bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of surfactants on superstructure and dielectric breakdown strength of crosslinked polyethylene insulation
Authors: Ishida Masayoshi , Okamoto Tatsuki 
Published: July 2007

AbstractThis paper describes the influences of a surfactant on crosslinked polyethylene (XLPE) insulation. Several kinds of additives are mixed into the insulation in order to improve the dielectric breakdown strength of XLPE cables. It has been verified that the interfacial diffusion method, which modifies the interfacial region between the insulation and the semiconducting layer by a surfactant, is effective. The effects of the surfactant on the morphology in the XLPE insulation were studied with two kinds of specimens.In the first kind of specimens, a mill was used to disperse the surfactant throughout the insulation material. Alternating current dielectric breakdown tests were performed on disk specimens. Their average breakdown strengths were improved, but the breakdown strengths were not increased at the low probabilities of the hazard function. In the other specimens, the surfactant was milled into the semiconducting layer, and later allowed to enter the insulation by diffusion during the high‐temperature crosslinking process. It was found that the average breakdown strengths were improved further. Moreover, the breakdown strengths were found to increase significantly at the low probabilities of the hazard function.The two kinds of specimens were followed by material analysis using analytical methods, such as TEM, FT‐IR, etc. Results from the milled specimen indicated that the improvement in property was probably due to the increase in density of the amorphous portion, the increase in the lamella thickness, and the increase in spherulite radius created by the additive content. Therefore the insulation near the interface where a concentration gradient was established by diffusion from the semiconducting layer is considered to have similar morphological changes caused by the additive. In addition, the diffusion specimen was observed to have an absence of introduced microdefects that existed in the milled specimen.
Preventive control in an autonomous decentralized system
Authors: Kurihara Ikuo , Takahashi Kazuhiro 
Published: July 2007

AbstractFor more rational operation and control of future electric power systems which would continue to expand in size and complexity, an autonomous decentralized control system is proposed as one of the new control architectures. In the autonomous decentralized control system, each generating station and substation behaves independently and cooperatively without being controlled by the central station. Besides the inherent fault‐tolerant characteristics of the architecture, flexible and rapid control depending on the circumstances can be achieved.In this paper, the fundamental logic of preventive control in an autonomous decentralized system is developed. It is based on the bidding method in which each station proposes its own output taking into consideration its own situation and cooperation with others. The economic load dispatch including preventive control can be performed, based on the bidding rule adopting the equivalent incremental generating cost curve in which the security constraints are incorporated. Application of the logic to a model system revealed satisfactory control performance for preventing the overload of transmission lines and the undervoltage.
A new combined system of active and passive filters to obtain harmonic compensation for large‐capacity thyristor converters
Authors: Tanaka Toshihiko , Akagi Hirofumi 
Published: July 2007

AbstractShunt passive filters, which are connected in parallel to harmonic‐producing loads, have been used widely for harmonics suppression in power systems because of low cost and high efficiency. However, they have such inherent problems as series and parallel resonance. On the other hand, shunt active filters, which are also placed in parallel, have such an inherent problem as initial and running costs are high compared with those of shunt passive filters. To solve these inherent problems in shunt passive and shunt active filters, the authors have proposed a combined system of a shunt passive filter and a small rated series‐active filter.The purpose of this paper is to reduce the required rating of the series‐active filter, considering a practical application of the combined power filter to harmonic compensation for large‐capacity thyristor converters. The points are summarized as follows:

The required rating of the series‐active filter can be reduced less than one‐tenth by connecting a series‐resonant circuit in parallel to the secondary of current transformer.
It is clarified theoretically and verified experimentally that compensation characteristics of the new combined system are equivalent to those of the already‐proposed system with no series‐resonant circuit.
An AC voltage switching regulator with instantaneous output voltage control
Authors: Nomura Hiroshi , Kawasaki Naoya 
Published: July 2007

AbstractThis is the first attempt to control the instantaneous output of an ac/ac direct power converter. The ac chopper‐type regulator has the potential ability of quick response to the control command. However, detecting the mean or effective value of the ac output voltage, as is commonly done in the conventional closed‐loop ac regulators, greatly degrades the inherent fast response capability of the chopper circuit.The proposed ac switching regulator adopts the Cuk converter for the main circuit and an instantaneous voltage control technique. A practical state feedback scheme together with the integral control was devised to stabilize the system and also minimize the steady‐state error. The response speed is so fast (about 300 μs with resistive load) that the converter can produce a sinusoidal output voltage even from a distorted source voltage. The four‐quadrant operation can handle any kind of ac load. A complete analytical description and relevant design data of this new regulator are provided with some experimental results.
Ac losses in superconducting coils
Authors: Akita Shirabe , Ishikawa Tadao , Tanaka Toshikatsu 
Published: July 2007

