表面电荷积聚对冲击电压下绝缘子沿面放电的影响

绝缘子的表面缺陷会导致表面电荷积聚，使绝缘子表面的电场发生畸变，影响冲击电压下绝缘子的沿面放电。研究了表面电荷对绝缘子沿面放电进程的影响，发现表面电荷积聚可以降低绝缘子沿面放电的起始电压。外施冲击电压的极性与绝缘子表面电荷极性是否相同会影响绝缘子的电晕起始时刻、由流注向先导的转变时间间隔和流注电晕电流。表面电荷对GIS支撑绝缘子的50％冲击闪络电压和伏秒特性也有一定的影响。     

常压介质阻挡放电平均放电电流的实验研究

为了优化介质阻挡放电(DBD)发生器设计,提高放电效率,实验研究了介质阻挡放电装置的平均放电电流特性,包括用Q-U李萨如图形测量法研究了激励电源特性和发生器结构参数对平均放电电流的影响。实验结果表明:采用高频电源、薄介质和小放电间隙可得到均匀放电;在DBD发生器结构和工作气体属性固定的情况下,提高激励电压幅值和激励频率可增大平均放电电流、提高放电强度;采用薄介质和减小放电气隙宽度都可提高放电强度,得到较大的平均放电电流。因此可以通过改变激励电源参数和放电装置结构有效地调节放电电流。     

Surface-discharge characteristics in a ferrite-cathode diode

The surface-discharge characteristics of a HV diode with a planar ferrite cathode are described. This experimental setup consists of a constant HV power supply, a polarity inversion line pulser with a 200 m coaxial cable, a turbomolecular pump and a discharge chamber. The chamber was of a diode type which was evacuated by a turbomolecular pump with a pressure of 13.3×10^-3 Pa and was composed of a tungsten disk anode, a planar ferrite cathode, and a polymethylmethacrylate tube body. The cathode was set perpendicular to the anode plane, and the space between the anode and cathode electrodes had a value of 0.5 mm. The coaxial cable of the pulser was charged from 10 to 40 kV by the power supply, and the rectangular pulses with output voltages of -1× the charged voltage were produced with short rise times of ~20 ns. The effective duration of the pulse was determined by the cable length and had a value of ~1 μs. The process of the flashover investigated in this report consisted of two stages. In the first stage, because the discharge current flowed inside the cathode plate, the current was primarily regulated by the cathode impedance in proportion to the resistance. Next, the current substantially increased with corresponding growth of the surface discharge on the ferrite cathode. The duration of the initial current increased with the thickness of the cathode and the diameter of the contact electrode. In the present work, the maximum current was determined by the characteristic impedance of the pulser cable since the discharge impedance in the diode substantially decreased during the surface discharge     

Influence of insulating barrier on the creepage discharge intransformer oil

The propagation aspects of a creepage discharge in transformer oil are observed simultaneously and in detail under a positive impulse voltage condition, by means of a high-speed Schlieren optical system, an LED current measurement system and a charge measurement system using a capacitor. In the present paper, the influence of the material type and the thickness of insulating barriers on the propagation of the impulse creepage discharge are discussed for a point to plane electrode geometry. In addition, the influence of a barrier surface to the electric field direction on the propagation of the impulse creepage discharge is discussed for a parallel plane electrode gap with a protruding point     

Effect of lightning impulse prestress on AC partial discharge characteristics in cast resin transformer

It is crucial for cast resin transformer to detect void and delamination existing in the cast resin because these defects reduce insulation performance of cast resin equipment. Furthermore, defects are likely to be mixed in cast resin because of several surface boundaries between resin and conductor. It is considered that detecting partial discharge (PD) is effective to diagnose equipment of power equipment. However, it is reported that withstand lightning impulse voltage test may give influence on AC partial discharge test, especially partial discharge inception voltage. This paper deals with accumulated charge in a void under AC voltage to investigate the effect of the impulse voltage prestress on subsequent AC PD characteristics in cast resin transformer. AC PD characteristics were compared before and after impulse application. In addition, recovery of PD characteristics was measured to investigate charge decay. As a result, the mechanism of prestress effect is revealed and surface charge density is estimated quantitatively in cast resin transformer.     

Propagation velocity and photoemission intensity of a localdischarge on an electrolytic surface

An electrolytic solution surface was used to simulate the surface of wet polluted insulators. A local discharge propagates on the solution surface when an impulse voltage is applied to the surface. The intensity of photoemission from the tip of the local discharge, the propagation velocity of the local discharge, and the discharge current were measured simultaneously. It was found that the propagation velocity increases with the photoemission intensity and the resistivity of the solution, and the influence of the air pressure and the applied voltage waveform on the velocity is very small. Furthermore, it was deduced that the ratio of the current through the local discharge tip to the total discharge current is not influenced by the local discharge length and the applied voltage waveform     

正弦激励的大气压空气放电过程和作用机制

为了从机理上研究大气压介质阻挡表面放电,采用数值方法模拟了正弦激励下的放电过程,得到了随时间变化的电子浓度、离子浓度、电场、电极电流以及体积力,分析了放电电流特征,发现等离子体放电起动时的伪辉光-辉光-丝状放电模式转换过程,电子雪崩不对称-电场不对称-体积力不对称是正弦激励产生单向体积力的机理,"推-拉"机制为等离子体流动控制的作用机制,而负半周期诱导速度更大的原因在于粒子惯性延迟。最后,提出了一个初步的电势优化波形。     

Light emission in PE with a needle-like microvoid at themetal-polymer interface under impulse voltages

Light emission from polyethylene with a needle-like microvoid has been investigated under the application of a negative impulse voltage in order to examine the temporal behavior of discharge in the microvoid at the metal-polymer interface. The light emission was observed distinctly during the voltage rise and fall phases with a period of no light emission between the two light emitting phases. The emitted light consisted of sequential light pulses which appeared regularly, according to the temporal variation rate of the voltage. The sequential light pulses corresponded to the sequential discharge in the microvoid which occurred to keep the voltage across the microvoid below the discharge inception voltage. The characteristics of light emission revealed the occurrence of intermittent discharges in the microvoid during the voltage variation phase of the impulse voltage, caused by charge deposition on the polymer surface of the microvoid     

Influence of charged droplet cloud on flashover of air gaps for lightning impulse voltage

Transmission lines passing through a mountainous region often are struck by winter lightning. As a result, numerous double-circuit faults occur. Space charge might be responsible for this phenomena. Several investigations on flashover characteristics have been performed focusing on reduction of flashover voltage due to ionic space charge formed by corona discharge. In this paper, flashover characteristics of an air gap within a charged droplet cloud ejected from an airless nozzle using an induction charging method are discussed. The droplets are charged in the range -200 to 200 μC/kg, forming the space-charge density of approximately 13 μC/m³. The flashover voltage and the time lag to flashover were measured when 1.2 × 50 μs lightning impulse voltage applied to a rod-sphere gap is placed within the charged cloud. Flashover voltage for a positive rod increased markedly within a positive charged cloud by increasing the charge-to-mass ratio. The increase of flashover voltage was up to 80 percent in comparison with uncharged droplets. Flashover voltage for the negative rod decreased about 20 percent in the cloud of either polarity. The results show that the presence of charged droplets in the air gaps affects the discharge process significantly.     

交流与雷电冲击叠加电压下SF6气体中沿面局部放电测量与数值计算

由冲击过电压所引发的环氧绝缘沿面局部放电往往会造成严重的绝缘事故,威胁设备的运行安全。采用不同的测量方法对交流与雷电冲击叠加电压下SF6气体中环氧绝缘沿面局部放电进行测量。分析讨论冲击叠加相位和冲击电压极性对沿面局部放电激发过程的影响。基于试验结果的讨论分析和沿面局部放电基本物理过程,建立交流与冲击叠加电压下沿面局部放电激发过程的数学模型,对不同极性冲击叠加在交流电压不同相位后沿面局部放电的放电时延、放电量进行数值计算。同时,对放电所产生的沿面、空间电荷衰减过程进行定量分析,实现了电荷衰减过程中电荷记忆效应对沿面局部放电影响的量化描述。该研究结果为沿面局部放电过程的分析提供了一定的试验及理论依据。     

Flashover from surface charge distribution on alumina insulators invacuum

Surface charge distributions of disk type aluminas held between a backside electrode (alumina holder) and a needle electrode to be excited by an impulse voltage (rise time 64 μs, wave tail 700 μs) were measured. The measurement of surface charge distribution on the whole surface area of alumina YSA998 and UHA99 after impulse voltage application revealed that the surface charging can be initiated either from the anode or from the cathode triple junction. The charging initiated from the anode triple junction (for positive polarity) produced positive charge at the anode region and the density is dependent on the applied voltage, while the charging initiated from the cathode triple junction region (for negative polarity) produced negative charge around the cathode region. For positive polarity, the critical values of charge density to the flashover for alumina YSA998 and UHA98 are 5.70 and 17.2 μC/m², respectively     

螺旋针-环结构等离子体射流放电过程分析

为降低气体的击穿和维持电压,设计一种螺旋针-环电极结构的等离子体射流装置,研究不同电压下的放电电压、电流波形。研究表明,氦气等离子体射流放电可以分为电晕放电、介质阻挡放电和射流放电三个阶段,并且可以通过放电电压、电流波形的特征进行区分。分析可知,射流管管径较大时,采用螺旋针状内电极结构可以减小电极间的平均气体间隙距离,从而降低气体的击穿和维持电压,使放电更加容易进行;电压反向过程中残留电荷使得合成电场得到加强,气体将"提前"发生放电;由于电极结构的不对称,气体在正半周期更容易发生放电,放电产生的电流脉冲数目更多,电流值更大;随着外加电压增大至14k V,放电最终过渡到丝状放电状态。     

The influence of surface charge on lightning impulse breakdown ofspacers in SF6

We have investigated the influence of surface charges on the discharge development across particle contaminated spacer surfaces under SF₆ for lightning impulse (LI) voltages (1.2/50 μs). Surface charges may be generated by dc, ac or lightning impulse stress. The discharge characteristic shows a strong reduction of the insulation strength if the applied voltage and the surface charge have opposite polarities. The investigations were performed with a needle protrusion attached to the bottom electrode to give severe field distortion. The bottom electrode was biased positively. The influence on the discharge process is observed by measuring the surface charge distribution and predischarge currents. The results reveal changes in streamer onset voltage, streamer to leader transition, and leader development     

介质阻挡放电电参数计算软件设计及应用

介质阻挡放电是产生低温等离子体的一种重要方法,其应用近年来受到关注。笔者基于介质阻挡放电中经常测量的电压和电流,设计用于介质阻挡放电实验的人机界面,有利在不同的外电压波形、阻挡介质参数、间隙距离等条件下的大量实验数据的分析和计算,得到介质阻挡放电相关的气隙电压、电流及放电功率、电荷量等参数。最后利用交流和脉冲条件下介质阻挡放电的实验波形对其进行了测试。     

Barrier effect under nonuniform field in atmospheric pressure SF6 gas

Generally, it is known that insertion of a barrier under a nonuniform field in air increases the flashover voltage. This is called the barrier effect. However, there are many uncertainties that remain to be clarified about the barrier effect in SF₆ gas. Therefore, the influence of the barrier shapes and positions on the flashover voltage for the lightning impulse voltages and voltages (50 Hz) is examined by inserting a barrier between a hemispheric-end rod and a plate in SF₆ gas under near-atmospheric pressure. As a result, the following findings were obtained:. (1) Insertion of a disk-shaped barrier reduces the flashover voltage; a cup-shaped barrier whose surface curves almost along the equipotential line increased the flashover voltage by 30 to 40 percent;. (2) trapped charge on the barrier surface is of the same polarity as the applied voltage and the magnitude of positive charge was greater than that of negative charge. It was found also that there is a correlation between the amount of trapped charge and the flashover voltage; and. (3) application of a barrier under a nonuniform field in the atmospheric pressure SF₆ gas helps reduce the size of, for example, a cubic-type gas-insulated switchgear.     

