bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recovery characteristics of a YBCO high‐temperature superconducting current‐limiting element for use in low‐voltage distribution systems
Authors: Yokomizu Yasunobu , Ito Koji , Matsumura Toshiro , Okubo Hitoshi , Kito Yukio 
Published: July 2007

AbstractRecovery characteristics of a YBa2Cu3O7‐y high‐temperature superconductor after its quenching are investigated experimentally in this paper. The zigzag‐shape superconducting elements 310 mm in effective length and 1.5 mm × 1 mm in cross section are examined. AC current injection tests are carried out. It is clarified that the high‐temperature superconducting element has a quick transition characteristic between the super‐ and normal‐conducting states.The test elements recover to zero impedance state from high impedance state just after removing the over‐current when the magnitude of accumulated heats due to the over‐current during the quenching period is less than 1 J. Furthermore, it is found from experiments that the critical current level might be reduced by some self‐magnetization due to a high current during the quenching period.
Application of a two‐degrees‐of‐freedom controller to chaotic dynamical systems
Authors: Kameda Toshio , Aihara Kazuyuki , Hori Yoichi 
Published: July 2007

AbstractWe apply a TDOF (two‐degrees‐of‐freedom) robust controller to chaotic dynamical systems. We show that the TDOF controller is effective not only for rejection of chaotic disturbance but also for control of a chaotic plant.
A method for analysis of back‐swing phenomena of synchronous machine in multimachine power systems
Authors: Mitani Yasunori , Tsuji Kiichiro 
Published: July 2007

AbstractThis paper describes a new approach to the analysis of the back‐swing phenomena in multimachine power systems. When a short‐circuit fault occurs in a power system, some generators decelerate in a short period immediately after the fault in some cases. The phenomenon called back swing is caused by the transient responses in armature winding of synchronous machines and in transmission lines. To represent the back swing in detail by a mathematical model, these transient behaviors have to be described by sets of differential equations. Then not only does the order of differential equations increase, but the convenient expression of the transmission system by a set of node equations becomes useless.In this paper an equivalent power system model for the simple representation of the back swing has been proposed. First, an impedance for each machine that represents the transient of transmission system has been introduced. It is assembled into the differential equations associated with armature winding response. Then the transmission system is represented by a constant impedance matrix. This model makes it possible to calculate the transient behavior of armature flux in multimachine power systems. The transient torque brought to the rotor shaft by the flux is calculated directly and it represents the back‐swing phenomena effectively.
Molten carbonate fuel cell stack performance with gas recycling
Authors: Watanabe Takao , Izaki Yoshiyuki , Mugikura Yoshihiro , Abe Toshio , Saito Hajime , Matsuyama Toshiyuki , Shimizu Toru , Sato Seiji , Ogoshi Mutsumi 
Published: July 2007

AbstractThe molten carbonate fuel cell (MCFC) power plant is expected to be one of the most promising future power generation systems for the electric utilities because of its high efficiency, environmental suitability and capability of using coal as fuel. To obtain such attractive performance, it is necessary for the plant to adopt the gas‐recycling operation system. The authors tested a 6‐kW class MCFC stack with three types of gas recyclings, i.e., cathode, anode and carbon dioxide ones, including pressurized conditions.This paper describes the test results and the effects of the gas‐recycling operations. Cathode gas recycling is proved to be able to control the stack temperature and give the flexibility for setting oxygen utilization. Anode gas recycling is proved to be able to suppress the methane formation and decrease the deviation of the stacked cell voltages. Including the starting‐up process, it is proved that the electricity can be generated from the stack without supplying carbon dioxide from outside the system by carbon dioxide gas recycling. In such a process using a burner for carbon dioxide gas recycling, burner temperature must be controlled to a certain value. It is important to adjust the fuel supplying rate, load current and cathode gas‐recycling ratio to each other. At the load change process, constant gas utilization operation is not effective in changing the burner temperature.
A study on the condition of reverse control action of tap changer in a single on‐load tap changer power system
Authors: Yorino Naoto , Funahashi Atsushi , Sasaki Hiroshi , Kubokawa Junji 
Published: July 2007

