Effect of Discharge Electrode Parameters on the Flow Velocity Profile of the Wire?rod Type Electrohydrodynamic Gas Pump Exit

Experimental investigation has been conducted to study the effects of corona wire diameter, pipe length, and corona polarity on outlet flow velocity distribution profile of a wire-rod type electrohydrodynamic (EHD) gas pump. Upon applying negative or positive dc high voltage between a wire electrode (outer diameter (o.d.) 60 μm, 200 μm, or 300 μm) and a rod electrode (o.d. 3 mm) in atmospheric air, corona discharge occurs and EHD gas flow is generated in the direction from the wire electrode to the rod electrode through a cylindrical pipe (inner diameter (i.d.) 20 mm). For both polarities, the discharge current and average flow velocity increase monotonically on increasing the applied voltage before the onset of spark discharge. Using wire electrodes with a smaller diameter, stable corona discharge between corona onset and spark onset is generated in a wider voltage range, and the discharge current becomes larger, resulting in a higher flow velocity. The maximum average flow velocity of 2.0 m/s, corresponding to a flow rate of 38 l/min, was achieved with a wire of diameter 60 μm by applying a voltage of ?16 kV.     

多针电极结构双极电晕放电伏安特性

为提高电晕放电的能量密度和放电稳定性,提出了针阵列电极结构的双极电晕放电方式并研究了多针电极结构双极电晕放电的伏安特性。实验得出放电电流I随针尖半径a和电极间距d的增大而减小,随相邻针尖间距s的增大而增大,但当s≥40 mm时,相邻针尖的相互作用已很小,I几乎不变;d对火花击穿电压的影响较大,a对其的影响较小。由于电极结构的对称性,高压电极的极性对放电无明显的影响,正负电晕放电的伏安曲线和火花击穿电压均较为接近。将多针电极双极电晕放电电流I等效成电极间距为d/2的多针对板正、负电晕放电电流I1和I2相加,分析了I>I1+I2的原因,并推知其电离区内电子密度也有相应规律。     

DC corona discharge from a wire particle floated with a microgap in parallel plate electrodes

Conductive particles existing in a high-voltage system could deteriorate the system performance owing to an electric discharge via the particles. In case when the particles exist in a dc high-voltage electrode system, the location of the particle would inevitably affect the discharge aspect. A corona-onset and breakdown voltage from a metallic wire particle were measured in detail. The wire particle has a length ranging from 6 to 12 mm, and a diameter of 0.25 mm. It was fixed between a parallel plate electrode with a spacing of 20 or 30 mm. When the particle was close to the negative electrode, a corona discharge occurred stably, and the corona-onset voltage was increased as the gap length between the negative electrode, and the positive end of the particle increased up to 0.8 mm. In contrast, when the particle was close to the positive electrode, the breakdown always occurred without preceding the corona discharge. At the middle region between the electrodes, the corona onset occurred at almost constant voltage.     

邻近直流导线时交流电晕电流脉冲特性试验

本文搭建交直流并行线路电晕放电试验平台,研究邻近直流电压时交流单点电晕放电下的电晕电流脉冲特性。并对交流电晕电流脉冲的分布模式、重复频率以及波形等特征参数进行统计分析。试验结果表明,邻近的正极性直流电压会促进交流负半周电晕放电而抑制交流正半周电晕放电,邻近的负极性直流电压作用正好相反。直流电压对交流负半周电晕电流脉冲波形参数无明显影响,而正半周电晕电流脉冲的幅值会随负极性直流电压的增加有所升高。同时发现,随着交流电压幅值的升高,促使其正半周发生电晕放电所需要的负极性直流电压幅值也相应地升高,并基于电晕放电的发展过程中电离强度的计算提出种子电子的缺失是造成该现象的原因。最后,在电晕放电离子云模型基础上,提出脉冲序列发展的过程中电离区域电场强度恒定不变的假设,从而对邻近直流电压影响下的交流电晕电流脉冲波形参数特性给出了合理的解释。     

基于脉冲电流法判断输电线电晕放电研究

对输电线电晕放电的起晕电压、电晕脉冲电流、起晕场强进行了研究。采用基于脉冲电流法判断电晕笼内单根输电线起晕电压。通过局部放电检测回路中的检测阻抗,获取电晕脉冲电流波形。当脉冲电流持续出现时,此时导线所加电压,即为电晕起始电压。根据实验得到的起始电晕电压,借助有限元法计算笼内导线表面及其附近场强,结果与通过皮克经验公式得到的较为接近,验证了脉冲电流法判断输电线路起晕电压的合理性。     

多高压电极系统电晕放电的研究

研究了多高压电极的放电特性现象。结果表明，由于各高压电极间受电场相互屏蔽作用的影响，使电晕放电通道的光学图形发生了向电极外侧偏移，同时各高压电极间距处在一定范围内可提高电晕放电起始电压。还利用分割电极的方法测量了平面电极上的电流密度，其极大值点可相应向外侧偏移，在负极性放电时在一定条件下能产生正流注放电。     

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。     

不同海拔下电晕笼分裂导线起晕电压的计算分析

为了研究海拔高度对电晕笼分裂导线起始电晕电压特性的影响,建立电晕笼钢芯铝绞线起始电晕电压的计算模型,并开展相应试验研究。采用模拟电荷法计算钢芯铝绞线的空间电场强度。依据极不均匀电场下自持放电判据,建立不同海拔高度电晕笼分裂导线电晕起始电压的计算模型。在超/特高压人工环境气候试验室内,以500 m海拔高度为间隔,系统开展19~4-000-m海拔高度范围内六分裂导线起始电晕电压的试验研究。试验获得超高压电晕笼不同海拔高度下6-LGJ—400/50、6-LGJ—500/45分裂导线的起晕电压。计算获得不同海拔高度、分裂间距、导线分裂数及绞线表面粗糙系数下的导线起晕电压曲线族,以及不同绞线半径及最外层铝绞线股数的表面粗糙系数计算结果。分析结果表明:计算模型能够较好地计算电晕笼内绞线的起晕电压;在350~500-mm分裂间距范围内,分裂导线起晕电压随着分裂间距的增大而降低,随着导线分裂数的增加而升高;绞线表面粗糙系数与绞线最外层铝线半径与绞线半径之比相关。     

DC corona discharge of a metal filament particle withinparallel-plate electrodes

For the prevention of a particle-initiated breakdown within gas-insulated switchgear, fundamental characteristics of particle motion were investigated. It was found that the particle motion depends not only on Coulombic force, but on the corona discharge from the tip of a particle. Thus, the corona current from a fixed particle on the lower electrode was measured, for either positive or negative corona case. The measured current showed different characteristics of current depending on the polarity. The corona onset voltage of negative corona is somewhat lower than positive, but the breakdown voltage of negative corona is much higher. Although the current characteristics follow the square law, the applicable region of this law for positive corona is very small. Positive corona depends on the tip configuration contrary to negative corona     

Experimental studies of free conducting wire particle behavior between nonparallel plane electrodes with AC voltages in air

When a spherical conducting particle exists in an electrode system where electrical gradient force acts along the electrode surface, the particle tends to move towards the high field region. The possibility of appearance of this phenomenon is experimentally investigated with wire particles, which can easily produce the corona discharge on their ends resulting the action of a reactive force on the particle by a corona wind. The results show that a hovering particle travels deeper into the high electric field regions regardless of the corona discharge. Moreover, it is found that wire particle with corona discharge hovers near the negative electrode under DC voltage in atmospheric air due to different characteristics of corona discharge by the polarity. But under the AC voltage, the particle hovers near the bottom electrode only and invades in the high field region deeper than under the DC voltage.     

导线全面工频起晕电压测量新方法

电晕放电会带来诸多危害,起始电晕电压的测量对于改进电气设备绝缘结构,提高起晕电压具有重要的意义,为此提出了一种测量导线起始电晕电压的新方法,即在导线附近安装非接触式电压传感器。导线发生电晕放电时电极表面出现的电离层改变了传感器分压比,因此利用分压比导数最大值可确定起始电晕电压。在介绍传感器测量的基本原理并通过工频试验验证传感器的测量精度后根据电晕套理论设计工频起晕试验,借助光子数切线法进行了对比研究。结果表明传感器可以准确测量导线全面起晕电压值,且通过传感器分压比的变化可以描述工频电晕的伏库特性。该方法简单便捷,易于实现,适合进行电晕试验研究。     

静态模拟气固两相体起晕和击穿的实验研究

研究了非均匀电场中的静态模拟气固两相体放电的击穿、起晕特性及固相物介电常数、占空比、放电间隙、电压极性和种类对击穿电压与起晕电压的影响。结果表明:实验范围内,正极性大占空比时,随放电间隙的增加,两相体的起晕电压逐渐低于空气的起晕电压。正极性和交流电压下,两相体的击穿电压比空气高。     

