加压乙二醇/水混合液耐μs级高电压击穿实验研究

 采用同轴电极实验装置，在μs级充电时进行了加压乙二醇/水混合液正电极击穿实验，并对实验结果进行了分析和解释，得出结论如下：击穿场强随静压以1/8次幂的关系而增加；击穿场强系数随乙二醇浓度的增加而增加；加压和添加乙二醇对于提高水介质耐高电压击穿的能力具有可叠加性，加压比添加乙二醇更有效；在静压12×10⁵ Pa下乙二醇浓度80%的混合液击穿场强比常压下纯水击穿场强高112.2%。加压提高乙二醇/水混合液击穿场强的主要机制是加压增加了击穿延迟时间。     

加压去离子水短脉冲击穿特性的初步研究

 液体的介质气泡击穿理论作为研究基础，开展了两种短脉冲下高压强水介质开关的击穿实验，获得了水介质击穿场强及耐压时间与水中压强关系的数据，通过分析比较得出：在脉宽300 ns和1 μs两种脉冲电压作用下，当水中压强逐渐提高时水介质击穿电压和耐压时间均呈上升趋势，压强越高趋势越明显，而且作用脉冲越宽水中压强对于水介质击穿特性的影响越显著。     

电极表面光滑程度对水介质高电压击穿的影响

 采用水介质同轴实验装置，改变电极表面的光滑程度，在μs级充电时进行水介质击穿实验，并对实验结果进行了分析和解释。结果表明：抛光电极表面可有效提高水介质耐高电压击穿能力；表面粗糙度为0.4～0.8 μm的抛光电极表面的击穿场强比表面粗糙度为1.6～3.2 μm的粗糙抛光电极表面，更符合Martin公式。电极表面光滑程度的改善，使阴极场致发射电流减弱进而击穿延迟时间变长，气泡也更难以附着在光滑的电极表面，从而可以提高水介质耐高电压击穿能力。     

液体介质快脉冲电压下击穿特性研究

 设计了液体介质快脉冲击穿试验装置和电压电流测量系统，研究了重复频率、电极形状及电极间距与介质击穿场强、击穿电压和击穿时延等击穿特性参数的关系，比较了变压器油、十二烷基苯、蓖麻油三种典型液体绝缘介质在直流及快脉冲电压作用下的绝缘性能。结果表明：短脉冲持续时间下液体绝缘材料有异常高的击穿场强；重复脉冲串作用下的击穿场强比单个脉冲下明显减小，重复频率2 kHz时击穿场强减小了约30％；电极头半径大小对击穿也有影响，半径R＝5 mm时，击穿电压最高；击穿时延随击穿场强减小而变长，在其他条件相同的情况下，测得击穿时延随机波动；蓖麻油的快脉冲电压绝缘性能最好，变压器油次之。     

液体介质快脉冲电压下击穿特性研究

设计了液体介质快脉冲击穿试验装置和电压电流测量系统，研究了重复频率、电极形状及电极间距与介质击穿场强、击穿电压和击穿时延等击穿特性参数的关系，比较了变压器油、十二烷基苯、蓖麻油三种典型液体绝缘介质在直流及快脉冲电压作用下的绝缘性能。结果表明:短脉冲持续时间下液体绝缘材料有异常高的击穿场强；重复脉冲串作用下的击穿场强比单个脉冲下明显减小，重复频率2 kHz时击穿场强减小了约30％；电极头半径大小对击穿也有影响，半径R＝5 mm时，击穿电压最高；击穿时延随击穿场强减小而变长，在其他条件相同的情况下，测得击穿时延随机波动；蓖麻油的快脉冲电压绝缘性能最好，变压器油次之。     

甘油介质在同轴形成线中的击穿特性研究

针对甘油介质在形成线中的应用,总结了甘油作为储能介质已开展的相关研究工作,并在缩比的同轴电极试件中进行了电极表面、磁场、耐压极性、含气量等条件对甘油介质击穿特性影响的实验研究。搭建了基于晶闸管控制的空心脉冲变压器升压实验平台,设计了浸没于脉冲磁场中的同轴电极击穿试件,实验平台最大输出电压500 kV,上升时间26 s,最大磁场1 T,可通过控制晶闸管的先后触发使击穿过程发生于准稳衡磁场中,并制作了外形一致、表面不同的砂纸打磨、羊毛抛光、金属电镀和非金属电镀四种电极。实验结果表明:甘油的击穿是没有极性的;1 T量级磁场对甘油介质的击穿特性无影响;不同电极表面微观形貌差异较大,使甘油介质具有不同的击穿特性,说明甘油击穿在电极表面的过程具有较大影响;充分的排气能减少甘油中直径较大的气泡,减少概率性的低击穿场强,击穿后产生的大量微小气泡会整体降低甘油的击穿阈值,使甘油的平均击穿场强降低。     

