摘要:

AbstractInformation on space‐charge behavior in thick insulated samples aids in understanding the dc characteristics of polymer‐insulated dc cables. The pulsed electroacoustic method is used to investigate several space charge formation factors in 2 mm‐thick polyethylene (PE). The following results were obtained.For measurement factors:(1) A polymeric semiconducting electrode provides a more accurate measurement than does a metal electrode as a result of better matching of acoustic impedance with PE.(2) Within a dc electrical stress range of several tens kV/mm, the space charge distributions under and after dc voltage application are almost the same; this is due to a comparatively long time of space‐charge decay.(3) The space‐charge distribution of a plate sample agrees with that of a cable sample having the same insulation thickness.For insulating material factors:(1) The amount of space charge in crosslinked polyethylene (XLPE) is much larger than that in low‐density PE (base of XLPE).The space charge of XLPE continues to increase even after dc voltage application (24 h); that of LDPE reaches equilibrium with a few hours.(2) The aforementioned space charge difference between XLPE and LDPE is assumed to be caused by ionic impurities in XLPE, not by the additives themselves (acetophenon and cumylalcohol as byproducts of cross linking and a

ISSN:0424-7760    

DOI:10.1002/eej.4391160101

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

年代:1996

数据来源: WILEY

摘要:

AbstractSince most problems in distribution lines are ground faults, the technology to distinguish the causes in the distribution lines will be very useful in preventing faults beforehand or, at least finding any problems at an early stage.The waveforms of ground faults which were collected from data concerning problems in the distribution lines and ground fault experiment are analyzed. The technology which could predict classified groups drawn from the scale ofI0(the waveform of ground fault current) andV0(the waveform of ground fault voltage), and both of them in the ground faults is studied.The results demonstrated thatI0could be classified into three groups, that is, leaking ground faults are sine curve shaped, gap discharge ground faults are triangular, and intermittent discharge ground faults are needle shaped.Also, simulated equivalent impedance of the causes of ground faults by EMTP is calculated. Furthermore, the influence caused by the condition of the distribution lines is investigated. With these results, a technique is proposed which could predict the cause of problems in ground faults.

ISSN:0424-7760    

DOI:10.1002/eej.4391160102

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

年代:1996

数据来源: WILEY

摘要:

AbstractStability of large‐scale coal‐fired MHD channels is studied by (1) linearized stability analysis, and (2) time‐dependent 1‐D analysis. The channel length is 15 m with 600 electrode pairs, and the output power ranges from 220.6 MW through 258.7 MW. Linearized stability analyses show that the Faraday channels operated with fixed loading resistance are stable, whereas the two waves of u and u–a (u, a: gas and sound velocity) become unstable in the Faraday channel with fixed loading factor. Two waves of u and u–a are unstable in the diagonal channel with fixed loading current and the u + a wave becomes unstable in the diagonal channel with fixed electrode current.Time‐dependent one‐dimensional analyses indicate that the Faraday channels with fixed load resistance are smooth without growth of fluctuation. The diagonal channels with fixed electrode current are smooth with no fluctuation, though the linear theory indicates that the u + a wave is unstable. The diagonal channel with fixed load current suffers large disturbance along the latter half of the channel, being consistent with the linearized analysis which indicates that the u ‐ a and u w

ISSN:0424-7760    

DOI:10.1002/eej.4391160103

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

年代:1996

数据来源: WILEY

摘要:

AbstractA 3000/6000V, 1000 kVA class superconducting transformer (SC‐Tr) was developed for aProspective Power TransmissionModel SystemIntegrated underSuperconductingEnvironment (PROMISE). In this transformer, the core and superconducting windings are immersed in liquid helium and the major insulation is provided by the liquid helium. This paper describes both the design features and measured characteristics of the SC‐Tr. Fundamental characteristics of the SC‐Tr are obtained through no‐load, short‐circuit tests and quench experiments. The results of the no‐load test have verified that the SC‐Tr has the capability to withstand ac voltage of 3000/6000 V of 60 Hz without any partial discharge. The short‐circuit tests have proved that the SC‐Tr is capable of carrying ac current of 170 Arms without quench in the superconducting windings. Furthermore, in a real‐load experiment with the PROMISE, electric power of 3800 V‐460 kVA of 50 Hz in high‐voltage side is transmi

ISSN:0424-7760    

DOI:10.1002/eej.4391160104

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper presents a new switching control scheme for static var compensator (SVC) using fuzzy logic control rules to enhance the overall stability of electric power systems. In addition, the coordination with power system stabilizers (PSS) is also considered to achieve a wider stable region. An SVC is set on one of the busbars in the transmission system, where the real power flow signal is utilized at the location of the SVC to determine the firing angle of the thyristor switch. The switching control scheme is simple so as not to require heavy computation on the microcomputer based switching controller. The PSSs are also set on the generators in the study system. Simulation results show the effectiveness of the proposed fuzzy logic switching control scheme for the SVC. The coordination between SVC and PSS is also effective to enlarge the stable region.