Corona onset as a design optimization criterion for high voltagehardware

Hardware for use on HV systems is designed to be corona free. Recent hardware design activity has been centered around attempts to increase the corona onset voltage by optimizing the electric field distribution on its surface. Corona onset, however, is not only a function of the surface electric field, but also its rate of decay away from the surface, and the temperature and pressure of the gas in which it is immersed. While corona onset is a better criterion, formulas for predicting it have been validated only for simple geometries. The first goal of this work, then, is to validate corona onset conditions for more practical electrode geometries. The second goal is to determine whether the use of corona onset rather than surface electric field as an optimization criterion can result in hardware with a measurably higher corona onset voltage. To test this idea, two electrodes were designed, one using electric field optimization and the second using corona onset optimization. The corona onset voltage of each electrode was then measured and the results compared with predicted values. It was found that the measured results compared favorably with the predicted values and that the use of corona onset optimization can result in a modest but measurable increase in corona onset voltage     

特高压双回直流架空线路电晕起始电压的计算分析

为研究特高压双回直流架空线路的电晕起始特性,本文考虑线路排列方式和绞线的实际结构,结合气体放电理论建立了特高压双回直流线路的起晕电压计算模型。根据正负极起晕的不同机理,在利用优化模拟电荷法对绞线表面空间电场求解的基础上,计算了各极子导线的起晕电压。分析并讨论了导线布置、温度与气压及绞线参数等因素对起晕电压的影响。计算结果表明：-+/-+排列方式时线路起晕电压值较高。另外,导线半径的增大、气压的升高、分裂数的增加都能显著提高起晕电压。导线对地高度、极间距、上下层导线高度及分裂间距也都会不同程度影响起晕电压。绞线绞入率逼近于0时,绞线起晕电压接近光滑导线的起晕电压。     

Calculation of corona onset voltage for duct-type precipitators

A pure theoretical method for calculating the onset voltage of corona in duct-type electrostatic precipitators that is independent of the arrangement of discharge wires relative to the collecting plates is described. This method is based on a criterion for self-recurring single electron avalanches in a known electric field distribution in the ionization zone surrounding the discharge wire. The results computed by this method are in reasonable agreement with those measured experimentally     

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.     

EHD喷雾电晕放电现象研究

通过水滴在电流波形中形成的明显规律性波谷来研究水滴在直流电场作用下的快慢情况、雾化场强和放电电流等 ,并对正负极性作了比较 ,研究了电水力喷雾的电晕阵列放电     

Mathematical?Physical Model of Corona from Surges on High-Voltage Lines

A mathematical-physical model of corona current pulses from voltage surges on HV lines is presented. Distributed representation of corona along infinitely long transmission lines is suggested. The surge corona current pulse flows through the transmission line as a series of successive generations of electron avalanches, which develop in the ionization zone around the HV conductor. The initiatory electrons for triggering the current pulse under a positive applied surge are those available in the atmosphere surrounding the HV conductor. The two corona current components, the image component due to the presence of charge carriers (electrons and ions), and the convection component due to the motion of charge carriers in the interelectrode spacing were calculated. The calculated corona current pulse and the charge flow voltage curve agreed reasonably with those measured experimentally for a coaxial transmission line.     

基于紫外成像技术的极不均匀电场电晕放电

为监测电气设备外绝缘缺陷、灵敏观察和准确定位电晕放电,以紫外光谱特征量为量化电晕放电强度的表征参数,以相同工频电压等级下的放电水平和电晕脉冲电流峰值作为量化比较参数,在基本相同的大气条件下,利用紫外成像技术试验研究了极不均匀电场工频电压下电晕放电。结果表明,电晕放电强度量化表征参数与量化比较参数之间的对应关系很好;表征参数可反映电晕放电的几个阶段;结合紫外成像反映的放电形态,可分辨电晕放电过程的各阶段,且紫外光谱特征量在电晕放电过程各阶段的分布具有一定的统计规律。最后提出选取流注放电阶段的紫外光谱特征量交集作为空气间隙击穿的注意范围判据。     

直流电晕电流时域脉冲特性的统计分析

为了研究直流正负电晕电流时域脉冲的特性,基于实验室开发的高频电晕电流高压端测量系统,开展了不同条件下直流正负电晕的线板放电实验。基于大量实验数据,统计、对比了正、负极性电晕脉冲的幅值、上升时间、半波时间和重复频率等特征参数随导线电压及导线半径变化的规律。实验结果表明：导线电压对单个正、负脉冲波形的影响较小,主要影响脉冲的重复频率;负脉冲的上升时间平均值为20~30 ns,半波时间的平均值为90~110 ns;正脉冲的上升时间平均值为40~50 ns,半波时间的平均值为140~160 ns;随着导线电压的升高,正、负脉冲重复频率均迅速增大,但相同电压下,正脉冲的重复频率显著小于负脉冲的重复频率,负脉冲重复频率约为正脉冲的15~25倍。