Breakdown voltage of electrode arrangements in vacuum circuit breakers

The prediction of HV strength of electrode arrangements in vacuum is complex. A comparison of experimental results from different labs is quite difficult, because they are influenced by a wide range of parameters like electrode material, surface finish, surface area, conditioning state of the surface and the geometry of the electrode arrangement. The aim of this work is to find an empirical relation between the breakdown voltage and different electrodes parameters. Shielding arrangements and main contacts of vacuum tubes are of particular interest. For this purpose, models of contacts and shield electrodes made of stainless steel are stressed with lightning impulse voltage. Several methods of surface finishing are applied to obtain reproducible conditions. The experimental results and deliberations for an empirical approach are presented. In addition the results are related to numerical field calculations.     

Improvement of electrode/organic layer interfaces by insertion of monolayerlike aluminum oxide film

We studied improvement of the electrode/organic interface in organic electroluminescent diodes which consist of 8‐hydroxyquinoline aluminum (Alq₃) and diamine derivative (TPD). An aluminum oxide (Al₂O₃) monolayer was inserted between TPD and the indium tin oxide (ITO) anode. An improvement of emission is observed in a diode with an Al₂O₃ layer between 0.5 and 1 nm thick inserted in the surface of the anode/organic layer. The mechanism of increase in emission efficiency is discussed. © 2000 Scripta Technica Electr Eng Jpn 132(3): 14–18, 2000     

极性反转电压下变压器油的击穿特性

为了获得换流变压器中变压器油在极性反转电压下的击穿特性,使用一种三电极模型,在不同间隙和温度下,对变压器油隙进行了极性反转电压击穿实验研究.击穿结果表明:极性反转电压下,变压器油的击穿场强没有随油间隙增加而降低;变压器油的击穿场强与温度相关,在实验温度范围内,40℃时出现了最大值.监测流过油隙的电流,发现在极性反转后电...     

On the Electric Breakdown Behavior of Silicone Gel at Interfaces

Electrically stressed interfaces between solids are considered as weak points in the electrical insulation technology. This matter of fact is founded in the presence of microscopic cavities or areas with a low material density in the interface layer. Silicone gel, which is a soft and conformable solid with certain tackiness, offers a good adaptation to any surface and the ability to fill in voids completely. Due to these properties the silicone gel is predestinated for the use at electrically stressed interfaces. The work presented, describes the electric breakdown behavior of the material used at interfaces. The results provide practical information for the design of electrical insulation using silicone gel.     

Local properties at interfaces in nanodielectrics: An ab initio computational study

First-principles computational methodologies are presented to study the impact of surfaces and interfaces on the dielectric and electronic properties of emerging technologically important systems over length scales of the order of inter-atomic distances. The variation of dielectric constant across Si-SiO₂, Si-HfO₂ and SiO₂-polymer interfaces has been correlated to interfacial chemical bonding environments, using the theory of the local dielectric permittivity. The local electronic structure variation across Si-HfO₂ and SiO₂-polymer interfaces, including band bending, band offsets and the creation of interfacial trap states have been investigated using a layer-decomposed density of states analysis. These computational methods form the groundwork for a more thorough analysis of the impact of surfaces, interfaces, and atomic level defects on dielectric and electronic properties of a wide variety of nano-structured systems.     

Dielectric behavior of insulating liquids at very low frequency

Dielectric spectroscopy in the wide frequency range of 1 mHz to 1 kHz has been used to study the polarization and conduction phenomena in insulating liquids. The dielectric spectroscopy of mineral oil and ester oil at different conditions, i.e. temperatures and electric fields, has been measured. It came out that at low frequencies, space charge polarization changes the permittivity of insulating liquid and at very low frequencies, the consideration of a RC parallel model for the dielectric behavior of insulating liquids is not adequate. The results indicate that the permittivity of insulating liquid increases with aging duration and therefore it can be used as a diagnosis parameter for insulating liquids. The calculation of the activation energy of the conduction process shows that consideration of single activation energy for compensation of temperature effect on dielectric loss for dielectric spectroscopy in the wide frequency range is not perfect.     