ISSN:0424-7760    

DOI:10.1002/eej.4391160105

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper presents a fuzzy‐based method for determining a flexible generator maintenance scheduling by means of subjective relaxation of constraints imposed on the maintenance scheduling problem. The constraints are divided into hard (crisp) constraint set and soft (fuzzy) constraint set according to reflecting conditions which surround power systems. The problem is formulated as a fuzzy mathematical programming problem and solved with the fuzzy branch‐and‐bound method using Bellman‐Zadeh maximizing decision. The proposed approach provides not only a new flexible concept of planning problems in power systems, but also natural expansion of conventional approaches based on crisp set theory. The effectiveness and feasibility of the proposed approach are demonstrated on two typical power system models which consist of 15 generators and 60 generators, respe

ISSN:0424-7760    

DOI:10.1002/eej.4391160106

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

年代:1996

数据来源: WILEY

摘要:

AbstractA technique for forecasting daily peak load in a utility power system is presented. After embedding time series data of daily peak load into a reconstructed state space, a nonlinear mapping is constructed by a local approximation method based on the orthonormal Gram‐Schmidt bases. This method utilizes only the past load data for short‐term prediction of the daily peak load, while many conventional methods make predictions with various kinds of data such as temperature and weather. The quality of prediction by the proposed method is as good as those with other prediction methods. Moreover, the results of short‐term prediction by this method are satisfactory even with data as small as 250 p

ISSN:0424-7760    

DOI:10.1002/eej.4391160107

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

年代:1996

数据来源: WILEY

摘要:

AbstractA micro‐eddy current testing (ECT) probe, which consists of a planar microloop inductive magnetic sensor array and a pancake‐type exciting coil, was developed to upgrade the ECT technology, especially as it is used for inspecting steam generator tubing in a pressurized nuclear power plant (PWR). Eddy currents and resultant magnetic fields are perturbed due to a flaw in a conductor. The flaw is detected via perturbation of the electromotive force (EMF) and phase from the array. Flaws manufactured by electric discharge machining in INCONEL 600 planar specimens, the thickness of which was 1.25 mm, were detected and reconstructed by using stacked database and simplified algorithm. Even an outer‐edged 10 percent flaw could be detected. Measured EMF and phase signals were compared with numerical results obtained by using a three‐dimensional eddy current and field analysis code and then verified. The experiment confirmed that the spatial resolution of detection of the micro‐ECT probe is superior to that of the conventional pancake‐type ECT probe. Finally, it was demonstrated that it is possible to establish the same measurement speed using the micro‐ECT probe as it is by using the pancake

ISSN:0424-7760    

DOI:10.1002/eej.4391160108

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

年代:1996

数据来源: WILEY

摘要:

AbstractA new motor (ADTR‐motor: Anti‐Directional Twin Rotary Motor) for electric vehicle drive is proposed. A stator in a conventional motor is reformed to be movable, and the stator (outer rotor) and the rotor (inner rotor) rotate in anti‐directions. The IM‐type ADTR‐motor and the SM‐type ADTR‐motor are considered, and in this paper a prototype of the IM‐type ADTR‐motor is constructed experimentally. When the ADTR‐motor is used for an EV drive, the direction of one of the rotors should be reversed. Both rotors, when rotated in the same direction, propel the two wheels of EV. The torque of the wheels can be balanced without differential gear. The fundamental characteristics of ADTR‐motor are clarified. The characteristics are the structure of ADTR‐motor, the equivalent circuit parameters, the torque balance theory, the torque‐speed characteristics, the rotor speed transient characteristics, and the transient response under the speed

ISSN:0424-7760    

DOI:10.1002/eej.4391160109

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

年代:1996

数据来源: WILEY

摘要:

AbstractA new type of actuator with both magnetic levitation and linear drive is proposed. The actuator, called magnet wheel, has a rotating magnetic field obtained by revolving permanent magnets with high coercivity mechanically. The induction repulsive‐type magnetic lift force with self‐stabilization can be obtained by linking the rotating flux to a conducting plate. The induced simultaneous drag torque, which causes power loss, is used to obtain thrust in two proposed ways. These are called “tilt type” and “partial overlap type,” respectively. In the tilt type, the magnet wheel is tilted against the surface of a conducting plate. In the partial overlap type, the magnet wheel operates near the edge of a conducting plate.In this paper, the fundamentals of the structure of proposed magnet wheels are described. The basic characteristics at parallel to the conductor are shown by using a numerical three‐dimensional electromagnetic analysis and measured results. The generation of both lift force and thrust in tilt type and partial overlap type magnet wheel are proved by experiments,

ISSN:0424-7760    

DOI:10.1002/eej.4391160110

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

年代:1996

数据来源: WILEY