bluuebunny/crossref_metadata_2025_split huggingface dataset:
Estimating power‐frequency characteristics in power systems by means of spectral analysis techniques
Authors: Hayashi Shigeo , Kawata Akira , Nagasawa Takashi , Yokoyama Naoto 
Published: July 2007

AbstractThis paper shows that normal power system operating data may be used to determine the power‐frequency characteristics in power systems. Data are processed as random signals using spectral analysis techniques, and the results estimate the generator and load power‐frequency characteristics as transfer functions. The generator characteristics Kg are determined as a transfer function of the system in which input signals are frequency fluctuation ΔF and generator power setting signal ΔPg, and output signal is generator power output ΔPe, To estimate the load characteristics Kl, a difficulty arises. There is a relation ΔP/ = ΔLo + KlΔF between actual load ΔPl, ideal load under the state of nominal frequency ΔLo, and fluctuation of system frequency ΔF. Because it is impossible to measure ΔLo directly, ΔLo and KlΔF cannot be separated.With regard to a partial system, when its capacity is small enough compared with the total system capacity, the contribution of ΔLo in a partial system to ΔF of the total system may be ignored, that is, ΔF and ΔLo are considered as independent phenomena. Thus the cross spectrum of ΔF and ΔLo decreases to zero according to the increase of data in number, and Kl of the partial system can be estimated.
Stabilizing control of variable impedance power systems: Applications to variable series capacitor systems
Authors: Okamoto Hiroshi , Yokoyama Akihiko , Sekine Yasuji 
Published: July 2007

AbstractIn future electric power systems, it will be very important to utilize existing ac networks more effectively with the help of power electronics technology. It has become clear that various types of apparatus utilizing such power electronics technologies as variable series capacitors (VSrC) and high‐speed phase shifters (HSPS) can improve transient stability and damping in one‐machine, infinite‐bus power systems. This paper presents a novel control scheme for variable impedance apparatus such as VSrC and HSPS devices in multi‐machine power systems.First, this paper describes a comprehensive approach for control design of VSrC and HSPS apparatus. The proposed control scheme is based on the energy function of multi‐machine power systems. The controllers are designed so that the time derivative of the energy function has a smaller negative value than that without controllers. In this sense, the present method assures the improvement of first‐swing stability and damping.Next, the proposed control scheme is applied to VSrC apparatus. Digital simulations and eigenvalue analysis are conducted for a three‐machine loop system and a five‐machine radial system to demonstrate the effectiveness of the proposed method. The results make it clear that the proposed controllers for VSrC can significantly improve both the transient stability and the steady‐state stability of power systems.
Use of permeance‐based air‐gap flux density analysis in the development of a synchronous generator model
Authors: Takase Fuyuto , Matsumura Toshiro , Ueda Yoshisuke 
Published: July 2007

AbstractThe magnetic flux inside a synchronous generator is regarded as a characteristic that dominates a generator operation. This paper develops a simple model of a synchronous generator by which it is possible to easily estimate an air‐gap flux as well as electrical characteristics. The air‐gap flux density can be related to a permeance and a magnetomotive force (mmf) along its magnetic path by the Ampere's laws. These relations are used in this paper.We estimate the distribution of the permeance along the air‐gap and the mmf profiles of the stator and the rotor of a 6 kVA scaled‐down tested synchronous generator. From these estimated profiles, the relations among the air‐gap flux, field current, and armature current are represented by a linear equation system. Consequently, the static electrical and magnetic characteristics of a synchronous generator can be estimated by giving only field exciting voltage and load impedance. The distributions of the air‐gap flux density and waveforms of the field and armature currents are simulated for various unbalanced‐load conditions. The simulated results well agree with experimental ones not only for fundamental components but also for higher harmonic components. Therefore, our method, based on the permeance profile, is available to calculate the static characteristics of synchronous generators.
Prevention of reignition overvoltages by phase‐angle‐controlled switching of a gas circuit breaker at shunt reactor current interruption
Authors: Yamagata Yoshifumi , Kumagai Tsutomu , Nishiwaki Susumu , Toda Hiroaki , Ishikawa Masayuki , Yokota Takeshi 
Published: July 2007

AbstractShunt reactors installed at gas‐insulated switchgear substations (GIS‐substations) are switched relatively frequently by large‐capacity gas circuit breakers (GCBs). Surge voltages appear at such switching operations through various mechanisms. Among them, high‐frequency current interruption and subsequent multiple reignition might cause the highest overvoltage and may be harmful to the insulation of the components of the substation.In this paper, shunt reactor current‐interrupting tests are conducted in high‐power laboratory. The existence of critical arcing time above which reignitions never occur is shown through these tests. From this fact, a phase‐angle‐controlled‐interruption system is proposed. With this system, arcing time is set artificially so that reignitions should be prevented. The reliability of this system is confirmed through the reactor current‐interrupting test in the laboratory as well. Afterward the phase‐angle‐controlled‐interruption system is applied to the shunt reactor switching at an actual 275‐kV substation. The switching performance of this system is measured over three months. Reignition‐free interruption is shown to be attained with this system.
Experimental study on hunting phenomena in synchronous generators
Authors: Matsuki Junya , Okada Takao , Tamaishi Zen'ichi , Kotsuji Akihiro 
Published: July 2007

AbstractNumerous studies have been made on the hunting phenomena of synchronous machines. However. most of them have been concerned with the mathematical analysis based on equivalent‐circuit models of machine and system, and experimental studies are quite rare. However, few papers have treated the phenomena from the viewpoint of internal air‐gap fluxes which actually govern the machine behaviors.This paper describes the experimental results on hunting phenomena of synchronous generators caused by a fast‐acting AVR (Automatic Voltage Regulator) in a laboratory‐model one‐machine/infinite‐bus power system. Changes of air‐gap fluxes in the process of hunting phenomena are measured by a search coil wound around a stator tooth on top of the tested synchronous generator and are examined. The interaction is made clear between field fluxes and quadrature‐axis fluxes both of which directly influence the hunting phenomena. The results obtained are confirmed by simulation studies. Thus, the relationship between system stability and machine fluxes is given a clearer understanding than before.
A PWM‐controlled rectifier step up/down output voltage with a high power factor
Authors: Funabiki Shigeyuki , Toita Noriyuki 
Published: July 2007

AbstractIt is desirable that the rectifier that is an ac‐to‐dc converter, have the characteristics of fast response and the wide range of the output voltage control, and the sinusoidal source current waveform. In this paper, a step up/down output voltage PWM‐controlled rectifier is proposed. The features of the proposed rectifier are as follows.(1) The calculation of pulsewidth is based on the geometrical technique and the source current can be inphase with the source voltage.(2) The output voltage is controlled from about zero to more than the maximum value of the source voltage.The aforementioned features are clarified by simulation and the steady‐state characteristics are discussed. Further, these results are verified in experiment using the microprocessor‐based control system.
Structure of a simulated muscle system
Authors: Murakami Toshiyuki , Ishibashi Hirozumi , Ohnishi Kouhei 
Published: July 2007

AbstractThis paper describes a network system designed to realize the motion of a muscle. First, the motion of the network system is analyzed by a model system which consists of many electromagnets. Second, the control strategy of the network motion system, implemented with microactuators, is described. In the proposed network motion system, the total system consists of many force transmission lines and the superposition of the force signals propagated by the lines acts on the final actuator. The proposed motion control method is therefore called the Delay Superposition Method (DSM). Several experimental and numerical results confirm the validity of the proposed method.
Suppression control of speed variation in an induction motor with fluctuating load by repetitive learning control
Authors: Ishda Muneaki , Hori Takamasa , Ohno Masaharu 
Published: July 2007

AbstractInduction motors are robust and inexpensive machines and are used widely for variable speed control because of the recent development of electronic technique. In the case where loads of the motors are compressors, pumps, and so on, the constant V/F control of the induction motors usually is employed because it is difficult to install speed sensors and accurate speed control is not required. In such loads, the rotational speed of the motors fluctuates considerably because the load torque is pulsated. When the frequency of the torque pulsation is close to the resonant frequency of the mechanical system, large vibration and acoustic noise are produced especially in the low‐frequency region.This paper proposes a method to suppress the variation of the rotational speed of the V/F controlled induction motor with a fluctuated load by feedforward compensation using a timing sensor of 1 pulse/rev, considering that the load torque varies periodically. The feedforward data by a period for the compensation is obtained by the learning control based on the repetitive control in which the motor speed is controlled by periodically reflecting the past speed error on the present V/F input to the inverter. Effectiveness of the proposed method is confirmed by approximate analysis, simulations and experiments.
Magnetic core properties and their thermal stability in a BCC Fe‐Zr‐B‐Cu alloy with nanoscale grain size
Authors: Makino Akihiro , Suzuki Kiyonori , Inoue Akihisa , Masumoto Tsuyosi 
Published: July 2007

AbstractA mostly single bcc phase with nanoscale grain size of 10 to 20 nm has been found to form by annealing amorphous Fe‐Zr‐B, Fe‐Hf‐B and Fe‐M‐B‐Cu (M = Ti, Zr, Hf, Nb and Ta) alloys. It has further been clarified that the newly developed nanocrystalline bcc alloys exhibit high permeability (μe) combined with high saturation magnetization (Bs).Subsequently, the possible application potentials of the bcc alloys were investigated. The core loss is as small as 66 mW/kg at 1 T and 50 Hz for a nanocrystalline bcc Fe86Zr7B6Cu1 alloy obtained by annealing for 3.6 ks at 873 K. This value is 45 and 95 percent smaller than those for amorphous Fe86Si9B13 alloy and Fe‐3.5 percent Si alloy, respectively, which are presently in use as core materials in electric power transformers. The frequency dependence of the core loss for the bcc alloy at 0.2 T is almost the same as that for an amorphous Co70.5Fe4.5Si10B15 alloy with zero magnetostriction.In the frequency range of 10 to 300 kHz, the core loss for the bcc alloy is slightly smaller than the Co base amorphous which has been used as core material in high‐frequency transformers. Furthermore, the core losses of the nanocrystalline Fe86Zr7B6Cu1 alloy also were found to have high stability against thermal aging. Thus, nanocrystalline bcc Fe‐Zr‐B‐Cu alloys with the advantages of high Bs, high μe, and low core loss is expected to be used as a core material in various transformers.
Cluster pulse criteria for recognition of partial discharge
Authors: Tsutsumi Yasuyuki , Yonekura Tatuhiro , Kikuchi Tsuyoshi 
Published: July 2007

AbstractStatistical calculating programs simulating partial discharge appearance are developed and applied to evaluations of criteria for discrimination of the partial discharges from noises. According to the simulation, clusters of sequential pulses appear at the partial discharge inception voltage, and have never been utilized at the usual pattern recognition of the partial discharges. Two original indexes that are a pair pulse rate and a maximum sequential pulse rate are defined to describe the time sequential features of the partial discharge and their signal distinguishable capabilities from noises are evaluated. A new logical index describing the signal distinguishable capability of the usual ø‐q pattern of the partial discharges from the noises also is proposed and compared with those of cluster pulses. The maximum sequential pulse rate gives most sensitive criteria in the bounds of calculating conditions.A 66‐kV cross‐linked polyethylene cable with an artificial defect is used to detect cluster pulses. By adding twice as many noise pulses as measured partial discharge pulses, the usual ø‐q pattern criteria becomes powerless, but cluster pulse criteria are still informative for the recognition of the partial discharges.
Approach and structure of stabilizing control system preventing an extension of synchronism loss
Authors: Ōura Yoshifumi , Suzuki Mamoru , Yanagihashi Ken , Sato Masihiro , Tsukui Ryouichi , Matsushima Tetsuro , Omata Kazuya 
Published: July 2007

AbstractRecently, large‐capacity power stations have been built far from load centers with long‐distance transmission lines. Therefore, if a fault occurs at the line, generators in the large‐capacity power station may lose synchronism from the remaining generators [1, 3]. To prevent an extension of loss of synchronism to other generators, fast shedding of some generators is an effective measure.The following methods have been proposed so far: A method [3] based on energy function approach; and a method [2] which estimates and predicts the relative swing among generators using data measured on‐line at each generator and proposes shedding some generators for stabilization. This method requires a large communication network for an exchange of data between power stations.This paper presents a new stabilizing method and a newly developed stabilizing control system which does not require a large communication network because it utilizes generator output, voltage and current measured on‐line in the vicinity of the large‐capacity power station. Using these measured data, the system estimates and predicts the relative swing between generators in the large‐capacity power station and the remaining generators. Finally, the number of generators to be shed for stabilization is decided and shedding is performed. Configuration and characteristics of the developed stabilizing control system are shown. The validity of this method is confirmed by simulation and testing using an artificial power system.
Economical preventive control of power flow after disturbances in the decentralized power system
Authors: Uriu Yoshihisa , Koyanagi Fumiko , Yokoyama Kiyoshi 
Published: July 2007

AbstractThis paper discusses the preventive controls of the generator outputs to improve security in the decentralized power system. Preventive controls of the power system can improve security level. However, the preventive control requires too much computation time because of too many considerable faults in the power system. Multiarea decentralization can be considered to reduce computation time of the power flow calculation. It is assumed that the effects of disturbances in the external systems are relatively smaller than the effects of disturbances in the study area.Linearized sensitivity analysis is used to evaluate the effects of the external systems to reduce computation time. Linear programming is used to determine the control signals of generators considering the incremental cost of generators. The New England 38 buses system is used as an example system to check the validity of the algorithm in this paper. The calculations of the example system show satisfactory results.
Ripple compensation of a single‐phase rectifier by two‐quadrant chopper and auxiliary capacitor
Authors: Irie Hisaichi , Takemoto Nobuyuki , Yamashita Takeshi 
Published: July 2007

AbstractThe single‐phase converter or rectifier always has a voltage ripple in the output dc voltage because the instantaneous power of the single‐phase ac line varies on the double frequency of the line. To obtain a smooth dc voltage, an energy‐storing element is necessary. The smoothing capacitor is used to reduce the ripple voltage in the dc output. Usually, it has much larger capacitance than that needed to absorb the ripple energy.This paper discusses the required capacitance to absorb the ripple energy, and represents a ripple‐compensation circuit with a small auxiliary capacitor controlled by a 2‐quadrant chopper connected in parallel to the smoothing capacitor. The appended capacitor works under large ripple voltage and efficiently absorbs the ripple energy. The ripple‐compensation circuit works as an equivalent capacitor with a large capacitance.
Structure and operation mechanism of a friction‐type piezoelectric motor utilizing the principle of strain‐wave gearing
Authors: Ishida Muneaki , Shirasuka Keiichi , Hori Takamasa 
Published: July 2007

AbstractThis paper proposes a new type of motor which utilizes multilayer piezoelectric devices for electromechanical power conversion and the mechanism of the strain‐wave gearing to generate traveling waves and motive force. The construction and basic operation of the motor are described. The motor can be operated in variable frequency because piezodevices are operated in the nonresonant mode. Approximate analysis is performed to clarify the operating mechanism of the motor and to obtain characteristics on the rotational speed in the case of no‐load. Experimental results on rotational speed of the prototype motor made of metals except for the piezoelectric devices also are presented, which verifies the feasibility of the proposed motor.
A sinusoidal PAM‐PWM inverter
Authors: Inoue Masakazu , Taniguchi Katsunori 
Published: July 2007

AbstractA new strategy, using both PAM (pulse amplitude modulation) and PWM (pulsewidth modulation) in combination for a power inverter is described. The output waveforms in the proposed PAM‐PWM inverter are investigated both theoretically and experimentally. The line‐to‐line voltage waveform includes the fundamental component and the sidebands of the carrier frequency. Lower‐order harmonics are not included in the output waveform. The amplitude of the fundamental component increases 15 percent more than that of a conventional sine‐wave inverter. Since each inverter arm does not operate during two‐thirds of the period, the heat generated in the devices is reduced, i.e., the size of the inverter system can be minimized because of the reduction in the heat dissipating equipment.
Harmonic analysis of a single‐phase rectifier with a DC filter capacitor
Authors: Sakui Masaaki , Kitamura Toshihiro , Fujita Hiroshi 
Published: July 2007

AbstractA single‐phase diode bridge rectifier with a filter capacitor on the dc side is often employed to convert ac input into a dc voltage. The input current of the rectifier contains harmonic currents which cause undesirable power line effects. Recently, a method using the time domain analysis has been proposed to calculate the harmonic currents of rectifier considering noninfinite capacitance, i.e., non‐zero dc side impedance. This method is very accurate, but it requires a long computing time and a complicated algorithm.This paper proposes a new method that makes it possible to easily calculate the harmonic currents taking into account the effects of the ac and dc side impedances of rectifier. The proposed method, which is based on the frequency domain method, can be executed only with the algebraic computation, and its accuracy is quite high. The validity of the proposed method is also demonstrated by comparison with the results of time simulation.
Suppression of electrical treeing by addition of lithium carbonate to low‐density polyethylene
Authors: Hoshimura Yoshikazu , Yamamoto Shigeru 
Published: July 2007

AbstractLow‐density polyethylene (LDPE) is used widely as an electric insulating material in electric power cables. The generation of electrical treeing due to aging of LDPE may lose the reliability of its insulating capability. Therefore it is important to suppress its treeing and to improve its electrical properties so that the reliability of cables can be improved. For this purpose, the authors prepared LDPE to which various inorganic materials were added.This investigation focuses particularly on lithium carbonate and quartz which were effective in suppressing the treeing when added to LDPE. Lithium carbonate‐added (0.25 phr) LDPE in two hours of discharge showed the tree length 150 μm shorter than that (560 μm) of nonadded LDPE, exhibiting an obvious suppressing effect on treeing generation. It was found that this effect was more significant than quartz‐added LDPE and even at elevated temperatures lithium carbonate‐added LDPE exhibited suppression of treeing. The thermal decomposition temperature at which lithium carbonate‐added (1 phr) LDPE loses 50 percent of its weight rose 100°C more than nonadded LDPE and 60°C more than that of quartz‐added LDPE, which showed improvement in heat resistance of LDPE.
Magnetic properties of melt‐spun Nd‐Fe‐Co‐B‐Cu‐Nb system alloys and their bonded magnets
Authors: Yamamoto Hiroshi , Katagiri Eito 
Published: July 2007

AbstractMelt‐spun ribbons of Nd‐Fe‐Co‐B‐Cu‐Nb system alloys were prepared by the single roller rapid‐quenching method. The effects of composition, wheel velocity and heat‐treatment on the magnetic properties were investigated. The magnetic properties of bonded magnets prepared by compression molding of optimally annealed ribbons were also measured. A maximum energy product of 152.1 kJ/m3 was obtained for the Nd11Fe72Co8B7.5Cu0.5Nb1.0 alloy ribbon prepared at a wheel velocity of 17.1 m/s.From the TEM observation on the above Nd11Fe72Co8B7.5Cu0.5Nb1.0 ribbon, the particle size of these ribbons was determined to be between 10 and 40 nm. It is conjectured that the high remanence is observed by the magnetic interaction of these fine particles, and it was found that these fine particles were achieved by Nd‐Fe‐Co‐B compound in addition with Nb and Cu at the same time.The amorphous Nd11Fe72Co8B7.5Cu0.5Nb1.0 ribbons prepared at a wheel velocity of 20.7 m/s were crystallized by heat treatment, and the optimum annealing condition was found to be at 650°C for 15 min. Its corresponding value of (BH)max is 144.5 kJ/m3. A maximum energy product of 88.1 kJ/m3 was achieved with Nd11Fe72Co8B7.5Cu0.5Nb1.0 bonded magnets made from the optimally prepared ribbons.