摘要:

AbstractHigh critical current densities of 1.61 × 1010A/m2at 1 T, 6.1 × 109A/m2at 3 T and 2.9 × 109A/m2at 5 T were achieved by controlling the distribution of Nb artificial pins in NbTi multifilamentary superconducting wires for ac applications. The critical current densities attained are over two times higher than those of conventional ac superconducting wires. This increase can be attributed to the shift of the peak of pinning force density to higher magnetic field by optimizing the pinning parameters.The benefits of increasing critical current densities for ac applications are demonstrated. A 2.5 T/100 kVA ac superconducting magnet was designed and made by using high Jcwire with controlled distribution of Nb artificial pins. Compared with conventional ac superconducting magnets, the new magnet exhibits a drastic decrease in size as well as in ac loss

ISSN:0424-7760    

DOI:10.1002/eej.4391160301

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

年代:1996

数据来源: WILEY

摘要:

AbstractDevelopment of sodium‐immersed‐type Electromagnetic Pumps (EMP) is expected to improve reliability, safety, maintainability, and construction cost of the Fast Breeder Reactor (FBR) compared with the conventional mechanical pumps. To realize the EMP, establishment of a high‐temperature‐resistant electrical insulating system is indispensable.A mica‐alumina combination is selected for the insulating system at temperatures higher than 500°C. Using this insulating system, an aging pretest was performed. The aging condition was to apply 1.5‐kV ac voltage in the nitrogen atmosphere at 550°C for 4000 hours. The dielectric properties before and after the aging were measured to understand the tendency of temporal change in the aging.In this result, the dielectric performance after aging was improved compared with the initial performance. The curious phenomenon was clarified to be caused by a decrease of organic component in the insulation, which remained due to incomplete burning. Also, the possibility of thermal runaway was considered to be higher as a dielectric breakd

ISSN:0424-7760    

DOI:10.1002/eej.4391160302

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

年代:1996

数据来源: WILEY

摘要:

AbstractVarious countermeasures are taken against lightning faults in power transmission lines to decrease their occurrence and improve transmission reliability. However, how much they enhance the power transfer capability has not yet been quantitatively evaluated. The conventional deterministic approach, which is widely used in power system planning methodology, is inadequate to deal with this issue.This paper proposes a new method for numerically defining the power transfer capability enhanced by countermeasures against lightning. The proposed method is based on a probabilistic approach in which several fault patterns are taken into consideration with their occurrence frequency and maximum transferable power. This paper also gives an example application of the proposed method to a model trunk transmission system. The effect of a third overhead ground wire on the increase of transfer capability of a 500 kV transmission line has been quantitatively evaluated.

ISSN:0424-7760    

DOI:10.1002/eej.4391160303

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

年代:1996

数据来源: WILEY

摘要:

AbstractStorage batteries or pumped hydraulic power stations have been used to store electric energy. However, there are problems with storage batteries, e.g., long charging time, limited cycle life, low Coulomb efficiency, and inaccurate residual power meters. Because of these problems, practical power applications have not been achieved.To solve these problems, a complex system of capacitors and electronic circuits called the ECS (Energy Capacitor System) is proposed. The capacitor part of the ECS is a group of electric double‐layer capacitors of increased energy density. The circuits part is built around switching regulators. Although the capacitors alone are not capable of delivering stable output, the accompanying circuits compensate for various characteristics throughout the charge and discharge cycle.This combination of capacitors and electronic circuits increases the energy density by about 16 times that of the conventional electric double‐layer capacitors, close to the level of lead‐acid batteries but with lower output resistance and better voltage stability. The ECS inherently features short charging time, very long cycle life, and good Coulomb efficiency. The cells are completely sealed and made from materials which are not harmful to the enviro

ISSN:0424-7760    

DOI:10.1002/eej.4391160304

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

年代:1996

数据来源: WILEY

摘要:

AbstractResults of experimental studies on behavior of a supersonic flow and of a nonequilibrium plasma in a disk MHD generator are presented. The experiments with cesium seeded argon were carried out under high MHD interaction conditions. Effects of seed fractions on static pressure distributions, flow Mach numbers, electron temperatures and uniformity of discharge in the disk MHD channel were investigated. The results have shown that the flow is kept supersonic throughout the disk MHD channel when a sufficient Joule heating exists in a supersonic nozzle and the seed is fully ionized. It was found that there was an optimum seed fraction at which the power output became maximum and, at the same time, the seed was fully ionized. Furthermore, an almost uniform discharge due to the full ionization of seed was observed. It is noted that enthalpy extractions and adiabatic efficiencies were increased remarkably, and the highest enthalpy extraction of 26.5 percent was achieved for cesium seeded argon. However, adiabatic efficiencies remained still low due to large pressure losses.

