Performance evaluation of squirrel‐cage damper structure for superconducting generators

Superconducting generators have many advantages such as increasing generation efficiency and improving power system stability. In Japan, 70‐MW‐class superconducting generators have been developed through the national project “Electric Power Application of Superconducting Technologies (1988–1999).” In this paper, performance evaluation of the rotor damper structure for the 70‐MW‐class model generator is discussed. Double‐layered damper structure, which consists of a squirrel‐cage warm damper and a single‐layered cold damper, was set as the target. As the first step, basic electromagnetic and thermal performances were obtained. Consequently, it was proven that the damper structure had the performances to satisfy the requirements of the superconducting generators. Performances obtained from the experimental model, design of the 70‐MW model rotor, and evaluation by the verification tests are described in this paper. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(1): 19–33, 2005; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20025     

Performance evaluation of 6000‐A‐class superconducting field windings for 600‐MW‐class superconducting generators

Superconducting generators have many advantages such as increasing generator efficiency and improving power system stability. In Japan, a national project has been conducted since 2000 which is aimed at the development of fundamental technologies required for high‐output‐density and large‐capacity superconducting generators. This paper describes the results of this project, focusing on 6000‐A‐class field winding development. Copyright © 2004 Wiley Periodicals, Inc. A superconducting generator with a high output density and a large capacity has inherent factors that decrease superconducting stability. These are: (1) increase in the magnetic field in the winding which is caused by the increase in winding current density and (2) difficulty in fabricating windings which increases as a conductor diameter becomes larger. To secure the stability, we adopted a higher‐copper‐content conductor and a design that increases winding fixing pressure, along with devising a winding method that accommodates larger conductor diameter. These improvements were applied to a partial model of a 600‐MW field winding. Test results of the model showed good stability, indicating that design and fabrication technique for a 6000‐A‐class superconducting field winding has been successfully evaluated. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(2): 7– 18, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20332     

Measurement and numerical analysis of flammability limits of halogenated hydrocarbons

Flammability limits measurement was made for a number of halogenated compounds by the ASHRAE method. Most of compounds measured are the ones for which discrepancy was noted between the literature values and predicted values of flammability limits. As a result, it has been found that most of the newly obtained values of flammability limits are not in accordance with the literature values. Numerical analysis was carried out for a set of flammability limits data including the newly obtained ones using a modified analytical method based on F-number scheme. In this method, fitting procedure was done directly to flammability limits themselves instead of fitting to F-number. After the fitting process, the average relative deviation between the observed and calculated values is 9.3% for the lower limits and 14.6% for the upper limits.     

RF number as a new index for assessing combustion hazard of flammable gases

A new index called RF number has been proposed for assessing the combustion hazard of all sorts of flammable gases and their mixtures. RF number represents the total expectancy of combustion hazard in terms of flammability limits and heat of combustion for each known and unknown compounds. The advantage of RF number over others such as R-index and F-number for classification of combustion hazard has been highlighted.     

Crystallization of amorphous carbon at high static pressure and high temperature

Amorphous carbons prepared from furfuryl alcohol resin have been studied in a high-pressure apparatus of octahedral anvil type at pressures up to 18 GPa and at temperatures up to 2000° C. The amorphous carbons, when heated under pressure, crystallized first into graphite at 450 to 600°C and then into diamond at 1120 to 2000° C. The temperatures for the onset of these crystallizations,T ₉ andT _d, were determined by a simple technique. As the temperature for the preparation of the amorphous carbons was raised from 700 to 1000° C,T ₉ at 15 GPa increased slightly whereasT _d at the same pressure turned from a decrease into an increase beyond 750° C for the preparation temperature. For amorphous carbon prepared at 850° C,T _g increased a little whileT _d decreased markedly with increasing pressure.     

