光参量振荡器激发的光激电流测量系统

为了研究有效的光激电流测量系统,分析光激电流测试原理和测量系统中对激发光源的要求.根据光参量振荡器的原理实现波长可调的激光激发光源,其输出激光波长可在210～420nm范围内连续变化,并且光脉冲平均能量为2.3mJ.以这一激发光源为基础建立了光激电流测量系统,利用该系统对聚酰亚胺/无机纳米复合材料薄膜进行光激电流谱测量.通过比较连续2次测量结果中电流峰的位置和强度关系,证明了系统测量结果的有效性.并且测得在该材料中具有3.88eV、3.61eV和3.38eV 3种类型的深电荷陷阱.实验结果表明,该系统可以有效地完成光激电流谱的测试,并且能够获得电介质材料中的深电荷陷阱参数,为电介质材料理论和应用的深入研究提供可靠的实验依据.     

茂金属聚乙烯改性低密度聚乙烯中电荷入陷与传输特性

聚合物的电性能与其物理、化学、微观结构密切相关.通过电声脉冲(PEA)法测量少量茂金属聚乙烯(MPE)与低密度聚乙烯(LDPE)共混物在不同场强作用下的去极化特性.根据空间电荷限制电流(SCLC)理论,通过公式推导求解共混物平均电荷体密度、视在迁移率、陷阱深度分布及阈值场强.结果表明,1%MPE与LDPE共混,能有效减少深陷阱密度,增加浅陷阱密度,提高电荷迁移率和阈值场强.     

热老化下双层聚酯薄膜空间电荷特性的试验与数值仿真研究

双层电介质广泛应用于高压电气设备绝缘系统中，由此引入的空间电荷积聚和局部电场畸变问题已得到普遍关注。为揭示界面空间电荷特性及其影响影响因素，文中以热老化处理（130℃）的双层聚酯薄膜（PET）为研究对象，采用电声脉冲法（PEA）测量技术对不同热老化程度双层介质的空间电荷特性进行研究，基于测试结果从3个方面对双层介质表面态特性进行表征，建立改进的双极性电荷输运模型（BCT），模拟空间电荷的动态演变过程，揭示了表面态对电荷特性的影响规律。试验结果表明：随着老化时间增加，界面电荷密度先增加后减小，界面区域以电子性陷阱为主，但该区域电子和空穴陷阱呈现非对称特性。仿真结果表明：表面态对界面电荷行为有重要影响，介质表面陷阱深度、密度及其分布范围的增加导致界面电荷的积聚更加严重。     

全尺寸空间电荷测量在水中老化电缆状态评估中的应用

水树老化严重威胁电缆的运行可靠性,为有效评估电缆绝缘状态,选取未老化电缆与水中老化电缆作为研究对象,通过等温松弛电流(isothermal relaxation current,IRC)法检测了其老化状况,并应用全尺寸空间电荷测量法研究了电缆本体的空间电荷分布。研究结果表明:电缆经水中老化后,去极化电流曲线上移、老化因子增大,深能级陷阱大量增加;极化时空间电荷积累加剧,高场下阳极附近注入同极性电荷,短路时浅陷阱电荷逐渐消失,处于深能级陷阱的电荷仍驻留形成一明显正电荷峰,短路平均体电荷密度增加。分析认为电缆经过水老化处理后,由于绝缘外界环境的水分侵入而可能导致外半导电层处产生"外导水树枝",同极性电荷由"外导水树枝"尖端注入,处于较深能级陷阱,与IRC法测量到的去极化电流、陷阱密度、老化因子等均高于未老化电缆的结果一致。实验结果证明了IRC法的有效性以及全尺寸空间电荷测量能够评估电缆的局部绝缘状态,可有效用于电缆高危故障点的诊断与排查。     

热刺激电流试验系统的研制及应用

热刺激电流技术是研究电介质电荷存储及陷阱能级分布的有力工具,因此开发了热刺激电流试验系统,它由加热装置、微电流测量装置(静电计Keithley6514),温控仪.直流高电压发生器、真空系统、计算机等部分组成。以Lab-view为软件平台实现了电流、温度的数据实时采集和存储。在国际上首次测量了厚达1mm的氧化铝陶瓷的热刺激电流曲线。     

