纳秒快脉冲下气体开关的过电压击穿

纳秒快脉冲过电压击穿方式适合应用于长寿命高同步两电极气体开关.基于过电压击穿型气体开关的工作机制,建立了气体间隙在脉冲过电压击穿模式下击穿电压和时延的统计数学模型,该模型证明电极表面微观场强、间隙气压、初始电流大小、触发电压上升陡度等关键电气参数对间隙击穿分散性有重要影响.提出了纳秒快脉冲下气体开关过电压击穿参数的等效计算方法.实验证明,对于一般工况条件下的石墨电极气体开关,随着气压间距乘积值的增大和脉冲变化梯度超过一定门限值,纳秒快脉冲过电压击穿过程会逐渐由经典流注理论向快电子击穿修正理论过渡.快电子效应导致的电场增强系数在1.2～2.4之间变化.     

低抖动大气压空气电晕均压多间隙气体火花开关

为了发展结构简单、便于维护的大功率气体火花开关,研制了大气压空气电晕均压多间隙气体火花开关,该开关采用电晕放电均压方式,由9个相同的间隙构成。利用有限元分析方法对9间隙电晕均压气体火花开关的电场进行了分析,发现适合长度的电晕针对开关主间隙的电场影响很小,且加载触发脉冲时可在中间间隙形成了强烈的畸变电场。在理论分析的基础上,开展了开关击穿特性研究,实验结果表明电晕均压有利于提升开关的稳定性,开关自击穿电压分散性降低,自击穿电压略微增大;同时多间隙开关实现了良好的触发导通,在工作电压60～85 kV(工作欠压比56.8%～80%)范围内,开关的击穿延时抖动均小于20 ns,当工作电压达到80 kV以上时,抖动可小于10 ns。文中设计的大气压空气电晕均压多间隙气体火花开关可用于直线脉冲变压器等脉冲功率系统,使用的基于电场模拟对电极结构进行优化的方法对设计其他类型的开关具有借鉴意义。     

气体火花间隙开关的自击穿性能研究

为了解气体火花间隙开关的自击穿性能,文中从自击穿实验角度着手,对电场不均匀度进行了仿真计算,测量了两电极气体火花间隙开关不同间隙距离下的自击穿电压,通过计算相对极差和变异系数来分析自击穿电压的稳定性并进行韦布尔检验。实验结果表明,自击穿电压随间隙距离的增大而增大并近似线性关系;间隙距离是影响自击穿电压稳定性的重要因素,自击穿电压的稳定性随间隙距离的增大而增大。从自击穿稳定性角度来看,可以适当增大气体火花间隙开关的电极之间间隙距离来增强自击穿电压稳定性。     

多级多通道气体火花开关的同步放电特性

具有广阔应用前景的气体开关是快脉冲直线型变压器(LTD)这种新型初级储能脉冲功率源的关键部件,为提高其工作性能,对多级多通道气体开关多路同步放电特性进行了初步的实验研究。在优化设计标称电压200kV多级多通道气体火花开关的电极支撑结构后采用绝缘子内抠槽平面支撑结构,使用圆环形凸面结构电极代替圆环形平面电极。利用电磁场分析软件计算开关的电场分布表明:直流高压作用下,开关各间隙电压分布较均匀;触发脉冲作用下触发间隙电场畸变明显。10只开关的同步放电实验研究结果表明,10只气体开关的自击穿特性和触发特性有一定个体差异,其中5只开关并联放电同步性能良好,输出电流脉冲能有效叠加;工作气体为0.14MPa氮气,正负充电60kV,5只开关并联放电,能够产生上升沿约100ns,峰值约100kA的电流脉冲。     

