Epstein Test Research Articles

Investigative study on the properties of magnetic materials for electrical machines

<p><span>The paper attempts to investigate the properties of the magnetic materials used in the construction of rotating electric machines, with a view to arrive at the appropriate choice for the induction motors in particular. Measurement of magnetic properties for rotating electrical machines are more important to both machine designer and operator. This paper discusses the influence of magnetic properties of electrical steel on performance of electrical machine. Here properties like BH curve, core loss, permeability and other vital parameters are measured using 400×400 Epstein tester over wide range flux density and frequency up to 50 Hz and 400 Hz. The results measured in terms of the core loss, BH curve and permeability showcase the benefits to decide on the suitability of the material for use in practice.</span></p>

Examination of magnetic properties of nonoriented electrical steels using ring-type specimens

The Epstein frame test is commonly used for investigating the magnetic properties of electrical steels because of the convenient sample preparation. This test requires the samples to be cut half-parallel and half-perpendicular to the direction of rolling to account for the magnetic anisotropy of the sheet. An alternative method to evaluate the magnetic properties of electrical steels is the ring core test. This test more closely represents the magnetic cores in rotating machinery such as motors and generators because the sample shape for this test resembles the practical rotating applications. The measured results may vary according to the test methods. In this study, the differences between the results of the Epstein frame tests and ring core tests were investigated for the various grades of NO steels. For the magnetic induction measurements, results of the ring core test showed a trend of lower values than in the results of the Epstein frame tests. The core losses measured by the ring core tests are generally greater than those of the Epstein frame tests. The difference in results due to the test methods can be attributed to the anisotropy parameter, A(h), which can be obtained from the crystallographic texture of the sheet sample. The difference becomes significant when an area fraction of the texture component shows a high 1-A(h) value by the Epstein test but a low value by the ring test.

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.

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.

Physical Assessment of the Magnetic Path Length of Energy Loss Testers

Magnetic energy losses of SiFe sheets are determined by the standardized methods of single sheet tester (SST) or Epstein tester (ET). According to IEC standards, the total power consumption is measured in Watt-metric ways, and the portion that concerns the homogeneously magnetized region(s) is estimated on a nominal value l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> of the so-called conventional effective magnetic path length (PL). A clear definition of PL is lacking-a suggestion being provided here. Standards express l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> through the dependence between the magnetic field strength H and the magnetization current. However, they apply the same value l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> also for the determination of losses P. From the viewpoint of physics, two PL quantities l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m,H</sub> and l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m,P</sub> would be preferable. The problematic is enhanced by the fact that the flux distribution within the magnetic circuit of a tester may change dynamically during the period of time, with induction changes B(t). This means that the physical PL L is a function of time, according to a PL function L[B(t)]. Finally, dynamic changes in flux distributions prove to be distinctly influenced by hysteretic mechanisms which means that L[B(t)] exhibits loop character. The resulting complexity indicates that the concept of PL is not promising, if high accuracy of testing is demanded. However, for purposes of material comparisons, optimum PL values LOPT may be suitable that are determined for individual material families. Analyses of instantaneous loss power values p(t) indicate that energy dissipation is weak during high induction. Thus, determinations of LOPT should be focussed on moderate induction. The ET is characterized by strong modifications of 3-D flux distributions which means that individual values LOPT would be needed. On the other hand, the SST shows a clear design. For moderate induction, some energy dissipation is expected to occur within the yoke region. This indicates that LOPT exceeds the conventional value of 450 mm, in weak ways.

3-D MACC Modeling of Instantaneous Magnetic Flux Distributions in Epstein Tester

Magnetic energy losses of silicon iron (SiFe) sheets are determined by the standardized methods of single sheet tester (SST) or Epstein tester (ET). The ET is much more compact and can be applied in a large range of frequency. However, it suffers from several sources of systematic errors. The most severe one is given by the magnetic cores flux distribution that shows a strong degree of inhomogeneity. This fact is highly evident. However, it never has been investigated in detail so far. Herein, we report results of a 3-D modeling, performed by magnetic anisotropic circuit calculation (MACC), considering non-linearity in connection with anisotropy, for both non-oriented (NO) steel and grain-oriented (GO) steel. The results reveal substantial differences of the corresponding flux distributions. NO steel proves to be characterized by high homogeneity of induction in rolling direction in the middle sections of the four limbs. However, the four corners show strong inhomogeneity in instants of low global induction, while a transition to more balanced flux arises at peak magnetization. On the other hand, this transition is much less pronounced for GO steel. As a conclusion for the evaluation of losses, a distinction is needed for the two different types of material.

Non-Oriented Electrical Steel Sheet: The Magnetic Properties Losses on Thickness Lamination Using Epstein Tester Frame

Reducing lamination thickness of steel sheets can reduce the overall loss especially in core loss and copper loss. These research paper shows the impact of lamination thickness on the voltage induced of power loss for the Non-Oriented Electrical Steel Sheet. This study was conducted by using Epstein test which is an outflow of flux investigated throughout the measurement of power loss at corner and limb likewise for each thickness. This data shows and is presented based on different frequency such as 45 Hz, 50 Hz and 55 Hz. It indicates that 0.50 mm lamination thickness has a lot of losses instead of 0.35 mm.