AbstractAC superconducting wire is being developed for such electrical equipment as superconducting transformers and superconducting generators. AC loss reduction is of primary concern in the development of such high‐efficiency equipment. In reducing ac losses, it is necessary to develop assessment methods for ac loss in test samples which have shapes similar to the end‐product equipment.This paper described a least squares calculation of ac losses of superconducting wire as a function of frequency and magnetic field strength measured in test coils.Two sample solenoid coils were made to test the influence of different capacities and winding methods on ac losses in ac superconducting coils with rated capacities of 500 kVA and 20 kVA, and impregnated (epoxy resin) and nonimpregnated windings.The ac losses in the superconducting coils were measured by a calorimetric method using the evaporating rates of liquid helium. Estimated ac losses in the superconducting wire of the two coils were compared with Joule losses of copper conductors at ambient temperature. As a result of this comparison, a low‐loss ac superconducting wire winding can be made for electrical equipment rather than employing conventional copper winding when used under low magnetic fields less than 0.5 T.
Optimal capacities of large‐ and small‐scale power plants in the face of uncertain demand
Authors: Matsuhashi Ryuji , Ishitani Hisashi , Hayashi Takehito , Kaya Yoichi 
Published: July 2007

AbstractThe future demand for electricity is uncertain and difficult to forecast, but it is necessary to do so in order to construct power plants. In that sense, a large‐scale power plant is disadvantageous because it takes a long time to construct. On the other hand, although it takes less time to construct, a small‐scale power plant is more expensive. Therefore large‐ and small‐scale power plants could complement the disadvantages of each other. This paper develops a stochastic dynamic programming model to investigate the possibility. The model determines the capacities of large‐ and small‐scale power plants in the face of uncertain demand to minimize the expected value of the total cost. Computed results have shown that small‐scale plants can play a significant role in this case even if they are more expensive than large‐scale plants.
Practical method for generation expansion planning based on dynamic programming
Authors: Tanabe Ryuya , Yasuda Keiichiro , Yokoyama Ryuichi 
Published: July 2007

AbstractThis paper presents an efficient method which provides the optimal generation mix and the optimal generation construction process. The approximation method in which the dynamic programming technique and gradient method are combined is applied to determine the optimal generation mix with hydropower generation technologies. The successive approximations dynamic programming (SADP) technique, which is very suitable for high‐dimensional multistage decision process problems, is used for obtaining the optimal generation construction process. The effectiveness and feasibility of the developed technique are demonstrated on a practical power system model which has five types of generation technologies including a hydropower generation technology.
Measurement of the radial temperature distribution in the central part of an arc burning through a polyethylene tube
Authors: Takikawa Hirofumi , Sakakibara Tateki , Miyashita Mafumi , Kito Yukio , Sakuta Tadahiro 
Published: July 2007

AbstractThe radial temperature distributions in the central part of arcs burning through polyethylene (PE) tubes are estimated by measuring the half‐width of Hα line spectrum and using the electron density versus Stark half‐width and the electron density versus temperature characteristics. Estimation is carried out for various tube inner diameters (2 and 4 mm) and dc arc currents (5, 10 and 15 A). The result shows that the temperature at the arc center is around 10,000 K, and it tends to increase as the tube inner diameter becomes narrow and/or the arc current increases.The overall temperature distributions from the arc axis to the tube wall are obtained by combining these inner temperature distributions with outer temperature distributions which have been derived from C2 spectra. They are found to take a form of typical two‐temperature distributions of ablation stabilized arcs.The electric field strengths of PE arcs are evaluated from the temperature distributions and the electrical conductivity versus temperature characteristics of thermally decomposed polyethylene vapor gas. The results agree well with experimental values.
Development of railgun accelerator at the institute of space and astronautical science (ISAS)
Authors: Yamori Akra , Yanagisawa Masahisa , Kawasima Nobuki , Furukawa Suguru 
Published: July 2007

AbstractThis paper describes the current status of the development of electromagnetic launchers such as the railgun at ISAS. The railgun is the most improved accelerator of Electromagnetic Launchers (EML). EML offers a potential for accelerating a projectile to much greater velocities than achieved with conventional powder guns or light gas guns. However, there has been little progress in increasing the velocity of EMLs since the experiment by Rashleigh and Marshall. A few experiments have been reported achieving velocities greater than 6km/s.The authors have achieved velocities greater than 6 km/s by reducing plasma leakage which is one of the factors limiting velocity.In this paper a 6 km/s launch is reported, compared with the results of two other shots considered from the viewpoint of plasma leakage, and the effect of entrainment of eroded material into the armature by rail ablation was discussed on the basis of simulated numerical calculations.
Decentralized voltage control in multiarea power system
Authors: Iwase Noriyuki , Okada Kenji , Yasuda Keiichiro , Yokoyama Ryuichi 
Published: July 2007

