直流偏磁对500 kV变压器振动特性的影响分析

特高压直流工程单极-大地回路运行时,直流电流侵入大型变压器绕组,致使变压器振动加剧。为了深入了解直流偏磁对大型变压器振动特性的影响,分析了变压器的振动机理及直流偏磁的影响机制。在白鹤滩—江苏 ± 800 kV特高压直流输电工程调试期间,对500 kV三相变压器的中性点电流、振动信号进行了实测,量化了直流偏磁程度,分析了不同直流偏磁程度下变压器振动信号时域及频谱特征。提取了波形畸变比、奇偶次谐波能量比、累计能量占比、功率谱熵等特征量来分析直流偏磁对大型变压器振动特性的影响。结果表明：直流偏磁导致波形畸变,1个工频周期内2个半周期对应的振动波形不再对称分布;随着直流偏磁程度增加,振动信号主频分量改变,50 Hz倍频谐波分量增多,其中50 Hz奇次谐波增幅要大于偶次谐波,且影响主要集中在600 Hz以内;由于铁心饱和作用,直流偏磁增大到一定程度时,磁不平衡性降低,振动信号复杂度不再增加。     

一种飘动性分析的视频烟雾快速检测新算法

针对DSP视频监控系统中,实时视频烟雾检测功能的需求,提出一种基于烟雾飘动性分析的快速视频烟雾检测算法.相比于现有相关算法,在完成对给定视频样本学习后,该算法无需存储视频的历史帧数据,也不需要学习场景背景,而直接对原始视频图像分块提取烟雾飘动特征,然后经Bayesian决策输出检测结论.结合提出的一组新颖的视频烟雾飘动特征,新算法同时获得了较低的计算复杂度和较高的检测性能.综合来看,新算法能更好地适用于实时视频监控系统中的烟雾检测需求.     

基于0.13μm工艺的8Mb相变存储器

采用0.13 μm工艺,4层金属布线,在标准CMOS技术的基础上增加3张掩膜制备了一款8 Mb相变存储器.1.2V的低压NMOS管作为单元选通器,单元大小为50 F2.外围电路采用3.3V工作电压的CMOS电路.Set和Reset操作电流分别为0.4 mA和2 mA.读出操作的电流为10 μA,芯片疲劳特性次数超过了1...     

卫星移动通信信道特性与模型研究

从多径效应、阴影效应、多普勒效应和电离层闪烁等方面具体分析了卫星移动通信信道传输特性,并从单状态统计模型和多状态统计模型两方面详细介绍了瑞利信道模型、莱斯信道模型、对数正态衰落信道模型、Loo模型、Corazza模型、Lutz两状态信道模型和五状态M arkov信道模型,最后对未来卫星移动通信信道模型研究做了展望。     

采用光激励和光检测的LED电特性测试方法

针对目前用于测试LED光电特性多采用接触式的电注入检测方法存在系统复杂、成本高、检测效率低且易造成芯片损伤等不足,提出一种采用光激励和光检测的非接触式检测方法。通过获取光激励LED p-n结产生的光致发光（PL）光谱,在建立了LED PL、电致发光（EL）效应间的确切联系以及LED发光光谱特性与其电特性间的对应关系的基...     

一种CMOS工艺离子敏场效应型晶体管的模型

采用CMOS工艺可以实现离子敏场效应型晶体管(ISFET),若在栅极氧化层之上保留多晶硅层,并通过引线使其与 外界的金属层相连作为悬浮的栅极,可实现悬浮栅结构ISFET.从ISFET的传感机理出发,根据表面基模型,利用HSPICE建 立了悬浮栅结构ISFET的物理模型.以该模型为研究对象,探讨了薄膜等效电阻、薄膜等效电...     

有机非挥发存储器件:浮栅结构有机薄膜晶体管

提出了一种浮栅结构的新型有机薄膜晶体管(FG-OTFT)器件,并阐述了这种器件的工作机理.该器件通过控制浮 置栅上的电荷来控制 FG-OTFT 器件的阈值电压的大小,而器件不同的阈值电压便可用来存储“0”和“1”两个状态,故这种器 件可以被用作有机非挥发存储器.我们通过计算机数值模拟的方法对这种器件进行了研究.研究表明...     

Research of the traffic characteristics for the real time online traffic classification

Aiming at the hysteretic characteristics of classification problem existed in current internet traffic identification field,this paper investigates the traffic characteristic suitable for the on-line traffic classification,such as quality of service (QoS).By the theoretical analysis and the experimental observation,two characteristics (the ACK-Len ab and ACK-Len ba) were obtained.They are the data volume which first be sent by the communication parties continuously.For these two characteristics only depend on data’s total length of the first few packets on the flow,network traffic can be classified in the early time when the flow arrived.The experiment based on decision tree C4.5 algorithm,with above 97% accuracy.The result indicated that the characteristics proposed can commendably reflect behavior patterns of the network application,although they are simple.     

Potential of asymmetrical Si/Ge and Ge/Si based hetero-junction transit time devices over homo-junction counterparts for generation of high power

Static and dynamic properties of both complementary n-Ge/p-Si and p-Ge/n-Si hetero-junction Double-Drift IMPATT diodes have been investigated by an advanced and realistic computer simulation technique, developed by the authors, for operation in the Ka-, V- and W-band frequencies. The results are further compared with corresponding Si and Ge homo-junction devices. The study shows high values of device efficiency, such as 23%, 22% and 21.5%, for n-Ge/p-Si IMPATTs at the Ka, V and W bands, respectively. The peak device negative conductances for n-Si/p-Ge and n-Ge/p-Si hetero-junction devices found to be 50.7 ? 10⁶ S/m² and 71.3 ? 10⁶ S/m², which are ～3-4 times better than their Si and Ge counterparts at the V-band. The computed values of RF power-density for n-Ge/p-Si hetero-junction IMPATTs are 1.0 ? 10⁹, 1.1 ? 10⁹ and 1.4 ? 10⁹ W/m², respectively, for Ka-, V- and W-band operation, which can be observed to be the highest when compared with Si, Ge and n-Si/p-Ge devices. Both of the hetero-junctions, especially the n-Ge/p-Si hetero-junction diode, can thus become a superior RF-power generator over a wide range of frequencies. The present study will help the device engineers to choose a suitable material pair for the development of high-power MM-wave IMPATT for applications in the civil and defense-related arena.     

塑壳断路器延时特性自动检测系统

针对塑壳断路器出厂前延时特性可靠性检测,开发一套塑壳断路器延时特性自动检测系统。该系统以PLC为核心,通过触摸屏设置参数,恒流源输自动调节所需试验电流,并根据测试结果进行分类,提高了生产效率和生产的规范性。