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Pole-mounted transformers are especially vulnerable to lightning damage. The progress of the information society imposes increasingly stringent requirements for the reliability of electric power supply, and this in turn necessitates a reduction in lightning damage to pole-mounted transformers. Lightning protective devices (surge arresters) are now being installed around the primary bushing of the transformers, which has decreased the number of disconnections around the primary bushing due to lightning. But surge arresters installed on the primary side of the transformer cannot protect it against backflow lightning entering the secondary side of the transformer. The characteristic of transformer damage by backflow lightning is that the electromagnetic force produced by the current flowing into the secondary side deforms the transformer windings. This paper elucidates the mechanism of transformer damage by lightning flowing into the secondary side by comparing actual lightning damage cases with the results of verification tests using a short-circuit generator. Effective countermeasures against transformer damage by backflow lightning are examined by EMTP calculations, which indicate that neutral grounding on the low-voltage distribution line is the most effective way of decreasing the current flowing into the transformer. The lower the grounding resistance, the less current flows into the transformer. In addition, decreasing the voltage on the secondary side is important in order to protect the secondary-side bushing. The calculation results indicate that surge arresters installed around the secondary side of the transformer are effective in decreasing the voltage on the secondary side. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(2): 1–11, 2010; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20921

It is essential to prove that the technology of metal (zinc) oxide surge arresters born in Japan is very creative, originative, and useful to insulation coordination for power systems. Surge arresters investigating R&D Committee of Japan have summarized 'power technology of Japan through the experience of developments and applications of surge arresters—AC 3.3―1100 kV and HVDC 125―600 kV power systems'. This technical report No. 1132 describes lightning phenomena, manufacturing of ZnO elements, surge arresters and insulation coordination for AC 3.3―550 kV, 800 kV, 1100 kV substations, 22―500 kV transmission lines, power cables, HVDC 125―DC 600 kV systems, 6.6―33 kV distribution lines, 100―200 V surge protective devices, and maintenance methods. This paper describes that the creative, originative and useful progress of metal (zinc) oxide surge arresters contributes drastically to the insulation coordination for AC 66―1100 kV power systems.

Melt spinning process of polymethylsilsesquioxane (PMSQ) at 403–453 K was investigated as a SiOC fiber precursor in terms of averages and distributions of spun fiber diameters. Because of fusible character of PMSQ at low temperature, the spun fibers were exposed to vapors of various metal chlorides (SiCl4, Si(CH3)Cl3, TiCl4, and BCl3) to promote the fiber curing. Cured fibers were investigated by FTIR and TG analyses. In a case of the fiber synthesized with SiCl4 curing, tensile tests on the pyrolyzed fibers were performed. Exposure of the synthesized fiber at high temperature with a flame of an oxygen-gas burner was examined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Polymethylsilsesquioxane (PMSQ), compounded with particles of Al2O3 (22–47 nm), micro size aluminum (30 µm) or nano size aluminum (50 nm) with a starting Al:Si molar ratio of 1.0, was prepared in a thick sheet form and pyrolyzed at various temperatures up to 1673 K to investigate the filler effect on the ceramization. By adjusting the concentrations of PMSQ, filler and cross-linking agent in ethanol, self-standing ceramic sheets were obtained after pyrolysis without fragmentation. The phases formed in each sheet during pyrolysis were identified by using X-ray diffraction patterns. The resulting micro structures were characterized by the Archimedes method, SEM observation and electron micro probe analysis. Copyright © 2009 John Wiley & Sons, Ltd.

A superconducting fault current limiter (SFCL) for 6.6 kV and 400 A installed in a cubicle for a distribution network substation was conceptually designed. The SFCL consists of parallel- and series-connected superconducting YBCO elements and a limiting resistor. Before designing the SFCL, some tests were carried out. The width and length of each element used in the tests are 30 mm and 210 mm, respectively. The element consists of YBCO thin film of about 200 nm in thickness on cerium dioxide (CeO2) as a cap-layer on a sapphire substrate by metal-organic deposition with a protective metal coat. In the tests, characteristics of each element, such as over-current, withstand-voltage, and so on, were obtained. From these characteristics, series and parallel connections of the elements, called units, were considered. The characteristics of the units were obtained by tests. From the test results, a single phase prototype SFCL was manufactured and tested. Thus, an SFCL rated at 6.6 kV and 400 A can be designed.

