Evaluation of pulse voltage generators

In this paper, the electrical characteristics of the positive pulsed corona in a wire-cylinder type reactor are investigated. The injected energy and charge into the discharging volume per pulse and per unit length of corona emitting wire are adopted to evaluate the power source, electric circuits, and the corona wire. The discharging current lasts from several hundred nanoseconds to a few microseconds. The current, power peak values, and the injected energy and charge per pulse per unit length of emitting wire can reach up to 60 A/m, 5 MW/m, 480 mJ/m, and 8 μC/m, respectively. The energy conversion efficiency related to the output energy from the pulse forming capacitor and the energy delivered to the discharging volume can reach up to 90%. All results are obtained at room temperature and in air     

Corona Transmission Line Energized by Very Short Pulse Voltages as Applied in Electrostatic Precipitators

The corona-producing characteristics of a corona wire energized by a very short pulse voltage superposed on top of a dc base voltage are investigated in consideration of its application in electrostatic precipitators. A ``formation region' of the pulse-induced negative corona is determined in terms of a Vb - Vp domain where Vb represents the dc base voltage and Vp the pulse peak voltage. A pulse voltage propagates in a form of a traveling wave along a transmission line out of an elongated corona wire and collection plates. It produces streamer coronas and loses its energy during propagation and finally becomes inactive so as not to produce coronas. As a result, a longitudinal distribution of the ionic current shows a decay towards the end of the line. An ``effective pulse energy' We is defined as an energy to produce uniform current distribution on the entire collection plates. This value of We amounts to 0.8 J for a 200-m corona line. A ``pulse peaking' to squeeze more corona energy from the pulse after corona-induced deterioration is tested using partial and total reflections, and its effectiveness is confirmed. A matched feeder concept to enable uniform distribution of pulse power to a number of corona transmission lines is also presented.     

Large area pulsed corona discharge in water for disinfection and pollution control

To investigate the efficiency of submerged pulse corona (SPC) discharges in water we built a laboratory scale, parallel-plate reactor that is part of a closed loop water circulation system. A pulsed voltage is applied across the electrodes. One of the electrodes is coated with a porous ceramic layer to create local field enhancements to initiate corona discharges. For energization of the SPC reactor a pulse generator was developed which is based on a capacitor discharge initiated by a semiconductor switch. A pulse transformer, followed by two magnetic pulse compression stages, produces voltage pulses with amplitudes of up to 30 kV at a pulse width of 0.3 μs. Simulation of the circuit behavior leads to good agreement with voltage and current measurements. Details of the pulse generator and first experimental results concerning the efficiency of radical production are presented. Depending on the conductivity of the water to be treated, pulse currents of > 600 A at a voltage of 20 kV to > 30 kV are obtained for electrode sizes of around 50 cm². The efficiency of the radical production is measured in terms of the hydrogen peroxide (H₂O₂) concentration, which is formed by recombination of hydroxyl radicals (OH.) at sufficiently high concentrations downstream of the plasma reactor. At pulse repetition rates of 20 to 100 Hz, H₂O₂ concentrations of several mg/l are produced, at efficiencies in the range of up to ?1 g/kWh.     

Gas Heating and Formation of Single Linear Discharge Channel on Repetitive Branched Streamer Corona

Under a nonuniform field in an atmospheric short gap, a branched pulse streamer corona changes to a single filamentary discharge (SFD) for a split second just before sparkover occurs. This SFD is a pretransitional phenomenon of sparkover. Therefore, it is very important to study SFD for an understanding of the sparkover mechanism. In this work, the SFD was recreated well by applying a highly repetitive impulse voltage to a needle‐plane gap in synthetic air with dilute CO₂. The characteristics of the SFD, including the channel temperature, the propagation of the streamer head, and the formation process, were investigated by means of an intensified charge coupled‐device (ICCD) camera and a spectroscopic measurement system. It was found that the transition to SFD progresses with localized gas heating along the discharge channel. Furthermore, it was revealed that the SFD is a nonbranched positive streamer.     

