摘要:

AbstractTo design optimal electrical machines, it is necessary to develop an optimal design method for determining the shapes, sizes, positions of the cores, permanent magnets and windings which produce such specified values as flux distributions and torques.In this paper, a design method for determining the optimal sizes of cores taking into account the nonlinearity of the core has been developed by using the nonlinear programming method and the magnetization integral equation method. The pole shape of an electromagnet which produces the uniform flux distribution is determined by using the design method for determining the optimal sizes of cores. The effectiveness of the method is shown by designing the pole piece of the permanent magnet‐type MRI devic

ISSN:0424-7760    

DOI:10.1002/eej.4391120601

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

年代:1992

数据来源: WILEY

摘要:

AbstractNonpolar polymers such as polyethylene or polypropylene are widely used as insulation materials, often under conditions involving strong electric fields and high temperatures. Under these conditions, the conduction loss due to DC‐like carrier transport may give rise to a high‐field AC dissipation factor (tan δ).This paper describes the high‐field dielectric properties of polyethylene films at frequencies from 50 to 400 Hz and temperatures from room temperature to 100°C, as measured with a new type electrode design developed by the authors. In the high‐temperature region, the AC dissipation current waveform at 50 Hz was also measured. At room temperature, the electric‐field dependence of tan δ is almost unaffected by the frequency of the applied field. But at high temperatures and strong electric fields, tan δ tends to have a large field dependence and to be almost inversely proportional to the frequency. Thus the AC conductivity becomes independent of the frequency of the applied field in the region of strong fields and high temperatures. A theoretical analysis shows that the high‐field dielectric loss is governed by two processes, namely, the dielectric relaxation loss inherent to the AC field and the DC‐like carrier transport loss that becomes prominent in the high‐temperature region, where AC dissipation current waveform becomes signific

ISSN:0424-7760    

DOI:10.1002/eej.4391120602

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

年代:1992

数据来源: WILEY

摘要:

AbstractDischarge phenomena in positive rod‐to‐plane air gaps under lightning impulse and dc voltages were investigated.Under impulse voltages, the 50 percent flashover voltages agree with the 50 percent corona inception voltages only in a gap shorter than a certain valuedcwhich increases with the rod diameter φ. The 50 percent flashover voltage atdcrises at a rate of about 14 kV/cm withdcin the range ofdc<2.8 cm (φ ⩽ 1.5 cm), and then it rises at a rate of about 5 kV/cm. Experimental results show that the flashover process in the former region (termed the Gp process) is different from that in the latter region (the Lp process).Under dc voltages, the critical gap length, at which the first corona may lead to flashover without any succeeding streamer corona, corresponds todcunder impulse voltage. In a gap shorter thandcflashover occurs through the Gp process (φ ⩽ 1 cm) or Lp process (φ ≥ 2 cm), but in gap longer thandcflashover may occur through another process which cannot be seen under impulse voltages.In this paper, those flashover characteristics and processes are described on the basis of experimental results and photographic observations with an image con

ISSN:0424-7760    

DOI:10.1002/eej.4391120603

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

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper deals with static var compensators using self‐commutated inverters (which is so‐called SVG) compared with conventional SVC and Rotary Condenser.Improvement of power system stability is explained by using simple system model and checked by dynamic digital simulation.In the latter part of this paper, system outline, basic specifications and control diagram of the SVG rated 154 kV, ±80 MVA, which has been installed at INUYAMA Switching Station, are briefly presented.Field tests at INUYAMA verify that power swing is effectively damped and transmission capacity is incre

ISSN:0424-7760    

DOI:10.1002/eej.4391120604

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

年代:1992

数据来源: WILEY

摘要:

AbstractIn recent years, the sizes of Energy Management Systems (EMS) and Supervisory Control and Data Acquisition (SCADA) systems have grown to huge proportions for two reasons:The power systems to which they are applied have grown in size and complexity; andTheir own functions have become more diverse and sophisticated.This raises the following problems: degradation of response time; decreased reliability; limited expandability; less maintainability; and increased costs.A functionally distributed system that is characterized by parallel processing and independent subsystems (parallel‐independent architecture) will solve these problems.The system is comprised of a group of functional units, each of which runs in parallel, independently and asynchronously. Copies of some programs and power system status data are stored in the relevant functional units, and data‐driven architecture is adopted, which eliminates the need for a centralized control mechanism.The feasibility of a functionally distributed system was tested through construction of a prototype. The results were satisfact

