Resonance characteristics and identification of modes of electromagnetic waves excited by partial discharges in GIS

Electromagnetic waves are used for detection of partial discharges (PD) in GIS (gas‐insulated substations). A very wide frequency band up to 1.5 GHz is utilized for detection. There are three categories of electromagnetic wave which can be excited and propagate in coaxial cylindrical structures like GIS, namely, TEM, TE, and TM modes. The characterization and identification of each mode is indispensable to understanding the partial discharge phenomena in GIS. In this paper, peaks in the frequency spectrum excited by PD are identified in each mode and the resonant characteristics of each mode are studied. The following are the major results: (1) The resonance peaks appear at the frequencies defined by the spacer distance. (2) The intensity of each mode depends on the position of discharge source along the radial direction. The lower‐order modes including TEM are excited when a discharge source is located near the center conductor. On the other hand, higher‐order modes are excited when the discharge source is at the enclosure surface. (3) The experimental profile of each mode excited by PD along the radial direction approximately agrees with the general theory of electromagnetic wave propagation in coaxial cylindrical cavity. © 2000 Scripta Technica, Electr Eng Jpn, 131(2): 1–11, 2000     

New fixture applications for compact twin tube fluorescent lamps

New and efficient luminaires have been designed for compact, twin tube-type fluorescent lamps. One important example of these new fixture applications is the 1×1 ft luminaire with three 18 W high lumen twin tube fluorescent lamps. Performance comparisons with this luminaire type have been made using different 18 W lamps operating on preheat and rapid start-type ballasts. The preheat (switch start) measurements were made at 240 V and 50 Hz using single lamp reactor type ballasts, and the rapid start measurements were made at 120 V and 60 Hz using three-lamp electromagnetic and electronic ballasts. In addition, comparisons are made against an older technology 150 W incandescent downlight fixture with approximately the same light output level indicating the substantial improvement in system photometric performance for these new compact fluorescent light sources     

小功率金卤灯电子镇流器控制策略研究

本文提出一种适用于金卤灯负载特性的新型控制策略,解决了半桥低频方波变换器用作金卤灯电子镇流器时开路电压偏低的问题、实现了灯启动过程的恒流和限流控制、稳态时的恒功率控制。采用零电流检测电路使电感在低频正负半周内均工作在临界电流模式,开关管实现了零电流接通。采用差分平衡电路对灯电压、灯电流进行取样,解决了悬浮的灯电压、电流信号与驱动电路的共地问题。给出了主要参数的计算方法。实验结果验证了所提出的方案是可行的。     

德国节能环保新举措：路灯随用随开

作为节约资金和保护环境政策的一部分，英国许多城镇将在明年实行夜晚关闭路灯的措施，但有人担心这会给人们的出行带来诸多不便。正在德国进行的一项既环保又便民的路灯随用随开测试有望解决这个难题。     

Electromagnetic effects excited by magnetic loops

Contents An analysis is made of the electromagnetic effects in the space around magnetic loops moving in inertial systems. The methods of the relativistic electrodynamics, a four-dimensional potential, and the concepts of a model of a magnetic charge have been used. The obtained results allow to correct certain inaccuracies connected with the application of the magnetic loops theory. Conclusions are made about the applicability and the perspectives concerning the development of the magnetic loops theory.

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Elektromagnetische Effekte die durch magnetische Kreise angeregt werden

Übersicht Es werden elektromagnetische Effekte von sich in Inertialsystemen bewegenden magnetischen Kreisen analysiert. Man wendet Methoden der Relativitätselektrodynamik, das vierdimensionale Potential, die Darstellungsmodelle der magnetischen Ladung und die entsprechenden Tensoren des Elektromagnetischen Feldes an. Die gewonnenen Ergebnisse gestatten es bestimmte Ungenauigkeiten in den existierenden Anwendungen der Theorie der magnetischen Kreise zu korrigieren. Es werden Schlußfolgerungen bezüglich der Praxis und der Perspektiven der Entwicklung und Anwendung der Theorie magnetischer Anregungskreise gemacht.

     

Antiferroelectric lead zirconate thin films by excimer laser ablation

Abstract

Utilization of antiferroelectric thin films was proposed for high charge storage capacitors and transducer applications. The volume changes that are associated with the AFE? FE and FE ? AFE phases are high enough to use them in MEMs device technology. Lead zirconate was the first identified antiferroelectric compound with a reported dielectric phase transition temperature of ～ 230°C. In this article, deposition of lead zirconate thin films by a pulsed excimer laser ablation technique is reported. The antiferroelectric nature of the lead zirconate thin films were confirmed by the presence of double hysteresis loop in polarization vs. applied electric field response as well as double butterfly behavior in capacitance vs. voltage characteristics. The variations in the polarization hysteresis with temperature were elucidated in detail. The switching times between the field induced FE and AFE phases (backward switching) were studied at various applied electric fields.     

Deterministic and stochastic assessment of the harmonic currents consumed by discharge lamps

The paper examines the deterministic and stochastic behavior of magnetic ballast discharge lamps. Expressions to deterministically calculate the harmonic currents of discharge lamps are provided and analytical expressions of the probability density functions of these harmonic currents are obtained. The results are validated with experimental measurements.     

