一种新的电缆单端故障测距方法研究

本文对一种新的不受波速影响的电缆单端故障测距方法进行研究.该方法用小波变换检测出前3个故障行波到达测量端的时间,并将2个时距方程联立,求解出不受波速影响的故障测距公式.仿真表明该方法理论正确并切实可行.     

基于行波法的架空地线融冰故障定位技术研究

地线融冰目前缺乏有效的故障定位测距方法,人工巡线时间较长,导致地线融冰工作效率较低。现采用分布式行波定位技术,通过分析行波在地线融冰故障过程中的传输规律及折反射规律,提出了地线融冰故障行波单端及双端定位方法。开发了地线融冰故障定位系统,通过安装在地线上的监测装置采集融冰故障行波电流,实现故障点精确定位。在500 k V施黎甲线上应用地线融冰故障定位系统,现场融冰试验验证了该技术的可靠性,对于保障覆冰期地线融冰顺利实施具有重要意义。     

距离保护两种接线方式分析

对距离保护中的带零序电流补偿的接线方式和零序接线方式进行了分析,分析表明距离保护以接地阻抗继电器和相间阻抗继电器为核心,可以保护各种短路故障.     

基于行波分析的变压器绕组匝间短路故障定位

针对变压器绕组匝间轻微短路故障定位问题,本文提出基于行波分析的故障定位方法。该法在绕组线端输入低压脉冲以获取行波反射信号,基于相关系数和SG滤波的改进EEMD降噪法降低噪声对行波的干扰,分别采用相似度分析法与能量比值法分析行波,得到大致随故障位置单调变化的故障特征集,再结合遗传神经网络建立起故障特征与故障位置的映射关系,实现匝间短路故障定位。仿真和样本实验结果表明了本文方法的可行性。     

基于PSCAD线路距离保护的仿真分析

本文主要就电力线路的距离保护做了具体介绍,主要包括距离保护的基本原理、整定计算,阻抗继电器的动作特性、实现方法。并利用PSCAD软件对单相短路接地,三相短路接地故障进行仿真,并把仿真结果和理论计算进行了比较,因此更容易找到可靠性高,经济性好,便于实施的距离保护。     

煤矿井下电缆故障快速定位技术研究

针对煤矿井下低压电网故障点的快速定位问题,首先对常见故障类型和原因进行了分析,在分析基础上,详细研究了阻抗法和行波法等故障点粗定位方法的实现原理,以及音频感应法等故障精确定位方法,并对方法的适用范围和存在的问题进行了分析,随后对近年来出现的电网故障定位新技术的原理进行了研究。该研究对煤矿低压电网常见故障的定位和排除具有积极的指导意义。     

基于VMD-GST的TEO的煤矿供电线路单相接地故障测距方法

煤矿井下供电线路工作环境恶劣,时常发生故障,且存在故障定位的难度大、研究较少等问题.据此提出了基于VMD-GST的TEO行波故障测距方法,用于煤矿井下输电线路故障定位.首先,提取故障信号,并经K=3层VMD分解,得到波动较大的IMF分量;然后再将选择的IMF分量经广义S变换得到S模矩阵,并采用Teager能量算子法标定波头;最后通过行波测距公式得出故障位置.结果表明,所提故障测距方法于单相接地故障而言,有较高的精度.     

基于VMD-GST的TEO的煤矿供电线路单相接地故障测距方法

煤矿井下供电线路工作环境恶劣,时常发生故障,且存在故障定位的难度大、研究较少等问题.据此提出了基于VMD-GST的TEO行波故障测距方法,用于煤矿井下输电线路故障定位.首先,提取故障信号,并经K=3层VMD分解,得到波动较大的IMF分量;然后再将选择的IMF分量经广义S变换得到S模矩阵,并采用Teager能量算子法标定波头;最后通过行波测距公式得出故障位置.结果表明,所提故障测距方法于单相接地故障而言,有较高的精度.     

防止反向故障误动的自适应距离继电器

反向经过分支支路时产生的故障对距离保护有所影响,结合实用的四边形继电器特性对这种故障情况进行了分析.通过分析不同条件情况下继电器的误动情况,给出了解决方案,提出了自适应判据.通过仿真计算表明,这种继电器有很好的自适应性和选择性,能防止误动,具有广阔的推广应用前景.     