高寒条件下变压器油击穿特性试验

对变压器油在低温环境下击穿特性的研究有助于确保高寒地区变压器的运行可靠性。为此建立了高压低温试验系统,利用该系统试验研究了在-50~10℃温度范围内,不同电压形式、电极模型、水分体积分数下的油隙击穿特性;并根据试验结果给出了高寒条件下对变压器投运及交接试验的建议。结果表明:交流电压和直流电压下,油隙击穿电压随温度的变化曲线呈U形,冲击电压下则无明显规律;平板电极模型、球–板电极模型和针–板电极模型击穿电压随温度的变化曲线均呈U形,且击穿电压值受电极间电场均匀程度的影响;低温下水分体积分数会对油隙的低温击穿电压产生直接影响,且在-10~0℃范围内影响最为显著。     

Breakdown behavior of SF6 gas-insulated systems at lowtemperature

The controversy surrounding low-temperature SF₆ breakdown is addressed in detail. Earlier relevant studies are reviewed, some of the existing data is analyzed in a new light, and further theoretical considerations are presented. These discussions served to outline an experimental approach aimed at confirming or invalidating breakdown invariance at subnormal temperatures. Low-temperature dc breakdown of an SF₆ gas-insulated system was investigated experimentally for temperatures ranging from -50 to 24°C, using associated pressure values that had been selected carefully to avoid phase transition of the gas-insulating medium. The context allowed experimentation under both uniform and nonuniform field conditions; the nonuniformity was due to the active role of the cathode-gas interface at high fields. The experiment was conducted for molecular densities ranging from 2.596 to 16.43×10¹⁹ cm^-3 (equivalent to pressures of 105 and 624 kPa, respectively, at 24°C) and for gap lengths starting at 0.5 mm and extending to 7 mm. Data sets show consistency, low statistical scattering, and high reproducibility. Data analysis led to several major conclusions. At constant density, the breakdown of the SF₆-insulated system is temperature dependent, which is responsible for a decrease in the electric strength, by ~10%. This decrease occurs for uniform field conditions, the effect being small if not negligible for nonuniform field conditions, and is noted to appear at a threshold temperature (-25 to -30°C), take a constant value, and be fairly independent of density     

大型变压器近区故障损坏原因分析

通过理论分析和在线采集近区故障信息的方法对某系统联络变压器连续 4次故障损坏原因进行了重新分析 ,提出了该变压器损坏的主要原因是变压器固有电气频率与系统近区接地故障时的高频含量频率非常接近 ,因而激发了变压器内部谐振。     

Normal molecular repair mechanisms in regenerative peripheral nerve interfaces allow recording of early spike activity despite immature myelination

Clinical use of neurally controlled prosthetics has advanced in recent years, but limitations still remain, including lacking fine motor control and sensory feedback. Indwelling multi-electrode arrays, cuff electrodes, and regenerative sieve electrodes have been reported to serve as peripheral neural interfaces, though long-term stability of the nerve-electrode interface has remained a formidable challenge. We recently developed a regenerative multi-electrode interface (REMI) that is able to record neural activity as early as seven days post-implantation. While this activity might represent normal neural depolarization during axonal regrowth, it can also be the result of altered nerve regeneration around the REMI. This study evaluated high-throughput expression levels of 84 genes involved in nerve injury and repair, and the histological changes that occur in parallel to this early neural activity. Animals exhibiting spike activity increased from 29% to 57% from 7 to 14 days following REMI implantation with a corresponding increase in firing rate of 113%. Two weeks after implantation, numbers of neurofilament-positive axons in the control and REMI implanted nerves were comparable, and in both cases the number of myelinated axons was low. During this time, expression levels of genes related to nerve injury and repair were similar in regenerated nerves, both in the presence or absence of the electrode array. Together, these results indicate that the early neural activity is intrinsic to the regenerating axons, and not induced by the REMI neurointerface.     