SiC powder, polycarbosilane and xylene mixed slurries were prepared for microstructure observation and viscosity measurement. Slurries with averaged primary SiC size of 270 or 50 nm revealed existence of isolated secondary particles smaller than 1 μm in optical microscope observation. These secondary particles showed a Brownian motion in a xylene-PCS medium. On the other hand, slurry with an averaged primary SiC size of 20 nm revealed existence of large secondary particles in the size of 2–5 μm. The apparent area occupied with these secondary particles was far larger than that occupied by secondary particles of 270 or 50 nm in spite of a low SiC content. It was suggested that the secondary particles observed in the 20 nm slurry possessed small spaces among the primary SiC particles. Viscosity measurement presented that apparent viscosity of the slurry was high in general when the primary SiC particle size was small. In particular, the 20 nm SiC slurries showed quite high viscosity even at a SiC content of 5–6 mass%, which almost corresponded to that of 40 mass% for a SiC 270 nm slurry. Shear thinning effect was also remarkable when the primary SiC particle size was small.

Pole-mounted transformer is one of the equipment that is easier to receive lightning damage. As our information society advances, the needs for supply reliability of electric power become higher, and the decreasing of lightning damages of pole-mounted transformers becomes necessary. In recent years, lightning protective devices (surge arresters) have been installed around the primary bushing of the transformers. Therefore, the number of disconnections around the primary bushing caused by lightning has been decreasing. However, the surge arrester that installed at the primary side of transformer cannot protect the transformer against backflow lightning that invades to the secondary side of transformer. The characteristic of the transformer damage by the backflow lightning is that electro-magnetic force occurring by the current flowing into the secondary side of transformer deforms the windings of the transformer. In this paper, the mechanism of transformer damage by the current flowing into the secondary side is clarified by the comparison between actual lightning damage case and the results of verification test using short-circuit generator. Effective counter measures against the damage of transformer by the backflow lightning are examined by EMTP calculations. From the calculation results, neutral grounding on low-voltage distribution line is the most effective measures in the point of decreasing of the amount of current flowing into the transformer. The less the grounding resistance, the less the amount of current flowing into the transformer. Moreover, decreasing the voltage of the secondary-side of the transformer is important to protect the bushing of the secondary-side. By the calculation result, it is clarified that the surge arresters installed around the secondary side of the transformer are effective for decreasing the voltage of the secondary side of the transformer.

We have proposed a flat type of the superconducting fault current limiter (FCL) which is a modified version of a magnetic shielding type of the fault current limiter. The flat type FCL basically consists of a pancake coil and doughnut-like form high Tc superconductor (HTS) disk, each of which works as a primary winding and a secondary one-turn winding, respectively. In order to clarify the static current-limiting performance of the flat type FCL, the magnetic field analyses were carried out for the small modules of the FCL. The inductance values of the FCL in the superconducting state and normal-conducting state of the HTS disk, L o and L limit , were calculated and their ratio L limit/L o was estimated. The high performance of the FCL must be brought about by the large inductance ratio. It was confirmed that lower L o was derived by sandwiching the pancake primary winding with two HTS disks and by using thin spacer between them, and larger L limit a is produced by connecting the built-up pancake primary windings in series. This suggests that a full-scale FCL may be designed and produced by building up many modules whose pancake winding is sandwiched with the HTS disks.

The 500 m high temperature superconducting (HTS) cable developed by the Super-ACE (R&D of fundamental technologies for superconducting ac power equipment) project included copper layers as protection against short circuit current. The design policy was that liquid nitrogen would not vaporize when it was exposed to the short circuit current of 31.5 kA with 0.5 s. In order to establish the design policy, we have made nine 10 m samples with the same construction of the 500 m HTS cable and set three cables in the liquid nitrogen vessel. Both of balanced fault of three-line grounding (3LG) and unbalanced faults of one line grounding (1LG) and two-line grounding (2LG) have been set and fault currents have been applied to the HTS cables. After each fault, the critical current has been measured and we have confirmed no variation of Ic before and after each fault. HTS cables have not been damaged mechanically by the fault current of 31.5 kA with 0.5 s.

