bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development and characteristics of superconductor for 70‐MW class high‐response excitation superconducting generator
Authors: Yamaguchi Mitsugi , Nakanishi Kazuo , Ohmatsu Kazuya , Meguro Shinichiro , Kobayashi Yoshio 
Published: July 2007

AbstractThe superconducting field winding of the 70‐MW classhigh‐response excitation superconducting generator requires a maximum operation current of 4.5 kA at the field of 6 T and needs to allow the field change of 10 T/s. In addition, superconductors have to meet the requirements of saddle‐shape winding in the rotor slot and require the mechanical strength withstanding the centrifugal force as well as electromagnetic force.The developed conductor has the configuration of double stranded cable, consisting of NbTi, Cu and CuNi. An optimization was made, taking into account the requirement of low ac loss and high current density. The critical current of 13.6 kA was achieved at the field of 6 T and the ac loss was 6.9 kW/m3. The developed low‐loss high‐current density superconductor will be able to be applied to the field winding of the 70‐MW class high‐response excitation superconducting generator.
Line fault test of model power system with three‐phase superconducting fault current‐limiting reactors
Authors: Kado Hiroyuki , Uriu Yoshihisa , Ishigooka Takeshi 
Published: July 2007

AbstractA 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.
Conditions for existence of optimal solution in the synthesis of a multivariable control problem for power systems by using optimization problem
Authors: Kaizu Hiroyuki 
Published: July 2007

AbstractThis paper considers the synthesis of a multivariable control problem for power systems by using the optimization method. The power system dynamics based on the usual assumptions can be formulated as a class of nonlinear dynamic systems which contain the sinusoidal functions associated with the power torque‐angle curve of the ac generator. Then, an optimal control law, which retains the principal nonlinearity of the power system, is derived by using the optimization techniques in the linear optimal control theory. The feedback gain matrices are obtained by solving matrix equations which appear in the optimization procedure.In this paper, the conditions for the existence of an optimal solution of these matrix equations are derived by using Anderson's theorem. The stability criterion for the control system is discussed from the viewpoint of a Lur'ye‐type Lyapunov function. Thus, the optimal control law can be applied to a class of nonlinear dynamical systems represented by the ordinary differential equations divided into linear and nonlinear terms.
Radial flux type hysteresis motor with rotor ring of copper‐sprayed surface layer
Authors: Wakui Genjiro , Kurihara Kazumi , Kubota Tomotsugu 
Published: July 2007

AbstractThis paper describes a new form of radial flux type hysteresis motor having large output, high efficiency, and high power factor. The rotor has a copper‐sprayed surface layer on the rotor ring, which is made of Fe‐Cr‐Co magnet steel and has magnetic anisotropy and slits. The new configuration has two features. First, it is designed to give a combined hysteresis and reluctance‐motor action effectively, particularly at a synchronous speed. Second, it is designed to give a combined hysteresis torque and large torque due to eddy current in asynchronous conditions, particularly at starting.To analyze motor performance at synchronous and asynchronous operations, the finite‐element method is used. In this paper, magnetic hysteresis is considered by using complex permeability. The agreement between predicted and measured values of motor performance characteristics is good.
Characteristics of superconducting generator at high response excitation
Authors: Nitta Tanzo , Tanaka Shoichi , Okada Takao 
Published: July 2007

AbstractSuperconducting generators have many advantages, one of which is their ability to improve the stability of power systems because of their low synchronous impedances. The advantage may be increased by adoption of high‐response excitation. The first 100 kVA high‐response excitation superconducting generator has now been built. One of the problems in the design of such generators involves the characteristics of the field circuit, i.e., the field armature winding, losses in the component materials, and loss in the superconducting field winding. In this paper, a 2‐dimensional electromagnetic field analysis of field circuit characteristics is presented.
Transient sheath voltage characteristics of a crossbonded cable installed within a tunnel
Authors: Nagaoka Naoto , Ametani Akihiro , Yoshida Kyoto , Karasaki Takashi 
Published: July 2007