ISSN:0424-7760    

DOI:10.1002/eej.4391160305

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

年代:1996

数据来源: WILEY

摘要:

AbstractTransmission lines passing through a mountainous region often are struck by winter lightning. As a result, numerous double‐circuit faults occur. Space charge might be responsible for this phenomena. Several investigations on flashover characteristics have been performed focusing on reduction of flashover voltage due to ionic space charge formed by corona discharge.In this paper, flashover characteristics of an air gap within a charged droplet cloud ejected from an airless nozzle using an induction charging method are discussed. The droplets are charged in the range ‐200 to 200 μC/kg, forming the space‐charge density of approximately 13 μC/m3. The flashover voltage and the time lag to flashover were measured when 1.2 × 50 μs lightning impulse voltage applied to a rod‐sphere gap is placed within the charged cloud. Flashover voltage for a positive rod increased markedly within a positive charged cloud by increasing the charge‐to‐mass ratio. The increase of flashover voltage was up to 80 percent in comparison with uncharged droplets. Flashover voltage for the negative rod decreased about 20 percent in the cloud of either polarity. The results show that the presence of charged droplets in the air gaps affects the discharge proces

ISSN:0424-7760    

DOI:10.1002/eej.4391160306

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

年代:1996

数据来源: WILEY

摘要:

AbstractIt is well known that voltage transients are caused by the operation of switchgears in a power system. The voltage transients travel along the power line as a traveling wave, and cause malfunction of electrical devices, communication systems, and the operational error of a control system.The voltage transients at the making operation of switchgear were examined to obtain the fundamental data for considering the immunity of communication systems used on a power system. However, it was difficult to observe the voltage transients using the potential transformer and the capacitance potential device because the transients were very rapid.Therefore, a measurement method using the coupled transmission line system is proposed to measure the high‐speed and high‐voltage transients, and the actual experimental results on the 6.9‐kV power system are presented. This method enables the measurement of high‐speed voltage transients in out of contact with the power

ISSN:0424-7760    

DOI:10.1002/eej.4391160307

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe ultrasonic motor has an excellent level of performance and many useful features, including high torque, low speed, compactness in size, and absence of electromagnetic interference. This motor has an especially large holding torque and a high response characteristic, making it ideal for use as a servomotor. The drive principle of the ultrasonic motor is, however, different from that of electromagnetic motors and its mathematical model has not been developed yet. Its speed characteristics, moreover, vary with the driving conditions. Consequently, it is difficult to control the ultrasonic motor while maintaining performance. In this paper, a position control scheme using adaptive control is proposed. The utility and validity of the proposed control scheme is tested in experiment.

ISSN:0424-7760    

DOI:10.1002/eej.4391160308

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

年代:1996

数据来源: WILEY

摘要:

AbstractA high‐temperature superconductorYBa2Cu3O7‐xwith strong pinning force has allowed stable magnetic suspension with no control to be developed. Two types of superconducting magnetic bearings (SMB) using YBCO and permanent magnet were assembled. The two types are radial and axial. The dynamic stiffness of each SMB as it was cooled down under a magnetic field by liquid nitrogen was measured both radially and axially. As a result, it was found that the spring constants of these SMBs were almost as large as a practically desirable value; however, their damping coefficients were lower than the practical level. These findings are useful as one of the data bases for development of an optimum SMB design to support the weight of rotors in an axial direct

ISSN:0424-7760    

DOI:10.1002/eej.4391160309

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

年代:1996

数据来源: WILEY

摘要:

AbstractA static induction (SI) thyristor using a normally‐off planar‐gate structure in a low power class has been developed to be used as a power switching device in a three‐phase inverter circuit. A 600 V‐15 A class SI thyristor with very fast switching time (tgt, tgq) and low forward voltage drop (VTM) was designed and created. This design was performed with a reasonable wafer structure (n−/n/p+), an n−base carrier concentration and thickness, and a gate structure (gate diffusion length and gate‐gate pitch). Microscopic processing was used to obtain this SI thyristor. The performance trade‐off between turn‐off time and forward voltage drop is controlled by a lifetime control process using proton irradiation that results in a very fast switching time with tgt of 500 ns and tgq of 500 ns with VTMof 1.5 V (at IT= 18 A). At a current level of IT= 18 A, the current density in the active area becomes 200 A/cm2, which indicates that the performance of the SI thyristor is superior to that of conventional

ISSN:0424-7760    

DOI:10.1002/eej.4391160310

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

年代:1996

数据来源: WILEY