bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of combined levitation and guidance eds maglev system
Authors: Fujiwara Shunsuke , Fujimoto Tsuyoshi
Published: July 2007

A levitation method has been introduced which uses 8‐shape levitation coils arranged on the vertical surface of the guideway. These coils can act as a guidance means as well as the levitation means. The characteristics of this system are examined using numerical examples and experimental data. The cables connecting right and left coils are not connected to a high‐voltage power source unlike the usual guidance system which is combined with propulsion. Thus the electric insulation of the cables is not a problem at present. Numerical examples show that the levitation characteristics of the combined levitation and guidance system are almost the same as in the system without the guidance function, and that it attains reduced running resistance with necessary guidance stiffness obtained. A test run was done at Miyazaki Test Line equipped with coils of this type arranged about 120 m, and the results show stable running and balanced displacement which agrees with calculated values.
Basic design of 70‐MW‐class superconducting generators
Authors: Uyeda Kiyotaka , Shimizu Kohsaku , Maki Naoki , Ueda Akinori , Itoh Kaoru
Published: July 2007

The application of superconductivity technology to electric power apparatus is very important from the viewpoint of energy saving. Especially, the superconducting generators using superconductors as the field windings have many merits compared with conventional generators. Super‐GM has been researching and developing 70‐MW‐class model machines since FY 1988 for a scheduled period of eight years, aiming at a 200‐MW‐class superconducting generator. This paper describes the basic specifications and designs of 70‐MW‐class superconducting generators by Super‐GM and also describes the propriety of these basic specifications and designs.
A calibration method for the energy‐integrating function in photovoltaic system monitoring
Authors: Kurokawa Kosuke
Published: July 2007

Solar radiation has an irregularly varying factor due to a basic day and night cycle and climatic conditions. For such conditions a data sampling interval is important to ensure the accuracy of energy monitoring in a photovoltaic system. While treating a system monitoring equipment as a black box. the author has developed the method of calibrating an energy‐integrating function.

At first for various input waveforms, the relationship between sampling intervals and quasi‐integration outputs have been examined by trapezoidal rule. In the numerical simulation the phases of the sampling clock also are considered Then it is concluded that a sampling interval can be inspected through outside observation only by using a rectangular single pulse. By applying the pulse to the energy‐integrating process, two kinds of integrated outputs can be obtained for different sampling phases. The calculated difference between both outputs can uniquely give the sampling interval being inspected. Conditions to ensure measuring accuracy are discussed and the validity of this method has been demonstrated experimentally. Practical calibrating procedures also are proposed for the integrating function of PV system monitoring.
Laser‐guided discharge characteristics of long air gaps and observation of the discharge process
Authors: Aihara Yoshinori , Shindo Takatoshi , Miki Megumu , Suzuki Toshio
Published: July 2007

Laser‐guided discharge is promising for protection of power transmission systems against lightning. Several experiments concerning the laser‐induced electrical discharge have been performed up to now. However, it is necessary to understand the mechanism of the laser‐induced electrical discharge to achieve the laser‐triggered lightning.

When a high‐power laser beam is focused in air, a high degree of ionization is produced as brilliant beams near the focus. In this paper, the electrical discharge induced up to 2‐meters with a high‐power CO2 laser focused by a 10‐meter focal length mirror is described.

Experiments of the laser‐guided discharge were carried out by application of an impulse voltage to a rod‐rod gap after laser radiation. This paper deals with the effects of delay times and polarity of the impulse voltage on 50 percent flashover voltage characteristics and the observation results of discharge phenomena taken by a still camera, a special camera named ALPS (Automatic Lightning Discharge Progressing Feature Observation System) and an image converter camera.
A voltage‐source PWM rectifier‐inverter with feedforward control of instantaneous power
Authors: Ogasawara Satoshi , Yamagishi Naoyuki , Totsuka Hiroyuki , Akagi Hirofumi
Published: July 2007

In general, diode rectifiers with electrolytic capacitors on the dc side have been used as dc power supplies for voltage‐source inverters. Rectifiers of this type, however, cause many problems such as poor power factor and harmonics. Recently, voltage‐source PWM rectifier‐inverters have been studied to provide the following advantages: (1) harmonic‐free on both ac sides; (2) unity power factor on the input ac side; (3) power flow of either direction or power regeneration; (4) reduction of the dc capacitor. However, it is difficult for a conventional voltage‐source PWM rectifier‐inverter to regulate the capacitor voltage on transient states because it has only a voltage feedback loop.

