Influence of electrode separation on ion density in the vacuum arc

The density of singly ionized chromium shortly before and after forced extinction of vacuum arcs between chromium-copper electrodes was measured by laser-induced fluorescence for 2- and 10-mm contact gaps and currents between 200 A and 1 kA. In all cases studied, the ion density was constant before ramping down to the current and decayed exponentially after current zero. The ion density at current zero was found to be lower and to decay faster for a short gap than for a longer one, clearly indicating the effect of the contact separation on the charge carrier density. The variation of the time constant for the ion density decay with contact separation is closely analogous to the influence of contact separation on the recovery time of a switch gap. Furthermore, the recovery of dielectric strength of a chromium-copper gap proceeds on the same timescale as the decay of the density of singly ionized chromium. Both of these findings confirm that the ion density has a strong impact on the recovery of a vacuum gap     

Measurement of the tungsten ion concentration after forcedextinction of a vacuum arc

The concentrations of singly ionized and neutral tungsten atoms were measured by laser-induced fluorescence after the forced extinction of vacuum arcs between tungsten-copper butt contacts, 28-mm in diam. and 10-mm apart. The 50-Hz current was forced to zero at its maximum of 200 A in 1.3 μs by application of a reverse voltage. Near current zero, the ion concentration of 4×10¹⁷ m^-3 is of the same order of magnitude as the atomic tungsten concentration, which is 6×10¹⁷ m^-3. While the concentration of the neutrals remains virtually constant during 20 μs after current zero, the ion concentration decays by three orders of magnitude in the same time. The decay-time constant varies from 1.9 μs close to the postarc cathode to 3.6 μs near the postarc anode. It is concluded that the dielectric recovery of vacuum gaps after diffuse arcs is mainly controlled by residual charge carriers     

流动氩气介质阻挡放电特性及振动温度研究

采用双水电极介质阻挡放电装置,在流动氩气中通过改变气隙间距、驱动电源频率和气体流量等研究放电电学特性和振动温度的变化。电学测量结果发现如果固定其他实验条件而只改变某一参数,小气隙间距放电的电流峰值和功率比大气隙间距的高。同样,增大驱动电源频率也能够使放电的电流峰值和功率增加,而增加气体流量使得放电电流峰值和功率减小。最后利用光谱学方法,通过对放电发射光谱中氮分子振动带系的分析,发现振动温度随着放电气隙间距、电源频率和气体流量的变化关系与放电的电流峰值和功率的变化关系基本一致。这些结果对流动气体中大气压介质阻挡放电的应用具有重要意义。     

Study of a circuit-breaker arc with self-generated flow. III. Thepost-arc phase

For pt.II see ibid., vol.16, p.615-22, 1988. The third part of this study of a circuit-breaker arc with self-generated flow concerns the model of the post-arc phase. The greater interruption capability of SF₆ compared to N₂, already suggested in pt.II, is confirmed by the following results: amplitude and duration of the postarc current are much lower in SF₆ and the maximum value of the rate of rise of recovery voltage is about three times higher in SF₆ than in N₂. The model also predicts the existence of a plateau in post-arc current variation and the original behavior of this type of circuit-breaker: interrupting efficiency increases with the current peak in the initial phase     

An experimental investigation on high-frequency vacuum arcinterruption at small gap length

An experimental study of high-frequency (126, 230 kHz) vacuum arc interruption behavior and the voltage escalation processes at a small gap length (⩽1 mm) for three contact materials (Cu, CuCr, and CuTeSe) is discussed. Two experimental methods have been used: current injection in a low-voltage circuit and in a 10-kV AC circuit. Experimental results of the high-frequency current interruption ability and the dielectric breakdown voltage are presented. Three kinds of breakdown are distinguished: the reignition voltage, the breakdown voltage, and the cold breakdown voltage. It has been found that the interruption ability is directly related to the reignition voltage     

Influence of interrupted current amplitude on the post-arc currentand gap recovery after current zero-experiment and simulation

For commercial vacuum circuit interrupter valves with radial field contact, the post-arc current (PAC) waveform was measured after short circuit current interruption applying a transient recovery voltage (TRV) of about 15 kV/s (RRRV). Keeping the current decline di/dt at current zero constant, the power frequency (PF) current amplitude Iˆ_PF was varied from 0.5 up to two times of the rated short circuit current. Significant influence of Iˆ_PF on the gaps memory is shown in particular effecting the post-arc current duration which varies in a range between 2 and 8 μs. Based on the existing physical models an interpretation of the results is given. It is shown that the memory effect influences the gap recovery time. The experimental results were further used to determine the parameters of the sheath growth model described by Andrews and Varey (1971). The initial ion density is fitted according to the current ramp di/dt before current zero (CZ) and according to the measured Q_PF=∫i _PF×dt during the arcing phase. The results of two different test procedures were applied in order to separate the effect of current ramp di/dt and Q_PF=∫i_PF×dt. The influence of both parameters and of the rate of rise of the recovery voltage du/dt (RRRV) on the sheath edge velocity could be demonstrated by simulation     

