bluuebunny/crossref_metadata_2025 huggingface dataset:
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

The 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

Gas‐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

Once 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

This 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

A 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

The 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

Molten 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

Hopfield 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

Harmonic 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

This 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

The 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

The 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.
H∞ control approach to a magnetic levitation system by 4‐point attraction with nonlinear characteristics
Authors: Qi Run‐De , Tsuji Teruo , Yang Zi‐Jiang , Oguro Ryuichi
Published: July 2007

An H∞ control system design for a magnetic levitation system by 4 points attraction is presented. In the levitation system, a vehicle which runs as the secondary in a reluctance‐type linear motor is levitated by four pairs of attraction forces and guided by two pairs of attraction forces. Because it has contactlessness, in the field of semiconductor products, its application is favorable for ultraclean environments in microscopic processing.

In the control system design, the influence of both disturbances and uncertainties in the model is considered. The main disturbances stem from the position sensors. The uncertainties are divided into electromagnetic and mechanical ones: the former are due to the gain change in the current amplifier, the influence of leakage flux and linearization error in the magnetic circuit, and the latter are due to the changes of the mass and the moment of inertia of the vehicle. Therefore, the designed controller is indispensable to guarantee robustness of this system for both stability and performance. The controller design is based on the standard H∞‐optimal control problem.

As the novel features in this paper, the low sensitivity and the robust stability for this system design is obtained. Further, there are two‐poles on jω‐axis in the controlled model, and an integrator is included in the controller so that equivalently there are three poles on the jω‐axis in the model. Finally, several experiments, comparisons and simulations are carried out to verify the low sensitivity and robustness of the designed control system.
Computer‐aided protective relay setting system for large power networks
Authors: Fujita Nobuo , Ichie Ryozo , Ogawa Shigeaki , Kudo Hiroyuki , Fukui Chihiro , Nakata Yuji
Published: July 2007

This paper introduces a protective relay setting system capable of handling a large network up to 10,000 buses. The remarkable features are such useful functions as network analysis (fault analysis, load flow calculation, zero‐sequence current calculation, etc.), relay operation simulation, and automated setting coordination tasks.

Fault currents in the maximum and the minimum operation networks are calculated to examine the setting values. The protection zones are searched automatically along the network connection. Protection coordination tasks among the primary and the backup relays composed of different types of relays can be performed by the relay operation simulation.

The system is built on an engineering workstation, which works in cooperation with other network operation support systems. Its graphical user interface helps every engineer to examine the relay setting using a variety of databases.
Nuclear reactor diagnostic system using genetic algorithm (GA)‐trained neural networks
Authors: Chen Yan , Narita Masakuni , Yamada Takayoshi
Published: July 2007

Several nuclear reactor diagnostic systems using neural networks have been proposed in recent years. Neural networks trained by backpropagation, the standard training algorithm, have certain problems such as local minima and long training times.

In this paper, neural networks trained by genetic algorithms are used in a nuclear reactor diagnostic system to solve these problems. The system is tested by simulated data modeled on the experimental fast reactor JOYO, and two categories of abnormality (abnormal control rod vibration and abnormal coolant flow) are identified. The comparisons to networks trained by back‐propagation also are discussed.
Giant magnetoresistance and magnetic anisotropy of Co9Fe/Cu/Co9Fe multilayer thin films on an MgO(110) substrate
Authors: Inomata Koichiro , Saito Yoshiaki
Published: July 2007

Magnetoresistive effects have been investigated using Co9Fe/Cu/Co9Fe that were deposited on an MgO(110) substrate by ion beam sputtering with a 21‐A‐thick CU layer and with various thicknesses of the Co9Fe films. The influence of a 50‐A‐thick Fe buffer layer has also been investigated. In addition to a cubic symmetry anisotropy (K1), an in‐plane uniaxial magnetic anisotropy (Ku) was induced, which easy axis is parallel to the (110) plane of the MgO substrate and the (001) plane with and without the 50‐A‐thick Fe buffer layer, respectively. The magnetoresistance (MR) ratio decreased monotonically with increasing thickness of the Co9Fe films from 25 A to 70 A. A maximum MR ratio of 11.5 percent was obtained at room temperature. With increasing magnetic field, the MR ratio reached a plateau gradually after a steep drop at small magnetic fields without the Fe buffer layer. It reached a plateau rapidly at small magnetic fields with the Fe buffer layer. By considering both Ku and K1, these behaviors can be accounted for by the magnetization processes involved.
Application of parallel genetic algorithms to generation expansion planning using parallel processors
Authors: Fukuyama Yoshikazu , Ueki Yoshiteru
Published: July 2007

