小电流接地系统故障选线的一种新方法

小电流接地系统的故障选线一直备受供电部门关注.分析了中性点不接地系统单相接地故障及其选线存在的问题,并在此基础上提出了一种新的选线方案,即基于TVS的可控短路方案.利用MATLAB/Simulink进行仿真,结果表明该方法不仅能够弥补传统选线法的不足,而且具有一定的优势.     

PoE交换机雷击浪涌防护设计

PoE（Power over Ethernet）交换机雷击浪涌防护设计在现阶段具有重要意义。本文分析了三种主要浪涌防护器件特性,比较其各自优缺点,在针对不同使用环境下PoE交换机的防护电路设计中,将三种防护器件分别组合使用,得到具体防护电路。最后,将所得电路进行雷击测试,测量经过防护电路之后的波形,最终证明,所设计电路能够起到抗雷击浪涌保护电路的作用。     

Optimisation of very low voltage TVS protection devices

This paper is aimed at the design and optimisation of advanced Transient Voltage Suppressors (TVS) devices for IC protection against ESD. A four-layer N⁺P⁺PN⁺ structure has been used to achieve breakdown voltages lower than 3 V. The effect of the critical geometrical and technological parameters on the TVS electrical characteristics is analysed with the aid of technological and electrical simulations. In this sense, the trade-off between voltage capability, leakage current and clamping voltage has been optimised. Fabricated TVS devices exhibit better electrical performances than those of the equivalent three-layer TVS device counterparts.     

棒形天线耦合雷电电磁波及抑制方法

针对棒形天线耦合雷电电磁波信号的问题,利用实验和理论相结合的方法,建立了棒形天线接收雷电电磁波信号的等效电路,分析了雷电电磁波信号的频谱及能量分布规律,提出了利用暂态抑制二极管器件(Transient Voltage Suppressor,TVS)抑制棒形天线耦合雷电电磁波能量的重复方法.实验表明:在馈电端并联TVS管后,从棒形天线S11曲线得出的天线中心频率及带宽略变小;馈电端并联TVS管可有效地抑制棒形天线耦合雷电电磁波电压的幅值,在馈电端并联两种不同型号的TVS管,棒形天线耦合雷电电磁波电压的幅值可分别被抑制到6.8V至7V以内.实验结果和理论分析结论基本吻合.研究结果对棒形天线耦合雷电电磁波能量的抑制方法具有一定的指导意义.     

瞬变电磁发射机的无源恒压钳位技术

传统的准谐振和电压源恒压钳位方法可以使电流关断延时减小,电流下降线性度变好。但其控制电路比较复杂,且均引入了电容,容易和线圈发生谐振而使电流下降沿两端的抖动加剧。为此提出了用TVS和SIDAC器件来实现无源恒压钳位电路。这样不仅可以使电路简单,而且由于2种器件的结电容较小,电流下降沿两端的抖动也较小。对2种器件来实现恒压钳位电路进行了分析,表明2种器件设计的电路均能满足恒压钳位的要求。实验结果表明:无源恒压钳位方法可以使电流下降线性度好,下降沿两端抖动小,且电路较为简单。     

聚合物ESD抑制器抑制特性的测试方法

为了消除静电放电时产生的辐射场对静电放电抑制器测试结果的影响,基于法拉第笼的屏蔽效应、依据国际电工委员会IEC61000-4-2标准和国军标GJB911-1990,利用静电放电模拟器和静电放电电流波形测试装置等设备,测试了某型号聚合物静电放电抑制器的抑制特性。测试结果表明,采用IEC61000-4-2标准规定的电流靶结合法拉第笼的方法,测试静电放电时通过抑制器的电流,能够保证电流波形不失真;而加在抑制器两端的电压,须使用有效带宽足够宽的电压探头配合示波器来测量,同时应尽可能消除静电放电时产生的辐射场对电压探头的影响。     

典型ESD防护器件失效机理研究

瞬态电压抑制管(TVS)是电子线路设计中常用的静电放电(ESD)防护器件,其可靠性将直接影响整个电路的安全。选取常见的TVS器件PESD5V0U1BA进行研究,通过实验和仿真分析了TVS器件的短路失效机理及其影响。研究表明,当TVS器件注入高压时,器件存在缺陷的SiO2层会发生自愈性击穿。当器件的pn结发生击穿时,器件将失效。如果两个pn结都被击穿,器件的I-V曲线表现为电阻特性。当TVS器件出现损伤后,器件仍具有箝位作用,且其表现的箝位电压更低,但由于器件的漏电流发生较大的增长,将影响被保护电路的正常工作。     

沈水湾污水处理厂的过程监控系统改造

本文以沈阳市沈水湾污水处理厂的自动化控制为例,介绍污水处理厂控制系统配置和各个过程控制功能,若保证其污水处理系统可靠运转,一套高性能的自动化控制系统是必不可少的。本工程采用的集散控制系统对污水处理系统的正常运转起到至关重要的作用。     

Prototype reduction schemes applicable for non-stationary data sets

All of the prototype reduction schemes (PRS) which have been reported in the literature, process time-invariant data to yield a subset of prototypes that are useful in nearest-neighbor-like classification. Although these methods have been proven to be powerful, they suffer from a major disadvantage when they are utilized for applications involving non-stationary data, namely, time varying samples, typical of video and multimedia applications. In this paper, we suggest two PRS mechanisms which, in turn, are suitable for two distinct models of non-stationarity. In the first model, the data points obtained at discrete time steps, are individually assumed to be perturbed in the feature space, because of noise in the measurements or features. As opposed to this, in the second model, we assume that, at discrete time steps, new data points are available, and that these themselves are generated due to a non-stationarity in the parameters of the feature space. In both of these cases, rather than process all the data as a whole set using a PRS, we propose that the information gleaned from a previous PRS computation be enhanced to yield the prototypes for the current data set using an LVQ-3 type “fine tuning”. The results are, to our knowledge, the first reported PRS results for non-stationary data, and can be summarized as follows: if the system obeys the first model of non-stationarity, the improved accuracy is as high as 90.98% for artificial data “Non_normal 2”, and as high as 97.62% for the real-life data set, “Arrhythmia”. As opposed to this, if the system obeys the second model of non-stationarity, the improved accuracy is as high as 76.30% for the artificial data, and as high as 97.40% for this real-life data set. These are, in our opinion, very impressive, considering that the data sets are truly time-varying.     

高压断路器在线监测设备浪涌抗扰度试验

为了执行国家电磁兼容抗扰度试验等级选择要求规定在电力系统运行的在线监测设备必须通过浪涌(冲击)第3等级抗干扰试验,按照电磁兼容国家标准构建了试验环境,对高压断路器在线检测设备进行了浪涌(冲击)抗扰度试验。通过改进检测设备的电源部分结构,在易受干扰部位增加压敏电阻、瞬态电压抑制器(TVS)2种电磁兼容器件来抑制干扰;仿真和理论分析了TVS的安装位置对干扰的影响。试验结果表明,改进后的在线监测设备能有效抑制浪涌(冲击)干扰,通过了第3级浪涌(冲击)抗扰度试验。