The Magnetic properties of high-silicon steel sheets of thickness range from 0.35mm to 0.03mm and silicon content from 3% to 7.5% were investigated. The minimum iron losses were obtained with the silicon higher than 6.5% at high frequency range over 30kHz. The sheet thickness dependency index m was estimated. The heat treatment effects to soft magnetic properties were also studied.

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Materials with higher induction are required for smaller magnetic cores with higher efficiency. Doubly oriented silicon steel is one of the materials which could be applied to cores designed for higher induction use. Here, the magnetic properties of doubly oriented sheets were examined crystallographically firstly. Then, the magnetic properties of rectangular cores with no joint were measured in DC and AC magnetization, comparing with FeCo alloy which has high saturation induction, and other soft magnetic materials. The core loss of the doubly oriented silicon steel was about a half of that of FeCo alloy (permendur).

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It was found that the grain size of very thin(40μm) grain oriented silicon steels can be controlled by selecting conditions of the annealing for making the grain texture of (110) [001] on the sheets. The grain size became smaller by the annealing of higher temperature or larger heating rate. The magnetic domains and losses of the very thin grain oriented silicon steels with different grain sizes were observed. The eddy current losses of the sheets were decreased with decreasing the grain size because steels with smaller grains have narrower magnetic domain wall spacings. The hysteresis losses were independent on the grain size. Therefore the iron loss of the very thin grain oriented silicon steels could be controlled by the grain size. In this work it was clarified that we can obtain the very thin grain oriented silicon steels with very low iron loss by controlling the annealing condition.

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The measuring method and the experimental results of the magnetic characteristics in any direction for the oriented silicon steel are described in this paper. The single sheet tester for rotational loss has been used in order to simulate conditions existing in real devices. The flux of any direction is induced on specimen by exciting from X and Y directions in the same phase. The flux density was measured by the each search coils. The magnetizing force was measured by a double H-coil method. The outputs of the B-coils and the H-coils were treated by sending from the wave digitizer to the personal computer.
In X and Y directions components of magnetic characteristics, for small values of B all characteristics are the same. Only the saturation value changes, and it depends on the direction of flux.

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Thin-gage grain-oriented silicon-iron sheet is expected as a low power loss core material in the future. With lowering thickness the hysteresis loss tends to increase while the eddy current loss decreases. It is important to suppress the increasing tendency of hysteresis loss to realize thin-gage silicon-iron with low power loss. In this paper the mechanism of the thickness dependence of hysteresis loss in (110)[001] oriented silicon-iron was discussed on the basis of the analysis of magnetization process and the experiments using single crystal specimens. It was revealed that the magnetization jump which occurs as a result of the magnetostatic interaction of surface free pole causes a great increase of hysteresis loss at lower thickness when the tilt angle of [001] axis out of the surface is large. The role of the surface closure domain on hysteresis loss was also studied.

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Effects of superposition of higher harmonics on magnetostriction of non-oriented electromagnetic steel sheets were examined. Magnetostriction was measured using base-less semiconductor strain gauges applied at four points on ring specimens.
Higher harmonic components of magnetostriction were markedly observed by the PWM inverter excitation, although magnetic flux contained only a small amount of higher harmonic components. They have been considered to be the main cause of noise in the electrical machine driven by the inverter.
To evaluate contribution of the superimposed higher harmonic magnetization, specimens were magnetized at power frequency superimposed with the 49th higher harmonic frequency. Magnetostrictive components at the superimposed frequency resulted in about 100 times higher value than that obtained from magnetization at the frequency corresponding to higher harmonics. This fact means that the superimposed higher harmonics is supported by the rotational components of magnetization such as the 90° wall movement, which is in part included in magnetizing processes at the fundamental frequency.

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Magnetic Properties of Ultrathin Co-Based Amorphous Ribbon Cores Masaaki Yagi, Member (Miyagi National Colledge of Technology), Takao Sawa, Nonmember (Toshiba, New Materials Engineering Laboratory), Jiro Yamasaki, Member (Kyushu Institute of Technology) Ultrathin[((Fe0.05Co0.95)0.95Cr0.05)75(Si0.5B0.5) 25, ((Fe0.05Co0.95)0.94Cr0.06)76(Si0.5B0.5)24] amorphous ribbons were fabricated by a single roller technique in vacuum. Extremely low core loss and high initial permeability were attained in the range of 100 kHz-10 MHz for the cores made of 4-5μm thick ribbons. For 4.7μm thick ribbons, the core loss at 1MHz was 0.86 J/m³(=860 mW/cc)for Bm=0.1T. This value was about 30-40% of those of Mn-Zn high-frequency ferrites and 5μm Supermalloy tape wound cores. In addition, the initial permeability of this core measured at 1 and 10MHz were about 13, 000 and 1, 200 for Hm=2mOe, respectively.
Furthermore, the effect of transverse magnetic field annealing on the magnetic properties was also studied. The domain patterns of some ultrathin ribbons were observed by the Kerr effect and their relation to the soft magnetic properties was discussed.

