摘要:

AbstractThe initiation and growth of the electrical tree in crystalline polymers are influenced by the superstructure. However, there are still many unclear points in the relationship between the tree deterioration and the superstructure (spherulites).To study the relationship between the tree deterioration and the spherulite, we designed the measuring apparatus which allows simultaneous observation of these phenomena. The sample was set on the stage of the polarizing microscope to make observations of the tree initiation and growth in polypropylene.This paper reports the results of some observations concerning the tree initiation and growth in polypropylene with 60‐Hz ac voltage. The results are as follows:1Prior to the initiation of trees, a fine deterioration zone is formed on spherulite surfaces. Thereafter, the discharge occurs along the spherulite surface, and the trees occur.2Tree shapes change under the influence of the distribution state of spherulite.3Tree initiation voltage is 5.8 kV for the spherulite inside and 5.1 kV for the spherulite boundary, respectivel

ISSN:0424-7760    

DOI:10.1002/eej.4391120101

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

年代:1992

数据来源: WILEY

摘要:

AbstractA 66‐kV network generally is grounded through a neutral grounding resistor. In this network a single‐phase ground‐fault current is limited to as small as 100 to 400 A. There are parallel four‐circuit transmission lines mounted on the same tower in the 66‐kV network. In such transmission lines, the load and the fault currents could induce circulating current that flows through the lines. Since the circulating current has zero‐phase‐sequence and negative‐phase‐sequence components, it could cause unwanted operation of a balance ground relay using zero‐phase‐sequence current. However, it is difficult to compensate for the circulating current by the conventional vector compensation scheme.This paper presents a new balance ground relay to deal with the circulating current. In the relay from the ground‐fault inception until first tripping, the difference current Δ3I2dof negative‐phase‐sequence current 3I2dof the differential current between two protected lines is used as an input current. The Δ3I2dis the difference current of 3I2dbetween, before and during faults. After the first tripping, the difference current of positive‐phase‐sequence load current and zero‐phase‐sequence current of the forementioned differential current are used as an input current. Consequently, a higher sensitivity of the ground‐fault protection for these lines has been achieved. The correct operation of the new balance ground relay was confirmed when a single‐phase‐ground‐fault occurred in the parallel four‐circuit tr

ISSN:0424-7760    

DOI:10.1002/eej.4391120102

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe recent increase in the demand for power in urban areas has caused changes in the way power is supplied. Underground distribution systems have been introduced for convenience in urban areas and to prevent injuries in case of a crisis. As a result, many new types of power cables are being used. One type, XPLE cables (also called CV cables) have been rapidly taking the place of conventional cables such as OF or SL cables since the 1960s because of their relatively easy installation and maintainability. However, distribution cables used under severe environmental conditions deteriorate rapidly (due mainly to water treeing), and some cables experience insulation breakdown. Therefore, many diagnostic methods have been developed, though they have not been very effective. By combining methods, a high reliability can be achieved in comparison to the use of a single method. However, processing the data is difficult for on‐site personnel, so many experts are required. But there is a lack of qualified experts, hence we have turned to the development of expert system

ISSN:0424-7760    

DOI:10.1002/eej.4391120103

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

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper presents an on‐line stabilization control method developed with the aim of maintaining transient stability in a local power system which includes large‐capacity generation plants. The characteristics of this method are that the power/angle curve is estimated from the on line active and reactive power measured at the generator terminal, and the optimum generation shedding for stabilization is determined by applying the equal area method to this curve.Simulation tests using detailed models of the power system confirmed that the optimum generation shedding for stabilization could be computed for various fault conditions, both symmetrical or asymmetrical.It was also determined that the on‐line data could be sampled for several tens of milliseconds after clearing the fault. Thus, this method provides effective control logic for practical stabilizing sy

ISSN:0424-7760    

DOI:10.1002/eej.4391120104

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

年代:1992

数据来源: WILEY

摘要:

AbstractIn high‐voltage measurement, the digital measuring system is used widely because of its attractive features, for example, automatic data acquisition. However, the accuracy in the measurement of both the amplitude and time parameters by the digital measuring system is not known in detail, especially in the measurement of single‐shot waveforms.In this paper, the accuracy of the peak value and the virtual front time of the standard lightning impulse without any signal processing of raw data is shown. From these results, the required characteristics for the digital measuring system to satisfy the IEC Draft on digital recorders for measurement in high‐voltage impulse test techniques are shown. In addition, the accuracy of the peak voltage and the rise time of the Gaussian pulse is