Silicon carbide powder, polycarbosilane (PCS) and xylene mixed slurries were prepared for viscosity measurement and microstructure observation. Absolute slurry viscosity and shear rate dependence of viscosity were investigated at various SiC concentrations and particle sizes. Temperature dependence of viscosity was also investigated. As the primary particle size in powders decreases, viscosity increases relatively at a low SiC concentration. Microstructure observation on diluted slurries revealed the existence of secondary particles composed with primary nanoparticles and network formation by physically or chemically contacted secondary particles. Some of the microstructure changes with shearing was consistent with a strong shear thinning phenomenon of slurry viscosity.

We have proposed an inductive (magnetic shielding) type of superconducting fault current limiter which consists of a high Tc superconducting plate in doughnut shape and spiral coil as the primary winding. In this paper, the current density distribution in the superconducting plate was theoretically investigated to understand the fundamental performance of this type of current limiter. For the analysis, we developed the calculation method for the current density. The current density is distributed almost uniformly in the superconducting plate. The impedance of the current limiter changes every moment not only in current limiting operation but also normal operation. That is because the resistance in the superconducting plate and magnetic coupling condition in the current limiter also change with time. Relatively large impedance rapidly appears in the current limiter when the current density in all the area of the superconducting plate attain to the critical current density.

We have proposed a flat type of the superconducting fault current limiter (FCL) which is a modified version of a magnetic shielding type of the fault current limiter. The new FCL basically consists of a doughnut-like form high Tc superconductor (HTS) plate and spiral coil, each of which works as a secondary one-turn winding and a primary winding, respectively. The FCL modules can be easily built up to make a large scale FCL. This simple construction may enable us to reduce the manufacturing costs. We made two small modules of the flat type FCL with Bi2223 bulk plate and YBCO thin film plate and investigated the generation of the limiting impedance due to an excess current. Higher ratio of the limiting impedance to normal one was produced by the YBCO thin film plate than by the Bi2223 bulk plate.

We have been developing an inductive type superconducting fault current limiter with a superconducting cylinder. For practical use, a high critical current density (Jc) is needed in a large diameter. To achieve these items, we have developed a Bi-2223 thick film on a MgO substrate, with a Bi-2212 buffer layer. This cylinder was 450 mm in diameter and 120 mm in length. We describe the superconductive characteristics of this cylinder, and the limiting properties of the fault current limiter using these cylinders.

Superconducting fault current limiter (SCFCL) is expected to be a first application of high-TC superconductors to electric power systems. We have been developing a magnetic shielding type of SCFCL. In this paper, we propose a design method for the magnetic shield SCFCL. The method is based on a newly developed computer program which can evaluate the dynamic thermal and electromagnetic behaviors of high-TC superconducting cylinder in fault current limiter operation. As an example, the trial design of a model system, which is 6.6 kV (rms) in rated voltage, 400 A(rms) in rated current, and 12.5 kA(rms) in maximum prospective short-circuit current, is shown. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(2): 50–57, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10197

Fault current limiters for electric power systems have been researched. We have studied a inductive type superconducting fault current limiter. The limiter has superconducting cylinder as active element. We developed a high Jc Bi-2223 thick film on a MgO cylinder. Jc was over 5800 A/cm/sup 2/ at 77 K. We made a inductive type superconducting fault current limiter with the Bi-2223 thick film cylinder and investigated limiting performances.

Fault current limiters for electric power systems have been researched. We have been studying on a inductive type superconducting fault current limiter. The limiter has superconducting cylinder as active element. It is necessary for practical use of the superconducting fault current limiter that superconductor has high critical current density (Jc). So as to get high Jc, we tried Bi-2223 as a material for the superconductor, and prepared Bi-2223 thick film. Raw paste of Bi system was coated on a polycrystalline MgO substrate and then was sintered in the air with intermediate pressing by a cold-isostatic-pressing (CIP) technique. The sintered Bi-2223 thick film had good crystal orientation. The Jc of the 500 /spl mu/m thick film was over 6000 A/cm/sup 2/ at 77 K.

