bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental analysis of lightning overvoltages induced on low‐voltage distribution lines
Authors: Imai Yasutomo , Tsuchihashi Hachiro , Asakawa Akira , Yokoyama Shigeru 
Published: July 2007

AbstractProblems have often been caused in low‐voltage distribution lines such as single‐phase 100/200 V and three‐phase 200‐V systems. For instance, the burning of low‐voltage devices and the unnecessary operation of ground fault interrupters have occurred, which are caused possibly by lightning overvoltages.Experimental analysis was performed on the generation modes of lightning overvoltages on low‐voltage distribution lines.A scale model line, one‐fourth the size of an actual power distribution line of Tokyo Electric Power Company (TEPCO), was installed for experimental analysis on the lightning protection of an overhead ground wire, an overhead common grounding wire (system neutral conductor), surge arresters and pole transformers against the overvoltages induced on low‐voltage distribution lines due to a nearby lightning stroke.A balloon was flown at a location 30 km away from the scale model line in a normal direction to it. A 200‐m long wire is suspended from the balloon to simulate a lightning path. Pulse current is applied to the simulated path using a pulse generator and the voltages induced on the line conductors are measured.This paper analyzes those overvoltages by means of the experimental and the theoretical methods.
Analysis and evaluation of integrated energy system
Authors: Matsuhashi Ryuji , Hayashi Takehito , Kaya Yoichi 
Published: July 2007

AbstractFuture energy supplies are uncertain, especially in view of environmental problems, fuel prices, and energy demand.In this paper two types of novel energy plants and a novel energy system have been proposed to cope with these conditions. The first type can utilize multiple kinds of fossil fuels and economically remove CO2 and the second can produce multiple kinds of final energy to cope with fluctuations in the energy demand.Characteristics of a novel energy system (a Flexibly Integrated Energy System; FIES), which includes novel energy plants as described in the foregoing, have been investigated with a linear programming model. A reference system has also been represented which behaves similarly to the present energy system for comparison. Computed results have demonstrated that CO2 emissions can be reduced more economically and efficiently than in the reference system if it is combined with CO2 removal systems.
Preparation of Y‐Ba‐Cu‐O tapes by pyrolysis of organic acid salts
Authors: Shiono Takeo , Nakamoto Takao , Nasu Hiroyuki 
Published: July 2007

AbstractHigh‐TC superconducting Y‐Ba‐Cu‐O films were prepared on certain ceramic and metal substrates by pyrolysis of 2‐ethylhexanoates. Only the films on MgO, yttria‐stabilized zirconia (YSZ), and Ag substrates exhibited the superconducting transition above liquid nitrogen temperature. Transition temperatures (TC) of 82, 85, and 82 K were observed in films of MgO, YSZ, and Ag substrates. The important factors in preparing superconducting films on substrates are the reactivity of the films and the substrates and the difference in their thermal expansions. The Y‐Ba‐Cu‐O films were well suited for use with MgO, YSZ, and Ag substrates. Long superconducting tapes were produced on Ag substrate; flexible tape with a critical current density JC of 3 · 103 A/cm2 at 77 K has now been prepared.
An application of the residual voltage for diagnoses for detecting irradiated degradation of insulating materials
Authors: Yamanaka Sanshiro , Kabeya Takashi , Fukuda Tadashi , Sawa Goro , Ieda Masayuki , Ito Masayuki , Kawakami Waichiro 
Published: July 2007

