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     

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.

     

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     

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.     

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 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     

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     

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     

水舌运动界面的格子Boltzmann仿真研究

应用格子Boltzmann两相流模型,采用Young的界面重构技术,对水舌在空气中的运动进行了数值模拟,得到水舌在空气中的运动界面和流速矢量,数值模拟结果与实际问题的物理规律一致,验证了模型的有效性与可靠性.     

Characteristics of elastic waves caused by corona discharges in anoil-immersed pole transformer

Measurements of elastic waves brought by a pulse of simulated corona discharge in an oil immersed pole transformer and a model tank filled with oil were performed in order to identify the location of insulation deterioration, using an acoustic emission (AE) technique. The detected AE signals were analyzed by means of a fast Fourier transform (FFT), and properties of elastic waves influenced by the existence of insulated windings and magnetic core for power transformation in the transformer were investigated. The result shows that almost all the initial AE signals detected on the-wall of the transformer tank were Lamb waves caused by the oscillation waves passing through the insulating paper and oil with repeating transmission, reflection and refraction. Also, it was possible to recognize whether the measured elastic wave was influenced by windings and their insulating papers or not, by FFT analysis. This suggests that the location accuracy of the corona discharge in the transformers would be improved     

Calculating the level of noise created by steam discharges from power-generating boilers

Specific features of calculating the level of noise generated by a discharge of steam from power-generating boilers are considered. Different approaches and calculation formulas used for determining the noise level from a steam discharge are analyzed, a formula is given for calculating the general level of acoustic power for a steam discharge from power-generating boilers as a function of the critical flowrate of steam through a valve, and adjustment corrections are proposed for determining the octave levels of a steam jet acoustic power. A comparison is made between the obtained data and other known data.     

Decrease in ac partial discharges on insulating materials by use ofdye additives

The purpose of this study is to decrease PD at a triple junction by addition of a dye to an insulating material. PD is produced on a test specimen subjected to ac voltage under a sphere-plane electrode configuration. The specimen is composed of two layers: a PMMA film with additive, which is 100 μm thick; the lower layer a PMMA board 3 mm thick. The film with the additive was prepared by the solution-grown casting method. Five kinds of dye were used as the additive; p-aminoazobenzene (Ab), p-nitrobenzeneazoresorcinol (Nb), methyl yellow (My), methylene blue (Mb) and methyl red (Mr). In the case of the films with Ab and Mb at 0.05% wt, the magnitude and number of PD pulses were reduced to ~50% less than those in the case of the films without the additive. The decrease in PD was effective under an electric field strength slightly higher than the PD inception. In the case of the other dyes, decrease in PD was not observed. The surface voltage distribution due to the charge by PD depended on the kind of dye additive. The decrease in PD for the Ab and Mb films was explained from the dependence of the surface voltage distribution on the dye. It was concluded that ionization of the dye molecules in the film changes the distribution of surface voltage     

Characteristics of partial discharges caused by trees in contact with covered conductor lines

Characteristics of partial discharges (PD) caused by trees in contact with covered conductor (CC) lines have been studied. A tree in contact with a CC distorts the electric field around the conductor and causes partial discharges. According to tests conducted in a high voltage laboratory the rise time of the PD current pulses caused by the trees is relatively long, in the order of 60 ns...0.8 μs. The fault impedance and PD magnitude caused by a tree in contact with a CC and the propagation attenuation of PD pulses was studied in different seasonal conditions in September, November and March on a full scale 110 kV CC trial line. In case of an intact CC the fault impedance is several MΩ. After breakdown of the conductor covering the fault impedance collapses in summer to tens and in winter to hundreds of kΩ. The average PD magnitude measured in March was approximately one fifth of that in September. On a 9.3 km line portion the observed propagation attenuation of the PD signal was 0.37...3.7 dB. The variation in the attenuation is attributed to the variation in the rise times of the PD pulses and the modal composition of the PD signal. The results indicate that PD measurements can be used to detect trees fallen on CC lines.