氧化铝陶瓷绝缘子真空沿面闪络过程中的陷阱机制

采用热刺激电流法(TSC)研究了不同烧结温度和掺有不同添加剂的氧化铝陶瓷的陷阱能级密度分布特性以及在负脉冲电压作用下的真空中表面带电和沿面闪络特性。研究发现，氧化铝陶瓷的陷阱分布与其真空中的表面带电和沿面闪络特性之间存在一定的内在联系，即材料中的陷阱密度越大，其表面电荷密度越高，且沿面闪络电压越低。上述结果表明，氧化铝陶瓷在真空沿面闪络过程中，除了电介质的二次电子发射作用外，载流子的入陷、脱陷机制也起着相当重要的作用。     

真空中绝缘子闪络前表面带电现象的仿真研究

真空中绝缘子发生沿面闪络之前存在绝缘子表面的带电现象,该现象对闪络的发展具有重要影响,到目前为止对该现象进行实时测量还存在很大的难度。基于二次电子发射雪崩(secondary electron emission avalanche,SEEA)模型,利用Monte Carlo法研究了真空中圆柱型和圆台型绝缘子在闪络前表面电荷密度的二维分布。仿真中采用了氧化铝陶瓷、聚四氟乙烯(PTFE)、聚酰亚胺(PI)以及聚甲基丙烯酸甲酯(PMMA)等不同绝缘材料。考察了绝缘材料、施加电压以及圆锥绝缘子不同锥角对表面电荷密度和分布的影响。仿真结果表明,在靠近阴极处的绝缘子表面存在小区域的负电荷区,而后变为较大区域的正电荷区;二次电子发射系数较小的绝缘子表面的正电荷密度较小;随外施电压升高,负电荷的密度及区域减小,而正电荷的密度及区域增大,且正电荷区域的峰值向靠近阴极方向移动;圆台绝缘子的锥角为负时其表面正电荷密度大于锥角为正时的情况,当锥角在-22.5°~-30°之间时表面正电荷密度达到最大,而此时对应的闪络电压最低。仿真结果与实验结果有较好的对应关系。     

Influence of sintering temperature on the flashover performance of alumina insulators in vacuum

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.     

聚乙烯陷阱特性对真空直流沿面闪络性能的影响

介绍在低密度聚乙烯中添加成核剂酚酞,研究半结晶聚合物的结晶行为、显微结构、陷阱参数以及真空直流沿面闪络性能之间的关联。扫描电镜及差式扫描量热测试结果表明,酚酞掺杂明显改变了低密度聚乙烯的结晶行为及显微结构,增加了结晶度及片晶厚度,减小了球晶尺寸,并使球晶分布更加均匀。热刺激电流结果表明,酚酞掺杂在低密度聚乙烯中引入了更多的深陷阱,增加了α及γ陷阱的深度。分析聚乙烯结晶行为与陷阱之间的关系表明,低密度聚乙烯的陷阱深度随球晶尺寸减小而增大,陷阱密度随结晶度增大而减小。酚酞改性后试样的真空沿面闪络电压整体有所提升,最高提升了48.42%。分析陷阱深度及陷阱密度与闪络电压之间的“U”型关系,认为陷阱深度及陷阱密度在影响闪络性能过程中起着相互协调、配合及转化的作用。     

玻璃陶瓷表面浅陷阱分布对其真空沿面闪络特性的影响

长期以来沿面闪络现象一直制约着真空绝缘系统的整体性能,极大地限制了高压电真空设备的发展进程。针对一种具有良好加工性能及表面耐电特性的低熔点可加工微晶玻璃陶瓷引入真空绝缘的背景,研究了不同制备工艺的可加工陶瓷试品在进行表面氢氟酸处理前后其电学特性的变化。利用表面电位衰减法测量了材料表层陷阱分布,分析了表面酸处理对其陷阱分布的影响;采用光电结合的方法,测量了不同表面处理的材料在真空中的表面耐电情况,分析了材料表面陷阱的密度和能级对闪络特性的影响。发现玻璃陶瓷材料表面存在的玻璃相结构是造成存在大量浅陷阱的重要原因,而浅陷阱对沿面闪络特性造成不利影响。得知通过氢氟酸处理可以腐蚀掉材料表面的玻璃相结构,从而降低浅陷阱密度,进而明显提高材料表面闪络的稳定性和降低分散性。     

Ti02/环氧复合材料脉冲真空沿面闪络特性

为了揭示微米TiO2填料对环氧复合材料真空快脉冲作用下的沿面闪络特性的影响,并探讨相关影响因素的作用机理,制备了6种不同填料含量的TiO2/环氧复合材料,测试了各种试样在30 ns(脉冲前沿)/200ns(半高宽)脉冲作用下的真空沿面闪络电压,并测量了介电频谱和热刺激去极化电流(TSDC)。结果显示,TiO2质量分数(wt%)的变化对Ti02/环氧复合材料的闪络电压有显著影响,但两者之间并不是线性关系;随着填料质量分数的增加,复合材料的介电常数和电导率都逐渐增加;所有实验材料都存在深、浅两种不同的陷阱能级,深陷阱电荷量和浅陷阱电荷量随填料质量分数的变化呈现出不同的变化规律。分析认为,Ti02/环氧复合材料的真空快脉冲沿面闪络特性不能由介电常数和电导率等影响因素的变化趋势单独解释,而针对闪络的深浅陷阱共同作用模型可以很好地解释闪络电压的实验结果。同时,根据实验结果对闪络的深浅陷阱共同作用模型进行完善,提出了当填料质量分数较低时,浅陷阱将显著降低材料的闪络强度,而当填料质量分数较高时,深陷阱对闪络强度的增强作用更为明显。     

新型可加工陶瓷真空中冲击闪络特性的研究

为了克服氧化铝陶瓷存在加工难度及脆性大等缺点,研制成功了一种新型低熔点可加工微晶玻璃陶瓷,它具有良好的力学、热学和可加工性能,但需进一步了解其电气性能。因此,测量了这种新型陶瓷的介电特性;考察了其在真空中脉冲电压下的沿面耐电特性;对比分析了氧化铝陶瓷和可加工陶瓷的表面耐电性能及不同添加剂成分与不同比例的添加剂对可加工陶瓷表面耐电性能的影响。结果发现,这种可加工陶瓷符合电工陶瓷的标准,其表面耐电性能优于氧化铝陶瓷,可替代现有的陶瓷材料,并获得了较好的配方设计。     

真空中绝缘子沿面预闪络现象的研究

真空中绝缘子沿面闪络现象是制约真空系统电绝缘性能的一个重要因素。通过实时观察冲击电压作用下真空中绝缘子上的冲击电压波形,以及相应的冲击电流和绝缘子表面的发光信号,并在线测量真空中绝缘子的表面电荷分布,研究了高纯度Al2O3陶瓷绝缘子在真空中的沿面预闪络现象。研究结果表明,绝缘子预闪络现象与施加冲击电压的大小、施加次数等有关,同时,沿面预闪络现象也与表面电荷分布有关,根据试验结果提出了一种关于绝缘子预闪络现象的模型,该模型能够较好的用来解释真空中绝缘子沿面预闪络现象以及沿面闪络发展过程。     

弯曲电极结构对真空中氧化铝陶瓷沿面闪络耐压的影响

氧化铝陶瓷以其良好的绝缘性能广泛应用于高压真空器件,起到绝缘和支撑作用,但氧化铝陶瓷的沿面闪络现象严重制约了其耐压性能。分析了阴极金属-陶瓷-真空三结合处电场局部增强的原因,对阴极金属电极结构对柱状氧化铝陶瓷三结合处电场分布影响进行了仿真和单次脉冲耐压试验研究,给出了不同电极情况下,氧化铝陶瓷的耐压结果。结果表明,弯曲电极结构能有效减弱氧化铝陶瓷三结合处的电场强度,并且随着金属电极弯曲长度的增加而明显减小;相对于平板电极,弯曲电极的平均最高耐压提高了45%。     