The behavior of charged conducting particles in electric fields

The presence of metal particles within a gas-insulated switchgear (GIS) might initiate a sparkover and lead to fatal failure of an electric power transmission system. In order to investigate the behavior of a particle in a GIS, the model electrodes and the measuring system are constructed. The motion of a particle was investigated by using a CCD camera and a high-speed video camera. Different shapes of elongated particles were made from 0.1-mm and 0.25-mm diameter wires. The measured values of lift-off field strength of a particle lying on the electrode agreed quite well with the theoretical predictions. The initial raising up of a particle usually started at the sharper edge, as expected. There were two types of different modes of particle motions: one is the bouncing motion between two electrodes or one electrode, and the other is the standing motion on the electrode. An interesting thing is that the standing motion is on the upper electrode, when a negative voltage is applied to the upper electrode. This phenomenon could be explained from the difference of positive and negative corona currents starting from both edges of a standing particle     

A phase-related investigation of AC corona in air

A computer-based partial discharge detector has been used to measure AC corona pulses in air in a point-cup electrode system. The pulse height distribution was measured as a function of phase angle and pulse height for a range of voltages. The onset voltages for both positive and negative half-cycles are the same, and significantly lower than for the DC case, due to space charge effects. In all other respects the patterns for the two half-cycles are different: pulses only occur at the onset voltage (rising) for the positive half-cycle, but continuously for the negative half-cycle, except for the higher applied voltages which exhibit a glow discharge transition near the (negative) peak. Differences between the distributions for avalanches and streamers increase as the breakdown voltage is approached. Qualitative explanations of the patterns and behavior are given, together with calculations showing that space charge from one cycle can linger in the gap between half-cycles.     

高压脉冲负电晕荷电喷雾试验研究

为减少化学农药带来的污染,采用了荷电喷雾新技术。首先对负高压脉冲电晕荷电机理进行了理论分析,再用网状目标法通过调节电压、极距、电极直径、电极数目等参数进行电晕荷电试验,比较各因素对电晕放电伏-安特性影响及荷电后雾化效果;测量不同电压下雾滴的索太尔直径;并用高速摄影拍摄雾滴带电射流破碎时的状态,得到射流破碎时的雾滴形状。理论分析和试验结果表明,电压越高,雾滴谱较窄,雾滴粒径变细,均匀度越高;揭示了不同影响因素下的雾滴荷电特性,为负高压脉冲电晕荷电喷雾技术的应用和设计提供了理论基础和试验数据。     

Control of corona characteristics with third electrode and biasvoltage

A novel corona control system consisting of a point-to-plate air gap with a cylindrical third electrode has been proposed. Negative and positive coronas from a point-to-plate air gap with a cylindrical third electrode set up close to the corona point of the needle have been investigated with emphasis on the role of the cylindrical third electrode, the bias voltage amplitude and polarity. It was found that the point-to-plate air gap with the cylindrical third electrode had a negative resistance characteristic on its I-V characteristic for negative polarity discharge, which is very different from the same electrode system without the third electrode. Discharge characteristics of the needle point, such as the corona onset voltage and the corona activity, could be controlled by adjusting the field intensity of the corona point by changing the corona point height from the third electrode and varying the bias voltage amplitude and polarity of the third electrode     

纳秒脉冲表面滑闪放电的电气和光学特性

为了研究纳秒脉冲表面滑闪放电特性,本文采用一种新型三电极结构的激励器,通过纳秒脉冲叠加负直流的混合激励模式产生表面滑闪放电。实验研究了电压脉冲分量、电压直流分量及两者的差值对纳秒脉冲表面滑闪放电特性的影响。实验结果表明,当脉冲电压幅值固定时,直流电压幅值的改变对脉冲侧电流的影响较小,但对直流源侧电流却影响显著,直流源侧电流随直流电压幅值的增加而增加,发生表面滑闪放电后峰值和速度均增加。直流电压幅值越大,直流源侧电流出现时刻越早。当直流电压幅值固定时,脉冲侧电流和直流源侧电流均随着脉冲电压幅值的增加而增加。实验中存在一个电压阈值(脉冲分量和直流分量电压差值)使纳秒脉冲表面滑闪放电发生,该阈值为22k V。此时发生表面滑闪放电,瞬时功率峰值、单脉冲能量峰值和稳态能量均迅速增加。脉冲直流电压差值相同时,脉冲分量主导脉冲侧电流的大小,直流分量主导直流源侧电流的大小,脉冲分量所占比例的大小对功率和能量损耗的影响较大。此外,利用数码相机拍摄放电图像研究了纳秒脉冲表面滑闪放电的光学特性,放电图像表明,在电极间施加合理的脉冲电压和负直流电压均可产生表面滑闪放电,实现等离子体的拉伸效果,在阻挡介质表面获得大面积的等离子体。     

