摘要:

AbstractThe radial temperature distributions in the central part of arcs burning through polyethylene (PE) tubes are estimated by measuring the half‐width ofHαline spectrum and using the electron density versus Stark half‐width and the electron density versus temperature characteristics. Estimation is carried out for various tube inner diameters (2 and 4 mm) and dc arc currents (5, 10 and 15 A). The result shows that the temperature at the arc center is around 10,000 K, and it tends to increase as the tube inner diameter becomes narrow and/or the arc current increases.The overall temperature distributions from the arc axis to the tube wall are obtained by combining these inner temperature distributions with outer temperature distributions which have been derived from C2spectra. They are found to take a form of typical two‐temperature distributions of ablation stabilized arcs.The electric field strengths of PE arcs are evaluated from the temperature distributions and the electrical conductivity versus temperature characteristics of thermally decomposed polyethylene vapor gas. The results agree well with experimental

ISSN:0424-7760    

DOI:10.1002/eej.4391130101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper describes the current status of the development of electromagnetic launchers such as the railgun at ISAS. The railgun is the most improved accelerator of Electromagnetic Launchers (EML). EML offers a potential for accelerating a projectile to much greater velocities than achieved with conventional powder guns or light gas guns. However, there has been little progress in increasing the velocity of EMLs since the experiment by Rashleigh and Marshall. A few experiments have been reported achieving velocities greater than 6km/s.The authors have achieved velocities greater than 6 km/s by reducing plasma leakage which is one of the factors limiting velocity.In this paper a 6 km/s launch is reported, compared with the results of two other shots considered from the viewpoint of plasma leakage, and the effect of entrainment of eroded material into the armature by rail ablation was discussed on the basis of simulated numerical calculations.

ISSN:0424-7760    

DOI:10.1002/eej.4391130102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractGrowth of microscopic cones on PTFE surface by RF sputter etching process are studied. The surface texm changes from initial submicron hillocks to large cones during sputter etching. The height of these cones is 33 to 45 percent of the etching depth calculated from etching rate. The direction of these cones is nearly equal to the ion incident angle. Boundary energy of sputtering and growth of cones are 100 eV and 150 eV, respectively. It is obtained that the redeposition ratio by back diffusion to sputtered molecule is 11 percent from the experiment using collector. It is concluded that redeposition and repolymerization process of sputtered material occurs in parallel with the ion etching process, and cones continue to grow partly during etching.

ISSN:0424-7760    

DOI:10.1002/eej.4391130103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractMagnetic 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 the Fe‐Cu‐Nb‐X‐B system. Substitution ofPfor B made the coercive force small in the 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 characteristics and good noise attenuation characteristics. Hence, Fc‐based nanocrystalline alloys have high performance for such magnetic com

ISSN:0424-7760    

DOI:10.1002/eej.4391130104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractMelt‐spun ribbons of Nd‐Pr‐Fe‐Co‐B‐V system alloys were prepared by the single‐roller rapidquenching method. The effects of composition, wheel velocity and heat treatment on the magnetic properties were investigated. The magnetic properties of their isotropic compression bonded magnets prepared from optimally annealed ribbons also were measured. Remanence (Br) was found to increase with decreasing rare‐earth content, and a maximum value of more than 1.0 T was obtained. A maximum energy product of 164.0 kJ/m3was obtained for (Nd0.5Pr0.5)9Fe4Co8B7.5V1.5alloy ribbon prepared at a wheel velocity of 17.1 m/s.From TEM observation, the particle size of these ribbons was determined to be between 20 to 30 nm. It is conjectured that the high remanence is obtained by the interaction of these fine particles. The amorphous (Nd0.5Pr0.5)9Fe74Co8B7.5V1.5ribbons prepared at a wheel velocity of 20.7 m/s were crystallized by heat treatment, and the optimum annealing condition was found to be at 650°C for 20 min. Its corresponding value of (BH)maxwas 146.2 kJ/m3. A maximum energy product of 86.4 kJ/m3was achieved with (Nd0.5Pr0.5)9Fe74Co8B7.5V1.5bonded magnets made from the optimally