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Magnetic properties of Fe-Cu-Nb-X-B (X: Si, Ge, C, Ga) and Fe-Cu-Nb-Si-B-X (X: Ge, C, P, Ga, Al) nanocrystalline alloys were studied to improve soft magnetic properties and they were evaluated for some applications. Si was the best element for Fe-Cu-Nb-X-B system. Substitution of P for B made coercive force small in Fe-Cu-Nb-Si-B-X system having high saturation flux density. The cores using the Fe-based nanocrystalline alloys showed low core loss, excellent DC superimposed characteristic and good noise attenuation characteristics. Hence, Fe-based nanocrystalline alloys have high performance for magnetic components such as transformers and choke coils.

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A mostly single bcc phase with nanoscale grain size of 10 to 20nm has been found to form by annealing amorphous Fe-Zr-B, Fe-Hf-B and Fe-M-B-Cu (M=Ti, Zr, Hf, Nb and Ta) alloys. It has further been clarified that the newly developed nanocrystalline bcc alloys exhibit high permeability (μe) combined with high saturation magnetization (Bs).
We have subsequently investigated possible application potentials of the bcc alloys. The core loss shows as smaller as 66mW/kg at 1T and 50Hz for a nanocrystalline bcc Fe86Zr7B6Cu1, alloy obtained by annealing for 3.6ks at 873K. This value is 45% and 95% smaller than those for amorphous Fe86Si9B13 alloy and Fe-3.5% Si alloy, respectively, which are presently in use as core materials in electric power transformers. The frequency dependence of core loss for the bcc alloy at 0.2T is almost the same as that for an amorphous Co70.5Fe4.5Si10B15 alloy with Zero magnetstriction. In the frequency range of 10 to 300kHz, the core loss for the bcc alloy is slightly smaller than the Co base amorphous which has been used as core materials in high-frequency transformer. Furthermore, the core losses of the nanocrystalline Fe86Zr7B6Cu1 alloy were also found to have high stability against thermal aging. Thus, nanocrystalline bcc Fe-Zr-B-Cu alloy with the advantages of high Bs, high μe and low core l0ss is expected to be used as a core material in various transformers.

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Tape wound toroidal cores are widely used as magnetic devices of electronic equipment and instrument. In the design of the equipments employing magnetic core, it is necessary to know the relation between magnetic properties of the core and magnetic properties of the material. This paper describes the effect of the dimention ratio of the core on the magnetic properties with sinusoidal flux waveform driving condition.
In carrying out the analysis, a mode analysis in which the magnetization characteristics is approximated by a piecewise-linear curve, is adopted. From the results obtained by the numerical analysis, local flux waveforms and exciting current waveforms of the core are shown. As a concequence, relation between iron loss and magnetizing apparent power of the core and the dimention ratio was derived. These results were confirmed by expriments.

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In order to make more compact power supplies for electronic equipments, switching procedure is introduced and the conversion frequencies are increasing exceeding 100kHz. Magnetic amplifiers regulating these power supplies are spreading for the robustness, the noise suppressing capability and the simplicity of control. The properties of magnetic amplifier cores in the frequency range exceeding 100kHz are, however, not always clear.
The authors measure the dynamic characteristics of square-loop tape wound cores and discuss how to estimate the core properties appropriate to the high frequency magnetic amplifiers on the basis of magnetic domain theory. And formulae describing control magnetization characteristic are derived taking into account the variation of magnetic domain configurations.
We conclude that the cores should have good squareness, high resistivity and the tape thickness should be 15μm or less, and the lower saturation flux density is better.

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The breakdown test under DC-Impulse and DC-AC superposed voltage, of an oil impregnated capacitor dielectric is carried out to study the influence of a DC superposed voltage on the breakdown characteristics.
The insulation configuration of the dielectric includes three types-oil-impregnated paper, paperfilm (polypropylene), and all-film, each of which uses alkyl-naphthalene as the insulating oil in making a sample capacitor. From the DC-Impulse superposition test, it is found that the breakdown of each capacitor is determined by a certain algebraic sum of the DC and Impulse electric fields regardless of the polarity (forward or reverse polarity) and ratio of DC to Impulse.
From repetitive service-life test, it is found that the service life is inversely proportional to approx. the 13th power of the pulse electric field in the reverse-polarity pulse area of a paper capacitor and to approx. 55th power of it in the short-term area and short-time and sustained use areas of the foward-polarity pulse. For all-film and paper-film samples, it is found that the service life is inversely proportional to approx. the 55th power of the puls electric field in the sustained use area (several thousands of times) or both the foward and reverse polarities.
From the result of the DC-AC superposed voltage test, several facts can be obtained namely that the influence of the DC superposed voltage on the shortterm breakdown voltage is large for any dielectric configuration but, is small in the sustained use area.

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Thermal deterioration of transformer results in the decrease of tensile strength, rather than electrical strength of the insulating paper. The decrease of tensile strength has a constant relationship to both the decrease of average polymerization and the increase in the amount of furfural formed by thermal deterioration of insulating paper in insulating oil. The relationship between the decrease of average polymerization and the increase in the amount of furfural formed by thermal deterioration of insulating paper in insulating oil is cleared. The decrease of average polymerization has a constant relationship to the increase in the amount of furfural formed. Then an allowable limit for the drop in average polymerization was determined using the amount of furfural formation dissolved in insulating oil.

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