摘要:

AbstractThe purpose of large‐scale power system interconnection is to achieve extremely economical and reliable power generation and transmission. It has established the present power systems of high quality. On the other hand, in the large power systems with complex configuration, an undamped power swing with low frequency caused by the synchronous power between interconnected systems tends to occur as well as an undamped power swing caused by the synchronous power of specific generators.Several coordinated stabilizing control schemes for the power systems by sets of power system stabilizers (PSSs) have been investigated so far. PSS is very effective for the stabilization of power swing among a few specific generators because the function of PSS is achieved by the voltage control using the generator field winding circuit. However, it seems that PSSs do not have sufficient ability to stabilize the power swings between interconnected systems.In this paper, the superconducting magnetic energy storage (SMES) which is significantly effective for the power swings between interconnected systems is introduced and a coordinated power system stabilizing control by SMES and PSSs is proposed. The advantages of the proposed control scheme are: 1) high efficiency of the controller by the distribution of functions; 2) independency of the control design for PSS and SMES; and 3) robustness of the controller, and so o

ISSN:0424-7760    

DOI:10.1002/eej.4391130401

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe application of superconductivity technology to electric power apparatus is very important from the viewpoint of energy saving. Especially, the superconducting generators using superconductors as the field windings have many merits compared with conventional generators. Super‐GM has been researching and developing 70‐MW‐class model machines since FY 1988 for a scheduled period of eight years, aiming at a 200‐MW‐class superconducting generator. This paper describes the basic specifications and designs of 70‐MW‐class superconducting generators by Super‐GM and also describes the propriety of these basic specificati

ISSN:0424-7760    

DOI:10.1002/eej.4391130402

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

年代:1993

数据来源: WILEY

摘要:

AbstractDiameter of the superconducting ac composite strand is small, typically 0.1 mm, because the strand must be twisted in a very short pitch to reduce coupling losses. Therefore, current capacity of the single strand is small and in the range of ∼10 A. In large‐scale electric power apparatus, the conductors must be able to carry large currents and hundreds of these composite strands should be bundled. The composite strand is highly unstable and susceptible to a very small disturbance due to a frictional wire motion because the main matrix of the wire is highly resistive CuNi.For stable operation of an ac superconducting winding, every strand in the bundle cable should be fixed firmly. An effective technique to fix strands is to impregnate the winding by epoxy. In this case, the ac losses in the winding are to be cooled by heat conduction through the epoxy. Therefore, it is important to estimate the temperature rise of the winding to discuss the fact that the epoxy impregnation technique is applicable to the ac superconducting electric power apparatus.In this paper, the mechanism of thermal conduction of the epoxy‐impregnated winding at the 4.2 K region is discussed based on experimental data and the temperature rise of a large‐scale cable bundles by 7 × 7 × 7 strands calculated considering thermal resistivity at the interface between the epoxy and the strand. The calculated value agrees well with the measu

ISSN:0424-7760    

DOI:10.1002/eej.4391130403

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper proposes a simulation‐based learning environment called hypersimulator, as a thinking tool to enhance operators' understanding of complex phenomena in power systems. The hypersimulator is literally a simulator fused with a concept of hypertext, a personal visual simulator with user interfaces viewing multiple aspects of the phenomena in power systems.In the field of power system engineering, training simulators are used for operators to obtain the so‐called skill‐based and rule‐based expertise of an operation. However, the training simulators are not effective enough to provide knowledge‐based expertise based on deep understanding of a mechanism of complex phenomena. An aim of the hypersimulator is help the novice operator obtain such expertise through examining the phenomena and developing effective mental models (internal models formed in a person's mind) of them. The approach here to designing the system is a user‐centered one based on cognitive science and analysis of characteristics of power system phenomena and operators' ways of thinking.In this paper, first, the characteristics of operators' ways of thinking are analyzed as the preliminary investigation to obtain a basic design concept. Second, the concept and the features of hypersimulator are discussed. Finally, the effectiveness of the system is demonstrated using simulation of phenomena in po

ISSN:0424-7760    

DOI:10.1002/eej.4391130404

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

年代:1993

数据来源: WILEY

摘要:

AbstractPartial discharge (PD) detection on live UHVEHV power cables and accessories is one of the most important techniques to prevent cable systems from serious difficulties caused by slight errors in joining the cables. A new PD detecting method is proposed in this paper. A resonance‐type partial discharge (REDI) sensor is developed for detecting PD occurring inside the joints of live XLPE insulated cables. This sensor picks up the high‐frequency components of PD current pulses on the surface of live cables, hence the output signals can clearly be observed at the noiseless area (for example, 10‐60 MHZ).This new method was applied to the initial ac breakdown tests with three different types of joints of UHV/EHV power cables. The PD pulse sequence was detected before their breakdown in all cases. The charge quantity and the number of pulses increased tremendously just before the breakdown. In addition, the phase of PD pulse against the applied voltage (ϕ‐qcharacteristics) changes with time or with the progress of deterioration. According to these experimental results, the REDI sensor can be applied to the insulation diagnosis of live power cabl

ISSN:0424-7760    

DOI:10.1002/eej.4391130405

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

年代:1993

数据来源: WILEY

摘要:

AbstractSolar radiation has an irregularly varying factor due to a basic day and night cycle and climatic conditions. For such conditions a data sampling interval is important to ensure the accuracy of energy monitoring in a photovoltaic system. While treating a system monitoring equipment as a black box. the author has developed the method of calibrating an energy‐integrating function.At first for various input waveforms, the relationship between sampling intervals and quasi‐integration outputs have been examined by trapezoidal rule. In the numerical simulation the phases of the sampling clock also are considered Then it is concluded that a sampling interval can be inspected through outside observation only by using a rectangular single pulse. By applying the pulse to the energy‐integrating process, two kinds of integrated outputs can be obtained for different sampling phases. The calculated difference between both outputs can uniquely give the sampling interval being inspected. Conditions to ensure measuring accuracy are discussed and the validity of this method has been demonstrated experimentally. Practical calibrating procedures also are proposed for the integrating function of PV system monit

ISSN:0424-7760    

DOI:10.1002/eej.4391130406

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

年代:1993

数据来源: WILEY

摘要:

AbstractLaser‐guided discharge is promising for protection of power transmission systems against lightning. Several experiments concerning the laser‐induced electrical discharge have been performed up to now. However, it is necessary to understand the mechanism of the laser‐induced electrical discharge to achieve the laser‐triggered lightning.When a high‐power laser beam is focused in air, a high degree of ionization is produced as brilliant beams near the focus. In this paper, the electrical discharge induced up to 2‐meters with a high‐power CO2laser focused by a 10‐meter focal length mirror is described.Experiments of the laser‐guided discharge were carried out by application of an impulse voltage to a rod‐rod gap after laser radiation. This paper deals with the effects of delay times and polarity of the impulse voltage on 50 percent flashover voltage characteristics and the observation results of discharge phenomena taken by a still camera, a special camera named ALPS (Automatic Lightning Discharge Progressing Feature Observation System) and an ima

ISSN:0424-7760    

DOI:10.1002/eej.4391130407

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper shows that normal power system operating data may be used to determine the power‐frequency characteristics in power systems. Data are processed as random signals using spectral analysis techniques, and the results estimate the generator and load power‐frequency characteristics as transfer functions. The generator characteristicsKgare determined as a transfer function of the system in which input signals are frequency fluctuation ΔFand generator power setting signal ΔPg, and output signal is generator power output ΔPe, To estimate the load characteristicsKl, a difficulty arises. There is a relation ΔP/= ΔLo+KlΔFbetween actual load ΔPl, ideal load under the state of nominal frequency ΔLo, and fluctuation of system frequency ΔF. Because it is impossible to measure ΔLodirectly, ΔLoandKlΔFcannot be separated.With regard to a partial system, when its capacity is small enough compared with the total system capacity, the contribution of ΔLoin a partial system to ΔFof the total system may be ignored, that is, ΔFand ΔLoare considered as independent phenomena. Thus the cross spectrum of ΔFand ΔLodecreases to zero according to the increase of data in number, andKlof the partial sy

ISSN:0424-7760    

DOI:10.1002/eej.4391130408

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn future electric power systems, it will be very important to utilize existing ac networks more effectively with the help of power electronics technology. It has become clear that various types of apparatus utilizing such power electronics technologies as variable series capacitors (VSrC) and high‐speed phase shifters (HSPS) can improve transient stability and damping in one‐machine, infinite‐bus power systems. This paper presents a novel control scheme for variable impedance apparatus such as VSrC and HSPS devices in multi‐machine power systems.First, this paper describes a comprehensive approach for control design of VSrC and HSPS apparatus. The proposed control scheme is based on the energy function of multi‐machine power systems. The controllers are designed so that the time derivative of the energy function has a smaller negative value than that without controllers. In this sense, the present method assures the improvement of first‐swing stability and damping.Next, the proposed control scheme is applied to VSrC apparatus. Digital simulations and eigenvalue analysis are conducted for a three‐machine loop system and a five‐machine radial system to demonstrate the effectiveness of the proposed method. The results make it clear that the proposed controllers for VSrC can significantly improve both the transient stability and the steady‐state stability

ISSN:0424-7760    

DOI:10.1002/eej.4391130409

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe magnetic flux inside a synchronous generator is regarded as a characteristic that dominates a generator operation. This paper develops a simple model of a synchronous generator by which it is possible to easily estimate an air‐gap flux as well as electrical characteristics. The air‐gap flux density can be related to a permeance and a magnetomotive force (mmf) along its magnetic path by the Ampere's laws. These relations are used in this paper.We estimate the distribution of the permeance along the air‐gap and the mmf profiles of the stator and the rotor of a 6 kVA scaled‐down tested synchronous generator. From these estimated profiles, the relations among the air‐gap flux, field current, and armature current are represented by a linear equation system. Consequently, the static electrical and magnetic characteristics of a synchronous generator can be estimated by giving only field exciting voltage and load impedance. The distributions of the air‐gap flux density and waveforms of the field and armature currents are simulated for various unbalanced‐load conditions. The simulated results well agree with experimental ones not only for fundamental components but also for higher harmonic components. Therefore, our method, based on the permeance profile, is available to calculate the static characteristics of synchrono

ISSN:0424-7760    

DOI:10.1002/eej.4391130410

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

年代:1993

数据来源: WILEY