摘要:

AbstractIn this paper, a method is proposed to estimate the minimum breakdown voltages of surface flashovers initiated from the triple junction at which a solid insulator, SF6gas, and a metal electrode come in contact.Using four kinds of test samples, the flashover voltages Vfare measured. The voltages Vfbecome lower than the theoretical voltages Vsof streamer inception in the case of the test sample with the large electrode area at the triple junction. To understand the phenomena quantitatively, we estimated the real partial discharge voltages Vcfrom the voltages Vf, and investigated the relationship between the voltages Vcand the theoretical values Vs. The values of Vs/Vc, which characterize the properties of the partial discharges, can be shown by the product λS90%EavP of the following parameters: (1) coefficient λ representing the surface roughness of electrode at the triple junction; (2) effective area S90%of the electrode; (3) average field Eavat the area S90%; and (4) gas pressure p. The minimum surface flashover voltages in the insulators for coaxial electrode systems can be estimated precisely, considering the properties of Vs/V

ISSN:0424-7760    

DOI:10.1002/eej.4391160501

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

年代:1996

数据来源: WILEY

摘要:

AbstractA model vehicle is constructed which runs without contact to its magnetic rail using oxide superconductors. This paper describes the forces acting between the superconductor and the rail for such a purpose. The attractive and repulsive forces were measured at 77 K as a function of distance between the superconducting pellet and the magnetic rail. As suprconducting pellets, three kinds of materials, i.e., MPMG‐Y123, BiPb2223, and Hg1223, were investigated for three kinds of permanent magnets, i.e., Nd‐Fe‐B, Sm‐Co and

ISSN:0424-7760    

DOI:10.1002/eej.4391160502

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper proposes a forecasting method for shortterm peak electric loads using a 3‐layer neural network of locally active units. Each unit in the hidden layer of the neural network is activated only by input vectors in a bounded domain of vector space. This characteristic enables additional learning. Furthermore, it is supposed to provide the network structure with information that helps to improve forecasting accuracy. The neural network is applied to daily peak load forecasting simulations in summer. The results show that the proposed method is superior to a conventional neural network with the backpropagation algorithm. To make the best use of the neural network, an error‐oriented method of parameter modification is also exami

ISSN:0424-7760    

DOI:10.1002/eej.4391160503

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

年代:1996

数据来源: WILEY

摘要:

AbstractPartial discharge (PD) degradation phenomena is one of the most important factors to decide the performance and the lifetime of the high voltage apparatus. During PD degradation tests of an epoxy specimen with an internal void, PD often change to a large number of very small PD known as swarming pulsive microdischarges (SPMD). Because the appearance of SPMD is concerned with the degradation of the insulating materials, the insulation diagnosis with the detection of SPMD becomes possible. However, SPMD cannot be detected with the conventional PD Detector because the PD magnitude of SPMD is too small. The computer‐aided partial discharge analyzing system (CAPDAS) has been developed to detect and analyze the SPMD. Furthermore, a new PD parameter, the SPMD ratio has been introduced for quantitative analysis of SPMD. In this paper, the time variation of SPMD characteristics of a CIGRE Method‐II specimen are investigated by using the CAPDAS. Further, the effect of the frequency of the applied voltage on SPMD is also investigated at 60 Hz and a very low frequency of 0.1 Hz. As a result, the comparison of PD magnitudes measured at 60 Hz with those at 0.1 Hz enables a quantitative analysis of SPMD characteristics to be possible by using only the conventional PD detec

ISSN:0424-7760    

DOI:10.1002/eej.4391160504

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

年代:1996

数据来源: WILEY

摘要:

AbstractA CO2‐recovering hybrid power generation system utilizing solar thermal energy is proposed. In the system, relatively low temperature saturated steam around 220°C is produced by using solar thermal energy and is utilized as the working fluid of a gas turbine in which generated CO2is recovered based on the oxygen combustion method. Hence, solar thermal utilization efficiency is considerably higher as compared with that of conventional solar thermal power plants in which superheated steam near 400°C must be produced for use as the working fluid of steam turbines; the requirement for solar radiation in the location in which the system is constructed can be significantly relaxed. The proposed system is a hybrid energy system using both the fossil fuel and solar thermal energy, thus the capacity factor of the system becomes very high. The fuel can be used exergetically in the system; i.e., it can be utilized for raising the temperature of the steam heated by utilizing the turbine exhaust gas more than 1000°C. The generated CO2can be recovered by using an oxygen combustion method, so that a high CO2capturing ratio of near 100 percent as well as no thermal NOxemission characteristics can be attained. It has been shown through simulation study that the proposed system has a net power generation efficiency of 63.4 percent, which is higher than 45.7 percent as compared with that of the conventional power plant with 43.5 percent efficiency, when the amount of utilized solar energy is neglected and the temperature of the saturated steam is 2