Computer simulation of post-arc plasma behavior at short contactseparation in vacuum

Rapid commutation of a vacuum arc prior to zero results in the postarc current that subsequently flows due to the transient recovery voltage (TRV) developing across the interelectrode gap. If the rate of change of the arc current exceeds the ability of the device to interrupt the condition, it can be reestablished in the reverse direction, i.e. what was the anode becomes the new cathode. An attempt to model the postcurrent zero phenomena in the light of gas dynamics as applied to the plasma of the metal vapor arc is described. The basic conservation laws and the Maxwell equations, as well as the current continuity law, are formulated and the solutions of those equations are presented. The short distance between the electrodes in practice of much less than a millimeter is specifically noted     

Some Aspects of Current Interruption Physics in High Voltage Circuit Breakers

Recent results of experimental and theoretical investigations on current interruption processes are presented with a focus on SF₆ high voltage circuit breakers. Various aspects of thermal interruption at the zero crossing of the current are shown, including the scatter and the distribution of arc voltage shortly before CZ and the role of turbulence. The thermal interruption capability of air and CO₂ are compared to that of SF₆. Investigations on the dielectric recovery are shown for SF₆ and CO₂. The breakdown voltage during the dielectric recovery can be described by simple streamer and leader inception models. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

一维等离子体光子晶体的带隙研究

采用时域有限差分方法(FDTD),结合等离子体计算中的分段线性电流密度卷积技术(PLJERC)对一维等离子体光子晶体(1D-PPC)进行了数值模拟,给出了微分高斯脉冲在一维等离子体光子晶体中的传播过程。计算得到的带隙结构与K-P模型方法的结果一致。计算并分析了等离子体频率、介质介电常数、等离子体-介质层的厚度比以及周期厚度对一维等离子体光子晶体带隙结构的影响。     

常压窄间隙介质阻挡放电等离子体辐射特性

利用带有透明电极与可测向观察的一个介质阻挡放电(DBD)实验装置对它的常压窄间隙等离子体辐射特性进行了实验研究。结果表明：这一DBD装置的辐射特性会受激励电压、激励频率、DBD结构等多种因素影响。在频率为10～20kHz高压电源激励下,采用窄间隙、薄电介质层结构DBD可以大幅度提高放电空间的电场强度,增加放电功率密度,提高了放电装置性能。     

Dielectric Recovery of an Axially Blown SF6-Arc after Current Zero: Part I?experimental Investigations

The results are presented of a model experiment to investigate the dielectric recovery of an axially blown sulphur hexafluoride (SF6) arc after current zero. With the aid of Schlieren pictures and interferometry, the temperature decay after current zero is observed up to the point of complete recovery of the gap. The dielectric recovery is directly measured by applying voltage pulses across the gap which causes breakdown at different times after current zero. Residual charges, which play a role in the early recovery phases, are detected using a specialiy developed technique. Variations of the shape of the voltage pulses and the geometry cause characteristic changes of the recovery, which support the interpretation of the experimental data.     

Electrical characterization of dielectric barrier discharge driven by repetitive nanosecond pulses in atmospheric air

Dielectric barrier discharge (DBD) is an important method to produce non-thermal plasma, which has been widely used in many fields. In the paper, a repetitive nanosecond-pulse generator is used for the excitation of DBD. Output positive pulse of the generator has a rise time of about 15 ns and a full width at half maximum of 30–40 ns, and pulse repetition frequency varies from single shot to 2 kHz. The purpose of this paper is to experiment the electrical characteristics of DBD driven by repetitive nanosecond pulses. The variables affecting discharge conditions, including air gap spacing, dielectric thickness, barrier fashion, and applied pulse repetition frequency, are investigated. The relationship between electric field, discharge current, instantaneous discharge power across air gap, and estimated electron density with the length of air gap, dielectric thickness, barrier fashion, and pulse repetition frequency is obtained respectively, and the experimental results are also discussed. In addition, two typical images exhibiting homogeneous and filamentary discharges are given with different experimental conditions.     