AbstractThis paper investigates the voltage stability in a single OLTC (On‐Load Tap Changer) system, which consists of a single OLTC and multiple generators as well as loads. It is shown that the sensitivity of the load voltage to tap position dV/dn = (I1 = exact value) plays an important role, independently of the existence of the equilibrium of the tap position. That is, when the equilibrium exists, the region where I1 > O is in the stability region; if the equilibrium disappears, the stability region also disappears but the voltage is still recovering in the region where I1 > O. Based on these results, the region of reverse control action of OLTC is defined as the region where I1 > O. It is proved that another sensitivity I2, which is defined as dV/dn when constant power characteristics are assumed for loads, can be used to estimate the region of reverse control action when the exact load characteristics are not available.
Neural‐network‐controlled superconducting magnetic energy storage for power system stabilization
Authors: Ohsawa Yasuharu , Kanemitsu Tomohiko , Kawakami Tetsuya , Shintaku Mikio , Arai Kenji 
Published: July 2007

AbstractIt has been clarified that a superconducting magnetic energy storage (SMES) is very effective for power system stabilization. The control methods proposed for power system stabilization by SMES are the pole assignment, the optimal control, and so on, each of which, however, has its drawbacks.This paper is concerned with the power system stabilization by neural network control of the active power of SMES. First, the optimal stabilizing control of the SMES power for the model power system is calculated for various power system operating conditions and fault conditions. Then these optimal controls are used as training data for the neural network. The neural network used is a multilayer type with a feedback from the output layer to the input layer. The trained neural network is examined by untrained operating conditions and faults.
Development of reliability analysis system of transmission network for primary substations
Authors: Naito Katsuyuki , Sugiyama Tomonari , Morozumi Satoshi 
Published: July 2007

AbstractThis paper describes the development of the reliability analysis system for transmission systems from primary substations on high‐voltage trunk line systems to distribution substations. This system has been developed on an engineering workstation. The user can input the network data of power systems from primary substations to distribution substations and the structure of buses and connections of transformers in substations using graphics. This analysis system can evaluate reliability at each distribution substation by simulating outage and recovery process for all fault modes which can occur, defining the capacity of facilities, probability of fault at each facility, the value of load at each bank, and the points where switching elements are turned off in the network as input data. In the calculation of the recovery process of each fault mode, the constraints of operation of radial power systems are considered.
Armature current and magnetic force at rotor dampers in superconducting generator on sudden three‐phase short circuit
Authors: Kometani Haruyuki , Sakabe Shigekazu , Hirao Toshiki , Nakabayashi Yukio 
Published: July 2007

AbstractThe important design factor of a superconducting generator is estimating the electromagnetic forces at the rotor dampers on a sudden three‐phase short‐circuit. In this paper, the armature current and electromagnetic forces on such a short‐circuit are simulated directly by two‐dimensional transient analysis, considering the following complex terms: 1 induced current by the speed electromotive force caused by the rotor rotation; the connection of three‐phase windings; and 3 the resistance and reactance at the armature coil‐end.The speed electromotive force is considered by using the combination method, which is FEM combined with BEM at the air gap. The connection of the armature winding and the effect of the armature coil‐end are considered by using the analysis combined with the external circuit equations. Moreover, the effect of the Röbel transposition of the armature winding is approximately considered.As a result of analysis, the electromagnetic forces at the rotor dampers can be calculated with a high accuracy.
Development of partial discharge detection method using an autoregressive model in gas‐insulated switchgears (GIS)
Authors: Inujima Hiroshi , Masui Takeshi , Maekawa Hiroshi 
Published: July 2007