AbstractElectrical cables in nuclear power generating stations must be highly reliable. For further improvement of reliability, the development of nondestructive diagnoses seems desirable for cable maintenance. The authors have been studying residual voltage for developing a diagnosis of electrical cables. The purpose of this paper is to give a foundation for development of diagnostic technology for detecting the irradiated degradation; the relations between γ‐irradiation dose and the leakage current, the discharge current, and the residual voltage were studied and attempts made to calculate the amount of polarized charge and characteristic dielectric relaxation times by using data on the residual voltage. The calculated results agreed with the results obtained from the leakage current and the discharge current. These results suggest that the residual voltage in diagnostic technology for detecting the irradiated degradation can be employed.
Effect of the small arc current generated by a poor contact on the breakdown voltage in SF6 gas
Authors: Sekiya Yoshihisa , Hosokawa Tatsuzo , Morita Tadashi , Sugiyama Shuichi , Mukaiyama Yoku , Takagi Isao 
Published: July 2007

AbstractOne of the failures related to gas‐insulated switchgear is caused by the poor contact between conductors. This causes breakdown between the contact and the wall of chamber, initiated by the small discharge due to the poor contact.In this paper, the modeled experimental apparatus for the contact portion of the gas‐insulated switchgear assumed a rod‐to‐plane gap with small arc current. The influence of the arc current on the breakdown into the chamber was investigated experimentally, and the breakdown mechanism between the contacts and the wall was studied.It was clarified that the breakdown voltage between the contact and the wall decreased by increasing the current, and the small arc current in the contact portion played an important role in the breakdown between the contact and the wall.The reduction ratio of the breakdown voltage increased with increasing gap length of the small gap. The breakdown voltage was different depending on the duration of the small arc current.
Development of a 275‐kV liquid cooling‐type gas‐insulated transformer
Authors: Hasegawa Taizo , Betsui Takashi , Onishi Shuichi , Itoh Katsuaki , Kohan Toyakazu , Makino Yoshihiro , Nakazawa Hiroshi 
Published: July 2007

AbstractConstruction of 275‐kV and 500‐kV substations in densely populated areas is thought to be necessary in the future to maintain a stable supply of electricity. The use of gas‐insulated transformers is now considered for substations because such transformers are non‐flammable and nonexplosive. Since the completion of the 77‐kV gas‐insulated transformer in 1979, we have continued research to develop gas‐insulated transformers applicable to a higher voltage level up to 500 kV. As the results of the research, 275‐kV, 300‐MVA a liquid cooling‐type gas‐insulated transformer has been developed.
A method of transient stability estimation for power systems by lyapunov function
Authors: Taira Eikichi , Miyagi Hayao , Yamashita Katsumi 
Published: July 2007

AbstractThe power system stability problem has been one of the major subjects concerning power system engineering, and is becoming much more significant today due to the increasing size and complexity of interconnected power systems. In this problem, it is well known that the direct method of Lyapunov is the most suitable method of on‐line transient estimation for power systems, and several different techniques have been proposed for the construction of functions up to this time. However, the effectiveness of these Lyapunov functions for power systems have been demonstrated using only digital computer simulations.The purpose of this paper is to construct a microprocessor‐based, on‐line, transient‐stability estimation system using the Lyapunov function constructed by the Lagrange‐Charpit method, and to estimate the transient stability of an alternator connected to a large system. The experimental results show that this system can act satisfactorily for estimating the transient stability of the power systems.
Insulation performance and flashover mechanism of bridged vacuum gaps
Authors: Yamamoto Osamu , Hara Takehisa , Ohmae Kimihito , Hayashi Muneaki 
Published: July 2007

AbstractThe insulation performance and the flashover mechanism of a vacuum gap bridged by an insulator in the shape of a conical frustum have been studied. The cone angle of the insulator is varied from 0 to 45 deg and the thickness of the insulator is varied from 5 to 15 mm. The gap is subjected to a lightning impulse voltage of 2/50 μs. The insulation performance is investigated by observing the ratio of the flashover voltage of the bridged gap to that of the gap without insulators.The flashover mechanism is investigated by observing the distribution of traces on the cathode surface due to flashovers and by analyzing the electric field near the insulator‐cathode junction. Charging of the insulator due to electron collisions on its surface is considered in this analysis. As a result, it is found that the ratio is greater than 90 percent for a cone angle greater than a critical one when the top of the frustum is subjected to the positive impulses. It is found also that the trace distribution is related closely to the insulation performance.
Measurement of AC dissipation current in oil‐film composite insulating system
Authors: Tokoro Tetsuroh , Nagao Masayuki , Kosaki Masamitsu 
Published: July 2007