Flashover voltage of alumina ceramic contaminated by metal vapor in vacuum interrupters

We investigated the influence of metal vapor contamination of ceramic surfaces on flashover voltage (FOV) in vacuum. First, disk shape alumina (Al/sub 2/O/sub 3/) ceramics with surface resistivity (/spl rho/) of 10/sup 2/-10/sup 15/ /spl Omega/ were produced using deposition phenomena of metal vapor emitted from CuCr contacts. The impulse FOV for the ceramics decreased, as /spl rho/ reduced; FOV, the conditioning effect on FOV, and the scattering of FOV decreased when /spl rho/ was below 10/sup 12/ /spl Omega/. Therefore, the criterion value /spl rho/, which maintains excellent flashover performances of ceramic surface, is 10/sup 12/ /spl Omega/. Second, experimental vacuum interrupters (VIs) were produced to measure breakdown voltage before and after forty short-circuit current switchings with 20-40 kA/sub rms/ and were disassembled to measure the /spl rho/ of their inner ceramic surface. In a VI, which has inside diameters at both ends of the main shield much larger than the contact diameter, /spl rho/ was reduced to 10/sup 4/ /spl Omega/, further decreasing breakdown voltage between terminals.     

Charging characteristics and electric field distribution on alumina as affected by triple junctions in vacuum

This paper describes the dependence of the charging characteristics on the electric field distribution on the alumina (Al/sub 2/O/sub 3/) surface as affected by the triple junction in vacuum. For HV electrical insulation design of vacuum interrupter, surface flashover in vacuum is very important problem to be solved. Attention should be paid to the fact that the insulation characteristics on the dielectric surface are strongly influenced by field emission of electrons from the triple junction and the accumulated charges on the dielectric surface. In order to clarify the charging mechanism, we measured the charging characteristics for various types of triple junctions. In particular, we focused on the influence of the electric field distribution along the solid dielectrics and near the cathode triple junction (CTJ) on the charging characteristics. The results confirmed that the electric field distribution strongly affected the 2-dimensional (2D) distribution of the surface charge on the dielectric sample. Consequently, it was found that positive charging was generated on alumina, when the incident angle of the electric line of force on the alumina surface became >60/spl deg/.     

Vacuum flashover on diamond-like carbon-coated insulators

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     

真空中高压电极结构的单次脉冲沿面闪络耐压研究

电极作为高压绝缘子的加载对象,在电真空器件中有着至关重要的作用,合理的电极结构设计可以有效地提高高压器件的沿面耐压。笔者从实际的应用出发,针对几种新型电极结构进行了电场仿真和实验耐压实验,给出了不同电极情况下,氧化铝陶瓷的耐压结果。结果表明,新型电极结构能有效减弱氧化铝陶瓷三结合处的电场强度,并在一定程度上提高绝缘子耐压能力,相对于平板电极,其平均最高耐压提高了55%。     

Surface flashover characteristics of diamond-like carbon thin filmsin vacuum

Synthetic thin films such as diamond-like carbon (DLC) and polycrystalline diamond thin films can be used to increase surface flashover voltage of dielectric materials used in HV devices operating in vacuum. This work presents experimental results identifying some surface flashover characteristics of diamond-like carbon (DLC) thin films in space vacuum conditions. The DLC samples used in the experiments are produced by a microwave plasma deposition technique. The electrode material was copper, and a dc voltage was applied between the electrodes. Surface flashover voltage characteristics and the breakdown voltage wave forms of DLC thin film samples were determined. The results showed that DLC thin films may not be suitable materials for HV applications as dielectric materials in vacuum when coated onto semiconductor materials. Additionally, these results were compared with the surface flashover characteristics of polycrystalline diamond thin film and quartz samples     

