Effect of electric field,stress and environment on delayed fracture of a PZT-5 ferroelectric ceramic

The combined effect of electric and mechanical loading on fracture of a PZT-5 ferroelectric ceramic in silicone oil has been investigated using a single edge notched specimen. The results show that the fracture toughness and the threshold stress intensity factor of delayed fracture in silicone oil, i.e. stress corrosion cracking, decrease linearly with the increasing applied electric field, either positive or negative. For the PZT-5 ferroelectric ceramics, delayed fracture in silicone oil under sustained positive or negative field can occur, and the threshold field for delayed fracture under sustained positive or negative field decreases linearly with applied stress intensity factor. The combined effect of electric and mechanical loading on delayed fracture in silicone oil includes field-enhancing delayed fracture under sustained load and stress-enhancing delayed fracture in silicone oil under sustained field.     

Effects of electrode and filter element shapes on characteristics of charge injection type of electrostatic oil filter

This paper reports on an improvement of the filtration speed of charge injection type of electrostatic oil filter. Numerical simulations of the ion drag flow field and electric field are performed to compare the charge density distribution, ion drag flow pattern, and electric field strength distribution for different electrode and filter element shapes. Filtration experiments are conducted and the experimental results are discussed in relation to the simulation results. It is shown that the numerical simulations used in this study can contribute in predicting a better structure for electrostatic oil filters.     

基于铜网置换反应的微纳结构SERS基底制备和应用

电力能源发展与国家经济发展关系密切,因此电网稳定、安全地运行是人民稳定生活的保障。而与稳定可靠的电网的运行有关的是变压器的绝缘水平,因此始终注意电气设备的状况和运行非常重要。而仅由纸绝缘产生的糠醛是目前用于评估电力变压器老化状况最常用的指标之一,所以准确测量变压器油中糠醛含量具有重大意义。拉曼光谱法可以实现对待测物的快速、无损检测,但受限于拉曼散射信号弱,对油中老化特征物这种微量物质检测难度大。表面增强拉曼光谱可以解决痕量物质检测的灵敏性问题,使溶解在变压器油中的老化特征物得到快速、无损地检测。故将SERS应用到变压器油中糠醛的检测对于变压器运行状况的评估具有重要的意义。围绕着变压器油中糠醛作为痕量物质检测灵敏度低的问题,基于置换反应在TEM铜网上制备了微纳米结构的SERS基底,以检测变压器油中的糠醛,为高效,准确地检测变压器油的老化水平提供一种快速、有效的新技术。选择了特定的实验材料,在控制特定的实验条件下基于置换反应制备出微纳结构SERS基底,经过电镜扫描对其表面形貌进行表征;在不同位置进行拉曼检测得到特征拉曼峰峰强的变异系数仅为3.55％,表明该基底的“热点”分布均匀和检测可重复性高;定性分析了一定浓度梯度的变压器油中糠醛和背景噪声的拉曼光谱。选择了1 702 cm-1的拉曼峰作为油中糠醛的特征拉曼峰。定量分析中,建立内标峰和1 702 cm-1处峰强比与变压器油中糠醛浓度的线性函数,得到良好的线性关系。使用3δ准则计算变压器油中糠醛在微纳结构SERS基底上的检测下限约为0.51 mg·L-1。研究说明基于铜网置换反应的微纳结构SERS基底对于变压器油中糠醛具有更灵敏的检测。这对于诊断电力变压器绝缘状况和维护电网稳定非常重要。     

