摘要:

AbstractMany efforts towards a settlement of the CO2problem have already been made through internationally organized meetings. It is not unlikely that some targets will be set for the reduction of CO2emissions. If a stringent reduction target should be imposed on CO2emitted from a national energy system, this can possibly have as severe an impact upon electric power sectors as the oil price crises experienced in the seventies. It is, however, quite uncertain whether or not political muscles will be used specifically for tackling the CO2problem in the near future.In such a context, this paper presents a new method for optimal power system planning under uncertain CO2emissions control policies. The derived optimal expansion plan gives us the minimum expected value of the sum of the total system cost and the total amount of carbon taxes levied on net CO2emissions from fossil fuel‐fired power plants. The stochastic dynamic optimization problem discussed here is formulated as a linear programming problem decomposable into several small subproblems. The proposed method can take into account a specific future scenario of the magnitude of control policy uncertainties, which can be presumably resolved in the first half of the next century due to the increase in scientific wisdom.In order to evaluate the usefulness of the method proposed here, the authors also present a simple case study with the Japanese national power system up to the year 205

ISSN:0424-7760    

DOI:10.1002/eej.4391170501

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe possibility of forecasting cloud‐to‐ground discharges is investigated. It is empirically well known that the cloud‐to‐ground discharges occasionally follow the cloud discharges, and the objective of this paper is to determine if it is true or false, using the SAFIR data for a few years. Since the development of thunderclouds is determined by the movement of its active area, the coordinate fixed to the moving thunderclouds is applied for analysis.The analyzed results suggest that forecasting cloud‐to‐ground discharges with 10‐min advance notice for both summer and winter thunderstorms is

ISSN:0424-7760    

DOI:10.1002/eej.4391170502

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper describes a newly developed impulse voltage generator (IG). It has the following features: (1) The IG consists of three components (a 1.6 MV unit, a 1.4‐MV unit and a base box); this facilitates mounting on 10‐ton trucks, therefore making it easier to move to a test field. (2) Capacitors, discharge gaps and a control unit are enclosed in fiber‐reinforced plastics, making it possible to use the IG in all weather. (3) The IG can generate several ten kA when a load is a few ten Ω. (4) Composition of the circuits for lightning/switching impulse voltage/current tests can be easily done by changing the damping and discharge resistance cassettes. Control and data acquisition are made by personal computer.For IG application during an outdoor test, this paper presents the characteristics of resistances of a 77‐kV substation grounding and a concrete pole when applying a high impulse current. The resistances are dependent on the crest value of the applied

ISSN:0424-7760    

DOI:10.1002/eej.4391170503

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

年代:1996

数据来源: WILEY

摘要:

AbstractRecently, multifilamentary superconducting wires with very low ac losses have been produced and practical applications will now be considered. To realize actualsize power machines and apparatuses, it is necessary to develop 1 ‐ 10 kA ac conductors. However, the critical currents of multifilamentary wires at 1 T are several tens of A, and therefore it is necessary to use multistrand conductors consisting of several tens or several hundreds of strands. Such conductors sometimes show ac current degradation because of such factors as (1) nonuniform current distribution, (2) wire motion, (3) temperature increase, (4) longitudinal magnetic field effect, etc.Formerly, a coreless transformer was considered unpractical because of its large exciting current. However, Yamamoto and others proposed that a coreless superconducting transformer could be used as a stepdown autotransformer at the receiving side, utilizing its large exciting current as the reactive power source to cancel the charging current of an underground transmission line or UHV line, and therefore the shunt reactors could be eliminated.In this paper, development of ac‐superconducting conductors aimed at prevention of current degradation are discussed, as well as quench test results of two small coils made with these conductors. In these conductors, low ac low strands with ultrafine NbTi filaments are twisted around a central bundle of stainless steel wires. One of the coils has been designed as a model coreless autotransformer, and its test result is also descri

ISSN:0424-7760    

DOI:10.1002/eej.4391170504

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

年代:1996

数据来源: WILEY

摘要:

AbstractA distributed diagnosis system combining Immune Network (IN) and Learning Vector Quantization (LVQ) for detecting fault sensors accurately in industrial plants is proposed. It has two execution modes, namely, its training mode where LVQ extracts correlation between each two sensors from their outputs when they work properly, and its diagnosis mode, where LVQ contributes to testing each two sensors using the extracted correlation, while IN contributes to determining fault sensors by integrating these local testing results obtained from LVQ. Discussed here is how to improve diagnosis capability of the developed system. It is shown that the thresholds can be determined effectively by the constraint that the hyperregion corresponding to the normal sensor outputs in each quantization vector space is a single region.Diagnosis capability of the developed system is evaluated using a prototype system for detecting fault sensors of a reheating furnace plant. With the proposed method, abnormal sensors, such as aged deteriorated ones, which have been difficult to be detected only by checking each output of sensor independently, are possible to be specified.