AbstractThe wave‐propagation characteristics of a cable installed within a tunnel has been investigated. The transient characteristic of this cable system differs from that of a cable system in which the cables are buried without tunnels. The transient characteristic is heavily dependent on both the distance from the cable to the tunnel wall and the physical parameters of the tunnel. A modeling method of the cable system installed within a tunnel is proposed based on investigation.A field measurement of transient sheath voltages on a 275 kV crossbonded cable system is made. Numerical results obtained using the proposed model agree well with field test results; thus the accuracy of the modeling method proposed in this paper is confirmed.The effects of the circuit parameters, such as inductance of the sheath bonding wire and the equivalent capacitance of the sheath protection arrester, are studied.
A sensorless brushless dc motor system
Authors: Ogasawara Satoshi , Suzuki Kazuto , Akagi Hirofumi 
Published: July 2007

AbstractThis paper describes a brushless dc motor system without position or speed sensor. The brushless motor consists of a permanent magnet synchronous motor and a voltage‐source inverter capable of controlling the amplitude and frequency of voltage. The rectangular‐shaped stator current with a conducting interval of 120° (electrical) is controlled to be in phase with the trapezoidal back electromotive force. This results in producing maximum torque. Variable speed is achieved by adjusting the average motor voltage similarly to chopper control of dc motors.In this paper, two sensorless position detecting methods, i.e., an “indirect method” suited for the lower‐speed range and a “direct method” suited for the higher‐speed range are proposed. The combination of the two makes it possible to detect the rotor position over a wide‐speed range. Furthermore, a speed‐sen‐sorless PLL control is proposed in applying the principle of the direct method. Experimental results obtained from a prototype brushless dc motor are shown to confirm the validity of the sensorless drive. The starting procedure of the motor also is discussed because it is impossible to detect the rotor position at a standstill.
Flashover phenomena in positive rod‐to‐plane air gaps under impulse and DC voltages
Authors: Tsuneyasu Itaru , Nisijima Kiyoto , Izawa Yasuji 
Published: July 2007

AbstractDischarge phenomena in positive rod‐to‐plane air gaps under lightning impulse and dc voltages were investigated.Under impulse voltages, the 50 percent flashover voltages agree with the 50 percent corona inception voltages only in a gap shorter than a certain value dc which increases with the rod diameter φ. The 50 percent flashover voltage at dc rises at a rate of about 14 kV/cm with dc in the range of dc < 2.8 cm (φ ⩽ 1.5 cm), and then it rises at a rate of about 5 kV/cm. Experimental results show that the flashover process in the former region (termed the Gp process) is different from that in the latter region (the Lp process).Under dc voltages, the critical gap length, at which the first corona may lead to flashover without any succeeding streamer corona, corresponds to dc under impulse voltage. In a gap shorter than dc flashover occurs through the Gp process (φ ⩽ 1 cm) or Lp process (φ ≥ 2 cm), but in gap longer than dc flashover may occur through another process which cannot be seen under impulse voltages.In this paper, those flashover characteristics and processes are described on the basis of experimental results and photographic observations with an image converter camera.
Distributed architecture for energy management D‐structure
Authors: Kokai Yutaka , Fukuhara Akira , Morita Ken'Ichi , Kanke Tatsunori , Kata Mamoru , Hayashi Tatsuo , Takenuki Toru 
Published: July 2007

AbstractElectric power systems are expanding in size and complexity, and the requirement for the energy management system (EMS) is becoming more important. In this computer control system, a single control computer is used mainly as the primary computer and its software is very complicated because of its hugh number of small, quick tasks to obtain high response speed. Therefore, much effort is needed to develop and modify the programs, and the responsiveness of this centralized architecture varies greatly when many faults occur in the power system.This paper describes a new distributed architecture for the EMS. Distributed processors execute the functions cooperatively with periodic access to the common bulletin board database in which information about the power system exist. This architecture facilitates the software development and maintenance, and it also enhances the performance by the parallel processing of the distributed functions.
Development of three‐dimensional electric field computation system by surface charge method
Authors: Hanai Etsuyo , Oyama Mitsutoshi , Aoyagi Hirokuni , Murase Hiroshi , Oshima Iwao 
Published: July 2007

AbstractThis paper describes development of three‐dimensional electric field computation system by surface charge method. Using this system, both potential and electric field in the case which includes resistance or true electric charge can be calculated. And this system is able to be connected to the pre‐post processors, which is useful for us to make arbitrary shape and to display results of analysis.
Comparisons of direct‐current breakdown characteristics in dry air and SF6 gaps using a parallel‐plane arrangement with variable height protrusion
Authors: Nishijima Kiyoto , Tsuneyasu Itaru 
Published: July 2007

