摘要:

AbstractThe electrical breakdown and electrical conduction of ethylene copolymers have been studied. The electric strength of ethylene copolymers containing an optimum content of halogen moieties such as bromophenyl and fluoroethylene groups was found to be higher than that of LDPE over the wide temperature range from −196°C to 90°C. Also, conduction currents in the copolymers were suppressed at high electric fields. X‐ray‐induced thermally stimulated currents (TSC) revealed that halogen comonomers act as carrier traps with a depth of about 0.4 eV. Consequently, the introduction of comonomer‐containing halogen groups into polyethylene suppresses electron acceleration as a result of an increase in trapping and scattering of conduction electrons. This leads to an increase in electric strength which is determined by the electron avalanche

ISSN:0424-7760    

DOI:10.1002/eej.4391120701

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

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper describes the development of three‐dimensional electric field analysis by using the so‐called segment method which enables the electric field to be calculated with high accuracy and with enhanced efficiency, for high‐voltage apparatus.In the segment method, electrode configuration of high‐voltage apparatus is simulated by small components which are called segments and by the arrangement of several kinds of such segments.In this calculation, the charge simulation method is used which is suitable for segment application. As basic segments, spherical, cylindrical and ring segments are used and in addition to these, as subsegments, disc and elbow segments are adopted for good simulation of the total electrode configuration.In this paper, the fundamental construction and arrangement parameter of segments were discussed. Moreover, the segment method was applied to an actual high‐voltage apparatus and the calculation accuracy was discussed. It was clarified that the segment method has sufficient calculation accuracy and is a very efficient means for three‐dimensional electric fie

ISSN:0424-7760    

DOI:10.1002/eej.4391120702

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

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper describes the influences of a surfactant on crosslinked polyethylene (XLPE) insulation. Several kinds of additives are mixed into the insulation in order to improve the dielectric breakdown strength of XLPE cables. It has been verified that the interfacial diffusion method, which modifies the interfacial region between the insulation and the semiconducting layer by a surfactant, is effective. The effects of the surfactant on the morphology in the XLPE insulation were studied with two kinds of specimens.In the first kind of specimens, a mill was used to disperse the surfactant throughout the insulation material. Alternating current dielectric breakdown tests were performed on disk specimens. Their average breakdown strengths were improved, but the breakdown strengths were not increased at the low probabilities of the hazard function. In the other specimens, the surfactant was milled into the semiconducting layer, and later allowed to enter the insulation by diffusion during the high‐temperature crosslinking process. It was found that the average breakdown strengths were improved further. Moreover, the breakdown strengths were found to increase significantly at the low probabilities of the hazard function.The two kinds of specimens were followed by material analysis using analytical methods, such as TEM, FT‐IR, etc. Results from the milled specimen indicated that the improvement in property was probably due to the increase in density of the amorphous portion, the increase in the lamella thickness, and the increase in spherulite radius created by the additive content. Therefore the insulation near the interface where a concentration gradient was established by diffusion from the semiconducting layer is considered to have similar morphological changes caused by the additive. In addition, the diffusion specimen was observed to have an absence of introduced microdefects that existed in the milled speci

ISSN:0424-7760    

DOI:10.1002/eej.4391120703

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

年代:1992

数据来源: WILEY

摘要:

AbstractBy utilizing the laser induced pressure‐pulse (LIPP) technique, the behavior of space charge in low‐density polyethylene (LDPE) and crosslinked polyethylene (XLPE) films in contact with metal or carbon‐loaded semiconducting layers was studied quantitatively to clarify the space‐charge characteristics in power cables.Negative heterospace charge near the anode and positive space charge in the bulk were observed in unoxidized LDPE under the fields above 120 kV/mm. The amount of negative space charge increased with applied field, while positive space charge in the bulk disappeared with increasing applied field. This indicates that electron injection and ionization are enhanced by applied field.Prominent negative homospace charge was formed near the cathode in oxidized LDPE, which indicates that oxidation enhanced electron injection. The depth of charge centroid from the cathode became larger with increasing temperature. This indicates that the effective electron mobility increases with temperature.Negative space charge also was formed in the bulk in XLPE films with metal electrodes, which indicates that crosslinking enhanced electron injection. XLPE films with a carbon‐loaded semiconducting layer showed both negative and positive homospace charges near the semiconducting layers, which indicates that both electrons and holes were injected from the semiconduct

ISSN:0424-7760    

DOI:10.1002/eej.4391120704

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

年代:1992

数据来源: WILEY

摘要:

AbstractBreakdown voltages in uniform and quasi‐uniform field gaps are sensitive to the presence of small protrusion on the electrode surface in SF6at high pressures. The aim of the present work is to study direct breakdown and corona stabilized breakdown for the transitive region from uniform to nonuniform gap in dry air and SF6at low pressures up to a critical pressure when direct breakdown takes place by a leader discharge crossing the gap in SF6. In a parallel‐plane gap with a variable‐height protrusion subjected to the dc voltage, corona onset voltage is remarkably controlled by the protrusion height. The present electrode arrangement has the advantage of directly measuring the minimum critical guiding field strength for the propagation of a streamer discharge at corona onset.The experimental observations have been explained qualitatively on the basis of a streamer model and precise electric field calculations o