3-D Printed Magnetic Field Coil for Medium Frequency Epstein Tester

For the determination of magnetic energy losses of SiFe sheets as applied for technical frequencies, the most effective tool is given by the standardized single sheet tester (SST). However, for measurements at elevated frequency, as becoming relevant in increasing ways, the SST fails due to strongly enhanced eddy currents. An alternative is given by the Epstein tester (ET). However, its results are affected by edge effects from sample slitting and strong inhomogeneity of flux distribution. Here, we propose the so-called Grand ET where these impacts are restricted through doubled strip width and through an extra-thin, precisely, 3-D printed tangential field coil of reduced edge height. Moreover, a restricted coil length yields concentration to the sample region of acceptable homogeneity. The coil is manufactured by the so-called 3-D-assembler that allows printing of all components, including the windings. Presentation of loss results is given for a medium frequency range of 1 kHz up to 20 kHz where losses reach the order of hundreds of W/kg. Rapid testing is favored by a restriction to just two sample strips.

Estimation of the Core Losses of Induction Machines Based on the Corrected Epstein Test Method

A revised method based on the standard Epstein test is proposed to improve the accuracy of the estimation of the core losses of induction machines (IMs). Since the magnetic field strength patterns at the four corners of the standard test samples are non-uniform, high-order excess losses at the corners would deteriorate the accuracy of the model for core losses. To address this issue, test samples were designed which have an appropriate geometry for the measurement of core losses under the test conditions. The excess losses could be eliminated by introducing an air-gap magnetic reluctance at the four corners so that the core-loss data from the tests consist of only hysteresis and eddy current parts. In experimental validations, three 5-HP IMs were bench-tested for the verification of the core-loss estimation. The use of commercial computer-aided engineering software packages allowed for the estimated core losses to be recorded and compared. The results indicate that high-order excess losses could account for 7% of the total core losses.

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.

Core Loss Analysis of Permanent Magnet Synchronous Generator With Slotless Stator

This paper proposes an analysis method of the core loss for a slotless type permanent magnet linear synchronous generator. Core loss is usually calculated using the Steinmetz equation, but this cannot be interpreted correctly. Consequently, several researchers have proposed modified versions of this equation. In this study, we calculate core loss coefficients from the Epstein test data using a curve fitting method for accurate core loss analysis. Moreover, owing to the time harmonics observed with changes in the magnetic flux density, we separate the rotating magnetic field and alternating magnetic field in our calculations. In addition, we consider the magnetic flux leakage as a parameter. Finally, core loss of the slotless type linear generator is calculated using a modified Steinmetz equation that considers the flux leakage.

Core Loss Analysis of Permanent Magnet Linear Synchronous Generator Considering the 3-D Flux Path

This paper presents an analysis of the core loss observed in the stator of a permanent magnet linear synchronous generator. Core loss is usually calculated using the classical Steinmetz equation, but it leads to erroneous results. Consequently, several researchers have proposed modified versions of this equation, taking into account the hysteresis loss, eddy current loss, and excess loss. In this paper, we calculated all loss coefficients from the Epstein test data using a curve fitting method. Moreover, we separated the rotating and alternating fields based on the time harmonics observed with changes in the magnetic flux density. In addition, we considered the 2-D and 3-D plane flux paths that cause magnetic flux leakage. Finally, the core loss of the linear machine was calculated using a modified Steinmetz equation that considers the flux path.

High-Frequency Characterization of Losses in Fully Assembled Stators of Slotless PM Motors

The recent emergence of wide-bandgap power transistors enables higher switching frequencies in electrical motor drives. Their full utilization from a system point of view requires quantification of the corresponding time-harmonic motor losses. As an initial step, this paper presents a unique study of stator losses for three different commercially available nonoriented silicon–iron steel grades (with lamination thicknesses 0.1, 0.2, and 0.3 mm). The investigations cover a wide frequency range (10–100 kHz) at different levels of dc bias (up to 1.6 T). Iron losses are identified from measurements on fully assembled stators deploying a novel technique. By utilizing fully assembled stators, no additional samples are required. Manufacturing influence is inherently incorporated. Results show that measured iron losses are twice as high at 10 kHz compared with Epstein test results, which emphasizes the need to incorporate manufacturing influence on iron losses at high frequencies. The level of dc bias is also observed to have a significant impact on iron losses (up to 30%). Even though thinner laminations are known for reducing iron losses, the reduction is much lower than anticipated in the studied frequency range due to skin effect. Using a 0.1-mm lamination gauge instead of 0.3 mm reduces losses by 50% at 10 kHz, while the same substitution at 100 kHz only reduces losses by 30%. Future work includes loss separation in complete converter-fed machines.

