摘要:

AbstractThis paper discusses newly developed control strategies of a self‐commutated converter applied to the HVDC system. An upper and lower power‐limited dc voltage control establishes high performance in a two‐terminal HVDC system. A voltage margin method to reverse dc transmission power also is introduced. Even when the communication system is shut down, if required, dc transmission power can be changed with the authors' proposed controls applied to the terminal control. Furthermore, the dc voltage control scheme with two‐stage voltage control characteristic is presented for multiterminal HVDC system use. When one terminal is collapsed, the multiterminal HVDC system can be operated because of the proposed control characteristics.Simulator studies were carried out to verify the proposed control performance in the two‐terminal HVDC system and successful test results such as power reversal and a terminal start‐up during other terminal operation

ISSN:0424-7760    

DOI:10.1002/eej.4391130501

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

年代:1993

数据来源: WILEY

摘要:

AbstractShunt reactors installed at gas‐insulated switchgear substations (GIS‐substations) are switched relatively frequently by large‐capacity gas circuit breakers (GCBs). Surge voltages appear at such switching operations through various mechanisms. Among them, high‐frequency current interruption and subsequent multiple reignition might cause the highest overvoltage and may be harmful to the insulation of the components of the substation.In this paper, shunt reactor current‐interrupting tests are conducted in high‐power laboratory. The existence of critical arcing time above which reignitions never occur is shown through these tests. From this fact, a phase‐angle‐controlled‐interruption system is proposed. With this system, arcing time is set artificially so that reignitions should be prevented. The reliability of this system is confirmed through the reactor current‐interrupting test in the laboratory as well. Afterward the phase‐angle‐controlled‐interruption system is applied to the shunt reactor switching at an actual 275‐kV substation. The switching performance of this system is measured over three months. Reignition‐free interruption is shown to

ISSN:0424-7760    

DOI:10.1002/eej.4391130502

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

年代:1993

数据来源: WILEY

摘要:

AbstractForced‐flow‐cooled superconducting coil (FCC) has several advantages: large stability margin; high mechanical rigidity; and good electrical insulation. As a result, FCC could provide efficient superconducting magnet systems for such large machines as fusion devices.Cable‐in‐conduit conductor (CICC) is regarded to be most attractive for FCC because of its good heat transfer characteristics which make the magnet more stable against disturbances. However, there are some problems. One problem is that the coolant pressure will become very high during a quench because its hydraulic diameter is relatively small. Also. the propagation of a normal zone has a close relation with the pressure rise. These characteristics must be considered in designing and protecting FCC.This paper describes the results of the stability tests of FCC and the analyses of these characteristics. and compares them with the results of numerical simu

ISSN:0424-7760    

DOI:10.1002/eej.4391130503

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

年代:1993

数据来源: WILEY

摘要:

AbstractNumerous studies have been made on the hunting phenomena of synchronous machines. However. most of them have been concerned with the mathematical analysis based on equivalent‐circuit models of machine and system, and experimental studies are quite rare. However, few papers have treated the phenomena from the viewpoint of internal air‐gap fluxes which actually govern the machine behaviors.This paper describes the experimental results on hunting phenomena of synchronous generators caused by a fast‐acting AVR (Automatic Voltage Regulator) in a laboratory‐model one‐machine/infinite‐bus power system. Changes of air‐gap fluxes in the process of hunting phenomena are measured by a search coil wound around a stator tooth on top of the tested synchronous generator and are examined. The interaction is made clear between field fluxes and quadrature‐axis fluxes both of which directly influence the hunting phenomena. The results obtained are confirmed by simulation studies. Thus, the relationship between system stability and machine fluxes is given a clearer understand

ISSN:0424-7760    

DOI:10.1002/eej.4391130504

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

年代:1993

数据来源: WILEY

摘要:

AbstractPower transformers have been expected to work with safety and reliability over a period of more than 30 years. The life expectancy of transformers depends upon the degree of deterioration of insulating materials, particularly conductor insulating paper. Many attempts have been made in recent years to estimate the degree of deterioration of transformers but no diagnostic techniques have been put into practical use because of the difficulty of taking into account the service conditions.It is well known that materials change color when they deteriorate, but no colorimetry study has been made on material deteriorations. According to the recent advances in instrumentation and data processing equipment, the color of materials has become easy to measure qualitatively. Therefore, the basic investigation on colorimetry of insulating papers has been made to clarify the applicability to power transformers. Test results showed a strong correlation between the color difference and the deterioration of insulating paper. This report discusses the effect of materials of papers and impregnating oils on colorimetry.