常压介质阻挡放电间隙的选择及其在材料表面改性中的应用

使用自制介质阻挡放电装置，分析了常压等离子体放电电流和放电功率与放电间隙的变化关系，提出了“放电临界间隙”的概念，并应用该装置对PBT熔喷非织造布进行表面改性，讨论了放电间隙和放电气体等因素对改性效果的影响．     

Neutral copper vapor density and electric recovery after forcedextinction of vacuum arcs

Dielectric recovery data were obtained for vacuum arcs between chromium copper butt contacts 30 mm in diameter and 2 mm apart. The 50-Hz arc current was forced to zero at its maximum of 200 A in about 1 μs. Following current zero, high-voltage pulses of a sufficient amplitude to always cause breakdown were applied to the gap. Gap recovery is characterized by the measured breakdown voltage as a function of time. Dielectric strength of the gap rises sharply within the first few microseconds after current zero, reaching its final value in about 10 μs. Neutral copper concentration in the center of the gap was measured by laser-induced fluorescence under conditions very similar to those of the recovery measurements. In contrast to the fast gap recovery, the copper vapor concentration does not change substantially during the first 100 μs from its value of 1.4×10¹⁸ m ^-3 near current zero. It is concluded that the neutral copper vapor concentration does not play a decisive role in gap recovery under these experimental conditions. This is corroborated by the fact that the mean free path for electron-impact ionization of copper atoms exceeds the gap length by four orders of magnitude     

Compact pulsed power generator using an inductive energy storagesystem with two-staged opening switches

The pulsed power generator, named ASO-I, is extremely compact and light in comparison with a conventional pulsed power generator, which consists of a Marx bank and a water pulse forming line. The ASO-I has a two-staged opening switch, consisting of fuses in water and a plasma erosion opening switch, and can be operated hundreds of times a day at an output power of 230 kV and 35 kA. The parallel fuses are effective for power multiplication, and small differences in length of the parallel fuses do not influence the output power. The risetime of current through the short-circuit load decreases with the increase of the gap length of the spark gap, which is placed between the fuses and the load. The plasma erosion opening switch can be operated as a second opening switch, and the risetime of the current through the short-circuit load decreases from 250 to 10 ns. The maximum resistance of the plasma erosion opening switch is 3.5 Ω with an open-circuit load     

微秒脉冲激励的大气压氦等离子体射流放电特性北大核心CSCD

研究了不同电极结构以及放电参数对微秒脉冲激励的氦等离子体射流放电特性的影响。实验中采用不同管内径、不同电极形状、不同重复频率等参数,通过采集放电阶段的电流电压图、发光图像以及发射光谱等,对等离子体射流的电学特性和光学特性进行诊断。实验结果表明,随着管内直径的增大,氦等离子体射流的长度减小;管内径为8mm时,等离子体射流的击穿电压与放电电流最小,同时,其发射光谱中第二正带系N2,N+2和O等高能活性粒子的强度最高;管内径为5mm的等离子体射流的放电电流、功率及消耗的能量最大;在相同实验条件下,针尖电极结构中的放电电流、消耗的功率还有发射光谱强度都较大;随着重复频率的增加,氦等离子体射流的长度会增加,但击穿电压减小。     

电力故障运行下磁偏置超导限流器超导限流单元的电-热特性分析与验证

本文的磁偏置高温超导故障限流器(SFCL)是一种新型超导限流器,在系统出现短路故障时,发生失超现象,产生高阻抗限制短路电流,达到一定时间后断开超导单元,再由双分裂电抗器二次限流.当短路电流消失后,自动快速恢复到无阻特性,然后重新合闸投入系统运行.在SFCL并网运行前,要对并网运行中出现相间短路等故障的暂态运行特性进行分析,了解并网运行时的状况.本文利用Matlab/Simulink构建了SFCL的仿真分析模型,包含超导限流单元的等效电路模型和热模型.该模型被接入一个由Matlab/Simulink构建的10kV电力系统模型中,用来仿真SFCL的并网运行特性.仿真结果表明了SFCL在并网运行中的效果,以及相间短路故障下失超电阻、通过电流和超导限流单元温度的变化.同时,在中国国网辽宁电力虎石台对SFCL进行了并网运行试验,得到了相间短路故障下的暂态运行特性和失超恢复时间.本文的仿真分析和试验结果,证明了该SFCL样机具备10kV 并网能力,以及快速响应、逐级限流和快速恢复能力     

半超结SiGe高压快速软恢复开关二极管

将SiGe材料的优异性能与半超结结构的优势相结合,提出了一种半超结SiGe功率二极管, 可适应高频化电力电子电路对功率二极管低通态压降、高击穿电压、较小的反向漏电流以及快而软的反向恢复特性的要求,显著提高器件的各种特性. 关键词： 半超结 硅锗二极管 高压 快速软恢复     

磁导率对二维蜂窝结构光子晶体带隙的影响

利用平面波展开法对二维六角晶格结构磁性光子晶体的带隙特性进行了研究，给出其能带结构分布图，并与非磁性介质构成的光子晶体进行了比较.结果表明，由磁性材料构成的光子晶体更易出现带隙，磁导率对带隙结构影响很大.空气背景磁性散射子情况，磁导率增加较小时，二个绝对光子带隙宽度逐渐减小，直至消失.继续增加磁导率，在较低频率范围内出现一个绝对光子带隙，占空比逐渐加大，且最佳填充系数基本保持不变.磁性背景空气散射子，类似地在较低频率范围内也出现了一个绝对光子带隙.磁性背景非磁性散射子与空气背景磁性散射子情况相似.