Load Section Design of a Pulsed Power Generator for X-pinch

The load section of a pulsed power generator for X-pinch was designed. It is a work that repeats itself in cycles as follows: making small changes in size and configuration of the electrode system in order to reduce inductance rarr calculating the inductance rarr calculating the load voltage with the measured forward going voltage wave along the pulse transmission line (PTL) incident upon the load rarr calculating the electric field rarr checking if any surface flashover or breakdown in vacuum happens. In the final designed load section, the highest field on the surface of the insulator, a plexiglass diaphragm, is 113 kV/cm and the highest field in vacuum is 298 kV/cm, respectively lower than the surface flashover voltage and the vacuum breakdown voltage in case of an applied pulse voltage of 100 ns of full width at half maximum (FWHIVI) and 500 kV in amplitude.     

Flashover from surface charge distribution on alumina insulators invacuum

Surface charge distributions of disk type aluminas held between a backside electrode (alumina holder) and a needle electrode to be excited by an impulse voltage (rise time 64 μs, wave tail 700 μs) were measured. The measurement of surface charge distribution on the whole surface area of alumina YSA998 and UHA99 after impulse voltage application revealed that the surface charging can be initiated either from the anode or from the cathode triple junction. The charging initiated from the anode triple junction (for positive polarity) produced positive charge at the anode region and the density is dependent on the applied voltage, while the charging initiated from the cathode triple junction region (for negative polarity) produced negative charge around the cathode region. For positive polarity, the critical values of charge density to the flashover for alumina YSA998 and UHA98 are 5.70 and 17.2 μC/m², respectively     

表面粗糙度对绝缘材料真空闪络特性的影响

在高电场作用下,在真空、气体或液体介质中常常会发生沿固体绝缘表面的破坏性放电现象,即表面闪络,而发生闪络的电压往往远低于固体和氛围介质本身的击穿电压,其中尤以真空中的闪络现象最为严重.本文针对真空条件下PTFE和可加工陶瓷在冲击电压下的沿面闪络现象进行了观测和研究.发现改变绝缘材料粗糙度对其闪络特性有明显的影响,并对这些现象进行合理解释.     

瓷和玻璃绝缘子人工污秽交流闪络特性比较

人工污秽绝缘子的闪络电压、污闪电压梯度和有效爬电系数均与其材质和型式有关,国内虽对污闪特性研究较多,但对不同绝缘子的有效爬电系数研究不多。为此在人工雾室中对5种典型结构的瓷和玻璃绝缘子的污闪特性进行了试验研究,根据试验结果分析和计算了5种典型绝缘子的闪络电压、闪络电压梯度、有效爬电系数。结果表明:在人工污秽试验条件下,不同型式绝缘子的污闪电压有较大差异,盐密对不同型式绝缘子的闪络电压的影响程度也有差异;三伞型绝缘子和玻璃绝缘子具有较高的闪络电压;不同绝缘子的有效爬电系数与其结构型式和材质有关,玻璃绝缘子的有效爬电系数高于瓷绝缘子,且玻璃绝缘子的有效爬电系数随污秽程度的增加而增加,而瓷绝缘子的有效爬电系数随污秽程度的增加而减小。     

固体电介质真空沿面闪络研究进展

针对真空中复合绝缘体系的耐电强度受到沿面闪络现象限制问题,综述了国内外真空沿面闪络相关的研究进展。研究发现,真空中固体绝缘介质的沿面闪络性能受老练方式、介质的表面特性及体特性、介质表面沉积电荷、绝缘体系的电场分布等因素影响。机理分析认为真空中的沿面闪络现象实质上是高场下电荷在气-固界面的输运行为,其过程涉及到介质表层中的电荷捕获/脱陷特性、二次电子的发射特性、以及气相中的气体(或解吸附气体)分子的碰撞电离/电子倍增等过程,沿面闪络的发展和形成是以上几个因素相互耦合作用结果。基于以上分析及认识,认为可以从改变材料表面特性及体特性和改善整个绝缘体系的电场分布方面,来提升真空沿面闪络电压。     

Dielectric surface flashover in vacuum. Experimental design issues

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