一种多间隙气体开关击穿特性的实验研究

快前沿直线型变压器驱动源(FLTD)是一种可以直接获得100 ns脉宽的脉冲功率源新技术,在Z箍缩、闪光照相、强激光和高功率微波方面具有重要应用。为了寻求用于FLTD的多间隙气体开关的合适结构,设计了一种场畸变多间隙气体开关。该开关含有6个间隙,各个间隙距离相等,开关间隙总长度为30 mm。开关中间电极为锚式固定结构,每个电极由3只螺钉固定在绝缘筒壁内侧,数值计算了开关的电场分布,实验研究了开关的自击穿及触发特性。结果表明,开关自击穿特性曲线与经验公式曲线基本符合,自击穿电压的分散性<3.2%;在工作系数为50%时,开关仍能正常触发,触发时延约百ns;在工作系数为60%时,触发脉冲为150 kV/15 ns的情况下,开关触发时延约60 ns,抖动时间约5 ns。     

石墨型高能气体开关的电极使用寿命分析

两电极气体开关是大型激光装置能源模块中开关元件的重要候选方案。分析石墨材料相比于传统金属材料烧蚀的特殊性。由于高能脉冲放电(转移电荷量大于25 C)时,石墨烧蚀质量损耗与转移电荷量呈线性关系,提出可用于评估电极使用寿命的烧蚀速率,并给出了实用的烧蚀速率测算方法。针对等电场面设计的石墨电极,提出表征石墨电极在使用过程中的电气寿命模型及相应的寿命终结判据,并对所研制的一种单次转移电荷量超过100 C的石墨型高能气体开关进行了寿命预测和试验验证。所得结论对石墨型高能气体开关的研制和使用具有参考意义。     

串联补偿电容装置火花间隙自触发原因分析

分析查找＂4·10＂多个串联补偿电容装置火花间隙自触发原因。通过对XLSK-20PL强制触发型火花间隙装置进行触发间隙自放电电压测试、均压电容参数测试和火花间隙击穿特性测试,发现石墨电极表面存在鸟粪等污物是火花间隙自触发的根本原因。火花间隙击穿特性测试结果显示,当石墨电极表面有尖端、水珠或污秽物等时,火花间隙的主间隙击穿电压分散性很大,交流击穿电压最低约为正常值的65.0%。提出了加强火花间隙运行维护等改进措施。     

触发管型气体开关导通时延的分析及估算

触发管型三电极气体开关导通时延的分析估算对于开关工程设计具有重要意义。结合近年来国内外对触发管型气体开关放电物理机制的研究进展,利用电子崩–流注理论分析解释了触发管气体开关主间隙的击穿过程,由Raether击穿判据推导了以空气为绝缘介质的触发管型气体开关导通时延的数值计算模型,并制作了一个触发管型气体开关及其触发装置进行验证性实验。仿真和实验结果的比较表明:Raether判据可用于判定快、慢导通机制的发生;高欠压比和低欠压比下,计算模型能够正确地反映出触发管型气体开关的导通时延特性,而且符合理论研究中的慢触发和快触发机制特点;触发间隙的击穿在中等欠压比值下,对促进主间隙流注的形成有作用,导致实测导通时延减小。分析计算模型可作为触发管型气体开关设计的参考依据。     

空气间隙击穿后放电通道内的气体运动特性

空气间隙击穿后放电通道内气体的运动关系着间隙绝缘强度的恢复,而绝缘强度的恢复程度对输电线路因间隙放电而跳闸后的重合闸成功与否具有决定性的影响.该文采用高速纹影技术,获得棒-板空气间隙击穿后放电通道演化过程的纹影图像,并基于光流法获得了间隙击穿后放电通道内气体速度场的时空分布.观测结果表明:间隙击穿后放电通道内气体运动的平均速度以"双指数"方式衰减;放电通道在边缘处的射流发展成为湍流的概率较小,同时,射流的发展使放电通道先呈现"由弯变直"的趋势,而后逐渐变得不规则;间隙击穿后的初期,靠近棒电极的放电通道内气体的运动方向呈现相反的趋势,这有助于棒电极附近的放电通道先恢复到放电前的状态.     

多隔板气固复合绝缘工频击穿特性研究

在空气间隙中引入隔板组成气固复合绝缘,可以显著提高间隙的耐压水平.为了研究不同因素对多隔板气固复合绝缘工频击穿特性的影响,本文通过改变多层隔板的水平位置、竖直尺寸、材料进行耐压实验,用摄像仪捕捉击穿路径分析放电规律,最后结合仿真分析电场分布变化.结果 表明:双层隔板和三层隔板都对击穿电压起到了提升作用,隔板竖直尺寸越大...     

Monte Carlo simulation of microparticle motion in vacuum gap

Breakdown voltages of vacuum gaps become lower when the gaps are contaminated by metallic and ceramic microparticles. In this paper, the motion of the microparticles in the gap is simulated using Monte Carlo method in order to evaluate the effect of parameters upon motion and the removal time of the microparticles. As the parameters, we focused on the material of the microparticle, the frequency, the peak value of the applied voltage, the gap length, and the diameter of the lower and upper electrodes. It turned out that the maximum time needed to remove all microparticles could be expressed as multiple regression function. It is suggested that the reliability of the microparticle removal can be increased by spark conditioning with opening/closing operation.     

A probabilistic analysis of spark paths in point/plane air gaps

Analysis of data derived from sparks in point/plane gaps ranging from 45 to 400 mm has shown the similarity of the probability functions determining the shape of the spark paths. This is true, regardless of gap width, when each path is divided into equal steps, here 2% of the gap width. The probability functions were used to develop improved simulations of the spark paths. The simulations had been seen previously to give visually similar tracks, but in this work improved simulations are shown to give similar values for the small amount by which the spark paths are, on average, displaced when the pointed electrode is tilted. The same agreement was found for the degree of scatter of the spark paths about the mean. It is anticipated that the simulations can be generalized to a variety of geometries and scaled up, to simulate and predict lightning strike probabilities     

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.     

An analysis of spark paths in air using 3-dimensional imageprocessing

A video camera has been used to record the path of spark breakdowns across a positive point/plane air gap. By using a prism as a mirror, two images were obtained from which the path could be determined in three dimensions by subsequent computer processing and analysis. Some 80 images were analyzed for each of five angular positions of the point electrode's axis, the gap remaining constant. The fractal dimension of each path was determined and found to increase slightly with the inclination of the pointed electrode. Each spark appeared to have propagated semi-randomly in a direction which included a `memory' factor, i.e. it tended to follow the previous direction while moving monotonically towards the opposite electrode. This was confirmed by considering a projection of the spark path onto the plane electrode which was found to form a semi-random walk in which each step was influenced by the previous step. These, and other analysis, suggest that the development of spark paths in air by successive steps is in a direction suggested by an angular probability distribution related to the field at the tip of the propagating leader     

Correlation between Brightness and Channel Currents of Electrical Discharges

Channel brightness of 500 mm long electrical discharges were measured by analyzing a set of digitized images taken by 3 cameras placed symmetrically around a discharge gap at a radial distance of 200 cm from the axis of the spark. The sparks were generated between a steel rod and a plane electrode. The distribution of the brightness across the channel represented a Gaussian distribution. A linear correlation was seen between the channel brightness measured by different cameras looking at the same spark channel. No correlation was seen between the channel brightness and the channel depth (direction perpendicular to the camera plane). The measured peak current and the brightness of the main spark channel show a high degree of correlation (R²=0.97). The sum of brightness of branches was equal to the brightness of the parent channel. One can use this result to calculate the relative distribution of branch currents in complex electrical discharges including natural lightning flashes. If the current in the parent channel is known, branch currents can be calculated by measuring the optical intensities using photographic techniques.     