正极性雷电冲击电压下天然酯绝缘油油纸沿面流注动态变化规律研究

油纸绝缘复合电介质沿面放电是电力设备内绝缘的研究基础,其在雷电冲击电压下的绝缘特性是变压器绝缘设计的重要参数之一。为了获得油纸沿面流注传播与消散过程中电学、空间电荷分布演化规律及其关联关系,以交界面平行于施加电场方向的油纸系统为研究对象,通过构建适用于绝缘油油纸沿面流注动态变化特性的试验观测系统,可同步获得正极性雷电冲击电压下流注传播和消散过程中的电压、放电电流和放电通道流注阴影图像。利用该平台还测量了油纸沿面正极性雷电冲击击穿电压。试验结果表明,在正极性雷电冲击电压下天然酯绝缘油油纸绝缘相对介电常数差异并不会促进油纸沿面流注的传播过程,而粘度对于油纸沿面流注侧向分支影响显著。粘度越低,空间电荷在迁移过程中所受到的阻力越小,流注头部空间电荷在受到表面电荷的斥力后越容易往油中扩散,空间电荷在绝缘油中所形成的空间电场使得油纸沿面流注的主分支能够在绝缘油中传播,增加了油纸沿面流注传播距离,从而使低粘度天然酯绝缘油油纸沿面正极性雷电冲击击穿电压略高于其纯油击穿电压。     

有关线路避雷器标准和参数设计中的几个问题

结合新制订的电力行业标准“交流输电线路用复合外套金属氧化物避雷器”（讨论稿）,对一些参数设计问题,如线路避雷器设计的基本要求,额定电压、直流1mA参考电压、方波冲击电流值、操作冲击通流能力、串联间隙的放电电压特性、串联间隙支撑绝缘子试验电压值的确定等,提出一些看法与建议,供有关部门特别是制订标准的部门参考和讨论,以期有利于该类新产品的推广使用和设计水平的提高。     

Self-controlled pre-breakdown discharges in planar symmetry

In measurements on Teflon FEP films charged in ⩽50 μm air gaps by microsecond impulse voltages, a uniform charge deposition on the films was observed. A regular increase of the film surface potential from a threshold value of the peak impulse voltage was found. However, for 300 μm air gap it was observed that abrupt charging occurs at a lower threshold voltage, indicating breakdown, and the charge deposition on the film becomes nonuniform. The behavior in air gaps <50 μm is explained here using Townsend's theory of pre-discharges. It is shown how and why the interposed insulating film acts to make the system self-controlled, thus avoiding breakdown in the air gap, despite the large values of the applied peak impulse voltage     

Creepage discharge propagation in air and SF6 gasinfluenced by surface charge on solid dielectrics

Influence of surface charging on creepage discharge propagation in air and SF₆ gas was investigated. The authors have employed a surface charging system using corona discharges, which permitted the deposition of surface charge on solid dielectrics with a given density distribution. By applying a lightning impulse across the charged surface of polyester film, they measured the discharge extension length as a function of surface potential generated by the surface charge. It was found that the impulse creepage discharges along the charged surface under a potential of 2 to 3 kV, extended a distance which was maximum 6× longer than the case of the uncharged surface both in air and SF₆ gas. Experimental results were also discussed from the viewpoint of the specific capacitance, permitting their application to actual HV apparatus such as GIS     

Insulator surface charge accumulation under impulse voltage

The surface charge distribution under impulse voltage is measured using a static capacitance probe. A probe with very small charge leakage is designed. The condition of surface charge accumulation under impulse voltage is analyzed, and it is concluded that micro discharges in the gas near the insulator surface such as the corona caused by free and fixed metal particles is usually a prerequisite condition. The dynamic equation describing the relationship between surface charge density and the applied voltage is established, and the process of surface charge accumulation under impulse voltage is analyzed. Theoretical analysis and experimental results show that the decrease of wave front time of the impulse voltage can result in an increase of surface charge accumulation. A GIS spacer is used to investigate the influence of charge accumulation on the flashover characteristics. It is shown that the 50% impulse flashover voltage can be reduced by 23.4%, and the lower limit of the V-t characteristics can be lowered drastically if the polarity of the surface charge is opposite to that of the applied voltage.