摘要:

AbstractWhen an ac voltage is applied to a low‐density polyethylene (LDPE) film placed under a needle‐plane electrode system, there is a possibility of the formation of the space‐charge field in the vicinity of the needle electrode by electrons (or holes) injected from the needle electrode. In this paper we investigated the properties of the space charge, e.g., the total amount of trapped charge formed in the vicinity of the needle electrode by using electrical measurements of thermally stimulated current (TSC) and thermally stimulated surface potential (TSSP).From the investigation, it was concluded that a space‐charge field is formed in an LDPE film by the application of the ac voltage, and that the total amount of trapped charge by the application of the ac voltage is less than that by the application of the dc voltage, etc. Finally, on the basis of the present experimental results, we studied the space‐charge effect on the ac treeing

ISSN:0424-7760    

DOI:10.1002/eej.4391120401

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

年代:1992

数据来源: WILEY

摘要:

AbstractA self‐extinguishing principle of a gas circuit breaker (GCB) without puffer action (autopuffer GCB) using an external magnetic field was investigated to improve the interrupting capability in the small current region (several kA). Properties of the rotating speed of an arc, the arc voltage, and the gas pressure rise in an expansion space under the external magnetic field were studied experimentally. The relation between the interrupting capability and the radial magnetic flux density in the autopuffer GCB with a permanent magnet (magnet‐assisted autopuffer GCB) was obtained experimentally and also analyzed numerically. The results are summarized as follows.1The arc column is driven in the azimuthal direction by the radial component of the external magnetic field.2The rotating speed of the arc driven by the radial magnetic field of a permanent magnet remains constant in the arc current range below several kA, and it decreases with an increasing current in the current above several kA.3Since the arc rotation raises the arc voltage and gas pressure in the expansion space, the gas flow from the expansion space to the arc increases in the vicinity of current zero. The interrupting capability is then improved in the small current region.4It is confirmed that the magnet‐assisted auto‐puffer GCB has a good interrupting capability not only for the large current region but also for the small current

ISSN:0424-7760    

DOI:10.1002/eej.4391120402

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe authors have already clarified that case‐based reasoning (CBR) is very useful for the fault‐restoration support system in electrical power networks. This paper describes the case‐based construction method, adaptation and modification method of a case which is a fundamental process of CBR, and the results of evaluation.The following points were clarified through the simulations of fault restoration under various conditions with electrical power networks of practical scale: (1) a case‐based construction method and the guide to the selection of cases which should be included in the case were made clear. Restoration plans which include many cases are registered in the base. Cases which would require long computation time are also registered in the case base. In the application which requires high‐speed processing, such as fault restoration, there exists an optimum value in the total numbers of cases in the case base; (2) the function of load switching which is essential to perform adaptation and modification of a case flexibly was studied and embedded in the system herein. Inference power was augmented by the implemented of this function, and optimum for suboptimum solutions were obtained. Processing time with CBR is considerably shorter than other methods, and this feature is remarkable with complica

ISSN:0424-7760    

DOI:10.1002/eej.4391120403

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe superconducting field winding of the 70‐MW classhigh‐response excitation superconducting generator requires a maximum operation current of 4.5 kA at the field of 6 T and needs to allow the field change of 10 T/s. In addition, superconductors have to meet the requirements of saddle‐shape winding in the rotor slot and require the mechanical strength withstanding the centrifugal force as well as electromagnetic force.The developed conductor has the configuration of double stranded cable, consisting of NbTi, Cu and CuNi. An optimization was made, taking into account the requirement of low ac loss and high current density. The critical current of 13.6 kA was achieved at the field of 6 T and the ac loss was 6.9 kW/m3. The developed low‐loss high‐current density superconductor will be able to be applied to the field winding of the 70‐MW class high‐response excitation superconduct

ISSN:0424-7760    

DOI:10.1002/eej.4391120404

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

年代:1992

数据来源: WILEY

摘要:

AbstractAC superconducting wire is being developed for such electrical equipment as superconducting transformers and superconducting generators. AC loss reduction is of primary concern in the development of such high‐efficiency equipment. In reducing ac losses, it is necessary to develop assessment methods for ac loss in test samples which have shapes similar to the end‐product equipment.This paper describes a least‐square calculation of ac losses of superconducting wire as a function of frequency and magnetic field strength measured in test coils.Two sample solenoid coils were made to test the influence of different capacities and winding methods on ac losses in ac superconducting coils with rated capacities of 500 kVA and 20 kVA, and impregnated (epoxy resin) and nonimpregnated windings.The ac losses in the superconducting coils were measured by a calorimetric method using the evaporating rates of liquid helium. Estimated ac losses in the superconducting wire of the two coils were compared with Joule losses of copper conductors at ambient temperature. As a result of this comparison, a low‐loss ac superconducting wire winding can be made for electrical equipment rather than employing conventional copper winding when used under low magnetic fields unde

ISSN:0424-7760    

DOI:10.1002/eej.4391120405

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

年代:1992

数据来源: WILEY

摘要:

AbstractWith the recent advent of high‐performance ac superconductors with very small ac loss and large current‐carrying capacity, the possibility of an air‐core superconducting transformer is being studied. Although the exciting current is very large, the air‐core transformer has the following merits: (1) no iron loss; (2) no insulation care of the core; (3) no harmonics, and no in rush current induced by iron saturation, etc. Thus, the authors fabricated and tested a small experimental transformer (2.5 kVA, 330/150 V). As easily predicted, the exciting current becomes very large. It occupies about 45 percent of the rated current. Meanwhile, the leakage reactance increase considerably. The %IX becomes about 28 percent. These experimental results show good agreement with the theoretical analysis based on an equivalent

ISSN:0424-7760    

DOI:10.1002/eej.4391120406

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

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper describes superconducting magnets coupled with two kinds of disk‐type MHD generators. One is coupled with a disk generator in the closed‐cycle MHD experimental facility FUJI‐1. The other is for a full‐scale disk MHD generator. These are split‐pair magnets.In the magnet for the FUJI‐1 facility, a unique structure which supports the coils against the electromagnetic force has been fabricated and the magnet has been operating stably. During MHD power generation experiments, an induced voltage across the terminals of the coil was measured. A magnitude of the Faraday current in the generator was calculated from this induced voltage.A possible construction of magnetics for a full‐scale disk MHD generator is indicated. It is suggested that a high performance of the generator (output power density of 0.3‐1 GW/m3) can be obtained with high magnetic f

ISSN:0424-7760    

DOI:10.1002/eej.4391120407

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe static and dynamic characteristics of power supply to each node in a hybrid ac‐dc power system are analyzed by means of static and transientP‐Vcurves. Three kinds of dc transmission control scheme are compared. DC transmission systems are more effective in delivering power to inverter nodes. The constant firing angle, constant current control techinque provides more power to inverter nodes than the conventional constant current, constant voltage and constant power, constant extinction angle techniques. Transient digital simulations indicate that dc interconnection improves voltage stability to both the opening of a dc interconnected line and one‐line opening of ac double‐circuit interconnecte

ISSN:0424-7760    

DOI:10.1002/eej.4391120408

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

年代:1992

数据来源: WILEY

摘要:

AbstractA novel three‐phase conducting fault current limiting reactor (SCFCLR) is fabricated. The SCFCLR has three superconducting windings with the same number of turns wound on an iron core. The rating of SCFCLR is 200 V, 10 A. Two SCFCLRs are inserted in the sending and the receiving ends of the model power‐transmission line. The line fault test of a model power system with two SCFCLRs is undertaken. The fundamental behavior of this reactor is confirmed. In the case of single‐line‐to‐ground fault, the fault current is limited to a very small value by the large zero‐phase sequence reactance of the SCFCLR without quench. In the case of a three‐phase short circuit, the SCFCLR quenches, and the short‐circuit current is limited by the normal conducting resitance of the winding. It is confirmed that the transient stability of the system during line faults is greatly improved by the inser

ISSN:0424-7760    

DOI:10.1002/eej.4391120409

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

年代:1992

数据来源: WILEY

摘要:

AbstractRenewable energy utilization and electricity storage will soon be introduced into the conventional electric power system. This study assumes that a photovoltaic (PV) power generation system, a set of the PV units, is installed into the electric power system with electricity storage; moreover, the effects of uncertain variation characteristics of the PV system output on the operations of the conventional power generation system and the storage units are evaluated by simulations, with cost a major consideration. According to the simulation results, it is clearly demonstrated that the costs of the PV system are influence sharply by the prediction accuracy of their output.

ISSN:0424-7760    

DOI:10.1002/eej.4391120410

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

年代:1992

数据来源: WILEY