W = 90 mm. As a global conclusion, the Epstein frame represents a system of extreme 3D inhomogeneity, especially in the corners. The grade of inhomogeneity reaches its maximum in instants of high permeability. It may be strongly increased through coarse cutting. On the other hand, consequences of cutting can be decreased by increasing the strip width. This would allow for loss measurements using tangential field coils arranged in the central limb regions of TET.

Role of asymmetric critical current on magnetization loss characteristics of (RE)Ba2Cu3O7−d coated conductors at various temperatures

Commercial high-Tc superconducting (HTS) coated conductors exhibit asymmetric Ic(B,θ) characteristics, where B presents a DC magnetic field and θ is defined as the angle between an applied magnetic field and the normal component of the superconductor plane. The asymmetric Ic(B,θ) characteristics have a non-trivial influence on the dominant loss component, magnetization loss, of various HTS applications where HTS conductors are exposed to an AC magnetic field. Here, we present measurements of Ic(B,θ) and magnetization loss in a 12 mm-wide (Rare Earth)Ba2Cu3O7−d (REBCO) commercial coated conductor at 77, 70, and 65 K. In the Ic(B,θ) measurement, θ was varied around a full 360° revolution and B was varied up to 0.2 T. In terms of the magnetization loss measurement, the applied AC magnetic field amplitude is up to 110 mT and the field angle varied from 0° to 180°. At the three given temperatures, we observed magnetization loss variations among the field-angle range, in particular, for θ and 180°-θ, which are in mirror symmetry relative to the superconducting plane. Furthermore, this asymmetric field-angle dependence of the magnetization loss becomes more apparent at higher applied field amplitudes and lower operating temperatures. A finite element method simulation using H-formulation was carried out by directly interpolating the measured Ic(B,θ) data, and the simulation results reproduce the trend of the experimental results. We also found that the magnetization loss is not equivalent within the positive and negative half field cycles due to the asymmetric Ic(B,θ) characteristics of the conductor. Numerical simulations revealed a clear correlation between the magnetization loss and the asymmetric Ic(B,θ) data for the whole 360° field-angle range in the REBCO conductor. The asymmetry in the Ic(B,θ) data about the ab-peak causes differences in magnetization loss values for the mirror-symmetric field angles. The asymmetry in the Ic(B,θ) data upon field reversal also results in differences between magnetization loss values for the positive and negative cycles.

Direct in-situ Measurement of Magnetic Loss in Power Electronic Circuits

Timing skew between measurement channels can introduce an unacceptable error in power loss measurement and is difficult to quantify, rendering precise in-situ measurement of magnetic loss essentially unattainable. This article rams the issue head-on by presenting the mathematical model for the timing skew and developing two methods based on the model to realize in-situ direct magnetic loss measurement. The mathematical model is first established to analyze the effects of timing skew on the measured magnetic loss in a dc–dc converter. The first method, called intersection method, illustrates how to unravel the entangled relationship between the actual timing skew and real magnetic loss in the circuit with the aid of the mathematical model. The second method, called derivative method, builds on the intersection method and greatly enhances the accuracy and the repeatability of the loss measurement. Our novel approach for in-situ magnetic loss measurement is verified in simulation and experiment with a conventional dc–dc step-down buck converter under various operating conditions and design parameters.

Coupling Time Constant Measurements of Spirally-Twisted Striated Coated Conductors With Finite Transverse Conductance Between Filaments

Striation is effective for AC loss reduction of coated conductors, but it must be associated with twisting. Instead of direct twisting like in low Tc metallic superconductors, we spirally-twisted “striated and copper-plated coated conductor”, in which filaments are electrically connected. The thickness of the plated-copper was varied to examine its influence on filament decoupling. The magnetization losses of these conductors were measured along a transverse magnetic field with a small amplitude, where the coupling loss was dominant. From the frequency dependence of the measured magnetization loss, the coupling time constants of samples with different copper thicknesses, different spiral pitches, and different core diameters were determined. This study demonstrates filament decoupling by spiral twisting the striated and copper-plated coated conductors.

A thermographic camera method for measuring the core loss distribution

Motor core losses are usually evaluated as the total loss minus known losses, including copper and mechanical losses. However, it is difficult to identify the main cause of core losses based on this evaluation method. In our previous study, we proposed a method for directly evaluating core loss distribution based on heat measurements using a thermographic camera. In this paper, we examine the reliability of thermal measurements using a device that can simultaneously measure core loss both by the general magnetic method and by the thermal measurement method. In the comparison method, the magnetic loss and thermal measurements are conducted simultaneously using an open magnetic path single sheet tester that permits simultaneous direct imaging of a sample with a thermographic camera, and the core loss values are compared and examined. We demonstrate a good agreement between the thermal and magnetic measurement below 10% difference for flux densities higher than 1T.