基于我国高压线路故障测距方法的研究

论文就我国高压线路的故障测距方法进行了分析比较,最后确定采用基于双端的行波测距法。由于现用的行波测距法在实际使用中存在一些制约因素,提出了使用小波变换技术及行波测距装置校验仪使问题得以改善。综合经济性、可实现性等因素,行波测距方法具有可靠性强、测距精度高等特点,完全不受故障类型、过渡电阻和系统参数的影响。     

Measuring-sequence planning by the nearest neighbour method and the refinement method

This paper focuses on the measurement, using a coordinate measuring machine (CMM), of the shape of a workpiece made up of geometric elements. It explores how a CMM can complete the whole measuring process with an optimised measuring sequence to reduce measuring time, after a CAD/CAM software system has planned the number and positions of the measurement points. In this paper, the nearest neighbour method and the refinement method are proposed to plan the measuring sequence. The nearest neighbour method uses individual element faces as the subject of planning. It takes the position closest to the starting point as the initial measuring face, and then gradually completes the sequence of all points. It arranges the sequence of measurement points on the initial measurement face by means of the nearest neighbour method as described in the aforementioned algorithm. It calculates the distance between the final point on the initial measurement face and all of the unmeasured points on the other faces. The point with the shortest distance between the final point on the initial measurement face and all of the unmeasured points on the other faces is selected as the next measurement point and the measurement face of this selected point is considered as the next initial measurement face. It determines whether all of the faces and measurement points are completely planned. The refinement method does not distinguish among element faces, but treats all planning points as the goal. The method is often used to handle the measurement-sequence problem where a large area and a large number of points are involved. The CAD/CAM software and power of calculation and analytical capability of the system can quickly obtain a suitable measuring sequence.     

Celling the japanese method

Just how do the Japanese make such a success of manufacturing. Ross Banerjee thinks the answer lies in continuous improvement?or Kaizen.     

抑制磨削颤振的实用方法--工艺条件适配法

在一系列磨削试验的基础上 ,提出抑制磨削颤振的实用方法———工艺条件适配法。并由实验验证了该方法的有效性。     

On the improved phase-grating method

A new method for computing scattering amplitudes in high resolution transmission electron microscopy has been examined. The method, which is called the improved phase-grating (IPG) method, is shown to produce reasonable results only for very small specimen thicknesses and diverges for thicknesses larger than 20–40 Å in copper [001] for accelerating voltages between 200 kV and 1 MV. The validity of the method is discussed and is shown to depend on electron wavelength, slice thickness, the number of reflections that are included in the calculation and the choice of specimen. It is also shown that the method does not readily allow for slice thicknesses smaller than the specimen periodicity along the incident electron beam direction.     

Research on the fracture process of steels by the acoustic method and the pitch net method

The results of experimental investigations on the process of damage accumulation in low-carbon and medium-carbon steels subjected to static and cyclic loading are presented. The algorithm of the damage evaluation of steels under static loading and high-cycle fatigue with the use of results of acoustic measurements, the measurement of hardness, and the evaluation of the microplastic deformation by the net method is proposed.     

浅议PDCA循环方法和统计分析方法在质量控制中的应用

在机电安装施工过程中,针对工程质量较难控制的问题,文中阐述了对影响施工质量的因素,采用PDCA循环方法和统计分析方法可对施工质量进行有效控制.     

确定冲模压力中心的计算机作图法

提出基于AutoCAD软件的确定冲模压力中心的计算机作图法 ,这种方法理论严谨 ,结果准确 ,比原有的计算法和作图法简捷、快速 ,具有应用推广价值     

基于最小距离法和近邻法的数字图像识别

模式识别诞生于20世纪20年代。随着40年代计算机的出现、50年代人工智能的兴起,模式识别在60年代迅速发展成一门学科。模式识别系统主要由4个部分组成:数据采集及预处理,特征生成,特征选择与提取,分类器的设计与识别。主要应用方法分为两类:几何(非参数法)和概率(参数法)。其中几何方法包括:最小距离法、近邻法、梯度下降法、神经网络以及支持向量机。概率法包括:最小错误率Bayes决策,最小风险Bayes决策、聂曼-皮尔逊法。本文运用最小距离法和近邻法对数字图像进行识别,进而对两种方法做出比较。     

机械零件强度的可靠性设计与传统设计

从基本原理上对机械零件的可靠性设计方法与传统设计方法进行了比较, 指出了可靠性设计方法的重要性与必要性。     

Relative errors in evaluating the electromagnetic flowmeter signal using the weight function method and the finite volume method

In the signal analysis of an electromagnetic flowmeter, the weight function method (WFM) involves a numerical integration of products between the magnetic flux density vector, the weight function and the velocity profile function in two-dimensional analysis. The electromagnetic flowmeter signal can also be predicted by solving the governing flowmeter equation by the finite volume method (FVM). The present study is aimed at comparing the calculation accuracies of WFM and FVM. The test flows are fully developed laminar and turbulent flows in a straight pipe under uniformly distributed magnetic field. The calculation accuracies are also compared between different O-type grid systems. It was found that the accuracy of both methods depended strongly on the grid system. In particular, for turbulent flow whose axial velocity component changes very rapidly near the wall, the accuracy of WFM was found to depend strongly on the cell configuration near the electrodes.