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.     

Conducting particle motion and particle-initiated breakdown in dcelectric field between diverging conducting plates in atmospheric air

This paper deals with the analysis of spherical conducting particle motion as well as particle initiated breakdown in electric fields between diverging conducting plates with dc voltage in atmospheric air. Motion of spherical particle was estimated by solving the motion equation numerically, and the results agreed well with the experimental ones. It was found that when the particle is placed on the horizontal electrode surface where the electric field is nearly equal to the lifting field, the particle progresses towards a higher electric field region by the effect of Coulomb force and electrical gradient force. This is true for a nonspherical conducting particle. The obtained results for particle motion suggest that much attention should be paid in the design of GIS particle traps to forces acting on the particle directly towards the higher electric field region. Moreover, the particle-initiated breakdown is discussed on the basis of the experimental and theoretical results. It was found that one of the reasons for reduction of the breakdown voltage is the effect of microdischarge between the particle and an oppositely charged electrode     

Modeling of conductive particle behavior in insulating fluidsaffected by DC electric fields

Several electrostatic technologies, such as separation of granular mixtures, flocking, printing, or biological cell manipulation, are based on the accurate control of conductive particle motion in insulating gases or liquids by means of relatively high DC electric fields. This paper is aimed at characterizing the behavior of such particles by numerical modeling of two aspects: (1) particle motion under the action of electric field forces and (2) insulation breakdown triggered by mobile particles. The equations of particle motion were written by taking into account both gravitational and drag forces, as well as the rebound at particle impact with the electrodes. If the particles move in ionized air, their charge varies in time. In that case, the equation of particle charge should be added to the mathematical model. The output data of the programs for numerical simulation of particle behavior are in good agreement with the available experimental results. Particle movements were shown to be influenced by the intensity of the electric field, by the density of the space charge, by size and mass density of the particles, as well as by their coefficient of restitution at impact with the electrodes. The conclusions regarding the behavior of conductive particles in insulating fluids are useful for the development of improved electrostatic separation technologies; they are of particular interest to all manufacturers of high-voltage equipment     

导电复合材料双极板制备中的颗粒级配研究

通过导电复合材料采用模压法制作燃料电池用双极板是最有前途的一个研究方向,关键问题是双极板的电导率和力学强度必须同时满足使用要求,根据单一粒径颗粒堆积、双级配颗粒堆积和多元级配颗粒堆积的基本理论和计算结果,得到了通过颗粒级配提高导电复合材料电导率的方法,在使用较少的导电填料时,合理的颗粒级配有利于电导率的提高。     

发电机通风系统流场及转子温度场分析

针对电机温度场与通风系统流场间的耦合问题,依据流体力学和热传导理论,建立了某电站700kW灯泡贯流式水轮发电机的通风系统流场及转子温度场的三维有限元模型.采用有限元分析方法,分析了通风系统的流场,获得了通风系统压降和流体流速的分布,进而得到各表面的散热系数,并结合电机各部分损耗热源的计算,分析了发电机的转子温度场分布.结果表明:在满足风机流量下的电机通风压降为464 Pa,与实际运行时的实测数据483 Pa基本吻合;转子温度在其设计的绝缘容许温度范围内,且有足够裕度.     

旋转圆盘涡动过程中的流体力矩试验

本试验模拟了混流式水轮机转轮上冠在不均匀径向间隙情况下产生涡动时所受的流体力矩.通过模型实验和数值模拟研究了混流式水轮机涡动过程中作用在其上冠的转动流体力矩的基本特性.模型实验中水轮机转轮用一个圆盘来模拟,其上冠与外壳之间形成一个很小的轴向间隙.用圆盘圆周和外壳之间的径向间隙来模拟实际水轮机中的密封.内向流由外部水泵供...     

Distribution of electric field strength around a large-scalecharged particle cloud

To investigate an electrical discharge occurring from or in a space-charge cloud, a large-scale charged particle cloud was formed by using a cloud generator consisting of a blower and corona charger. The distribution of the electric field strength around a charged particle cloud has been investigated to determine the behavior of charged particles. The soil-conditioning particles were charged by corona charging and blown by high-speed air flow in a test room, 5 m wide, 10 m long, and 3 m high. The average charge-to-mass ratio of the particles blown by this method was 170 μC/kg. The space-charge density of the cloud was calculated at the order of 10 μC/m³ from the electric field strength outside of the cloud. While the electric field strength at the outside of the cloud increased up to 52 kV/m within 2 m downstream from the cloud generator, it decreased below 25 kV/m farther than 2 m away from the cloud generator due to dispersion of charged particles. The change in the electric field strength due to dispersion of charged particles can be qualitatively explained by a simple cloud model. The velocity of charged particles transported by air flow and mobility of charged particles are found to be effective factors increasing the electric field strength around the large-scale charged particle cloud     

非均匀磁场中磁流变液剪切应力实验与分析

为探究磁流变器件失效机理,用两块C型电磁铁耦合建立非均匀磁场。基于提拉法原理设计磁流变液剪切应力测量装置,得到非均匀磁场中剪切应力曲线。对比基于静态匀强磁场的圆筒剪切模型剪切应力理论曲线,发现虽然两者整体趋势一致,但同等磁场强度下两者剪切应力值存在不同程度差异,同时发现电磁铁气隙磁场也存在非均匀性。上述结论说明静态匀强磁场磁流变液剪切特性理论并不能直接应用到非均匀磁场剪切应力计算中,可能的原因包括铁磁颗粒体积分数的分布不均等,需要后续探索。     

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.     

兆瓦级风力发电机在极限工况下流体场与温度场数值分析

针对风力发电机在恶劣环境下温度升高、严重影响电机安全运行和使用寿命问题,笔者以1台在高海拔地区运行的水冷双馈风力发电机为研究对象,研究了其在极限工况下流体流动和电机传热特性。依据流体流动和电机传热特点,在基本假设条件下建立发电机求解域模型,根据风力发电机所处的特殊环境和运行状况对求解域边界进行设置。借助于CFD技术对发电机内三维流体场和温度场进行耦合求解,得出了电机内流体流动特性和温升分布规律。该规律可为使用在高海拔地区的发电机设计和安全运行提供指导建议。     

Electric field and space charge of spherical electrode at highvoltage concentric with a grounded conductive sphere

The solution of the space-charge Poisson's equation is presented for a spherical electrode at high voltage concentric with a grounded conductive sphere. The obtained electric field is given in terms of the ion current emitted by the electrode and an integration constant. Both parameters are functions of boundary conditions. Using measured values of the ion current for a range of boundary conditions and applying these boundary conditions to determine the integration constant suggest a minimum value for the ion mobility of 1.9×10^-4 m² /V.s. Approximate formulas for the ion current and the electric field in terms of the independent parameters were also developed. Also, it was shown that this spherical system with its solution can be used to make accurate evaluation of the ion mobility. The obtained solutions can be applied with good approximation to many practical electrostatic systems involving point electrode at high voltage generating ions. Although the subject matter is very general and could have a fundamental research aspect, in this paper, it is meant to be applied to the area of electrostatic powder paint coating. Therefore, all the examples of boundary conditions and illustrations are typical of the electrostatic powder paint coating     

Electric field effect on metallic particle contamination in a common enclosure gas insulated busduct

Sulphur hexaflouride (SF₆) is generally found to be very sensitive to field perturbations such as those caused by conductor surface imperfections and by conducting particle contaminants. A study of CIGRE group suggests that 20% of failures in gas insulated substations (GIS) is due to the existence of various metallic contaminations in the form of loose particles. The presence of contamination can therefore be a problem with gas-insulated substations operating at high fields. If the effects of these particles could be eliminated, then this would improve the reliability of compressed gas insulated substation. It would also offer the possibility of operating at higher fields to affect a potential reduction in the GIS size with subsequent savings in the cost of manufacture and installation. The purpose of this paper is to develop techniques, which will formulate the basic equations that will govern the movement of metallic particles like aluminum and copper in a bus duct. The simulation considers the electric field effect on particle movement and the results have been presented and analyzed     

静水中抛泥所形成的泥沙云团运动特征试验研究

本文在试验中运用成像分析方法,研究在静水中抛泥所形成的泥沙云团的运动。根据泥沙云团的运动触底前后,分扩散沉降和水平异重流扩展两个阶段分别进行分析。通过泥沙云团的面积、相对特征扩散度、前锋扩展速度、平均浓度等特征要素来分析扩散沉降阶段;通过泥沙云团的面积、前锋移动速度及沉积分布等特征要素来分析底面水平异重流扩展阶段。     

运动物体的时空光场渲染

本文将配准技术与插值算法相结合,通过对场景中运动物体的时间帧配准、时间域和空间域的插值,生成了任意时刻、任意视点处的渲染罔像,完成对运动物体时空域的光场渲染。该研究结合并推广了传统光场渲染方法,放宽了对场景的要求。和现有的方法相比,该方法适应性强、鲁棒性好。实验结果进一步体现了该方法较好的应用前景与可操作性。     

大型油浸式风冷变压器绕组温度场及流场分析

阐述了油浸式风冷变压器绕组的热源和冷却结构,采用热-流耦合方法建立了温度场和绝缘油流场的有限元模型,通过fluent软件对1台180 MVA油浸风冷变压器进行计算,得到了绕组稳态温度分布及油流分布,并分析了挡油板位置及数量对绕组温度场及油流分布的影响.计算结果表明,在绕组辐向加油道和加挡油板均会起到较好的散热效果,在端部设置较少的挡油板会比沿绕组轴向均匀设置挡油板散热效果好.