bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of extruded ethylene propylene rubber insulated superconducting cable
Authors: Kosaki Masamitsu , Nagao Masayuki , Mizuno Yukio , Shimizu Noriyuki , Horii Kenji 
Published: July 2007

AbstractA superconducting power cable is one of the promising ways of underground transmission of huge electric power in the future. The authors have long proposed the idea of the extruded polymer insulation for superconducting cables. The prominent features of the design are to exploit the excellent electrical properties of polymer in the cryogenic temperatures and to separate the helium coolant from the electrical insulation. Although the extruded cross‐linked polyethylene cable has proved ability at the liquid nitrogen temperature, the cable insulation cracked due to mechanical stress during cooling to the liquid helium temperature.To overcome this problem, ethylene propylene rubber (EPR) was selected as a new insulating material considering the good results of mechanical and electrical tests of EPR samples at cryogenic temperatures. An extruded EPR insulated superconducting cable 15 m in length was fabricated and a cooling test down to the liquid helium temperature and a voltage test at the liquid helium temperature were carried out with fair success. This is a breakthrough in terms of the electrical insulation design of cryogenic cables.
DSP‐based real time output waveform synthesis for three‐phase PWM inverter
Authors: Ishihara Kiyoshi , Kawamura Atsuo 
Published: July 2007

AbstractA new digital control technique is proposed to synthesize an arbitrary three‐phase PWM inverter output. Sensing two line‐to‐line voltages, the required pulse patterns for deadbeat response are computed in a real time manner based on the predicted voltage by an observer at 18‐kHz sampling frequency. When used for the uninterruptible power supply, this closed‐loop voltage control inherently results in a very low THD and a very quick transient response with less filter capacity. Also, with the repetitive compensator, the proposed scheme has advantages in improving the output waveform for nonlinear load. This paper describes the modeling technique, theoretical analysis, simulations and experimental results.
Fundamental characteristics of a brushless and self‐excited sinusoidal‐wave single‐phase synchronous generator having a two‐phase field winding excited by a half‐wave rectified current
Authors: Shibata Fukuo , Naoe Nobuyuki 
Published: July 2007

AbstractIt is desired from the viewpoints of maintenance and construction to make single‐phase synchronous generators of brushless and self‐excited types.A novel brushless and self‐excited single‐phase synchronous generator was devised by one of the authors. The stator exciting current is made to flow simultaneously with the load current in the armature winding. Thus, the iron core for the magnetic circuit can be both for the synchronous generator itself and for the exciter.Experimental studies of the brushless and self‐excited single‐phase synchronous generator of which the rotor winding is used as a rotor exciting winding and a field winding are described in this paper.In the proposed generator, the rotor is provided with a balanced two‐phase field winding to improve the voltage wave distortion. The terminal voltage of this generator can be kept constant in spite of the load variation. Therefore, the proposed synchronous generator can be expected to be used widely.
On‐line preventive control for power system transient stability based on the energy function method
Authors: Kita Hirokuyi , Nishiya Ken‐Ichi , Hasegawa Jun 
Published: July 2007

AbstractFor the purpose of maintaining the power system security, an integrated security monitoring and control (ISMAC) system, is being developed in which both preventive and emergency control have important roles. Static security control strategies which deal with the steady state after the contingency is cleared, have been studied by various researchers including the authors. However, the basic research on dynamic security control which deals with the transient state immediately after the contingency has occurred is seldom found.This paper presents a method of dynamic preventive control for the transient stability considering plural contingencies and coordinating in a flexible way the requirements of both security and economy.In the preventive control for transient stability, it is necessary to judge the transient behaviors properly and also to evaluate the security quantitatively for a postulated contingency. The authors define a security index which represents absorbing capacity of post‐fault kinetic energy based on the energy function method. The index has these advantages: it is possible to calculate values rapidly; and physical meanings are easily understood. The effectiveness of the proposed method is ascertained through numerical examples for model power systems.
Direct calculation of voltage‐stability limit of electric power systems
Authors: Suzuki Mamoru , Masegi Ken 
Published: July 2007