An attenuated total reflectance far-UV spectrometer

An ultraviolet spectrometer based on attenuated total reflection (ATR) has been developed and tested for liquid water (light and heavy water) in the wavelength range from 140 to 300 nm, which includes the far ultraviolet (FUV) region. One of the principal limitations of FUV transmission spectra is the strong absorption of the solvent itself. High absorptivity of the n --> sigma(*) transition in water molecule has thus far prevented meaningful spectral measurements of aqueous solutions in the wavelength region under 170 nm. Our technique uses the evanescent wave created through total reflection when light is passed through an internal reflection element (IRE) in contact with the sample. Since the evanescent field is used as an optical path length, the method allows spectral measurements favorably comparable with that of transmittance method with a shorter path length than the wavelength of FUV light. In this study, we have designed an original miniature IRE probe made of sapphire that allows detection of the whole n --> sigma(*) transition absorption band of water down to 140 nm. The obtained ATR-FUV spectra closely match calculations based on the Fresnel formula. It is also confirmed that this spectrometer is equally effective for spectral measurements of nonaqueous solvents with significant absorptivities in the FUV region.     

High‐Speed Organic Single‐Crystal Transistor Responding to Very High Frequency Band

Although high carrier mobility organic field‐effect transistors (OFETs) are required for high‐speed device applications, improving the carrier mobility alone does not lead to high‐speed operation. Because the cut‐off frequency is determined predominantly by the total resistance and parasitic capacitance of a transistor, it is necessary to miniaturize OFETs while reducing these factors. Depositing a dopant layer only at the metal/semiconductor interface is an effective technique to reduce the contact resistance. However, fine‐patterning techniques for a dopant layer are still challenging especially for a top‐contact solution‐processed OFET geometry because organic semiconductors are vulnerable to chemical damage by solvents. In this work, high‐resolution, damage‐free patterning of a dopant layer is developed to fabricate short‐channel OFETs with a dopant interlayer inserted at the contacts. The fabricated OFETs exhibit high mobility exceeding 10 cm² V^?1 s^?1 together with a reasonably low contact resistance, allowing for high frequency operation at 38 MHz. In addition, a diode‐connected OFET shows a rectifying capability of up to 78 MHz at an applied voltage of 5 V. This shows that an OFET can respond to the very high frequency band, which is beneficial for long‐distance wireless communication.     

Preparation of niobium oxide films as a humidity sensor

Niobium oxide films were prepared over a quartz plate by withdrawing it from a solution of niobium penta-isopropoxide (NIP) dissolved in sec-propyl alcohol. The films calcined at 673 K were well controlled in the film thickness either by NIP concentration in the solution or by the withdrawing rate of the quartz plate from the solution. BET surface area of the calcined films was as huge as around 400 m²g₋₁ and was not reduced by cyclic adsorption/desorption of water vapor. A rapid decrease and increase in the electrical resistivity of the calcined films was well associated with the cyclic adsorption/desorption of water vapor. The decrease in the electrical resistivity of the films by water vapor adsorption was more than 10 times sensitive than the decrease caused by the adsorption of ethanol, hydrocarbons, carbon monoxide and carbon dioxide. These results suggest an application of the niobium oxide films as an element of a humidity sensor.

The calcined films were proved by SEM observation to consist of tiny particles possessing a lotofmicropores sized less than 20 A. The decrease in the electrical resistivity of the films, or the increase in the electrical conductivity, was attributed to the water vapor adsorbed in these micropores. In order to identify the charge carriers during water vapor adsorption on the films, changes in the impedance and the phase shift caused by water vapor adsorption were measured using an LCR meter in AC frequency range of 10 Hz to 100 kHz. From a complex impedance plotting, single semicircule was obtained for water vapor adsorption onto the films, suggesting single adsorbed species as a charge carrier. Assuming an equivalent electric circuit for the films adsorbing water vapor, a constant capacitance was calculated under various partial pressures of water vapor, probably suggesting that the charge carriers will be H₃O⁺ on the films.     

Characterization of micro‐cell discharge in AC‐PDPs by spatio‐temporal optical emission spectroscopy

Abstract— We have developed highly resolved spatio‐temporal optical emission spectroscopy to investigate the discharge characteristics of coplanar type ac plasma‐display panels (AC‐PDPs). Spatio‐temporal emission profiles were measured for relevant lines of atomic He, Ne, Xe, and ionic Xe in He‐Xe and Ne‐Xe systems with various Xe concentrations and total gas pressures. The surface‐discharge behavior in coplanar PDPs has been clarified.