Nanoporous silicon doped by Cu for gas-sensing applications

The effect of hydrogen sulphide on the current–voltage characteristics of metal–insulator–semiconductor (MIS) structures based on nanoporous silicon (Si_nanopor) under copper doping has been investigated. Scanning electron (SEM), atomic force (AFM) and optic microscopes and/or secondary ion mass spectroscopy (SIMS) were used to obtain detailed characterisation of copper cluster distribution present at the surface and pores, respectively. SIMS spectra reveal that finite gradient in copper distribution along the pores and oxidation of nanoporous silicon simultaneously can be obtained successfully under electroless deposition process. It was also shown that the doping of nanoporous silicon by Cu leads to enhanced hydrogen sulphide sensitivity of MIS structures even without catalytic active top electrodes (for example, Pd) at room temperature. Furthermore, for different types of familiar MIS structures based on nanoporous silicon, e.g., MIS structures doped or undoped by copper and by using Pd metal electrodes, the hydrogen sulphide detection at room temperature mainly depends on the modification in the height of barrier of hetero- (Al–Cu–Si_nanopor–c-Si) or Schottky-like (Pd–Cu–Si_nanopor–c-Si) structures resulting the chemical interaction of molecular H₂S gas with copper clusters at the surface and in the pores. It is demonstrated that MIS structures based on the nanoporous silicon with copper doping are more sensitive to H₂S action at room temperature. In addition, the physical mechanism explaining the observed phenomena is also discussed.     

High-voltage insulation of a high-power pulse transformer

The results of the development and operation of a high-voltage insulation are described. The insulation has been developed for the secondary turn of a high-power pulse transformer. The operating electric field in the insulation on the nanosecond scale is 1.5 MV/cm. The prospects for using this insulation are discussed. Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 15–19, December, 1999.     

Measurement and simulation of partial discharge in oil-paper insulation under the combined AC–DC voltage

Depending on unique operation characteristics for voltage applied on valve side winding of the converter transformers, it is extraordinarily significant to study the partial discharge (PD) behavior with oil-paper insulation under combined AC–DC voltage. Therefore, this paper investigated PD inception characteristics by pulse current methods with needle-plate electrode system under combined AC–DC voltage. Furthermore, 3D electric field distributions versus combined AC–DC voltage in different ratios were calculated by Finite Element Analysis (FEA). An experimental conclusion was drew that AC partial discharge inception voltage (PDIV) in pure oil would decrease linearly with the DC component increasing but the inception voltage with oil-paper insulation appeared to be independent of DC voltage and dependent of AC voltage. And 3D electric field distribution deduced from simulation provided a supplementary proof on the experimental results. Moreover, high speed photography was used to capture emitted light produced by discharge, estimate streamer velocity (1.8 km/s) and record streamer initiation and propagation process in oil gap. Previous studies have shown that the prebreakdown phenomena involving the generation and propagation of vapor channels through the oil could be divided into a three-stage process.     

用扫描隧道显微镜操纵Cu亚表面自间隙原子

在超高真空环境下使用扫描隧道显微镜研究了吸附有双甘氨肽分子的Cu(001)表面.在一定的 偏压条件下，针尖在该表面扫描后会形成纳米尺度的Cu团簇，这些团簇可以根据意愿排列成 字母或图形.团簇的高度同偏压、隧道电流以及时间等条件有密切关系.在室温下可以稳定存 在的团簇为制造纳米器件提供了技术上的可能性.实验结果表明，形成团簇的Cu原子不是来 自Cu衬底表面或是针尖.化学吸附在Cu表面的双甘氨肽分子，受到隧道电场的作用会在Cu表 面形成张应变场，Cu亚表面自间隙原子在张应变场作用下迁移到表面是形成团簇的原因. 关键词： 扫描隧道显微镜 纳米尺度Cu团簇 自间隙原子     

Uncommon corrosion phenomena of archaeological bronze alloys

In the framework of the EFESTUS project (funded by the European Commission, contract No. ICA3-CT-2002-10030) the corrosion products of a large number of archaeological bronze artefacts are investigated by means of the combined use of scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and optical microscopy (OM) and tentative correlation of their nature with the chemical composition of the artefacts and the burial context is proposed.The results provide good insight into the corrosion layers and evidence in some bronze Roman coins and artefacts; the occurrence of uncommon corrosion phenomena that give rise to the formation of a yellowish-green complex chlorine-phosphate of lead (pyromorphite, (PbCl)Pb₄(PO₄)₃) and of a gold-like thick layer of an iron and copper sulphide (chalcopyrite, CuFeS₂). The micro-chemical and micro-structural results show that the coins were buried in a soil enriched in phosphorus for the accidental presence of a large amount of decomposing fragments of bones or in an anaerobic and humus rich soil where the chalcopyrite layer has been produced via the interaction between the iron of the soil, the copper of the coin and the sulphur produced by the decomposition of organic matter in an almost oxygen free environment. Finally, some unusual periodic corrosion phenomena occurring in high tin bronze mirrors found at Zama (Tunisia) are described. PACS 68.55Jk; 68.35 Dv; 68.37Hk; 68.55 Nq; 81.05 Bx     