AbstractOn‐line monitoring of voltage‐stability conditions is a new requirement for the energy management systems of the electric power industry. Preferred by the utility engineers and dispatchers is an index which represents explicitly the margins to a voltage‐stability limit (collapse point) expressed in a physical unit ordinarily used. For example, such indices are the system load and voltage‐voltage‐stability‐margins (SVVSM) between the present operating point and a voltage collapse point. However, long computer time is required to calculate accurately the voltage collapse point by the conventional method because many multiple load‐flow solutions are required.This paper presents a new algorithm to calculate directly, exactly, and rapidly the voltage‐stability limit. The algorithm uses the load‐flow equations and the explicit expressions of the voltage collapse root conditions are expressed as dR/dV = 0, where R is active or reactive power node injection, and modifying the conventional N‐R load‐flow program, and is not affected numerically by singular Jacobians. The proposed algorithm is verified through calculating the voltage stability limit of a 176‐node power system.
Fault location for transmission lines using inference model neural network
Authors: Kanoh Hitoshi , Kaneta Masahisa , Kanemaru Kimaharu 
Published: July 2007

AbstractThe authors propose a new fault location method that uses a neural network to analyze the distribution pattern of the ground wire current along the power line. This method is able to locate the fault section even for secondary power lines with complicated configurations. The method is based on the inference process, i.e., human experts will analyze the distribution pattern of the current amplitude and phase angle. In locating fault sections, higher precision than ordinary three‐layer neural network or the expert system of previous development can be obtained.The proposed neural network comprises three sets of three‐layer neural networks which follow the back‐propagation learning procedure. The 1st and 2nd neural networks calculate the candidate‐1 and candidate‐2 for the fault section using current amplitude and phase angle distribution patterns, respectively. The 3rd neural network then performs final fault location using these candidates and a current amplitude distribution pattern. The results evaluated with all possible fault causes indicate that the new method is precise to as high as 98.4 percent even when the measured values differ by 30 percent from predicted ones with EMTP.
Three‐phase voltage‐fed type PWM power converter via power factor control
Authors: Ohnishi Tokuo 
Published: July 2007

AbstractRecently, the voltage‐fed type PWM converters have been investigated for their ideal and inherent properties as a dc power source. However, the current control system generally used may be somewhat complicated due to dc voltage detection.We propose here a simple control system of the PWM converter using the power factor control in which dc voltage detection is not always needed. In this system, the dc voltage is given by the line voltage and the modulating index of the PWM converter.The principle of the PWM control system is shown at first. From the simplified circuit model and its phasor diagrams, some basic relations of the PWM converter system are obtained and some fundamental characteristics are shown. From these investigations, it is seen that the phase control region is restricted to a certain angle, which depends on the setting power factor, the modulating bypass index of the PWM and the load. Under the operating condition of unity power factor, it is given by ±π/4 for both the converting and inverting operations. The system can be operated over the all‐control range of the modulating index by restricting the angle to this critical value for the angle over this control range.The ideal operating characteristics as a dc power source can be verified by some experimental results, including the operating waveforms of line current, the steady state characteristics and the transient response between both operations of the converter and inverter.In this system it is simple to construct the control circuit; it also has some inherent and excellent characteristics as a voltage fed type dc power source.This control system may be applicable to any types of PWM converter used today.
Examination of simple analytical method for calculating 60‐Hz magnetic field in power substations
Authors: Hayashi Noriyuki , Katsuo Isaka , Yokoi Yoshihide 
Published: July 2007

AbstractIn the last decade, increasing attention has been paid to ELF (Extremely Low Frequency) electromagnetic environments in work areas as well as in and near homes, regarding their interaction both with electric apparatus such as CRT's and with biological systems. Experimental and theoretical analyses are presented of 60 Hz magnetic field (B‐field) characteristics at and near ground level in both 187/66‐kV EHV and 66/6.6‐kV HV power substations.Experimental results of B‐field profiles along horizontal paths as well as harmonic contents in B‐field waveforms at several positions are shown and discussed.Furthermore, analytical B‐field profiles calculated by using a B‐field approximation method based on Biot‐Savart law are shown and compared with the measured ones. The comparisons verify that the assumptions employed are applicable to the substation B‐field calculation, and that the B‐field calculation method employed can estimate B‐field in EHV and HV power substation to significant accuracy, except for areas where localized B‐field sources, such as power transformers and underground power cables, exist. The analytical profiles of three orthogonal components of B‐field are also described in terms of equiflux contour maps, which show 3‐D characteristics of B‐field in power substations.
Optimal scheduling of hydraulically coupled power plants with runoff prediction
Authors: Yamashiro Susumu , Nakamura Kouichi , Hiraki Toshiyuki , Tatekoji Takashi 
Published: July 2007

AbstractThis paper discusses an optimal short‐range scheduling of multireservoir hydrothermal power systems considering runoff prediction. Using Prasad's rainfall‐runoff model and the Kalman filter‐based, second‐order filtering technique, the hour‐by‐hour characteristic is estimated for a given short‐range forecasted rainfall pattern. Unlike the usual hydroscheduling problem in which a single‐reservoir operating condition is specified at the end of the scheduling period, various end point conditions are examined to deal with the predicted runoff characteristic and to avoid possible water spillages from reservoirs.Dynamic Programming Successive Approximations are applied successfully to obtain optimum operating strategies for many end point conditions at a time. A rapid convergence characteristic coupled with a simple computation algorithm makes the proposed method one of the attractive approaches for scheduling of complicated multireservoir hydrothermal systems considering runoff prediction.
An algorithm for discrete optimal power flow
Authors: Fan Mingtian , Aoki Kenichi , Nishikori Akimine , Nara Koichi 
Published: July 2007

AbstractThis paper presents a new algorithm to solve an optimal power flow problem which can take into consideration the discrete nature of some facilities in power systems. The optimal power flow problem is formulated as a nonlinear mixed‐integer programming problem in which the number of transformer taps and the number of shunt capacitor units and reactor units are treated as discrete variables.This paper attempts to solve such a large‐scale nonlinar mixed‐integer programming problem by some effective programming techniques. The optimization procedure of the algorithm is that the nonlinear mixed‐integer programming problem is linearized iteratively and solved by an approximation method for linear mixed‐integer programming.A fundamental feature of the algorithm is that it can guarantee a solution which is discrete, feasible and near‐optimal. The validity and efficiency of the algorithm is demonstrated by the numerical results of real‐scale optimal power flow problems.
Power swing analysis in a future metropolitan electric power system on a contingent trip of cryogenic high‐power cables
Authors: Hayakawa Naoki , Kito Yukio , Matsumura Toshiro 
Published: July 2007

AbstractA cryogenic power cable is expected to be capable of carrying bulk power as a main transmission line in a future metropolitan electric power system. It is important to establish a strategy of how to sustain power supply when such a highly densified power supply route trips from the network due to contingency.It is proposed here that the bulk power transmitted by the cryogenic cable could be distributed into the parallel conventional transmission lines by suitable circuit breaker operations in the system. In this process, power‐flow routes are forced to be changed with a remarkable modification in the system configuration.In this paper, the power swings associated with the large power‐flow change following contingent faults are analyzed by means of a transient network analyzer. It is found that the proposed system modification could be realized without any harmful power swing if the parameters in generators as well as in control devices have conventional magnitudes. It is shown also by simulations that the margin to occurrence in an unstable power swing is left sufficient even if the parameters deviate somewhat from the present magnitudes.
Fabrication and fundamental characteristics of a superconducting air‐core autotransformer
Authors: Ishigohka Takeshi , Okada Naotaka , Kamijo Hiroki , Yamamoto Mitsuyoshi 
Published: July 2007

AbstractWith the recent advent of high‐performance ac superconductors with very small ac loss and large current‐carrying capacity, the possibility of an air‐core superconducting transformer is being studied. Although the exciting current is very large, the air‐core transformer has the following merits: (1) no iron loss; (2) no insulation care of the core; (3) no harmonics, and no in rush current induced by iron saturation, etc. Thus, the authors fabricated and tested a small experimental transformer (2.5 kVA, 330/150 V). As easily predicted, the exciting current becomes very large. It occupies about 45 percent of the rated current. Meanwhile, the leakage reactance increase considerably. The %IX becomes about 28 percent. These experimental results show good agreement with the theoretical analysis based on an equivalent circuit.
Influence of AC‐DC parallel interconnection on voltage stability of AC systems
Authors: Tada Yasuyuki , Yokoyama Akihiko , Sekine Yasuji 
Published: July 2007

AbstractThe static and dynamic characteristics of power supply to each node in a hybrid ac‐dc power system are analyzed by means of static and transient P‐V curves. Three kinds of dc transmission control scheme are compared. DC transmission systems are more effective in delivering power to inverter nodes. The constant firing angle, constant current control techinque provides more power to inverter nodes than the conventional constant current, constant voltage and constant power, constant extinction angle techniques. Transient digital simulations indicate that dc interconnection improves voltage stability to both the opening of a dc interconnected line and one‐line opening of ac double‐circuit interconnected lines.
Three‐dimensional magnetic field analysis by T‐Ω method using the finite element method coupled with integral equations
Authors: Tanaka Yoshifumi 
Published: July 2007