This paper describes a voltage‐source PWM rectifier‐inverter with feedforward control of instantaneous power. Based on the pq theory, the instantaneous power which is calculated in the control circuit of the inverter is fed forward to the control circuit of the rectifier. The feedforward control of instantaneous power contributes greatly to sufficiently suppress voltage fluctuation of the dc capacitor on transient states. Transient characteristics are discussed, and some interesting experimental results of a laboratory model are shown.
Use of compensating magnets to reduce thrust imbalance in cylindrical linear pulse motors
Authors: Sanada Masayuki , Takeda Yoji , Ishikawa Sadao , Hirasa Takao
Published: July 2007

A linear pulse motor (LPM) has many advantages for a high‐accuracy positioning actuator because it has linear motion without any mechanical link. The flat‐type LPM generally is used in many industrial applications. However, it has a disadvantage in that the mover support mechanism becomes complex and heavy because the attraction force between the stator and the mover is very large. As the attraction force is balanced in the cylindrical structure, the cylindrical LPM is allowed to have a simple and lightweight support mechanism.

The inset magnet‐type cylindrical LPM, which has a permanent magnet between the A‐phase and B‐phase stator, has such merits as a magnet of simple shape and a reduction of the motor diameter. Its weak point is that thrust unbalance occurs because the magnetic flux pass of the outer poles is longer than that of the inner poles. The thrust unbalance decreases the pull‐in thrust force and increases the positioning error.

This paper proposes two practical methods to improve the thrust unbalance: 1) the exciting current adjustment; and 2) the method with compensation permanent magnet. These effects are examined with theoretical and experimental results.
Diagnosis of oil‐immersed transformers by colorimetry of insulating paper
Authors: Yorozuya Tsuruo , Takasu Nobuo , Isaka Susumu , Suzuki Toshio , Hashimoto Yukihiro , Ishioka Yasuaki
Published: July 2007

Power transformers have been expected to work with safety and reliability over a period of more than 30 years. The life expectancy of transformers depends upon the degree of deterioration of insulating materials, particularly conductor insulating paper. Many attempts have been made in recent years to estimate the degree of deterioration of transformers but no diagnostic techniques have been put into practical use because of the difficulty of taking into account the service conditions.

It is well known that materials change color when they deteriorate, but no colorimetry study has been made on material deteriorations. According to the recent advances in instrumentation and data processing equipment, the color of materials has become easy to measure qualitatively. Therefore, the basic investigation on colorimetry of insulating papers has been made to clarify the applicability to power transformers. Test results showed a strong correlation between the color difference and the deterioration of insulating paper. This report discusses the effect of materials of papers and impregnating oils on colorimetry.
Long‐term characteristics of XLPE cables
Authors: Ohata Katsuichi , Katsuta Ginzo , Iwata Zensuke , Maruyama Yoshio , Sekii Yasuo , Kanaoka Mamoru
Published: July 2007

To study the long‐term characteristics of XLPE cables installed in free air and in water, aging tests were conducted under various testing conditions using XLPE cables with both 3.5 mm and 6 mm insulation.

From the Weibull plots of lifetime distribution under the voltage stress EL as the minimum breakdown strength, the minimum value of time to breakdown tL under the constant voltage was estimated. The results of accelerated aging tests of XLPE cables installed in free air demonstrated that the V‐t characteristics of XLPE cables could not be described by the conventional inverse power law (t ∝ V−n) with a single constant life exponent n.