Influence of ground and corona currents on dielectric behavior of small air gaps

This paper investigates the influence of grounding on the field distribution and on the dielectric behavior of small rod-plate and rod-rod air gaps. This effect can be attributed to the grounding of one electrode. In the different arrangements with one electrode grounded or with the electrodes symmetrically charged the experimental results of the corona and breakdown are recorded and compared to the simulation results of the field distribution. It is resulted that the grounding influences significantly the electric field distribution, the dc corona and the dc breakdown. The field is less inhomogeneous in grounded rod - plate air gaps and in rod-rod air gaps with symmetrically charged electrodes, and consequently the values of the corona onset and the breakdown voltage are higher. In longer air gaps the corona current influences the field distribution and consequently the dc breakdown. The effect of grounding on the breakdown is weakened when the dc polarity of the voltage is negative, otherwise it is enhanced. In air gaps with lengths > 3 cm (negative dc polarity) or >8 cm (positive dc polarity) it is overlapped by the effect of the corona current. Relations between the field strength, the corona current, the corona onset and the breakdown voltage arise. The principle of action-reaction is valid.     

棒极结构对棒-板间隙操作冲击放电特性影响的试验研究

棒-板间隙是研究空气间隙放电的最典型间隙,其操作冲击放电特性是输电工程线路和换流站／变电站空气间隙选择的重要依据之一。为了更深入地研究棒-板间隙的操作冲击放电特性,选择不同直径的棒电极,以及半球彤和圆锥形2种棒电极端部形状,在2～5m间隙距离下进行了正极性操作冲击放电特性的试验,得到了棒电极端部形状和棒电极直径的改变对棒-板间隙正极性操作冲击50％放电电压造成的影响。另外,在北京、西宁和羊八井等几个不同海拔地区进行了临界半径的对比试验。通过改变棒电极端部连接球面的半径,得到了不同间隙距离对应的临界半径。由试验可以得出,当棒电极结构的半径小于临界半径时,棒电极半径和端部形状的改变不会对间隙的50％放电电压产生明显影响;临界半径随间隙距离的增加而增加,且随着海拔高度的增加,同一间隙对应的临界半径也随之增加。     

水中脉冲电晕放电的声学特性研究

为研究水中脉冲电晕放电的声学特性,由水听器测量了放电产生的压力信号,在以放电电极为圆心、电极到水听器的距离为半径的球面对压力信号积分,得到放电的声能和放电的声效率;利用快速傅立叶变换(FFT)得到同轴电极下电晕放电的频谱分布;比较尖—尖电极下电弧放电晕放电的频谱发现电晕放电声信号的主频比电弧放电的高。     

Analysis of influence of imperfect contact between grounding electrodes and surrounding soil on electrical properties of grounding loops

The measurements of the grounding resistance of grounding loops installed in soils characterised by the structure that prevents a good contact between the grounding electrodes and the surrounding soil (e.g. karst and sandy terrains) showed that it is considerably influenced by the effective contact surface. Therefore, in such cases the grounding resistance cannot be predicted using the standard engineering methods based on the Laplace solution of the problem, where the perfect contact was assumed. The aim of this research was the estimation of the influence of imperfect contact on the loop grounding resistance and potential distribution in the soil during the earth fault. The research is performed applying the finite-element method on a real grounding loop buried in a two-layer soil. Imperfect contact is modelled by air gaps placed between the grounding loop electrodes and the surrounding soil. The analysis of the influence of size, number and position of such air gaps on the loop grounding resistance and potential distribution in the soil showed the dominant effect of the grounding loop surface covered with air gaps.     

压缩气流灭弧条件下配网线路雷击跳闸率计算

压缩气流灭弧防雷间隙是一种冲击电弧诱导型灭弧防雷装置,它通过灭弧管道的特殊排列结构使得冲击电弧能够被优先吸引进入在压缩管道内并形成压力梯度产生自膨胀气流,在各个相邻灭弧管道拐点处粉碎性截断电弧直至电弧熄灭。为了计算在安装压缩气流灭弧防雷间隙后的雷击跳闸率,文中根据并联间隙与绝缘子串的放电电压分布特性得出了灭弧防雷装置的有效保护系数,通过数理统计的方法处理了试验数据,得出了安装压缩气流灭弧防雷间隙后配网线路上的建弧率,同时建立了压缩气流灭弧防雷间隙下的雷击跳闸计算模型。通过算例计算了某线路在安装灭弧装置前后的雷击跳闸率,通过数据分析可知安装压缩气流灭弧防雷间隙后有效降低了雷击跳闸率。