Superconducting fault current limiters have been researched to protect electric power systems. We have developed a superconducting fault current limiter. As the active element, we choose Bi-2212 thick film for the superconductor cylinder. In order to attain practical use of the superconducting fault current limiter, larger scale superconducting cylinders must be developed. Processing energy increases as the size of the limiter is increased. If there are local defects in the superconducting cylinder and the processing energy is concentrated on them, there is a possibility that the cylinder will be damaged. We therefore investigated the thermal runaway propagation of the Bi-2212 thick film from a local heat point and how local defects affect the current-carrying capacity. The result is that the velocity of the thermal runaway propagation in the thick film from the local heat point is very slow. Thermal runaway doesn't propagate within a few milliseconds. If there are local defects such as cracks in the superconducting cylinder, the current will concentrate at the tip of the defect and the Joule temperature rises. The cracks then grow as the result of thermal stress. When a crack runs from end to end on the cylinder, superconductor on the cylinder melts due to arc discharge.

Superconducting fault current limiter (SCFCL) is expected to be the first application of a high-temperature superconductor (HTS) to electric power systems. The authors have been developing a magnetic shielding type of SCFCL that uses a cylindrical Bi-2223 HTS bulk. Short-circuit fault tests in a small SCFCL model were performed experimentally. A computer program based on the finite element method (FEM) taking the voltage-current (E-J) characteristics of the bulk material into account was developed to analyze the performance in the short-circuit fault tests and to investigate the dynamic electromagnetic behavior within a bulk superconductor. Because the E-J characteristic of HTS bulk depends on temperature and magnetic field, they investigated experimentally the E-J characteristics of a bulk superconductor in various operating temperatures and magnetic fields. The computer program considering the measured E-J characteristics simulated the electromagnetic behaviors in an SCFCL test model successfully (BiPb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/.

The superconducting fault current limiter is expected to be the first application of high-TC superconductors to electric power systems. To analyze the performance of the magnetic shielding-type superconducting fault current limiter, the dependence of the voltage-current (E-J) characteristics of high-TC superconducting bulk on temperature and magnetic field have been measured. Short-circuit fault tests with a small limiter model have been carried out. A computer program based on the finite element method was used for evaluation of the dynamic electromagnetic behavior of the HTS cylinder in a time-varying external magnetic field. The computer program, considering the voltage-current (E-J) characteristic, successfully simulated the electromagnetic behavior in the fault current limiter test.

The superconducting fault current limiter (SCFCL) is expected to be the first application of high-T/sub C/ superconductors (HTSs) in power systems. To develop a magnetic shielding type superconducting fault current limiter, we have carried out some fundamental experiments concerning the magnetic shielding characteristics of an HTS bulk cylinder. In this paper, the experimental results of magnetic flux penetration into a Bi(2223) cylinder are shown. AC magnetic field is applied to the sample by a primary winding (copper coil) excited by AC triangular- and sinusoidal-waveform currents in the frequency range of 0.1 Hz to 100 Hz. We also developed a finite element method (FEM) computer program for evaluation of the dynamic electromagnetic behavior of the HTS cylinder in a time-varying external magnetic field. The results of computer simulations considering the voltage-current (E-J) characteristic are compared with experiments.