Based on the microscopic observation of a sliced insulation removed from XLPE cables, it was concluded that bow‐tie trees with longer tree length observed in cables tested in water were caused by the moisture from outside, whereas the trees in cables tested in free air were caused by the residual moisture originally existing in the insulation. The breakdown strength of the aged cables tested in water increases through cable drying. However, it does not recover to the original values.
Inrush currents of induction generators due to abrupt connection to utility power networks
Authors: Sato Masaki , Shima Yoshio , Takahashi Hiroo , Sanpei Yoshitaka
Published: July 2007

The squirrel‐cage‐type induction generator is suitable for small water power stations and wind power stations because of its simple and rugged structure, and low construction cost. However, the transient rush current flows into the primary and secondary windings when an induction generator is connected abruptly to a utility power network. The inrush current causes the voltage fluctuation in the power system. Therefore, electric power companies need a control method with low cost of the inrush current of the induction generator.

Many properties of the inrush current must be known in detail. The factors affecting inrush currents are system voltages, control of the system voltage phase angle, rotary speed, residual magnetism of the core, and residual electric charge of the primary windings. In this paper, the inrush current is analyzed by the instantaneous value symmetrical coordinates. The experimental study of the inrush current using phase control equipment and a small induction generator is presented.

The conclusions of this investigation are summarized as follows:

(1) The factor that gives the strong influence on the inrush current is the voltage phase angle.

(2) Although rotary speed changes from 0.9 to 1.15 times as much as the synchronous speed, the maximum value of the inrush current is nearly constant.

(3) The maximum amplitude of the inrush current is definitely seen in the first or second wave.
In‐service methods for distinguishing the dc component due to water treeing from noise currents in xlpe cable
Authors: Iga Atsushi
Published: July 2007

This paper describes the water tree diagnoses of 6.6‐kV class XLPE cables by the dc component method. The dc current component is measured by energizing the cable with ac high voltage, therefore, it would be suitable for on‐line diagnoses. The dc component is considered to be caused by the rectifying effect of water trees inside the insulation.

In laboratory tests, the dc component showed a good correlation with the degradation. However, almost no correlation was seen in the on‐site measurement. The authors found that the cause of this bad correlation is the galvanic effect inside the jacket. This generates the noise current through the grounding circuit when the jacket resistivity is low. Based on this finding, the equivalent circuit of on‐site measurement was proposed.

Considering the equivalent circuit, this paper proposes nine methods for discriminating the dc component due to water tree from noise current. Also described are the analytical results of each method. Furthermore, the on‐site or laboratory tests show that some of them are effective in separating the dc component due to water tree from noise current.
A method for evaluating effects of energy efficiency improvement on carbon dioxide emission reduction
Authors: Endo Eiichi
Published: July 2007

Global warming due to increasing atmospheric carbon dioxide (CO2) is a matter of serious concern. Energy efficiency improvement has been considered to be the most effective strategy for reducing CO2 emissions. The acceleration of R&D for energy technologies which have large effects on CO2 emission reduction should be effective in abating global warming.

In this study, the author proposes a method for evaluating the effects of energy efficiency improvement on CO2 emission reduction. This method utilizes a compact energy system model combined with analytical calculations.

Using this method, effects of energy efficiency improvement in Japan in the year 2030 are analyzed. Energy efficiency improvement in thermal power generation, nuclear power generation, and heat utilization are especially effective for reducing CO2 emissions. The author estimates that CO2 emissions per capita can be stabilized at the present level by energy efficiency improvement.
A new method for the analysis of cross‐country multifaults in a double‐circuit transmission line
Authors: Kai Takaaki , Funabashi Toshihisa
Published: July 2007

To analyze multifaults on a power line, many complex calculations must be performed. Hence, in many cases, computers are employed in the actual phase domain. However, it is difficult to determine the property and/or the physical meaning of the calculated results because the computer method is based on many complex numerical calculations.

This paper represents a new analytical method for short‐circuit studies which can deal with cross‐country multifaults in a double‐circuit transmission line with zero‐sequence mutual coupling. This method is based on the well‐known “two‐component network theory” for a balanced three‐phase double‐circuit. Procedure steps are: (1) represent the network as seen from the faulted points with symmetrical component impedance; (2) construct the symmetrical equivalent circuits for faults with imaginary phase‐shifting transformers; (3) combine these equivalents with each other and erase the symmetrical voltages at faulted points because the phase voltages at such points are known; and (4) calculate the currents at the faulted points by solving the simultaneous linear equations.