ISSN:0424-7760    

DOI:10.1002/eej.4391130505

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

年代:1993

数据来源: WILEY

摘要:

AbstractTo study the long‐term characteristics of XLPE cables installed in free air and in water, aging tests were conducted under various testing conditions using XLPE cables with both 3.5 mm and 6 mm insulation.From the Weibull plots of lifetime distribution under the voltage stressELas the minimum breakdown strength, the minimum value of time to breakdowntLunder the constant voltage was estimated. The results of accelerated aging tests of XLPE cables installed in free air demonstrated that theV‐tcharacteristics of XLPE cables could not be described by the conventional inverse power law (t ∝ V−n) with a single constant life exponentn.Based on the microscopic observation of a sliced insulation removed from XLPE cables, it was concluded that bow‐tie trees with longer tree length observed in cables tested in water were caused by the moisture from outside, whereas the trees in cables tested in free air were caused by the residual moisture originally existing in the insulation. The breakdown strength of the aged cables tested in water increases through cable drying. However, it does not recover to the origin

ISSN:0424-7760    

DOI:10.1002/eej.4391130506

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe squirrel‐cage‐type induction generator is suitable for small water power stations and wind power stations because of its simple and rugged structure, and low construction cost. However, the transient rush current flows into the primary and secondary windings when an induction generator is connected abruptly to a utility power network. The inrush current causes the voltage fluctuation in the power system. Therefore, electric power companies need a control method with low cost of the inrush current of the induction generator.Many properties of the inrush current must be known in detail. The factors affecting inrush currents are system voltages, control of the system voltage phase angle, rotary speed, residual magnetism of the core, and residual electric charge of the primary windings. In this paper, the inrush current is analyzed by the instantaneous value symmetrical coordinates. The experimental study of the inrush current using phase control equipment and a small induction generator is presented.The conclusions of this investigation are summarized as follows:(1) The factor that gives the strong influence on the inrush current is the voltage phase angle.(2) Although rotary speed changes from 0.9 to 1.15 times as much as the synchronous speed, the maximum value of the inrush current is nearly constant.(3) The maximum amplitude of the inrush current is definitely seen in the first or second w

ISSN:0424-7760    

DOI:10.1002/eej.4391130507

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

年代:1993

数据来源: WILEY

摘要:

AbstractIt is desirable that the rectifier that is an ac‐to‐dc converter, have the characteristics of fast response and the wide range of the output voltage control, and the sinusoidal source current waveform. In this paper, a step up/down output voltage PWM‐controlled rectifier is proposed. The features of the proposed rectifier are as follows.(1) The calculation of pulsewidth is based on the geometrical technique and the source current can be inphase with the source voltage.(2) The output voltage is controlled from about zero to more than the maximum value of the source voltage.The aforementioned features are clarified by simulation and the steady‐state characteristics are discussed. Further, these results are verified in experiment using the microprocessor‐based contr

ISSN:0424-7760    

DOI:10.1002/eej.4391130508

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper describes a vector control system of an induction machine using a neutral‐point‐clamped voltage‐source inverter (NPC‐VSI) that is one of the double series‐connected inverters.The NPC‐VSI is able to output five‐level step‐shaped line‐to‐line voltage without output transformers or reactors, and it may reduce harmonic currents corresponding to torque ripples. However, the NPC‐VSI has a problem in that excessive high voltage is applied to switching devices when a neutral point of two dc capacitors of the NPC‐VSI varies from the center of the dc link voltage, because the neutral point is floating.This paper proposes also a current controller to which the space vector theory is applied. This can reduce harmonic currents to one‐fourth those of a conventional voltage‐source inverter using six switching devices, and regulate the neutral point potential within a preset range. To simplify the current controller, information about voltage space vectors is given from the vector controller to the current controller. The validity of the current controller is confirmed by a prototype using an

ISSN:0424-7760    

DOI:10.1002/eej.4391130509

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

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper describes a network system designed to realize the motion of a muscle. First, the motion of the network system is analyzed by a model system which consists of many electromagnets. Second, the control strategy of the network motion system, implemented with microactuators, is described. In the proposed network motion system, the total system consists of many force transmission lines and the superposition of the force signals propagated by the lines acts on the final actuator. The proposed motion control method is therefore called the Delay Superposition Method (DSM). Several experimental and numerical results confirm the validity of the proposed method.

ISSN:0424-7760    

DOI:10.1002/eej.4391130510

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

年代:1993

数据来源: WILEY