This paper presents an application of parallel genetic algorithms (PGA) to the optimal long‐range generation expansion planning. The problem can be formulated as a combinatorial optimization problem that determines the order of introduced generation units at each interval of the year. The proposed method considers introduced power limits of each technology, maximum loads at each interval, and load duration curves at each interval. Appropriate string representation for the problem is presented. Binary and decimal coding and three selection methods are compared. The method is developed on a transputer that is one of the parallel processors. The feasibility of the proposed method is demonstrated using a typical expansion problem with four technologies and five intervals. The method is then compared with conventional dynamic programming and a simple genetic algorithm with promising results.
Analysis of high‐power factor AC‐DC boost converter
Authors: Nagao Michihiko , Nakakohara Takashi , Jinno Masahito , Harada Koosuke
Published: July 2007

This paper presents analysis of a high‐power factor ac‐dc converter with a boost converter operating in the discontinuous conduction mode (DCM) and the critical conduction mode (CRM). The converter can be expressed by a nonlinear differential equation for each mode. The equation in DCM is solved analytically by separating its variable (output voltage) into two terms of a ripple component and a direct component, and by linearizing the equation for the ripple component. On the other hand, the equation in CRM can be solved analytically. Furthermore, the source current waveform of the converter is expanded into the Fourier series. As a result, the output voltage, its ripple and the power factor of the converter in DCM and CRM are derived as a function of the circuit parameters, respectively, and verified experimentally. These equations exhibit clearly the effect of each circuit parameter of the converter and the difference between the converter in DCM and in CRM. The converter operating in CRM produces sinusoidal ac current with unity power factor.
Instantaneous value control of current vector of energy transfer circuit with inductor converter bridges between superconducting magnets
Authors: Shirai Yasuyuki , Nitta Tanzo , Suzuki Tomohiro , Yajima Syuichi , Okada Takao
Published: July 2007

Energy transfer circuits of inductor converter circuits (ICB), used for power supplies for superconducting magnets, are studied. Analytical solutions of steady‐state characteristics of ICB energy transfer circuits are analyzed. On the basis of these solutions, a discussion is presented regarding a new control method of ICB transfer circuit to reduce a voltage ripple across a load superconducting magnet. This paper will propose a new control for line‐commutated converters of ICB energy transfer circuit for quick changes in a transfer angle and a transfer frequency for the voltage ripple reduction control. Speeding‐up of the proposed controls is also discussed. Validity of the proposed controls is confirmed by computer simulations.
A study on the deterioration characteristics of power capacitors with oil‐impregnated paper
Authors: Okabe Shigemitsu , Koto Masanori , Fukuda Yoji , Hayashi Yoshinori , Nara Toshio , Takahashi Kunihiko
Published: July 2007

Power capacitors are highly reliable due to their completely enclosed configuration. They are relatively trouble‐free over the long term. However, their dielectric strength can be reduced due to some stresses, including overvoltage application or thermal degradation of the insulation material during long periods of operation; these events can result in dielectric breakdown of capacitors in extreme cases.

Since almost all power capacitors with oil‐impregnated paper have been operated for more than twenty years, some kind of failure should be expected. To prevent these incipient accidents, it is important to examine the insulation deterioration mechanism and evaluate the degree of deterioration before capacitor breakdown. To establish a diagnostic method of deterioration of the capacitors with oil‐impregnated paper, we have conducted thermally and electrically accelerated deterioration tests and investigated the changes of their characteristics. Based on the experimental results we obtained, it can be concluded that the behavior of the oil‐dissolved gases can be used as a useful index to diagnose the insulation deterioration of these capacitors.
Assessment of transient voltage stability based on critical operating time of emergency control using neural networks
Authors: Maeda Tatsumi , Takigawa Kiyoshi , Minato Yoshinori , Yokoyama Akihiko
Published: July 2007

Since unstable phenomena that load bus voltages collapse rapidly after a large disturbance occurred in a bulk power system, it is becoming necessary to develop a fast and precise evaluation method of what is called transient voltage stability. Although many indices have so far been proposed for static voltage stability assessment, there are few evaluation methods, digital simulation analysis for example, for the transient voltage stability assessment that deals with the dynamic characteristics of generators, loads, etc.