This method is applied to an investigation of distance‐relay “underreach” phenomena where crosscountry multifault occurred on a double‐circuit transmission line. Effects of line constants on these phenomena have been well understood.
Monitoring power system dynamic stability with a kohonen neural net
Authors: Tamaru Yoshihito , Mori Hiroyuki , Tsuzuki Senji
Published: July 2007

This paper presents a method for monitoring the dynamic stability of power systems using a Kohonen‐type neural network. The QR factorization algorithm is widely used in eigenvalue calculations for power system dynamic stability studies, due to its numerical stability. However, the method has the drawback that the computational requirements increase as the cube of the problem size. The S‐matrix method is therefore attractive, because it focuses on the most critical eigenvalue. However, this method is difficult to use in numerical calculations. The method proposed here makes use of a mapping of the eigenvalues that allows us to regard the absolute value of the most critical eigenvalue as a quantitative dynamic stability index.

In this paper, a Kohonen‐type neural network is used to estimate the index. The neural network has the following advantages: (1) it uses a simple algorithm which requires no training signal, (2) it effectively classifies the input data, and (3) it presents at the outputs a two‐dimensional mapping of the input data which makes it easy to visually comprehend their classification.
Optimal electric power‐plant planning under uncertainty of demand by means of the scenario aggregation algorithm
Authors: Nishikawa Yoshikazu , Tezuka Tetsuo , Kita Hajime , Nakano Shinichi
Published: July 2007

Recently, electric power systems have faced increasing uncertainties in demand, energy price and environmental constraints in the future. In such a situation, a plan for expansion of the system capacity must be made robust against the aforementioned uncertainties. Large‐scale power plants require a long time for construction so that the decision of construction must be made under much uncertainty in the future. On the other hand, small‐scale plants require less time for construction, i.e., the decision can be made under less uncertainty in spite of their relatively higher costs.

This paper is concerned with an optimal combination of the large‐scale and the small‐scale plants having the aforementioned characteristics under uncertainty of future demand. First, the demand growth in the future is described by scenarios of demand growth branching like a tree. Then the optimization problem of the system expansion is formulated into a stochastic linear‐programming problem. An optimal solution of the problem is obtained by using the scenario‐aggregation algorithm proposed by Rockafellar and Wets. The simulation results, yielded by using a parallel computation on transputers, show that there is a possibility of constructing small‐scale power plants to cope with the uncertainty even if they are more expensive than the large‐scale plants.
Morphological and dielectric changes of XLPE insulation due to thermal aging
Authors: Ishida Masayoshi , Okamoto Tatsuki
Published: July 2007

Transmission power cables are heated by conductor current. The morphology of the XLPE insulation may be changed by thermal aging. Disk‐shaped insulating materials with semiconductive electrodes were used to understand this thermal effect against the dielectric breakdown strengths. The disk specimens were aged at 80 and 100°C before the breakdown strength measurements.

These results showed that the dielectric breakdown strengths were improved with aging time. Analytical investigation of the insulating materials indicated that there were morphological changes such as increases of the lamella thickness and the spherulite diameter and decrease of the averaged lamella angle through heating. Cable specimens aged thermally with the same condition as the risk specimens also were observed with similar morphological changes in the insulation. Therefore it is concluded that the promotion of the crystallization by thermal aging is effective in improving the breakdown strength of the XLPE insulation unless it causes extreme deterioration.
Analysis of a zero‐power flow phenomenon in an interconnecting power system
Authors: Miyazawa Masaki , Kuboki Minoru
Published: July 2007

Today's power systems are characterized in that more power demand is concentrated in urban areas, increasingly centralized power facilities are becoming larger in size and located in more remote places, and power condensers tend to be upgraded to improve the power factor. These movements each reduce the stability power limit, thereby permitting the effect of a power failure to spread much farther.

