Transformer Sheets Research Articles

The effect of small amount of Sb on the texture and magnetic properties of grain-oriented Fe-Si alloys

This paper describes the study of the influence of antimony on the development of the preffered {110} ⟨001⟩ texture in modelling treated Fe-3.1% Si alloys. A small amount of Sb (0.040 and 0.048 wt.%) added to commercial iron-silicon steel leads to more precise (110) [001] texture, higher magnetic induction and to lower core losses in so prepared transformer sheets.

A Hall-sensor for automatic detection of domains in coated silicon iron

For automatic detections of domains in SiFe sheets, field sensors of both, small effective area and very high sensitivity, are needed. In the case of the described sensor, high sensitivity is attained by means of a commercially available Hall plate with integrated pre-amplifier. Small effective area and close contact to the specimen are attained by means of a 25 μm thick strip of soft magnetic amorphous material, which is used as a bridge between sample and Hall plate. The presented results demonstrate that main domains of stress coated transformer sheets can be detected in an effective way.

Stray-field profile of single g.o. M-shaped Si-Fe transformer sheets and the resulting interaction in a stack

The stray fields of a single and of two laminated M-shaped g.o. SiFe transformer sheets were studied in order to get more information about the stray-field behaviour and hence about the flux losses of transformer cores. The investigations were performed under static conditions and with a sinusoidal external field, respectively. A comparison of both methods proves the relevance of static stray-field investigations concerning the leakage flux.

Investigation of Si-Fe transformer sheets by scanning electron acoustic microscopy (SEAM)

Scanning electron acoustic microscopy (SEAM) is a fairly new technique in the microcharacterization of materials in which an intensity-modulated electron beam is used to generate an acoustic signal within the probed specimen location. These signals can be used for location and identification of many material parameters. Detection of the sound at the modulation frequency,f, results in so-called linear images, whereas the use of signals at even harmonics of this frequency (especially:2f) yields images as a consequence of nonlinear interactions. These nonlinear techniques were first introduced to the microscopy of semiconductors and have proven now to be very advantageous for the investigation of metals, ln this paper both the linear and the nonlinear technique are applied to the characterization of Si-Fe-transformer steel sheets. It can be shown that the linear mode exhibits only the grain structure of the material, whereas the nonlinear mode reveals the magnetic domain structure of the sheets. Thus by one experiment it is possible to immage grains and domains separately. Furthermore, this is possible even without any specimen preparation,especially without removal or polishing of the ceramic coating.

Effects of torsion on domains of coated Si-Fe sheets

The paper discusses consequences of twisting a grain oriented transformer sheet of conventional type and HI-B type, respectively, around an axis parallel to the rolling direction; a situation which (in a less defined way) will occur in regions close to core bands, for example. Mechanically, apart from shear stress, there results tension at the sheet's peripheral regions which is counterbalanced by compression in the central region. Here, torsion leads to domain widening and, in the case of higher twist angles, to extensive domain reconstructions connected with increases of iron losses. Quantitatively, the effectiveness of a given twist angle increases strongly with increasing sheet width.

The use of electrical sheets in construction of cryoresistive transformers

The paper discusses the use of electrical sheets with particular emphasis placed on cryogenics transformers. Since the construction of cryoresistive transformers - and not superconducting ones - seems to be more likely, the anisotropy of resistivity and magnetoresistance of the transformer sheets were examined. It is pointed out that both the phenomenon of magnetocrystalline anisotropy and that of anisotropy of resistivity are encountered. Thus, while designing magnetic cores of cryo-resistive transformers it is necessary to consider a much greater range of anisotropy of the sheet core losses than in the case of oil transformers.

Mössbauer spectroscopy measurements of the magnetic properties of oriented Si-Fe sheets

This paper describes an investigation of the magnetization process in polycrystalline grain-oriented Si-Fe transformer sheets. The aim of this work was to prove a dependence of the ratio of the first two lines of Mössbauer spectra on the magnetic domain orientation.

Desulphurization of grain-oriented silicon iron during heat treatment in vacuum

The kinetics of desulphurization has been studied in 0.35 mm thick grain-oriented 3% silicon iron strips with various contents of sulphur (0.007, 0.020 and 0.060% S) and of manganese (0.11 and 0.31% Mn) in vacuum at pressures of 1330 Pa (10 Torr) and 0.0122 Pa (10 −4 Torr), at temperatures of 1150 and 1200°C. The specimens were examined without a coating and, after a previous oxidation, coated with a layer of MgO suspension with and without the addition of 7% Cr 2O 3 and of 0.5% CaO. It was proved that in the course of the vacuum heat treatment of transformer sheets the application of high vacuum is favourable for steel refining. The state of the surface has a considerable influence on the desulphurizing process; an addition of Cr 2O 3 and of CaO to the coating based on the MgO suspension retards the desulphurization process, while without that addition to the MgO suspension the desulphurization process proceeds as of uncoated strips.

