共查询到20条相似文献,搜索用时 15 毫秒
1.
Chalmers I.D. Lei J.H. Yang B. Siew W.H. 《Dielectrics and Electrical Insulation, IEEE Transactions on》1995,2(2):225-230
Investigations have been carried out on right cylindrical Teflon spacers in vacuum under dc stress to study the effect of cathode geometry on surface charging and flashover. Three cathode support arrangements were used. Type 1 involved a recess in the cathode into which the spacer was located, type 2 was a simple flat plate cathode, while type 3 had a raised insert on the cathode surface over which the spacer was located. In all cases the surface charge density and distribution is primarily dependent upon the magnitude of the electric stress. Using the type 1 arrangement inception for charge deposition was always ~10 kV even when the spacer had been subjected to repeated flashovers. At applied voltages higher than this the density of the charge, which was fairly uniformly distributed around the surface, was more or less proportional to the applied voltage. For the type 2 and type 3 arrangements, a distinct, uniformly distributed negative charge of ⩽20 μC/m2 was always detected at low values of applied stress and at a fairly well-defined transition voltage this gave way to a distribution which was substantially uniform in the case of type 2 but quite filamentary in type 3, and both involved the deposition of positive charge 相似文献
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Halverson W. Patel R. Horenstein M. Moustakas T. Tsai K.C. McGurrin G. 《Dielectrics and Electrical Insulation, IEEE Transactions on》1996,3(1):108-112
Thin coatings of diamond-like carbon (DLC) were applied to cylindrical alumina and high temperature polyimide insulator samples. The coated insulators and uncoated controls were tested for resistance to surface flashover in vacuum under a dc voltage gradient. The DLC-coated insulators had significantly higher flashover potential than the controls and showed no visible tracking on their surface, even after multiple discharges. DLC coatings, applied at temperatures <350°C, show promise for improving the performance of HV vacuum feedthroughs, switches, and in other applications 相似文献
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This work presents experimental results of optical emission from polycrystalline, as well as single crystal diamonds, during the surface flashover events in a vacuum environment. Optical emission spectra were recorded and the source of this luminosity was investigated. Analysis showed that the surface flashover events were associated with relatively high intensity optical emissions. The light emission started much earlier than the voltage collapse, increased very rapidly with the breakdown, and eventually ended after few seconds; much later than the voltage across the surface was recovered. The polycrystalline diamond sample used in the experiments was produced by a microwave plasma CVD (chemical vapor deposition), and the sample surface was polished to optical quality before the experiments. The electrode material was copper, and a dc voltage was applied between the electrodes. Surface flashover voltage characteristics and breakdown voltage waveforms of both samples were determined 相似文献
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Shioiri T. Shindo T. Kamikawaji T. Kaneko E. Ohshima I. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2002,9(3):416-420
Experiments were carried out to study the effects of surface polishing and annealing of ceramic specimens on the dielectric breakdown characteristics of their surfaces. It was found that when the samples were annealed at 1000°C, allowing the residual stresses in their surfaces to decrease, the breakdown voltage rose, whereas with the polished samples, reductions of residual stresses resulted in a slight rise of the breakdown voltage. Prior to dielectric breakdown, a surface glow was observed, due to luminescence from electron bombardment and insulator surface defects. The starting voltage of luminescence rose when residual stresses were reduced. It is suggested that the mechanical strain due to surface defects contributes to dielectric breakdowns on ceramic surfaces 相似文献
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Galstjan E.A. Ravaev A.A. 《Dielectrics and Electrical Insulation, IEEE Transactions on》1995,2(2):312-316
Threshold characteristics of pulsed dielectric breakdown in vacuum, obtained at various experimental conditions, are considered in detail. As would be expected, the breakdown time delay τd (supposing τd<τp, the microwave pulse duration) depends on many initial parameters, such as the microwave intensity J, the nature of the irradiated material and its surface quality and the vacuum characteristics, At the same time experimental results, for microwave intensities above the continuous wave threshold of J=107 W/cm2, showed that the energy density W=J/τd is approximately constant for a given material and its operating conditions. An increase of pulsed microwave surface flashover thresholds after preliminary surface conditioning by a discharge series or under the application of a constant electrical potential from an external source to the dielectric sample was observed and measured. Experimental data allowed us to clarify the physical model of the microwave surface flashover phenomenon. It is based on the dominating role of the saturated secondary electron emission avalanche, electron stimulated gas desorption, and the resultant microwave breakdown of the surface gas cloud. Experimental and theoretical results are in satisfactory agreement 相似文献
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Neuber A. Butcher M. Hatfield L.L. Kristiansen M. Krompholz H. 《Dielectrics and Electrical Insulation, IEEE Transactions on》1999,6(4):512-515