In such an interconnecting power system, when power is transmitted from a power source (a small system) in a remote place to a large city (a large system) with great power demand, it is expected that a zero‐power flow phenomenon will occur where power transmission is impossible when power flow in the interconnecting power system is zero depending on a combination of the size of branch load and its power factor. In future power systems that will extend farther, have a larger capacity, and be more capacitive, such a phenomenon would be more iable to take place. In this paper, a new formula to analyze a zero‐power flow phenomenon is derived, and using the formula, areas in which a zero‐power flow phenomenon takes place also are discussed. With an experimental system simulating a practical 500‐kV power system, the occurrence of a zero‐power flow phenomenon could be verified.
Power system stabilization by switching‐over control of transmission lines
Authors: Okamoto Hiroshi , Yokoyama Akihiko , Sekine Yasuji
Published: July 2007

New technologies such as synchronized switching and power electronics will make it possible to change the configuration of a transmission network in future electric power systems. It is called VIPS (Variable Impedance Power System) by the authors who have been studying the effects of those technologies on power system stabilities.

This paper considers the improvement of transient stability by means of switching‐over control of transmission lines. It is clear that in some power systems, the simultaneous energization of the line de‐energized in the normal state with the fault clearing better improves first‐swing stability than the pre‐ and post‐fault energization of the line. The energy function‐based index to select such a transmission line is derived. In addition, this paper shows that multiple switching of a transmission line improves damping of post‐fault conditions, where minimization of time derivative of energy functions is used. The switching‐over control is applied to multimachine power systems and its effectiveness is demonstrated.
Load‐flow equivalents for decentralized monitor and control of power systems
Authors: Tanaka Kazuyuki
Published: July 2007

Load‐flow calculation on electric power systems is one of the most fundamental analyses in system operation and planning. There are many reasons to calculate load‐flow solutions, and the contingency evaluation is a representative one.

In contingency evaluation, it is necessary to repeat load‐flow calculation for tremendous patterns depending on branch or generation outages. Then, computing efforts are generally very heavy. Thus various techniques have been proposed to reduce computing time, especially by adopting equivalencing for external network. On the other hand, the network equivalents techniques also become important at present from the viewpoint of the necessity of decentralized monitor and control on bulk power systems.

This paper describes a newly developed method of load‐flow equivalents based on the Ward equivalent for both direct (dc) solution and (ac) solution. Numerical results also are shown to clarify the accuracies and practicality of the proposed method through the comparison of the representative REI approach.
Current distribution in superconducting multistrands for ac use before and after quenching
Authors: Oh Bong‐Hwan , Ishikawa Kazuaki , Hayakawa Naoki , Okubo Hitoshi , Kito Yukio
Published: July 2007

A superconducting multistranded cable is used to realize high current capacity for ac use. The critical current value of the cable is reported to be less than the simple summation of the individual critical current value of each strand. The causes for such a degradation of the critical current value have not been revealed.

This paper investigates the current distribution in multistrands before and after their quenching by using seven‐strand superconducting cable and 7x7 cable. The following experimental results are derived: (1) the quenching is initiated at one strand in the cable; (2) the current in the quenched strand is transferred into the other strands; (3) an avalanche of quenching is induced among the strands; and (4) the central strand is quenched finally among the strands. The critical current values of the 7‐ and 7 × 7‐stranded cables also are measured. These values are in good agreement with the predicted values based on the mutual inductance among the strands. It is concluded that the unbalance of the current distribution in the superconducting multistrands can be one of the promising causes for the degradation of the critical current value.
Loop‐shaping based H∞ robust control of a horizontal shaft magnetic bearing
Authors: Matsumura Fumio , Hatake Kazuhiro , Fujita Masayuki
Published: July 2007

This paper considers H∞ control design of a magnetic bearing from the viewpoint of loop shaping. Feedback control is indispensable for a magnetic bearing, since it is essentially an unstable system. For feedback control, a mathematical model is required. However, it does not always express the exact behavior of the system, hence the model has various uncertainties such as the errors of parameters, neglected nonlinearities, or unmodeled dynamics. The controller is needed to guarantee robustness for both stability and performance against these uncertainties on the model.