Small angle neutron scattering from steels

By small angle neutron scattering from steels valuable quantitative parameters of the microstructure can be obtained in a non-destructive way. Various features of this method are discussed. Microstructural results are presented which were obtained from neutron scattering experiments with neutron-irradiated pressure vessel steel, with a creep-tested super alloy and transformer sheets.

The penetration of magnetic field in ferromagnetic transformer sheet

The paper deals with the penetration of magnetic field in ferromagnetic transformer sheet. The flux-density distribution is computed using Galerkin's procedure. The different boundary conditions and the nonlinearB/H characteristic is taken into account.

Assessment of grain-oriented transformer sheets with respect to transformer noise

Sheet mills supplying transformer sheets usually specify the ac magnetostriction amplitude as an acoustical characteristic. With grain-oriented sheets this is no longer adequate; the assessment of the sheets can be greatly improved by focussing attention on measurements of the A-weighted vibration velocity. The measurements can be carried out with existing test equipment. The importance now attached by transformer manufacturers to the magnetostrictive properties of core sheets increasingly puts sheet suppliers under an obligation to specify the A-weighted vibration velocity.

Influence of grain orientation on local losses in oriented transformer sheets

This paper presents the results of the experimental study of local magnetization losses on differently oriented Fe-Si single crystal samples. On the bi-crystalline sample the influence of grain boundaries on magnetization losses was investigated. Results are also discussed in relation to the Barkhausen effect.

Influence of tensile stress on permeability of grain oriented transformer sheets

The influence of stress on components of the complex permeability of grain oriented transformer sheets has been investigated. Results show the best quality factor Q = μ′ μ″ may be attained at optimal tensile stress. From this point of view, and with respect to magnetostriction, a suitable surface coating on sheets must be chosen.

Anticlastic curvature in anisotropic beams

When a rectangular beam is bent by two end moments about a transverse axis, it is well known that an “anti-clastic” curvature about a longitudinal axis also tends to occur. The theory for this phenomenon in isotropic beams has been previously discussed. For some recent work on the elastic properties of oriented silicon-iron transformer sheet, which is not only anisotropic but also has a non-linear stress-strain curve due to magnetic domain effects, a theory for anticlastic bending was necessary. The experimental results are reported elsewhere, but the theory used for anticlastic bending may find wider application. An expression is derived for the effective Young's modulus for a wide sheet; and its significance is demonstrated for transformer sheets of different width, ignoring the magnetic effects.

The AC magnetostriction of 3.25-percent grain-oriented silicon-iron under combined longitudinal and normal compressive stress

The ac magnetostriction of transformer sheet has been measured with longitudinal compression up to 2000 lbf/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (13 800 kN.m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ). Longitudinal stress causes a sudden increase in magnetostriction, while normal stress smooths out the steplike change. Si-Fe sheet from three different manufacturers is shown to have widely varying stress sensitivities, which are due entirely to differences in the insulating coatings on the laminations. Application of a glass coating greatly reduces the stress sensitivity, such that longitudinal stresses over 1100 lbf/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (7600 kN.m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ) are needed to produce any increase in magnetostriction. Both longitudinal and normal compression change the domain structure from simple 180-degree walls to a more complicated structure where most of the magnetization is at 90 degrees to the rolling direction. This stress structure is conducive to high positive magnetostriction.

The Frequency Dependence of Domain Wall Motion and Wall Bowing in Silicon–Iron Sheet

AbstractMeasurements of 180° domain wall motion in (110) [001] grain oriented 3% silicon‐iron transformer sheet have been made under alternating magnetizing conditions up to 100 Hz. The observations were made by means of the longitudinal Kerr‐optic effect using stroboscopic illumination. Peak wall displacements for individual walls showed a very irregular frequency dependence, whereas the mean displacements gave a linear increase with increasing frequency, even for constant mean flux density. This has been attributed to domain wall bowing within the sheet. Calculations of the expected surface displacements of the walls based on domain wall micro‐eddy current theory give a good correlation with experiment.

1197. Changes in the nitrogen content of metal during smelting and its effect on the properties of a transformer sheet

1197. Changes in the nitrogen content of metal during smelting and its effect on the properties of a transformer sheet

Flux-Density Time Variation in Transformer Sheet and It's Influence on the Characteristics of Current Transformer

Flux-Density Time Variation in Transformer Sheet and It's Influence on the Characteristics of Current Transformer

Experience in the production of large transformer sheets

Experience in the production of large transformer sheets

A major advance in magnetic materials

Within the space of one week last year, the two leading producers of electrical equipment, General Electric Co. and Westinghouse Electric Corp., both announced the development of a cube-oriented silicon-iron transformer sheet. Below, Journal of Metals presents two papers, one from Westinghouse, on the nature and uses of the new material, and one from General Electric, describing its magnetic properties. Although not mentioned in the papers, the General Electric product is called “Four-Square,” while Westinghouse has chosen “Cubex” as the trade name for its cube-oriented sheet.