Review of the Lightning Shielding Against Direct Lightning Strokes Based on Laboratory Long Air Gap Discharges

长间隙放电是研究地面物体雷电屏蔽问题的最有效手段之一。首先介绍了国内外在雷电击距、直击雷防护措施的屏蔽性能试验和雷电迎面先导过程研究3个方面所取得的进展，并结合最新开展的长达6m问隙尺度的放电试验观测，对现阶段上述3个方面研究所存在的问题进行了分析。认为基于雷电击距建立的电气几何模型（electricgeometrymodel，EGM）仅适用于小尺度目标物的雷电屏蔽性能分析，现有的雷电屏蔽模拟试验方法仅能近似模拟不存在雷电迎面先导时的雷击过程，无法完全证明以提前流注发射模型装置为代表的非传统防雷装置具有比传统措施更优越的屏蔽性能。大尺度目标物的雷电屏蔽问题应聚焦于雷电迎面先导过程的研究，建立并完善雷电迎面先导过程的模拟试验方法和物理仿真模型。

Experimental Study on Branch and Diffuse Type of Streamers in Leader Restrike of Long Air Gap Discharge

One of the main problems in the Ultra High Voltage （UHV） transmission project is to choose the external insulation distance, which requires a deep understanding of the long air gap discharge mechanism. The leader-streamer propagation is one of most important stages in long air gap discharge. In the conductor-tower lattice configuration, we have measured the voltage, the current on the high voltage side and the electric field in the gap. While the streamer in the leader-streamer system presented a conical or hyperboloid diffuse shape, the clear branch structure streamer in front of the leader was firstly observed by a high speed camera in： the experiment. Besides, it is found that the leader velocity, width and injected charge for the branch type streamer are greater than those of a diffuse type. We propose that the phenomenon results from the high humidity, which was 15.5-16.5 g/m3 in our experiment.

Research and Development on Short Gap Streamer Discharge Simulation Methods

流注放电是间隙放电研究的重要内容与切入点,仅靠实验手段仍然无法获得流注放电的微观机制及放电通道内的全部物理参数,因此,数值仿真成为推动流注放电理论发展的一种重要方法。文章阐述了短间隙流注放电仿真的流体模型及其假设,分析了数值仿真算法中的3个难点问题,即粒子输运方程的准确求解、不规则区域中泊松方程的快速求解以及光电离项的快速求解。在回顾流注放电数值仿真领域解决上述3个难点问题的历史过程与取得进展的基础上,提出了解决上述问题的可能途径与努力方向。

Treatment of Invasive Marine Species on Board by Using Micro-gap Discharge Plasma

A pilot-scale experiment of 20t/h for the treatment of ship＇s ballast water is reported in this paper. When the concentration of the dissolved OH. was 0.68 mg/L during the experiment, the rate of destroying bacteria, mono-algae, protozoan reached 100% within 2.67 s. The effect of hydroxyl radicals on biochemical processes was also studied. The attenuation rate of photosynthesis pigment was 100%. And the main reason for the cells＇ death was the strong destruction of the monose, amylose, protein, DNA and RNA in the cells. As an advanced oxidation method, the procedure can destroy invasive marine species when a ship is in the process of discharging its ballast water.

Characteristics of a large gap uniform discharge excited by DC voltage at atmospheric pressure

A large-gap uniform discharge is ignited by a coaxial dielectric barrier discharge and burns between a needle anode and a plate cathode under a low sustaining voltage by feeding with flowing argon. The basic aspects of the large-gap uniform discharge are investigated by optical and spectroscopic methods. From the discharge images, it can be found that this discharge has similar regions with glow discharge at low pressure except a plasma plume region. Light emission signals from the discharge indicate that the plasma column is invariant with time, while there are some stochastic pulses in the plasma plume region. The optical emission spectra scanning from 300 nm to 800 nm are used to calculate the excited electron temperature and vibrational temperature of the large-gap uniform discharge. It has been found that the excited electron temperature almost keeps constant and the vibrational temperature increases with increasing discharge current. Both of them decreases with increasing gas flow rate.

Effects of Hydroxyl Radicals on Introduced Organisms of Ship's Ballast Water Based Micro-Gap Discharge

With the physical method of micro-gap gas discharge, OH. radicals were produced by the ionization of O2 in air and H2O in the gaseous state, in order to explore more effective method totreat the ship＇s ballast water. The surface morphology of Al2O3 dielectric layer was analysed using Atomic Force Microscopy （AFM）, where the size of Al2O3 particles was in the range of 2 μm to 5 μm. At the same time, the biochemical effect of hydroxyl radicals on the introduced organisms and the quality of ship＇s ballast water were studied. The results indicate that the main reasons of cell death are lipid peroxide and damage of the antioxidant enzyme system in Catalase （CAT）, Peroxidase （POD） and Superoxide dismutase （SOD）. In addition, the quality of the ballast water was greatly improved.

