陕湖直流岗上湾接地极周边220 kV变压器直流偏磁噪声的试验研究北大核心CSCD

随着±800 kV陕北—湖北直流输电工程建设,受端武汉换流站岗上湾接地极周边交流变压器受到直流偏磁的影响严重,产生了振动噪声加剧等一系列问题,影响电网的安全稳定。本文针对存在严重直流偏磁的220 kV永阳变电站,结合±800 kV陕湖工程直流偏磁测试,开展了变压器实际运行工况下的声级现场试验,研究了直流偏磁电流对变压器噪声的影响,比较了变压器不同部位的噪声差异。得到了变压器噪声随直流偏磁电流的非线性增加的规律,且变压器短轴侧有载调压机构箱右上方在直流偏磁影响下的噪声变化最严重。该试验结果为变压器实际运行工况下的直流偏磁噪声诊断和特性研究提供数据支撑。     

小功率水电站变速恒频控制系统研究

针对传统小水电站并网系统控制复杂、低流量下效率低等问题,提出一种基于电压空间矢量脉宽调制的永磁直驱水电并网控制系统。该系统采用背靠背的双PWM变流器将水轮发电机组和电网分离,通过电压空间矢量脉宽调制法实现能量的双向流动。机侧变流器采用单位功率因素控制,以发电机转速为控制对象,将水流冲击产生的有功电能输送到直流母线上,同时实时跟踪水轮机最佳转速点,实现水轮机组最大功率输出。网侧变流器采用基于电网电压矢量定向的有功、无功分解控制,以直流母线电压为控制对象,往电网传输有功电能,同时进行无功补偿。最后仿真及实验验证了该控制系统的有效性。     

不一致信息系统的粗糙集快速约简算法

针对以依赖性作为属性重要性度量的约简算法效率较低、不能有效处理不一致信息系统的问题,提出一种时间复杂度为O（｜A｜2｜U｜）、基于错误分类率（ER）的快速约简算法。根据等价类计算的包含关系和正区域与属性个数的单调关系,采用ER作为属性重要性的度量。在UCI数据集合上测试该算法,结果证明了其有效性。     

Structure and Waveguide Properties of Sol-Gel Derived Gd2O3 Films

Pure and rare earth doped gadolinium oxide (Gd2O3) waveguide films were prepared by a simple sol-gel process and dip-coating method. Structure of Gd2O3 films annealed at different temperature was investigated by X-ray diffraction and transmission electron microscopy. Oriented growth of (400) face of Gd2O3 has been observed when the films were deposited on amorphous substrate. The refractive index and thickness of films were determined by m-lines spectroscopy. The laser beam (λ= 632.8 nm) was coupled into the film by a prism coupler and the propagation length is about 3.5 cm. Luminescence properties of europium ions doped films were measured by waveguide fluorescence spectroscopy, which shows disordered environment for Eu^3 at 400℃.     

Preparation,Structural Analysis and Luminescence Properties of Nanocrystalline Phosphor Gd2O3∶Eu

Nanocrystalline monoclinic and cubic Gd2O3∶Eu with different Eu3 concentration were prepared using glycine-nitrate combustion synthesis. By changing the ratio of glycine to nitrate and proper heat treatment, pure monoclinic and cubic Gd2O3∶Eu with particle size less than 40 nm can be easily formed. Under ultraviolet excitation, main emission of Eu3 (5D0→7F2) locates at 624 nm in monoclinic Gd2O3∶Eu and 611 nm in cubic sample. In excitation spectrum two broad bands corresponding to the host absorption and charge transfer state(CTS) and f-f transitions of Gd3 and Eu3 were observed and discussed. The quenching concentration of monoclinic and cubic Gd2O3∶Eu is 10% and 15%, respectively, both of which are much higher than that of bulk Gd2O3∶Eu.     

BaTiO3基多层陶瓷电容器抗还原介质材料的研究进展

多层陶瓷电容器(MLCC)是一类重要的片式元器件,内电极的贱金属化已成为其产品开发的主流。MLCC内电极贱金属化的关键技术是获得抗还原性能优异的瓷料,能够与贱金属镍电极实现共烧的BaTiO3基抗还原瓷料的研究是目前MLCC研究的热点。本文综述了BaTiO3基抗还原介质材料的抗还原机理、制备方法及研究进展。     

图文互斥版面中文字阅读顺序的确定

图文互斥版面中确定文字的阅读顺序是排版及版面理解过程中的一个难点。尤其是中文等东方文字特有的分栏串文互斥,其空间关系的复杂性使得阅读顺序存在歧义。针对此问题,建立新的版面布局模型,并引入新的版面对象PMRegion。给出了版面逐层快速分解构造版面对象和基于有序树的阅读顺序确定算法。已成功运用于专业中日文排版系统,取得了满意的效果,并对更深入研究文档图像理解具有十分重要的理论和实践意义。     

基于SGML/XML的文件结构化研究与实现

由于计算机普及和Internet发展的迅速，信息传播和利用的多样化对信息的标准化需求日趋迫切，依照SGML／XML语言，从分析文件结构入手，设计文件类型定义（DTD），并用结构制导方法实现文件编辑器，以自动生成符合DTD语法的结构化文件，而达到文件信息的标准化要求。     

固态熔盐堆全厂断电ATWS事故工况下的堆芯安全探讨

利用修改后的适用于固态熔盐堆的RELAP5/MOD4.0系统分析程序,对固态熔盐堆全厂断电ATWS(Anticipated Transient Without Scram)事故进行了分析。主回路系统进行了合理简化建模,模拟系统在全厂断电ATWS事故时非能动余热排出系统有效与否两种情况下的瞬态响应过程。分析结果表明:非能动余热排出系统在全厂断电ATWS事故初期作用不明显,但长期作用较明显,投入使用后最终将使堆芯温度和主冷却剂温度达到稳定;对于固态熔盐堆来说,即使非能动余热排出系统失效,燃料元件温度上升也很缓慢,给人员干预采取必要措施提供了超过20天的宽限时间。分析结果表明了固态熔盐堆在应对极端事件时具有高的安全性。     

Er^3＋ Doped BaTiO30ptical-Waveguide Thin Films Elaborated by Sol-Gel Method

Erbium doped BaTiO3 optical-waveguide films on Pyrex substrate was elaborated successfully through sol-gel method. BaTiO3 is well crystallized when the film is annealed at 650℃ in air circumstance. The so-prepared films with 13 layers have comparatively lower refractive index than bulk BaTiO3, and it can support two TM and TE modes. Photoluminescence and up-conversion luminescence spectra proved the successful doping of rare earth ions.