AbstractGas‐insulated switchgears (GIS) are important equipment in electric‐supply stations where advanced techniques for safety and maintenance are required. As a result, a system is being developed that can automatically monitor and diagnose a GIS in service.This article focuses on some problems concerning insulating functions of GIS to discuss a method of signal processing for partial discharge detection and position identification. For sensors, potential detectors were installed on flanges of the GIS. Focusing on the potential fluctuations measured by these detectors, an autoregressive model is designed for potential fluctuation in a state without any partial discharge. This model is called a normal state model. The difference was found between potential fluctuations measured during partial discharge and those of the normal state model.The index of whiteness test method of the residual random process is a useful parameter for representing this difference, and the use of this method allowed detection of partial discharge that could not be found at normal potential levels. These results indicate bright prospects for manufacturing a monitoring system that can detect deterioration in GIS insulation with a high sensitivity in an early stage and that also operates on‐line.
Fault section estimation in power systems by discrimination analysis
Authors: Oyama Tsutomu , Horiguchi Akira 
Published: July 2007

AbstractOnce a fault occurs in a power system, the fault section must be estimated from inadequate information on protective relays and circuit breakers. There have been several studies to develop an automatic estimation method, e.g., knowledge engineering, neural network, etc. However, it was very difficult to obtain a method which is powerful enough and easy to maintain.In this paper, the discrimination analysis theory is applied to the fault section estimation. Using the theory, it is expected that the inference speed can be improved. It is expected also that the knowledge about the fault section estimation can be collected.First, using the small model system, the fault section estimation method with the discrimination analysis theory is described and compared to the method with neural network. Next, it is illustrated that the method can be applied to a large system.
Expert system for voltage control in restoration of EHV power system following complete blackout
Authors: Kakimoto Naoto , Lin Bunpin , Sugihara Hiroaki 
Published: July 2007

AbstractThis paper considers voltage control in restoration of EHV power systems. Restoration of a power system is performed by energizing transmission lines sequentially from initial power sources. These operations have already been programmed into an expert system developed by the authors. However, energizing no‐load transmission lines causes some bus voltages to rise 20 percent more than rated voltages, and transformers can tolerate a 20 percent voltage rise only for 1 min.Here, the expert system is supplemented with a function for checking bus voltages and reactive powers of initial sources, and which automatically switches on reactors. Conditions for switching reactors and selecting appropriate reactors are written by rules, hence they are easy to modify. The target of voltage control is to keep bus voltages with in ±5 percent, and to keep reactive powers of generators within 30 percent of generator capacity. Applying this method to three basic restoration patterns of a model power system shows that small adjustment of switching conditions is sufficient for two patterns, and some modification of the restoration procedure is necessary for the other pattern to obtain good voltage profiles through the restoration process.
Capacitive voltage sensor for measuring very fast transient overvoltages in GIS
Authors: Yashima Masafumi , Fujinami Hideo , Takuma Tadasu 
Published: July 2007

AbstractA reliable technique is needed for accurate measurement of very fast transient overvoltages such as disconnector‐induced surges occurring in GIS which have very steep front and high‐frequency oscillation. Recently, capacitive voltage sensors with very short response times have been proposed for this purpose. However, few studies have been made on the dielectric properties of materials used for a low‐voltage‐side capacitor, as well as the frequency bandwidth of the measuring system.In this paper a thin mica plate is proposed for a low‐voltage‐side capacitor which has a surface coated with silver on both sides. This material has been shown to have stable and high static capacitance up to a high‐frequency range. A quantitative estimate also is given for the frequency bandwidth of the measuring system. Furthermore, a practical‐scale sensor of this type has been developed which can successfully measure simulated disconnector‐induced surges of several hundred kilovolts under similar conditions in GIS.
Characteristics of photovoltaic/fuel cell power hybrid system. (Effect on electrical load form factors)
Authors: Sekiguchi Naotoshi , Fujiki Yasuyuki , Tani Tatsuo 
Published: July 2007