AbstractThe electric field dependence of tanδ in oil‐film composite insulating system sometimes has a peak and then decreases. This is known as the Garton effect. It is caused by the fact that at high voltages, the contribution of carriers in oil to the conduction loss does not last through an entire alternating field cycle. Since the separation of the loss current from the extremely large capacitive current is usually very difficult, the nonlinear ac dissipation current waveform caused by the Garton effect has not been measured.The authors developed a new method for the measurement of high‐field ac dissipation current in polymeric insulating materials. This technique was applied to the detection of nonlinear dissipation current and its waveform in oil‐film composite insulating system associated with the Garton effect. We measured the variation of dissipation current with applied field and its frequency.
Electromagnetic field analysis by boundary element method using spatial eigenmodes
Authors: Tsuboi Hajime , Naito Tadashi , Sakurai Akihiro 
Published: July 2007

AbstractThis paper proposes a boundary‐element method using spatial eigenmodes for electromgnetic field analysis. Mapping the computation model with rotational symmetries, reflective symmetries or rotational symmetries including reflective symmetries to a group of spatial eigenmodes, the equivalent reduced models are obtained. In the method, the applicability becomes wide because arbitrary external source terms can be chosen. Furthermore, in a model including asymmetry regions, a new method which can save the merit of the symmetries is proposed. Finally, the validity of the proposed method is proved by numerical simulations.
Experimental study of squirrel‐caged damper structure for superconducting generator
Authors: Maeda Susumu , Izumi Akifumi , Ueda Akinori , Sakabe Sigekazu , Kometani Haruyuki , Nomura Tatsuei , Tanaka Massaki 
Published: July 2007

AbstractIn this paper a double‐layer damper is developed which will consist of a squirrelcaged warm damper and a cylindrical cold damper as a part of a 70‐MW superconducting generator development project. To evaluate the characteristics of unbalance current capability, magnetic shielding and damping for rotor swing, a one‐half scale rotor model is constructed and an experimental study is made. From analysis of the experimental results, design guidelines have been developed and the FEM magnetic field analysis technique is refined.The main results are summarized as follows:

The squirrel‐caged warm damper has sufficient capability against negative sequence current;
Damping characteristics can be designed to be effective near the rotor swing frequency;
Flux shielding at low frequencies corresponding to quick response excitation is sufficiently small so as not to prevent field flux change; and
Magnetic field can be analyzed by the refined FEM field analysis technique which now takes into account the effects of the rotor end region by estimating the end resistance based on the eddy current flow path.
H∞ optical control applied to a generator control system
Authors: Ohtsuka Kei , Taniguchi Toshiyuki , Sato Takayuki , Yokokawa Sumio , Uyeki Yoshiteru 
Published: July 2007

AbstractThe advantages and disadvantages of H∞ optimal control as compared with LQ optimal control in generator control systems are investigated, focusing on such disturbances as 1LG faults, clearing and reclosing in the power system, and changes in terminal voltage settings and generator outputs.
Estimation method of frequency bias using normal operating data
Authors: Hamaba Kunihiro , Yokoyama Naoto , Kato Masakazu , Takabayashi Yoshiki 
Published: July 2007

AbstractA technique of calculating the frequency bias of an electric power system from frequency fluctuation data and total output power is described. An evaluation method for testing the calculations by the new method is developed. The results are in good agreement with estimates based on generator speed regulation but the method gives an excessively high figure for the load frequency bias.
A compensation method of ripple voltage on DC tachogenerator
Authors: Sekine Hideomi , Ishikawa Takeo , Sato Shinichi , Suto Tugumasa 
Published: July 2007