Pulse energization system of electrostatic precipitator forretrofitting application

A pulser module has been developed for electrostatic precipitators for upgrading the performance of existing plants. The module is inserted between the existing DC power supply and corona electrodes. A sawtooth voltage appears on the corona electrodes at a switching frequency, including at its leading edge a transient LC oscillation with a very sharp first peak and fast-decaying amplitude. This acts as the submicrosecond pulse energization, producing very active negative streamers in uniform distribution along the entire length of corona wires of the conventional construction. The average of the sawtooth voltage produces a DC field between the corona and the collecting electrodes. This direct-coupled pulse energization indicates in present laboratory tests exactly the same collection performance as the hitherto most effective submicrosecond pulse energization using a coupling capacitor and a DC bias voltage. A specific feature of the present pulse energization system is its simplicity in construction and low initial and operating costs     

脉冲放电降解垃圾焚烧飞灰PAHs和二恶英的研究

焚烧炉处理城市垃圾后排放的粉尘中含有严重危害人类身体健康，甚至危害生命安全的有机污染物多环芳烃(PAHs)和二恶英。该文采用高压正脉冲电晕放电低温等离子体对垃圾焚烧炉布袋除尘器中飞灰进行处理，并对处理后飞灰的孔隙结构、微观表面形态及其PAHs和二恶英含量进行了观察分析。结果发现高压正脉冲电晕放电可以使颗粒表面产生物理脆性变化，从而改变其原有的孔隙结构。含量分析结果表明放电后粉尘中PAHs和二恶英含量明显降低，而且随着放电峰值电压升高，降解效率逐渐增加。随着粉尘中PAHs和二恶英初始浓度的增加，降解效率有所减小，峰值电压为30 kV时对高浓度二恶英的降解效率为5%~15%，对低浓度二恶英的降解效率可以高达50%。随着放电时间的增加，PAHs的降解效率逐渐增加，放电时间3 min对其降解效率可达80%。     

Characteristics of a fast rise time power supply for a pulsedplasma reactor for chemical vapor destruction

Rotating spark gap devices for switching high voltage direct current (DC) into a corona plasma reactor can achieve pulse rise times in the range of tens of nanoseconds. The fast rise times lead to vigorous plasma generation without sparking at instantaneous applied voltages higher than can be obtained with DC. The resulting energetic plasma is effective for destroying a variety of molecules. The spark gap circuit configuration plays an important role in the effectiveness of the plasma generation. A single-gap circuit is effective for generating moderate peak voltages, but is limited by a multiple sparking phenomenon. A double-gap circuit can achieve equal peak voltages with every spark, but with a reduced number of pulses, compared to the single gap. Both configurations have an upper voltage imposed by the changing impedance of the reactor as voltage and frequency are varied. The pulse characteristics are reported for both types of circuits. The general performance of the reactors for destruction of some compounds with both circuits is also reported     

Compact, Nanosecond, High Repetition Rate, Pulse Generator for Bioelectric Studies

The high dielectric strength and high permittivity of water allow for its use for energy storage and switching in compact pulse power systems. A 10-Omega pulse generator with flowing water as dielectric and as the switching medium is presented here. It can provide a 10-ns pulse with a risetime of approximately 2 ns and an amplitude of up to 35 kV into a matched load. The system was operated in burst mode with repetition rates of up to 400 Hz, limited by the charging power supply. For a switch with two pin electrodes, strong electrode erosion limits the use of the pulser to less than 1,000 pulses before electrode readjustment is necessary. A considerable reduction of the erosion effect on breakdown voltage was obtained with coaxial electrodes. The pulse generator was used to study the effect of the repetition rate (or the time between successive pulses) on the viability of B16 murine melanoma cells.     