The superconducting fault current limiter is expected to be the first application of high-Tc superconductors (HTSs) in power systems. To develop a magnetic shielding-type superconductor fault current limiter, we have carried out some fundamental experiments on the magnetic shielding characteristics of an HTS bulk cylinder. In this paper, the experimental results of magnetic flux penetration into Bi-2223 cylinders are shown. An ac magnetic field is applied to the sample by a primary winding (copper coil) excited by ac triangular- and sinusoidal-waveform currents in the frequency range from 0.1 Hz to 100 Hz. We also developed a finite element method computer program for evaluation of the dynamic electromagnetic behavior of the HTS cylinder in a time-varying external magnetic field. The results of computer simulations considering the voltage–current (E–J) characteristic are compared with experiments. Next we carried out a current-limiting test with a small limiter model, and the developed finite element method computer program successfully simulated the electromagnetic behavior in current-limiting operation. © 2000 Scripta Technica, Electr Eng Jpn, 134(1): 17–27, 2001

We analyze the negative magnetoresistance observed in the c-axis transport of ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{\mathit{x}}$ single crystals based on the density of states fluctuation conductivity by taking renormalization effects into account. It is shown that the calculated magnetic field dependence of the c-axis conductivity fits to the experimental results below as well as above critical temperature (${\mathit{T}}_{\mathit{c}}$) reasonably well using a single set of parameters. This gives strong evidence to indicate important roles of fluctuation effects arising from the density of states term in high-${\mathit{T}}_{\mathit{c}}$ superconductors. \textcopyright{} 1996 The American Physical Society.

A novel three-phase conducting fault current limiting reactor (SCFCLR) is fabricated. The SCFCLR has three superconducting windings with the same number of turns wound on an iron core. The rating of SCFCLR is 200 V, 10 A. Two SCFCLRs are inserted in the sending and the receiving ends of the model power-transmission line. The line fault test of a model power system with two SCFCLRs is undertaken. The fundamental behavior of this reactor is confirmed. In the case of single-line-to-ground fault, the fault current is limited to a very small value by the large zero-phase sequence reactance of the SCFCLR without quench. In the case of a three-phase short circuit, the SCFCLR quenches, and the short-circuit current is limited by the normal conducting resitance of the winding. It is confirmed that the transient stability of the system during line faults is greatly improved by the insertion of SCFCLRs.

We have developed a new precise imaging technique for atomic force microscopy (AFM) and observed complicated surface structures of integrated circuit (IC) devices by this technique. This technique consists of a hopping mode operation and use of a zinc oxide whisker as a probing tip with high aspect ratio. In this operation, topographic data of the surface structures are obtained under a constant repulsive force at each measuring point, and after each measurement the probing tip is withdrawn from the surface and moved to the next measuring point. The contact holes with a diameter of ∼1 μm and a depth of 1.5 μm fabricated on IC devices have been successfully imaged in this AFM imaging technique.

The atomic force microscope has been developed and used to image arrays of molecules at the (001) and (100) faces of aspirin crystals in water and in air. Lattice spacings composed of methyl groups and the part of the phenyl groups on the surface of the (001) in water, are consistent with X-ray diffraction data. The surface of (100) face which shows most perfect cleavage in bulk, is more difficult to image. This initial success in imaging at drug crystal surfaces clarified the different structural behavior at the submolecular level for three crystal faces, and the close relationship to the differences in the dissolution velocity.

Fault current limiters (FCLs) are expected to reduce fault current and improve stability of power systems. A flat type fault current limiter consisting of the pancake primary winding and a high-Tc superconducting (HTS) disk was proposed as a modified version of a conventional magnetic shield type of the FCL with the superconducting cylinder. The flat type FCL has the advantage of being manufactured smaller than the cylinder type FCL. It is pointed out, from a magnetic field analysis, that the volume of the flat type FCL is smaller than that of the cylinder type FCL with same magnitude of the limiting inductance. Further, the magnetic field analysis suggests that a high inductance ratio can be realized by radially enlarging both the primary winding and the HTS disk, stacking the FCL modules in layers and sandwiching the primary winding with superconducting disks. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

An ultra high density recording with scanning probe microscopes (SPMs) has been studied extensively in recent years to overcome the limits in optical and magnetic storage devices (1-3). In the SPMs, a scanning tunneling microscope (STM) and a scanning near-field optical microscope (SNOM) are not considered suitable for high speed recording operations, because they require precise control of the distance between the probe and the storage media at a nanometer scale using a feedback control system. On the other hand, an atomic force microscope (AFM) does not require the precise control if the surface of storage media is smooth at a nanometer scale, because its probe is mounted on a flexible cantilever and touches the media with an extremely weak force. In this paper, we describe an erasable recording technique with the AFM by locally controlling the conductance of phase change media without a topographic change.

