摘要:

AbstractA new type of superconductor with high elastic modulus fibers is being developed for the application of high‐field pulsed superconducting magnets called Fiber‐Reinforced Superconductors (FRS). FRSs have great potential for the construction of a 15‐T class pulses magnet with its size kept equal to ITER because stainless steels of cable‐in‐conduit‐conductors could be reduced considerably.This paper presents a technique of preparing FRS and measuring its superconducting characteristics including strain‐Ic relation. FRS has a critical current density of 600 (A/mm2/initial niobium) at 15 T, which is almost equal to one of the commercial bronze‐processed wires. The intrinsic strain vs.Iccharacteristics are similar to that of bronze‐processed wire. Thermal strain on FRS also is discussed because materials with high elastic modulus tend to have low thermal contraction which leads to degradation of the superconducting characteristics of the Nb3Sn layer. Possibilities of overcoming the degradation while maintaining very high elastic modulus of tungsten fiber for reinfo

ISSN:0424-7760    

DOI:10.1002/eej.4391140301

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe magnetic properties of La2Co17‐x‐yFexTiyand La2Co17‐x‐yFexTiyNδintermetallic compounds have been investigated. La2Co17‐x‐yFexTiyhas the rhombohedral Th2Zn17structure and exhibits the following magnetic properties: saturation magnetization>1.0 T; Curie temperature>873 K; and easyc‐axis.Nitrogen is introduced into these compounds interstitially through the nitrogenation process. The saturation magnetization and Curie temperature of La2Co17‐x‐yFexTiyNδis decreased by the introduction of nitrogen, in

ISSN:0424-7760    

DOI:10.1002/eej.4391140302

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

年代:1994

数据来源: WILEY

摘要:

AbstractIt has been proposed that vapor‐mist dielectrics in which mixing liquid droplets such as tetrachloroethlene in a gas have the ability of increasing flashover, impulse voltage, and of suppressing partial discharge. Vapor‐mist methods have been performed on other materials and the effect of the mist can also be obtained on benzene, hexane, and even water as general materials. Although these studies have been carried out, neither the discharge mechanism on vapor‐mist nor the reason for the increase of the discharge voltage is understood fully because the mist is of various sizes. On the other hand, agglomeration of water molecules can be studied with the FR‐IR method, and are classified into monomer, dimer, trimer (including polymer). Water gives mist stats which are significant in discussing effects.This paper describes states of water mist and their effect under nonuniform field with positive and negative polarities. Water mist in vapor exists as dimer and trimer, and their amount decreases with the reduction of temperature. These mists have no effect on discharge suppression. However, when the mists are formed by space charges, the inception voltage is increased by these mists in the negative p

ISSN:0424-7760    

DOI:10.1002/eej.4391140303

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper presents an application of fuzzy control to enhance power system stability. The proposed control consists of the controller for large disturbance (FU 1), the fuzzy controller for small disturbance (FU 2), and the fuzzy judgment mechanism (FU 3).FU 1 is determined based on the fuzzy controller [FU 1(F)] is determined according to the control rules and its input signals, i.e., speed deviation and acceleration at every sampling time of the machine. FU 2 consists of two controllers, namely, FU 2‐ω and FU 2‐P;FU 2‐ω has the same mechanism as FU 1, while the output signal of FU 2‐Pis determined according to the rules together with the change of error of electrical power and terminal voltage. To obtain the optimal desired control signal during both the large and the small disturbances, the operations of FU 1 and FU 2 are judged by FU 3, where the magnitude of speed deviation is chosen as its input signal. The determined control signal is fed to AVR of the machine.The implementation of the proposed control is simple due to the small amount of calculations and required data. The effectiveness of the proposed control is demonstrated by the one‐machine infinite‐bus system model and very good system performance is obtained throughout all th

ISSN:0424-7760    

DOI:10.1002/eej.4391140304

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

年代:1994

数据来源: WILEY

摘要:

AbstractPower system stability is essential to reliable and economical operation of power systems. The quick‐response excitation control with PSS is used as a power system stability improvement measure at the generator. However, this method is not always sufficient to apply in a wide operation range of power system configuration, load flow, and so on.This paper includes results of experiments of fuzzy excitation control system on the ac/dc Power System Simulator of CRIEPI. This control system is verified to improve power system stability and has better performance than the conventional excitation control on a one‐and two‐machine to infinite bus s

ISSN:0424-7760    

DOI:10.1002/eej.4391140305

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

年代:1994

数据来源: WILEY

摘要:

AbstractAn expert system is presented that produces the operation sequence for disconnecting apparatus from a power system under normal operating conditions.To maintain the reliability of power supply on the network during the operation, the operation sequence must be produced in due consideration of network states, such as load factors and routes of transmission line. Besides, since the network which the system manages includes many high‐voltage consumers, the operation sequence for each consumer should be divided into detailed switch operation sequence.To produce a detailed switching operation sequence simultaneously with macronetwork operation sequence, we introduce the multilayered object‐oriented network model for the knowledge base of this expert system.Each layer of this model represents network configuration in the different degree of detail, and the consistency between states of layers is maintained by an interlayer message‐passing mechanism. On the layer which represents apparatus and their connections in detail, the inference engine can generate the switching operation sequence. On another layer which represents control centers and consumers, the inference engine can search for routes of power supply and can generate the sequence of changing over the network. Therefore, by using each layer properly, the inference engine can produce various kinds of operation sequences.Furthermore the object‐oriented network model facilitates maintenance and extension of the

ISSN:0424-7760    

DOI:10.1002/eej.4391140306

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

年代:1994

数据来源: WILEY

摘要:

AbstractA 50‐MVA self‐commutated Static Var Compernsator (SVC) using the worlds's largest GTO thyristors rated 6 kV‐2500 A has been developed for voltage control of electric power systems. The rated dc voltage is 16.8 kV which is four times higher than the highest one manufactured so far. To achieve the high dc voltage, eight GTO thyristors are connected in series. Voltage unbalance between GTOs during switching transient was investigated. A new overcurrent limiting method is proposed, since conventional fuse protection cannot be applied due to such high voltage. Newly developed technologies for this large and high‐voltage self‐commutated SVC are described.Although simple star‐delta connection transformers are used, harmonics generated from SVC are almost equivalent to the 24‐pulse converter by shifting the pulse timing appropriately. The PWM control based on 150 Hz is applied and the SVC is designed to continue operation during system faults. The performance of the controller is tested successfully by a simulator, and typical rest results a

ISSN:0424-7760    

DOI:10.1002/eej.4391140307

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

年代:1994

数据来源: WILEY

摘要:

AbstractA carbon dioxide‐recovering high‐efficiency gas‐turbine power‐generation system is proposed in which carbon dioxide (CO2) generated is recovered by adopting the oxygen (O2) combustion method and no thermal nitrogen oxide is generated. In the system, saturated steam produced by utilizing waste heat is adopted as the working fluid of the gas turbine. Thus, the compressing process of the working fluid gas, which is the most energy‐consuming process in generating power by using a gas turbine, is not needed. This makes the system extremely high efficient.By taking saturated steam of 210°C as an example, the characteristics of the system were simulated. The net exergetic efficiency of the system has been estimated to be 48.4 percent by considering both the exergy of the saturated steam and the electric power required not only to generate high‐pressure oxygen, but also to liquefy the recovered CO2. The value is higher than the exergetic efficiency 37.8 percent of large‐scale thermal power generation plants using the same natural gas, and is 28.0 percent higher than its efficiency of 37.8 percent, the one estimated if the CO2generated is removed and recovered from the stack gas by using alkanolamine‐based solvent and the recovered

ISSN:0424-7760    

DOI:10.1002/eej.4391140308

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn urban areas there is a growing need to ensure bulk power distribution, service reliability and an interconnection to dispersed generators. It is effective to improve the network distribution system for the foregoing view. Regular network systems often are used for the area, but coordinations of the protection are complex as usual.This report describes the protective coordinations of the regular network system that performs a bulk power distribution and includes dispersed generators. The interconnections influence the coordination of substation protective relays and network protectors at the primary feeder fault. The increase of the network currents associated with the bulk network system makes the protection difficult at low‐voltage grid cable faul

ISSN:0424-7760    

DOI:10.1002/eej.4391140309

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper describes overvoltage caused by disconnecting a lot of motor‐loads on a power distribution line with power‐factor‐correcting capacitors during a transmission line open‐phase. The overvoltage phenomena are studied by a field test, a steady‐state analysis and a transient analysis. Experimental results show that the line‐to‐line voltage on a 6.6 kV distribution line with an open‐phase 22 kV transmission line amounts to 1.7 per unit. The overvoltages are caused by two types of resonance. One is the linear circuit resonance between the power‐factor‐correcting capacitors and the secondary side impedance of motors. The difference between positive components and negative ones of the impedance produces the resonance. The other is the nonlinear circuit resonance between the power‐factor‐correcting capacitors and the saturated reac

ISSN:0424-7760    

DOI:10.1002/eej.4391140310

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

年代:1994

数据来源: WILEY