GIS中不均匀直流电场下球状自由导电微粒运动分析

针对气体绝缘系统(GIS)中自由导电微粒无害化的问题,研究导电微粒在GIS中不均匀电场作用下的运动规律,建立球状自由导电微粒在楔形不均匀电极系统中的受力模型,采用Runge-Kutta方法对微粒运动方程进行求解,并对球状自由导电微粒在不均匀直流电场中的运动轨迹进行仿真,同时考虑电压波动和电极表面粗糙等随机因素对微粒运动轨迹的影响。另外,研究了自由导电微粒的运动轨迹与施加电压、微粒初始位置、微粒和电极材料的性质及电极表面状况的关系。研究结果表明:在一定的电场条件下,微粒运动会处于一种谐振状态,而施加电压的幅值、波形以及电极表面的反射系数对微粒运动轨迹有显著影响     

Charging and behavior of a spherically conducting particle on a dielectrically coated electrode in the presence of electrical gradient force in atmospheric air

This paper discusses the charging and behavior of a spherically conducting particle on a dielectrically coated electrode in non-uniform dc and ac electric fields between non-parallel plane electrodes in atmospheric air. The charging mechanism of a particle resting on a dielectrically coated electrode is investigated by observing light emissions from partial discharges and by utilizing the dust figure technique. The charge acquired by a particle is estimated from the results of particle motion onset voltage measurement and direct measurement with a Faraday cage. The basic particle movement as well as particle-triggered breakdown characteristics under non-uniform electric field distribution along the electrode surface is also investigated. The results suggest that the effect of the electrical gradient force/dielectro-phoretic force on particle motion on a dielectrically coated electrode should be adequately considered in the design of gas insulated systems (GIS). This is because a particle can move laterally on the coated electrode toward increasing electric field regions by the action of the electrical gradient force which is independent of the charge on the particle. Also the possibility of the particle charging and lifting at high field regions or reaching and adhering onto an insulating spacer further increases the risk of breakdown.     

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.     

交流电压下绝缘子附近导电微粒运动特性

在施加交流电压条件下,对楔形布置的电极间聚四氟乙烯(PTFE)绝缘子附近自由导电微粒运动进行了实验观察.通过对微粒运动过程进行摄像和记录微粒起始运动电压,讨论球形导电微粒和线形导电微粒的运动特性.对不同外形绝缘子附近导电微粒运动规律进行了分析,认为绝缘子的存在能够降低微粒运动起始电压,并且能够吸引部分球形导电微粒沿电极表面滚动到达绝缘子表面;当绝缘子表面与接地电极夹角为锐角时绝缘子附近的微粒运动起始电压会显著降低.对绝缘子存在情况下的楔形电极间电场进行计算,并对微粒运动规律做出了合理的解释.     

Electrical breakdown triggered by a free conducting spherical particle in saturated liquid He I and He II under uniform dc field

This paper is concerned with the pre-breakdown phenomena and the breakdown voltage characteristics, in the presence of a free moving conducting spherical particle, of saturated normal liquid helium (He I) and saturated superfluid liquid helium (He II) under uniform dc field. Experiments show that the particle lifts off around the theoretical value of the lift-off electric field, and the particle oscillates between the electrodes at higher applied voltages. In that case, the microdischarge appears just before the charged particle collides with the oppositely charged electrode, and the bubble is generated at the moment of every collision of the particle with the electrode. It is confirmed theoretically as well as experimentally that the maximum bubble radius in He II is nearly proportional to the E/sub in//sup 1/3/, which is the released energy from the particle for the bubble generation. The insulation environment before the electrical breakdown suddenly changes at the /spl lambda/-point since the bubble behavior in He I and He II greatly differs. In the characteristics of the breakdown voltage vs. liquid pressure, a clear discontinuity appears at the /spl lambda/-point. Furthermore, the breakdown voltage in the parallel plane gap contaminated by a particle is lower than that in the rod-plane gap without a particle. It is found that the breakdown voltage characteristics are closely related to the trigger effect of the microdischarge and the bubble generation.     

Theoretical and experimental studies for spherical free-conducting particle behavior between nonparallel plane electrodes with AC voltages in air

This paper deals with free-conducting particle motion and particle-triggered breakdown in AC electric fields between nonparallel plane electrodes in atmospheric air. Spherical particle motion was investigated theoretically and experimentally under AC voltages with various frequencies, considering the effect of the electrical gradient force and the dependence of the Coulomb force magnitude on the distance between a particle and an electrode. The result shows that when the Coulomb force acting on a bouncing particle changes its direction periodically under AC voltage whose frequency is around commercial power frequency, the electrical gradient force can become effective in initiating particle motion toward decreasing electrode gap regions, causing the particle to trigger breakdown. Moreover, it was found that the direction in which a particle advances horizontally is greatly influenced by microdischarge occurrence when the particle bounces very near to the grounded electrode under high-frequency AC voltage, and that when a particle bounces on an electrode, particle-triggered breakdown voltage is decreased by the effect of microdischarge.     

Motion behavior and deactivation method of free-conducting particle around spacer between diverging conducting plates under DC voltage in atmospheric air

This paper deals with free conducting particle motion around different shaped spacers between diverging conducting plates under DC voltage in atmospheric air. Spherical particle motion was observed experimentally and the results were discussed on the basis of the electrostatic force acting on the particle with and without spacer. The results show that a particle around a spacer tends to move laterally towards or away from the spacer towards higher field regions, depending on the spacer configuration. It lifts at higher field positions and sometimes adheres to the spacer. The effects of spacer angle and spacer material (permittivity) on free conducting particle motion are also discussed. For comparing the results obtained with a sphere, a wire particle motion around different shaped spacers is also investigated. The obtained results suggest one of the methods to prevent/suppress the conducting particle from approaching or adhering to spacers, is to reduce the field strength in the vicinity of the triple junction of gas, solid dielectric and electrode in gas insulated system (GIS).     

Dynamic motion of a conductive particle in viscous fluid under DCelectric field

When plastic waste is liquefied for recycling, the impurities present could influence the quality of the reprocessed products. In order to explore the possible method for removing solid impurities using electrostatic forces, the motion of spherical conductive particles under a uniform electric field has been carefully investigated. In this paper, a solid impurity and liquefied plastics are simulated by a conductive spherical particle and viscous insulating liquid, silicone oil, respectively. Experimental results indicate that the particle undergoes repeated motion between the parallel electrodes. The motion of the particle can be divided into four modes: settling on the lower electrode, moving upward, settling on the upper electrode, and moving downward. The higher the applied voltage, the faster the average particle velocity and the shorter the resting time of the particle. The particle accelerates after leaving the electrode and decelerates before reaching the other electrode. This deceleration could be explained by the viscous effect of the liquid layer between the particle and the electrode. The settling mode could be explained by the fact that there is a liquid flow induced by the particle motion and it pushes the particle against the electrode until the flow decreases. It is, therefore, suggested that the hydrodynamic effect is dominant in our case, as well as the electrostatic force     

稍不均匀电场中绝缘子附近导电微粒受力分析

建立稍不均匀电场中绝缘子附近的自由导电微粒所受作用力的2-D计算模型,通过对微粒表面Maxwell应力张量进行计算,得到微粒在电场中所受的静电力。改变电极倾斜角、绝缘子材料以及绝缘子的外形,对影响自由导电微粒运动的因素进行了分析,结果显示通过减小高压电极倾斜角度,减小绝缘子材料的介电常数,并采取合适的绝缘子外形, 可减小微粒受到的向上的静电力和微粒受到的指向绝缘子方向的水平静电力,从而可以减小微粒浮起和附着于绝缘子表面的概率。     

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     

DC breakdown voltage characteristics of saturated liquid helium in the presence of metallic particles

This paper deals with the breakdown voltage characteristics of saturated liquid helium in the presence of a needle-shaped or spherical metallic particle to obtain insulation design data for pool-cooled, low-temperature superconducting coils and to find the predominant factor affecting the breakdown voltage of liquid helium at a given state. The results show the following. (1) The generation of bubbles at the instant of collision of a particle with an electrode is caused mainly by the kinetic energy released from the moving particle to the liquid helium, while the electrostatic energy accompanying the microdischarge between the particle and the electrode has a lesser effect on it. (2) The lowest breakdown voltage at different particle conditions appears in the case of a free needle particle. The low breakdown voltage is caused by the bubble triggered by the particle collision, the high electric field at the tip of the needle particle, and the rich initial electrons supplied by the microdischarge.     

Proposal for new particle deactivation methods in GIS

This paper deals with consideration of particle motion control and its trapping in the deactivation of foreign contaminating moving particle in simulated GIS. The particle motion behavior in nonuniform field gap without/with different shaped spacers was investigated experimentally under DC and 60 Hz AC voltages. The obtained results were confirmed experimentally as well as by calculating the electrostatic force acting on the particle in the nonuniform field gap and are reported elsewhere. Whereas, in this paper, the observed particle motion behavior around simple shaped spacer is simulated by solving the particle motion equations analytically in the presence of electrical gradient and image forces. The simulation agreed fairly well with the experimental results. Furthermore, in the nonuniform electric field, the effect of dielectric coating on the grounded electrode on the particle motion and particle deactivation is also briefly discussed. On the basis of the obtained results of particle motion behavior without/with different shaped spacers and the effect of dielectric coating on the ground electrode, different methods of particle deactivation are suggested as well as confirmed experimentally     

交流电压下预埋电极对绝缘子附近导电微粒运动的影响

为防止自由导电微粒浮起或附着于绝缘子表面而引起绝缘闪络故障,该文建立楔形平板电极系统来模拟SF6气体绝缘系统中可能出现的不均匀电场,实验研究交流电压下预埋电极对微粒的驱散作用,包括对微粒运动轨迹与起始运动电压的观测。通过有限元法进行电场计算,对自由导电微粒的受力情况进行分析,理论验证了实验结果。结果表明,对于表面与接地电极表面夹角呈锐角或直角的绝缘子,无论其表面带棱与否,预埋电极可防止自由导电微粒附着于其表面,同时能够提高绝缘子附近微粒浮起所需的电压,对微粒浮起有抑制作用。     

直流电压下SF_6气体中电极覆膜对金属微粒启举的影响机理

为研究直流电场下SF_6气体中低压电极覆膜对金属微粒启举的影响机理,搭建了实验平台并使用高速摄像机记录运动轨迹。实验结果表明,随着SF_6气体压力的增大,微粒启举场强升高,且启举后到达高压电极的时间缩短。基于图像处理获得了微粒的瞬时位移,结合运动力学方程和最小二乘法提出了启举时电荷量的计算方法,微粒电荷量的计算分析表明启举时的电荷量减小。建立了覆膜后金属微粒周围电场分布的理论模型,电场分析表明金属微粒与薄膜间的电场明显增大及表面电荷密度分布的改变,使得金属微粒受到向下的极化作用力。研究认为:电荷量减小和极化作用力向下综合导致金属微粒的启举场强提高;覆膜后局部放电是金属微粒的带电机理;SF_6气体压力增大使得金属微粒发生局部放电的起始场强升高,导致极化作用力增大,需要更高场强发生启举。     

DC pre-breakdown phenomena and breakdown characteristics in thepresence of conducting particles in liquid nitrogen

DC pre-breakdown phenomena and breakdown characteristics in the presence of free conducting particles in liquid nitrogen are studied experimentally. The results show that a microdischarge occurs when a charged particle is approaching an oppositely charged electrode. An intense microdischarge can trigger a complete breakdown of the gap. The breakdown voltage of a uniform field gap with a free metallic particle of mm size might be reduced well below that of a point-to-plane gap without a particle in liquid nitrogen. Heavy contamination by a metallic powder produces a large reduction in the breakdown voltage with a horizontal spacer surface. However carbon powder is less hazardous compared to metallic powder     

