摘要:

AbstractThe measurement method and the experimental results on the magnetic characteristics of oriented silicon steel in any direction are described in this paper. A single sheet tester of rotational loss has been used in order to simulate conditions existing in real devices. The flux of any direction is induced in the specimen by exciting fromXandYdirections in the same phase. The flux density was measured by each search coil. The magnetizing force was measured by the doubleH‐coil method. The outputs of theB‐coils and theH‐coils were treated by sending the outputs from the wave digitizer to the personal computer.The components of the magnetic characteristics in theXandYdirections for small values ofBare the same. Only the saturation value changes, and it depends on the direction of

ISSN:0424-7760    

DOI:10.1002/eej.4391130601

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe vector potential in electrodynamics is investigated through the decomposition of its form to the following two parts: 1) the so‐called transverse part represented by a divergenceless vector; and 2) the longitudinal part represented by an irrotational vector. The decomposition can be done by the Helmholtz theorem in the vector analysis because the conditions which should be required when the Helmholtz theorem is used are satisfied for the almost vector potentials of physically interesting problems.As an example of such interesting problems, the Aharonov‐Bohm effect is chosen here. As for the Aharonov‐Bohm effect, the vector potential given in the original paper of Aharonov and Bohm has the singularities along thez‐axis. It is shown that even for such a singular potential the Helmholtz theorem is held provided that the concept of the distribution is introduced in it. Generally, the transverse part of the vector potential obtained through such a decomposition is determined uniquely by the magnetic field and does not alter by a gauge transformation. On the other hand, the longitudinal part depends on the choice of special gauge. It is shown that the Aharonov‐Bohm effect is due to the contribution of the transverse part of the vector potential and therefore should not be influenced by any gauge transf

ISSN:0424-7760    

DOI:10.1002/eej.4391130602

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper describes the water tree diagnoses of 6.6‐kV class XLPE cables by the dc component method. The dc current component is measured by energizing the cable with ac high voltage, therefore, it would be suitable for on‐line diagnoses. The dc component is considered to be caused by the rectifying effect of water trees inside the insulation.In laboratory tests, the dc component showed a good correlation with the degradation. However, almost no correlation was seen in the on‐site measurement. The authors found that the cause of this bad correlation is the galvanic effect inside the jacket. This generates the noise current through the grounding circuit when the jacket resistivity is low. Based on this finding, the equivalent circuit of on‐site measurement was proposed.Considering the equivalent circuit, this paper proposes nine methods for discriminating the dc component due to water tree from noise current. Also described are the analytical results of each method. Furthermore, the on‐site or laboratory tests show that some of them are effective in separating the dc component due to water tree from nois

ISSN:0424-7760    

DOI:10.1002/eej.4391130603

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

年代:1993

数据来源: WILEY

摘要:

AbstractGlobal warming due to increasing atmospheric carbon dioxide (CO2) is a matter of serious concern. Energy efficiency improvement has been considered to be the most effective strategy for reducing CO2emissions. The acceleration of R&D for energy technologies which have large effects on CO2emission reduction should be effective in abating global warming.In this study, the author proposes a method for evaluating the effects of energy efficiency improvement on CO2emission reduction. This method utilizes a compact energy system model combined with analytical calculations.Using this method, effects of energy efficiency improvement in Japan in the year 2030 are analyzed. Energy efficiency improvement in thermal power generation, nuclear power generation, and heat utilization are especially effective for reducing CO2emissions. The author estimates that CO2emissions per capita can be stabilized at the present level by energy efficiency improvement.

ISSN:0424-7760    

DOI:10.1002/eej.4391130604

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

年代:1993

数据来源: WILEY

摘要:

AbstractTo analyze multifaults on a power line, many complex calculations must be performed. Hence, in many cases, computers are employed in the actual phase domain. However, it is difficult to determine the property and/or the physical meaning of the calculated results because the computer method is based on many complex numerical calculations.This paper represents a new analytical method for short‐circuit studies which can deal with cross‐country multifaults in a double‐circuit transmission line with zero‐sequence mutual coupling. This method is based on the well‐known “two‐component network theory” for a balanced three‐phase double‐circuit. Procedure steps are: (1) represent the network as seen from the faulted points with symmetrical component impedance; (2) construct the symmetrical equivalent circuits for faults with imaginary phase‐shifting transformers; (3) combine these equivalents with each other and erase the symmetrical voltages at faulted points because the phase voltages at such points are known; and (4) calculate the currents at the faulted points by solving the simultaneous linear equations.This method is applied to an investigation of distance‐relay “underreach” phenomena where crosscountry multifault occurred on a double‐circuit transmission line. Effects of line constants on these phenom