ISSN:0424-7760    

DOI:10.1002/eej.4391120705

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

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper studies the feasibility of applying the Hopfield‐type neural network to unit commitment problems in a large power system. The unit commitment problem is to determine an optimal schedule of what thermal generation units must be started or shut off to meet the anticipated demand; it can be formulated as a complicated mixed integer programming problem with a number of equality and inequality constraints. In our approach, the neural network gives the on/off states of thermal units at each period and then the output power of each unit is adjusted to meet the total demand. Another feature of our approach is that an ad hoc neural network is installed to satisfy inequality constraints which take into account standby reserve constraints and minimum up/down time constraints. The proposed neural network approach has been applied to solve a generator scheduling problem involving 30 units and 24 time periods; results obtained were close to those obtained using the Lagrange relaxation metho

ISSN:0424-7760    

DOI:10.1002/eej.4391120706

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

年代:1992

数据来源: WILEY

摘要:

AbstractFor more rational operation and control of future electric power systems which would continue to expand in size and complexity, an autonomous decentralized control system is proposed as one of the new control architectures. In the autonomous decentralized control system, each generating station and substation behaves independently and cooperatively without being controlled by the central station. Besides the inherent fault‐tolerant characteristics of the architecture, flexible and rapid control depending on the circumstances can be achieved.In this paper, the fundamental logic of preventive control in an autonomous decentralized system is developed. It is based on the bidding method in which each station proposes its own output taking into consideration its own situation and cooperation with others. The economic load dispatch including preventive control can be performed, based on the bidding rule adopting the equivalent incremental generating cost curve in which the security constraints are incorporated. Application of the logic to a model system revealed satisfactory control performance for preventing the overload of transmission lines and the undervoltag

ISSN:0424-7760    

DOI:10.1002/eej.4391120707

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

年代:1992

数据来源: WILEY

摘要:

AbstractA new method was used to measure the characteristics of partial discharge (PD) for an active 9.5‐km long‐distance 275‐kV XLPE cable line with insulating joints. It was found that the detection of PD and the calibration of detection sensitivity were carried out safely and easily. The proposed method includes:1detection of PDs and injection of calibration pulses using two pairs of metal electrodes placed on PVC jackets with anti‐corrosion layers separated by a joint sleeve sectionalizing insulator;2measurement of detection sensitivity with distance using calibration pulses injected from an adjacent insulating joint;3detection of PDs with a highS/Nratio measured at a frequency corresponding to the lowest noise level; and4usage of rf cores attached at cross‐bonding leads and wires for sheath current limiters to reduce the crosstalk of signal and noise through these lines at insulating joints.Using a combination of these techniques, the highest detection sensitivity was 1 pC in the vicinity of an insulating joint, and 15 pC at 617 m from the adjacent joint. The sensitivity obtained by the conventional PD measurement using a low‐frequency method was at m

ISSN:0424-7760    

DOI:10.1002/eej.4391120708

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

年代:1992

数据来源: WILEY

摘要:

AbstractPiezoelectric and ferroelectric properties of bismuth sodium titanate, (Bi1/2Na1/2)TiO3(BNT)‐based solid solution, that is, (Bi1/2Na1/2)(1‐x)(PbaBab)xTiO3(a + b= 1) [BNPB(100x‐100a/100b)], are studied from the viewpoint of a new group of lead‐free or low‐lead content piezo‐electric ceramics with a rhombohedral(Fa‐tetragonal (Fβ) morphotropic phase boundary (MPB). It is evident that the MPB seems to be remarkably efficacious in promoting piezoelectric and pyroelectric activities by electrical poling.X‐ray diffraction data, dielectric properties andD‐Ehysteresis loops show that the MPB exist near (Bi1/2Na1/2)TiO3[BNT] atx= 0.13–0.14, 0.08–0.09 and 0.06–0.07 in the case ofb= 0,b= 0.5 andb= 1, respectively. BNPB ceramics are superior for piezoelectric ceramics in high‐frequency ultrasonic uses, or special piezoelectric actuator materials with a lower free permittivity ε33Tε0, and a high electromechanical coupling factork33, along wit

ISSN:0424-7760    

DOI:10.1002/eej.4391120709

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

年代:1992

数据来源: WILEY

摘要:

AbstractMagnetostatic wave (MSW) devices are potentially very promising for carrying out signal processing directly at microwave frequencies, and recently have been receiving much attention. Although the development of a general design theory is essential for significant progress in the signal processing capabilities of the MSW devices, relatively few design theories have been discussed in the past.This paper extends and improves the general equivalent circuit approach to the magnetostatic wave devices proposed and discussed earlier. Based on the definitions of the purely magnetostatic terminal parameters and the magnetostatic characteristic impedance, the electromagnetostatic energy conversion is discussed and the appropriate general equivalent circuit models for the MSW devices are developed. Calculated insertion losses for various MSW devices are in excellent agreement with experimental results.

ISSN:0424-7760    

DOI:10.1002/eej.4391120710

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

年代:1992

数据来源: WILEY