Electrode conditioning characteristics in vacuum under impulse voltage application in nonuniform electric field

In this paper, we quantitatively investigated the impulse conditioning mechanism under nonuniform electric field electrodes in a vacuum. A negative standard lightning impulse voltage was applied between rod and plane electrodes whose materials were Cu-Cr, stainless steel and Cu and the gap lengths were d=5 and 10 mm, respectively. Experimental results revealed the transition of the breakdown (BD) sport region on the rod electrode and the corresponding BD field strength in the conditioning process. As a result, we found that the BD spot region started at the tip of the rod electrode and moved to the wider region of the rod electrode with lower electric field as the shots of the voltage application increased before the saturation of the BD voltage. Finally, by analyzing the results with an electric field strength, we propose that "the conditioning degree" along the electrode surface distributed directly proportional to the electric field distribution under a nonuniform electric field in a vacuum, irrespective of the electrode materials     

变压器油中导电颗粒运动轨迹的计算

给出了计算变压器油中导电颗粒运动的理论模型。模型表明电场力、惯性力、粘滞阻力、颗粒密度是影响油中导电颗粒运动的重要因素。通过计算变压器油中导电颗粒在球板电极油隙中交流电压下的运动轨迹,得出大颗粒与小颗粒运动的不同特点,并根据计算结果探讨了导电颗粒对变压器油电气性能的影响,指出变压器油中导电颗粒是导致变压器油电气性能下降的一个重要因素。     

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.     

Dynamic analysis of motion of spherical metallic particles in non-uniform electric field

This paper presents a theoretical analysis of the dynamics of motion of spherical metallic particles under non-uniform fields for direct-current gas-insulated switchgear (dc GIS) and for electrostatic separators/sizers (ESS). The particle equations of motion between a pair of diverging conducting plates are numerically solved in three dimensions using a computational algorithm. The upper plate is energized by HV dc or HV ac of variable frequency, while the lower one is grounded. In the case of ESS, the lower electrode is also mounted horizontally on a vibratory conveyor. The results reveal that the particle exhibits several phenomena during motion depending on its initial position, radius and density, angle between the diverging plates, tilt angle of the electrode system, and frequency and amplitude of the applied voltage. The influence of vibratory-conveyor variables on the separation/sizing process is studied in the light of the particle trajectory in the third dimension. Moreover, the results are interpreted using dimensional analysis. The use of HV ac causes the separation/sizing process to be imprecise; the higher the applied-voltage frequency and the larger the particle radius, the higher is the risk of breakdown. Depending on the tilt angle and orientation of the earthed electrode relative to the divergent angle between the electrodes, particle trapping can be helped or hindered. Therefore, several factors should be taken into consideration in the design and installation of the particle drivers and traps in GIS. Finally, the effects of dielectric coating on the electrode and of gas pressure on the particle trajectory are also studied.     

Deterioration characteristics of insulating spacer model in repeating impulse voltage

To discuss the UHV GIS test voltage, the deterioration characteristics of the GIS insulating spacer model were studied by repeating lightning or switching impulse voltage. The deterioration factor indicating the decrease of lightning or switching impulse breakdown voltage applied up to 1000 times was found to be 35.7/45.5. The relationship between the partial discharge inception voltage and the breakdown voltage after 1000 impulse applications was also studied. It was found that the partial discharge inception voltage increases despite a decrease in breakdown voltage due to the impulse voltage. In addition, to elucidate the deterioration phenomenon, a study was made of the breakdown characteristics of models with various boundary conditions between the electrode and epoxy resin, as well as the relationship between the boundary conditions. Microdischarge was also studied. The results of the investigation suggest that the deterioration by repeating voltage is caused by microdischarge due to electric field intensification on microprotrusions of the electrode surface.