Effect of actuating voltage and discharge gap on plasma assisted detonation initiation process

The influence of actuating voltage and discharge gap on plasma assisted detonation initiation by alternating current dielectric barrier discharge was studied in detail.A loose coupling method was used to simulate the detonation initiation process of a hydrogen–oxygen mixture in a detonation tube under different actuating voltage amplitudes and discharge gap sizes.Both the discharge products and the detonation forming process assisted by the plasma were analyzed.It was found that the patterns of the temporal and spatial distributions of discharge products in one cycle keep unchanged as changing the two discharge operating parameters.However,the adoption of a higher actuating voltage leads to a higher active species concentration within the discharge zone,and atom H is the most sensitive to the variations of the actuating voltage amplitude among the given species.Adopting a larger discharge gap results in a lower concentration of the active species,and all species have the same sensitivity to the variations of the gap.With respect to the reaction flow of the detonation tube,the corresponding deflagration to detonation transition（DDT） time and distance become slightly longer when a higher actuating voltage is chosen.The acceleration effect of plasma is more prominent with a smaller discharge gap,and the benefit builds gradually throughout the DDT process.Generally,these two control parameters have little effect on the amplitude of the flow field parameters,and they do not alter the combustion degree within the reaction zone.

Analysis on discharge process of a plasma-jet triggered gas spark switch

The plasma-jet triggered gas switch （PJTGS） could operate at a low working coefficient with a low jitter. We observed and analyzed the discharge process of the PJTGS at the lowest working coefficient of 47% with the trigger voltage of 40 kV and the pulse energy of 2 J to evaluate the effect of the plasma jet. The temporal and spatial evolution and the optical emission speclrum of the plasma jet were captured. And the spraying delay time and outlet velocity under different gas pressures were investigated. In addition, the particle in cell with Monte Carlo collision was employed to obtain the particle distribution of the plasma jet varying with time. The results show that, the plasma jet generated by spark discharge is sprayed into a spark gap within tens of nanoseconds, and its outlet velocity could reach 104 m s-1. The plasma jet plays a non-penetrating inducing role in the triggered discharge process of the PJTGS. On the one hand, the plasma jet provides the initial electrons needed by the discharge; on the other hand, a large number of electrons focusing on the head of the plasma jet distort the electric field between the head of the plasma jet and the opposite electrode. Therefore, a fast discharge originated from the plasma jet is induced and quickly bridges two electrodes.

A Repetitive Nanosecond Pulse Source for Generation of Large Volume Streamer Discharge

Using a unipolar pulse with the rise time and the pulse duration in the order of microsecond as the primary pulse, a nanosecond pulse with the repetitive frequency of several kilohertz is generated by a spark gap switch. By varying both the inter-pulse duration and the pulse frequency, the voltage recovery rate of the spark gap switch is investigated at different working conditions such as the gas pressure, the gas composition as well as the bias voltage. The results reveal that either increase in gas pressure or addition of SF6 to the air can increase the voltage recovery rate. The effect of gas composition on the voltage recovery rate is discussed based on the transferring and distribution of the residual space charges. The repetitive nanosecond pulse source is also applied to the generation of large volume, and the discharge currents are measured to investigate the effect of pulse repetition rate on the large volume streamer discharge.

Three Discharge Modes of Dielectric Barrier Discharge in a Two-phase Mixture

两相体介质阻挡放电（dielectric barrier discharge in atwo-phase mixture,TPM-DBD）是在大气压下产生低温等离子体的重要方法,因具有很高的能量密度而被广泛应用在污染治理中。为研究介质颗粒的填充方式对TPM-DBD的影响,以γ-Al2O3作为填充介质颗粒,将数码相机与体视显微镜连体拍摄放电显微照片。结果发现,随着电压变化,TPM-DBD由3种依次串联发生的放电构成。电压较低时,首先在颗粒与极板间发生剩余间隙放电;随着电压增加,颗粒沿面放电串联发生;电压继续增加,孔隙放电串联发生。当颗粒间距较大时,在颗粒的远域出现典型的丝状放电,而近域内出现可能为汤森放电的放电＂暗区＂。外电场的数值计算结果初步说明了上述现象,电场畸变是其主要原因。研究结果为调节TPM-DBD的放电形式,进而高效率应用提供了较好的支持。