空间电荷测量表征聚乙烯中电荷输运特性

通过电声脉冲(PEA)法测量了低密度聚乙烯(LDPE)在不同场强作用下的去极化特性。根据空间电荷限制电流(SCLC)理论,通过公式推导求解了聚乙烯的平均电荷体密度、视在迁移率、陷阱深度分布及阈值场强。结果表明聚乙烯中的陷阱或缺陷,即其微观形态与宏观上空间电荷的分布密切相关。     

纳米金属Ag/高纯聚酯改性硅漆复合介质的介电行为

聚酯改性硅漆(SP)是用于硅器件表面保护的高纯绝缘材料.采用溶胶法制备的纳米Ag(直径小于20nm)均匀地分散到SP中后,对纳米复合材料的介电特性进行了研究.合适的纳米Ag含量使得纳米复合材料击穿场强提高,达到纯SP的112%,同时介电损耗也明显增加.采用热刺激退极化电流(TSDC)测量的结果表明纳米复合材料中存在两个较浅的陷阱能级,分别为0.52eV和0.62eV,陷阱密度分别为1.2×1010/cm3和2.0×1011/cm3,与纯SP中浅陷阱深度0.58eV、陷阱密度3.1×1010/cm3明显不同.复合材料低温下(77K)的体积电阻率明显高于纯SP,可以看作是库仑阻塞作用的结果.从介质物理的角度探讨了纳米复合材料与纯SP的特性差别.     

固体绝缘介质表面陷阱参数的分析

为了研究聚合物绝缘材料表面陷阱参数对其绝缘性能的影响,在简述了等温电流衰减理论后依该理论设计了材料表面陷阱分布测量装置,并实际测量了聚合物低密度聚乙烯、聚丙烯和聚四氟乙烯的表面陷阱分布。在对材料直流充电后将其短路1min以清除表面沉积的自由电荷,再移去短路电极并将探头迅速移至材料表面充电区域记录表面电位。实验保持恒温条件,用等温电流衰减理论计算材料的陷阱分布参数。实验表明电子空穴陷阱与材料的分子结构密切相关,聚合物不同高分子链影响着陷阱电荷的分布。     

基于离子计数法的直流线路空间电荷密度测量

当特高压直流输电线路途经地区的空中悬浮颗粒物较多且空气干燥时,空间电荷分布的变化导致地面合成电场异常增大。为对该问题进行研究,测量空间电荷分布是一种直接且有效的手段。通过分析基于离子计数法的空间电荷密度测量原理和装置电流检测部分的等效电路模型,提出了装置的设计要求,对基于该原理的电荷密度测量装置进行了设计,并采用间接校准方法对装置进行了标定。采用该装置对直流输电试验线段下的空间电荷密度进行了实测,测量结果表明电荷密度的横向分布规律、随导线加压的变化情况与合成电场、离子流密度类似。装置可以实现输电线路周围空间电荷密度的测量。     

温度及湿度对不同应力模式下低密度聚乙烯薄膜电击穿强度的影响

本文讨论温度及湿度对不同应力模式下低密度聚乙烯(LDPE)薄膜电强度的影响。发现水分子既可作受主,俘获电子,又可作增塑剂,从而给高聚物的介电击穿特性带来复杂的影响。直流预应力愈高,注入到更深陷阱中的电荷就愈多。由于深陷阱中的电荷在直到70℃的温度范围内仅部分消失,因此反场下干样品的归一化脉冲击穿场强 E_(fo)/E_(ib)的恢复特性变慢甚至消失。这些推论可由热激及载流子输运测量证实。     

Space charge trapping in electrical potential well caused by permanent and induced dipoles for LDPE/MgO nanocomposite