压力水介质脉冲击穿实验研究

 为了提高水介质脉冲形成线的储能密度和减小大型加速器的脉冲功率系统几何尺寸，实验研究了水在静压力作用下的耐压强度。简要介绍了液体绝缘介质的击穿机理，在设计的水介质耐压实验装置上研究了去离子水介质在压力作用下的脉冲击穿特性。结果表明，当压强由0.1MPa增加到0.7MPa时，水的击穿场强由25.3MV/m增加到46.7MV/m。     

高压重复频率快脉冲下变压器油中的闪络

介绍了重复频率快脉冲下固/液体介质交接面闪络初步的实验结果.脉冲功率源为基于半导体断路开关(SOS)的SPG200,固体介质为有机玻璃和尼龙,液体介质为变压器油.在相对低频阶段,闪络耐压时间与闪络场强随外加电压脉冲频率的增加非线性迅速减小,在约200 Hz以后,两者下降的趋势明显减缓.随着脉冲频率的增加,闪络耐压时间在统计上变小的同时,在一定区间内的分布也更均匀.分析表明,在不同实验条件下,重复频率显著低于单次下的沿面闪络和体击穿场强.两类场强都随脉冲频率增加非线性下降,在约200 Hz以后,下降的程度减弱.闪络场强随重复频率电压脉冲频率的变化表明,电压作用时间是绝缘介质击穿的根本要素,脉冲电压对绝缘介质的作用时间越长,沿面闪络越容易发生.     

4MV同轴-三平板型水介质自击穿开关的电路模拟与实验

在PTS单路样机上进行了4 MV水介质同轴-三平板型水介质自击穿开关实验研究,开关由3个线性排列的球-板结构的电极间隙构成。根据PTS单路样机部件组成及其结构,建立了单路样机Pspice全电路模型及开关等效电路。给出了开关在自击穿电压3.3 MV和2.9 MV状态下的电路模拟与实验对比,模拟结果与实验结果一致。实验及模拟结果表明,装置和开关模型与参数选取及设置合理,水介质自击穿开关的参数与实际值相近。     

介质阻挡放电丝模式和均匀模式转化的特性

利用水电极介质阻挡放电装置，采用电学方法和发射光谱，研究了空气中介质阻挡放电从微放电丝模式向均匀放电模式转化的过程. 结果表明，大气压下增大外加电压或者电压一定减小气压，放电都能够从微放电丝模式过渡到均匀模式. 高气压下放电为流光击穿而低气压下为辉光放电. 利用放电发射光谱，研究了高能电子比例随实验参数的变化. 结果表明气压减小时高能电子比例增大，电压增加时高能电子减少. 利用壁电荷理论对以上实验结果进行了定性分析. 结果对介质阻挡均匀放电的深入研究具有重要价值.     

Cobalt iron-oxide nanoparticle modified poly(methyl methacrylate) nanodielectrics

In this paper, we report the dielectric properties of composite systems (nanodielectrics) made of small amounts of mono dispersed magnetic nanoparticles embedded in a polymer matrix. It is observed from the transmission electron microscope images that the matrix polymeric material is confined in approximately 100 nm size cages between particle clusters. The particle clusters are composed of separated spherical particles which comprise unconnected networks in the matrix. The dielectric relaxation and breakdown characteristics of the matrix polymeric material are altered with the addition of nanometer size cobalt iron-oxide particles. The dielectric breakdown measurements performed at 77 K showed that these nanodielectrics are potentially useful as an electrical insulation material for cryogenic high voltage applications. Finally, structural and dielectric properties of nanocomposite dielectrics are discussed to present plausible reasons for the observed low effective dielectric permittivity values in the present and similar nanodielectric systems. It is concluded that polymeric nanoparticle composites would have low dielectric permittivity regardless of the permittivity of nanoparticles are when the particles are coordinated with a low dielectric permittivity surfactant.     

Effects of barium on the nonlinear electrical characteristics and dielectric properties of SnO2-based varistors

The effects of barium on electrical and dielectric properties of the SnO_2·Co_2O_3·Ta_2O_5 varistor system sintered at 1250℃ for 60min were investigated. It is found that barium significantly improves the nonlinear properties. The breakdown electrical field increases from 378.0 to 2834.5V/mm, relative dielectric constant (at 1kHz) falls from 1206 to 161 and the resistivity (at 1kHz) rises from 60.3 to 1146.5kΩ·cm with an increase of BaCO_3 concentration from 0mol% to 1.00mol%. The sample with 1.00mol% barium has the best nonlinear electrical property and the highest nonlinear coefficient (α=29.2). A modified defect barrier model is introduced to illustrate the grain-boundary barrier formation of barium-doped SnO_{2}-based varistors.     