On the Formation of a Bead Structure of Spark Channels during a Discharge in Air at Atmospheric Pressure

The conditions for the formation of spark channels with a bead structure in an inhomogeneous electric field at different polarities of voltage pulses are studied.Voltage pulses with an amplitude of up to 150 kV and a rise time of≈1.5μs were applied across a 45-mm point-to-plane gap.Under these conditions,spark channels consisting of bright and dim regions(bead structure)were observed.It is shown that when current is limited,an increase in the rise time and the gap length does not affect the formation of the bead structure.It was found that an increase in the amplitude of voltage pulses leads to an increase in the length of beads.The appearance of the bead structure is more likely at negative polarity of the pointed electrode.The formation of spark channels was studied with a four-channel ICCD camera.

Generation characteristics of a metal ion plasma jet in vacuum discharge

To improve the performance of a metal ion plasma jet in vacuum discharge, an anode-insulated cone-cylinder electrode with insulating sleeve is proposed in this paper. Discharge characteristics and generation characteristics of plasma of the electrode are investigated, effects of diameter of insulating sleeve, variety of cathode material and length of the insulating sleeve on characteristics of metal ion plasma jet are discussed. Results indicate that a directional and steady plasma jet is formed by using the novel electrode with insulating sleeve under high vacuum conditions. Moreover, the properties of metal ion plasma jet are improved by using the aluminum cathode and thin and long insulating sleeve. The study provides strong support for research of vacuum metal ion plasma thruster and ion implantation technology.

Dynamic Characteristics of SF_6-N_2-CO_2 Gas Mixtures in DC Discharge Process

Dynamic characteristics of discharge particles are described within the framework of a two-dimensional photoionization-hydrodynamic numerical model for the discharge process of SF6-N2-CO2 gas mixtures at atmospheric pressure, under a uniform DC applied field. The finite difference flux corrected transport （FD-FCT） algorithm is used in the numerical implementation for improving the accuracy and efficiency. Then the tempo-spatial distributions of the gap space electric field and electron velocity are calculated from the microscopic mechanism, and the dynamic behaviors of charged particles are obtained in detail. Meanwhile, the tempo-spatial critical point of the avalanche-to-streamer in this model is discovered, and several microscopic parameters are also investigated. The results showed that the entire gap discharge process can be divided into two phases of avalanche and streamer according to Raether-Meek criterion; the electron density within the discharge channel is lower compared to that of positive and negative ions; space charge effect is a dominant factor for the distortion of spatial electric field, making the discharge channel expand toward both electrodes faster; photoionization provides seed electrons for a secondary electron avalanche, promoting the formation and development speed of the streamer.

Simulated and experimental studies on the array dielectric barrier discharge of water electrodes

A kind of dielectric barrier discharge（DBD） device composed of water electrodes with 3×3forms can produce large-area low-temperature plasmas at atmospheric pressure.To reflect the discharge characteristics of DBD better,a dynamic simulation model,which is based on the voltage controlled current source（CCS）,is established,then the established model in Matlab/Simulink is used to simulate the DBD in air.The voltage-current waves and Lissajous at a voltage of 10 kV,11 kV and 12 kV peak value with a frequency of 15 kHz are studied.The change of the discharge power of DBD with a different amplitude and frequency of applied voltage is also analyzed.The result shows the voltage-current waves,Lissajous and discharge power of DBD under different conditions from the simulation agree well with those of the experiment.In addition,we propose a method to calculate the dielectric barrier capacitance Cd and the gap capacitance Cg,which is valid through analyzing the variation of capacitance at different voltage amplitudes.

气隙长度对大气压下环氧树脂阻挡放电的影响研究

为了研究气隙长度对大气压下介质阻挡放电的影响机制,从而进一步明晰介质阻挡放电的放电机理及特性,基于气体放电流体模型,针对长度3 mm以下的环氧树脂阻挡同轴电极气隙,在外施电场恒定的条件下对其放电微观过程进行仿真,从带电粒子微观运动角度研究气隙长度对气隙放电特性的影响。仿真结果表明:在长度小于3 mm的气隙中,环氧树脂的阻挡导致电子崩无法发展成为流注,其放电形式为汤森放电;气隙长度对放电过程的影响主要通过改变带电粒子的分布和电场强度来实现;气隙长度对放电发展速度几乎没有影响;当电子崩靠近较短气隙的阳极时,其崩头密度低于较长气隙;随着气隙长度的增加,放电电流峰值增大,上升速度和降落速度增加,脉冲宽度减小。通过对比理论计算与实验结果,证明了仿真方法的合理性。

