The effect of water treeing on the electric field distribution ofXLPE. Consequences for the dielectric strength

This paper describes the influence of water trees on dielectric properties of flat samples cut from a HV crosslinked polyethylene (XLPE) cable insulation. In order to obtain experimental results in a short period of time, we used accelerated aging conditions of voltage and frequency as well as different techniques for producing a multitude of artificial water tree inception points. The average value of the water tree permittivity and a law for the time-dependence of permittivity inside the treed degraded areas were deduced from measurements of capacitance and water tree lengths. On the basis of the experimental knowledge of permittivity and water tree length, we determined with analytical numerical methods, the distribution of the electric field for different shapes of treed regions. Because of the increase in length and permittivity of the water tree, the electric field in front of the degraded area is amplified, which is an important factor of risk leading to the electric breakdown     

The effect of porosity on the electric strength of heat-resistantconcrete

In many applications where both high temperature and high electrical stress exist, little is known about the interaction of the electrical and thermal properties of the materials involved. This paper is a study of this interaction for a material which we call a concrete, and is a fine alumina powder mixed with a cement, i.e. calcium aluminate (CaOAl₂O₃) slurry, which cures in the same manner as a concrete. The porosity of the product depends upon the relative volume of the hydrated cement to the volume of the spaces between the alumina particles, and the shapes of the pores may be changed by choosing the mix of various particle sizes of alumina particles. In this study, specimens of this material were cast between uniform field electrodes in one case, and between nonuniform field electrodes in the other, cured and dried to remove residual moisture, and tested for electric strength. It is well known that the electric strength of porous materials is low and nearly the same as the electric strength of the gap between the same electrodes in air in the absence of the solid porous material. This paper shows that for this material and only at porosities <20%, as measured by a mercury porosimeter, does the electric strength become larger than that of air and become a significant function of the porosity and of the distribution of pore volume among pores of differing equivalent pore diameter. The uniformity of the field had no noticeable effect     

The control of mechanical strength by an electric field in ceramic composites dispersed with piezoelectric particles

The control of mechanical strength in structural ceramic composite has been proposed and demonstrated by dispersing piezoelectric particles. The change in strength of barium titanate/zirconia composite on polarization treatment was evaluated, and the mechanism of this phenomenon is discussed based on the previously proposed mechanism for monolithic piezoelectric ceramics. The bending strength of BT/8YSZ composite increased upon longitudinal poling and decreased upon transverse poling compared to the untreated samples. Both the strengthened and weakened specimens tended to return almost to their original strength by heating over the T _c of barium titanate. Scanning electron microscopy was then used to examine the crack propagation after the polarization treatment, and cracks going in the poling direction were found to detour around the barium titanate grains, which was attributable to the increase in strength in the poling direction.     

空间电荷及金属颗粒对换流变阀侧套管的电场分布影响

换流变压器阀侧套管承受交、直流复合电压,对套管的性能和质量有严格的要求。直流电压下,不同介质界面处空间电荷积聚会引起局部电场的畸变,金属颗粒的存在也会大幅提高局部场强,二者均会降低套管的绝缘性能。文中根据换流变压器阀侧套管的结构,采用有限元分析软件,建立了阀侧套管的仿真模型,分析了加入空间电荷后不同类型电压下套管的电场分布以及金属颗粒对局部电场的影响。结果表明,直流电压下介质界面处空间电荷更容易积聚,交直流复合电压下空间电荷能够引发套管内部局部电场的畸变。与交流电压相比,直流电压下金属颗粒对局部电场的畸变程度影响更大,在SF₆气体中金属颗粒对电场畸变程度的影响大小与其所在位置的关系不大。     

电场强度对ADSS光缆的影响

为了保证ADSS光缆悬挂在安全的电场环境中，主要分析电场强度和电位对ADSS光缆的影响，并通过三维实例计算，分析各种因素对ADSS光缆电场强度的影响。     

Calculation of the electric field for lined-up spherical dielectric particles

This paper calculates the electric field in arrangements of dielectric particles. An analytical method is presented in the paper. The method repetitively inserts monopoles and multipoles until all the boundary conditions are satisfied, so that unlike the existing methods, it does not require setting up a linear equation system in the calculation. It can be applied to various types of energization such as a uniform field, spherical electrodes, or planar electrodes. The method and the BEM, a numerical method, have been utilized to investigate the effects of the particle number and particle permittivity. The authors have compared the results by the analytical method with those by the numerical method, and found that the accuracy of the numerical method greatly varies from less than 10/sup -4/% to more than 2%, depending on the condition of the calculation arrangements.     

基于嵌入式平台的分布式光伏发电监测系统

1光伏发电监测系统光伏发电也称太阳能发电,即利用太阳能级半导体电子器件吸收太阳光辐射能,并使之转换为电能。光伏发电系统主要由太阳能电池、蓄电池、控制器和逆变器构成。蓬勃发展的光伏产业,一方面带动了相关技术领域的快速发展,另一方面也对光伏配套产业链提出了更高的要求。为保证光伏发电系统可靠稳定运行,需要有完备的发电监测系统进行长期监测,并能根据实时监测结果提供完善     

触头盒内最大电场强度的计算

建立了舌形触头盒内最大电场强度的计算公式。公式表明触头盒的介电常数愈大,盒内触头最大电场强度愈小,公式计算结果与实测相当接近,可供舌形触头盒绝缘结构设计参考。     

Development of three-dimensional electric field computation system by surface charge method

This paper describes development of three-dimensional electric field computation system by surface charge method. Using this system, both potential and electric field in the case which includes resistance or true electric charge can be calculated. And this system is able to be connected to the pre-post processors, which is useful for us to make arbitrary shape and to display results of analysis.     

Window effect of pulsed electric field on biological cells

Based on multilayer dielectric model, for the spherical biological cell subjected to pulsed electric field (PEF), an equivalent circuit model is presented. Frequency-domain analysis shows that inner and outer membranes exhibit band-pass and low-pass filter characteristics in response to PEF, respectively. Therefore, different biomedical effects will be induced by the field with different frequency spectrum. The method to calculate the transmembrane potentials induced by time-varying PEF is introduced, and the relationship between rectangular pulse and transmembrane potentials is also discussed. It is found that because of different charging time constants, different durations have selective effects on inner and outer membranes. The analyses in both the frequency-domain and time-domain show a window effect of PEF on biological cells. When duration is reduced from microsecond to submicrosecond, and to nanosecond, the target induced is changed from the outer membrane to the inner membrane gradually. The window effect gives preliminary explanation for various bioelectric effects such as electroporation, intracellular electromanipulation and nanopores, providing help to the applications of PEF in tumor treatment.     

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     

基于表面电荷法的输电线路表面电场强度计算

三相输电线路导线表面电荷的分布是不均匀的,各点电场强度的大小也不同.文中采用表面电荷法计算导线表面的电荷密度,然后求出导线表面各点的最大电场强度值.计算方法能够反映出电荷密度及电场强度沿导线圆周分布的情况,根据计算结果优化高压输电线路的布置.     

On the screening of the electric field at the cathode surface by anelectron space charge at intense field emission

The paper considers the effect of the space charge of emitted electrons on the electric field at the tip of a field emitter. To analyze this phenomenon, the Poisson equation was solved numerically for a spherical vacuum diode with a field emission cathode. The dependence of the electric field on the geometric field has been compared with the known approximate dependencies, Strong screening of the electric field at the cathode by the space charge of emitted electrons at fields >5×10⁷ V/cm is noted. Based on the obtained dependencies of the actual field on the geometric one and using the SuperSAM code, the field emission occurring in a Muller projector has been simulated. It has been shown that the “ring effect” appearing in field emission patterns can well be explained by field emission from the peripheral regions of the field emitter. The current density distributions over the surface and in the bulk of the emitter have been analyzed     

基于Pockels效应的大气电场测量研究

为解决常用场磨式大气电场仪体积大、机械磨损严重、易受电磁干扰、测量带宽窄等问题,在研究分析Pockels效应原理的基础上,提出应用Pockels效应来测量大气电场的方法。对晶体、光源的选择及传感器设计中出现的问题进行了分析,设计了一种基于Pockels效应原理的脉冲电场传感器,该传感系统包括稳定高效的光源、Pockels晶体探头、数据采集及处理电路。通过模拟仿真,说明了这种测量方法是可行的,为进一步研制大气电场测量传感器,提高其性能提供了理论依据。     

一种基于交流电场感应的取能电源设计

基于交流电场感应的取能电源是输电线路在线监测装置的一种新型供电方式,但由于其输出功率较低,目前还难以满足在线监测装置的用电需求。针对此问题,文中在理论分析影响取能功率因素的基础上,提出了一种新型的感应电极结构,并进行了仿真分析和实验验证。研究表明,在10kV电压等级下,所设计的感应电极可产生3.35mA的位移电流,在负载电阻大于5kΩ时取能电源可输出600mW以上的连续功率。本文的原理和方法为解决在线监测装置的供电问题提供了新的思路。     

Generalized charge simulation method for the calculation of the electric field in high voltage substations

This paper deals with the calculation of the electric field strength in high voltage (HV) substations comprising complex geometrical structures. Generalized charge simulation method is proposed for improving the precision of the calculation of the electric field strength. The objective of this analysis is to examine the influence of towers, HV apparatus and fences on the spatial electric field distribution. For this purpose, a three-dimensional generalized model of HV substation has been developed, including phase conductors, bypass busbars, HV apparatus, fences and towers (denoted as Full model). The obtained results of the calculation of the electric field strength are compared with the Simplified model, which only includes phase conductors connected to HV network. Verification of the proposed Full model performed by comparing the calculated and in-field measured values of the electric field strength within HV substations and in their vicinity gives very promising results.     

HVDC输电线路合成场强数值计算方法研究

直流输电线路产生的地面合成场强是输电线路设计、建设和运行中必须考虑的技术问题。基于上流有限元方法计算直流输电线路的地面合成场强及离子流密度,通过对同轴圆柱结构的解析解及实际测量数据的对比证实了该计算方法的有效性。