This paper presents the transient voltage stability evaluation system that consists of two artificial neural networks (NNs). The first NN judges whether the system is stable or not under a given operating condition, load composition and fault location from the viewpoint of the transient voltage stability. If it is judged to be unstable, the second NN estimates critical operating time of emergency control action as a severity index of the transient voltage instability. Here, closing of a bus tie that is switched off in the normal state is adopted as the emergency control for voltage stabilization. Numerical examples for a 26‐bus model system are shown in order to check the effectiveness of the proposed evaluation system.
Optimal planning for introducing dispersed generating sources in power systems based on an economical viewpoint
Authors: Nishiya Ken‐Ichi , Kita Hiroyuki , Hasegawa Jun , Haga Yoshihiro , Minagawa Kazushi , Simazu Kenji , Nakamura Hideo
Published: July 2007

This paper discusses optimal planning problems for dispersed generating sources so as to provide a guideline for their introduction to power systems. First, a recursive method is developed from the viewpoint of supplying electric power only where solutions for one unit are superposed. The computational loads are decreased by selecting alternatives of buses based on the so‐called penalty factor. However, for effective utilization of dispersed generating sources, it is indispensable to consider their thermal merits in addition to electric power. After applying the Kuhn‐Tucker theory to the optimal dispatching problem including boiler fuel costs, thermal values of the dispersed generating units are evaluated quantitatively. Finally, the above‐mentioned technique for the optimal planning basically is also effective and is extended into this case. The validity of the proposed algorithms are demonstrated using a real‐scale model system.
Some factors for the space charge formation in polyethylene
Authors: Takahashi Tohru , Miyata Hiroyuki , Nakatuka Tohru , Yokoyama Ayako
Published: July 2007

Information on space‐charge behavior in thick insulated samples aids in understanding the dc characteristics of polymer‐insulated dc cables. The pulsed electroacoustic method is used to investigate several space charge formation factors in 2 mm‐thick polyethylene (PE). The following results were obtained.

For measurement factors:

(1) A polymeric semiconducting electrode provides a more accurate measurement than does a metal electrode as a result of better matching of acoustic impedance with PE.

(2) Within a dc electrical stress range of several tens kV/mm, the space charge distributions under and after dc voltage application are almost the same; this is due to a comparatively long time of space‐charge decay.

(3) The space‐charge distribution of a plate sample agrees with that of a cable sample having the same insulation thickness.

For insulating material factors:

(1) The amount of space charge in crosslinked polyethylene (XLPE) is much larger than that in low‐density PE (base of XLPE).

The space charge of XLPE continues to increase even after dc voltage application (24 h); that of LDPE reaches equilibrium with a few hours.

(2) The aforementioned space charge difference between XLPE and LDPE is assumed to be caused by ionic impurities in XLPE, not by the additives themselves (acetophenon and cumylalcohol as byproducts of cross linking and antioxidant).
Stability of large‐scale coal‐fired MHD channels
Authors: Ishikawa Motoo , Kyogoku Akihiro , Umoto Juro
Published: July 2007

Stability of large‐scale coal‐fired MHD channels is studied by (1) linearized stability analysis, and (2) time‐dependent 1‐D analysis. The channel length is 15 m with 600 electrode pairs, and the output power ranges from 220.6 MW through 258.7 MW. Linearized stability analyses show that the Faraday channels operated with fixed loading resistance are stable, whereas the two waves of u and u–a (u, a: gas and sound velocity) become unstable in the Faraday channel with fixed loading factor. Two waves of u and u–a are unstable in the diagonal channel with fixed loading current and the u + a wave becomes unstable in the diagonal channel with fixed electrode current.