AbstractThe photovoltaic power system has a great future as a clean‐energy alternative to fossil fuel which has many environmental problems such as gas exhaustion or air pollution. Sunlight, a source of energy for the system, is influenced greatly by weather conditions, seasons and times of day. Therefore it cannot supply constant electric power.The photovoltaic/fuel cell power hybrid system is assumed. It combines PV array, hydrogen generator, storage tank and fuel cells by using hydrogen. This system can supply constant electric power to the electric load in a solitary island separated from a commercial electric network.The possibility of this system is examined by computer simulation. Input data include the global irradiance on inclined plane and temperature of HASP data of Tokyo, ten kinds of electrical load forms with 400 MWh electric power a year, and conversion efficiencies of each subsystem.As a result of simulation, it was revealed that the area of PV array with 8170 m2 and the volume of hydrogen tank from 22 × 103 to 30 × 103 kl are necessary.
Development of indirect internal reforming molten carbonate fuel cell
Authors: Ohtsuki Jitsuji , Seki Tatsuyoshi , Miyazaki Masayuki , Sasaki Akira 
Published: July 2007

AbstractMolten carbonate fuel cell (MCFC) has high potential for use as an energy converter of various fuels to electricity and heat. MCFC causes the environmental pollution and helps to reduce the greenhouse problem. The development of an indirect internal reforming molten carbonate fuel cell (IIR‐MCFC) was initiated by the Kansai Electric Power Company and Mitsubishi Electric Corporation. IIR‐MCFC has several advantages, for example: (1) higher efficiency is expected because of efficient utilization of heat from cell reaction to reforming reaction; and (2) longer life compared with direct internal reforming MCFC is expected by means of loading reforming catalyst in the cell separated from the electrolyte vapor which causes deactivation of the reforming catalyst.Class stacks of 3 kW, 10 kW, 30 kW and a 100 kW were operated successfully. Output power of the 100‐kW class stack generated 109 kW in IIR mode (direct methane feed). In the test of the 30‐kW and the 100‐kW class stacks, PSA (pressure swing adsorption) to separate carbon from the anode exhaust gas is installed in the anode gas recycle loop to the cathode.
A solution to combinatorial optimization problems using an accelerated hopfield neural network
Authors: Oohori Takahumi , Yamamoto Hiroaki , Setsu Nenso , Watanabe Kazuhisa 
Published: July 2007

AbstractHopfield has shown that the combinatorial optimization problem can be solved on an artificial neural network system by minimizing the quadratic energy function. One of the difficulties in applying the network to actual problems is that the network converges to local minimum solutions very slowly because the sigmoid function is used for an input‐output function of the neuron. To overcome this difficulty, this paper proposes an accelerated Hopfield neural network which can control the speed of convergence near the local minima by an acceleration parameter. Computational results for the combinatorial problems with two and twenty‐five variables show that: (1) the proposed model converges to the local minima more quickly than the conventional model; (2) that the acceleration of convergence makes the attraction region of each local minimum change and worsens the accuracy of the solution; and (3) that if an initial point is selected around the center of the unit hypercube, the proposed network converges to a local minimum very quickly with high accuracy, and these good properties remain unchanged by the acceleration parameter.
Harmonic power detection based on the pq theory and its applications
Authors: Tanaka Toshihiko , Akagi Hirofumi 
Published: July 2007

