摘要:

AbstractA mostly single bcc phase with nanoscale grain size of 10 to 20 nm has been found to form by annealing amorphous Fe‐Zr‐B, Fe‐Hf‐B and Fe‐M‐B‐Cu (M= Ti, Zr, Hf, Nb and Ta) alloys. It has further been clarified that the newly developed nanocrystalline bcc alloys exhibit high permeability (μe) combined with high saturation magnetization (Bs).Subsequently, the possible application potentials of the bcc alloys were investigated. The core loss is as small as 66 mW/kg at 1 T and 50 Hz for a nanocrystalline bcc Fe86Zr7B6Cu1alloy obtained by annealing for 3.6 ks at 873 K. This value is 45 and 95 percent smaller than those for amorphous Fe86Si9B13alloy and Fe‐3.5 percent Si alloy, respectively, which are presently in use as core materials in electric power transformers. The frequency dependence of the core loss for the bcc alloy at 0.2 T is almost the same as that for an amorphous Co70.5Fe4.5Si10B15alloy with zero magnetostriction.In the frequency range of 10 to 300 kHz, the core loss for the bcc alloy is slightly smaller than the Co base amorphous which has been used as core material in high‐frequency transformers. Furthermore, the core losses of the nanocrystalline Fe86Zr7B6Cu1alloy also were found to have high stability against thermal aging. Thus, nanocrystalline bcc Fe‐Zr‐B‐Cu alloys with the advantages of highBs, high μe, and low core loss is expected to be used as a core materia

ISSN:0424-7760    

DOI:10.1002/eej.4391130701

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

年代:1993

数据来源: WILEY

摘要:

AbstractIt has been reported that the flashover voltage of gaseous dielectrics may increase greatly when they are mixed with carbon‐halide mist. However, the factors which bring about the increase of the flashover voltage still are not clarified fully. Based on the study on the basic flashover characteristics of vapor‐mist dielectrics, the authors have suggested the scarcity of initial electrons as the predominant factor.This paper investigates further the effect of UV light irradiation, flashover characteristics under forced supply of initial electrons, and for lightning impulse superimposed on dc voltage. These results have verified that the scarcity of initial electrons is the decisive factor in increasing the lightning impulse flashover voltage of vapor‐mist dielectrics. It is clarified also that the scarcity is attributed principally to: (1) the reduction of effective period (lifetime) of initial electrons, and (2) the suppression of photoelectric emission from elect

ISSN:0424-7760    

DOI:10.1002/eej.4391130702

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

年代:1993

数据来源: WILEY

摘要:

AbstractStatistical calculating programs simulating partial discharge appearance are developed and applied to evaluations of criteria for discrimination of the partial discharges from noises. According to the simulation, clusters of sequential pulses appear at the partial discharge inception voltage, and have never been utilized at the usual pattern recognition of the partial discharges. Two original indexes that are a pair pulse rate and a maximum sequential pulse rate are defined to describe the time sequential features of the partial discharge and their signal distinguishable capabilities from noises are evaluated. A new logical index describing the signal distinguishable capability of the usual ø‐qpattern of the partial discharges from the noises also is proposed and compared with those of cluster pulses. The maximum sequential pulse rate gives most sensitive criteria in the bounds of calculating conditions.A 66‐kV cross‐linked polyethylene cable with an artificial defect is used to detect cluster pulses. By adding twice as many noise pulses as measured partial discharge pulses, the usual ø‐qpattern criteria becomes powerless, but cluster pulse criteria are still informative for the recognition of the partial d

ISSN:0424-7760    

DOI:10.1002/eej.4391130703

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

年代:1993

数据来源: WILEY

摘要:

AbstractControl and protection of equipment in power systems generally require a high‐information processing capability to cope with today's power system requirements. Then, new digital control and protection equipment have been developed using high‐speed and high‐precision processors.Essential requirements for the new control and protection equipment are a multiprocessor architecture of distributed functions to retain sufficient computing power (fast and high‐precision operations), and flexible and expandable hardware with high reliability. In multiprocessor architecture, it is important to determine how the distributed processors share the functions. By analysis and synthesis of relaying and control processings, we divided them into six processing circuits.This paper proposes a multiprocessor architecture of distributed functions, using 32‐bit floating‐point and 16‐bit microprocessors depending on the computational requirements. In addition a digital filter for fast sampled data is described along with performance of a

ISSN:0424-7760    

DOI:10.1002/eej.4391130704

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper proposes double‐rod‐type jumper horns in strain assemblies with pipe jumpers for 500‐kV transmission lines, the structure of which is very simple. It can be estimated that no corona discharge appears on the horns under the line voltage of 525 kV. The arc behavior on the double‐rod‐type jumper horns is similar to that on the single‐rod‐type horns. The arc can be held stably for 60 ms against strong wind (10 m/s). The stable duration increases more than 300 ms under windless condition, therefore the horns have been adopted for

ISSN:0424-7760    

DOI:10.1002/eej.4391130705

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

年代:1993

数据来源: WILEY

摘要:

AbstractRecently, large‐capacity power stations have been built far from load centers with long‐distance transmission lines. Therefore, if a fault occurs at the line, generators in the large‐capacity power station may lose synchronism from the remaining generators [1, 3]. To prevent an extension of loss of synchronism to other generators, fast shedding of some generators is an effective measure.The following methods have been proposed so far: A method [3] based on energy function approach; and a method [2]which estimates and predicts the relative swing among generators using data measured on‐line at each generator and proposes shedding some generators for stabilization. This method requires a large communication network for an exchange of data between power stations.This paper presents a new stabilizing method and a newly developed stabilizing control system which does not require a large communication network because it utilizes generator output, voltage and current measured on‐line in the vicinity of the large‐capacity power station. Using these measured data, the system estimates and predicts the relative swing between generators in the large‐capacity power station and the remaining generators. Finally, the number of generators to be shed for stabilization is decided and shedding is performed. Configuration and characteristics of the developed stabilizing control system are shown. The validity of this method is confirmed by simulation and testing using an artificial

ISSN:0424-7760    

DOI:10.1002/eej.4391130706

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper discusses the preventive controls of the generator outputs to improve security in the decentralized power system. Preventive controls of the power system can improve security level. However, the preventive control requires too much computation time because of too many considerable faults in the power system. Multiarea decentralization can be considered to reduce computation time of the power flow calculation. It is assumed that the effects of disturbances in the external systems are relatively smaller than the effects of disturbances in the study area.Linearized sensitivity analysis is used to evaluate the effects of the external systems to reduce computation time. Linear programming is used to determine the control signals of generators considering the incremental cost of generators. The New England 38 buses system is used as an example system to check the validity of the algorithm in this paper. The calculations of the example system show satisfactory results.

ISSN:0424-7760    

DOI:10.1002/eej.4391130707

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

年代:1993

数据来源: WILEY

摘要:

AbstractRecently, electric power systems have faced increasing uncertainties in demand, energy price and environmental constraints in the future. In such a situation, a plan for expansion of the system capacity must be made robust against the aforementioned uncertainties. Large‐scale power plants require a long time for construction so that the decision of construction must be made under much uncertainty in the future. On the other hand, small‐scale plants require less time for construction, i.e., the decision can be made under less uncertainty in spite of their relatively higher costs.This paper is concerned with an optimal combination of the large‐scale and the small‐scale plants having the aforementioned characteristics under uncertainty of future demand. First, the demand growth in the future is described by scenarios of demand growth branching like a tree. Then the optimization problem of the system expansion is formulated into a stochastic linear‐programming problem. An optimal solution of the problem is obtained by using the scenario‐aggregation algorithm proposed by Rockafellar and Wets. The simulation results, yielded by using a parallel computation on transputers, show that there is a possibility of constructing small‐scale power plants to cope with the uncertainty even if they are more expensive than the large

ISSN:0424-7760    

DOI:10.1002/eej.4391130708

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

年代:1993

数据来源: WILEY

摘要:

AbstractA superconducting compact synchrotron light source, the NIJI‐III, has been completed. The development of the NIJI‐III was assigned to Sumitomo Electric Industries Ltd. by the Research Development Corporation of Japan and was deemed successful in October 1991 with the attainment of the design goal of the stored beam current of 200 mA at the final beam energy of 600 MeV. The lattice has a four‐sector configuration: four superconducting bending magnets and eight quadrupole magnets, achieving the optimum beam characteristics for lithography. The world's first superconducting bending magnet was developed and adapted, and was characterized by a cosθ type without an iron, a large bore of 200 mm, and a strong curvature of 0.5 m. Furthermore, a newly developed vacuum system and an rf system were installed.The high‐speed electron‐beam wobbling method was investigated at a 20‐Hz triangular wave for the exposure of the vertical field of synchrotron light. It was demonstrated that the expansion of the vertical exposure area agreed with the theoretical calculation, and that there was no effect on the beam lifetime.The achievement of the NIJI‐III can be expected to contribute much to the development of various research applications of syn

ISSN:0424-7760    

DOI:10.1002/eej.4391130709

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe single‐phase converter or rectifier always has a voltage ripple in the output dc voltage because the instantaneous power of the single‐phase ac line varies on the double frequency of the line. To obtain a smooth dc voltage, an energy‐storing element is necessary. The smoothing capacitor is used to reduce the ripple voltage in the dc output. Usually, it has much larger capacitance than that needed to absorb the ripple energy.This paper discusses the required capacitance to absorb the ripple energy, and represents a ripple‐compensation circuit with a small auxiliary capacitor controlled by a 2‐quadrant chopper connected in parallel to the smoothing capacitor. The appended capacitor works under large ripple voltage and efficiently absorbs the ripple energy. The ripple‐compensation circuit works as an equivalent capacitor with a large

ISSN:0424-7760    

DOI:10.1002/eej.4391130710

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

年代:1993

数据来源: WILEY