Time‐dependent one‐dimensional analyses indicate that the Faraday channels with fixed load resistance are smooth without growth of fluctuation. The diagonal channels with fixed electrode current are smooth with no fluctuation, though the linear theory indicates that the u + a wave is unstable. The diagonal channel with fixed load current suffers large disturbance along the latter half of the channel, being consistent with the linearized analysis which indicates that the u ‐ a and u waves are unstable.
Flexible generator maintenance scheduling based on subjective relaxation of constraints
Authors: Miao Zhiyong , Yasuda Keiichiro , Yokoyama Ryuichi
Published: July 2007

This paper presents a fuzzy‐based method for determining a flexible generator maintenance scheduling by means of subjective relaxation of constraints imposed on the maintenance scheduling problem. The constraints are divided into hard (crisp) constraint set and soft (fuzzy) constraint set according to reflecting conditions which surround power systems. The problem is formulated as a fuzzy mathematical programming problem and solved with the fuzzy branch‐and‐bound method using Bellman‐Zadeh maximizing decision. The proposed approach provides not only a new flexible concept of planning problems in power systems, but also natural expansion of conventional approaches based on crisp set theory. The effectiveness and feasibility of the proposed approach are demonstrated on two typical power system models which consist of 15 generators and 60 generators, respectively.
ADTR‐motor drive for electric vehicle
Authors: Kawamura Atsuo , Yokoyama Tomoki , Kume Tsuneo
Published: July 2007

A new motor (ADTR‐motor: Anti‐Directional Twin Rotary Motor) for electric vehicle drive is proposed. A stator in a conventional motor is reformed to be movable, and the stator (outer rotor) and the rotor (inner rotor) rotate in anti‐directions. The IM‐type ADTR‐motor and the SM‐type ADTR‐motor are considered, and in this paper a prototype of the IM‐type ADTR‐motor is constructed experimentally. When the ADTR‐motor is used for an EV drive, the direction of one of the rotors should be reversed. Both rotors, when rotated in the same direction, propel the two wheels of EV. The torque of the wheels can be balanced without differential gear. The fundamental characteristics of ADTR‐motor are clarified. The characteristics are the structure of ADTR‐motor, the equivalent circuit parameters, the torque balance theory, the torque‐speed characteristics, the rotor speed transient characteristics, and the transient response under the speed sensorless torque control.
Revolving magnet wheels with permanent magnets
Authors: Fujii Nobuo , Ogawa Kokichi , Matsumoto Toshio
Published: July 2007

A new type of actuator with both magnetic levitation and linear drive is proposed. The actuator, called magnet wheel, has a rotating magnetic field obtained by revolving permanent magnets with high coercivity mechanically. The induction repulsive‐type magnetic lift force with self‐stabilization can be obtained by linking the rotating flux to a conducting plate. The induced simultaneous drag torque, which causes power loss, is used to obtain thrust in two proposed ways. These are called “tilt type” and “partial overlap type,” respectively. In the tilt type, the magnet wheel is tilted against the surface of a conducting plate. In the partial overlap type, the magnet wheel operates near the edge of a conducting plate.

In this paper, the fundamentals of the structure of proposed magnet wheels are described. The basic characteristics at parallel to the conductor are shown by using a numerical three‐dimensional electromagnetic analysis and measured results. The generation of both lift force and thrust in tilt type and partial overlap type magnet wheel are proved by experiments, respectively.
A method of predicting transient constants of synchronous machines
Authors: Ara Takahiro , Akima Tsunaki , Oda Shoichi
Published: July 2007

It is difficult to determine the subtransient (transient) reactance and subtransient (transient) short‐circuit time constants of medium and large synchronous machines by the sudden three‐phase short‐circuit test because large‐capacity equipment is required.

This paper describes a new method of measuring these constants by means of a simple test using a small dc power supply.

The key points of this method are as follows.

(1) A dc voltage is applied to the armature winding (two terminals with the third one open) of a stationary synchronous machine through a resistance. When the two terminals are closed, the winding is short‐circuited and the current in the armature winding decays. The whole process of decaying current is recorded.