AbstractThis paper discusses the feasibility of a decentralized voltage control scheme for large‐scale power systems. The algorithm is intended to apply to a reactive normal operating state from an emergency state caused by illcondition and also to keep the operating state away from approaching unstable boundaries in preventive control. The procedure for releasing voltage deviation (over/under voltage) is formulated as a multistage decision process over a certain time interval. The optimization problem is transformed into a two‐point boundary value problem using the discrete maximum principle and is solved easily by using the discrete Riccati equation.For a large‐scale power system, control values must be computed from a large number of state variables, and this inevitably prolongs the slow dynamics with controllers. The centralized control system in a large‐scale system cannot be justified from the economical and technical viewpoints. To resolve the foregoing problems, a decentralized voltage control system incorporating slow voltage dynamics is presented.
Effect of applied voltage frequency on swarming pulsive microdischarges in closed voids
Authors: Hasegawa Taketoshi , Kimura Ken , Shibuya Yoshikazu 
Published: July 2007

AbstractThe extinction of the partial discharge (PD) pulse has frequently been observed in an epoxy specimen with a closed void during voltage endurance tests using a CIGRE Method‐II electrode. The individual discharge pulse becomes so small that the discharges cannot be detected by conventional pulse detection methods. Such discharges are known as “swarming pulsive microdischarges” (SPMD).In this paper, the SPMD characteristics are investigated by varying the frequency of the applied voltage from 0.1 to 240 Hz. As a result, the SPMD are found to occur less frequently as the frequency is lowered. To seek this cause, one‐shot voltages were applied repeatedly at constant intervals. By varying the interval from 0.02 to 100 s, the PD off an electrically aged specimen was measured. It was revealed that the discharge magnitude increases as the interval becomes longer. The onset of SPMD was found to depend on the preceding discharge. The results explain the reason why swarming is harder to occur at lower frequency with a longer discharge interval. Hence, in the conventional pulse detection, it is useful to employ the very low frequency for diagnosis of machine insulation containing enclosed voids.
Stabilization of a fully superconducting, damperless generator by excitation control
Authors: Tsukamoto Osami , Chen Jianzhong , Morimoto Akihiro , Akita Shirabe 
Published: July 2007

AbstractThe development of ultrafine filaments superconductors for 50/60 Hz makes possible a fully superconducting generator which has superconducting field windings and armature windings. By omitting dampers and narrowing gaps between the field and the armature windings, the size and the weight of the fully superconducting generator can be drastically decreased. However, the damperless generator is inherently unstable and thus must be stablized by an appropriate method. We have investigated a method of stabilizing the generator in which the excitation voltage of the field winding is controlled by the state value feedback technique. The state values of the system are estimated by a state‐value observer and the feedback constants are determined according to optimal control theory. It is shown that this method is effective in stabilizing a fully superconducting, damperless generator.
Power‐generating performance of alkali metal thermoelectric converter
Authors: Masuda Toshihisa , Negishi Akira , Tanaka Kotaro , Honda Takeo , Fujii Takahiro 
Published: July 2007

AbstractThe alkali metal thermoelectric converter (AMTEC) utilizing the sodium ion conducting β‐alumina is a device to convert heat energy to electric energy directly. It is characterized by high conversion efficiencies, high power densities, no moving parts and low maintenance requirements. Because of these merits, AMTEC is one of the most promising candidates for aerospace power systems, remote power stations and dispersed small‐scale power stations.In this paper, the experimental results of the series‐connected cells and the theoretical considerations about internal resistances have been reported. For the single cell, the open voltage of 1.37 V and the maximum power of 7.89 W and maximum power density of 0.40 W/cm2at the sodium temperature of 1077 K have been obtained. For the two series‐connected cells, the open voltage of 2.60 V and the maximum power of 12.3 W at the sodium temperature of 1016 K have been obtained. This power was about 90 percent of the sum power of two cells. This power decrease is due to the resistance of the current‐collecting busbar. It is necessary to optimize the current‐collecting busbar considering the electrical resistance and heat conductance.
An analysis of the field acceleration method and of vector control of induction motors
Authors: Tsuji Mineo , Yamada Eiji , Yamada Katsuhiro , Oyama Jun 
Published: July 2007

AbstractThe two‐axis theory and vector control based on this theory are well known. On the other hand, Yamamura has proposed the phase segregation method (spiral vector method) for the analysis of induction motors along with the field acceleration method (FAM). In this paper these analytical and control methods are compared.We begin by analyzing the equations for phase segegation, which contain information derived from the three‐phase stator and rotor equations. We next demonstrate that the vector control system for constant rotor flux is obtained from the type T‐I type field acceleration method when the transient term is zero. By By using the equivalent circuit for a T‐I transient, we readily obtain the desired vector control system, because the circuit is identical to the steady‐state circuit when the rotor flux is constant. An analytical solution of the transient response for the vector control system is obtained for arbitrary initial conditions. Finally, the stability of type T‐II FAM is discussed, with special emphasis on the effect of changes in stator resistance, by computing the torque transfer function. When the stator resistance is correctly estimated, pole‐zero cancellation occurs on the imaginary axis.
Analysis of characteristics of half‐wave rectified brushless synchronous motor with permanent magnets
Authors: Oyama Jun , Higuchi Tsuyoshi , Abe Takashi , Yamada Eiji 
Published: July 2007