AbstractBreakdown voltages in uniform and quasi‐uniform field gaps are sensitive to the presence of small protrusion on the electrode surface in SF6 at high pressures. The aim of the present work is to study direct breakdown and corona stabilized breakdown for the transitive region from uniform to nonuniform gap in dry air and SF6 at low pressures up to a critical pressure when direct breakdown takes place by a leader discharge crossing the gap in SF6. In a parallel‐plane gap with a variable‐height protrusion subjected to the dc voltage, corona onset voltage is remarkably controlled by the protrusion height. The present electrode arrangement has the advantage of directly measuring the minimum critical guiding field strength for the propagation of a streamer discharge at corona onset.The experimental observations have been explained qualitatively on the basis of a streamer model and precise electric field calculations of gap.
Evaluation of a cogeneration system treating and utilizing municipal refuse cleanly and efficiently for district heating and cooling
Authors: Pak Pyong Sik , Nakamura Kenichi , Suzuki Yutaka 
Published: July 2007

AbstractThis paper is a comprehensive analysis of the characteristics and economics of systems which treat municipal refuse and utilize its contained energy as the energy source to generate not only electric energy but also the heat energy for district heating and cooling. The following two systems are investigated: (1) System A which is composed of a plant to incinerate municipal refuse and a cogeneration system with a bleeder/condensate turbine power generation unit; and (2) System B which is the system proposed here and is composed of a pyrolysis furnace for treating municipal refuse, a two‐stage‐cleaning process for refining generated pyrolysis gas, and a cogeneration system constructed by a combined cycle power generation unit using cleaned pyrolysis gas as its fuel gas. It was estimated that the maximum net power‐generating efficiency of System B is 24.8 percent, and is higher by 63 percent compared to that of System A.Economics of the systems have also been investigated, and it was shown that System A if the extra electric energy of the systems can be supplied directly to various facilities, which is different from the case where it should be sold only to electric companies. Effects of changes in major social and technological factors which affect the economics of the two systems are also analyzed, and it was shown that the possibility is considered to be high that the economics of System B will become more advantageous than that of System A in the future.
Sliding mode control with adaptive vss observer
Authors: Chen Yi‐Feng , Mita Tsutomu 
Published: July 2007

AbstractThe conventional sliding mode control or variable structure control (VSC) of a nonlinear uncertain system is well known for its robust property and simplicity of control law. However, the use of either is permitted only on the assumption that the upper bound of parameter variation or nonlinearity is known and that the complete information about the state is available. Although the former has recently been solved with adaptive robust control theory, the latter does not appear to be solved.This paper attempted to solve this problem using the technique of VSS adaptive robust control theory. That is, a VSS adaptive observer and a sliding mode control incorporated with this observer was proposed. The robust stability of the closed system can be proved applying Lyapunov's second method.
A magnetic semiconductor protective device with built‐in multifunction sensors
Authors: Seki Kyoshiro , Osada Hiroshi , Chiba Shigeki , Shida Jun‐Ichi , Murakami Koichi 
Published: July 2007

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 described.
Analysis of terminal voltage waveform of AC exciting synchronous generators
Authors: Ide Kazumasa , Takahashi Miyoshi , Ito Motoya , Tsuji Eiji , Yasaka Yasuhiro , Fujimoto Takashi 
Published: July 2007

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 experimental ones.
A saturable reactor‐assisted soft switching PWM DC‐DC converter
Authors: Hamada Satoshi , Ogino Yasumasa , Nakaoka Mutsuo 
Published: July 2007

AbstractOwing to the demand to increase the power density of switched‐mode power converters, resonant topologies have attracted much attention because of their low switching losses and low EMI. However, they require relatively large resonant components and necessitate high current or voltage ratings at semiconductor devices.This paper describes a new soft‐switching PWM full‐bridge DC‐DC converter which can overcome these drawbacks by utilizing a small saturable reactor. The principles of operation and the steady‐state characteristics are illustrated and the role of the saturable reactor is discussed. Moreover, the voltage and current stresses for active and passive components are also presented.To verify the results, experiments were performed with a 350 W, 500 kHz prototype converter. They demonstrated that the converter achieves soft switching in a wide load range with no substantial increase in voltage and current stresses on active and passive components.
Impulse insulation characteristics of a composite insulation system having a wedge gap in SF6 gas
Authors: Inui Akifumi , Yamada Shin , Murase Hiroshi , Teranishi Tsuneharu , Ohshima Iwao 
Published: July 2007

AbstractImpulse insulation characteristics were investigated in a composite insulation system having a wedge gap in SF6 gas. The partial discharge inception voltages of wedge gaps with various types of film were measured and compared with the calculated breakdown voltages estimated from Paschen's curve of SF6 gas. Also discussed is how the charge accumulated on the film surface due to a partial discharge had an effect on the creepage breakdown voltage. Partial discharge inception voltages in wedge gaps were higher with higher SF6 gas pressures and with lower film permittivities.Creepage breakdown voltages depended little on gas pressures or on creepage distances. The dependency of breakdown voltages on gas pressures and the effect of polarity on the breakdown voltage differed with the types of film. This may be partly because the charge on the film due to partial discharge had an effect on the discharge propagation, and that charging of the film differed with the types of film.
Digital input filters for measurement, control and protection in electric power systems
Authors: Kido Mitsuyasu , Chiba Tomio , Kudou Hiroyuki , Kawakami Junzou , Kawai Tadao 
Published: July 2007

AbstractPower system control and protection equipment is subject to especially stringent sensitivity and operational reliability requirements.Projected digital signal processing systems suitable for electric power systems fulfill these requirements by means of fast sampling and digital filtering by a 32‐bit floating point DSP (Digital Signal Processor). The sampling rate of 3 kHz is carefully selected in order to separate the power spectra of the A‐D conversion output errors from the signal bandwidth. The new 12‐bit A‐D conversion unit equipped with a recursive‐type digital filter achieved a high resolution equivalent to 14‐bit conversion.This paper describes the design concept and the operating characteristics and illustrates applications to current differential relays, distance relays and power system controllers.
Dynamics of an HVDC system in the presence of unbalanced AC transmission line faults and a stabilization scheme
Authors: Takasaki Masahiro , Takenaka Kiyoshi 
Published: July 2007

AbstractThe introduction of an HVDC system into the trunk power supply system requires transmitting as much dc power as possible for improving the whole ac/dc system stability. The continued operation scheme of an HVDC system which makes it possible to operate even under very low commutation bus voltage is adopted to cope with such system requirement. Further stability improvement can be achieved by adding damping control which modulates converter active and/or reactive power.To take full advantage of these control effects, it is essential that the HVDC system can maintain stable operation during the ac system faults and reclosing. Particular attention should be given to a repetitive commutation failure following the unbalanced ac transmission line faults.This paper discusses first the cause of the repetitive commutation failure when supplied with unbalanced ac system voltage based on an experiment using the CRIEPI AC‐DC Power System Simulator. Then a stabilization control scheme with an on‐line extinction angle estimation is proposed and the effect is verified by digital simulation.
An experimental study of the flux control characteristics of a magnetic fluid controlled by a parallel or orthogonal magnetic field
Authors: Oka Hideo 
Published: July 2007

AbstractThis paper presents experimental results of the flux control characteristic and the inductance control characteristic of magnetic fluid which is controlled by the permanent magnets. Two kinds of magnetic field, parallel and orthogonal, are discussed comparatively. The position between the magnetic fluid and the permanent magnet determines the magnetic field. The results are useful when employing magnetic fluid as a sensor or a control element.
Combined system of a series active filter and a shunt passive filter—an optimum design of the shunt passive filter
Authors: Fujita Hideaki , Akagi Hirofumi 
Published: July 2007

AbstractThe combined system of a series active filter and a shunt passive filter that is proposed by the authors has the ability to eliminate a major disadvantage of shunt passive filters, namely, harmonic amplification. The series active filter needs a much smaller kVA rating than a conventional shunt active filter, and as a result, the combined system has good filtering characteristics and high efficiency.This paper presents an optimum design of the shunt passive filter that makes possible a great reduction in the required kVA rating of the series active filter. It can minimize the peak voltage across the series active filter and reduce the required kVA rating of the filter to 60 percent. A computer simulation geared to practical applications of large three‐phase. twelve‐pulse thyristor rectifiers is used to compare the compensation characteristics of the optimized system with those of a combined system that uses a conventional shunt passive filter. Experimental results obtained with a laboratory model of the filter corroborate the design approach.