辅助放电针对气体间隙直流自击穿特性的影响

为降低气体放电间隙直流条件下自击穿电压分散性,尽可能不影响其自击穿电压,基于环形电极放电间隙,设计了一种在阴极中心植入辅助放电针的辅助放电电极结构。通过电场仿真,研究了辅助放电针直径、长度和顶部倒角对放电间隙场畸变的影响。实验研究了放电间隙无辅助放电针和植入辅助放电针后,其在干燥空气和SF_(6)气体中的直流自击穿特性。结果表明:辅助放电针直径越小、长度越长,电极环对其电场屏蔽作用越弱,放电间隙场畸变强度越大;辅助放电针对SF_(6)气体放电间隙直流自击穿电压影响较小,随着场畸变系数的增大,同一气压下干燥空气自击穿电压下降百分数为SF_(6)气体自击穿电压下降百分数的2~3倍;辅助放电针对直流条件下干燥空气和SF_(6)气体放电间隙自击穿电压稳定性具有有益作用,分散性减小百分数较无辅助放电针结构均提高约25%。

基于图像信息熵与多元变分模态分解的电缆局放信号去噪方法

局部放电(PD)检测是评估交联聚乙烯(XLPE)电缆绝缘状态的主要手段。针对电缆终端与中间接头局部放电现场检测时存在白噪声、周期性窄带干扰,以及去噪过程中自适应性较弱的问题,该文提出了一种基于图像信息熵与新型自适应多元变分模态分解的去噪方法。首先,对信号进行多元变分模态分解,重组信号并转换成灰度图像,进而计算图像一维信息熵。在考虑算法执行效率的同时,将Pearson相关系数与图像信息熵优化算法的模态参数相结合。其次,通过计算各本征模态分量的峭度来判定其主导分量的性质特征,利用峭度对噪声敏感的特性区分PD特征信息与噪声干扰分量,进而对噪声干扰分量进行3σ准则滤波。最后,通过新型改进小波阈值算法得到去噪信号。利用该方法对PD信号进行去噪,并与基于Spearman的变分模态分解(S-VMD)法、自适应集合经验模态分解(NAEEMD)法、短时傅里叶变换-奇异值分解(STFTSVD)法进行对比分析。结果表明,该方法对现场PD信号具有良好的抑噪性能,且耗时少、执行效率高、工程应用价值高。

2/3匝线圈式纵磁触头大开距真空断路器分闸速度设计

合理设计纵磁触头真空断路器的分闸速度特性,可有效避免大电流开断过程中真空电弧阳极斑点的形成或缩短阳极斑点持续时间,显著提升断路器短路电流开断性能。然而,现阶段仍然缺乏线圈式纵磁触头真空断路器全行程分闸速度特性的量化设计方法。该文试验研究了电弧电流、分闸速度对2/3匝线圈式纵磁触头大电流真空电弧阳极放电模式演变的影响规律,获得了不同分闸速度下线圈式纵磁触头阳极放电模式图,据此提出线圈式纵磁触头分闸速度的量化设计方法:初始分闸速度v1应不小于其从强电弧模式演变为扩散态电弧模式的临界触头开距峰值所对应的分闸速度;平均分闸速度v2应不大于大开距活跃阳极放电模式形成的临界触头开距峰值所对应的分闸速度;同时,对比实际开断过程中触头间隙磁感应强度与阳极放电模式演变的临界纵向磁感应强度,可校验上述分闸速度特性设计的合理性,并能预测该纵磁触头以任一分闸速度开断任一短路电流时的阳极放电模式演变特性。应用上述方法,该文确定了126 kV单断口真空断路器的分闸速度特性设计值为v1=3.5 m/s、v2=3.0 m/s,并通过型式试验验证了断路器在上述分闸速度特性下的短路电流开断性能。

FPGA高速数据采集的WEDM在线脉冲识别

为了提高电火花加工放电间隙的实时识别准确率,文中提出了一种基于FPGA高速数据采集的神经网络的放电间隙在线识别方案。利用FPGA和AD模块对加工间隙电压数据进行高速采集,通过FPGA内部的FIFO和串口协同实现周期性数据传输。在Python的Pytorch库构建了CNN GRU融合神经网络模型,对所采集的数据进行在线识别,验证了该采集系统的可行性。实验结果表明:文中方案对加工电压脉冲的离线识别准确率达到了97.35%,优于CNN和GRU方法,满足了电火花加工对间隙电压识别的高精度要求,实现了神经网络的实时在线识别放电间隙。