Finite element simulation of stress distribution and development in 8YSZ and double-ceramic-layer La2Zr2O7/8YSZ thermal barrier coatings during thermal shock

In this paper, the thermal stress of the double-ceramic-layer (DCL) La₂Zr₂O₇/8YSZ thermal barrier coatings (TBCs) fabricated by atmospheric plasma spraying (APS) during thermal shock has been calculated. The residual stress of the coating after being sprayed has been regarded as the initial condition of the first thermal cycle. The characteristic of the stress development during the thermal cycle has been discussed, and the influence of the defects on the failure mode during the thermal cycle has also been discussed systematically. Finite element simulation results show that there exist higher radial thermal shock stresses on the ceramic layer surface of these two coatings. There also exist higher thermal stress gradient at the interface between the ceramic layer and the metallic layer. Higher thermal stress in 8YSZ/NiCoCrAlY coating lead to the decrease of thermal shock property as compared to that of LZ/8YSZ/NiCoCrAlY coating. The addition of LZ ceramic layer can increase the insulation temperature, impede the oxygen transferring to the bond coating and can also reduce the thermal stress. Considering from the aspects of thermal insulation ability and the thermal shock resistance ability, DCL type LZ/8YSZ TBCs is a more promising coating material compared with the single-ceramic-layer (SCL) type 8YSZ TBCs for the application.     

MICE超导耦合磁体线圈等效弹性模量辨识

应用于"μ介子离子化冷却实验装置(MICE)"的超导耦合磁体系统是MICE中的三大关键设备之一。耦合磁体线圈内径为1 500mm,长度为285mm,厚度为110.4mm,采用方形截面1.65×1.00mm2的NbTi复合超导线。每层导线之间为环氧和绝缘玻璃纤维布,每匝导线之间为环氧,线圈具有复杂的正交各向异性性质。根据线圈横截面细观结构的周期性,选出单根导线与周围的绝缘材料为代表性体积元(Representative Volume Element,RVE),基于能量等效原理得出线圈等效弹性模量的含义,然后根据细观力学有限元法,采用有限元软件计算了不同边界条件下细观结构代表性体积元的力学响应,得出了线圈平面径向和环向等效弹性模量,结果已经作为基础数据运用在MICE超导耦合磁体的力学计算中。     

聚丙烯中电树枝生长机理研究

耐电树枝老化特性是表征聚合物绝缘材料介电性能的重要参数之一.聚丙烯(PP)是典型半结晶聚合物,其复杂的非均匀聚集态结构影响电树枝的生长.本文对PP及加入成核剂的PP试样进行了耐电树枝化性能实验,通过偏光显微镜(PLM)及差示扫描量热法(DSC)分析加入成核剂前后PP的结晶形态、结晶度以及结晶结构对电树枝生长特征的影响.以相界面自由能的热驱动作用以及放电雪崩理论为基础,对电树枝生长的热力学和动力学机理进行分析,阐明电场分布对电树枝生长的重要作用.根据半结晶材料的结晶相和非晶相的物理性能,建立材料内部电场分布计算模型,模拟针-板电极条件下聚合物材料内部的局域电场分布情况,分析了电树枝通道的动力学生长特征,探讨了成核剂改变PP的结晶结构抑制电树枝沿电场生长的作用.     

Formation mechanism of ordered stress-relief patterns in a free sustained Cu film system

A nearly free sustained copper （Cu） film system has been successfully fabricated by thermal evaporation deposition of Cu atoms on silicone oil surfaces, and a characteristic ordered pattern has been systematically studied. The ordered pattern, namely, band, is composed of a large number of parallel key-formed domains with different width w but nearly uniform length L; its characteristic values of w and L are very susceptible to the growth period, deposition rate and nominal film thickness. The formation mechanism of the ordered patterns is well explained in terms of the relaxation of the internal stress in the films, which is related to the nearly zero adhesion of the solid-liquid interface. By using a two-time deposition method, it is confirmed that the ordered patterns really form in the vacuum chamber.     

