Small field of view imaging using wavelet encoding with 2 dimensional RF pulses and gradient echo: phantom results

Object  

The objective of this work is to propose an imaging sequence based upon the wavelet encoding approach to provide MRI images free from folding artifacts, in the small field of view (FOV) regime, such as dynamic magnetic resonance imaging (MRI) studies.     

Protection of parallel transmission lines using wavelet transform

A new scheme to enhance the solution of the problems associated with parallel transmission line protection is presented in this paper. The scheme depends on the three line voltages and the six line currents of the two parallel lines at each end. Fault detection, fault discrimination, and calculation of the phasors of the measured signals are done by using wavelet transform (WT). By comparing the magnitudes of the estimated current phasors of the corresponding phases on both lines, internal faults on the parallel lines can be identified. Also, by calculating the distance element of the phases on which a disturbance is detected and having a very small current difference magnitude can enhance and strengthen the scheme. Studies show that all types of faults at different loading conditions can be correctly identified in less than one cycle of the fundamental frequency.     

公路外场监控数据传输与对象规范研究

随着智能交通系统(ITS)的发展,ITS通信网中出现了数据源与数据的多样性等诸多因素,造成了监控中心与外场设备之间不能建立实时信息沟通.在研究了ITS的通信协议架构的基础上,改进了协议体系和编码规则,规范了可变情报板等外场设备的数据对象,统一了数据格式与通信规约,更好的实现了监控中心与外场设备之间数据交互的互操作性和可...     

基于分离模型的双回平行输电线路可靠性评估

提出了基于分离模型的考虑独立停运、共因停运和相关停运的双回平行输电线路可靠性评估模型,解决了传统的评估模型计算量大等缺点,在电力系统中双回路使用越来越多的情况下,使可靠性评估计及其他停运模型的影响成为可能。该模型可以很容易地计及不同的停运模型,采用交集的概念计算系统的失效概率和等效故障率,并分析不同停运模型对系统故障率的影响,算例分析验证了分离模型的有效性。     

发输电组合系统可靠性评估的Monte-Carlo仿真及并行处理

并行处理为大规模电力系统问题的分析和计算提供了新的机会和挑战，为大大缩短电力系统可靠性评估的计算时间，实现在线应用提供了强有力的支持：本文介绍了发输电组合系统可靠性评估的基本概念，并详细分析了各种Monte-Carlo仿真的基本原理，提出了一种基于粗颗粒异步算法的并行处理的网络拓扑结构，并分析其基本原理，最后介绍了实现主从处理器以TCP／IP方式通信的方法。     

An accurate fault location algorithm for parallel transmission lines using one-terminal data

An accurate fault location algorithm for parallel transmission lines, using fundamental frequency components of post-fault voltage and current measured at one terminal, is described in this paper. Parallel transmission lines can be decoupled into the common component net and differential component net. In differential component net, the current distributing coefficient is a function of fault distance, and the differential component current at the fault point can be expressed in terms of the current at the local terminal. Therefore, for asymmetrical faults, the phase fault current can also be expressed as a function of local terminal current and fault distance. With the fault boundary conditions for a given fault type, the fault location equations can then be derived. Based on distributed parameter line model, the proposed algorithm achieves superior locating accuracy, with mutual coupling between circuits, source impedance and fault resistance having very little influence on the locating accuracy. The performance of new algorithm is verified by computer simulation results for transposed and non-transposed lines.     

Determining generator contributions to transmission system using parallel vector evaluated particle swarm optimization

In this paper, the generator contributions to the transmission system are determined by an evolutionary computation technique. Evaluating the contributions of generators to the power flows in transmission lines is formulated as a multiobjective optimization problem and calculated using a parallel vector evaluated particle swarm optimization (VEPSO) algorithm. Specifically, the contributions are modeled by particles of swarms whose positions are optimally determined while satisfying all multiobjectives and other physical and operating constraints. The VEPSO method is parallelized by distributing the swarms in a number of networked PCs. The proposed parallel VEPSO algorithm accounts for nonlinear characteristics of the generators and transmission lines. The applicability of the proposed parallel VEPSO algorithm in accessing the generator contributions is demonstrated and compared with analytical methods for four different systems: three-bus, six-bus, IEEE 30-bus, and 136-bus test systems. The experimental results show that the proposed parallel VEPSO algorithm is capable of obtaining precise solutions compared to analytical methods while considering nonlinear characteristics of the systems.     

双模异构配电场域网多径并发传输动态决策算法

为提高配电场域网节点间的传输速率和连通率,构建了具有高速电力线宽带载波和微功率无线通信能力的混合多径双模异构配电场域网。首先论述了该场域网的拓扑结构、组网过程以及维护机制。其次设计了一种滑动窗口加权平均链路度量方法,采用改进的跳数受限Bellman-ford最短路径算法计算混合多径路由,并使用最近最多使用策略对各节点路由进行分散更新。在此基础上设计了一种自适应多径并发数据传输动态决策算法。最后将构建的该场域网应用到配电信息采集系统中,并在实验室和工程现场对其性能进行了测试。测试结果表明,该场域网比单模场域网在提高抄收率和缩短抄收时间方面效果明显。     

佛山地区典型变电站和输电线路电磁环境监测分析

通过对广东佛山地区110 ~500 kV典型架空输电线路和变电站周围的电磁环境参数（工频电场、工频磁场、无线电干扰）进行实际测量和仿真计算,分析了不同电压等级、不同类型典型架空线路和变电站周围的电磁环境水平及分布状况。统计结果表明,各电压等级、各类型输变电设备周围电磁环境参数均满足国内外相关标准限值要求。重点分析了500 kV输电线路、220 kV城区变电站等输变电设备周围电磁环境参数测试结果和分布特点,针对可能出现的输变电设备电磁环境超标问题提出输变电工程规划的设计建议。     