First, based on some assumptions, a linear state space model of a magnetic bearing is shown. Second, the experimental machine and the surroundings of its controller are introduced. The experimental machine is a 4‐axis controlled horizontal shaft magnetic bearing. The controller consists of a digital signal processor with fast A/D converters and D/A converters. Third, the control system is designed using normalized coprime factor plant descriptions. Selecting shaping functions in this procedure called “The Loop‐Shaping Design Procedure (LSDP),” shape the open‐loop transfer function and the transfer functions of the closed‐loop system can be shaped. Finally, several experiments are carried out according to the aforementioned designed controller.
Suppression of DC line current oscillation of HVDC transmission system using voltage source forced commutation converter
Authors: Funaki Tsuyoshi , Kimura Noriyuki , Matsu‐Ura Kenji
Published: July 2007

The conventional converter used in an HVDC system requires line voltage to turn off the current flowing through a thyristor or a mercury‐arc valve. Hence, the HVDC system cannot supply electric power to the system which has no ac source, such as a generator or a synchronous condenser. Thus, the HVDC system has some difficulties in operating with the weak system.

The conventional solution to avoid these problems is to install large‐capacity synchronous condensers which require considerable construction costs and maintenance. Another solution is the application of a forced commutation converter.

The recent development of high‐power and high‐frequency semiconductor devices with fast gate turn‐off ability (e.g., GTOs and SI thyristors) suggests the application of a voltage‐source‐type forced commutation converter (VSFC) to an HVDC system. To ensure the promising characteristics of the overall system, further investigation is of course necessary.

The performance of dc transmission into a remote load‐only system without ac source has been investigated by means of computer simulation. In many runs of a simulation program of the HVDC system using VSFC, we noticed that long sustaining oscillation of dc line current and dc voltage occurs when a large disturbance is applied. The performance is worse when series dc reactance (DCL) is installed to suppress higher harmonics of dc line current. To improve the performance of the HVDC system using VSFC, an attempt was made to install the L‐R parallel damper circuit in series of dc transmission line. Simulation results when DCL and L‐R damper are installed in series show that suppression of higher harmonics is as effective as the installation of DCL only, and the damping of oscillation also is substantial to improve the dynamic performance of the whole system.
Stabilizing control of power system using fuzzy control
Authors: Iskandar Marzan Aziz , Mizutani Yoshibumi , Suzuki Akio , Ishizeki Mitsuo
Published: July 2007

This paper presents an application of fuzzy control to enhance power system stability. The proposed control consists of the controller for large disturbance (FU 1), the fuzzy controller for small disturbance (FU 2), and the fuzzy judgment mechanism (FU 3).

FU 1 is determined based on the fuzzy controller [FU 1(F)] is determined according to the control rules and its input signals, i.e., speed deviation and acceleration at every sampling time of the machine. FU 2 consists of two controllers, namely, FU 2‐ω and FU 2‐P; FU 2‐ω has the same mechanism as FU 1, while the output signal of FU 2‐P is determined according to the rules together with the change of error of electrical power and terminal voltage. To obtain the optimal desired control signal during both the large and the small disturbances, the operations of FU 1 and FU 2 are judged by FU 3, where the magnitude of speed deviation is chosen as its input signal. The determined control signal is fed to AVR of the machine.

The implementation of the proposed control is simple due to the small amount of calculations and required data. The effectiveness of the proposed control is demonstrated by the one‐machine infinite‐bus system model and very good system performance is obtained throughout all the simulations.
Development of self‐commutated SVC for power system
Authors: Tokiwa Yukio , Ichikawa Fumitoshi , Irokawa Shoichi , Kitahara Tadayuki
Published: July 2007

A 50‐MVA self‐commutated Static Var Compernsator (SVC) using the worlds's largest GTO thyristors rated 6 kV‐2500 A has been developed for voltage control of electric power systems. The rated dc voltage is 16.8 kV which is four times higher than the highest one manufactured so far. To achieve the high dc voltage, eight GTO thyristors are connected in series. Voltage unbalance between GTOs during switching transient was investigated. A new overcurrent limiting method is proposed, since conventional fuse protection cannot be applied due to such high voltage. Newly developed technologies for this large and high‐voltage self‐commutated SVC are described.