ISSN:0424-7760    

DOI:10.1002/eej.4391160505

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

年代:1996

数据来源: WILEY

摘要:

AbstractA decentralized control system is studied for stabilizing multimachine power systems. A longitudinal power system with three areas, each having one machine, is considered in this study. A decentralized control design method is proposed, which is based on the optimal regulator theory. First a centralized control system is designed without any consideration on whether state variables are all available or not. Second a pseudo‐decentralized control system is designed by omitting control gains corresponding to state variables which give hardly any effects on the power system stability. It is found that only one variable of phase angle of each machine is absolutely necessary for the pseudo‐decentralized control system. This leads to an idea based on power system engineering, that is to say, new variables of tieline power flow are introduced in the decentralized control system design to substitute for the phase angle of each machine. Thus a decentralized control system for power system stability can be designed using the new variables of tieline power flow. It is demonstrated from simulation studies that the decentralized control system improves even longitudinal power system stability as well as the centralized control sys

ISSN:0424-7760    

DOI:10.1002/eej.4391160506

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe method for measuring insulation resistance by superimposing the dc voltage has potential for detecting the deterioration of cable insulations. The deterioration of cable insulations can be detected by measuring current which flows through a grounded shielding wire. However, the earth current also flows from the cable sheath into the grounding wire as noise. Thus, to assess the deterioration properly, it is necessary to separate the earth current from the total current. On the other hand, to improve detection sensitivity, it is desirable to superimpose the highest possible dc voltage. In this case, provision must be made so that there are no adverse effects on the GPT.The authors, placing special emphasis on the method of measuring high insulation resistance by configuring the bridge, have conducted an investigation on how to detect the insulation deterioration with high accuracy and sensitivity without impairing the functions of the GPT. The following issues were investigated and the results are reported in this paper:(1) It is possible to measure insulation resistance as high as 100,000 MΩ by superimposing 50‐V dc through the GPT after cancelling the earth‐current and by configuring a bridge for determining insulation resistance from voltage ratio.(2) Even if 50‐V dc is superimposed through the GPT, it is possible to prevent the magnetic saturation of GPT if the current injected by such superimposition is limited (i.e., below max. 5 mA).(3) In lieu of a variable resistor, a variable dc voltage supply is employed in the bridge. The variable dc voltage supply requires no mechanically driven part, thus making it possible to realize a fully automatic monitoring

ISSN:0424-7760    

DOI:10.1002/eej.4391160507

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper presents an application of parallel processing and pipeline processing to power system analysis. The system matrix is transformed to a bordered block diagonal form (BBDF) matrix for effective utilization of the processors. After LU factorization, subnetworks organize sparse matrices and the boundary network organizes a full matrix. First, a parallel processing technique is used to calculate subnetworks. Then, as pipeline processing is applied, inverse matrix of the boundary network is multiplied. The proposed method is made operational on a parallel computing system including a pipeline processor. A consideration on the transient stability analysis using the proposed method also is presented at the end of this paper.

ISSN:0424-7760    

DOI:10.1002/eej.4391160508

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

年代:1996

数据来源: WILEY

摘要:

AbstractA perfluorocarbon (PFC)‐immersed 275‐kV transformer with compressed SF6, gas has been developed. This paper describes the basic cooling and insulation characteristics of PFC, the ac partial discharge voltage, and the aging of PFC‐immersed insulation. The results demonstrate that a prototype 275‐kV 100‐MVA three‐phase transformer can be operated without any difficulties for an extended period of overvoltage. This prototype has an ac partial discharge initiation strength which is 1.5 times that of the ac test voltage and a lightning impulse breakdown strength which is 1.5 times that of the test voltage. A 275‐kV 250‐MVA three‐phase transformer was built and is being operated at the Abe substation of Chubu Electric Power Co., Inc. The transformer has been operati

ISSN:0424-7760    

DOI:10.1002/eej.4391160509

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

年代:1996

数据来源: WILEY

摘要:

AbstractA new concept to achieve an ideal transient control performance is described. It is also possible to examine control performance on the frequency domain. Generally speaking, better control performance will be realized by using more exact information on the plant. A simulator should be built that has both correct initial values of state variables and parameters on dominant parts of the plant. The internal states of the simulator are used to represent the internal states of the plant, and control input is synthesized with the internal states of the simulator and the plant output. Using information on the simulator allows an ideal control performance at a dominant frequency area to be obtained in spite of the existence of unmodeled dynamics at a higher frequency domain. This control system is called simulator‐based foresight control (SFC), and is available for both nonlinear and timevarying plant

ISSN:0424-7760    

DOI:10.1002/eej.4391160510

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

年代:1996

数据来源: WILEY