摘要:

AbstractA medium‐sized, high magnetic field magnet was designed using data on the mechanical properties of Bi/Ag oxide tape superconductors. Due to the poor mechanical properties of tape superconductors, the size of a superconductive magnet is limited to a narrow region of radius and magnetic field. In order to build a large superconductive magnet, key mechanical properties of the Bi/Ag oxide tape superconductors, such as irreversible strain and matrix yield strength, have to be improved significantl

ISSN:0424-7760    

DOI:10.1002/eej.4391170201

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

年代:1996

数据来源: WILEY

摘要:

AbstractResearch on decentralized control of an electric power system is important for stabilizing control problems. In particular, since an electric power system is a large‐scale nonlinear control system, decentralized (not divided) systems with cooperation should be constructed.This paper presents ways to construct decentralized systems for an electric power system. In section 2, swing data of a three‐machine model system are obtained, in section 3, coefficient parameters of the model equation based on one‐machine infinite‐bus system with AVR and GOV are estimated by the least square method. In section 4, the equivalence calculated using estimated values is discussed, and the effect of conditions on fault is considered. Finally, section 5 is devoted to summarizing results of decentralized system identif

ISSN:0424-7760    

DOI:10.1002/eej.4391170202

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

年代:1996

数据来源: WILEY

摘要:

AbstractFor lightweight and compact implementation of a generation set, many attempts have been made by some researchers to develop a brushless self‐excited synchronous generator without an ac exciter. A previous paper proposed a novel self‐excitation scheme by which the second‐space harmonic component of armature mmf is used for exciting the rotor field system. In this excitation scheme the effect of the series excitation characteristic, as well as a self‐excited and brushless implementation without an ac exciter is automatically obtained. However, in the case of system configuration of the generator already reported, voltage regulation in the inductive load condition was very large. To remove this problem, this paper presents a new system configuration of the generator with a self‐regulating feature that can compensate voltage regulation automatically. The new generator consists of a stator installing two three‐phase windings, externally connected to a load and a capacitor bank, respectively, and a rotor with field and harmonic windings.In this paper the system configuration and theoretical concepts of the presented generator are described and detailed experimental investigations with a laboratory machine are

ISSN:0424-7760    

DOI:10.1002/eej.4391170203

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper proposes a transmission line tower model in frequency domain for back‐flashover analysis, which has a uniform characteristic impedance and a uniform propagation constant. Most conventional tower models are constructed as a constant and uniform parameter transmission line that is independent of frequency. However, the authors' models have the frequency dependency of the characteristic impedance and the propagation constant to express the frequency characteristic of the transmission line tower.Two models, a cylinder model and a four‐frames model, were investigated to simulate the tower. Their surge responses were computed by numerical electromagnetic field analysis based on the moment method. From the results, the two‐port circuit constants were calculated in the frequency domain, and the characteristic impedance and the propagation constant are derived from them. The complex artificial oscillations appeared in frequency dependency of the parameters because the parameters were calculated numerically. The equations with analytical form were obtained by approximating with a smooth curve to the oscillations. It is possible for the equations to represent the transmission line constants as a function of geometrical parameters such as the tower height and the radius. Close agreement was found between the surge response computed by the numerical electromagnetic field analysis and the result calculated by inverse Laplace transformation of the analytical equations. To prove the model, the experimental results were compared with the computed ones of the cylinder model that has arms, and it was shown that the new model agrees closer with the experiment than conventional transmission line m

ISSN:0424-7760    

DOI:10.1002/eej.4391170204

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

年代:1996

数据来源: WILEY

摘要:

AbstractWhen electric power supply interruption is caused by a fault, it is imperative to restore the power system promptly to an optimal target configuration after the fault. The problem of obtaining a target system is referred to as power system restoration. Both mathematical programming (MP) and expert systems (ES) have been used to solve restoration problems. However, existing approaches based on either MP and ES alone have inherent limitations stemming from their own paradigms. Mathematical progressing can obtain an optimal configuration under specified operational constraints, but requires a relatively long solution time. Although ES are effective in that they can utilize expert knowledge, maintenance of large‐scale ES requires inordinate effort.This paper proposes a new approach to power system restoration that utilizes both methodologies so as to exploit both systems' advantages. That is, a system under study is decomposed into a set of subsystems based on the knowledge of restoration experts, which is realized as an expert system. Then, MP is applied to each decomposed subsystem to obtain an optimal target configuration. A feasible operation sequence leading to the target configuration is generated by ES. This approach reduces significantly the computation time required to obtain target systems and is far less than would be the case if the total system is solved (as a unity). Moreover, the number of rules in the knowledge‐base are greatly decrea