Breakdown Phenomena in Point-to-Point Gaps

Measurements with multiple techniques delineating the complete sequence of events from the primary streamer to the formation of the spark channel for relatively small point-to-point gaps are reported. The pulsed potential with 0.4 μs rise time and 1800 μs decay time was applied to the point-to-point gap, of which length was changed from 6 to 14 cm. The light pulses were observed by 5 photomultipliers as well as current and potential wave. It is shown that the spark channel can be materialized through the following three processes: 1) initial process, in which the primary, the secondary, and the tertiary streamers develop from both point electrodes into gap, and the ionizing wave bridges the gap; 2) intermediate process, in which the dark period proceeds with ion and electron movement if the applied potential is around the mean breakdown potential, or in the other case, the ``leader' develops from the anode with the help of ionizing waves; and 3) final process, in which the channel is highly ionized at first by the ionizing wave, then gas heating, to lead the formation of a spark channel. On the bases of the measurements of streamer speed and current, the ion and electron density were calculated. It is estimated that starting with the primary streamer with an electron density of 1012 cm-3, the electron density in the streamer channel is augmented by the ionizing wave up to 1012cm -3 when the gap is bridged by the ionizing wave.     

碳糊电极吸附伏安法测定EMD中的铅

以碳糊电极为工作电极,建立了一种测定电解二氧化锰(EMD)中铅含量的方法。在pH值为3.2的0.1 mol/L邻苯二甲酸氢钾-HCl缓冲溶液中,铅(Ⅱ)与桑色素形成络合物。在0.10 V时富集,铅(Ⅱ)-桑色素络合物吸附于电极表面,在-0.80 V静止还原后进行扫描,在-0.48 V处产生一个灵敏的氧化峰。铅(Ⅱ)浓度在2.0 nmol/L～0.5μmol/L的范围内与二阶导数峰高呈现出良好的线性关系。检测限为1.0 nmol/L(富集时间为200 s)。     

陶瓷化耐火电缆高温击穿影响因素研究

以聚烯烃树脂、高低熔点瓷化粉及其他助剂为组分,经熔融共混制备了陶瓷化聚烯烃材料及电缆,研究了陶瓷化耐火电缆高温击穿的原因。结果表明,材料组成是导致电缆高温击穿的根本原因。     

纳秒级高压脉冲下绝缘击穿特性的研究

研究了液体和固体绝缘材料的击穿特性 ,通过蓖麻油、变压器油、聚酯薄膜、聚酰亚胺薄膜的击穿实验的波形处理和分析 ,说明了击穿电压与脉冲陡度、脉冲宽度和作用时间的相互关系 ,相对于直流、慢过程条件下绝缘击穿特性 ,纳秒级快脉冲下绝缘材料的击穿场强会大幅提高 ,其击穿场强随脉冲缩短而提高 ,但作用减小。给出了一些具体的绝缘材料击穿值     

三卷变压器低压侧避雷器烧损原因分析

对哈西变近几年发生的变压器低压侧避雷器烧损的原因进行了分析,提出了采取的相应措施,实践证明是行之有效的.     

Discharge occurring at a grounded electrode located in a charged particle cloud

Electrical discharge phenomena from a grounded electrode located in a charged particle cloud have been investigated. Soil conditioning particles charged by corona charging were blown to form a space charge cloud. A grounded sphere electrode was placed at the center of the charged cloud to produce an electrical discharge. A positive pulse discharge extended from the sphere electrode toward the charged cloud with a strong luminescence. A brushlike streamer with a maximum length of 170 mm appeared at an interval of 30 ms. The maximum pulse height of the discharge was 2.4 A. The distribution of the electric field around the sphere electrode was obtained from field analysis using a concentric spherical model. It was found that the magnitude of the discharge depends on the radius of the grounded electrode and the size and charge density of the clouds. © 2001 Scripta Technica, Electr Eng Jpn, 136(4): 7–14, 2001     

基于分形理论的电介质放电仿真计算

为研究介质击穿现象,基于放电分形的模型,利用MATLAB工具计算机模拟了放电通道的发展并比较了NPW和WZ模型的仿真结果,得到不同电极条件下的放电图像。分析概率指数、放电阈值电压等参数对仿真影响的结果表明,概率指数越大阈值电压越高,则分枝数越少,分形维数越小。     

国内外铜大拉机的性能比较及其改进建议

简述了我国铜大拉机的现状,指出国产大拉机在实际使用过程中存在的不足,同时与进口大拉机的特性作了比较,并提出了一些建议。