(2) The value of the transient phenomena of the winding calculated from circuit equations (armature, field winding and damper winding circuits) is compared with actual data, and the unknown equivalent circuit constants are identified by the least squares method.

(3) Transient phenomena of the sudden three‐phase short‐circuit are calculated by the two‐reaction theory using identified constants, and, hence, these constants are calculated.

The transient constants of synchronous machines obtained by the new method agree closely with the observed values.
Tan δ of ethylene‐propylene rubber in cryogenic temperature region–effects of additives and sample thickness
Authors: Mizuno Yukio , Mitsuyama Yasuichi , Minoda Atsushi , Nagao Masayuki , Kosaki Masamitsu
Published: July 2007

The authors have been developing extruded polymer insulated superconducting power cables. Dielectric loss in electrical insulation cannot be ignored in superconducting cables since conductor loss in the cables is minimal. Studies so far show that ethylene‐propylene rubber (EPR) is suitable as an electrical insulating material in the extruded polymer insulated superconducting cable design because it demonstrates excellent mechanical and relatively good electrical qualities at a cryogenic temperature. Widely used EPR includes some kinds of additives; however, their effect on tan δ of EPR at cryogenic temperature remains unknown.

The effect of additives such as crosslinking agent and fillers on tan δ of EPR was examined at temperatures of between 4.2 K and 300 K. Thickness dependence of tan δ was also measured using EPR films of different thickness and an extruded EPR insulated cable sample. The results show that additives increase tan δ of relatively thin films of EPR even in the cryogenic temperature region; however, they do not have an intolerable dielectric loss in comparison with conductor loss and heat inflow of the superconducting cable. The remedy to tan δ increase due to the polymer contraction relative to shielding wires has been established.
Optimal load‐shedding using local information
Authors: Fujita Goro , Shirai Goro
Published: July 2007

This paper describes an optimal load‐shedding policy based on quadratic programming using only some power system state variables after severe generation outages. When generation outage is severe, the imbalance between supply and demand causes a declining frequency. Utilities generators cannot be operated excessively at frequencies above normal. Some of the load must be shed to prevent system damage. Optimal load‐shedding policies have been studied using all state variables of the power system. However, in real power system operations, it is difficult to obtain remote information in that fraction of a second following generation outages.

An optimal load‐shedding method is constructed in this research using quadratic programming (QP) under the assumption that all power system state variables can be available. However, these state variables cannot be easily accessible (as already mentioned). A suboptimal load‐shedding scheme based on the local state variables is then studied. The proposed load‐shedding method is based on the aforementioned optimal one. The change in line‐power flows and the amount of generation power outage are used as accessible data at each load point. Incorporating this local information into the optimal loadshedding method based on the QP method, the proposed load‐shedding method is established here.

The effectiveness of this proposed method is illustrated by two examples and simulation results on a model power system show that the method is encouraging.
Assessment of dynamic stability of large‐scale power system by Rayleigh's quotient
Authors: Kakimoto Naoto , Sugano Keiji
Published: July 2007

A method of assessing dynamic stability of large‐scale power system by Rayleigh's quotient is proposed. One‐machine infinite‐bus systems show damping torque characteristics similar to diagonal components of operational transfer matrices for original multimachine systems, which means that design of PSS with one‐machine systems controls those components. An expression for damping constants of oscillation modes is derived based on an energy function and its time derivative for a simplified system representation. This expression demonstrates that oscillations do not necessarily become unstable even if there are some generators with negative damping; and the effect of damping torque is determined by eigenvectors. The expression is generalized with Rayleigh's quotient, and a method of estimating eigenvalues of large‐scale power systems is proposed. With this method, approximate eigenvalues are refined to accurate eigenvalues. Only a specified number of eigenvalue analyses are required irrespective of the number of generators, hence much calculation is saved. Finally, this method is applied to a 107‐machine system to verify its effectiveness.
Deadbeat flux level control of direct‐field‐oriented induction motor
Authors: Huang Lipei , Tadokoro Yasuki , Tsukakoshi Masahiko , Matsuse Kouki
Published: July 2007

A method for the deadbeat flux level control of a direct‐field‐oriented induction motor with position control loop has been developed that employs an adaptive rotor flux observer. The observer is a full‐order type and is used not only in the direct‐field‐oriented controller, but also to identify stator and rotor resistances of the motor. The observer reduces the sensitivity of a deadbeat controller to fluctuations in the motor parameters. The main advantage of this method is that it improves the efficiency of an induction motor without sacrificing dynamic performance.

