摘要:

AbstractAC partial discharges from PMMA films doped with various dyes have been investigated. In this paper, the following three dye films were prepared by the solution‐casting method: p‐aminoazobenzene (Ab); p‐nitrobenzeneazo‐resorcinol (Nb); and methyl‐yellow (My). AC partial discharges were investigated by placing a 100‐μm thick film on a 3‐mm thick PMMA plate between a spherical high‐voltage electrode and planar ground electrode.The number of discharge pulses and total electric charge discharged from an Ab‐doped PMMA film was less than 50 percent of those without Ab. AC partial discharges were suppressed at electric fields which were slightly higher than the electric field for the onset of ac partial discharges. However, ac partial discharge characteristics of PMMA films doped with other dyes were not affected.Attempts have been made to elucidate mechanisms for the reduction in ac partial discharges on the PMMA film doped with Ab by examining the distribution of surface potential at zero crossovers. The ionization of Ab dye, which is an electron donor, is attributed to the reduction in ac partial discharges on the

ISSN:0424-7760    

DOI:10.1002/eej.4391170601

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

年代:1996

数据来源: WILEY

摘要:

AbstractBecause of its high–temperature chemical stability, SiC ceramic is a promising material for high‐temperature device applications such as thermoelectric energy converters. However, the electrical conductivity of SiC ceramic is too low for it to be used as a thermoelectric energy converter at the cold junction. Therefore, we propose a SiC‐Si functionally gradient material (FGM) in order to improve the electrical conductivity of the SiC ceramic at the cold junction.An SiC rod was fired in a temperature gradient furnace. One end of the SiC rod was maintained at 2473 K and the other end was maintained at 1973 K for 30 min. After firing, the porous SiC edge fired at 1973 K was dipped into molten Si in order to infiltrate molten Si into the porous SiC.The microstructure of the FGM is classified into three regions: the SiC‐Si composite material; the porous SiC ceramic; and the densified SiC ceramic. The electrical conductivity, the Seebeck coefficient and the thermal conductivity for each region of SiC‐Si FGM was measured at 300 K; a figure of merit was calculated. The figure of merit of the SiC‐Si FGM at the cold junction, at room temperature, was 108times higher than that of a nongradient

ISSN:0424-7760    

DOI:10.1002/eej.4391170602

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

年代:1996

数据来源: WILEY

摘要:

AbstractAn after‐laying test is required to demonstrate the soundness of XLPE underground cable lines with joints. AC voltage application is desirable for the test; however, the equipment for ac application must be very large because it must supply large capacitive current for cables. DC voltage is normally applied, which can be supplied with small equipment; however, the effectiveness of the dc application is questioned because the electrical stress distribution is quite different from that with ac application and, moreover, dc application could damage insulation properties of cables.The authors targeted the Oscillating Wave (OSW) method and the Very Low‐Frequency (VLF) method as alternative after‐laying tests. They first developed modeling methods of various defects on underground cable lines and applied OSW and VLF to these defect models. They found that OSW and VLF methods have higher fault detection capability than dc voltage application. They also demonstrated that the defects which can be easily detected with the OSW method are difficult to detect with the VLF method and vice versa. They showed that serial application of both methods highly improve the fault detection ability for XLPE underground cable

ISSN:0424-7760    

DOI:10.1002/eej.4391170603

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

年代:1996

数据来源: WILEY

摘要:

AbstractMost of the accidents on XLPE cable line are caused by defective construction of cable accessories. Thus the authors developed a method to measure partial discharges in pre‐mold cable accessories. The authors provided separated‐shielding layers as detection electrodes in accessories, and discriminate between partial discharge pulse and noise pulse using realtime comparison of pulse current magnitudes from both detection electrodes.This paper describes the principle of the noise discrimination method, portable partial discharge measurement apparatus, and the results of field t

ISSN:0424-7760    

DOI:10.1002/eej.4391170604

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

年代:1996

数据来源: WILEY

摘要:

AbstractImprovement of power system stability is the most important issue of generator excitation control. The combination of thyristor excitation with ΔP‐PSS is usually applied to recently installed very large turbogenerators. This power system generator (PSS) is not always effective for wide‐range operation of generators or for various changes of power system line impedance. The application of the optimal control theory, especially the multifeedback signal resulting from the Riccati equation has been studied and reported in many papers. These papers, however, do not clearly describe how to set performance index values and the studies reported in them also use inadequate signals. This paper presents a method to set the performance index values to make adequate feedback signals for selecting actual control on the application of the Riccati equation. Further, the developed PSS using multifeedback signals is applied to actual very large turbogenerators after confirming the performance of effective damping for power oscilla

ISSN:0424-7760    

DOI:10.1002/eej.4391170605

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

年代:1996

数据来源: WILEY

摘要:

AbstractOptical voltage and current measurement generally necessitates the compensation of light intensity variation which occurs in the optical measuring system, because it is possible the light intensity variation may give rise to a measuring error. Therefore, such compensation methods as dividing the ac component by the dc component of the light intensity are usefully introduced in optical ac voltage and current measurement, but those methods are not useful exactly for the optical measurement of the quantities including dc components.This paper deals with a new useful compensation method for light intensity variation in the optical dc current measurement. Linearly polarized light passes through two kinds of Faraday sensors, in which one detects dc magnetic field caused by dc current and the other detects externally applied constant ac magnetic field. Then, the compensation of the light intensity variation is carried out by measuring the dc and ac components of the beam. The principle of the compensation method using the ac component is described in the paper. Experimental results of this method using flint glass as the Faraday effect cells are reported and it is clarified that this method can decrease the measuring error of the modulation depth for dc current and compensate light intensity variation validity.

ISSN:0424-7760    

DOI:10.1002/eej.4391170606

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

年代:1996

数据来源: WILEY

摘要:

AbstractSolid friction in machine elements is one of the dominant nonlinearities affecting the control accuracy of servo drive systems. Many schemes, including feedforward control, observer‐based control and repetitive learning control have been proposed to compensate for nonlinear friction. These schemes show superior performance compared to that of the conventional P‐ and/or PI‐controller; however, friction model errors and bandwidth restriction of the observer cause compensation errors, thus decreasing control accuracy.This paper presents a new control algorithm for performance improvement of a motor speed control system having nonlinear friction. By analyzing characteristics of conventional compensation control schemes during velocity reversal, the relation between control parameters and control accuracy is examined so as to explore problems with each scheme. Based on these analyses, a new feedforward control algorithm is proposed. The proposed algorithm is verified by analyses of control characteristics and experiments using a prototype. Experimental results show the superior performance improvement of the proposed algo

ISSN:0424-7760    

DOI:10.1002/eej.4391170607

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper describes a traveling‐wave ultrasonic motor (USM)‐actuated positioning servo driver, suitable for direct‐drive motion systems, which incorporates a fuzzy‐reasoning software controller with speed and position‐variable feedback schemes. The experimental results of this USM position servo driver operating at two‐phase high‐frequency resonant inverter are illustrated and evaluated using a one‐axis servo motion drive system. The results show that the new system using a compact USM that incorporates a microprocessor‐based two‐input and one‐output fuzzy‐reasoning controller is cost effective and suitable for special purposes in the industrial, medical, automotive, sp

ISSN:0424-7760    

DOI:10.1002/eej.4391170608

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

年代:1996

数据来源: WILEY

摘要:

AbstractIn recent years, power source voltage waveform distortion has become noticeable, as electrical appliances with rectifier circuits have become widely used. Connecting capacitor inductor motor (CRM) to such distorted supply, or controlling CRM by simple controller with a switching device (such as triacs), harmonic voltage is supplied to CRM. In that case, CRM produces electromagnetic vibrations caused by not only the fundamental voltage but also time‐harmonic voltages in the distorted voltage. In addition, CRM produces electromagnetic vibration due to backward magnetic fields. Thus, it is difficult to clarify a relationship between electromagnetic vibration of CRM and harmonic voltages.In this paper, the causes of the electromagnetic vibration of CRM operating under distorted wave supply voltage are discussed. First, a general equation of dominant electromagnetic force waves is shown considering not only forward magnetic fields but also backward magnetic fields. Using a general equation, causes of dominant electromagnetic vibration can be clarified. Next, by discussing in detail some examples of the dominant vibration, the relationship between the vibration and harmonic voltages becomes evident. Furthermore, the relationship between the vibration and backward magnetic field is clarifie

ISSN:0424-7760    

DOI:10.1002/eej.4391170609

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

年代:1996

数据来源: WILEY

摘要:

AbstractSoft‐switching phase‐shifted PWM converters have attracted much attention because of their low switching losses, constant frequency operation and simple control. However, a circulating current flows through the transformer and the primary bridge circuit during the free‐wheeling interval, resulting in relatively high current stresses on the transformers and switching devices compared with those of conventional hard‐switching PWM converters.This paper presents an improved soft‐switching phase‐shifted PWM DC‐DC converter that can substantially reduce the circulating current by employing a tapped inductor for the output low‐pass filter. The principle of operation and the role of the tapped inductor are illustrated. The effectiveness of the tapped inductor is evaluated through simulation analysis. Moreover, a 500 W‐100 Hz prototype converter is implemented to demonstrate the excellent performances of both low switching and low

ISSN:0424-7760    

DOI:10.1002/eej.4391170610

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

年代:1996

数据来源: WILEY