ISSN:0424-7760    

DOI:10.1002/eej.4391120105

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe digital simulation method has been utilized to analyze phenomena in power systems. Since different algorithms can be applied, depending on the phenomena to be analyzed, digital simulation allows for high‐precision analysis.However, it also has a disadvantage: it produces continuous phenomena which occur in actual systems only fragmentarily. Thus, when discussing important projects at research centers such as IREQ in Canada, an analog simulator issued to continuously analyze the phenomena from the moment the fault occurs until steady state.These analog simulators, however, consist of only a few generator models. They are only effective for analyzing phenomena in small‐scale systems and do not allow for analysis of phenomena in large‐scale systems over a long period of time.For this reason, the Kansai Electric Power Company (KEPCO) in cooperation with Hitachi, Ltd., and Fuji Electric Co., Ltd., has developed the world's largest power system simulator (APSA: Advanced Power System Analyzer). The simulator will be used to analyze the evolution of accidents in actual systems and to analyze continuous system phenomena over a long period.This paper describes an outline of the simu

ISSN:0424-7760    

DOI:10.1002/eej.4391120106

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

年代:1992

数据来源: WILEY

摘要:

AbstractOne of the failures related to gas‐insulated switchgear is caused by the poor contact between conductors. This causes breakdown between the contact and the wall of chamber, initiated by the small discharge due to the poor contact.In this paper, the modeled experimental apparatus for the contact portion of the gas‐insulated switchgear assumed a rod‐to‐plane gap with small arc current. The influence of the arc current on the breakdown into the chamber was investigated experimentally, and the breakdown mechanism between the contacts and the wall was studied.It was clarified that the breakdown voltage between the contact and the wall decreased by increasing the current, and the small arc current in the contact portion played an important role in the breakdown between the contact and the wall.The reduction ratio of the breakdown voltage increased with increasing gap length of the small gap. The breakdown voltage was different depending on the duration of the small arc

ISSN:0424-7760    

DOI:10.1002/eej.4391120107

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

年代:1992

数据来源: WILEY

摘要:

AbstractConstruction of 275‐kV and 500‐kV substations in densely populated areas is thought to be necessary in the future to maintain a stable supply of electricity. The use of gas‐insulated transformers is now considered for substations because such transformers are non‐flammable and nonexplosive. Since the completion of the 77‐kV gas‐insulated transformer in 1979, we have continued research to develop gas‐insulated transformers applicable to a higher voltage level up to 500 kV. As the results of the research, 275‐kV, 300‐MVA a liquid cooling‐type gas‐insulated transform

ISSN:0424-7760    

DOI:10.1002/eej.4391120108

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

年代:1992

数据来源: WILEY

摘要:

AbstractIn the last decade, increasing attention has been paid to ELF (Extremely Low Frequency) electromagnetic environments in work areas as well as in and near homes, regarding their interaction both with electric apparatus such as CRT's and with biological systems. Experimental and theoretical analyses are presented of 60 Hz magnetic field (B‐field) characteristics at and near ground level in both 187/66‐kV EHV and 66/6.6‐kV HV power substations.Experimental results ofB‐field profiles along horizontal paths as well as harmonic contents inB‐field waveforms at several positions are shown and discussed.Furthermore, analyticalB‐field profiles calculated by using aB‐field approximation method based on Biot‐Savart law are shown and compared with the measured ones. The comparisons verify that the assumptions employed are applicable to the substationB‐field calculation, and that theB‐field calculation method employed can estimateB‐field in EHV and HV power substation to significant accuracy, except for areas where localizedB‐field sources, such as power transformers and underground power cables, exist. The analytical profiles of three orthogonal components ofB‐field are also described in terms of equiflux contour maps, which show 3‐D characteristics ofB

ISSN:0424-7760    

DOI:10.1002/eej.4391120109

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

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper discusses an optimal short‐range scheduling of multireservoir hydrothermal power systems considering runoff prediction. Using Prasad's rainfall‐runoff model and the Kalman filter‐based, second‐order filtering technique, the hour‐by‐hour characteristic is estimated for a given short‐range forecasted rainfall pattern. Unlike the usual hydroscheduling problem in which a single‐reservoir operating condition is specified at the end of the scheduling period, various end point conditions are examined to deal with the predicted runoff characteristic and to avoid possible water spillages from reservoirs.Dynamic Programming Successive Approximations are applied successfully to obtain optimum operating strategies for many end point conditions at a time. A rapid convergence characteristic coupled with a simple computation algorithm makes the proposed method one of the attractive approaches for scheduling of complicated multireservoir hydrothermal systems considering ru

ISSN:0424-7760    

DOI:10.1002/eej.4391120110

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

年代:1992

数据来源: WILEY