Single Strip Tester Research Articles

Diffusion of Alloying Cobalt Oxide (II, III) into Electrical Steel.

This paper aims to reduce power loss in electrical steel by improving its surface resistivity. The proposed approach involves introducing additional alloying elements through diffusion once the steel sheet reaches the desired thickness. Various effective techniques have been suggested and tested to enhance the resistivity of the strip. The method entails creating a paste by combining powdered diffusing elements with specific solutions, which are then applied to the steel's surface. After firing the sample, a successful transfer of certain elements to the steel surface is achieved. The amount and distribution of these elements can be controlled by adjusting the paste composition, modifying the firing parameters, and employing subsequent annealing procedures. This study specifically investigates the effectiveness of incorporating cobalt oxide (II, III) into non-oriented silicon iron to mitigate power loss. The experimental samples consist of non-oriented electrical steels with a composition of 2.4 wt% Si-Fe and dimensions of 0.305 mm × 300 mm × 30 mm. Power loss and permeability measurements are conducted using a single strip tester (SST) within a magnetic field range of 0.5 T to 1.7 T. These measurements are performed using an AC magnetic properties measurement system under controlled sinusoidal conditions at various frequencies. The research explores the impact of cobalt oxide (II, III) addition, observing successful diffusion into the steel through the utilization of a paste based on sodium silicate solution. This treatment results in a significant reduction in power loss in the non-oriented material, with power loss reductions of 14% at 400 Hz and 23% at 1 kHz attributed to the elimination of a porous layer containing a high concentration of the diffusing element. The formation of porosity in the cobalt addition was found to be particularly sensitive to firing temperature near the melting point. The diffusion process was examined through scanning electron microscopy (SEM) in combination with energy-dispersive X-ray spectroscopy (EDS). The results demonstrate improved power losses in the coated samples compared with the uncoated ones. In conclusion, this study establishes that the properties of non-oriented electrical steels can be enhanced through a safer process compared with the methods employed by previous researchers.

A new hysteresis simulation method for interpreting the magnetic properties of non-oriented electrical steels

The magnetic properties of non-oriented electrical steels (NOESs) are characterized using an analytical simulation method accounting for the microstructures in ferromagnetic materials. Complementary experimental data for thin sheet laminations, obtained using a standard single strip tester (SST), are employed with the hysteresis mechanism investigated in terms of the measurement system and Weiss Mean Field effects. It is shown that the magnetic hysteresis loops of NOESs of 3% SiFe can be generated with remarkable accuracy for a broad range of magnetization frequencies and peak flux densities. The simulation method is also suitable for performing an energy loss analysis with calculated energy losses, when compared to corresponding measured data, showing a strikingly accurate match with, in most cases, an error of less than 1%.

Impact of manganese diffusion into non-oriented electrical steel on power loss and permeability at different temperatures

Minimising power losses and their consequences is a significant matter in electrical steel applications. Increasing the resistivity of the steel strips has been confirmed as a successful method to overcome the problem of power losses. To increase the resistivity of the strip, different effective methods have been proposed and tested. In this work, a new material has been proposed to achieve the objective of increasing the resistivity of the steel samples by adding Manganese (IV) oxide based on a diffusion technique. The surface of the samples is to be coated with the proposed Manganese oxide. This should guarantee an increase in the resistivity of the samples, which in turn reduces the power losses caused by the eddy current. The samples tested were of non-oriented electrical steels containing 2.4 wt% Si-Fe (with a thickness of 0.305 mm*300 mm*30 mm). It was measured for losses and permeability before and after treatment by a Single Strip Tester (SST) at 0.5–1.7 T using an Alternating Current magnetic properties measurement system under controlled sinusoidal at different frequencies. The obtained results revealed that the depth of Manganese oxide diffusion is inversely proportional to the increase in the temperature. It was demonstrated that the best amount of diffusion of the element into the strips was achieved at 525°C, which was 60 weight % in comparison with 700°C which was 20 wt%. Likewise, at 800°C it was 7 wt%. However, the depth of diffusion of the manganese was the same at those tested temperatures, which were equal to 200 µm deep on each of the side strips. The diffusion of the material was investigated using Scanning Electron Microscope (SEM) coupled with Energy Dispersive X-ray Spectroscopy (EDS). Furthermore, from the results, it was concluded that the power losses in the coating samples were improved by 9% as compared with uncoated samples.

