bluuebunny/crossref_metadata_2025_split huggingface dataset:
A brushless three‐phase synchronous motor using the armature winding as both load and DC excitation winding
Authors: Shibata Fukuo , Fukami Tadashi 
Published: July 2007

AbstractThis paper presents a new brushless three‐phase synchronous motor which has no exciter. The technique applied to the motor provides an effective way for conventional brushless synchronous motors to simplify the system configuration. The stator of the motor is equipped with a double‐star connected armature winding which has two neutral points. The rotor is a cylindrical one, which is equipped with a two‐phase field winding. The field winding is connected with shaft‐mounted rectifiers.A dc voltage is applied to the two neutral points of the armature winding to obtain the rotor excitation when the motor is operated at synchronous speed. At that time. the armature winding acts as a stator dc exciting winding while also acting as a load winding.In this paper the principle and characteristics of the motor are described. and the experimental results are shown. It is confirmed that with a 2‐kW experimental machine, the proposed motor has good performance. For example, by adjusting the stator dc current, this motor power factor can easily be controlled within a wide range.
Levitation coil length optimization of a magnetically levitated train
Authors: Shibata Masayuki , Maki Naoki , Saito Toshio , Kobayashi Takashi 
Published: July 2007

AbstractAn experimental line of a magnetically levitated train (MAGLEV) using superconducting magnets (SCM) is now under construction in Yamanashi Prefecture. In the MAGLEV system, the levitation coils are mounted in the side walls. The induced current of the levitation coils generates magnetic flux that includes higher order harmonics. These harmonics generate eddy currents at the surface of the vacuum vessels of the SCM. Forces produced by interaction between the eddy current and the static magnetic field of the SCM cause evaporation of liquid helium, or SCM quenching in the worst case. The number of levitation coil layer is now restricted to one, but by removing the restriction, it is possible to reduce the amplitude of the harmonics of the magnetic flux. In this paper, the relationship of the flux amplitude to the levitation coil length is investigated; it is found that there is an optimum length at which the amplitude is minimized.
Effects of silicon content, thickness and heat treatment on iron loss properties of high silicon electrical steel sheets
Authors: Tanaka Yasushi , Namikawa Misao , Hiura Akira , Bi Xiao Fang , Takada Yoshikazu 
Published: July 2007

AbstractThe magnetic properties of high‐silicon steel sheets ranging in thickness from 0.35 to 0.03 mm and silicon content from 3 to 7.5 percent is investigated. The minimum iron losses are obtained with the silicon higher than 6.5 percent at the high‐frequency range over 30 kHz. The sheet thickness dependency index m is estimated. The heat treatment effects to soft magnetic properties also are studied.
Effect of dimension ratio on the magnetic properties of tape‐wound toroidal core with ac excitation
Authors: Saito Koichi , Shinya Kunihiro , Miyazawa Eijiro 
Published: July 2007

AbstractTape‐wound toroidal cores are used widely as magnetic devices of electronic equipment and instruments. In the design of equipment employing magnetic cores, it is necessary to know the relation between the magnetic properties of the core and the magnetic properties of the material. This paper describes the effect of the dimension ratio of the core on the magnetic properties for the sinusoidal flux waveform drive condition. In carrying out the analysis, a mode analysis in which the magnetization characteristics are approximated by a piecewise‐linear curve is adopted. From the results obtained by the numerical analysis, local flux waveforms and exciting current waveforms of the core are shown. As a result, the relation between iron loss and magnetizing apparent power of the core and the dimension ratio is derived. These results were confirmed by experiments.
Fault‐locating method using harmonic components of the arc‐voltage waveform
Authors: Okazaki Masayuki , Inaba Tsuginori 
Published: July 2007

AbstractThis paper describes a new type of the fault‐locating method by using voltage and current values measured in a substation or transmission lines. This method is based on the impedance method and consists of the following items: (1) analysis of harmonic components in voltage waveforms measured in the substation; (2) estimation of the arc fault voltage on the lines; (3) calculation of the line impedance voltage drop; and (4) determination of the fault‐locating distance.The availability of this method was confirmed by arc fault tests on 6‐kV cable and overhead distribution lines. As a result, the fault‐locating error of this method was proved to be roughly less than 10 percent.
Dual voltage converter with improved power factor and enabling voltage control
Authors: Mashiko Tomomi , Kamatani Masahiko , Sato Noriaki 
Published: July 2007

AbstractIn this paper, a novel version of the dual voltage converter is presented with improved voltage regulation and enabling a wide range of voltage control by using self‐turn‐off devices (power transistors) instead of diodes. Further, this system operates with unity displacement factor. We have obtained the analytical expressions of this circuit. The results are, however, quite complex. We could calculate values of the voltage and current waveforms by using a computer. The calculated values are essentially in agreement with the experimental values.Experimentally, an ideal load characteristic with null voltage regulation was obtained by the conduction angle control for power transistors. Further, a wide range of voltage from 220 V to 39 V was obtained.A disadvantage for this system is the requirement for snubber circuits with a larger value of capacitor in order to suppress the surge voltages at turn‐off periods.
High‐frequency link‐type dc/ac converter for ups with a new voltage clamper
Authors: Tokunaga Norikazu , Yamato Ikuo , Matsuda Yasuo , Amano Hisao 
Published: July 2007

AbstractThis paper proposes a new type of high‐frequency dc/ac converter developed for flexible, compact and high‐efficiency uninterruptible power supply (UPS) systems. The proposed dc/ac converter consists of a high‐frequency inverter, a high‐frequency transformer and a cycloconverter with a new voltage clamper. This cycloconverter is capable of being operated by both source‐commutation and self‐commutation (commutation by turning off the switching device). Consequently, by choosing between the two commutating methods, based on consideration and the internal voltage drop caused by commutating reactance, a compact and efficient UPS can be realized. The voltage clamper effectively reduces power loss of the conversion system. Fabrication of a 10‐kVA high‐frequency link‐type dc/ac converter is described and its loss reduction effect is demonstrated.
Characteristics of combined levitation and guidance eds maglev system
Authors: Fujiwara Shunsuke , Fujimoto Tsuyoshi 
Published: July 2007

AbstractA 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

AbstractThe 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

AbstractSolar 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

AbstractLaser‐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

AbstractIn 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

AbstractA 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

AbstractPower 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

AbstractTo 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

AbstractThe 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

AbstractThis 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

AbstractGlobal 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

AbstractTo 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

AbstractThis 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.