Although simple star‐delta connection transformers are used, harmonics generated from SVC are almost equivalent to the 24‐pulse converter by shifting the pulse timing appropriately. The PWM control based on 150 Hz is applied and the SVC is designed to continue operation during system faults. The performance of the controller is tested successfully by a simulator, and typical rest results are introduced.
A CO2‐recovering nonpolluting high‐efficiency gas‐turbine power‐generation system utilizing saturated steam as its working gas
Authors: Pak Pyong Sik , Suzuki Yutaka
Published: July 2007

A carbon dioxide‐recovering high‐efficiency gas‐turbine power‐generation system is proposed in which carbon dioxide (CO2) generated is recovered by adopting the oxygen (O2) combustion method and no thermal nitrogen oxide is generated. In the system, saturated steam produced by utilizing waste heat is adopted as the working fluid of the gas turbine. Thus, the compressing process of the working fluid gas, which is the most energy‐consuming process in generating power by using a gas turbine, is not needed. This makes the system extremely high efficient.

By taking saturated steam of 210°C as an example, the characteristics of the system were simulated. The net exergetic efficiency of the system has been estimated to be 48.4 percent by considering both the exergy of the saturated steam and the electric power required not only to generate high‐pressure oxygen, but also to liquefy the recovered CO2. The value is higher than the exergetic efficiency 37.8 percent of large‐scale thermal power generation plants using the same natural gas, and is 28.0 percent higher than its efficiency of 37.8 percent, the one estimated if the CO2 generated is removed and recovered from the stack gas by using alkanolamine‐based solvent and the recovered CO2 is liquefied.
Protection of bulk regular network system with dispersed generators
Authors: Okamura Yukio , Genji Takamu
Published: July 2007

In urban areas there is a growing need to ensure bulk power distribution, service reliability and an interconnection to dispersed generators. It is effective to improve the network distribution system for the foregoing view. Regular network systems often are used for the area, but coordinations of the protection are complex as usual.

This report describes the protective coordinations of the regular network system that performs a bulk power distribution and includes dispersed generators. The interconnections influence the coordination of substation protective relays and network protectors at the primary feeder fault. The increase of the network currents associated with the bulk network system makes the protection difficult at low‐voltage grid cable fault.
New design for the high‐performance drive system for DC brushless motor
Authors: Itoh Yuzo , Naitoh Yoshitaka , Tsuchiya Takeshi
Published: July 2007

The dc brushless motor, permanent magnet‐type synchronous motor (PM motor), has been used widely in industrial robots, the machine tools for factory, and factory automations. Therefore, it is more desirable to improve the performance of the PM motor variable speed control system. Although only the torque component current is adjusted as the control method for the PM motor, so‐called Vector Control, it is expected that the developed characteristics will be added to the PM motor.

In this paper, new driving methods for the PM motor and a new design method for the variable speed control system are presented. The new motor driving methods which bring to the PM motor a new driving performance, e.g., a quick transient response or high‐efficiency motor driving, can be implemented by controlling not only the torque component current, but also the magnetizing component current. A developed optimal control theory, i.e., the error system technique, is employed for designing the control system. The control law is endowed with a steady robustness against the variation of the system parameters and the ability of compensating the delay time due to the control processing.

The effectiveness of the proposed method is confirmed by simulations and experiments.
DC conduction associated with electric field‐induced motion in mineral oils
Authors: Nakano Mitsuaki
Published: July 2007

The contributions of the electrohydrodynamic (EHD) motion to the dc electric conduction in insulating oils are presented. The effects of solid/liquid interfaces on the EHD motion have been studied with a mineral oil‐polypropylene mixed dielectric and a mineral oil single dielectric. The time dependence of current, schlieren images of EHD motion induced in the oil layer and response signals of density change in the vicinity of the electrode/oil interfaces after application of step voltage are observed.

The results are as follows: (1) the EHD motion occurs at the positive electrode/oil interfaces when a voltage above critical voltage is applied; (2) a time delay exists between the application of step voltage and the onset of EHD motion. The time is inversely proportional to the applied voltage; (3) the EHD motion increases current and produces a peak phenomena in the current waveform; and (4) the time difference between peak current time and the delay time is inversely proportional to applied voltage.
Influence of electric conductivity and pH on propagation of impulse breakdown on the surface of artificial acid rain
Authors: Nakao Yoshitaka , Itoh Hidenori , Takeda Satoshi , Matsuyama Hiroshi , Katoh Takunori , Sakai Yosuke , Tagashira Hiroaki
Published: July 2007

Recently, acid rain has become a grave environmental problem. The authors realized artificial acid rain with any electric conductivity σ and pH value by a combination of dilute sulfuric acid and seven kinds of salts based on the chemical analysis of the ionic ingredient of rainwater. In this paper, a propagation of a streamer discharge on the surface of artificial acid rain is investigated in detail by using a high‐speed Schlieren method and a current‐measuring system by LED.