Cryogenic components in high power electrical systems and in power electronics gain more and more importance. The behavior of insulators for cryogenic conditions, however, is virtually unknown. In a fast coaxial setup, dielectric test sample and electrodes in vacuum are cooled to <100 K and flashover is characterized using fast electrical and optical diagnostics. Three consecutive development stages for flashover in self-breakdown mode with a gap distance of 0.5 cm can be distinguished: (1) a fast current rise to mA amplitudes within ~2 ns, probably associated with field emission, followed by, (2) a slow current rise to ~5 to 10 A amplitude with duration of 40 ns to 1 μs, associated with secondary emission avalanche saturation, and (3) a transition to a rapid gaseous ionization above the sample caused by electron induced outgassing, leading to impedance-limited current amplitudes of ⩽300 A. Phase (1) shows a higher final current at lower temperature, which is probably due to a higher initial velocity of the secondary electrons, the duration of phase (2) is a decreasing function of breakdown voltage and only slightly dependent on temperature, which points to a weak temperature dependence of the outgassing process. Flashover potentials show a slight increase at lower temperature 相似文献
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Osamu Yamamoto Takehisa Hara Kimihito Ohmae Muneaki Hayashi 《Electrical Engineering in Japan》1992,112(2):11-21
The insulation performance and the flashover mechanism of a vacuum gap bridged by an insulator in the shape of a conical frustum have been studied. The cone angle of the insulator is varied from 0 to 45 deg and the thickness of the insulator is varied from 5 to 15 mm. The gap is subjected to a lightning impulse voltage of 2/50 μs. The insulation performance is investigated by observing the ratio of the flashover voltage of the bridged gap to that of the gap without insulators. The flashover mechanism is investigated by observing the distribution of traces on the cathode surface due to flashovers and by analyzing the electric field near the insulator-cathode junction. Charging of the insulator due to electron collisions on its surface is considered in this analysis. As a result, it is found that the ratio is greater than 90 percent for a cone angle greater than a critical one when the top of the frustum is subjected to the positive impulses. It is found also that the trace distribution is related closely to the insulation performance. 相似文献
9.
Sudarshan T.S. Li C.R. 《Dielectrics and Electrical Insulation, IEEE Transactions on》1997,4(5):657-662
In order to determine the influence of intrinsic material properties of dielectric materials on high field surface flashover characteristics in vacuum, it is important that we minimize or eliminate the influence of the experimental test structure on the high field processes. In this paper we shall examine the flashover characteristics of polycrystalline alumina insulators, using a lateral test structure similar to the one used in semiconductor devices. A significant improvement in surface flashover strengths (~200%) was found using a metalized contact electrode system compared with a classical solid electrode system. The results indicate that, using a metalized film cathode, the scatter in the flashover data is significantly reduced compared with the solid electrode system, implying that the electron-dielectric interaction processes that lead to flashover occur in a more predictable fashion. The new metal contact electrode system reveals the dependence of flashover strength on the surface preparation and the grain size of the dielectric material. The average flashover strength increases and the scatter in the flashover data decrease with a decrease in the average grain size of the particles composing the alumina ceramic. Thus the surface flashover processes in vacuum are related to the dielectric surface microstructure, specifically the surface and sub-surface microdamage and grain-boundary defects 相似文献
10.
Ping Yan Tao Shao Jue Wang Wei Gao Weiqun Yuan Ruzheng Pan Shichang Zhang Guangsheng Sun 《Dielectrics and Electrical Insulation, IEEE Transactions on》2007,14(3):634-642
Based on a Marx generator and a coaxial pulse forming line, an experimental investigation of surface flashover characteristics in vacuum is conducted by using nanosecond pulses of 10 ns rise time and 30 ns full width at half maximum (FWHM). Insulator dielectrics chosen for this investigation are Teflon, PMMA and Nylon. The tested factors include gas pressure, cone angle of conical frustum, diameter and length of cylindrical insulator, material and shape of electrode, and contact style between insulator and electrodes. The effects of these parameters on the surface flashover characteristics are described and analyzed in this paper. In addition, the character of flashover time lag in the nanosecond range, and surface flashover theory in vacuum charged by nanosecond pulses are also discussed. 相似文献
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A lateral test structure with metalized film electrodes is shown to have distinct advantages over a conventional solid electrode structure for studying the HV characteristics of solid insulators in vacuum. The paper presents results of streak photography and spectral analysis of surface discharge luminosity, and of preflashover activity using time-coordinated current, luminosity, and imaging of light activity emanating from the surface of the stressed dielectric. The preflashover activity, consisting of bursts of time-correlated current and light emission, is associated with randomly distributed emission spots on the surface. It is proposed that the above observations are related to charge trapping and detrapping processes at localized energy levels associated with insulator surface defects 相似文献
12.