ISSN:0424-7760    

DOI:10.1002/eej.4391170205

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe recent drastic increase in the number of air conditioners has caused sharp and narrow peaks in summer seasons due to the inherent temperature‐sensitive characteristics. The authors propose a method to reduce the peak power demand by controlling air conditioner operations, and verify its effectiveness on clipping peak demand. However, former study has shortcomings in that no qualitative treatment of room temperature or comfort was attempted, and it did not provide a way of assessing peak demand clipping in a power system as a whole.In this paper, the authors propose a new control method that can deal with the maintaining of comfort and the reduction in power demand. Although air conditioners are used for “comfort,” this contradicts the reduction of power consumption and furthermore the concept of “comfort” is very vague. Hence, Weber‐Fechner's law is utilized to quantify the pleasant feeling which is treated as a fuzzy quantity. A fuzzy coordination method is used to resolve this difference between power demand curtailment and comfort.The second part of this paper prepares an approach for assessing the amount of peak load clipping when the newly proposed control strategy is adopted in a real‐size power system. A decrease in the required generation capacity is estimated provided that the loss of load probability (LOLP) is maintained at the same level before and after the application of the new control strategy. The reduction can be regarded as a dividend of lo

ISSN:0424-7760    

DOI:10.1002/eej.4391170206

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

年代:1996

数据来源: WILEY

摘要:

AbstractIn commercializing the superconducting Maglev system it is important to reduce the cost, especially that of ground coils constructed along the whole length of the guideway. For this purpose we have examined the combined propulsion, levitation and guidance system (PLG system) which can generate levitation, guidance and propulsion forces by the same coil. This paper describes the test run of the PLG system, whose ground coils (PLG coil) are constructed in one part of the Miyazaki test track. In designing the PLG coil, we make clear the magnitudes of the force acting both under normal and unusual conditions because the electromagnetic force, which levitates, guides, and propels the vehicle, directly acts on the magnet winding of the PLG coil. In the experiment, we examine both the performance of the vehicle and the force of a PLG coil. The measurement of the force at the PLG coil gives not only propulsion force and levitation force directly, but also guidance stiffness by sifting the measured coil. Good correlation recognized between the calculation and the experiment in the propulsion force, levitation force, and guidance stiffness proves that the required characteristics can be expected from the PLG system even under combination of propulsion, levitation and guidance.

ISSN:0424-7760    

DOI:10.1002/eej.4391170207

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper presents a new discrimination procedure of signal waveforms based on wavelet theory for the inspection of rotating machinery. The wavelet transform decomposes signals into time‐frequency space, rather than mere frequency space, limited by the uncertainty principle. This decomposition permits time‐frequency analyses and provides a more flexible means of signal processing than before.To examine a rotary compressor pump, particular waves in the rotational load torque signals that correlate with failure modes are discriminated from one another and evaluated. To extract the focal waves, the signal is decomposed with wavelets and then only particular waves, such as impulses, are reconstructed from a selected set of wavelet coefficients. This is called time‐frequency space filtering. The wavelet local modulus maxima are used to pen a time‐frequency window through which only the focal waves can pass with high fidelity. The maxima have information of the inflection points of the wave at each resolution that represent its waveform.The experimental results show the effectiveness of the pr

ISSN:0424-7760    

DOI:10.1002/eej.4391170208

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper deals with an advanced static Var compensator (ASVC) using quad‐series voltage‐source PAM inverters. The ASVC consists of four three‐phase voltage‐source inverters with a common dc capacitor and four three‐phase transformers, each primary winding of which is connected in series with each other. Each inverter outputs a square‐wave voltage, while the synthesized output voltage of the ASVC has a 24‐step wave shape. This results not only in a great reduction of harmonic currents and dc voltage ripples but also in fewer switching and snubbing losses.In this paper, transient analysis is performed with the focus on the response of reactive power and the resonance between the dc capacitor and ac reactors. Experimental results obtained from a small‐rated laboratory model of 10 kVA are also shown to verify analytical results based on thep‐qtransformation. The analytical results help in the design of system parameters such as the capacity of the dc capacitor a

ISSN:0424-7760    

DOI:10.1002/eej.4391170209

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

年代:1996

数据来源: WILEY

摘要:

AbstractWe wish to derive an improved analytic method and performance equations for estimation of the characteristics and the design of a reasonable LIM. An approximation that simplifies the estimation of the performance of the single‐sided linear induction motor is presented. The original equations were derived from the two‐dimensional electromagnetic analysis and the equivalent circuit quantities, such as the magnetizing reactance, the secondary resistance and reactance, and are given in combination with hyperbolic and trigonometric functions of complex number.In this paper, these functions are approximated by the MacLaurin's expansion, and the equivalent circuit quantities are expressed by polynomial approximations. The computed thrust, primary current, power factor and efficiency‐slip curves for the test of urban‐transit SLIM at Kyushu University, calculated from the original equation and the new approximation, show a close agreement. The magnetizing reactance plays an important role in the LIM performance and the larger it is, the better. The ratio of air gap length to pole pitch is the key to the performance of

ISSN:0424-7760    

DOI:10.1002/eej.4391170210

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

年代:1996

数据来源: WILEY