脉冲放电能量传输的实验研究

针对脉冲电压Up沿放电线传播发生流光电晕放电,脉冲能量注入反应器内产生活性自由基进行烟气脱硫脱硝过程中,沿线Up波形的变形及脉冲能量的衰减会影响活性自由基产生的问题,为给设计工业应用反应器的几何尺寸提供依据,研究了Up及脉冲能量沿放电线变形、衰减的特性,且研究了电压、脉冲成形电容Cp、线径d及线长l等因素对能量传输、衰减的影响。实验结果表明脉冲电压沿放电线传输时,电压波形发生衰减,随着传输距离的增大,电压波形变形严重;电压、Cp、d和l对能量衰减有一定的影响,增大电压、Cp和d,沿线脉冲能量的衰减速度增大;l越短,能量衰减越快。实验得出最佳l≤10 m。     

Industrial experiments on pulse corona simultaneous removal of NOx and SO2 from flue gas

The corona-induced simultaneous removal of NO_x and SO ₂ from flue gas is based on the application of narrow voltage pulses to an electrode structure similar to that of an electrostatic precipitator. The free electrons of the corona discharge, having energy up to 20 eV, originate active radicals which lead to the transformation of NO_x and SO₂ into their acids which can be neutralized to salt particulate by adding to the gas a basic compound such as ammonia and calcium hydroxide. The process has been investigated with a test rig installed in the slipstream of the flue gas duct of a coal-fired thermal power plant. The experiments were performed with three reactor modules of different geometries. Further experiments are necessary to assess the effect of different electrode geometries of the reactor, the efficiency of the process attainable with an improved coupling of narrow pulse power set to the reactor, and the practical ways for integrating the DeNO_x and DeSO₂ corona process with the solid particle collection system     

Electrical Characterization of a Corona Discharge for Surface Treatment

Electrical characterization is based on a display of voltage and charge which appears as a simple parallelogram. The area is a measure of energy input per cycle and is independent of voltage waveform but very dependent on the maximum voltage. A useful model for such corona discharges employs a Zener diode to simulate the corona drop. The buffer dielectric plays a major roll in controlling the corona power, and the air gap importance depends on the electrode system employed. Proper interpretation of the voltage-charge traces provides insight as to the corona performance and serves as a diagnostic procedure for obtaining optimum performance.     

气液混合两相体中脉冲放电现象的研究

研究了气液混合两相体中线线电极脉冲放电现象。观测表明两相体的起晕电压降低,电晕区域明显加大,并且较为稳定,电极背侧也有较大区域的放电现象。分析表明上述现象的出现和空间水滴有很大关系,其作用为形成大体积两相体放电提供了依据。     

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。     

低气压下直流正极性冰电极电晕特性研究

覆冰将改变绝缘介质的放电过程，导致电力系统绝缘性能下降，为深入研究覆冰绝缘子串中空气间隙的电晕放电特性，基于冰棱-冰板电极系统，通过脉冲电流传感器和紫外线成像仪CoroCAM IV+揭示了气压对起晕电压、放电模式、放电波形及其幅值等的影响。通过数学分析提出表征不同大气压下不同间隙长度时起晕电压的修正公式，分析和讨论气压对放电脉冲及其幅值的影响。理论分析表明，随着气压的降低，覆冰空气间隙起晕电压呈幂函数或指数函数降低，特征指数同间隙长度相关。试验结果与理论分析一致，进一步揭示了覆冰环境下电晕放电的特性。     

Characteristics of discharge induced by laser-generated plasmas in atmospheric air

The possibility of laser-induced lightning has been investigated for the future application in the protection of electric power systems from lightning strokes. This technique induces lightning strokes artificially along a laser-produced breakdown plasma channel and conducts them to a harmless place on the ground. To clarify the plasma formation mechanism and the discharge (sparkover) induction process, sparkover induction experiments are performed for two types of long-gap electrode configurations, plate-to-rod and plate-to-plate, with a 50-J TEA CO₂ laser. In the present paper, the sparkover voltage characteristics and interferometric measurement on laser-produced plasma mainly are described, together with sparkover induction for a series of metal beads arranged equidistantly which simulate a plasma channel.