Coaker B.M. Xu N.S. Latham R.V. Jones F.J. 《Dielectrics and Electrical Insulation, IEEE Transactions on》1995,2(2):210-217
An intensified high-speed imaging technique was used to observe the optical events associated with the pulsed-field breakdown of an alumina ceramic tube having two concentric planar electrodes metalized onto its end face. HV pulses, typically of 5 kV amplitude (5 kV μs -1 rate of rise), were applied to the radial MIM insulator-electrode regime under ultrahigh vacuum (pressure <5×10-7 Pa), with video recordings made at 1000 frames per second. Images of the observed breakdown phenomena are presented, viewed both along the center axis and also in the plane of the MIM structure. These breakdown images are discussed in relation to plasma jets associated with vacuum arcs and, in particular, on the nature of the ion species within such jets 相似文献
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Lijian Ding Li C.R. Jingchun Wang Wei Wang 《Dielectrics and Electrical Insulation, IEEE Transactions on》2002,9(2):182-186
This paper reports on the influence of sintering conditions on the flashover/pre-flashover characteristics of alumina insulators in vacuum under an impulse voltage. Four kinds of alumina insulator were studied, which were prepared using the same formula with different sintering conditions. The surface pre-flashover and flashover phenomena of different samples in vacuum have been observed under impulse voltage. Based on the experimental results, the characteristics of pre-flashover and flashover vary with different kinds of test samples. It was found that the insulators with a higher sintering temperature had a lower flashover voltage, and more active preflashover. From a scanning electron microscope (SEM) analysis of alumina insulators, we conclude that the methods of preparing alumina samples can affect their microstructure resulting in a change in the pre-flashover and flashover performance as alumina insulators. 相似文献
17.
Cheng Rong Li Li Jian Ding Jin Zhuang Lv You Ping Tu Yang Chun Cheng 《Dielectrics and Electrical Insulation, IEEE Transactions on》2006,13(1):79-84
Alumina ceramic samples prepared under different sintering temperatures and varied additives were measured to indicate the trap density and trap energy located in alumina materials by using thermally stimulated current (TSC). The surface charges on alumina in vacuum after applying a negative pulse voltage (0.7/4 /spl mu/s), and flashover performances of the materials in vacuum also were measured. We found that the trap distribution in alumina has a correlation with surface charges and flashover performances in vacuum. It is shown that the higher is the trap density in the material, the higher is the surface charge density, and the lower is the flashover voltage on alumina surface. It is believed that the trapping and de-trapping mechanisms of carriers could play an important role during the development of the discharge processes, together with the secondary electron emission mechanism. 相似文献
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Wilson M.P. Macgregor S.J. Given M.J. Timoshkin I.V. Sinclair M.A. Thomas K.J. Lehr J.M. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2009,16(4):1028-1036
The applied electrical fields required to initiate surface flashover of different types of dielectric material immersed in insulating oil have been investigated, by applying impulses of increasing peak voltage until surface flashover occurred. The behavior of the materials in repeatedly over-volted gaps was also analyzed in terms of breakdown mode (some bulk sample breakdown behaviour was witnessed in this regime), time to breakdown, and breakdown voltage. Cylindrical samples of polypropylene, low-density polyethylene, ultra-high molecular weight polyethylene, and Rexolite, were held between two electrodes immersed in insulating oil, and subjected to average applied electrical fields up to 870 kV/cm. Tests were performed in both uniform- and nonuniform- fields, and with different sample topologies. In applied field measurements, polypropylene required the highest levels of average applied field to initiate flashover in all electrode configurations tested, settling at ~600 kV/cm in uniform fields, and ~325 kV/cm in non-uniform fields. In over-volted point-plane gaps, ultra-high molecular weight polyethylene exhibited the longest pre-breakdown delay times. The results will provide comparative data for system designers for the appropriate choice of dielectric materials to act as insulators for high-voltage, pulsed-power machines. 相似文献