AbstractA dc tachogenerator has been used widely in such applications as computer peripherals and machine tools. However, this generator has some problems, e.g., the ripple voltage involved in the output voltage and the abrasion of the brush and the commutator. The ripple voltage of a general dc tachogenerator is from 1.5 to 5 percent of the output voltage. This voltage must be reduced to very small value in consideration of the influences on control systems.A compensation network of the ripple voltage on this generator was proposed in a previous paper. Here, the network is improved so as to operate effectively without losing the high response even when the rotating speed is changed slightly. The performance of the proposed network is discussed in detail, and the method for the design of the network to satisfy the requirements both of the ripple voltage and of the response time is proposed. The experimental results show that the ripple voltage is eliminated perfectly at the steady state, and that the high response is not lost.
Nonlinear magnetic levitation control by four‐point attraction
Authors: Tsuji Teruo , Takahashi Kazuo , Oguro Ryuichi 
Published: July 2007

AbstractRubber components of production equipment are a significant source of contamination in the fabrication of VLSI devices and other semiconductor products. One approach to solving this problem is to use a magnetic levitation system for noncontact transfer. The force nonlinearity of magnetic circuits presents a problem, particularly when the gap between the magnets and the levitated vehicle is small. Linearization methods that allow effective control do exist, but in this paper an alternative method not based on linearization is proposed. The design involves magnetic levitation control by 4‐point attraction. The experimental results indicate that the idea is an effective one.
Electrical breakdown and space‐charge effect in polyphenylene sulfide films
Authors: Umemura Akihiro , Hikita Masayuki , Kaneko Kazue , Mizutani Teruyoshi , Ieda Masayuki 
Published: July 2007

AbstractElectrical breakdown of polyphenylene sulfide (PPS) films, one of the high‐temperature engineering plastics, has been investigated. The results show that the dc breakdown strength is lower than the impulse one, and that the difference in electric strength between dc and impulse becomes wider as the sample thickness decreases. The result suggests space‐charge accumulation when dc voltage is applied.Further, the impulse breakdown strength in the presence of a dc prestressing voltage is measured in order to elucidate the space‐charge effect. The data on the contribution of the prestress voltage to electrical breakdown are used to estimate the amount of space charge accumulated in the specimen during the dc prestressing.
Effect of heat treatment on electrical properties of zinc oxides
Authors: Kawamura Hideaki , Yamada Katsuhisa , Nawata Masahito , Ieda Masayuki 
Published: July 2007

AbstractThe electrical properties of ZnO ceramics were studied from their voltage‐current characteristics, thermally stimulated current (TSC), and heat‐treatment effects.ZnO ceramic samples with a few mol% of insulating oxide components were prepared. After sintering at 1200°C in air, some of the sample were heat treated at various temperatures between 450 and 900°C in air.On the voltage‐current curves, the current varies as a function of applied dc voltage according to the relation I = CVα, where α is the nonlinear exponent. The nonlinear exponent α decreased with the heat‐treatment temperature in the low‐temperature region, became the lowest around 600–750°C, and almost recovered at 900°C.Three TSC peaks (designated by P1, P2 and P3 from the low‐temperature side) were observed in the nonheat‐treated samples. The samples heat treated at 600 and 750°C showed only the P1 and P2 peaks; the P3 peak increased in magnitude with the increase of biasing temperature tb, and it shifted toward the high‐temperature side.These results suggest that the electrical properties of ZnO ceramics will be associated with the phase transition of the Bi2O3‐ rich intergranular layers by heat treatment.
A method of power system simulation considering armature transients of synchronous machines
Authors: Tamura Junji , Takeda Ikuo , Hasegawa Jun 
Published: July 2007

