摘要:

AbstractThis paper describes results of the discharge luminescence and discharge magnitude measurements performed on the insulation materials exposed to partial discharge. Polymethyl methacrylate (PMMA) with an artificial needle shape void were used as the treeing specimens. The discharge luminescence is observed by image intensifier, and the luminous image is processed by computer. At the same time, the discharge magnitude distribution in relation to phase angle of the applied voltage was measured by a partial discharge measuring system. The mechanism of electric treeing was discussed by not only the measurement of the discharge pulses but also the local luminescence intensity of partial discharge.As a result, the luminescence intensity analysis showed the relation between tree growing length and void length when maximum luminescence intensity moved from the void area to the tree area. Both tree growth and maximum luminescence intensity at the tree area increase with constant ratio. The discharge luminescence intensity at the tree area increases significantly depending on the discharge magnitude in the specific phase angle area in positive and negative.

ISSN:0424-7760    

DOI:10.1002/eej.4391160401

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

年代:1996

数据来源: WILEY

摘要:

AbstractTo discuss the UHV GIS test voltage, the deterioration characteristics of the GIS insulating spacer model were studied by repeating lightning or switching impulse voltage. The deterioration factor indicating the decrease of lightning or switching impulse breakdown voltage applied up to 1000 times was found to be 35.7/45.5. The relationship between the partial discharge inception voltage and the breakdown voltage after 1000 impulse applications was also studied. It was found that the partial discharge inception voltage increases despite a decrease in breakdown voltage due to the impulse voltage.In addition, to elucidate the deterioration phenomenon, a study was made of the breakdown characteristics of models with various boundary conditions between the electrode and epoxy resin, as well as the relationship between the boundary conditions.Microdischarge was also studied. The results of the investigation suggest that the deterioration by repeating voltage is caused by microdischarge due to electric field intensification on microprotrusions of the electrode surface.

ISSN:0424-7760    

DOI:10.1002/eej.4391160402

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

年代:1996

数据来源: WILEY

摘要:

AbstractHigh‐voltage power distribution systems are connected in a branch configuration so as to meet the need for highly reliable power service. When service is interrupted the faulty section is automatically isolated and the power supply is rerouted from an adjacent power distribution system thereby minimizing the service interruption area. The faulty section in the power distribution system is quickly located by means of time relays installed in the switchgears. The settings of those time relays, however, must be monitored constantly.For this reason, we have proposed a “section management method” which can supervise each section of the power distribution system. From this method, we developed a prototype automated distribution system for overall management of time relays through the use of internal software, facilities and customer feedback.This paper describes the section management of power distribution sy

ISSN:0424-7760    

DOI:10.1002/eej.4391160403

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper proposes graphical representation methods of static and dynamic characteristics of power systems. The methods use the computed results of load flow calculation and dynamic stability calculation. This work develops three kinds of representation methods using maps and animation which are sequential graphical representation of maps based on dynamic stability calculation.Conventionally the results of load flow calculation and dynamic stability calculation are represented and comprehended using load flow maps or dynamic swing curve. However, quick and effective comprehension of power system characteristics by such conventional representation methods is becoming more difficult as power systems to be analyzed are becoming larger and more complicated, especially in power systems with many loops or grids. Graphical representation using the proposed methods makes it easy to understand the static and dynamic characteristics of power systems quickly and comprehensively.In addition to these methods, this paper proposes a heuristic logic that makes it possible to draw maps automatically. It is very convenient to apply these methods to arbitrary power systems even if their constitutions or characteristics are not well known.

ISSN:0424-7760    

DOI:10.1002/eej.4391160404

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

年代:1996

数据来源: WILEY

摘要:

AbstractTo evaluate an appropriate level of ac test voltage for 1000‐kV transformers, it is necessary to make an accurate estimation of ac V‐t characteristics. For the level of impulse test voltage, V‐N characteristics are important to evaluate effects of impulse stress repetition. Since both of the characteristics are dependent on insulation structures and manufacturing processes of transformers, it is important to make accurate simulations on transformer insulation for reliable insulation data.To obtain some of the basic data for 1000‐kV transformer test levels, long‐time ac V‐t tests and impulse V‐N tests of up to 1000 times voltage application were carried out on an insulation model simulating fundamental structure of shell‐form transformers. The model is composed of a parallel electrodes system with a compound structure of pressboard barrier and oil gap.The tests showed the following characteristics: ac V‐t characteristics of up to several ten days could be described by two lines, each representing short‐time and long‐time characteristics. V‐N characteristics of lightning and switching impulse were expressed by relatively flat lines, which showed a decrease in breakdown voltage by less than 10 percent after 1000 ti

ISSN:0424-7760    

DOI:10.1002/eej.4391160405

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

年代:1996

数据来源: WILEY

摘要:

AbstractThermal units must be maintained periodically as prescribed by the electric utility industry law. As time to execute maintenance works increases with thermal unit capacity, maintenance scheduling has a great influence on the reliability and economy of a power system. In the recent amendment in the law, three inspection rankings have been introduced and scheduling over several consecutive years becomes mandatory, thus making maintenance scheduling extremely difficult. Reflecting a recent stringent supply capability, the emphasis is laid on security rather than a minimum operating cost, having been the primary objective in determining the schedules. Therefore, this study aims to level the spinning reserve at each period under study in the maintenance scheduling while taking into consideration all the amendments in the law. Although rigorous methods such as integer programming and branch and bound method can solve small scale problems, large size problems are beyond these techniques due to an exponential explosion in the number of possible combinations.The prime objective of this paper is to investigate the capability of the Hopfield neural network (HNN) in solving the newly formulated maintenance scheduling problem. The scheduling problem has been mapped on the HNN with slight problem relaxations to facilitate the implementation. A small scheduling problem that determines the maintenance schedules of 3 generators over 3 years (divided to 78 periods) has been solved by the neural network simulator. It has been made clear from simulation results that the proposed approach is very promising in handling a complicated combinatorial optimization problem.

ISSN:0424-7760    

DOI:10.1002/eej.4391160406

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

年代:1996

数据来源: WILEY

摘要:

AbstractIn industrial motor drive systems such as industrial plants and industrial robots, a torsional vibration often is generated because of the elastic elements in torque transmission. This vibration makes it difficult to achieve quick responses of speed and may result in damage to the plant. Such systems simply are modeled as a two mass system. The shaft torque feedback system with the disturbance observer, which is called “resonance ratio control,” is proposed to suppress the vibration for the two‐mass system.In this paper, the design of controller gains in the shaft torque feedback system is examined considering not only the control performance such as the vibration suppression and dynamic responses, but also the robust stability against the noise and the model uncertainties. This paper shows the validity of the control system and the examinations by several experi

ISSN:0424-7760    

DOI:10.1002/eej.4391160407

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

年代:1996

数据来源: WILEY

摘要:

AbstractA slim flexible disk drive, which could be mounted on a hand‐held personal computer, is now under intensive study in Japan. The spindle motor for the flexible disk drive has an index‐position detecting means, an index magnet attached to the outer wall of the periphery of the rotor yoke, and a magnetic sensor which detects the magnetic flux from the index magnet. As a result, spaces for providing the index magnet and the magnetic sensor prevent the motor from being made smaller in size and reduced in thickness.This paper describes the method for detecting the index position of a spindle motor without both the index magnet and the magnetic sensor. This method detects an index position per rotation from two different kinds of frequency generating signals (main FG and sub FG) through an index‐detecting circuit. The thin spindle motor to which this index‐detecting method is applied, performed a smaller degree of rotational speed variation compared with another well‐known one without both the index magnet and the magnetic sensor. This index‐detecting method is most suitable for a less‐inertia‐thin spindle motor, and is e

ISSN:0424-7760    

DOI:10.1002/eej.4391160408

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

年代:1996

数据来源: WILEY

摘要:

AbstractLaboratory‐scale and parametric experiments of SO2and NOxremoval from the simulated combustion gas by pulsed corona discharge have been performed by changing the combustion gas composition and temperature, the electrode configuration of plasma reactor, and the polarity of high‐voltage electrode. The following results are obtained: 1) the higher the concentration of H2O and O2, the higher the efficiency of desulfurization and denitrification at the same specific input; 2) the pulsed corona discharge with a voltage pulsewidth as short as 200 ns of negative polarity shows the possibility to attain almost 90 percent deSOxand deNOxefficiency at the specific discharge input of 20 J/g, which is almost the same as the specific input in the electron‐beam process; 3) the deNOxcharacteristics show a little temperature dependence in the range of 70 to 130°C, but the deSOxefficiency increases rapidly in the temperature region below 100°C suggesting the thermochemical dependence of deSOxreaction; 4) when desulfurization and denitrification proceed, the white dendritic powder deposits on the plasma reactor whose composition is identified to be 49 mol% (NH4)2SO4and 47 mol% of 2NH4NO3· (NH4)2SO4, and the ratio of SO2, NO and NH3of the deposit is almost equal to that of supp

ISSN:0424-7760    

DOI:10.1002/eej.4391160409

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

年代:1996

数据来源: WILEY

摘要:

AbstractAn active filter (AF) is a device to eliminate switches. There are two types of AF, the voltage source type and the current source type. The voltage source type is common in practical use today. But we have studied and already reported that the AF of the current‐source type has the characteristics of rapid and precise controllability of the output current and little interference between the AF and the distribution line.In this paper, we propose two schemes to improve its performance and to reduce its capacitance.To improve the performance of AF, we changed the PWM carrier from the triangular wave used in a previous paper to the sawtooth wave. However, the switching rates remain the same. By using the 5 [kHz] sawtooth carrier (corresponding to 2.5 [kHz]triangular wave) and the multiplexed connection of AF, harmonic currents of less than 19‐th order can be eliminated in the distribution line.To reduce the capacitance of the AF, we proposed an AF which eliminates only harmonic currents. By using other apparatus for fundamental reactive power compensation, a more economical system can be achieved.The experimental results on the tested apparatus show that these methods are useful for realization of a current‐source ty

ISSN:0424-7760    

DOI:10.1002/eej.4391160410

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

年代:1996

数据来源: WILEY