ISSN:0424-7760    

DOI:10.1002/eej.4391120605

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

年代:1992

数据来源: WILEY

摘要:

AbstractElectric power systems are expanding in size and complexity, and the requirement for the energy management system (EMS) is becoming more important. In this computer control system, a single control computer is used mainly as the primary computer and its software is very complicated because of its hugh number of small, quick tasks to obtain high response speed. Therefore, much effort is needed to develop and modify the programs, and the responsiveness of this centralized architecture varies greatly when many faults occur in the power system.This paper describes a new distributed architecture for the EMS. Distributed processors execute the functions cooperatively with periodic access to the common bulletin board database in which information about the power system exist. This architecture facilitates the software development and maintenance, and it also enhances the performance by the parallel processing of the distributed functions.

ISSN:0424-7760    

DOI:10.1002/eej.4391120606

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe flashover characteristics of long air gaps submitted to switching surge voltages may be predetermined by use of a mathematical model of leader propagation.The present model is developed from each combination of previous engineering models, and is also applied to positive rod‐to‐plane geometries with gap lengths up to 20 m.However, four parameters to determine leader propagation with respect to our model are adjusted in the present calculation so as to fit experimental flashover voltages and calculated flashover voltages which depend on waveforms of the applied voltage and gap length. The calculations show that these parameters are only a function of gap length.Our combined engineering model using parameters that depend on gap length allows the flashover characteristics of long air gaps to be easily determined with a microcompu

ISSN:0424-7760    

DOI:10.1002/eej.4391120607

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

年代:1992

数据来源: WILEY

摘要:

AbstractWith the growing size and complexity of power systems, system analysis—such as transients calculation—takes much time. Hence, fast calculation methods are required. Although parallel processing is a hopeful method, there have been difficulties in the parallel solution of linear equations which appear in power‐flow calculations by the Newton‐Raphson method.This paper aims at the fast calculation of the power‐flow problem by means of parallel processing. In order to improve the suitability to the parallel solution of the differential equation in transients calculation, we assume the use of a direct‐mapping parallel processing machine to map directly the network of a power system onto a network of processors. Under this assumption, we propose a new parallel‐processing‐oriented method in which the linear equation is solved by linear iterations between nodes with Aitken acceleration. We simulate the method on three model power systems and compare this Parallel Iterative Method (PIN) with a Parallel Direct Method (PDM) which uses the banded matrix according to the number of operations required. As a result, we can expect that PIM may solve linear equations faster than PDM withmprocessors, although the PIM might be inferior to the PDM withm×mprocessors, wheremdenotes the half‐band width of

ISSN:0424-7760    

DOI:10.1002/eej.4391120608

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe authors propose a new power consolidation‐inversion‐control system for the Faraday MHD generator using the voltage source PWM inverters. The dc output power for each electrodes pair of the MHD generator is at first inverted into three‐phase ac power by a voltage source PWM inverter, and then the ac powers are consolidated by transformers. The proposed system does not need such expensive equipment as an ac filter or phase modifier and can independently and simultaneously control the active and reactive powers provided to the electric power system. Numerical simulations of the whole system, including the Faraday MHD generator, the proposed power consolidation‐inversion‐control system, and the electric power system, show that the proposed system can stably and steadily transmit and control the electric power from the MHD generator to the electric power system. It is also confirmed that the proposed system can independently and simultaneously control the active and reactive powers and can be used as a fast power c

ISSN:0424-7760    

DOI:10.1002/eej.4391120609

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

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper describes development of three‐dimensional electric field computation system by surface charge method. Using this system, both potential and electric field in the case which includes resistance or true electric charge can be calculated. And this system is able to be connected to the pre‐post processors, which is useful for us to make arbitrary shape and to display results of analy

ISSN:0424-7760    

DOI:10.1002/eej.4391120610

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

年代:1992

数据来源: WILEY