AbstractThis paper presents a new method of simulating transient responses of multimachine power systems following a large disturbance. The conventional model used in the simulation is composed mainly of synchronous machine models in which the armature transients are neglected, and steady‐state transmission system equations. This is because it is very difficult to treat the transmission system and the armature circuits of synchronous machines as differential equations. Naturally, the model cannot evaluate the effects of these neglected transients. The new method proposed herein uses the new synchronous machine model and the steady‐state transmission system model. The former is obtained by modifying slightly the conventional armature‐transient neglected model. Thus the resultant simulation model has almost the same structure as the conventional one. However, it can evaluate approximately the effects of armature transients on the dynamical behavior of the synchronous machines. For example, it can evaluate easily the angular backswing following a three‐phase short‐circuit fault. In addition, the new method can also estimate the maximum values of developed torque, induced voltage and armature current of synchronous machines at the moment when the disturbance occurred and when it was cleared.
Generalization of transient stability solution using neural network theory
Authors: Ikenono Katsumi , Iwamoto Shinichi 
Published: July 2007

AbstractThis paper presents a generalized online transient stability solution technique using the backpropagation method of the neural network theory. The proposed solution technique can be used for general generator models, including controllers such as AVRs and governors, that have been difficult for the energy function method to handle. The proposed method also considers alterations of network configurations and changes of the number of operating generators. Further, the relationship between input data and effects on the results of the neural network is considered.
A dual thyristor converter reducing harmonics of power supply without input transformer
Authors: Matsui Keiju 
Published: July 2007

AbstractIn general, the thyristor‐controlled rectifier circuit (thyristor converter) generates a large amount of harmonics in the input power supply. Consequently, in the power system, the harmonics become more increased for larger capacity of such a converter, thus it is important to improve their harmonic characteristics. Among such converters, the double three‐phase bridge converter with transformer of star and delta windings is well known. By application of such techniques, Miyairi and his group proposed a thyristor converter which has excellent harmonic characteristics. On the other hand, the multiple‐connected inverter circuit without output transformer had been already proposed. However, it contains the lower‐order harmonics.This paper proposes a converter which can reduce the harmonics similarly to the forementioned double‐bridge converter. This circuit has the center‐tapped reactor that can control the dc current like the current control of Miyairi's interphase reactor. This novel converter need not use the input three‐phase transformers that usually make the cost higher. The proposed circuit has a commutation one with capacitor that is analogous to the series diode‐type thyristor inverter. This circuit maintains the commutation to operate successfully with constant reverse bias time. The entire circuit operation and the commutation circuit operation are discussed and confirmed experimentally and theoretically.
Single‐phase PWM converter using balanced two‐phase rectification
Authors: Hashimoto Tatusaki , Sone Satoru 
Published: July 2007

AbstractEnergy storage devices, such as inductors or capacitors, are needed in single‐phase ac to dc converters because instantaneous power flow of input single‐phase ac is inherently pulsating and output dc power must have as little ripple as possible. Energy storage devices (such as smoothing inductors or capacitors) are usually inserted on the dc side. In those converters, energy storage ability of the devices cannot be used effectively, especially when dc power ripple is required to be very small.To solve such a problem, this paper presents novel single‐phase ac/dc conversion circuits, in which energy storage devices are used at the ac rather than at the dc side. That is, after converting single‐phase ac into balanced (rectangular) two‐phase ac using variable reactance element, reconversion of it into dc is carried out.This paper presents a control method for the converters and the variable reactance devices, and performance of the proposed circuits is confirmed using computer simulation.
Air gap flux analysis for cage rotor diagnosis
Authors: Morita Ikuro 
Published: July 2007

AbstractThe relationship between the magnetomotive force distribution of a three‐phase induction motor and various cage rotor faults, such as broken bars and end rings, is discussed in detail. Search coil output and its harmonic components are analyzed to allow the determination of faults from the air‐gap flux density. The results obtained in tests on a motor into which faults were intentionally introduced confirm the effectiveness of this method of analysis.