Thin grain oriented electrical steel for PWM voltages fed magnetic cores

This paper reports on performances of high permeability grain oriented electrical steel when used in association with power electronic switching devices. Loss measurement results obtained from the Epstein test, using sinusoidal or various PWM voltages in medium frequency range, show that for both studied thicknesses (HGO 0.23mm and HGO 0.18mm), comparing performances at a fixed induction level between the various situations may not be the most convenient method. The effect of magnetic domain refinement has been investigated. After having shown the interest of lowering the thickness, an alternative way of looking at losses is proposed that may help to design the magnetic core when it comes to the matter of reducing size in considering frequency and magnetization levels.

Determination of Specific Losses in the Limbs of an Epstein Frame Using a Three Epstein Frame Methodology Applied to Grain Oriented Electrical Steels.

An experimental method to characterize the magnetic properties of Grain Oriented Electrical Steel in the rolling direction is proposed in this paper. It relies on the use of three 25 cm Epstein frames combined to generate three test-frames of different lengths. This enables the identification of the effective specific losses of the electrical steel when magnetization is applied along the rolling direction. As a consequence, it evidences the deviation of the loss figures obtained using the standardised Epstein test. The difference in losses is explained by the fact that the described method gives “only” the losses attached to the straight parts. The concept of the magnetic path length as defined by the standard is discussed.

Comparison between the Nominal Loss in 3%SiFe and Amorphous Transformer Core Materials

An investigation of nominal loss in 3%SiFe and amorphous of the transformer core materials will evaluate in this paper. The investigation involves the variation of power loss, flux leakage, and total harmonic distortion. The nominal loss has been measured using Epstein test frame with three layers of lamination. The loss in the amorphous transformer core material is 57.46% better than the transformer core with 3% SiFe material at flux density of 1.2T, 50 Hz. The flux leakage at corner in the 3% SiFe transformer core material is the lowest than the two of transformer core material, over the whole flux density range. Total harmonic distortion flux is the largest in the amorphous of transformer core materials and the smallest in the 3% SiFe of transformer core material. Using the amorphous material in transformer core is more efficient than the two of transformer core materials.

Comparison between the Nominal Loss in 3%SiFe and Amorphous Transformer Core Materials

An investigation of nominal loss in 3%SiFe and amorphous of the transformer core materials will evaluate in this paper. The investigation involves the variation of power loss, flux leakage, and total harmonic distortion. The nominal loss has been measured using Epstein test frame with three layers of lamination. The loss in the amorphous transformer core material is 57.46% better than the transformer core with 3% SiFe material at flux density of 1.2T, 50 Hz. The flux leakage at corner in the 3% SiFe transformer core material is the lowest than the two of transformer core material, over the whole flux density range. Total harmonic distortion flux is the largest in the amorphous of transformer core materials and the smallest in the 3% SiFe of transformer core material. Using the amorphous material in transformer core is more efficient than the two of transformer core materials.

Building Factor of Grain-Oriented Silicon Iron (3% SiFe) with Different Thickness on 100kVA Three Phase Distribution Transformer Core

The power loss in laminated transformer cores is always greater than the nominal loss of the electrical steel laminations, by a factor known as the building factor. This paper discussed result of an investigation towards the effect of using two different Grain-Oriented Silicon Iron (3%SiFe) materials to the 100kVA three phase distribution transformer. The thicknesses of the material that have been used in this research are 0.23mm and 0.27mm. The transformer core will be assembled with 60o T-joint with 5mm mitred corner overlap length. Power loss has been measured using no-load test with 29 layer of lamination while nominal loss measured using Epstein test frame. At the operation mode flux density, 1.5T, the building factor of the transformer model core material with 0.23mm thickness is 1.219 while with the building factor for 0.27mm thickness is 1.250. This shows that thinner transformer core lamination is better than the other one by 2.5% during operation mode.

On the variation with flux and frequency of the core loss coefficients in electrical machines

A model of core losses, in which the hysteresis coefficients are variable with the frequency and induction (flux density) and the eddy-current and excess loss coefficients are variable only with the induction, is proposed. A procedure for identifying the model coefficients from multifrequency Epstein tests is described, and examples are provided for three typical grades of non-grain-oriented laminated steel suitable for electric motor manufacturing. Over a wide range of frequencies between 20-400 Hz and inductions from 0.05 to 2 T, the new model yielded much lower errors for the specific core losses than conventional models. The applicability of the model for electric machine analysis is also discussed, and examples from an interior permanent-magnet and an induction motor are included.

Iron loss analysis of linear oscillating actuator for linear compressor

PurposeAims to discuss iron loss analysis and experimenting with linear oscillating actuator for linear compressor.Design/methodology/approachThe iron loss analysis of the linear oscillating actuator is performed by using ANSYS and iron loss curves, which is obtained by an Epstein test apparatus.FindingsThe way to calculate the iron loss of the linear oscillating actuator for the linear compressor and the method to experiment the iron loss of that can be studied.Research limitations/implicationsIron loss analysis of the linear compressor considering the motor part and the structure part is needed.Originality/valueEach iron loss analysis method examined here can be used to analyze the iron loss of the linear motor.