Space charge accumulation in low-density polyethylene film containing a small amount of MgO nanoparticles (LDPE/MgO nanocomposite film) subjected to an electric field greater than 100 kV/mm has been studied using an improved pulsed electroacoustic (PEA) system. No marked space charge accumulation was observed in LDPE/MgO nanocomposite films. To determine the mechanism of no space charge accumulation in the LDPE/MgO nanocomposite film, we compared electric potential wells produced by a permanent dipole moment such as that of carbonyl groups (C=0) and an induced dipole consisting of MgO nanoparticles (spherical dielectrics) under a high electric field to create a trapping site for electric charge carriers. The trapping depth created by the permanent dipole moment such as that of the carbonyl groups (C=0) of chemical defects is approximately 0.45 eV. However, the potential well induced by high-permittivity dielectric nanoparticles (MgO) is about 1.5 to 5.0 eV, which is much deeper than that induced by chemical defects. The suppression of space charge formation is explained using the potential well model consisting of a dipole induced by a high-permittivity dielectric nanoparticle. We explained the suppression mechanism of charge accumulation in the LDPE/MgO film that contains deep traps.     

Effect of dipolar arrays on the localization of charge carriers inmolecular materials

The paper presents results of calculations of the depth and distribution of local states for charge carriers created by polar impurities in a model molecular material. Equations resulting from the electrostatic model due to Lyons have been employed in the calculations. The presence of polar species in a non-polar molecular material locally modifies the polarization energy, thus creating local states (traps) on neighboring molecules. Calculations performed for an isolated dipolar defect show that traps as deep as ~0.4 eV to ~0.5 eV can result in such a way, their depths and cross-sections depending on the dipole moment of the guest molecule. Results of similar calculations carried out for arrays of spatially connected dipoles indicate that local states of a considerable density may be created, modifying the density-of-states function, and hence influencing the effective mobility of charge carriers     

Charge transport and dissipative processes in insulating polymers: experiments and model

Electroluminescence in insulating polymers signs the existence of potentially harmful excited states because the excess energy can be released through degraded pathways, opening the way to chemical degradation. Excitation mechanisms involve impact excitation/ionization by hot carriers or bi-polar charge recombination. In order to discuss the relative contribution of these processes to light emission in polyethylene, we introduce a numerical model of charge transport postulating a recombination-controlled electroluminescence. Model outputs and experimental measurements are compared for three different protocols of DC voltage application considering especially the simulated recombination rate and the measured light emission. A fairly good agreement is found between model and experiment when considering electroluminescence under constant DC stress. The model fails to describe the measurement under time-varying DC stress suggesting that excitation by hot carriers should be taken into account.     

一种基于DSP的PSD相位法位移检测系统的研究

设计了一种利用PSD测量位移的系统,利用数字信号处理技术同时测量照射在单片PSD上多个光点的位置,实现多个光点的位移同步检测。根据检测系统的特点,提出了PSD相位法位移检测系统的总体方案,设计了检测系统的软件部分和硬件部分。搭建了检测系统的实验平台,在该实验平台上进行了PSD的多光束位移检测实验,实验表明,PSD在正弦调制光的照射下,PSD输出电流信号的相位差与光点的位置存在着明显的线性关系,PSD的转换灵敏度随着调制信号频率的增加而增加。研究工作为多光束位移同步检测提供了一种有效的解决方案。     

现场可编程外围芯片PSD4XXX系列及其应用

阐述了现场可编程单片机通用外围接口芯片PSD4XXX系列的特点和功能,给出了PSD4XXX系列芯片与单片机接口设计。实践表明用PSD与单片机组成的系统具有集成度高、体积小和功耗低等优点。     

激光平面测量系统的研究

介绍了一种可用于精密平面测量的新方法,以柱面透镜产生的激光平面作为基准平面,凭借激光平面的稳定性进行系统的精密测量。先利用激光平面产生系统将点光源变成线光源,即把线状光束变成光平面,位置敏感元件PSD安装在被测平面的测量靶上。测量靶一边移动,PSD一边拾取激光平面信号,经放大滤波、A/D转换、单片机（MCU）数据处理后,将结果输送到显示屏（LED）。     

Deep trapping centers in crosslinked polyethylene investigated bymolecular modeling and luminescence techniques