Deposition of diamond-like carbon films by excimer lasers usingfrozen acetylene

Diamond-like carbon (DLC) films were deposited by laser ablation with the target made of frozen acetylene, instead of conventional graphite. An ArF laser and a KrF laser were used to dissociate frozen acetylene and to deposit DLC films on quartz substrates below 300°C. The C-H bond was more abundant in the films deposited by the KrF laser. It was possible to deposit particle-free films in contrast to laser ablation of graphite targets. Experimental results suggested the importance of energetic and charged species ejected from frozen acetylene     

高频矩形波激励下磁芯损耗的研究

研究了高频变压器在不同占空比条件下磁芯损耗的变化趋势。在相同频率和磁通密度变化量条件下,占空比所引起的激励波形差异对磁滞回线包围面积的影响很小,磁滞损耗可近似认为是常量。涡流损耗与激励电压之间存在着近似线性等效关系,在此基础上提出了涡流损耗在不同占空比条件下的计算方法。理论计算表明:当占空比在0.283相似文献   

The excitation of UHF signals by partial discharges in GIS

The fundamental theory of the UHF method for detecting partial discharge (PD) in gas insulated substations (GIS) is presented. The effects of position, size, current amplitude and pulse shape of the PD source on the UHF signal can be predicted using this theory. Excitation of propagating electromagnetic waves by a PD current pulse within the coaxial waveguides formed by GIS components is explained by making use of dyadic Green's functions for the electric fields of propagating modes. Experiments with a coaxial test chamber are used to verify the theoretical predictions, and comparisons are made between measured and simulated UHF signals. Some implications for the UHF measurement of PD are discussed, together with positioning and sensitivity requirements for UHF couplers. A scheme is proposed for standardizing PD measurements made using the UHF technique     

Studies of elastic waves caused by corona discharges in oil

In order to diagnose the deterioration of insulation and evaluate its location in oil-filled pole transformers, measurements of elastic waves brought by corona discharges in oil were performed, based on an acoustic emission (AE) technique. The detected signals in these measurements were analyzed by means of a fast Fourier transform (FFT) and their properties were discussed theoretically. It was found that the AE signals due to the Lamb waves of symmetric mode caused in a thin steel tank could be recognized easily by the FFT analysis of initial stages of the detected AE signals. This suggests that the accuracy on location of the AE sources in the transformer would be improved. Also, it was shown that a low pass filter was effective in improving the location accuracy     

Super-resolution vibrational microscopy by stimulated Raman excited fluorescence

Inspired by the revolutionary impact of super-resolution fluorescence microscopy, super-resolution Raman imaging has been long pursued because of its much highe...     

Control of SF6 discharge gap switch by XeCl excimer laser

Experimental studies have been carried out on triggering characteristics of the SF₆ discharge gap switch by use of XeCl excimer laser (wavelength = 308 nm). First, laser irradiation characteristics are studied on a pure SF₆ in the pressure range of p = 160 ～ 3,800 torr. Using a lens of f (focal length) = 133 mm, the laser is irradiated into the gas, where the energy absorption is studied. If the laser is injected into the gas with the energy above a certain threshold for the breakdown, the rate of energy absorption is found to be ～ 17 percent of the incident energy at p > 760 torr. Injecting the laser into the SF₆-filled gap switch (gap length = 7 mm, p = 760 torr), we have studied the triggering characteristics. Excellent triggering characteristics were obtained; delay time for the discharge ～ 20 ns, and the jitter ～ 260 ps when the gap voltage is operated at 99 percent of the self-breakdown voltage. In addition, the triggering characteristics are studied by changing the focusing point axially. It is found that both the delay time and the jitter decrease when the focusing point tends to approach the high-voltage electrodes.     

The voltage distortion in low-voltage networks caused by compact fluorescent lamps with electronic gear

Commonly used compact fluorescent lamps (CFLs) with electronic gear are characterized by extremely distorted current, with total harmonic distortion (THD) usually exceeding 100%. That is why they cause a significant voltage distortion in electrical installations. The principal goal of this research was to determine their maximum permissible share in the total load installed for commercial customers, at which voltage distortion is still acceptable (according to international standards). An analysis regarding a low-voltage electrical installation of a hotel, representing a typical commercial customer, showed that maximum permissible share should not exceed 10%. As this maximum permissible share could restrict the installment of the intended quantity of CFLs, the costs of two possible solutions for this problem – the use of filters or a new generation of CFLs with a high power factor – are compared.     

Static electrification and partial discharges induced by oil flowin power transformers

This paper presents the study of the major parameters on static electrification, using full-scale shell type transformers (570 MVA, 405 kV and 100 MVA, 500 kV). The consequences of static electrification on the dielectric strength and the conditions of partial discharge occurrence also are studied with oil flow rate up to 5 times the nominal value. It shows that the leakage currents are strongly influenced by temperature, applied voltage and oil flow rate Q. The latter is the most influential parameter. The winding leakage current I varies as Qⁿ , where 1⩽n⩽3. The maximum value of I is observed at room temperature (20°C) when the transformer is energized     

Existence of partial discharges in low-voltage induction machinessupplied by PWM drives

When standard low voltage induction motors are supplied by pulse-width modulated (PWM) adjustable speed drives, some of the traditional sinusoidal system concepts cannot be applied. This paper reports the results of an investigation of the effect of PWM drives on the insulation of the stator winding. The characteristics of the employed dielectric material and the magnitude of the applied voltages led to the hypothesis of the possible existence of partial discharges within the insulation. Practical experiments were carried out and high frequency signals which could be associated with such a phenomenon were observed. These measurements also showed that the interturn insulation undergoes some high electrical stresses and that the nominal rotation speed (50 Hz) appears to be a point of high disturbance in the working of the motor. Further work is required, since most of the points identified here need to be understood fully