This paper describes the method as well as the fundamental characteristics of the system derived from experimental and simulation results.
Development of high‐Jc NbTi multifilamentary superconducting wire with Nb artificial pins for AC applications
Authors: Miura Osuke , Inoue Itaru , Matsumoto Kaname , Tanaka Yasuzo
Published: July 2007

High critical current densities of 1.61 × 1010 A/m2 at 1 T, 6.1 × 109 A/m2 at 3 T and 2.9 × 109 A/m2 at 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 Jc wire 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 losses.
Dielectric properties of mica‐alumina combined insulation at high temperatures
Authors: Ishida M. , Ikeda Y. , Naohara N. , Mitsui H. , Kumazawa R. , Kuroki T.
Published: July 2007

Development 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 breakdown mechanism.
An evaluation method for power transfer capability enhanced by lightning countermeasures
Authors: Takahashi Kazuhiro , Inoue Atsuyuki , Tanaka Kazuyuki
Published: July 2007

Various 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.
Experimental study of LIM‐driven, attraction‐type magnetically levitated carrying system
Authors: Hikihara Takashi , Hirane Yoshihisa , Uejyou Takeshi
Published: July 2007

Recently, many kinds of magnetic levitation systems have been proposed and developed for use in factory automation systems. This progress in the development depends on the appearance of new types of permanent magnets and new control theories. On the other hand, some systems have simple structures in which couples roles are given for both levitation and conveyance. As for these systems, however, many trials are needed to establish the system configurations and the control theory. The authors have developed a new magnetically levitated carrying system driven by LIM (linear‐induction motor). The system can be completely detached from a guideway both in mechanical and electrical meanings.

In this paper, the experimental results, especially the driving characteristics of a vehicle without any contacts to the LIM guideway, are discussed.
Inertia‐lowering control of induction motor
Authors: Terashima Masayuki , Ashikaga Tadashi , Kataoka Yasuo , Nakano Yoshinori , Nomura Masakatu , Hara Kiyoshi
Published: July 2007

There are many requests for selecting freely the moment of inertia, even though the moment of inertia is determined by the materials, structure, shape, and size of the motors. From the standpoint of control, reducing the moment of inertia will make it possible to construct well‐controlled drive systems and expand the applications in which a motor may be used to replace another nonelectric machine. An “inertia‐lowering control” system has been developed that uses disturbance observer to reduce inertia.

To realize this control system with vector‐controlled induction motors, the equations and machine constants needed for designing the systems have been clarified. A digital signal processor and a microprocessor were adopted for induction motor control, and good results were obtained through the experiments.
AC V‐t and impulse V‐N characteristics of shell‐form transformer insulation model
Authors: Okabe Shigemitsu , Ohno Takahiro , Zaima Eiichi , Kishi Akio , Aono Kazuaki , Hosokawa Noboru
Published: July 2007

To evaluate an appropriate level of ac test voltage for 1000‐kV transformers, it is necessary to make an accurate estimation of ac V‐t characteristics. For the level of impulse test voltage, V‐N characteristics are important to evaluate effects of impulse stress repetition. Since both of the characteristics are dependent on insulation structures and manufacturing processes of transformers, it is important to make accurate simulations on transformer insulation for reliable insulation data.

To obtain some of the basic data for 1000‐kV transformer test levels, long‐time ac V‐t tests and impulse V‐N tests of up to 1000 times voltage application were carried out on an insulation model simulating fundamental structure of shell‐form transformers. The model is composed of a parallel electrodes system with a compound structure of pressboard barrier and oil gap.

The tests showed the following characteristics: ac V‐t characteristics of up to several ten days could be described by two lines, each representing short‐time and long‐time characteristics. V‐N characteristics of lightning and switching impulse were expressed by relatively flat lines, which showed a decrease in breakdown voltage by less than 10 percent after 1000 times impulse application.