Effect of mechanical cutting on the energy loss of laser-scribed grain-oriented alloys

We investigate the effect of mechanical cutting on the magnetic properties of high permeability grain-oriented (HGO) laser-scribed Fe-Si sheets. Measurements have been performed on strips of different widths (5 to 60 mm) cut from 0.27 mm thick sheets. Normal magnetization curve and energy loss have been determined by means of a digitally controlled single strip tester from 1 Hz to 1 kHz at peak magnetic polarization values Jp = 1000 mT and 1700 mT. The results fit into a simple phenomenological model regarding the dependence of magnetization curve and energy loss on the strip width, in substantial continuity with the approach originally developed for non-oriented electrical steels. The hysteresis Wh and excess Wexc loss components are shown to depend on the strip width according to a hyperbolic law, with a limiting fully hardened strip predicted to occur for widths around 3.5 mm. It is then consistently observed that the mechanical cutting of standard 30 mm wide HGO Epstein strips is conducive to an increase of the energy loss at 50 Hz and 1.7 T of the order of 13 %.

Influence of mechanical and water-jet cutting on the dynamic magnetic properties of NO Fe-Si steels

Magnetization curve and energy losses have been analyzed in non-oriented (NO) Fe-Si alloys with variable thickness (0.20 mm–0.35 mm), cut at widths ranging between 5 mm and 60 mm, in order to assess the impact of cutting, either done by punching or water-jet techniques. Measurements were performed by means of a digitally controlled single strip tester, from dc up to 1.5 kHz, at peak polarization values Jp = 1.0 T and 1.5 T. The evolution of the magnetization curve and the structure-dependent hysteresis Wh and excess Wexc loss components have been assessed as a function of the strip width using a simple phenomenological model, by which the extension of the damaged area at the edges of the cut sheets is estimated. Such a model assumes a hyperbolic dependence of the measured polarization on the cut strip width. The limiting values of Wh and Wexc for the fully damaged and the pristine sheets are in this way estimated, showing that one can simply and affordably predict the magnetic behavior of NO Fe-Si steels subjected to cutting.

Optimization of a single strip tester to measure magnetic properties of electrical sheet steel at medium frequencies

Optimization of a single strip tester to measure magnetic properties of electrical sheet steel at medium frequencies

Degradation of magnetic properties of non-oriented silicon iron sheets due to different cutting technologies

The magnetic properties of non-oriented silicon iron alloys are strongly influenced by the cutting technology. Medium quality electrical steel M800-65A samples were cut through mechanical punching, laser, water jet and electro erosion technologies and were characterized with an industrial Single Strip Tester at the peak magnetic polarizations Jp of 0.5, 1 and 1.5 T, in the frequency range starting from 10 Hz to 200 Hz. The influence of the cutting technology on the energy losses and magnetic permeability was investigated.

Magnetic Materials Used in the Magnetic Core Manufacture of Electrical Machines and Transformers

Two types of silicon iron steels, M400-65A non-oriented and MOH grain-oriented alloys were characterized using an industrial Brockhaus Single Strip Tester at two peak magnetic polarizations of 500 mT and 1000 mT in the frequency range from 10 Hz to 100 Hz. The samples were cut parallel to the rolling direction trough different cutting technologies, which are the classical mechanical-, then the non-conventional laser-, water-jet-and traveling wire electro-erosion methods. The loss separation concept was applied and the total energy losses, determined experimentally, for each sample were decomposed into hysteresis, classical (Foucault) and excess (anomalous) energy losses. A detailed analysis of each type of losses as a function of the frequency was made and the influence of the cutting technology was analyzed.

