Transient stability of fully superconducting damperless generator at system fault and study of methods to suppress fault currents

A fully superconducting generator possesses both superconducting armature windings and superconducting field windings. Thus it has great potential merits to increase efficiency and decrease size and weight compared with a partially superconducting generator that has normal armature windings and superconducting field windings. To obtain these merits, the warm and cold dampers should be omitted. However, a fully superconducting and damperless generator (FSDG) has the following problems when it is operated while connected to a power line system: (1) the dynamic stability of the generator operation is deteriorated because the FSDG has no damping elements; and (2) when the power system is subject to a fault, large transient currents and electric torque are induced in the superconducting armature and field windings, which may cause quenching in the windings. As to problem (1), it was shown that the generator could be stabilized in wide range of the operation by controlling the excitation voltage of the field winding in the authors' previous work. In this paper, problem (2) is addressed. The authors investigate methods to suppress the peak values of the transient currents in the armature and field windings and the transient torque by adjusting electric parameters of the generator and introducing superconducting current limiters (the inductance type and the resistance type). Characteristics of these methods are studied by numerical simulation and it is shown that the introduction of the resistance-type current limiter is the most effective. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (1): 15–27, 1997     

Direct‐connected multiple current‐source converters for SMES system

The superconducting magnetic energy storage (SMES) system would be a valuable system for power line stabilization. It would increase stability by supporting peak energy and compensating generation shortage. With the development of a large‐capacity GTO thyristor suitable for 20‐MW‐level power conversion systems, it is possible to control the four‐quadrant real power (P) and the reactive power (Q) condition by self‐commutated power converters with high performance. This paper describes a new direct‐connected multiple current‐source converter, and also explains suitable control strategies for the pilot plant of an SMES system. The feasibility of the control strategies is demonstrated by EMTP simulation results. © 2000 Scripta Technica, Electr Eng Jpn, 133(1): 87–96, 2000     

Effects of a probiotic fermented milk beverage containing Lactobacillus casei strain Shirota on defecation frequency,intestinal microbiota,and the intestinal environment of healthy individuals with soft stools

The effects of drinking a fermented milk beverage that contains Lactobacillus casei strain Shirota (LcS) at 40 billion bacterial cells/bottle for 4 weeks (probiotics, 1 bottle/day) on defecation frequency, intestinal microbiota and the intestinal environment of healthy individuals with soft stools were evaluated. Thirty-four healthy adults who had soft stools were randomised into 2 groups, and the effects of a regular 4-week intake of probiotics were evaluated by a placebo-controlled, double-blind, parallel-group comparative design. Defecation frequency significantly decreased after the 4-week intake period compared with before the probiotic treatment. The stool quality significantly improved (hardened) compared to the placebo. Also, the water content of the stools was lower in the probiotic group than in the placebo group. Live LcS was recovered at 6.9 ± 1.3 and 7.2 ± 0.8 log₁₀ CFU per 1 g of stool after 2 and 4 weeks, respectively, of probiotic treatment. The number of bifidobacteria in the stools also increased significantly compared with the level before starting the probiotics. The organic acid levels (total, acetic acid, propionic acid, and butyric acid) significantly increased compared with the level before intake in both the probiotic and placebo groups, but they returned to the original levels after the end of the intake period. These results suggest that probiotic fermented milk beverage has an intestine-conditioning effect by improving the frequency of defecation and stool quality and increasing the intrinsic bifidobacteria in healthy individuals with soft stool.     

Mesoscopic architectures of porous coordination polymers fabricated by pseudomorphic replication

The spatial organization of porous coordination polymer (PCP) crystals into higher-order structures is critical for their integration into separation systems, heterogeneous catalysts, ion/electron transport and photonic devices. Here, we demonstrate a rapid method to spatially control the nucleation site, leading to the formation of mesoscopic architecture made of PCPs, in both two and three dimensions. Inspired by geological processes, this method relies on the morphological replacement of a shaped sacrificial metal oxide used both as a metal source and as an 'architecture-directing agent' by an analogous PCP architecture. Spatiotemporal harmonization of the metal oxide dissolution and the PCP crystallization allowed the preservation of very fine mineral morphological details of periodic alumina inverse opal structures. The replication of randomly structured alumina aerogels resulted in a PCP architecture with hierarchical porosity in which the hydrophobic micropores of the PCP and the mesopores/macropores inherited from the parent aerogels synergistically enhanced the material's selectivity and mass transfer for water/ethanol separation.     

Sinusoidal phase-modulating interferometer insensitive to intensity modulation of a laser diode for displacement measurement

In sinusoidal phase-modulating laser diode interferometers, an injection current of a laser diode is sinusoidally modulated to scan the laser wavelength. However, the modulation of the injection current also involves an intensity modulation of the light, which increases the measurement error if a conventional signal processing is used. A novel signal processing for displacement measurement is proposed to eliminate the influence of the intensity modulation. Numerical simulation results and experimental results make it clear that an optimal depth of the sinusoidal phase modulation exists that can reduce the measurement error to a few nanometers.     