颗粒堆内微观力学结构的离散元模拟研究

将离散单元法应用到三维堆积过程的模拟计算,探讨了滑动摩擦及滚动摩擦对堆积形成的影响,得到了颗粒堆内部的应力分布规律,发现颗粒堆的形态是由滑动摩擦和滚动摩擦共同决定的,在堆内颗粒间的作用力基本呈树状结构.在模拟得到的颗粒堆中出现了应力分布奇异现象,在堆积角较大的情况下,颗粒堆与地面间作用力的最大值常发生在距堆底中心不远的环状区域,而并非发生在堆底的中心;在堆积角相对较小时颗粒堆与地面间作用力的最大值较容易发生在堆底的中心.对于一个颗粒堆,具体会发生哪种受力情况具有一定的偶然性. 关键词： 堆积 离散单元法 计算颗粒力学     

Quasicontinuum analysis of the effect of tool geometry on nanometric cutting of single crystal copper

A dynamic multiscale simulation based on quasicontinuum method (QC) has been conducted to study the effect of tool geometry in nanometric cutting process of single crystal copper. In the simulation, the many-body EAM potential is used for the interactions between copper atoms in of the workpiece. The simulation captures the atomistic behaviors of material removal mechanisms from the free surface and the mobility of dislocations and their interactions with the computational cost of local atomistic simulation method. Simulations are performed on single crystal copper to study the atomistic details of material removal, chip formation, sub-surface deformation, and machining mechanism. The simulation results demonstrate that tool edge radius has significant effect on chip formation and subsurface deformation, because the effective rake angle varies with the tool edge radius. In addition, different effective rake angles result in different stress states and smoother surface can be obtained under bigger clearance angle. The variations of tangential force, normal force as well as the ratio of normal force to tangential force are obtained to analyze the effects of tool edge radius, rake angle and clearance angle in quantitative way.     

Water molecules migration at oil–paper interface under the coupling fields of electric and temperature: a molecular dynamics study

Moisture is an important factor affecting the insulation properties of transformers. Due to the limitations of macroscopic experimental methods, the diffusion of water at oil–paper interface cannot be accurately measured. Therefore, molecular dynamics method was used in this work to establish oil–paper layer model of 10⁵ atoms. Through jointly analysing the aggregation degree, diffusion coefficient, free volume as well as radial distribution function of water molecules, the diffusion mechanism of water molecules at oil–paper interface was studied. The results show that when the initial water content in paper was high, water molecules would accumulate at oil–paper interface to form the local high-water region during heating. The polarisation of the electric field strengthened the hydrogen bonding interaction between water molecules and increased the probability of occurrence of the high-water region. Meanwhile, electric field reduced the free volume and diffusion coefficient of water molecules and rendered its diffusion coefficient anisotropic. What’s more, when the electric field was combined with the temperature field, the electric field played a leading role in the diffusion of water molecules while the temperature field was less affected. Diffusion coefficients of water molecules at different temperatures from molecular dynamics simulations were well consistent with experimental results, which verified the rationality of the model.     

纳米TiO2颗粒对电流变悬浮液中硅油的挥发增强效应

物理化学性能稳定的二甲基硅油常作为电流变液分散相, 当与纳米量级的介电颗粒混合组成电流变悬浮液时, 在非密闭环境下极易挥发, 时间足够长时, 可完全挥发. 本文通过实验研究了纳米二氧化钛颗粒对二氧化钛和硅油组成的悬浮液中硅油挥发增强现象, 分析表明, 纳米颗粒在电流变悬浮液的硅油气-液界面上形成纳米尺度的凸型曲面, 使液面上蒸气压大大提高, 导致挥发增强. 本文还对颗粒浓度, 环境温度和硅油黏度等对硅油挥发增强效应的影响进行了系统的研究和分析.     