AbstractThe electromagnetic quantities of the magnetic bodies and conductors are calculated by the Finite Element Method with Integral Equation and it is not necessary to divide the free air space. The field at an arbitrary point in the free air is obtained from the Integral Equation after the FEM‐IEM analysis. In this paper, the magnetization is written in the terms of the unknown total scalar potential Ω, and the current vector potential T is added in the conductors. In order to calculate the unknowns defined in only the substances by FEM, it is necessary to establish the boundary condition by IEM. Then the calculation of the boundary condition on the surface of magnetic body requires high technical skills, so the formulation presented in this paper is improved by integration of parts. Results of the standard models specified by the I.E.E. of Japan suggest the validity of our method.
Digital input filters for measurement, control and protection of electric power systems
Authors: Kido Mitsuyasu , Chiba Tomio , Kudo Hiroyuki , Kawakami Junzou , Kawai Tadao 
Published: July 2007

AbstractPower system control and protection equipment has required higher sensitivity and operational reliability than conventional one.Studies of digital signal processing suitable for electric power systems fulfill this objective using fast sampling and digital filtering by a 32‐bit floating point DSP (Digital Signal Processor). The sampling rate of 3 kHz is carefully selected in order to separate the power spectrums of the A‐D conversion output errors from the signal bandwidth. The new 12‐bit A‐D conversion unit equipped with a recursive‐type digital filter achieved the equivalent high resolution of 14‐bit conversion.This paper describes the design concept and the characteristics showing applications to current differential relays, distance relays and power system controllers.
Analysis of moving magnet linear dc motor with two straight stators
Authors: Hanaoka Motoyasu , Miyaji Hiroshi , Kano Yoshio , Hasebe Shinya , Ohta Kenichiro 
Published: July 2007

AbstractThe thrust force of moving magnet‐type linear direct current motors (MM‐LDM) is analyzed in this study. A moving magnet‐type MM‐LDM consists of a stator and a carriage. The stator is composed of two stick shaped electromagnetics and the carriage consists of a movable permanent magnet that is located between the two electromagnets.One of the methods for calculating the thrust force of an MM‐LDM is to analyze the energy gradient which is determined by the distribution of magnetic flux. However, this method is very difficult when used to calculate the thrust force of this kind of LDM. This type of MM‐LDM can be considered to be a transformer in which the magnet of the mover is assumed to be a one‐turn coil carrying a large current. The stored energy in the MM‐LDM can be obtained by measuring the self‐inductance and the mutual‐inductance of the equivalent circuit of the MM‐LDM. And this energy gradient gives the thrust force.The calculation of the thrust force induced in this motor shows that the mutual inductance has a large influence on the generation of thrust force.
Analysis and improved control method of resonant DC link inverters
Authors: Sato Yukihiko , Matsumoto Yasushi , Kataoka Teruo 
Published: July 2007

AbstractHigh performance power conversion requires high switching frequency power converters. Resonant dc link inverters, which are investigated in this paper, are suitable for this purpose because they cause no switching loss in principle. But in these inverters, loss of the resonant oscillation and occurrence of high peaks in the resonant capacitor voltage are serious problems. In this paper, we investigate a control method for resonant dc link inverters which can overcome these problems.First of all, we summarize the basic control principle of an ideal resonant dc link inverter. Then we present an analyzing method for the practical resonant dc link inverter introducing two equivalent circuits in which the influence of the power losses in the resonant link and in the inverter load is considered. From these equivalent circuits, the problems of existing control methods are clarified. Based on the results of this analysis, we propose an optimum and keep the capacitor voltage at an allowable level. A simple compensation method for the influence of storage time of switching devices, which affects the implementation of the proposed control method, is described.Some experimental results are included to confirm the validity of the analytical results and the effectiveness of the proposed control method.
Development of three‐dimensional electric field analysis by segment arrangement based on a charge simulation method
Authors: Okubo Hitoshi , Yanabu Satoru 
Published: July 2007

AbstractThis paper describes the development of three‐dimensional electric field analysis by using the so‐called segment method which enables the electric field to be calculated with high accuracy and with enhanced efficiency, for high‐voltage apparatus.In the segment method, electrode configuration of high‐voltage apparatus is simulated by small components which are called segments and by the arrangement of several kinds of such segments.In this calculation, the charge simulation method is used which is suitable for segment application. As basic segments, spherical, cylindrical and ring segments are used and in addition to these, as subsegments, disc and elbow segments are adopted for good simulation of the total electrode configuration.In this paper, the fundamental construction and arrangement parameter of segments were discussed. Moreover, the segment method was applied to an actual high‐voltage apparatus and the calculation accuracy was discussed. It was clarified that the segment method has sufficient calculation accuracy and is a very efficient means for three‐dimensional electric field analysis.