A Simple Compensation Method for the Accurate Measurement of Magnetic Losses With a Single Strip Tester

We present a new method for the accurate characterization of soft magnetic sheets using a permeameter based on the precise compensation of the magnetomotive force (MMF) drop in the flux-closing yoke. It has been developed in order to overcome the systematic uncertainty affecting the value of the magnetic field strength in single sheet testers when obtained, according to the standards, through the measurement of the magnetizing current. This phenomenon is more critical to high-permeability materials, because of the reduced MMF drop across the sample. While additional sensors and auxiliary windings have been proposed in the literature, a novel approach is demonstrated here, based on the use of the permeameter upper half yoke as the MMF drop sensor and of an auxiliary winding on the lower half yoke, implementing compensation. This solution, dispensing one from dealing with the usually small signal levels of the conventional MMF drop sensors (e.g., Chattock coils), provides the best results with the introduction of wedge-shaped magnetic poles, in order to accurately define the magnetic path length. The method is validated by the measurements of power loss, apparent power, and hysteresis cycles on non-oriented and grain-oriented Fe-Si steel sheets, which are compared with local measurements performed on the same samples using H-coil and B-coil across a uniformly magnetized region.

Determination of the magnetic losses in laminated cores under pulse width modulation voltage supply

In the laminated ferromagnetic cores employed in transformers and electrical machines energy losses occur resulting in a warming effect and efficiency decrease. Normally, manufacturers only provide iron losses data when a sinusoidal voltage supply is applied, but the actual operating characteristics of electrical machines include non-sinusoidal supplies, in particular pulse-width modulation (PWM). This information can be experimentally obtained, but only measuring systems that have function generators with arbitrarily programmable waveforms allow measurements in the presence of higher harmonics. Therefore, having an analytical tool to obtain the most accurate estimation of the magnetic losses is of great interest in addressing the design of electric machines. This paper validates an analytical-expression-based procedure, which delivers results with acceptable accuracy under all operating conditions for the estimation of losses in laminated cores. In addition, it investigates the influence of the modulation amplitude and the switching frequency of the PWM signals in the magnetic losses of soft magnetic materials. For this purpose, non-oriented fully processed electrical steel strips have been measured in a commercial AC permeameter using a single strip tester.

Energy Loss Analysis and Magnetic Properties of Non-Oriented Electrical Steel Cut through Different Technologies

Non-oriented silicon iron (NO Fe-Si) alloys are soft magnetic materials used in the construction of medium and high power rotating machines. To obtain efficiency higher than 95%, it is necessary to promote a new design of their magnetic circuits and/or alternative cutting technologies. There were tested steel samples of fully processed non-oriented silicon iron (NO FeSi) grades, M400-65A and M800-65A, with an area of 300 × 30 mm2. The magnetic properties were measured with a single strip tester in the range of frequency from 10 ÷ 200 Hz at 1 T peak magnetic polarization. The sheet cutting technologies, involved in this study, are mechanical, laser, water-jetting and electro-erosion.

Magnetic Anisotropy in Silicon Iron Alloys

In this article it is presented a study of the magnetic anisotropy of non-oriented and grain oriented Fe-Si strips with the surface area of 280 x 30 mm<SUP>2</SUP>. The measurements were performed with a unidirectional single strip tester on Fe-Si strips cut at 0, 15, 30, 45, 60, 75, 90 with the rolling direction. For the representation of the magnetic field strength at constant magnetic flux density it was used a software program that interpolated the experimental results. It was determined the hard and the easy axis of the samples and the influence of the frequency on the anisotropy of the materials.The loss behaviour of these alloys was studied as a function of frequency in the range of 5 Hz to 200 Hz at a given magnetic polarization (<i>J</i><SUB><i>p</i></SUB>) of 1 T and using the concept of loss separation for the data analysis it was given a correlation between the different types of losses and the anisotropy axis.

Study of the Magnetic Anisotropy of the Grain Oriented (GO) and Non-Oriented (NO) Silicon Iron Materials

In this paper it is presented a study of the magnetic anisotropy of non-oriented and grain oriented Fe-Si strips with the surface area of 280 x 30 mm2. The measurements were performed with a unidirectional single strip tester on Fe-Si strips cut at angles of 0, 15, 30, 45, 60, 75, 90 with the rolling direction. For the representation of the magnetic field strength at constant magnetic flux density it was used a program that interpolated the experimental results. It was determined the hard and the easy axis of the materials and the influence of the frequency on the anisotropy of the materials.

