中阻抗母线保护差动回路过电压误动探索和实践

中阻抗型母线保护可以说是一种非常快速与灵敏并且应用比率制动式电流差动保护方式,具备低阻抗以及高阻抗的保护优势,却很巧妙的避开了相应的缺点。中阻抗型母线的差动保护最关键的就是有着相对高的稳定性以及高速的动作性能,尤其是在解决相关的电流互感器出现饱和有着很大的优势。本文分析了中阻抗母线保护差动回路过电压误动中存在的故障与问题,并提出了相应的改善策略。     

基于实时等值阻抗的电压稳定性分析

电压失稳有可能导致大面积的停电事故,对电网安全生产运营带来巨大的挑战。研究电力系统等值阻抗的基本算法,并在此基础上对等值系统电压稳定性条件,以及电压稳定的评估进行分析,最后运用该算法进行实证研究,研究证明,基于实时等值阻抗的电压稳定性分析简单、有效,可广泛的运用于电力系统的电压稳定性的监控。     

功放与扬声器系统的配接（一）

众所周知,功放与扬声器系统的配接是放声(扩声)系统中最重要的一个环节,功放是扬声器系统的功率源,扬声器系统是功放的负载,属音频功率传输,其功率传输效率是首要追求的,它与功放输出电路自身的输出参数及扬声器负载的特性密切相关,这是功放输出电路设计的一个重要环节。功放输出电路的设计应该以扬声器负载的量值和性质作为功放输出电路的最佳负载,功放电路的输出对于扬声器负载应该呈现一个功率源的状态。功放输出电路设计应以阻抗8?Ω扬声器系统作为最佳负载,并在输出效率降低量的允许范围内能适应阻抗4?Ω扬声器系统,以至阻抗2?Ω扬声器…     

低压电网的系统阻抗实用计算方法

低压电网的系统阻抗是影响低压线路继电保护一个十分重要的因素。系统阻抗影响系统短路电流的大小,短路电流是电力系统继电保护整定计算的重要依据,它的准确性直接关系到系统保护的选择性、可靠性、灵敏性、速动性。本文分别对无限大容量电力系统和有限大容量电力系统的系统阻抗计算进行了归纳和总结。     

WTWELD放热焊接工艺在电网直流工程接地设施中的应用

高压直流输电系统中接地极回线对于整个直流输电的正常运行但当着重要的位置,由于同材质接地体之间传统的焊接连接方式存在着电气导通率(电流容量)不足及强度较低、施工困难等缺陷,在国网直流工程建设伊敏换流站接地极极址工程建设中我们采用了新型的金属材料热熔焊接方式,从而改良了传统接地系统接地体之间的连接工艺,提高了整体的工程质量,极大程度的解决了接地极馈电棒在焊接施工中的困难。     

高压直流接地极腐蚀特性研究

直流接地极埋于土壤中会发生腐蚀,直接关系到其使用寿命。通过对直流接地极腐蚀特性分析,发现直流接地极导体在土壤的腐蚀主要是由电化学腐蚀引起的;并分析了土壤含水量、土壤通气性和松紧度、土壤的pH值、土壤含盐量和组成对直流接地极腐蚀率的影响规律;最后总结了直流接地极工程中常用的防腐措施。     

轨道交通分布式火灾自动报警系统的工程研究

本文结合分布式监控系统的原理和方法,分析了轨道交通火灾自动报警系统工程的分布式火灾监控特点,并重点对专用分布式火灾自动报警系统、综合监控分布式火灾自动报警系统以及双网冗余备份分布式火灾自动报警系统的组建进行了讨论。     

也谈接地保护装置的保护原理

一．中性点不接地系统的接地保护 在电力系统的供电中,按变压器中性点工作接地方式不同,常见有变压器中性点直接接地、变压器中性点不接地和变压器中性点经高阻抗接地三种方式。方式的选择直接影响到系统运行性能、人身安全和相应的保护方法。三种运行方式的性能各有优、缺点,没有一个是绝对完善的系统。     

用复数阻抗谱法对β″-Al_2O_3陶瓷的分析

应用复数阻抗谱测量方法及解析拟合程序,得到 Au/β″-Al_2O_3/Au 系统的阻抗谱及阻抗与频率的依赖关系,从而说明化学组分及埋料烧成时间对β″-Al_2O_3晶粒电阻和晶界电阻的影响。计算的均方根误差一般在0.05Ω左右。     

