Core Loss Measurements Research Articles

EEL Calculations and Measurements of Graphite and Graphitic-CNx Core-Losses

Core EEL spectra of MWCNTs (multi-wall carbon nanotubes) grown in a nitrogen atmosphere were acquired utilising a dedicated STEM equipped with a Gatan Enfina system. Splitting of the carbon K-edge π* resonance into two peaks provided evidence of two nondegenerate carbon bonding states. In order to confirm the presence of a CNx bonding state, a full-potential linearised augmented plane-wave method was utilised to simulate core EEL spectra of graphite and graphitic-CNx compounds. The simulations confirmed splitting of the carbon K-edge π* resonance in graphitic-CNx materials, with the pristine graphite π* resonance remaining unsplit. The simulations also confirmed the increasing degree of amorphicity with higher concentrations (25%) of substitutional nitrogen in graphite.

Lamination Core Losses in Motors With Nonsinusoidal Excitation With Particular Reference to PWM and SRM Excitation Waveforms

The effects of varying the modulation index and the switching frequency on steel lamination core losses when excited with pulse width modulated waveforms are first investigated. A switched reluctance motor flux model is also developed and flux waveforms for different parts of the machine are synthesized. Using these flux waveforms, the paper presents the loss trend inside a switched reluctance machine, showing the core loss variation of the machine. The rotor was found to incur higher losses than any other part inside the switched reluctance motor. The paper further identifies the flux density harmonics that contribute to higher core losses in the rotor. Using the Fourier series, an attempt to predict core losses under switched reluctance motor flux density waveforms is done and the predicted results are compared with measurements. An Epstein frame was used for direct core loss measurements on 0.0140 in. [0.36 mm] commercial electrical steel; the methods and test bench used, along with test results are detailed in the paper.

Prediction and measurement of core losses in a high-speed switched-reluctance Machine

We describe a procedure for calculating the core loss in high-speed switched-reluctance machines. The technique calculates core losses within a switched-reluctance machine to a high degree of spatial resolution over a wide range of operating conditions. We confirmed the calculations experimentally, using a loss segregation method, and found good correlation.

A novel technique for measurement of core loss in low permeability materials

A survey of existing techniques for measuring core loss in magnetic materials is presented. It is shown that the most challenging combination is a low permeability material at low measurement frequency. Such materials have application in components of power converters, and thus are of considerable technological significance. Measurement difficulties stem from losses in the windings employed, which are difficult to disentangle from loss in the core, as well as the stringent requirements on phase accuracy of measurement instruments. Another practical problem is the large power capacity required of the drive source to achieve significant induction levels. A new resonant measurement setup, which we call the “virtual impedance” technique, is proposed as a solution to these problems. Its utility is demonstrated with measurements of a commercial composite core with permeability 14 μ 0 whose low-core loss defeats conventional methods of measurement.

Measurement and modeling of core losses of soft magnetic composites under 3-D magnetic excitations in rotating motors

Soft magnetic composite (SMC) materials are especially suitable for construction of low cost high performance motors with three dimensional (3D) magnetic fields. The 3D finite element analysis (FEA) conducted in the design of a claw pole transverse flux motor (TFM) with an SMC core reveals very complicated B (flux density) loci in the core when the motor rotates. In order to understand and account for the effects of the patterns of B loci on motor parameters and performance such as core losses, a 3D magnetic property testing system was built for magnetic measurement on a cubic SMC sample. 3D rotational core loss models in SMC materials and rotating motors are developed and verified by the experimental results.

Core Losses in Motor Laminations Exposed to High-Frequency or Nonsinusoidal Excitation

This paper first reviews three internationally standardized core loss measurement methods: Epstein frame, toroids and single sheet testers. A comparison of the Epstein frame and toroid test results is presented for annealed and unannealed steel. Two methods are used to predict core losses under nonsinusoidal supplies. The first method uses the Fourier series and an improved loss separation algorithm to predict core losses under equivalent brushless DC motor flux waveform with known spectrum. For lower harmonics, superposition yielded results close to the measured values. The second method uses the form factor concept and an improved loss separation algorithm to predict core loss. The combination of the improved loss separation algorithm and the form factor concept was found to yield results close to the measured losses under high frequency supplies, such as pulse width modulated waveforms. An Epstein frame with commercial 0.0140-inch electrical steel was used for direct core loss measurements; the methods and test bench used are detailed in the paper, along with test results.