Phase-shifting laser diode interferometer using pulse modulation

A phase-shifting laser diode interferometer that uses direct pulse modulation is proposed and demonstrated. We found that a laser beam with a wide range of wavelength variation at constant optical power could be generated when a pulsed current was injected into the laser diode. We constructed a highly accurate interferometer by using a pair of interferometers. Several experiments, such as observations of temporal interference signals and spatial interferograms, measurement of a concave mirror, and duplicate measurements, confirmed the characteristics of pulse modulation and demonstrated the effectiveness of our technique.     

Corrosion Behavior of Aluminum Wire for Overhead Transmission Lines: Investigation and Analysis

The corrosion behavior of aluminum wire used for overhead transmission lines was studied in four corrosion environments: (1) sodium chloride solution, (2) sodium chloride solution with addition of alumina particles, (3) aluminum chloride solution, (4) aluminum chloride solution with addition of alumina particles. The corrosion tests and polarization measurements revealed that environments 2 and 4 with alumina particles roughened and rapidly corroded the surface of the aluminum wire. It is considered that wet and dry environments of overhead transmission lines change aluminum hydroxide, present as a corrosion product, to alumina (aluminum oxide), which acts as an abrasive and weakens the surface of the aluminum wire. It is also shown that the corrosion of the aluminum wire occurs in an abrasive corrosion environment caused by alumina and corrosion fatigue due to vibration of the overhead wires. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 185(4): 18–24, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22486     

Slope measurement of bent plates using double grating shearing interferometry

A grating-based shearing interferometeric setup for slope measurement of bent plates has been proposed. The specimen under test is illuminated by a collimated beam from the laser. Light reflected from the specimen passes through two identical holographic gratings placed in tandem. The grating frequency has been so chosen that the diffracted orders from each grating are separated out distinctly. Two first-order beams diffracted from each of the gratings superpose in space. In the resulting interferogram, the fringes due to slope information of the object are visualized. Mathematical formulation for experimental determination of slope values has been undertaken. Validation of the experimental results with theoretical predictions in case of cantilever beam provides good correlation. The main advantage of the technique has been the realization of very compact geometry without the need for spatial filtering arrangement commonly associated with the grating-based techniques used to date.     

Enhanced compatibility of SAN and PC in their blends exposed to extremely high shear field

Originally incompatible blends of SAN 30% and PC 70% were extruded with extremely high shear rate up to 10⁷ s⁻¹ as a typical example of the blends. The materials were examined with a scanning electron microscope (SEM), a pulsed NMR, etc. The molecular weight of the blends was also measured with gel permeation chromatography. The blends are of binary systems microscopically in the first run of extruding, in which the minor constituent is present as small spherical particles in the major constituent. The apparent volume fraction of the spherical minor constituent estimated from the microscopic photographs decreases with the shear rate. The fraction is decreased also with the repeated runs. SEM observation reveals that dimple fracture of microsize takes place on SAN sphere dispersed in PC matrix. And at the bottom of the dimple, a small particle, which would be composed of PC, is present. From these, SAN in the blend is thought to be partly ductile even at the temperature of liquid nitrogen. At the fifth run, the blend appears uniform or structureless. Dynamic loss tangent gives two peaks corresponding to that of SAN and that possibly attributed to PC. The latter shifts to lower temperatures with the number of extruding run. These show that some of SAN is mixed with PC in a compatible form. The pulsed NMR analysis supports the conclusion. Furthermore, the analysis suggests that some of SAN is mixed in PC. This result shows the compatibility of SAN with PC is enhanced in extremely high shear rate processing.     

Geo-referenced multimedia environmental fate model (G-CIEMS): model formulation and comparison to the generic model and monitoring approaches

A spatially resolved and geo-referenced dynamic multimedia environmental fate model, G-CIEMS (Grid-Catchment Integrated Environmental Modeling System) was developed on a geographical information system (GIS). The case study for Japan based on the air grid cells of 5 x 5 km resolution and catchments with an average area of 9.3 km2, which corresponds to about 40,000 air grid cells and 38,000 river segments/catchment polygons, were performed for dioxins, benzene, 1,3-butadiene, and di-(2-ethyhexyl)phthalate. The averaged concentration of the model and monitoring output were within a factor of 2-3 for all the media. Outputs from G-CIEMS and the generic model were essentially comparable when identical parameters were employed, whereas the G-CIEMS model gave explicit information of distribution of chemicals in the environment. Exposure-weighted averaged concentrations (EWAC) in air were calculated to estimate the exposure ofthe population, based on the results of generic, G-CIEMS, and monitoring approaches. The G-CIEMS approach showed significantly better agreement with the monitoring-derived EWAC than the generic model approach. Implication for the use of a geo-referenced modeling approach in the risk assessment scheme is discussed as a generic-spatial approach, which can be used to provide more accurate exposure estimation with distribution information, using generally available data sources for a wide range of chemicals.