The results obtained may be summarized as follows:

A flashover voltage Vf of rainwater decreases gradually with increasing the σ and an effect of the Vf on the pH cannot be seen obviously in this experimental condition;

On the propagation of the streamer discharge on the surface of artificial acid rain.

In case of rain which has nearly the same pH and the different σ, the propagation length ld of streamer‐like density changes becomes larger as the σ is made larger;

In case for rain which has nearly the same σ and the different pH, a remarkable difference cannot be seen in a propagation figure and a t‐ld characteristic of the streamer‐like density changes, and in a current waveform.
TRVs and fault clearing stresses in extra‐high‐voltage radial networks
Authors: Haginomori Eiichi , Yoshimura Kenji , Kobayashi Shunichi , Kaneko Sadanori , Yokota Takeshi , Ishikawa Masayuki
Published: July 2007

To cope with the high rate of increase of power demand in the main industrialized districts in Japan, 550‐kV transmission systems covering the districts have been reinforced, with most of the main power plants connected directly to these systems. Through 550‐/300‐kV substations, the majority of power to the districts is supplied by 300‐kV systems. To limit the excess short‐circuit capacity in the 300‐kV systems, they tend to be reconstructed as so‐called radial networks. In radial networks with high short‐circuit capacity and relatively small number of transmission lines connected to the substation busbars, the rate of rise of TRV can be far higher than standard value.

This paper analyzes the transient recovery voltages (TRV) in such extra‐high‐voltage radial networks in Japan, together with the relevant stresses to circuit‐breakers during fault clearings. Future system conditions have also been introduced. As the typical rate of rise of the TRV values, more than twice that of today's standard ones are probable.
Voltage and reactive power control using recurrent neural networks
Authors: Kojima Yasuhiro , Izui Yoshio , Kyomoto Sumie , Goda Tadahiro
Published: July 2007

Many controllers using neural networks have been recently developed. The hybrid and direct types are two major categories of such controllers. While the first type tunes the parameters of the conventional controller by means of neural networks, the latter constructs the controller by learning the inverse dynamics of the control target.

Electric power systems require voltage and reactive power (VQ) control to avoid voltage collapse. The conventional VQ control, however, meets this requirement unsatisfactorily because the control is only approximate.

In this paper, we will propose a new algorithm for VQ control using recurrent neural networks (RNNs), which have the ability to deal with the system's controlled target by means of RNNs. Second, we will apply this algorithm to VQ control. We will call this controller “neuroVQC.” Finally, the usefulness of the neuroVQC will be shown by comparison with the conventional VQ controller.
Research on high‐performance NdFeB magnets
Authors: Kaneko Yuji , Tokuhara Koki , Ishigaki Naoyuki , Majima Kazuhiko
Published: July 2007

The effects of the constituent phase of Nd‐Fe‐B magnets on sintering behavior are investigated. In the case of Nd‐Fe‐B magnets, a liquid phase forms by ternary eutectic reaction of Nd2Fe14B, Nd1.1Fe4B4 and Nd‐rich phase at 938 K. When the sintering temperature is raised above 1273 K, a remarkable shrinking occurs because of an increase in the amount of liquid phase which is supplied by the reaction between the Nd2Fe14B and the Nd1.1Fe4B4 phase. The residual flux density (Br) of Nd‐Fe‐B magnets increases in proportion to the increase in the among of the Nd2Fe14B phase. By contrast, the intrinsic coercivity (iHc) declined because of a decrease in the amount of the Nd1.1Fe4B4 and the Nd‐rich phase. As a result, new high‐performance Nd‐Fe‐B magnets with the maximum energy product of above 366 kJ/m3 (46 mgOe) have been developed by means of controlling the component ratios of these phases in Nd‐Fe‐B magnets.
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

Recovery 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

We 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

This 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

The 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

This 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

It 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

This 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.