ISSN:0424-7760    

DOI:10.1002/eej.4391130105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper discusses the feasibility of a decentralized voltage control scheme for large‐scale power systems. The algorithm is intended to apply to a reactive normal operating state from an emergency state caused by illcondition and also to keep the operating state away from approaching unstable boundaries in preventive control. The procedure for releasing voltage deviation (over/under voltage) is formulated as a multistage decision process over a certain time interval. The optimization problem is transformed into a two‐point boundary value problem using the discrete maximum principle and is solved easily by using the discrete Riccati equation.For a large‐scale power system, control values must be computed from a large number of state variables, and this inevitably prolongs the slow dynamics with controllers. The centralized control system in a large‐scale system cannot be justified from the economical and technical viewpoints. To resolve the foregoing problems, a decentralized voltage control system incorporating slow voltage dynamics is pr

ISSN:0424-7760    

DOI:10.1002/eej.4391130106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper describes protectors and multisensors using ferrite‐magnetic semiconductor (FMS). Useful FMS devices with Curie temperature from −15° to 300°C, in which the ferromagnetic properties below are retained below the Curie temperature, can be produced.The magnetic and electrical properties of FMS depend on temperature, humility, and gas concentration and can perform a switching function. The magnetic reluctance increases with temperature and approaches a maximum at the Curie temperature, but is independent of humidity or the concentration of combustible gases. The semiconducting resistance decreases from 225 to 170 kω as the humidity changes from 50 to 90 percent The FMS's specific dielectric constant above 900 is dependent on temperature, humidity, and the concentrations of combustible gases, including acetone, methanol, and ammonia In methanol, the capacitance increases from 0.18 to 0.5 nF as the concentration rises from 0 to 850 ppm. Bidirectional switching characteristics appear at voltages above 250 V. These characteristics should have practical applications in protective and measuring instruments. An overheating/overvoltage protector with temperatwe/humidity/gas concentration sensors composed of two annular FMSs is des

ISSN:0424-7760    

DOI:10.1002/eej.4391130107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractTo realize a general‐purpose magnetic field sensor having a detection sensitivity of the order of 10−12T/Hz at room temperature, a problem of removing the effect of the Earth's magnetism from the sensor must be solved because its magnitude is 4.5 × 104times larger than that in the range to be detectable. For this purpose, a well‐known approach of exciting the sensor in the opposite direction to the Earth's magnetism to cancel out the value has been adopted.This paper aims at realizing a magnetic field sensor free from the Earth's magnetism by introducing a method called “zero magnetic field.” In practice, such a sensor was developed and the tested results confirmed that the detection performance was maintained without losing the high s

ISSN:0424-7760    

DOI:10.1002/eej.4391130108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractRecently, adjustable speed hydroelectric power systems have been developed. In those power systems, ac exciting synchronous generators are used instead of the ordinary salient‐pole‐type synchronous machines. However, some higher harmonic sequences are included in the distribution of air‐gap magnetic flux density and in the terminal voltage waveform of the ac exciting synchronous machines because these machines have open winding slots. To develop better machines without terminal voltage waveform distortions, an evaluation method of the terminal voltage harmonics has been needed.This paper describes the mechanism of higher harmonics generation qualitatively and proposes an analytical method of no‐load terminal voltage waveforms on the basis of two‐dimensional magnetic field analysis considering movement of the rotor for quantitative higher harmonics analysis. The analytical results of higher harmonics show good agreement with the experime

ISSN:0424-7760    

DOI:10.1002/eej.4391130109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractA Static Var Generator (SVG) based on a self‐commutated inverter using GTO thyristors has been newly developed. The size of the SVG used for improving power system stability will be as large as approximately 100 MVA. The technical subjects to be solved for developing such a large SVG are summarized as follows:compact design;harmonic elimination by means of multiple transformers; andlarge inverter with series connection of GTO thyristors.This paper describes the solutions to these subjects, especially the application of a large number of multipulse connection and series connection of GTO thyristors, including the analysis of the basic performance of SVG and the multiple transformer. The test results of a 12‐pulse partial model (8 MVA) and a 48‐pulse miniaturized model prove the solutions proposed in this paper to be effective and reaso

ISSN:0424-7760    

DOI:10.1002/eej.4391130110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY