摘要:

AbstractAn experiment was carried out to investigate the effect of CaO and SiO2addition on the magnetic and physical properties of anisotropic Ba‐Zn W‐type hexagonal ferrite magnets. It was found that magnetic properties of BaO.2ZnO.8Fe2O3compounds added with CaO and SiO2were improved. The optimum conditions of typical specimens are as follows: chemical analysis composition‐Ba0.857Zn1.643Ca0.150Si0.266Fe2+0.030Fe3+15.857O27; semisintering condition‐1275°C × 1.0 h in air; sintering condition‐ 1250°C × in air, magnetic and physical properties areJm= 0.436 T,Jr= 0.393 T.Hcj= 64.4 kA/m,HcB= 64.1 kA/m, (BH)max= 16.1 kJ/m3,Tc= 357°C,HA= 971 kA/m,KA= 2.03 × 105J/m

ISSN:0424-7760    

DOI:10.1002/eej.4391140201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIt has been clarified that a superconducting magnetic energy storage (SMES) is very effective for power system stabilization. The control methods proposed for power system stabilization by SMES include the pole assignment, the optimum control, and so on, each of which, however, has its drawbacks. The application of fuzzy control is considered to overcome these drawbacks.This paper considers the power system stabilization by fuzzy control of the active and reactive power of SMES. First, the adequate fuzzy control rules of an SMES for the model power system is derived. Then, to alleviate the dependence of the fuzzy control on the operating condition and the fault, a method is proposed which adjusts the fuzzy parameter according to the operating condition and the fault using a neural network. The validity of the proposed method is examined by computer simulations.

ISSN:0424-7760    

DOI:10.1002/eej.4391140202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractPower system control equipment needs higher sensitivity and operational reliability. Advanced voltage control equipment is needed for reducing the frequency of tap changes and improving the characteristics (the relationship between the actual voltage and reference voltage) of the voltage to meet today's power system requirements. However, these objectives are in a trade‐off relationship. Studies of voltage control derived from a knowledge base suitable for electric power systems can satisfy these objectives using fuzzy inference. Compared with corresponding conventional equipment, the new equipment improved the deviation of 30 min average voltage of 30 percent.This paper describes the design concept of new voltage control equipment using fuzzy inference. In addition, field test results are described along with rules of fuzzy inference, membership functions, and the deviation of 30 min average voltage through detailed simulatio

ISSN:0424-7760    

DOI:10.1002/eej.4391140203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper presents a new solution method for computing the maximum loading point of a bulk power system under the condition where the loads of the nodes can be parameterized by a scalar which is the loading level of the system.A special loading model, in which the loading level of the system depends on the voltage magnitude of a loading node, is adopted for the purpose of releasing the load‐flow computation from the ill‐condition near and at the maximum loading point. The loading level of the system is unknown in the aforementioned loading model. The maximum loading point is obtained by adjusting the operating parameter so as to achieve the maximum loading.The operating parameter is adjusted in the converging process of the Newton‐Raphson iterative computation. The adjustment is computed based on the least squares estimation using the data set which is obtained from its own iteration process.It is shown in numerical examples that the proposed method is satisfactorily rapid, stable, and acc

ISSN:0424-7760    

DOI:10.1002/eej.4391140204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractShort‐circuit study is one of the most fundamental planning analysis procedures for electric power utilities. Measures for increasing transfer capabilities such as installation of additional facilities were originally implemented for the purpose of improving system stability. However, the reinforcement of transmission networks is commonly the major factor in increasing short‐circuit currents. Therefore, short‐circuit studies should be given greater attention in the future, especially with regard to coordination of power system availability and reliability.To effectively solve these problems, it is necessary to develop an advanced algorithm to easily compute short‐circuit currents in one round for a large number of alternative network configurations corresponding to operational changes in bus connections at main substations.This paper proposes a new calculation method to efficiently modify theZ‐bus matrix elements for short‐circuit studies of large power networks, and also demonstrates its practicality by applying the proposed method to the calculation of short‐circuit currents in two m

ISSN:0424-7760    

DOI:10.1002/eej.4391140205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIn modern industrialized societies, it is mandatory to provide an uninterrupted supply of high‐quality electric energy at modest cost while promoting a better environment. This can only be realized through very sophisticated power system operations that compromise several contradictory factors, namely, economy, security and environment. Since these factors are in trade‐off relationships to each other, they should be analyzed appropriately. One class of problems that simultaneously satisfy several criteria in trade‐off relationships is called “multiobjective optimization problems.” Optimal power flow (OPF) has been regarded as the most powerful means to obtain effective system operation plans since it only optimizes a single objective function.This paper proposes an efficient solution methodology for a class of multiobjective optimal power flow problems which makes use of a heuristic search method. An optimal solution can be found in the proposed heuristic search method based on local information about a preference index, which is chosen arbitrarily from a given set of objectives. This circumvents the exhaustive evaluation of all noninferior solutions needed in the existing multiobjective OPF algorithm proposed by the authors, thus dramatically reducing the solution time. The proposed method has been coded and applied to the IEEE 57 node test system. Simulation results have demonstrated the possibility of utilizing this method in on‐line e

ISSN:0424-7760    

DOI:10.1002/eej.4391140206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractFor the fault condition in dynamic stability study, balanced faults have mainly been utilized. Recently, however, with the progress of system protective control technologies such as the multiphase reclosing system for a faulted transmission line, the needs for stability software which would be able to calculate simultaneous faults without any restrictions on fault types, total numbers or location, have been increasing.This report presents the newly developed multifault calculation method based on symmetrical components which is able to calculate simultaneous faults without any restrictions on combination of fault types, and total numbers or location. Fault types consist of balanced/ unbalanced ground fault, short‐circuit fault, line‐out of transmission lines, and short‐circuit of series condenser. The proposed method also allows for calculation of faults at an arbitrary location on the line without any topological changes of each symmetrical network even if the faults include line‐end faults with ensuring outages.An example was shown to clarify the validity of the proposed method. Moreover, transient stability limits under the various fault conditions also were di

ISSN:0424-7760    

DOI:10.1002/eej.4391140207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractRecently, one type of thermal‐type IR detector, the pyroelectric sensor, has become of great interest in commercial applications, because of its ability to operate without cooling, its constant detectivity independent of wavelength, and its low cost. The conventional pyroelectric materials are usually normal ferroelectric materials with a first and second phase transition. The working temperatures are sufficiently below the Curie temperatureTcfor stable responsivity to temperature. Electric field induced‐type pyroelectric sensors have also been proposed. Relaxor ferroelectric materials such as Pb(Mg1/3Nb2/3)O3(PMN) and Pb(Sc1/2Ta1/2)O3(PST), which have a glassy Curie temperature near room temperature, are used in this type of sensor.This paper describes the sensor properties of electric field induced‐type pyroelectric sensors prepared by using PMN and PST ceramics as compared with the conventional type sensors. Material evaluations of PMN and PST ceramics were made to determine their dielectric and pyroelectric properties. PMN shows excellent induced pyroelectric properties for the sensors over a wide range of temperatures. On the other hand, PST seems to be inadequate for an IR detector because of a very narrow high‐response temperature range. The sensors with PMN and PST ceramics show enhanced pyroelectric activities under dc bias field. The measured sensor voltage responsivities agree with the calculated values for the PMN case. The electric field induced‐type infrared sensor with thick or thin film materials seems to be satisfactory as linear array IR detectors for thermal imaging, with application of a higher elect

ISSN:0424-7760    

DOI:10.1002/eej.4391140208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractBoth low‐speed wheel‐on‐rail and the medium‐speed Maglev transport system with single‐sided linear induction motor (SLIM) propulsion have been in practical application.This paper presents the method of optimizing the design parameters of SLIMs using the nonlinear optimization method. The optimization problem is formulated by the use of the design formulas taking into account the end effect, skin effect and airgap leakage, and the transformation method and the simplex method are applied to solve the problem.Seven parameters, such as the number of poles, the pole pitch and the stack height, are chosen as the independent variables. The outputkW/inputkVA, the maximum flux density in the core teeth, the temperature increase, the primary length, the stack height and the maximum thrust are selected as the constraint functions. The performance characteristics are estimated using space harmonic analysis as well as the approximate equations.The method is applied to the SLIM design for urban transit, and the maximum speed is about 70 km/h. As the transformation methods, the interior point transformation and the exterior point transformation are compared from the viewpoints of accuracy and CPU time. The design is analyzed under several objective functions, the primary weight, the inputkVAand the cost of secondary

ISSN:0424-7760    

DOI:10.1002/eej.4391140209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractActive power filters have been used in practice to suppress the harmonic interference in power systems. To compensate for harmonic currents of loads, active power filters usually are connected to power systems in parallel with the loads. These filters, which are called shunt active filters here, are very effective for loads that can be considered as current sources, such as thyristor rectifiers with large dc reactances. Many papers have covered the shunt active filters applied to these current‐source loads, however, none has discussed characteristics of the shunt active filters when they are applied to voltage‐source loads.On the other hand, since more and more diode rectifiers with capacitive dc filters have recently been used, harmonics generated by them have become an issue. The diode rectifier with capacitive dc filters behaves as a voltage source rather than a current source. When a shunt active filter is applied to such a diode rectifier, the current injected from the shunt active filter may flow into the diode rectifier. As a result, harmonics of the source current cannot be reduced effectively, and harmonic current flowing into the diode rectifier increases greatly.This paper presents the aforementioned problem of shunt active filters analytically and experimentally. Then a series active filter is proposed to suppress the harmonic current of the diode rectifiers. The features, operating conditions, and considerations of shunt active filters and series active filters are described analytically and demonstrated experimentally. Taking a diode rectifier with capacitive dc filter as a typical voltage‐source load, compensation characteristics of shunt active filters and series active filters are discussed by experiment and simulation. The validity of the series active filters is illustrated experimen

ISSN:0424-7760    

DOI:10.1002/eej.4391140210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY