摘要:

AbstractImpulse insulation characteristics were investigated in a composite insulation system having a wedge gap in SF6gas. The partial discharge inception voltages of wedge gaps with various types of film were measured and compared with the calculated breakdown voltages estimated from Paschen's curve of SF6gas. Also discussed is how the charge accumulated on the film surface due to a partial discharge had an effect on the creepage breakdown voltage. Partial discharge inception voltages in wedge gaps were higher with higher SF6gas pressures and with lower film permittivities.Creepage breakdown voltages depended little on gas pressures or on creepage distances. The dependency of breakdown voltages on gas pressures and the effect of polarity on the breakdown voltage differed with the types of film. This may be partly because the charge on the film due to partial discharge had an effect on the discharge propagation, and that charging of the film differed with the types of film.

ISSN:0424-7760    

DOI:10.1002/eej.4391130201

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

年代:1993

数据来源: WILEY

摘要:

AbstractBy relying only on the conventional technology, it may be difficult to meet the recent requirements of electric power systems such as further improvement of the quality of electric power supply, environmental compatibility, and so on. Some of the limitations of conventional technology can be eliminated by the application of superconductivity technology. Roughly speaking, superconductivity‐applied components which have relatively high feasibility are the superconducting generator, small‐capacity SMES. and liquid nitrogen‐cooled superconducting cable. To use them practically, reliability, maintainability, controllability and economy must be improved to the level of conventional compo

ISSN:0424-7760    

DOI:10.1002/eej.4391130202

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

年代:1993

数据来源: WILEY

摘要:

AbstractPower system control and protection equipment is subject to especially stringent sensitivity and operational reliability requirements.Projected digital signal processing systems suitable for electric power systems fulfill these requirements by means of fast sampling and digital filtering by a 32‐bit floating point DSP (Digital Signal Processor). The sampling rate of 3 kHz is carefully selected in order to separate the power spectra of the A‐D conversion output errors from the signal bandwidth. The new 12‐bit A‐D conversion unit equipped with a recursive‐type digital filter achieved a high resolution equivalent to 14‐bit conversion.This paper describes the design concept and the operating characteristics and illustrates applications to current differential relays, distance relays and power system

ISSN:0424-7760    

DOI:10.1002/eej.4391130203

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe introduction of an HVDC system into the trunk power supply system requires transmitting as much dc power as possible for improving the whole ac/dc system stability. The continued operation scheme of an HVDC system which makes it possible to operate even under very low commutation bus voltage is adopted to cope with such system requirement. Further stability improvement can be achieved by adding damping control which modulates converter active and/or reactive power.To take full advantage of these control effects, it is essential that the HVDC system can maintain stable operation during the ac system faults and reclosing. Particular attention should be given to a repetitive commutation failure following the unbalanced ac transmission line faults.This paper discusses first the cause of the repetitive commutation failure when supplied with unbalanced ac system voltage based on an experiment using the CRIEPI AC‐DC Power System Simulator. Then a stabilization control scheme with an on‐line extinction angle estimation is proposed and the effect is verified by digital simulat

ISSN:0424-7760    

DOI:10.1002/eej.4391130204

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

年代:1993

数据来源: WILEY

摘要:

AbstractTo explain contact failure phenomena and their development in the gas‐insulated switchgear (GIS). tests were conducted by simulating abnormal current‐carrying conditions using an actual 300‐kV, 2000‐A GIS.This paper describes the process observed. ranging from contact failures to ground faults, deteriorative phenomena and some detection methods for initial contact failure conditions. A summary of this study is as follows:(1) The contact resistances are greatly dependent on the materials and construction of contacts.(2) The relation between the initial contact resistance and the carried current resulting in arcing is derived with approximately constant Joule‐heat generation.(3) Ground faults result from sagging of a shield melted by arcing or a combination of two causes: (i) scattering of molten metal caused by arcing; and (ii) sagging of a conductor caused by bolt melt down.(4) To detect initial contact failures, it is recommended to observe the contact resistance, the temperature rise on the tank surface, or the electrical partial d

ISSN:0424-7760    

DOI:10.1002/eej.4391130205

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper presents experimental results of the flux control characteristic and the inductance control characteristic of magnetic fluid which is controlled by the permanent magnets. Two kinds of magnetic field, parallel and orthogonal, are discussed comparatively. The position between the magnetic fluid and the permanent magnet determines the magnetic field. The results are useful when employing magnetic fluid as a sensor or a control element.

ISSN:0424-7760    

DOI:10.1002/eej.4391130206

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

年代:1993

数据来源: WILEY

摘要:

AbstractFrom the viewpoint of maintenances and constructions, it is desirable that brushless and exciterless type three‐phase synchronous generators be made.To meet this requirement, one of the authors devised a brushless and exciterless synchronous generator in which exciting currents flow simultaneously with load currents in armature windings. Thus, generators can be used both as the generators themselves and as the exciters. A generator system has already been reported by one of the authors. In it, the dc stator exciting current flows between the middle points per phase of the double‐star armature winding through the rectifiers. However, the winding connection between the armature winding and the rectifiers are complicated. Three sets of rectifiers are needed by the stator excitation.The authors present a generator system by which the electric connection of between the stator armature winding and the rectifier can be simplified, and the number of the rectifiers can be reduced. In this system, the stator is provided with a double‐star armature winding having two neutral points.In this paper, first, a circuit constitution and the principle for the brushless and exciterless three‐phase synchronous generator are described, and second, the characteristics are elucidated by means of characteristic analysis. Further, the results of the experiments for the generator conducted on the test machine of 2.0 kW ar

ISSN:0424-7760    

DOI:10.1002/eej.4391130207

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe combined system of a series active filter and a shunt passive filter that is proposed by the authors has the ability to eliminate a major disadvantage of shunt passive filters, namely, harmonic amplification. The series active filter needs a much smaller kVA rating than a conventional shunt active filter, and as a result, the combined system has good filtering characteristics and high efficiency.This paper presents an optimum design of the shunt passive filter that makes possible a great reduction in the required kVA rating of the series active filter. It can minimize the peak voltage across the series active filter and reduce the required kVA rating of the filter to 60 percent. A computer simulation geared to practical applications of large three‐phase. twelve‐pulse thyristor rectifiers is used to compare the compensation characteristics of the optimized system with those of a combined system that uses a conventional shunt passive filter. Experimental results obtained with a laboratory model of the filter corroborate the design appro

ISSN:0424-7760    

DOI:10.1002/eej.4391130208

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper presents a new brushless three‐phase synchronous motor which has no exciter. The technique applied to the motor provides an effective way for conventional brushless synchronous motors to simplify the system configuration. The stator of the motor is equipped with a double‐star connected armature winding which has two neutral points. The rotor is a cylindrical one, which is equipped with a two‐phase field winding. The field winding is connected with shaft‐mounted rectifiers.A dc voltage is applied to the two neutral points of the armature winding to obtain the rotor excitation when the motor is operated at synchronous speed. At that time. the armature winding acts as a stator dc exciting winding while also acting as a load winding.In this paper the principle and characteristics of the motor are described. and the experimental results are shown. It is confirmed that with a 2‐kW experimental machine, the proposed motor has good performance. For example, by adjusting the stator dc current, this motor power factor can easily be controlled within a w

ISSN:0424-7760    

DOI:10.1002/eej.4391130209

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

年代:1993

数据来源: WILEY

摘要:

AbstractAn experimental line of a magnetically levitated train (MAGLEV) using superconducting magnets (SCM) is now under construction in Yamanashi Prefecture. In the MAGLEV system, the levitation coils are mounted in the side walls. The induced current of the levitation coils generates magnetic flux that includes higher order harmonics. These harmonics generate eddy currents at the surface of the vacuum vessels of the SCM. Forces produced by interaction between the eddy current and the static magnetic field of the SCM cause evaporation of liquid helium, or SCM quenching in the worst case. The number of levitation coil layer is now restricted to one, but by removing the restriction, it is possible to reduce the amplitude of the harmonics of the magnetic flux. In this paper, the relationship of the flux amplitude to the levitation coil length is investigated; it is found that there is an optimum length at which the amplitude is minimized.

ISSN:0424-7760    

DOI:10.1002/eej.4391130210

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

年代:1993

数据来源: WILEY