Magnetic local investigations of non-oriented electrical steels after tensile deformation

The experimental results of investigations of non-oriented steels after tensile deformation are reported. The steel samples were tested using the magnetovision method and the single strip tester. The applied deformation was up to 15% but the most significant changes were detected in the first step—at 0.5%. In several cases it was observed that after stress the homogeneity of the structure of the samples was destructed.

The study of a uniaxial deformation effect on the magnetic properties of a non-oriented electrical steel using acoustic emission characterization

Measurements of the bulk magnetic properties are reported for one fully processed non-oriented electrical steel after a uniaxial deformation. The magnetic measurements have been performed at a frequency of 50 Hz on a mini single strip tester especially developed for non-conventional ones. In this study acoustic emission (AE) and X-ray material characterization are both used. On the one hand an increase of the coercive field and losses, and on the other a drop of the relative differential permeability and the remanent induction with increasing deformation were observed. The use of AE defines deformation state areas during the uniaxial tensile test. These areas of acoustic activity correspond to the changes of behavior of the total losses: P, the remanent induction: B r, the relative permeability, maximum or average one: μm and μa, and the coercive field: H c.

Effect of stress on deviation of the in-plane flux from the longitudinal direction in single strip testers

Deviations of the flux from the longitudinal direction have been investigated in a single strip tester. Epstein strips of both non-oriented and grain-oriented electrical steels were investigated at various angles of magnetisation under applied linear compressive and tensile stress levels of up to ±40 MPa. The flux directions in non-oriented steels were not seen to be significantly affected by texture or the applied stress, whereas grain-oriented materials were seen to be affected by both. The highest deviation of the flux was seen to occur in grain-oriented steels, at high tensile stress levels. Compressive stress has the tendency to reduce flux deviations in all magnetisation directions.

Localised power loss measurement using remote sensors

A computerized system is designed and constructed to scan and measure localized power loss over an area of an electrical steel lamination. The local components of flux density (B) and field (H) are detected by a remote search coil and a magnetoresistive sensor, respectively. The results obtained show that the power loss varies over the sample surface and the surface of individual grains. A high average loss is observed over a grain with a yaw angle of 7 degrees , the minimum average loss is measured in a grain with a tilt angle of approximately 2 degrees to 3 degrees . The bulk average power loss over an area is comparable to that of a single strip tester (SST). >

Loss measurements on amorphous materials using a field-compensated single-strip tester

Conventional methods of single-strip testing are not suitable for the range of high-permeability thin materials that have been developed for power devices during the past few years. The authors describe a field-compensated single-strip tester designed to measure the power loss and permeability of amorphous materials and other thin ribbons as well as more conventional electrical steels. Measurements on grain-oriented silicon iron confirm the accuracy of the system by comparison with standard test methods allowing for their nonabsolute nature. Measurements were successfully made on strips of as-cast and annealed amorphous material, and the errors associated with other techniques were illustrated. Increased loss was found when groups of specimens of amorphous material were tested together; some possible explanations for the effect are presented. >

Comparison of loss measurements on sheets and strips

Due to good experience with the single strip tester using a self-compensating magnetic circuit, a single sheet tester based on the same principle was constructed. It was utilized for comparative loss measurements on specimens of different dimensions which give important hints for iron testing.

Comparison of the Epstein-square and a single-strip tester for measuring the power loss of nonoriented electrical steels

The Epstein-square is used as an internationally accepted standard for the measurement of the iron loss and permeability of electrical steels. In this investigation the power loss of nonoriented electrical steels was measured using the Epstein-square and also a single-strip tester. Single-strip testing showed important differences in anisotropy which are not detected using the Epstein-square in the standard way. Furthermore it is shown that the Epstein standard method on measurement can give a false indication of the quality of some nonoriented steels for many applications. Improved test procedures are suggested to overcome these problems.