Space charge in crosslinked polyethylene (XLPE) has been detected under both ac and dc fields. Its role in electrical aging and breakdown is recognized, but not deeply understood. It is thought that identification of the trapping centers in this material would help improve the modeling of conduction and electrical aging as well as making possible the design of crosslinked materials with improved properties. We have developed theoretical and experimental approaches to this problem which emphasize the role of chemical traps acting as deep trapping centers. Molecular modeling is used to estimate the trap depth for negative and positive charge carriers associated with the main by-products of crosslinking reactions (using dicumyl peroxide as a crosslinking agent) since their aromatic structure makes them candidates for deep traps. Calculations on acetophenone, n-methyl styrene and cumyl alcohol show that they indeed can act as deep traps. Because such deep traps can act as recombination centers, their involvement in charge trapping can be checked in specially designed luminescence experiments. In our experiments, charges of both polarities are generated at the surface of the material under study by using a non-reactive cold plasma in helium. The analysis of the decay kinetics and emission spectrum of the subsequent luminescence allows us to define unambiguously the time range in which charge recombination is the dominant excitation process of the luminescence. The emission spectra obtained within this time range provide the optical fingerprint of chromophores acting as deep traps in the material. The low-density polyethylene (LDPE) doped with crosslinking byproducts and XLPE (film and cable peeling) have been investigated. Their role in charge trapping is apparent in the luminescence experiments and in space charge distribution analysis. In thermally treated XLPE, it is shown that other species strongly bonded to the polymer chain are also able to trap electrical charges     

紫外-真空紫外光谱反射率测试系统

为获取紫外 真空紫外光学元件的光谱反射率,构建了一套反射率测试系统。该反射率测试系统主要由Seya Namioka紫外 真空紫外单色仪、样品精密转台为主体的光机结构和电子学系统组成。首先,介绍了系统测量原理,采用双光路补偿法消除了光源随时间的飘移,通过改变系统光路进行两次测量来获取反射光与入射光数据,进而得到光谱反射率。接着对电子学硬件系统进行描述,给出了驱动控制单元与信号处理采集单元的硬件设计与组成。因紫外 真空紫外光谱信号微弱,采用了锁相放大的方法提高了测量精度。该反射率测试系统测试结果表明波长重复性0.05 nm,反射率测量重复精度为1.8%,系统功能完备稳定性好,能够实现对光学元件的高精度测量。     

Charge trapping and conduction in pure and iodine-dopedbiaxially-oriented polypropylene

Study of charge trapping and conduction in pure and iodine doped biaxially oriented polypropylene (BOPP) is presented. Structural and chemical modifications induced by iodine were investigated using X-ray, optical and infrared methods. Optical spectra of doped BOPP show absorption at 290 nm from charge transfer complexes. X-ray examination revealed a decrease in crystallinity and crystallite size after doping. The effect of iodine on charge trapping was determined by thermally stimulated current technique. Deep traps (120°C peak) at crystalline-amorphous interfaces are destroyed by iodine, which provides new traps (68°C peak) with activation energy 0.9 eV. Pressure dependence of conductivity indicates ionic conduction in pure samples and electronic conduction in doped samples. Steady state currents in 0.5%wt iodine doped BOPP were measured for fields 1 to 5×10⁵ V cm^-1 and at elevated temperatures 22 to 50°C. Iodine enhances conductivity by ~700× in pure BOPP and the steady state conductivity shows a good fit of the 3-D Poole-Frenkel theory to the experiment. It is proposed that trapped electrons (arising due to donor-acceptor action) thermally released through PF lowering, predominantly contribute to the conduction     

Model for electrical tree initiation in epoxy resin

A model for electrical tree initiation in epoxy resins is presented in which the process is driven by the generation of new charge traps as a result of energy transferred to the polymer via charge recombination processes. The electroluminescence intensity expected from the model is computed and shown to be in agreement with the experimental data. In particular it is shown how the initial emission due to recombination can change to an emission arising from impact excitation in a natural way when the trap density reaches a level sufficient for the high electric field of the tree initiation region to connect shallow traps to form conducting filamentary paths in the form of percolation clusters. This result allows the electroluminescence behavior to be correlated with the observed onset of filamentary damage. The model is also shown to be able to explain the decrease in emission intensity observed at the time of transition between the two mechanisms for luminescence.