特高压直流接地极架空线路带电作业技术与工器具创新及应用

本文结合我国首次特高压直流接地极架空线路带电作业科研成果,简要介绍了我国特高压直流接地极架空线路带电作业关键技术和安全防护技术,作业方法研究、工器具研制和现场应用情况,研究结果可供其他±800kV直流接地极线路带电作业参考。     

Antenna model of the horizontal grounding electrode for transient impedance calculation: Analytical versus boundary element method

The paper deals with a simple and efficient procedure for the calculation of the transient impedance of the horizontal grounding electrode. This work represents an extension of a previous paper, published by the authors, on the antenna modeling of the grounding electrode with corresponding Pocklington integro-differential equation. The governing equation is solved in the frequency domain, both numerically and analytically, thus obtaining the solution for the current induced along the electrode. The numerical solution is undertaken via Galerkin–Bubnov scheme of the Indirect Boundary Element Method. Scattered voltage along the electrode is then calculated using Generalized Telegrapher?s equation. Time domain scattered voltage is evaluated via the Inverse Fast Fourier Transform. Subsequently, transient impedance is determined as a ratio of time domain voltage and current at the feeding point. Results obtained via different methods seem to agree satisfactorily.     

Generalised equation of soil critical electric field EC based on impulse tests and measured soil electrical parameters

The effective radius of the grounding electrode under high-impulse current becomes higher than the outer radius of the electrode because of soil ionisation. Because of this reason, the ground-impulse impedance is different from the 60-Hz grounding resistance, which is normally measured at low current. The impulse impedance for any given impulse current can be estimated if the critical electric field of the soil is known. It is therefore necessary to have a generalised soil critical electric field equation for grounding systems design as well as lightning performance study. A generalised equation for soil critical electric field Ec is proposed here as a function of soil dielectric constant kg and conductivity ^sigmag. Extensive impulse tests and electrical measurements were performed with different soils under different moisture contents. Dielectric constant kg was measured by the wave propagation technique using a soil-filled coaxial transmission line. Effect of waveshape on critical electric field Ec was statistically analysed for different soils.     

Polyelectrolyte Multilayer-Treated Electrodes for Real-Time Electronic Sensing of Cell Proliferation

We report on the use of polyelectrolyte multilayer (PEM) coatings as a non-biological surface preparation to facilitate uniform cell attachment and growth on patterned thin-film gold (Au) electrodes on glass for impedance-based measurements. Extracellular matrix (ECM) proteins are commonly utilized as cell adhesion promoters for electrodes; however, they exhibit degradation over time, thereby imposing limitations on the duration of conductance-based biosensor experiments. The motivation for the use of PEM coatings arises from their long-term surface stability as promoters for cell attachment, patterning, and culture. In this work, a cell proliferation monitoring device was fabricated. It consisted of thin-film Au electrodes deposited with a titanium-tungsten (TiW) adhesion layer that were patterned on a glass substrate and passivated to create active electrode areas. The electrode surfaces were then treated with a poly(ethyleneimine) (PEI) anchoring layer and subsequent bilayers of sodium poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). NIH-3T3 mouse embryonic fibroblast cells were cultured on the device, observed by optical microscopy, and showed uniform growth characteristics similar to those observed on a traditional polystyrene cell culture dish. The optical observations were correlated to electrical measurements on the PEM-treated electrodes, which exhibited a rise in impedance with cell proliferation and stabilized to an approximate 15 % increase as the culture approached confluency. In conclusion, cells proliferate uniformly over gold and glass PEM-treated surfaces, making them useful for continuous impedance-based, real-time monitoring of cell proliferation and for the determination of cell growth rate in cellular assays.     

用于结构健康诊断的压电阻抗技术

利用自驱动、自传感特性的压电陶瓷片 ,粘贴在外部结构的表面 ,结合动态阻抗的概念 ,提出了一种机电耦合的在线压电阻抗技术用于结构健康诊断。结构健康状况的改变 ,表现为结构动态阻抗的变化 ,则可以通过压电陶瓷片的导率表现出来。以含不同裂纹尺寸的梁结构为例 ,实验分析该种技术的有效性。结果表明 :随着裂纹尺寸的增加 ,压电陶瓷片导率的峰值不仅发生明显偏移 ,而且幅值下降。根据幅值的变化实验给出了能较好地衡量损伤程度的标尺     

Electrical impedance evaluation in a conductive–dielectric half space by the charge simulation method

Electrical impedance in a non-homogeneous half space is considered by the charge simulation method (CSM). The CSM is a kind of the direct boundary element method, which is suitable for the infinite exterior analysis, as it only requires the discretization over the boundary surfaces between the regions. The electrical grounding systems are modelled, in which some numerical solutions are demonstrated for the impedance evaluation at the electrode placed in the half space and the potential distribution is visualized.     