Electrical and infrared dielectrical properties of silica aerogels and of silica-aerogel-based composites

In this contribution we have studied the key electrical parameters of silica aerogels and of silica-aerogel-based composites, namely the dielectric constants , the dielectric losses tan (at 1 kHz), and the breakdown fields E _b (at 50 Hz). For low-density bulk silica aerogels we find =1.25 and tan =0.0005. E _b is about 500 kV/cm in quasi-homogeneous fields, and of the order of MV/cm in strongly inhomogeneous fields. The dielectric constants of partially densified aerogels increase linearly with density; their dielectric losses are relatively large and their breakdown fields are comparativiely low. The same results are found for aerogels in the form of settled materials, i.e. aerogel granules and powders in air. Acrylate-based aerogel composites with volume fractions larger than 70% have low dielectric constants but their losses are at least 10 times higher than those of low-density aerogels. These materials sustain high local fields in the MV/cm region, while in quasihomogeneous fields, breakdown occurs at about 100 kV/cm. Based on the present results and the interplay with other physical properties (low mechanical resistance, low thermal conductivity, adsorption of water, etc.), silica aerogels and silica aerogel-acrylate-based composites are predicted to have a low potential for electrical insulation.     

Electrical field on non-ceramic insulators and its relation to contact angles for constant volume droplets

The presence of water droplets on the surface of insulators provides intensification of the electric field, which are caused by the non-uniform voltage distribution and dielectric properties of the different materials. The degree of Electric field (E-field) intensification at the triple joint, the region where water, the non-ceramic dielectric and the air are in contact, must be carefully analyzed, because under certain conditions, breakdown voltages can be reached, sometimes, under very little or no contamination at all, which can cause the insulator wettability, tracking, flashover and degradation. In this paper, variations of the electrical field over two polymer compounds widely used in the insulator manufacturing industry, Silicone Rubber (SIR) and High Density Polyethylene (HDPE), are analyzed on a 2D geometry with respect to contact angles of constant volume water droplets. The Electrical field is also computed as a function of relative water droplets distances.     

激光空泡溃灭及其产生的声波

强激光脉冲在水中的自聚焦传输、成丝、击穿及击穿后产生的声波,近年来成为强激光脉冲传输应用研究领域的一个热点。强激光脉冲电离产生的空泡在溃灭过程中,对周围水体产生压缩,从而在水下产生声波。在现有理论基础上,考虑空泡含气量、水的粘滞系数和水的表面张力系数对空泡运动及其产生声波的影响。给出双空泡运动方程,分析空泡间距对空泡溃灭和其产生声压关系。根据实际情况,计算不同温度情况下单空泡和双空泡运动过程及其产生的声压,并进行相互比较。计算结果表明: 水温越高,空泡运动时达到的最小半径越小,空泡振荡周期和溃灭时间延长,产生声压越高。随双空泡间距减小,空泡溃灭时达到的最小半径线性减小,而其产生的最大声压则单调增大。     

Effect of mechanical loading on the electrical durability of polymers

A decrease in the electrical durability, which is defined as an amount of time required for dielectric breakdown at a constant electric field strength, of polyethylene and Lavsan (polyethylene terephthalate) films under tensile loading is registered in a temperature range from 100 to 300 K. It is established that the pulling apart of the axes of neighbor chain molecules in consequence of tensile loading gives rise to a decrease in the energy level of the intermolecular electron traps. In the amorphous region of a polymer, this accelerates the release of electrons from the traps through over-barrier transitions at higher temperatures ranging from about 230 to 350 K and quantum tunneling transitions at lower temperatures in the range from about 80 to 200 K. As a result, the time required for the formation of a critical space charge, i.e., the waiting period of dielectric breakdown, decreases, which means a reduction in the electrical durability of polymers.

     

加工工艺对微波窗材料介电性能的影响

聚四氟乙烯、聚乙烯、有机玻璃等介质材料因其良好的透波性能和优异的机械性能被广泛用作高功率微波的输出窗口,但关于窗口加工处理工艺对材料介电性能的影响却少有研究。利用高压电桥及高阻计对不同介质材料不同工艺下的基本介电参数进行了测量,利用静电感应法对不同介质材料表面0.8~0.9 eV浅能级的电子陷阱密度分布进行了测试,利用波导口开展了S波段800 MW、百ns微波脉冲作用下的介质击穿实验,考察了材料表面粗糙度、划痕对介质窗表面击穿的影响。结果表明:烘烤工艺在一定程度上降低了材料的耐击穿性能,增加了介质损耗;平行于电场方向的划痕形成了材料表面击穿的通道,而该通道的存在又进一步加剧了击穿的发生。