基于无线射频和PLC的智能水质监测系统

针对水质监测工作的特殊环境,将电力载波通信和无线射频相结合,设计了一种新型智能水质监测系统。系统采用KW01与SSC1641进行组网,实现基于无线射频模块与电力载波模块的有效通信模式,并基于此模式设计了由传感器节点、根节点、控制集中器以及主控计算机组成的整体监测系统。实验结果表明,该控制系统通信稳定、实时性高、成本低且易于实现,具有良好的应用前景。     

背靠背直流输电工程网络损耗监测系统研究与实现

为实现背靠背直流输电工程损耗的实时在线监测,文中设计了一套网络损耗监测系统,主要包括损耗监测装置和上位机软件平台两部分.该损耗监测装置基于两种数据采集方案,能够适应不同工程现场的需求,兼容多种类型的交、直流信号,实现整流侧与逆变侧、交流侧与直流侧的数据时间同步,彻底消除多台电能计量设备之间的误差一致性问题,达到系统各部...     

平行输电线路可靠性同调指标研究

对输电系统可靠性非同调的研究有助于提高输电利用效率和可用率。针对多回平行输电线路,基于单重原发故障,考虑保护拒动和相关跳闸,分析输电线路可用率和传输容量概率分布。提出两个绝对同调指标(降额运行概率比、期望载荷容量比)以及一个条件同调指标(满足给定载荷概率比),确定两回线路优于三回线路的非同调条件。对条件同调指标关于一次和二次设备可靠性参数进行灵敏度分析,以此量化相同同调水平下,一次和二次设备可靠性参数的换算关系。算例结果验证了所提方法的正确性。     

分布式源场极板结构射频LDMOS器件的设计

为了减小射频LDMOS器件中场极板寄生电容,提出一种具有分布式源场极板结构的射频LDMOs器件,给出了器件结构及工艺流程。借助微波EDA软件AWR对场极板进行了三维电磁仿真优化设计。仿真及测试结果表明,所设计的分布式源场极板结构在不影响器件击穿电压的条件下,能有效减小LDMOS器件寄生电容,提升器件增益、效率及线性度等射频性能。     

Remote sensing system for spatial electric field strength using free space light transmission

Most of the breakdowns in an electric power system are caused by lightning to the tower used for high‐voltage transmission wires. To avoid accidents due to lightning, it would be desirable to develop a measurement system for the spatial electric field distribution around the tower. We have developed a new system that can measure the electric field around the steel tower for electric power transmission by using an optical electric sensor. In conventional methods, the sensor is generally illuminated by light transmitted by optical fibers. On the other hand, the new measurement system illuminates the Pockels sensor directly by using a laser to measure the far electric field. Furthermore, our newly proposed feedback system makes it possible to measure the spatial electric field without concern for the change of Pockels sensor's operation point influenced by temperature change. This system is applicable as a remote sensing system to monitor the spatial electric field around a high‐voltage transmission line. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(2): 10–19, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20552     

输电线路动态监测增容技术

提高现有输电线路的输送容量有两种方法,即静态提温增容技术和动态监测增容技术。主要论述现有输电线路动态监测增容技术,指出其中的技术关键。     

梯度磁场标准装置组成及不确定度分析

介绍了梯度磁场标准装置的系统组成和工作原理,并对其测量不确定度进行分析.装置可单独产生梯度磁场,也可以在梯度磁场上叠加均匀磁场,两种磁场方向相同,以确保合成磁场仍具有优良的线性度,复现梯度磁场的范围1.5～120μT/m,测量不确定度为1.5×10–3(k=2).装置可用于校准矢量梯度磁强计,也可以用于校准原子式磁强计的梯度容差.     

一种同杆并架双回线接地距离保护方案

距离保护应用于同杆并架双回线时其动作性能受零序互感的影响.通过对同杆并架双回线接地故障时零序电流特点以及零序互感对接地距离保护影响的分析,指出两回线零序电流反向是同杆并架双回线接地距离保护误动的主要原因,根据两回线零序电流反向时,故障线路的零序电流大于非故障线路,提出了一种逻辑判断的零序电流补偿方法.数字仿真的结果表明,该方法提高了同杆并架双回线距离保护的性能.     

一种同杆架设多回线路简化零序互感计算方法

提出一种同杆架设多回线零序互感计算方法,指出线路的零序互感矩阵是一组独立的参数,线路不同运行方式下的零序参数可根据这些独立参数,由矩阵变换的方法计算得到.该方法不需要重复的试验实测,极大简化了零序互感参数的获取过程,提高了工作效率.同杆4回线路实际现场测试实例结果验证了该方法是正确的,且具有较高的精度.     

柔性直流输电系统交直流并列运行与孤岛运行方式间的切换控制

首先分析了系统在交直流并列运行和孤岛运行方式下的控制策略,基于此提出了系统从交直流并列运行转为孤岛运行和从孤岛运行恢复到交直流并列运行的切换控制方法。以某实际工程参数为例在PSCAD/EMTDC仿真平台上搭建了系统仿真模型,对所提出的切换控制方法进行了仿真验证。结果表明,所设计的切换控制方法能及时检测出系统的运行状态,并自动进行相关控制方式的切换,在切换过程中系统各电气量没有剧烈波动,不会影响系统的安全稳定运行。