Use of plasma impedance monitoring for the determination of SF6 reactive ion etch process end points in a SiO2/Si system

It is shown here that plasma impedance monitoring can be used successfully to determine the end point of reactive ion etching of a SiO₂ layer lying on a Si substrate in SF₆ plasma. The usefulness of this technique is demonstrated using a commercial Plasma Impedance Monitoring (PIM) system. The end point conditions are tested by monitoring changes in the fundamental and the first four harmonic components of the RF current, RF voltage, phase between RF voltage and current, RF discharge power and RF impedance. The best process monitoring parameter found in this work is modeled as a polynomial equation of RF input power, chamber pressure and gas flow rate, from which the end point can be predicted with good precision and easily detected by the PIM. The end point conditions are confirmed by both Fourier Transform Infrared Spectroscopy (FTIR) measurements and via observation of plasma color changes. Received:15 June 2001 / Accepted: 18 June 2001     

矿山瓦斯监控界面多目标视觉告警编码形式研究

目的 探究矿山瓦斯监控界面多个目标同时告警时的最优视觉告警编码形式。方法 以矿山瓦斯监控系统为研究背景,选取颜色、大小、字符三种视觉编码形式对注意、警告、危险三种告警等级进行单目标和双目标的视觉搜索实验。结果 通过对正确率、反应时间以及主观评分的分析发现,无论是单目标还是双目标视觉搜索实验,当界面视觉告警形式采用颜色编码时,搜索绩效最优;相比于采用字符编码,采用大小编码时的搜索时间更短,但其正确率却稍低。实验结果还发现在双目标视觉搜索实验中,告警等级的异同对反应时间具有显著性影响,告警等级相同的比告警等级不同的两目标搜索时间更短,且搜索过程中第二个目标比第一个目标更容易被发现。结论 研究结果对于提高矿山瓦斯监控系统界面的安全性,减少监控人员的认知决策失误具有重要意义,同时也对其他监控界面中多目标视觉告警形式的设计具有一定的指导价值。     

声波反射法测量电流变液参数

电流变(Electrorheological, ER)液是一种新型智能材料,在外部电场作用下其物理特性可调节。文章设计了一种电流变液的声学测量系统,利用声波反射法测量电流变液的反射系数和相位差,根据声阻抗率与弹性模量关系,得到电流变液储能模量、耗能模量和损耗角等参数。实验结果表明：声阻抗率、储能模量和损耗角等参数与所施加外部电场的电压有关,采用电极绝缘漆处理工艺能有效兼顾电流变液对较大剪切应力和快速响应时间的性能要求。     

基于MEMS技术的植入式柔性多触点平面电极阵列

为提高植入式电极阵列的分辨率,降低生物组织损伤,保证其在生物体内稳定工作,本文提出了一种基于聚对二甲苯(Parylene C)的柔性多触点平面电极阵列.该电极为Parylene C/Au/Parylene C 3层结构,共24个通道.电极采用标准MEMS工艺加工,触点分布精确,轮廓清晰,表面平整,粗糙度为23.8 nm.为评估电极的工作性能,采用磷酸缓冲液(PBS溶液)模拟生物组织液,对电极阵列进行了电化学阻抗测试及循环伏安测试.测试表明,电极在100 Hz与1 000 Hz的阻抗值约为400 kΩ与50 kΩ,满足记录电极对阻抗的要求,同时,不同通道之间具有良好的一致性.此外,对随机选取的一个通道进行的循环伏安法测试表明,电极在刺激模式下具有良好的可逆性,对组织无影响,该通道的电荷储存能力约为650μC/cm2,与文献报道电极相当.     

一种氦气供气系统的改进与研究

阐述了四套原氦气供气系统的设计方案,改进后增加监测报警装置,并介绍了测量氦气压力和流量的测点布置和传感器的选择安装,最终实现四套氦气供气系统的集中监控.