AbstractPreviously, the authors proposed a “half‐wave rectified brushless synchronous motor” as a novel servomotor. The rotor winding emf of the motor is induced by the stator current mmf which rotates at synchronous speed and pulsates at bias frequency. The field excitation is produced by the field current obtained from rectifying the emf with a diode inserted into the field winding. To improve the power factor and the efficiency, they also proposed a new‐type half‐wave rectified brushless synchronous motor with permanent magnets.This paper analyzes the flux distribution and the torque characteristics of the new half‐wave rectified brushless synchronous motor using the finite element method. The computed torque characteristics are confirmed with the experimental results.Furthermore, the steady‐state characteristic equations are derived and the effect of the modulation function waveforms on the motor performance is investigated. The theory also is confirmed by the experiments.
High‐power active filter using LC‐tuned filter
Authors: Takahashi Isao , Omura Yasushi 
Published: July 2007

AbstractUsually, to eliminate the harmonics of transmission lines, LC tuned filters are employed to bypass these harmonic components. However, the elimination ability is limited by its damping resistance. Therefore, active filters composed of high‐frequency PWM converters are desirable. In comparison with the LC tuned filters, the cost would be very high even in high‐power systems.In this paper, a low‐cost and high‐power active filters for a dc transmission system is proposed. It has active filter ability as well as low cost for high‐power uses. Its main circuit is composed of conventional LC filters in series with square‐wave voltage inverters. The voltage of the inverter is controlled to cancel the voltage drop of the internal resistance of the LC filter. Thus the Q‐factor of the filter can appear at infinity. Calculation of the harmonic and the control are done by DSP (TMS 32010). In the experimental system and simulations, two three‐phase tuned filters, 5th and 7th, are employed. Excellent results under 1 percent distortion voltage are obtained.
Coordinated stabilizing control for large‐scale interconnected power systems, by superconducting magnetic energy storage unit and power system stabilizers
Authors: Mitani Yasunori , Tsuji Kiichiro , Murakami Yoshishige 
Published: July 2007

AbstractThe purpose of large‐scale power system interconnection is to achieve extremely economical and reliable power generation and transmission. It has established the present power systems of high quality. On the other hand, in the large power systems with complex configuration, an undamped power swing with low frequency caused by the synchronous power between interconnected systems tends to occur as well as an undamped power swing caused by the synchronous power of specific generators.Several coordinated stabilizing control schemes for the power systems by sets of power system stabilizers (PSSs) have been investigated so far. PSS is very effective for the stabilization of power swing among a few specific generators because the function of PSS is achieved by the voltage control using the generator field winding circuit. However, it seems that PSSs do not have sufficient ability to stabilize the power swings between interconnected systems.In this paper, the superconducting magnetic energy storage (SMES) which is significantly effective for the power swings between interconnected systems is introduced and a coordinated power system stabilizing control by SMES and PSSs is proposed. The advantages of the proposed control scheme are: 1) high efficiency of the controller by the distribution of functions; 2) independency of the control design for PSS and SMES; and 3) robustness of the controller, and so on.
A hypersimulation‐based learning environment for operator understanding of complex phenomena in power systems
Authors: Yoshizawa Junichi , Muto Syoichi , Ueda Takao , Nishida Shogo 
Published: July 2007

AbstractThis paper proposes a simulation‐based learning environment called hypersimulator, as a thinking tool to enhance operators' understanding of complex phenomena in power systems. The hypersimulator is literally a simulator fused with a concept of hypertext, a personal visual simulator with user interfaces viewing multiple aspects of the phenomena in power systems.In the field of power system engineering, training simulators are used for operators to obtain the so‐called skill‐based and rule‐based expertise of an operation. However, the training simulators are not effective enough to provide knowledge‐based expertise based on deep understanding of a mechanism of complex phenomena. An aim of the hypersimulator is help the novice operator obtain such expertise through examining the phenomena and developing effective mental models (internal models formed in a person's mind) of them. The approach here to designing the system is a user‐centered one based on cognitive science and analysis of characteristics of power system phenomena and operators' ways of thinking.In this paper, first, the characteristics of operators' ways of thinking are analyzed as the preliminary investigation to obtain a basic design concept. Second, the concept and the features of hypersimulator are discussed. Finally, the effectiveness of the system is demonstrated using simulation of phenomena in power systems.