摘要:

AbstractA polymer dielectric material tends to be easily charged and may cause an electrostatic discharge, due to the serious problems that result when consequent electromagnetic noise damages the electronic circuits in various kinds of apparatus. The antistatic polymers that have been developed to prevent electrostatic discharge contain polymer solid electrolytes so that space charge originally exists inside them. The mechanism of the antistatic discharge effect of the polymer has been investigated by measuring the space charge distribution using the high‐resolution pulsed‐electroacoustic method. The experimental results suggest that the internal space charge of the polymer accumulates at the surface and forms heterocharge distribution at the interface between the electrodes and the specimen. Thus, internal space charge compensates the applied electric field, resulting in preventing the increase of the surface potential. In addition, internal space charge behavior relates to the dispersion condition of the polymer solid electrolyte that depends on the quantity of the electrolytes and the specimen procedu

ISSN:0424-7760    

DOI:10.1002/eej.4391160601

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

年代:1996

数据来源: WILEY

摘要:

AbstractBobbin‐coil‐type eddy current probes, which are conventionally used for nondestructive inspection of steam generator tubes in pressurized‐water‐type nuclear power plants, have poor detection sensitivity to circumferential flaws. Hence a new type of eddy current probe was proposed to effectively detect the magnetic flux component that is indicative of a flaw and thus to eliminate the dependency on sensitivity in flaw detection. In the course of development of the proposed method, probe structures were investigated based on the measurement of magnetic fields induced by variously‐shaped excitation flat coils. The new type of probe proposed here consists of differential pick‐up coils detecting magnetic flux and excitation coils having a parallelogrammic shape. The structure of the coils was fabricated in order to detect flaws independently of their directions in trial. Nondestructive flaw detection tests were then conducted with the probe. The results obtained concrete evidence showing that both the horizontal, the vertical slit‐flaws and even the small hole of 0.5 mm in diameter can be detected

ISSN:0424-7760    

DOI:10.1002/eej.4391160602

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

年代:1996

数据来源: WILEY

摘要:

AbstractTo improve the electricity service reliability, a distribution line state monitoring system has been developed. It is composed of a central control unit, remote control switches, the slave unit and monitoring sensors. The first system employed fiber‐optic voltage and a current sensor. The latest system employs a unique form of cost reduction, with no voltage sensors incorporated. This system can detect the grounding direction by the information of the phase difference between the line‐to‐line voltage and I0provided by the monitoring sensor, and grounded line information (64ϕ) from the substation. Installation of the system has been underway sinc

ISSN:0424-7760    

DOI:10.1002/eej.4391160603

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe primary aim of surge arresters in power distribution lines is to protect lines and equipment from the voltage induced by nearby lightning strokes. To further improve power systems, methods to protect distribution lines against direct lightning strokes are still needed. An effective measure against direct lightning strokes is to increase the number of arresters. However, if the surge current is too large, some surge arresters absorb energy in excess of their capability and may break; this leads to a line fault. To evaluate the protective effect of the surge arresters against direct lightning strokes to overhead ground wire, the authors measured both the voltage across the surge arresters and the energy absorbed by them using a full‐scale model line and a 12 MV impulse generator. The results were compared with simulation results by EMTP. There have been no previous studies making a comparison of this kin

ISSN:0424-7760    

DOI:10.1002/eej.4391160604

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

年代:1996

数据来源: WILEY

摘要:

AbstractRecently, the task of planning in power systems is becoming a very complicated process for utility planners. This kind of planning has many objectives to accomplish. This paper employs the negotiation algorithm, which was proposed by the Chen‐Ching Liu group for subtransmission power system planning to create a plan having many objectives. First, the goal‐decision network (GDN) is constructed to model this planning problem, and the negotiation algorithm is applied to utilize both subtransmission system planning GDN, which attempts to capture its knowledge, and negotiation operators, which search for the most feasible and promising decisions in this planning GDN. Finally, the negotiation expert system is demonstrated for the subtransmission system planning using a real sys

ISSN:0424-7760    

DOI:10.1002/eej.4391160605

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

年代:1996

数据来源: WILEY

摘要:

AbstractWhen a fault occurs on transmission or distribution systems due to lightning or overvoltage, often an arc discharge occurs at the fault point. The arc discharge, which is caused by a fault current, has a high current, high temperature, strong light emission, etc., thus it sometimes causes heavy damages to electric power equipment.The arc discharge is influenced by the conditions around the arcs, i.e., gas, insulation materials, gap length, weather, etc. Also, the arc voltage along the arc column indicates the characteristics of the arc. If the voltage waveforms of the arcs caused by the fault on transmission or distribution systems are classified, it is possible to find the location and the equipment where the fault occurred.In this paper, the arc voltage data in 6‐kV class XLPE cables and 6‐kV class overhead lines are analyzed and an artificial neural network method is applied to classify the arc voltage waveforms. The results obtained from the six artificial neural networks developed show that the artificial neural network method is effective for classification of arc voltage waveforms if adequate input parameters are selec

ISSN:0424-7760    

DOI:10.1002/eej.4391160606

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

年代:1996

数据来源: WILEY

摘要:

AbstractIn a three‐phase, three‐leg core of a core‐type power transformer, the yokes are magnetically connected to all three phases so as to ease the flow of the magnetic flux (generally by means of lap joints of yokes and legs), and at the same time to smooth the magnetic flux between phase legs through yokes. It has generally been assumed that a split core with full separation at the center of the leg including yokes is unsuitable for use in power transformers owing to core losses, local heating, and noise resulting from the imbalance and distortion of magnetic flux, even though it can be used in distribution transformers with wound cores. But since the split core has many advantages from the manufacturing viewpoint, the magnetic characteristics of small core models were studied in detail. Studies with a full‐scale 1500/3 MVA model transformer core indicate that the degradation of magnetic characteristics compares favorably with conventiona

ISSN:0424-7760    

DOI:10.1002/eej.4391160607

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

年代:1996

数据来源: WILEY

摘要:

AbstractA new type nonflammable large power transformer system is proposed in which the excellent cooling characteristics and insulation properties of nonflammable perfluorocarbon (PFC) liquid is utilized. In the system, transformer windings are put in an insulating cylinder filled with PFC liquid. The core includes cooling panel through the liquid. The space between the insulating cylinder and tank is filled with compressed SF6gas.This paper describes the insulation characteristics of main insulation and inter‐winding insulation models which simulate the transformer. It is found that (1) higher withstand voltage is expected by means of insulation barriers in the main insulation model; (2) partial discharge in inter‐winding insulation model is beginning to behave in a constant electric field strength on the point of 0.1 mm liquid gap len

ISSN:0424-7760    

DOI:10.1002/eej.4391160608

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

年代:1996

数据来源: WILEY

摘要:

AbstractBoth switching time and minimum firing voltage of a triggered vacuum gap employing a trigger electrode in the cathode and anode (double triggered vacuum gap) were measured. The double triggered vacuum gap was operated below 100 V independent of the high voltage main electrode polarity (positive or negative). This minimum firing voltage was lower than that of the conventional triggered vacuum gap. The switching time is approximately 0.5 μs in the range 3 to 18 kV.The conventional triggered vacuum gap has a trigger electrode that is placed at the center of the grounded main electrode. The polarity of the main electrode affected switching time characteristics. A trigger electrode was added to the high voltage main electrode. The double triggered vacuum gap was only slightly influenced by the polarity of the high voltage main electrode when both main electrodes were triggered at the same time

ISSN:0424-7760    

DOI:10.1002/eej.4391160609

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper deals with the problem of determination of feedback gains in order to achieve required performances under linear time invariant perturbations. Based upon the Lagrange multiplier method, the proposed method determines feedback gains that ensure both robust stability and robust performance for a linear uncertain system. It is applied to a nonlinear crane system control design. The nonlinear system is first partitioned into some uncertain linear systems. Then the proposed method is applied to each uncertain linear system. Application is easily demonstrated and, consequently, a nonlinear crane control system can be easily designed. Finally, it is shown in a numerical example that the proposed method is effective.

ISSN:0424-7760    

DOI:10.1002/eej.4391160610

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

年代:1996

数据来源: WILEY