bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimal electric power‐plant planning under uncertainty of demand by means of the scenario aggregation algorithm
Authors: Nishikawa Yoshikazu , Tezuka Tetsuo , Kita Hajime , Nakano Shinichi 
Published: July 2007

AbstractRecently, electric power systems have faced increasing uncertainties in demand, energy price and environmental constraints in the future. In such a situation, a plan for expansion of the system capacity must be made robust against the aforementioned uncertainties. Large‐scale power plants require a long time for construction so that the decision of construction must be made under much uncertainty in the future. On the other hand, small‐scale plants require less time for construction, i.e., the decision can be made under less uncertainty in spite of their relatively higher costs.This paper is concerned with an optimal combination of the large‐scale and the small‐scale plants having the aforementioned characteristics under uncertainty of future demand. First, the demand growth in the future is described by scenarios of demand growth branching like a tree. Then the optimization problem of the system expansion is formulated into a stochastic linear‐programming problem. An optimal solution of the problem is obtained by using the scenario‐aggregation algorithm proposed by Rockafellar and Wets. The simulation results, yielded by using a parallel computation on transputers, show that there is a possibility of constructing small‐scale power plants to cope with the uncertainty even if they are more expensive than the large‐scale plants.
Morphological and dielectric changes of XLPE insulation due to thermal aging
Authors: Ishida Masayoshi , Okamoto Tatsuki 
Published: July 2007

AbstractTransmission power cables are heated by conductor current. The morphology of the XLPE insulation may be changed by thermal aging. Disk‐shaped insulating materials with semiconductive electrodes were used to understand this thermal effect against the dielectric breakdown strengths. The disk specimens were aged at 80 and 100°C before the breakdown strength measurements.These results showed that the dielectric breakdown strengths were improved with aging time. Analytical investigation of the insulating materials indicated that there were morphological changes such as increases of the lamella thickness and the spherulite diameter and decrease of the averaged lamella angle through heating. Cable specimens aged thermally with the same condition as the risk specimens also were observed with similar morphological changes in the insulation. Therefore it is concluded that the promotion of the crystallization by thermal aging is effective in improving the breakdown strength of the XLPE insulation unless it causes extreme deterioration.
Analysis of a zero‐power flow phenomenon in an interconnecting power system
Authors: Miyazawa Masaki , Kuboki Minoru 
Published: July 2007

AbstractToday's power systems are characterized in that more power demand is concentrated in urban areas, increasingly centralized power facilities are becoming larger in size and located in more remote places, and power condensers tend to be upgraded to improve the power factor. These movements each reduce the stability power limit, thereby permitting the effect of a power failure to spread much farther.In such an interconnecting power system, when power is transmitted from a power source (a small system) in a remote place to a large city (a large system) with great power demand, it is expected that a zero‐power flow phenomenon will occur where power transmission is impossible when power flow in the interconnecting power system is zero depending on a combination of the size of branch load and its power factor. In future power systems that will extend farther, have a larger capacity, and be more capacitive, such a phenomenon would be more iable to take place. In this paper, a new formula to analyze a zero‐power flow phenomenon is derived, and using the formula, areas in which a zero‐power flow phenomenon takes place also are discussed. With an experimental system simulating a practical 500‐kV power system, the occurrence of a zero‐power flow phenomenon could be verified.
Power system stabilization by switching‐over control of transmission lines
Authors: Okamoto Hiroshi , Yokoyama Akihiko , Sekine Yasuji 
Published: July 2007

AbstractNew technologies such as synchronized switching and power electronics will make it possible to change the configuration of a transmission network in future electric power systems. It is called VIPS (Variable Impedance Power System) by the authors who have been studying the effects of those technologies on power system stabilities.This paper considers the improvement of transient stability by means of switching‐over control of transmission lines. It is clear that in some power systems, the simultaneous energization of the line de‐energized in the normal state with the fault clearing better improves first‐swing stability than the pre‐ and post‐fault energization of the line. The energy function‐based index to select such a transmission line is derived. In addition, this paper shows that multiple switching of a transmission line improves damping of post‐fault conditions, where minimization of time derivative of energy functions is used. The switching‐over control is applied to multimachine power systems and its effectiveness is demonstrated.
Load‐flow equivalents for decentralized monitor and control of power systems
Authors: Tanaka Kazuyuki 
Published: July 2007

AbstractLoad‐flow calculation on electric power systems is one of the most fundamental analyses in system operation and planning. There are many reasons to calculate load‐flow solutions, and the contingency evaluation is a representative one.In contingency evaluation, it is necessary to repeat load‐flow calculation for tremendous patterns depending on branch or generation outages. Then, computing efforts are generally very heavy. Thus various techniques have been proposed to reduce computing time, especially by adopting equivalencing for external network. On the other hand, the network equivalents techniques also become important at present from the viewpoint of the necessity of decentralized monitor and control on bulk power systems.This paper describes a newly developed method of load‐flow equivalents based on the Ward equivalent for both direct (dc) solution and (ac) solution. Numerical results also are shown to clarify the accuracies and practicality of the proposed method through the comparison of the representative REI approach.
Current distribution in superconducting multistrands for ac use before and after quenching
Authors: Oh Bong‐Hwan , Ishikawa Kazuaki , Hayakawa Naoki , Okubo Hitoshi , Kito Yukio 
Published: July 2007

AbstractA superconducting multistranded cable is used to realize high current capacity for ac use. The critical current value of the cable is reported to be less than the simple summation of the individual critical current value of each strand. The causes for such a degradation of the critical current value have not been revealed.This paper investigates the current distribution in multistrands before and after their quenching by using seven‐strand superconducting cable and 7x7 cable. The following experimental results are derived: (1) the quenching is initiated at one strand in the cable; (2) the current in the quenched strand is transferred into the other strands; (3) an avalanche of quenching is induced among the strands; and (4) the central strand is quenched finally among the strands. The critical current values of the 7‐ and 7 × 7‐stranded cables also are measured. These values are in good agreement with the predicted values based on the mutual inductance among the strands. It is concluded that the unbalance of the current distribution in the superconducting multistrands can be one of the promising causes for the degradation of the critical current value.
Loop‐shaping based H∞ robust control of a horizontal shaft magnetic bearing
Authors: Matsumura Fumio , Hatake Kazuhiro , Fujita Masayuki 
Published: July 2007

AbstractThis paper considers H∞ control design of a magnetic bearing from the viewpoint of loop shaping. Feedback control is indispensable for a magnetic bearing, since it is essentially an unstable system. For feedback control, a mathematical model is required. However, it does not always express the exact behavior of the system, hence the model has various uncertainties such as the errors of parameters, neglected nonlinearities, or unmodeled dynamics. The controller is needed to guarantee robustness for both stability and performance against these uncertainties on the model.First, based on some assumptions, a linear state space model of a magnetic bearing is shown. Second, the experimental machine and the surroundings of its controller are introduced. The experimental machine is a 4‐axis controlled horizontal shaft magnetic bearing. The controller consists of a digital signal processor with fast A/D converters and D/A converters. Third, the control system is designed using normalized coprime factor plant descriptions. Selecting shaping functions in this procedure called “The Loop‐Shaping Design Procedure (LSDP),” shape the open‐loop transfer function and the transfer functions of the closed‐loop system can be shaped. Finally, several experiments are carried out according to the aforementioned designed controller.
Suppression of DC line current oscillation of HVDC transmission system using voltage source forced commutation converter
Authors: Funaki Tsuyoshi , Kimura Noriyuki , Matsu‐Ura Kenji 
Published: July 2007

AbstractThe conventional converter used in an HVDC system requires line voltage to turn off the current flowing through a thyristor or a mercury‐arc valve. Hence, the HVDC system cannot supply electric power to the system which has no ac source, such as a generator or a synchronous condenser. Thus, the HVDC system has some difficulties in operating with the weak system.The conventional solution to avoid these problems is to install large‐capacity synchronous condensers which require considerable construction costs and maintenance. Another solution is the application of a forced commutation converter.The recent development of high‐power and high‐frequency semiconductor devices with fast gate turn‐off ability (e.g., GTOs and SI thyristors) suggests the application of a voltage‐source‐type forced commutation converter (VSFC) to an HVDC system. To ensure the promising characteristics of the overall system, further investigation is of course necessary.The performance of dc transmission into a remote load‐only system without ac source has been investigated by means of computer simulation. In many runs of a simulation program of the HVDC system using VSFC, we noticed that long sustaining oscillation of dc line current and dc voltage occurs when a large disturbance is applied. The performance is worse when series dc reactance (DCL) is installed to suppress higher harmonics of dc line current. To improve the performance of the HVDC system using VSFC, an attempt was made to install the L‐R parallel damper circuit in series of dc transmission line. Simulation results when DCL and L‐R damper are installed in series show that suppression of higher harmonics is as effective as the installation of DCL only, and the damping of oscillation also is substantial to improve the dynamic performance of the whole system.
Stabilizing control of power system using fuzzy control
Authors: Iskandar Marzan Aziz , Mizutani Yoshibumi , Suzuki Akio , Ishizeki Mitsuo 
Published: July 2007

AbstractThis paper presents an application of fuzzy control to enhance power system stability. The proposed control consists of the controller for large disturbance (FU 1), the fuzzy controller for small disturbance (FU 2), and the fuzzy judgment mechanism (FU 3).FU 1 is determined based on the fuzzy controller [FU 1(F)] is determined according to the control rules and its input signals, i.e., speed deviation and acceleration at every sampling time of the machine. FU 2 consists of two controllers, namely, FU 2‐ω and FU 2‐P; FU 2‐ω has the same mechanism as FU 1, while the output signal of FU 2‐P is determined according to the rules together with the change of error of electrical power and terminal voltage. To obtain the optimal desired control signal during both the large and the small disturbances, the operations of FU 1 and FU 2 are judged by FU 3, where the magnitude of speed deviation is chosen as its input signal. The determined control signal is fed to AVR of the machine.The implementation of the proposed control is simple due to the small amount of calculations and required data. The effectiveness of the proposed control is demonstrated by the one‐machine infinite‐bus system model and very good system performance is obtained throughout all the simulations.
Development of self‐commutated SVC for power system
Authors: Tokiwa Yukio , Ichikawa Fumitoshi , Irokawa Shoichi , Kitahara Tadayuki 
Published: July 2007

AbstractA 50‐MVA self‐commutated Static Var Compernsator (SVC) using the worlds's largest GTO thyristors rated 6 kV‐2500 A has been developed for voltage control of electric power systems. The rated dc voltage is 16.8 kV which is four times higher than the highest one manufactured so far. To achieve the high dc voltage, eight GTO thyristors are connected in series. Voltage unbalance between GTOs during switching transient was investigated. A new overcurrent limiting method is proposed, since conventional fuse protection cannot be applied due to such high voltage. Newly developed technologies for this large and high‐voltage self‐commutated SVC are described.Although simple star‐delta connection transformers are used, harmonics generated from SVC are almost equivalent to the 24‐pulse converter by shifting the pulse timing appropriately. The PWM control based on 150 Hz is applied and the SVC is designed to continue operation during system faults. The performance of the controller is tested successfully by a simulator, and typical rest results are introduced.
A CO2‐recovering nonpolluting high‐efficiency gas‐turbine power‐generation system utilizing saturated steam as its working gas
Authors: Pak Pyong Sik , Suzuki Yutaka 
Published: July 2007

AbstractA carbon dioxide‐recovering high‐efficiency gas‐turbine power‐generation system is proposed in which carbon dioxide (CO2) generated is recovered by adopting the oxygen (O2) combustion method and no thermal nitrogen oxide is generated. In the system, saturated steam produced by utilizing waste heat is adopted as the working fluid of the gas turbine. Thus, the compressing process of the working fluid gas, which is the most energy‐consuming process in generating power by using a gas turbine, is not needed. This makes the system extremely high efficient.By taking saturated steam of 210°C as an example, the characteristics of the system were simulated. The net exergetic efficiency of the system has been estimated to be 48.4 percent by considering both the exergy of the saturated steam and the electric power required not only to generate high‐pressure oxygen, but also to liquefy the recovered CO2. The value is higher than the exergetic efficiency 37.8 percent of large‐scale thermal power generation plants using the same natural gas, and is 28.0 percent higher than its efficiency of 37.8 percent, the one estimated if the CO2 generated is removed and recovered from the stack gas by using alkanolamine‐based solvent and the recovered CO2 is liquefied.
Protection of bulk regular network system with dispersed generators
Authors: Okamura Yukio , Genji Takamu 
Published: July 2007

AbstractIn urban areas there is a growing need to ensure bulk power distribution, service reliability and an interconnection to dispersed generators. It is effective to improve the network distribution system for the foregoing view. Regular network systems often are used for the area, but coordinations of the protection are complex as usual.This report describes the protective coordinations of the regular network system that performs a bulk power distribution and includes dispersed generators. The interconnections influence the coordination of substation protective relays and network protectors at the primary feeder fault. The increase of the network currents associated with the bulk network system makes the protection difficult at low‐voltage grid cable fault.
New design for the high‐performance drive system for DC brushless motor
Authors: Itoh Yuzo , Naitoh Yoshitaka , Tsuchiya Takeshi 
Published: July 2007

AbstractThe dc brushless motor, permanent magnet‐type synchronous motor (PM motor), has been used widely in industrial robots, the machine tools for factory, and factory automations. Therefore, it is more desirable to improve the performance of the PM motor variable speed control system. Although only the torque component current is adjusted as the control method for the PM motor, so‐called Vector Control, it is expected that the developed characteristics will be added to the PM motor.In this paper, new driving methods for the PM motor and a new design method for the variable speed control system are presented. The new motor driving methods which bring to the PM motor a new driving performance, e.g., a quick transient response or high‐efficiency motor driving, can be implemented by controlling not only the torque component current, but also the magnetizing component current. A developed optimal control theory, i.e., the error system technique, is employed for designing the control system. The control law is endowed with a steady robustness against the variation of the system parameters and the ability of compensating the delay time due to the control processing.The effectiveness of the proposed method is confirmed by simulations and experiments.
DC conduction associated with electric field‐induced motion in mineral oils
Authors: Nakano Mitsuaki 
Published: July 2007

AbstractThe contributions of the electrohydrodynamic (EHD) motion to the dc electric conduction in insulating oils are presented. The effects of solid/liquid interfaces on the EHD motion have been studied with a mineral oil‐polypropylene mixed dielectric and a mineral oil single dielectric. The time dependence of current, schlieren images of EHD motion induced in the oil layer and response signals of density change in the vicinity of the electrode/oil interfaces after application of step voltage are observed.The results are as follows: (1) the EHD motion occurs at the positive electrode/oil interfaces when a voltage above critical voltage is applied; (2) a time delay exists between the application of step voltage and the onset of EHD motion. The time is inversely proportional to the applied voltage; (3) the EHD motion increases current and produces a peak phenomena in the current waveform; and (4) the time difference between peak current time and the delay time is inversely proportional to applied voltage.
Influence of electric conductivity and pH on propagation of impulse breakdown on the surface of artificial acid rain
Authors: Nakao Yoshitaka , Itoh Hidenori , Takeda Satoshi , Matsuyama Hiroshi , Katoh Takunori , Sakai Yosuke , Tagashira Hiroaki 
Published: July 2007

AbstractRecently, acid rain has become a grave environmental problem. The authors realized artificial acid rain with any electric conductivity σ and pH value by a combination of dilute sulfuric acid and seven kinds of salts based on the chemical analysis of the ionic ingredient of rainwater. In this paper, a propagation of a streamer discharge on the surface of artificial acid rain is investigated in detail by using a high‐speed Schlieren method and a current‐measuring system by LED.The results obtained may be summarized as follows:
A flashover voltage Vf of rainwater decreases gradually with increasing the σ and an effect of the Vf on the pH cannot be seen obviously in this experimental condition;
On the propagation of the streamer discharge on the surface of artificial acid rain.

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

AbstractTo cope with the high rate of increase of power demand in the main industrialized districts in Japan, 550‐kV transmission systems covering the districts have been reinforced, with most of the main power plants connected directly to these systems. Through 550‐/300‐kV substations, the majority of power to the districts is supplied by 300‐kV systems. To limit the excess short‐circuit capacity in the 300‐kV systems, they tend to be reconstructed as so‐called radial networks. In radial networks with high short‐circuit capacity and relatively small number of transmission lines connected to the substation busbars, the rate of rise of TRV can be far higher than standard value.This paper analyzes the transient recovery voltages (TRV) in such extra‐high‐voltage radial networks in Japan, together with the relevant stresses to circuit‐breakers during fault clearings. Future system conditions have also been introduced. As the typical rate of rise of the TRV values, more than twice that of today's standard ones are probable.
Voltage and reactive power control using recurrent neural networks
Authors: Kojima Yasuhiro , Izui Yoshio , Kyomoto Sumie , Goda Tadahiro 
Published: July 2007

AbstractMany controllers using neural networks have been recently developed. The hybrid and direct types are two major categories of such controllers. While the first type tunes the parameters of the conventional controller by means of neural networks, the latter constructs the controller by learning the inverse dynamics of the control target.Electric power systems require voltage and reactive power (VQ) control to avoid voltage collapse. The conventional VQ control, however, meets this requirement unsatisfactorily because the control is only approximate.In this paper, we will propose a new algorithm for VQ control using recurrent neural networks (RNNs), which have the ability to deal with the system's controlled target by means of RNNs. Second, we will apply this algorithm to VQ control. We will call this controller “neuroVQC.” Finally, the usefulness of the neuroVQC will be shown by comparison with the conventional VQ controller.
Research on high‐performance NdFeB magnets
Authors: Kaneko Yuji , Tokuhara Koki , Ishigaki Naoyuki , Majima Kazuhiko 
Published: July 2007

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