ISSN:0424-7760    

DOI:10.1002/eej.4391170505

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe neutral‐point‐clamped (NPC) PWM inverters have many advantages such as the ability to operate the motor with nearly sinusoidal current waveforms. For this reason, in larger‐capacity inverter systems, NPC PWM inverters using the GTOs, etc., have also been put into practical use because of great advantages to large‐capacity ac motor drives such as lower ripple currents and higher output voltages. With the spread of applications, still larger‐capacity inverters also are expected. However, since the capacities of such switching devices are insufficient, a certain technique and controlling method are proposed for the parallel connections of NPC inverters. The output voltage waveforms of the proposed inverter have certain voltage levels, and thus it is anticipated that it will be difficult to analyze the output harmonics. For such waveforms of output voltage and current‐sharing reactor, a frequency analysis approach is described whose results are verified by

ISSN:0424-7760    

DOI:10.1002/eej.4391170506

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

年代:1996

数据来源: WILEY

摘要:

AbstractA new PWM technique for the current‐fed PWM converter is proposed. As the control variables, the instantaneous active and reactive powers are used instead of the line current. They are proportional to the instantaneous active and reactive current vector. The switching state of the PWM converter is given by the selection method of the appropriate current vector among the seven kinds of the current vectors with the zero current vector. The active current is controlled by the zero current vector and the reactive current depends on the kind of selected current vector. These variables basically are controlled by PWM switching from two kinds of hysteresis comparator. In addition to this, the compensation of the filter circuit can be obtained automatically by the PWM control based on the active and reactive current detected from the source current.In this paper, the principle of the PWM technique for the current‐source PWM converter is proposed. Then, some simulation results are shown. After that, the feasibility of the system is verified by experimental resu

ISSN:0424-7760    

DOI:10.1002/eej.4391170507

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

年代:1996

数据来源: WILEY

摘要:

AbstractWith the recent development of power electronics technology, thyristor‐controlled equipment has largely been introduced to the electric power system. These devices generate harmonics that cause voltage distortion and undesirable effects on the power system components. On the other hand, the damper windings of synchronous generators basically are designed to reduce harmonics as well as to damp out system oscillations. However, up to now, the effects of damper windings on harmonics have not been clarified fully in a quantitative way.In this paper, the results of experimental study on the harmonics reduction effect of damper windings have been presented. A specially designed 6‐kVA generator was connected to an infinite‐bus system to investigate the characteristics of damper windings. A new method to measure induced voltages between damper bars, damper bar currents and air‐gap flux densities in the tested generator was established. By comparing these measurements with and without the presence of damper windings, the effect of damper windings was quantified. Thus the reduction effects of the damper windings on slot ripples and harmonics caused by armature current mmf were investigated and were made clearer than before by the proposed

ISSN:0424-7760    

DOI:10.1002/eej.4391170508

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

年代:1996

数据来源: WILEY

摘要:

AbstractA novel design theory for a three‐phase self‐commutated power conversion system (PCS) to perform as an ac current source is proposed. In this new ac current waveform control method termed error tracking mode, the switching instructions of main devices are decided only by the error function of ac current at every data sampling time that comes in a constant period. The performance is theoretically evaluated. Simulation by SPICE also is executed and the characteristics are inspected.Error tracking mode has the following attractive features. It can treat two arbitrary current waveforms as target functions of two‐phase arbitrary ac currents. The error between actual ac current value and the objective function value can be controlled and guaranteed to be less than an arbitrary value, which is given beforehand. All control components can be digitized. The minimum continuous on and off time of main devices is guaranteed in advance. No special starting control is necessary because actual ac currents are guaranteed to start tracking the target functions automatically. Error tracking mode makes contributions to improve precision in current control and to reduce current harmonics of self‐commutated voltage source power con

ISSN:0424-7760    

DOI:10.1002/eej.4391170509

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

年代:1996

数据来源: WILEY

摘要:

AbstractPermanent magnet type synchronous machines have been widely used for industrial applications. It is commonly known that they are operated at high efficiency since no excitation input is required. However, it is difficult to control the air‐gap magnetic flux, because the magnetic flux is determined by the property of the permanent magnet and approximately kept constant.On the other hand, synchronous machines with the field winding make it easy to control the air‐gap magnetic flux. But the copper loss of the field winding becomes large at the rated load.In order to realize the magnetic flux control easily and improve the performance of the conventional synchronous machine, we propose a hybrid excitation type synchronous machine (HSY) with the permanent magnets and the field winding. Advantages of HSY are (1) it has no brushes (maintenance free), (2) required excitation input is small (high efficiency), (3) it is easy to get a sufficient magnetic flux control, and others. Therefore, HSY has a great possibility of use for various applications.In this paper, basic principles and characteristics of HSY are mainly discussed and made cl

ISSN:0424-7760    

DOI:10.1002/eej.4391170510

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

年代:1996

数据来源: WILEY