A New Method for Synchronous Generator Core Quality Evaluation

A new technique for detecting the presence and severity of inter-laminar short circuits as well as estimating the status of core compression (or looseness) in laminated magnetic cores of synchronous generators, with a single test equipment is demonstrated in this paper. The core loss measurement obtained from a flux injection probe that injects flux (of varying amplitude, frequency, and wave-shape) into two nominally adjacent teeth over a localized region, is used as an indicator for detecting and distinguishing the two fault conditions. An injection probe system was developed and tested, in the laboratory, using stacks of full size generator laminations with various induced fault conditions. The injection probe was shown to detect the presence of shorted laminations at the bottom of the slot and to gauge the degree of core compression or looseness. In addition, a unique differential probe was developed and tested to demonstrate the capability of detecting as few as five shorted laminations.

Induced Anisotropy in FeCo-Based Nanocrystalline Ferromagnetic Alloys (HITPERM) by Very High Field Annealing

Very high magnetic field annealing is shown to affect the magnetic anisotropy in FeCo-base nanocrystalline soft ferromagnetic alloys. Alloys of composition Fe/sub 44.5/Co/sub 44.5/Zr/sub 7/B/sub 4/ were prepared by melt spinning into amorphous ribbons, then wound to form toroidal bobbin cores. One set of cores was crystallized in a zero field at 600/spl deg/C for 1 h, then, field annealed at 17 tesla (T) at 480/spl deg/C for 1 h. Another set was crystallized in a 17-T field at 480/spl deg/C for 1 h. Field orientation was transverse to the magnetic path of the toroidal cores. An induced anisotropy is indicated by a sheared hysteresis loop. Sensitive torque magnetometry measurements with a Si cantilever sensor indicated a strong, uniaxial, longitudinal easy axis in the zero-field-crystallized sample. The source is most likely magnetoelastic anisotropy, caused by the residual stress from nanocrystallization and the nonzero magnetostriction coefficient for this material. The magnetostrictive coefficient /spl lambda//sub s/ is measured to be 36 ppm by a strain gage technique. Field annealing reduces the magnitude of the induced anisotropy. Core loss measurements were made in the zero-field-crystallized, zero-field-crystallized-than-field-annealed, and field-crystallized states. Core loss is reduced 30%-50% (depending on frequency) by field annealing. X-ray diffraction reveals no evidence of crystalline texture or orientation that would cause the induced anisotropy. Diffusional pair ordering is thought to be the cause of the induced anisotropy. However, reannealing the samples in the absence of a magnetic field at 480/spl deg/C does not completely remove the induced anisotropy.

Accuracy of iron loss estimation in induction motors by using different iron loss models

Abstract The paper presents iron loss estimation in a three-phase induction motor by using different iron loss models for the posterior iron loss calculation. The iron losses were determined by using modeled properties of used electrical steel and calculated distribution of magnetic induction B (t ) in all parts of the motor by using 2D finite element software for a complete cycle of field variation. The comparison between estimated and measured core losses for a 4 kW induction motor at no-load in dependency on supply voltage is given.

Cored rutherford cables for the GSI fast ramping synchrotron

The new heavy ion synchrotron facility proposed by GSI will have two superconducting magnet rings in the same tunnel, with rigidities of 200 T/spl middot/m and 100 T/spl middot/m. Fast ramp times are needed, which can cause significant problems for the magnets, particularly in the areas of ac loss and field distortion. This paper discusses the 200 T/spl middot/m ring, which will use Cos/spl theta/ magnets based on the RHIC dipole design. We discuss the reasons for choosing Rutherford cable with a resistive core and report loss measurements carried out on cable samples. These measurements are compared with theoretical calculations using measured values of inter-strand resistance. Reasonably good agreement is found, but there are indications of nonuniformity in the adjacent resistance R/sub a/. Using these measured parameters, losses and temperature rise are calculated for a RHIC dipole in the operating cycle of the accelerator. A novel insulation scheme designed to promote efficient cooling is described.

Magnetic properties of FeCo laminates subjected to axial loading

While manufacturing the stator/rotor assemblies of the aircraft power components, increased power losses are typically pronounced due to an imposed axial load onto the stack of magnetic laminates to increase the rigidity of the stack. An axial loader to enable core loss measurements to be made while the laminate stack is subjected to an axial load has been designed. The apparatus and multilayered slotted interface plates, allowing for the toroidal windings and simultaneous load application were used to evaluate the effect of compression up to 27.5 MPa on magnetic properties of commercially available Fe–Co based Hiperco® 50, Hiperco® 50 HS, and Hiperco® 27 alloys. For each composition, we tested two sets of samples: (1) completely insulated and (2) uninsulated. We report the increased losses due to an axial load and discuss the origin of these increased losses in terms of constant size anisotropy for completely insulated laminates.

Computation of the core loss in an induction motor using the vector Preisach hysteresis model incorporated in finite element analysis

This paper deals with the computation of the magnetic field and core losses in a squirrel-cage induction motor. The computational algorithm consists of the vector Preisach model incorporated in two-dimensional time-stepping finite element analysis. The hysteretic nonlinearity is handled by the fixed-point iterative technique. The comparison between the calculated and measured core losses for a 37 kW motor at no-load is given and indicates a reasonable agreement.

Method for measuring and characterizing core loss in a motor

Because of the complex shape and variable flux densities of the toothed cores of motors, characterization of their core losses has been difficult. Manufacturers' material specification sheets usually refer only to Epstein tests, based on sinusoidally varying flux densities in simple geometries. Here, a more accurate and direct method for measuring core loss is presented. The method spins the motor core in a magnetic field and then measures the spin speed and drag torque imposed on the core. This test was used to successfully characterize the core loss in a small dc brushless spindle motor. Among the parameters examined were the turning speed, maximum gap flux, lamination material, lamination thickness, and the effects of stress-relief annealing. Mathematical models of the core loss were constructed for specific core geometries based upon an assumed form for the empirical data. The actual core losses were higher than would have been predicted from conventional Epstein tests.

Fabrication and measurements of plastic scintillating fibers

Sixty kilometers of plastic scintillating fibers, 1 mm in diameter, have been manufactured using a preform/tube technology. The fibers consist of a polystyrene core surrounded by a polymethylmethacrylate cladding. The fabrication method is described and evaluated both qualitatively and quantitatively. A great effort has been made in order to measure the optical properties of the polymer at the different steps of the production. The global process efficiency is not more than 40% due to the yield of the polymerization process. Using a ternary blue scintillator, the mean light yield for a minimum ionizing particle, passing through a 1 mm diameter fiber at a distance of 1 m, is 5.4±0.6 photoelectrons. The mean attenuation length fitted between 0.5 and 2.0 m is 1.9±0.2 m. Some specific experiments that give independent measurements of core and interface losses are also reported. The principal cause of light loss is due to the lack of transparency of the polystyrene which leads to a spectral shift in fiber emission. This absorption already appears in the preform rods indicating that the purification and the polymerization process are of great importance. The attenuation length related to core losses is measured at the level of 3 m. The interface losses are about 10 −5–10 −4 per reflection leading to an equivalent attenuation length of 7 m.

Power losses of soft magnetic composite materials under two-dimensional excitation

Soft magnetic composite materials produced by powder metallurgy techniques can be very useful for construction of low cost small motors. However, the rotational core losses and the corresponding B–H relationships of soft magnetic composite materials with two-dimensional rotating fluxes have neither been supplied by the manufacturers nor reported in the literature. This article reports the core loss measurement of a soft magnetic composite material, SOMALOY™ 500, Höganäs AB, Sweden, under two-dimensional excitations. The principle of measurement, testing system, and power loss calculation are presented. The results are analyzed and discussed.

A simple method to estimate the magnetic field distribution due to current-carrying winding in toroidal core and its influence on the measurement of complex permeability and core losses

When we measure the power losses and the complex permeability μ= μ r′− jμ i″ of magnetic core, several turns of winding are wound tightly around the toroidal core to be measured. In order to make the magnetic field produced by the winding current in the core more uniform around the core, more turns of winding are needed. In this paper the distribution of the magnetic field strength produced by the winding current is analyzed based on the Biot–Savart law. According to the calculated result, we found the external field strength is much bigger in the area covered by the winding than the area unsurrounded by the winding. In order to study the influence of the nonuniform distribution of the external field strength on the measurement of the complex permeability and core loss, we use two sets of coils with the same turns connected in parallel which are arranged symmetrically around the core. From the measured results, it is found that core loss is not influenced by the distribution of the external magnetic field strength but the complex permeability is affected by the arrangement of the winding along the toroidal core.

Comparison of transformer loss prediction from computed and measured flux density distribution

Losses in power transformer cores can be predicted from knowledge of localised flux distribution within the assembled laminations. This together with a knowledge of the stress sensitivity of the losses of grain-oriented, 3% silicon iron can ideally be used to estimate the total core loss. The localised flux density is computed given the magnetic material B-H data and the core geometry. This paper reports results in which localised flux density and losses have been measured experimentally in model cores and compared with data obtained from a FEM analysis of the same core geometry. Effects of interlaminar flux, rotational flux and stress are taken into account. Agreement within 5% is found between the measured core loss and that calculated from the localised experimental data but predictions using the FEM results were only within 10% of the measured value. This greater difference is believed to be due to neglect of interlaminar flux and rotational magnetisation in the computation of flux distribution. However, these are shown to be accountable by using corrective factors whose magnitudes depend on core geometry.

Improved formulations for rotational core losses in rotating electrical machines

This paper presents the measurement and modeling of rotational core losses in electrical steel sheets and rotating electrical machines. Novel formulations of rotational hysteresis, eddy current, and excess losses in electrical sheet steels with circular and elliptical rotating flux density vectors are reported. These formulations are used together with the finite element method to calculate the core losses in rotating electrical machines according to the distribution of the rotating magnetic field. Theoretical results are compared with the experiments on both electrical steel sheets and electrical machines.

Martensitic Transformation in a Ti50ni48fe2 Alloy Studied by Eels

Abstract Martensitic transformation is the first-order diffusionless phase transformation in solids, and is responsible for unique phenomena such as shape memory effect and superelasticity. Recently, many researchers tried to explain the origin of martensitic transformations from a viewpoint of electronic structure. It is strongly required to investigate electronic state changes associated with a martensitic transformation by an accurate experiment. EELS (Electron Energy-Loss Spectroscopy) was successfully applied to study electronic state in several alloys and oxides, e.g. a composition dependence of density-of-state (DOS) in Cu-3d band was clearly observed for Cu1-xAlx alloys by a core-loss measurement. However, this method has been less applied to studies of phase transformations to date. The purpose of the present work is to investigate electronic state changes associated with a martensitic transformation in a Ti50Ni48Fe2 alloy by EELS. A Ti50Ni48Fe2 alloy was prepared by induction-melting method. Thin-foiled specimens were solution-treated in Ar atmosphere at 1173K for 1hr.,

Correction of the measured core losses under distorted flux [power transformers

This paper presents a new method that permits the determination of power transformer core losses under nonsinusoidal excitation. The method requires the measurement data of a transformer no-load test. This method is applied to predicting power transformer core losses under nonsinusoidal conditions with an adequate accuracy from test results obtained with a real nonsinusoidal voltage waveform.