ISSN:0424-7760    

DOI:10.1002/eej.4391130605

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe flow of fault currents in bundled conductors induces an electromagnetic attraction between subconductors and thereby the bus conductor system to an extremely high level of tension. This tension, which is the most important factor in designing the mechanical strength of the system, is determined by a large number of parameters—the magnitude of the fault current, the size and number of the subconductors, spacer interval, the spring of the structure, and so on.Full‐scale 63‐kA class fault current tests were carried out on eight types of bus conductors used in 275‐and 500‐kV subconductors, and measurements of fluctuation in tension were used to clarify the relationship between the various parameters and maximum tension at fault time.A method also was devised for calculating maximum tension at fault time on the basis of the various parameters, and it has been applied in the mechanical strength design of the bus conduct

ISSN:0424-7760    

DOI:10.1002/eej.4391130606

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper presents a method for monitoring the dynamic stability of power systems using a Kohonen‐type neural network. TheQRfactorization algorithm is widely used in eigenvalue calculations for power system dynamic stability studies, due to its numerical stability. However, the method has the drawback that the computational requirements increase as the cube of the problem size. TheS‐matrix method is therefore attractive, because it focuses on the most critical eigenvalue. However, this method is difficult to use in numerical calculations. The method proposed here makes use of a mapping of the eigenvalues that allows us to regard the absolute value of the most critical eigenvalue as a quantitative dynamic stability index.In this paper, a Kohonen‐type neural network is used to estimate the index. The neural network has the following advantages: (1) it uses a simple algorithm which requires no training signal, (2) it effectively classifies the input data, and (3) it presents at the outputs a two‐dimensional mapping of the input data which makes it easy to visually comprehend their classif

ISSN:0424-7760    

DOI:10.1002/eej.4391130607

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

年代:1993

数据来源: WILEY

摘要:

AbstractVoltage instability is now under intensive study in Japan, and some dynamic methods for analyzing voltage collapse have already been presented. However, the suitability of load models used in the methods and the generality of the results have not been verified.In this paper, useful voltage collapse data acquired in real power systems are presented. The measured data are compared with the result of dynamic digital simulation to verify the suitability of an induction motor load model.In the latter half of this paper, dynamic simulations of voltage collapse with consideration of generator dynamics are carried out. An interconnected power model system with 10 nodes is analyzed. The generality of basic characteristics concerning voltage collapse which have already been obtained without considering generator dynamics is verified by such simulations.

ISSN:0424-7760    

DOI:10.1002/eej.4391130608

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

年代:1993

数据来源: WILEY

摘要:

AbstractLightning voltage induced by nearby strokes is one of the causes of major overvoltages which threaten the insulation of power distribution lines. Surge arresters as well as an overhead ground wire usually are employed for the protection of equipment and line insulation on overhead power distribution lines.The fundamental mechanism of suppressing effects of overvoltages induced by nearby strokes has been demonstrated independently by one of the present authors for surge arresters and for an overhead ground wire.In this paper, the protective effect of the combination of surge arresters and overhead ground wire is analyzed. As a result, it is found that the effect of surge arresters used together with an overhead ground wire is almost the same as that of surge arresters alone.

ISSN:0424-7760    

DOI:10.1002/eej.4391130609

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe authors have already described the nine‐phase inverter driving system providing both the triple three‐phase voltage source inverter with 180‐deg conducting period and the ac motor windings with triple three‐phase construction. The nine‐pulse inverter driving system used three small‐capacity three‐phase coupling reactors having special windings for current balance and reduction of higher harmonics.In addition, for voltage control, current balance, and waveform improvement, optimal PWM pulse patterns were applied to the six‐phase inverter driving system using a three‐phase coupling reactor to provide double three‐phase construction.In the system based on the mode in the title, the PWM control was applied to the nine‐phase inverter driving system described in the foregoing. The coupling reactors in the system balance the fundamental currents of three sets of three‐phase inverters and also absorb higher harmonic voltages other than 18p±1 (p= 1, 2, …) orders. The optimal pulse patterns found by the approach to make the performance index minimum using the Lagrange multiplier method can be applied to the PWM to reduce the higher harmonic currents greater than those calculated by the modulation method comparing the sinusoidal signal wave with triangular carrier signal.This system can have a larger capacity than the six‐phase PWM inverter driving system in which coupling reactors absorb higher harmonic voltages other than the 12p±1 orders and also improve output current waveforms. In addition, the system includes the capacity of coupling reactors slightly larger than the six‐phase PWM inverter driving system but enables operation with smaller torque ripples and electromagnetic noises i

ISSN:0424-7760    

DOI:10.1002/eej.4391130610

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

年代:1993

数据来源: WILEY