AbstractHarmonic interference problems generated by bulk semiconductor power converters become more serious in power systems with their wide use in industrial applications. Shunt passive filters consisting of LC tuned filters or shunt active filters using PWM inverters have been used to suppress harmonic currents in distribution systems.To install the passive or active filters, it is necessary to find exactly a dominant harmonic source in distribution feeders. A harmonic power on each phase and order at a receiving terminal has been investigated by using a digital power meter including an FFT analyzer. However, the conventional detection method has a problem in that it is difficult to discuss exactly harmonic power flow because the detected harmonic power is much smaller compared with a fundamental active power at the receiving terminal.In this paper, the harmonic power in three phases, which can be detected on real time, is defined by applying the pq theory. Next, it is verified by a digital simulation that the proposed method can discuss harmonic flows more easily than the conventional method. As a result, it is more simple and precise to find the harmonic source. Moreover, measurement errors of the harmonic power are revealed quantitatively, and the validity of the proposed method is demonstrated by digital simulation.
Switching frequency and multiple connection at a bulk power self‐commutated converter system
Authors: Seki Nagataka , Uchino Hiroshi 
Published: July 2007

AbstractThis paper describes which is better, e.g., a single bridge or multibridges, what switching frequency is best, at a bulk power converter system for static var compensation from the viewpoint of power loss, utilization rate of power devices, distortion factor of current and voltage waveforms, control response and reliability. This study shows that multiple connection of single‐phase bridges with a one‐pulse PWM and that of three‐phase bridges with a three‐pulse PWM are superior to a three‐phase single bridge with multiple‐pulse PWM. These results are quite different from general considerations in UPS or general‐purpose motor drive systems, where higher switching frequency has resulted in less harmonics, better response and smaller size.At a bulk power converter system, many power devices are required, thus multiple connection can easily be applied without the sacrifice of economy. In addition, it is very important, that the newly adopted control strategy provides very quick transient response at the lowest (fundamental) switching frequency.
Effective lightning protection schemes for distribution line
Authors: Masaki Tokuji , Higuchi Kouji , Yokoi Yoshihide 
Published: July 2007

AbstractThe causes of lightning outage are subdivided into direct lightning strokes and induced lightning strokes, which are identified by the characteristics of the lightning overvoltage. In the past, lightning protection devices were directed mainly toward the latter, and attention has been focused on the installation of lightning protection devices, ground wires, and reinforcement of insulators. However, lightning outages continue to occur. Thus it is extremely important to clarify the fault characteristics of lightning surges and to study the effectiveness of various lightning protection devices by considering both direct lightning stroke and induced lightning stroke in order to prevent lightning outage in the future.In this research, the electromagnetic transients program (EMTP) has been applied to the direct lightning stroke, and the induced lightning outage analysis program for multiple conductor systems has been applied to the induced lightning stroke to study the effectiveness of lightning protection devices provided by combination of various lightning protection devices. The most effective lightning protection schemes are analyzed and evaluated based on verification tests on the full scale models as well as economic considerations.
Self‐rehealing characteristics of a sodium current limiter and its overcurrent coordination for low‐voltage distribution system
Authors: Wada Yuuichi , Hamano Suenobu , Mori Teijirou 
Published: July 2007

AbstractThe sodium current limiter developed and applied for low voltage use is not a current limiting fuse but a new type of reusable current limiting device that utilizes metallic sodium as a fusible element. Excellent current limiting performance and quick self‐rehealing properties of the sodium limiter allowed highly reliable electric power systems to be obtained economically and compactly.Here we examine experimentally the rehealing properties of the sodium limiter after current limiting operation and discuss the overcurrent coordination of the sodium limiter for a low‐voltage distribution system. The results are summarized here:

(1) The resistance of the sodium limiter, being between about one thousand and several thousand times its normal resistance r0 at room temperature during a current limiting operation of short circuit fault currents, changes abruptly to 30 to 40 times its ro value just after the disappearance of the fault current and falls steadily to ro.
(2) The sodium limiter can recover current‐carrying capability for an overload current even immediately after a current limiting operation and maintain its capability for the following normal load current. The upper limit of the recovery of the sodium limiter is given by its overcurrent against the time characteristics under the normal condition.
(3) The self‐rehealing characteristics of the sodium limiter presented here give the ability to design a low‐voltage motor control center using the sodium limiter which maintains maximum service continuity up to high fault currents.