摘要:

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 voltag

ISSN:0424-7760    

DOI:10.1002/eej.4391140401

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

年代:1994

数据来源: WILEY

摘要:

AbstractHard magnetic properties of nitrogen interstitially modified NdMxFe12‐xNycompounds and Fe3B‐based ultra‐fine crystalline NdFeCoTB alloys of low Nd content of 3 to 5 at. % are studied. The nitrogen‐modified compounds have been prepared via the rapid solidification route and the mechanical alloying route both followed by gas nitrogenation using N2. The Fe3B‐based materials have been prepared by means of rapid solidification and crystallization treatment. The latter materials appear promising as the base material for high‐remanence, easy‐to‐magnetize bonded magnets with small temperature coefficients of remanence. Typical magnetic properties of compaction isotropic bonded magnets produced from this material areBr= 0.80 T,HcJ= 350 kA/m,

ISSN:0424-7760    

DOI:10.1002/eej.4391140402

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

年代:1994

数据来源: WILEY

摘要:

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:(1)A flashover voltageVfof rainwater decreases gradually with increasing the σ and an effect of theVfon the pH cannot be seen obviously in this experimental condition;(2)On the propagation of the streamer discharge on the surface of artificial acid rain.(i)In case of rain which has nearly the same pH and the different σ, the propagation lengthldof streamer‐like density changes becomes larger as the σ is made larger;(ii)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 at‐ldcharacteristic of the streamer‐like density changes, and in a cu

ISSN:0424-7760    

DOI:10.1002/eej.4391140403

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper presents an efficient computational algorithm for selecting the optimal generation mix under uncertain circumstances. Subjective, experiential or linguistic uncertainties are selected from among various uncertainties, i.e., we treat fuzziness in generation expansion planning. The fuzziness can be divided into: (1) the fuzziness of decision making; and (2) the fuzziness of some planning parameters, such as load growth, fuel price, and so on. Both classes of fuzziness are integrated into a fuzzy decision based on fuzzy sets theory, and then the optimal generation mix can be determined by the Fuzzy Dynamic Programming (FDP) technique.The proposed method, which is based on the dynamic programming technique, is extended by using the Bellman‐Zadeh maximizing decision. In the method, each generation technology and generation capacity are selected as a stage and state, respectively. The proposed method can easily accommodate not only the fuzziness but also many constraints of generation expansion planning, such as integer solutions of unit capacities, condition of existing units, and so on. Furthermore, the arbitrary shape of membership function can be used. The effectiveness and feasibility of the proposed method are demonstrated on a typical power system mode

ISSN:0424-7760    

DOI:10.1002/eej.4391140404

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

年代:1994

数据来源: WILEY

摘要:

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 stand

ISSN:0424-7760    

DOI:10.1002/eej.4391140405

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper presents an efficient computational algorithm for selecting the optimal generation mix considering CO2emissions. To demonstrate the effectiveness and feasibility of the proposed method, a fundamental study of the evaluation of the optimal generation mix for controlling CO2emissions is indicated. Furthermore, by using a parametric analysis which considers load characteristics as parameters, a general trend for the optimal generation mix which is affected by controlling CO2can be derived.The proposed method is based on an optimization method known as simulated annealing. In the method, solutions in a generation mix problem are equivalent to state of a physical system, and the cost of a solution is equivalent to the energy of a state. The proposed method can easily accommodate not only CO2emissions but also many practical constraints of generation expansion planning, such as integer solutions of unit capacities, condition of existing units, and so on.Case studies with various annual load patterns (combinations of annual load factors and the shapes of annual load duration curve) are presented and discussed. Consequently, a general trend for selecting generation technologies that should be added to a power system is derived, i.e., a useful guideline for studying generation expansion planning under controlling CO2emissions can be provided.

ISSN:0424-7760    

DOI:10.1002/eej.4391140406

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper reports on the results of the optimization of the cross‐sectional shape of a magnet coil system including an MHD channel. This optimization was carried out for a 200‐MWe supersonic Faraday‐type MHD generator. It was shown that the channel length can be shortened more than 30 percent, without the decrease of the enthalpy extraction by the optimization of the coil shape from the crescent shape coil producing a uniform magnetic field. It was estimated also that the capital cost for a commercial MHD/steam combined plant can be decreased more than 6 percent by this coil shape optimiz

ISSN:0424-7760    

DOI:10.1002/eej.4391140407

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe earth‐return impedance and capacitance formulas of a finite parallel multiconductor with arbitrary positions have been proposed. A comparison with measured results has proved that the accuracy of the impedance formula is satisfactory. By applying the formulas, the characteristics of the finite line parameters such as a propagation constant and a characteristic impedance are investigated in comparison with those given by the conventional assumption of an infinite line. The impedance of the infinite line is greater and the capacitance is smaller than those of the finite line. The difference increases as the line length and source frequency decrease, and the height, radius and separation distance increase. According to the foregoing, the attenuation constant and the characteristic impedance of the infinite line are greater and the propagation velocity is smaller than those of the finite lin

ISSN:0424-7760    

DOI:10.1002/eej.4391140408

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

年代:1994

数据来源: WILEY

摘要:

AbstractSample cables having a few types of defects (such as voids, contaminants, and protrusions) with more volume than usual, were prepared intentionally to clarify how these defects affect separately insulation characteristics under the presence/nonpresence of moisture. In the case of void inclusion, insulation characteristics are even more susceptible to ac voltage than impulse voltage, and the distribution of lifetimes is classified into a wornout failure type due to discharge deterioration.While protrusions and some other contaminants can greatly deteriorate original dielectric strength, these defects have a relatively slight effect on long‐term endurance in the atmosphere. Therefore, the distribution of lifetimes is classified into an early‐failure type. With reference to the influence of moisture, in a strong electric field (exceeding 15 kV/mm) and in a short‐term region, there is an increase in harmfulness around defects with water absorbed, thereby inducing electrical trees and resulting in a breakdown. In the light electric field (no more than 15 kV/mm) and in a long‐term region, harmfulness of defects will not deepen to a considerable extent, and the growth of water trees very possibly is infl

ISSN:0424-7760    

DOI:10.1002/eej.4391140409

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe idea of unbalanced load flow calculation was proposed many years ago. At that time, however, the needs for such techniques was not urgent. Modern power system networks are comprised of long untransposed transmission lines. Therefore, for some kinds of analysis, it is now almost impossible to treat a system as though it were a symmetrical network. The aims of most previous studies were oriented to solve voltage/current imbalance in local or small systems, as local imbalance was a serious concern. This is still an important issue, but more recently needs have become concentrated on practical bulk power systems, since principal EHV lines are entirely untransposed.In this paper, the development of practical unbalanced load program and practical experience with it are reported. This program was developed for steady‐state analysis of large‐scale practical networks under many possible unbalanced conditions. The Newton‐Raphson method in polar coordinates is used, since fast and moderate convergent characteristics are suitable for solving solutions. The program was applied to practical case studies. The models contain all of the 500‐kV and most of the 275‐kV overhead transmission lines in TEPCO. Since the density of the Jacobian matrix is higher than in single‐phase load flows, the number of nonzero elements is extremely large. Convergent characteristics are excellent in all cases. The fear of numerical instability has b

ISSN:0424-7760    

DOI:10.1002/eej.4391140410

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

年代:1994

数据来源: WILEY