The effects of the heat treatment of ZnO varistors with added Bi-Mn-Co-Sb on their electrical degradation were investigated. Before heat treatment, the degree of the tolerance characteristics of varistors for electrical degradation was smallest for the sample with 0.12 mole-% of added Sb₂O₃. After heat treatment, the electrical degradation tolerance characteristic was markedly improved. It was found that the tolerance characteristics for electrical degradation after heat treatment strongly depend on the amount of added Sb₂O₃. For the samples with added Sb₂O₃, the tolerance characteristic for electrical degradation upon heat treatment is not affected by the intensity of the X-ray diffraction peak of the (004) plane for ZnO. For samples with 0.12 mole-% or less of added Sb₂O₃, the value of the nonlinearity index α of the voltage–current (V–I) characteristic after electrical degradation was proportional to the full width at half maximum (FWHM) of the X-ray diffraction peak at 29.4° for Zn_2.33Sb_0.67O₄ spinel particles in samples subjected to heat treatment under various conditions. Therefore, it is speculated that the increase in the FWHM for the spinel particles is due to the existence of fine spinel particles at grain boundaries or triple points of ZnO grains. Furthermore, it is speculated that the improvement of the electrical degradation tolerance characteristics is due to a decrease in the ion mobility of O^2– ions or Zn²⁺ ions due to their blocking by uniformly dispersed fine spinel particles at grain boundaries. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 1–10, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21229

3 ZnO varistors with excellent electrical degradation tolerance characteristics were made by addition of Bi₂O₃-MnO₂-Co₃O₄-Cr₂O₃-SiO₂-Sb₂O₃-NiO. The electrical degradation tolerance characteristics were evaluated by varying the amount of ZrO₂. The evaluation methods were voltage–current (V–I) characteristics, X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersion X-ray spectroscopy (EDX). Monoclinic and tetragonal ZrO₂ and compounds derived from Zr were observed at both the grain boundaries and triple points. Moreover, the compounds derived from Zr with added Sb showed improved electrical degradation tolerance characteristics. On the other hand, monoclinic ZrO₂ in particular degraded the electrical degradation tolerance characteristics. One factor in the improvement of the electrical degradation tolerance characteristics is that the mobility of oxide ions or interstitial Zn²⁺ ions might be hindered by the formation of compounds containing Zr, Sb, Si, and Bi atoms. The electrical degradation tolerance characteristics of ZnO varistors with added ZrO₂ were better than those of varistors without addition of ZrO₂ but subjected to heat treatment. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 11–19, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21228

The UTST (University of Tokyo Spherical Tokamak) device was constructed for the purpose of exploring the formation of ultrahigh-beta ST (spherical tokamak) plasma using the double null plasma merging method. When two plasmas merge together to form a single plasma, magnetic field lines reconnect, and magnetic field energy is converted to plasma kinetic energy, increasing the plasma beta. Merging start-up has been demonstrated in the TS-3/4, START, and MAST devices using coils inside the vacuum vessel, and the TS-3 plasma obtained a 50% beta. In order to demonstrate start-up in a more reactor-relevant situation, UTST has all poloidal field (PF) coils outside the vacuum vessel. The first plasma experiment on the UTST was begun in December 2007. In the results, the plasma obtained 10 kA by using only the outer PF coils and a single ST was generated in the lower area (z = –0.3 to –1.0 m) close to a washer gun. This result suggests that another washer gun on the top of the UTST can allow the generation of ST in the upper area and merging start-up by using outer PF coils. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 20–26, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21216

This paper proposes a new technique for determining state values in power systems. Recently, it has been useful for carrying out state estimation with PMU (Phasor Measurement Unit) data. The authors have developed a method for determining state values with an artificial neural network (ANN) considering topology observability in power systems. The ANN has the advantage of approximating nonlinear functions with high precision. The method evaluates pseudo-measurement state values of data which are lost in power systems. The method has been successfully applied to the IEEE 14-bus system. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 27–34, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21235

The use of superconducting magnetic energy storage (SMES) for smoothing power fluctuations in a railway substation has been discussed. This paper proposes a smoothing control method based on fuzzy reasoning for reducing the SMES capacity at substations along high-speed railways. The proposed smoothing control method comprises three countermeasures for the reduction of the SMES capacity. The first countermeasure involves modification of rule 1 for smoothing out the average electric power to its average values. The other countermeasures involve the modification of the central value of the stored energy control in the SMES and revision of the membership function in rule 2 for the reduction of the SMES capacity. The SMES capacity in the proposed smoothing control method is reduced by 49.5% compared to that in the nonrevised control method. Computer simulations confirm that the proposed control method is suitable for smoothing out power fluctuations in substations along high-speed railways and for reducing the SMES capacity. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 35–43, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21175

A linear induction motor (LIM) is suitable for use in trains. The motor can be used in both wheel-suspended and contact-less types such as the Linear Metro and HSST trains in Japan. The LIM has end winding as well as asymmetrical winding. The end effect is a major problem in the LIM, and it makes the analysis, design, and control of motors difficult. This paper describes a method that combines numerical analysis and the equivalent circuit for the LIM in order to design a high-performance controller for the LIM that includes the end effect. A sample basic field-oriented control scheme that is based on the plant model is applied to the LIM in order to check the control performance. The theory of rotary induction motors is used for verification. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 44–54, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21171

2,3 This paper proposes a DC voltage equalizing circuit for a diode-clamped linear amplifier (DCLA). The DCLA consists of series-connected complementary MOSFETs and diode clamping circuits, with an experimental efficiency as high as 90% without switching operation. The DCLA requires a DC voltage equalizing circuit to divide the DC voltage into several levels. The proposed DC voltage equalizing circuit allows the use of a diode rectifier with a smoothing capacitor as a power supply for the DCLA. Zero-sequence voltage control is proposed to improve the efficiency of the DCLA. As a result, a prototype 12-series DCLA demonstrates an experimental efficiency as high as 94.7%. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 55–63, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21131

This paper presents a general-purpose engine speed control system with an electronic governor in order to improve the current system with a mechanical governor, which shows unstable characteristics as a result of a change in mechanical friction or the A/F ratio (air–fuel ratio). The control system above has the problems that the feedback signal is only the crank angle because of cost, and the controlled object is a general-purpose engine, which is strongly nonlinear. In order to overcome these problems, a system model is presented for dynamic estimation of the amount of air flow, and a robust controller is designed. In concrete terms, the proposed system includes a robust sliding-mode controller using the feedback signal of only the crank angle, with a genetic algorithm applied to the controller design. Simulations and experiments performed using Matlab/Simulink show the effectiveness of our proposal. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 64–71, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21130