We measure and analyze the c-axis magnetoresistance of Bi-2212 single crystals annealed in O2 and Ar atmospheres with fields up to 30T applied along the c-axis. It is found that fluctuation conductivity below Tc at low field region is increased and decreased by the O2 and Ar annealings, while the magnitude of the increase in the conductivity at the higher field region is enhanced and suppressed by the annealings, respectively. The fitting of these experimental results by the fluctuation conductivity theory indicates that the O2 and Ar annealings strengthen and weaken the coupling between CuO2 planes, and decrease and increase the two-dimensional density of states of the Bi system, respectively. These are consistent with the observed changes in the conductivity and Tc by the annealings.

The power application of a superconductor to restrain a fault current has been researched. A superconducting fault current limiter using a Bi-Sr-Ca-Cu-O cylinder has been developed. This limiter consists of the primary winding for generating an AC magnetic field and superconducting cylinder for shielding the field. When fault occurs, the superconducting cylinder quenches and a magnetic circuit is formed inside the cylinder. In the result of that, the limiter has a high impedance thus the fault current is limited. Experiments were carried out in three conditions which are without an iron core, with an iron core, and with an iron core and a copper cylinder as a secondary winding. In each condition, the impedance of the limiter under fault conditions was 1.4 times, 10 times, and 5.9 times as high as the one under normal conditions.

We have developed a precise imaging technique of atomic force microscopy (AFM) for steep and fine structures. The technique consists of a new scanning mode operation and a use of a probing tip with high aspect ratio. In this operation, topographic data of surface structures are obtained under a constant repulsive force at each measuring point, and after each measurement, the probing tip is withdrawn from the surface and moved to the next measuring point. We use a zinc oxide whisker as a probing tip with high aspect ratio. The complicated surface structures of IC devices with contact holes (1.5 μ m in depth) were accurately imaged in this AFM imaging technique.

The atomic force microscope was developed in order to image arrays of molecules on the (001), (100) and (011) faces of aspirin crystals in water. Lattice spacings and symmetries of methyl groups and the part of the phenyl groups on the (001) face in water are consistent with X-ray diffraction data. Surfaces of the (100) face that show the best-developed cleavage, in general, are difficult to image. Although the lattice constant derived from (100) image is consistent with the X-ray diffraction data, the c-glide plane symmetry is lost and diffused spots are observed that are 1.8-3.1 times more elongated than (001) spots. It is not possible to image the (011) surface. This initial success in imaging the molecular crystal surfaces of drug compounds has clarified the different submolecular structures of the three different crystal faces, and the close relationship between the imaging difficulties and the differences in the dissolution process in water.

We have demonstrated a nanometer-scale recording technique using an atomic force microscope (AFM) with an amorphous GeSb2Te4 film as a phase change medium. Data are recorded by changing the local electric properties of the film using a conductive AFM probe. The conductance of the film can be increased by more than one hundred times by applying a pulse voltage between the probe and the film. The recorded data are read by detecting the change in the conductance using the probe. The smallest possible recording region is 10 nm in diameter, which corresponds to a data storage density of 1 Tbit/cm2. The data can be erased by applying a negative DC voltage to the probe while scanning the probe over the film. The mechanisms of the reversible conductance change in the film are also discussed.

In this article, it is demonstrated that atomic force microscopy (AFM) can be useful for observing surface microstructures on the bottom of contact holes used for large scale integrated devices. The AFM employs a zinc–oxide (ZnO) whisker tip with high‐aspect ratio and a hopping scanning mode operation. In the hopping scanning mode operation, the probing tip is moved up and down with a period synchronized with the movement in the x direction to avoid collisions against the acute protrusions. Some kinds of bottom surfaces of the contact holes with a diameter of 1 μm and a depth of 1.5 μm have been successfully imaged with nanometer‐scale resolution by this AFM technique.