Feasibility study for detecting copper contaminants in transformer insulation using laser-induced breakdown spectroscopy

In recent times, copper sulphide (Cu₂S) diffusion in the transformer insulation is a major problem reducing the life of transformers. It is therefore essential to identify a simple methodology to understand the diffusion of Cu₂S into the solid insulation [oil impregnated pressboard (OIP)]. In the present work, laser-induced breakdown spectroscopy (LIBS) was adopted to study the diffusion of Cu₂S into the pressboard insulation and to determine the depth of diffusion. The diffusion of Cu₂S in pressboard was confirmed by electrical discharge studies. In general, flashover voltage and increase in ageing duration of pressboard insulation/Cu concentration had inverse relationship. The characteristic emission lines were also studied through optical emission spectroscopy. Based on LIBS studies with Cu powder dispersed pressboard samples, Cu I emission lines were found to be resolvable up to a lowest concentration of 5 μg/cm². The LIBS intensity ratio of Cu I–Ca II emission lines were found to increase with increase in the ageing duration of the OIP sample. LIBS studies with OIP samples showed an increase in the optical emission lifetime. LIBS results were in agreement with the electrical discharge studies.     

真空隔热油管接箍传热实验与模拟研究

真空隔热油管井筒的传热计算是稠油开采领域的重要研究课题.注蒸汽采油井筒内,隔热油管是靠接箍连接在一起的,接箍虽然很短,但其隔热性能较差.目前,隔热油管接箍段引起的散热损失均按经验比例计算,本文对隔热油管接箍的传热进行了深入研究,提出用接箍视导热系数来衡量接箍的隔热性能.并通过现场实验、fluent模拟和理论计算相结合的方法,得到带衬套的接箍视导热系数为0.4 W/(m·K)左右.在实验条件下,接箍散热损失占总散热损失的比例大于1/3.因此,应采用必要措施提高接箍的隔热性能,以保证整个隔热油管的隔热效果.     

Contribution to static electrification of mineral oils and natural esters

A failure of an insulation system of a power transformer can result into an interruption of a power supply and subsequently to a large economic damage. In some cases, the malfunction is so serious that a transformer may explode and catch fire resulting in a direct threat to the life of the device operator. These devices rely on a combined insulation system oil-paper. The oil in a transformer not only impregnates the pressboard paper insulation, hence increases its electric breakdown strength, but also acts as a coolant of active parts of the device. During the cooling, the oil flows in the transformer tank around the core, windings and isolation barriers from hardened paper. At the interface of two dielectrics, the oil and the cellulose in the transformer, electrostatic charges appear. The charges of one polarity are carried in the oil, and the charges of the opposite polarity remain captured in the barrier that is formed by the internal structure of the transformer. The accruing of a certain amount of charge leads to discharges along the surface of the solid insulation and therefore to its partial damage. Ultimately, this can lead to the damage of the whole insulation system of the transformer by its breakdown. At present, the mineral oils are used as the main liquid insulating medium because of their good electrical insulating and cooling properties. On the other side, there is a high environmental burden for their operation and maintenance as well as the subsequent disposal of the discarded oil. The natural esters may be used as a replacement for the mineral oil. They go well with the environment, they are biodegradable and in case of the transformer malfunction, its disposal costs less money.This paper presents the results of the experiments of electrostatic charging of the mineral oils and natural esters and their comparison. The charging process in the transformer is modelled using a metal cylindrical container with a forced flow of oil using a controlled rotating circular disc from a hardened paper. The results indicate that increasing intensity of friction, increases the electrical charge, which is generated at the interface of the solid phase and the liquid. In these experiments two types of mineral oils were studied. For comparison, two types of natural esters (sunflower and colza oils) were selected and used in the same experiments. The charging of the oils was examined at various temperatures ranging from 25 °C up to 70 °C.     

100kV直流高温超导电缆终端应力锥设计

本文提出了一种新的单直线应力锥设计方法,根据PPLP材料的绝缘特性,结合超导电缆的本体尺寸和设计电压,给出了增饶绝缘厚度和应力锥轴向长度的设计数据,其中增饶绝缘厚度为3.5 mm,应力锥轴向长度为38.5 mm,并对单直线应力锥进行电场数值分析,结果表明,所设计的单直线应力锥满足100 kV直流高温超导电缆运行要求。