Magnetic loss measurement of surface‐mounted permanent magnet synchronous machines used in explosive environments

High energy-efficient permanent magnet synchronous machines (PMSMs) with low manufacturing costs and easy controllability are in high demand for the automotive and aerospace industries and in explosive environments (hazardous areas) like mines and the petrochemical industries. In explosive environments, the high surface temperature of PMSMs, due to magnetic losses and the irreversible demagnetisation of permanent magnets (PMs), could be a source of ignition leading to explosions. Therefore, this paper presents magnetic losses of a PMSM, which will help engineers to design robust machines with a high tolerance to explosive environments. Analytical calculations and finite element method (FEM) simulations of the magnetic losses of a PMSM are presented and compared with measured values from testing a PMSM.

Study on Magnetization Losses in Soldered-Stacked-Square (3S) HTS Wires with 1 mm Width

Magnetization loss of high-temperature superconducting (HTS) wires is usually considered as a critical issue in power applications. In order to reduce magnetization loss, a narrow soldered-stacked-square (3S) HTS wire with 1 mm width is firstly proposed by our group. And as a novel HTS wire type, its magnetization loss should be significantly understood before applied in further application. In this study, we fabricate the 1-mm-wide 3S wires with 2+4c, 4+2c, and 6+0c structures, and evaluate their magnetization loss experimentally and numerically. In the fabrication process of the 3S wires, a newly suggested technology, laser cutting, is adopted. The results show that the magnetization loss in (4+2c)-wire is independent of the frequency under perpendicular field but dependent on the frequency under parallel field. This may be considered that both eddy current loss and coupling loss are contained in the case of parallel field, besides hysteresis loss. Moreover, the different structures of the 3S wires will not affect the magnetization loss under perpendicular fields, but influence the magnetization loss under parallel fields. And these numerical results for parallel field have larger deviations compared with measured magnetization loss because only hysteresis loss is considered in the numerical model. Finally, a considerable reduction of the magnetization loss in the 3S wire is observed in the comparison with that in the original tape.

1-D and 2-D Loss-Measuring Methods: Optimized Setup Design, Advanced Testing, and Results

Accurate measurements of magnetic losses in laminations are a prerequisite for their theoretical assessment, as well as for satisfying calculations of energy dissipation in engineering systems. The standardized and universally applied measurement method, used as a reference for the definition of the material quality in the specification standards, is based on the Epstein test frame magnetizer. Its success relies on the reproducibility of the performed measurements. Its limitations come, on the one hand, from cumbersome sample preparation and, on the other hand, from a certain divergence of the measured loss figures from the true loss figures. Similar systematic differences between measured and true loss values are also observed with the standard single-sheet tester (SST) method. In both cases, measurements under bidimensional induction are or cannot be envisaged. The design of new measurement setups and magnetizers overcoming the drawbacks of the Epstein and SST methods and possibly becoming recognized standards in the future is welcome, but challenging. This paper is devoted to a comprehensive discussion of the state of the art in the alternating and 2-D measurements of energy losses in soft magnetic materials for electrical applications. We will summarize, in particular, measuring solutions proposed in the current literature, and we will discuss in detail recent developments achieved in the authors' laboratories regarding 1-D measurements with compensated permeameters and 2-D measurements at high inductions and high frequencies.

Magnetization Loss in REBCO Roebel Cables With Varying Strand Numbers

Assembled coated conductors are essential in many high-current high-temperature superconducting (HTS) applications. A promising option is to use Roebel cable, as it offers both low ac loss and mechanical flexibility. In this work, we measured magnetization loss at 77 K in REBCO Roebel cables with varying strand numbers from 6 to 14 to investigate the strand number dependence of ac loss characteristics of the Roebel cables. The 4-mm-wide Roebel strands were punched from nonstabilized 10-mm-wide Fujikura REBCO tapes. The applied field amplitude, frequency, and the field angle (the angle between the magnetic field and the tape wide surface) were varied. Three 10-mm-wide vertical stacks with conductor number of three, five, and seven were prepared as reference stacks using the same source Fujikura tapes. The measured magnetization loss values of the Roebel cables were compared with those of the equivalent stacks as well as with the results of COMSOL modeling of the stacks using the H -formulation. At magnetic-field amplitudes greater than the effective penetration field of the Roebel cables the cables have lower ac loss than equivalent stacks.