电网连锁故障的事故链模型

连锁故障是诱发电网大面积停电事故的主要原因之一。事故链可以恰当地表征连锁故障的特征。建立基于事故链的电网连锁故障模型,是实施连锁故障预测、预控的基础,对防止发生大停电事故具有重要意义。文中充分考虑连锁故障过程中的主要影响因素,利用现有PSASP等分析工具,建立用于监控的连锁故障的事故链模型。根据事故链与连锁故障的关系,提出将故障选择限制在供电路径上,从而有效降低了计算工作量;利用连锁故障的事故链模型,可以采用安全科学的相关方法实现连锁故障的监视和预控。对江西电网的实际应用表明,该方法对分析区域性大停电或电厂全停事故非常有效,并已在电网规划中得到应用。     

一种基于连续线性规划的静态稳定预防控制方法

针对故障后不存在静态稳定平衡点的严重失稳故障，提出了一种静态稳定预防控制算法。该方法基于连续线性规划技术，将预防控制问题分解为故障参数空间上虚拟稳定临界点及其控制灵敏度的计算子问题和基于灵敏度的线性规划控制子问题。在前一个子问题中，运用故障连续潮流工具分别计算得到每个失稳故障的虚拟稳定临界点；在后一个子问题中，采用了筛选参与控制集和限制可控区间等策略来提高线性规划问题计算的有效性。对国外一个3 000节点的实际系统的应用表明了所提出的算法是有效、实用的。     

小世界电网的连锁故障传播机理分析

随着复杂网络理论的发展，特别是电网的小世界特性的发现，电网的复杂结构特性对故障连锁反应的影响越来越受到关注。文中以复杂网络科学理论为基础，考察了小世界电网中节点的非均质特性，提出多种故障模式和故障指标，重点分析了连锁故障在小世界电网中传播的内在机理，并提出改善小世界电网承受故障能力的有效措施。对实际电网的拓扑特性研究和故障仿真结果表明:小世界电网本身的结构脆弱性是造成大规模连锁故障迅速蔓延的根本原因，外界因素不能从根本上改变这个弱点，改善电网资源配置、尽可能避免负荷分布的极不均匀性对预防大规模连锁故障和提高电网的可靠性将更有意义。     

基于隐性故障模型和风险理论的关键线路辨识

在大规模电网中，由简单故障触发的电力系统连锁故障常常会引起大停电的灾难性后果。为了研究复杂电网连锁故障的传播机理，同时找出对连锁故障产生重要影响的关键线路，文中基于模拟连锁故障的隐性故障模型和风险理论，提出了复杂电力系统的线路故障风险评估方法，并辨识出了对系统大停电产生重要影响的一系列关键线路。模型考虑了线路过负荷保护、隐性故障、控制策略及系统运行等参数，对IEEE 118节点系统仿真结果表明，在重负荷状态运行下只对辨识出的少量关键线路加以改善，就可以使系统停电概率大幅减小，特别是大停电概率;在临界状态运行下改善少量关键线路，则可以使系统脱离临界状态，避免大停电发生。     

基于蝴蝶优化算法的电力系统故障诊断应用研究

针对电力系统故障诊断的不确定性,以及保护开关和断路器动作信息中常出现的误动、拒动等问题,笔者提出一种基于蝴蝶优化算法的电力系统故障诊断方法,重点分析了该方法在解析大数据模型中对目标问题快速求解的特点,给出了数据引入时的预处理过程,充分利用蝴蝶优化算法在寻迹方面的推理能力,根据报警信息搜索电网数据库,提出故障假设及诊断结果。采用IEEE-39节点进行验证,并与人工神经网络方法进行比较。结果表明,该方法目标更加明确,且收敛速度更快,适用于网络规模大的电力系统故障诊断。     

电网连锁故障演化机理与博弈预防

连锁反应故障是导致大停电的重要原因。回顾了2003年以来世界范围内3次较为严重的连锁故障造成的大停电事故，通过对连锁故障发展过程的总结，得出了连锁反应故障的演化规律与一般特征。在此基础上，对连锁反应故障的机理进行了分析。文中将博弈思想应用于连锁故障的预防，将电网出现的扰动作为对弈中的进攻方，系统被动的调整作为被动的防御，提出连锁故障的对弈防御策略，一旦电网发生扰动则系统做相应调整，类似于对弈过程二人的交替走步。机理分析表明，这种调整削弱了元件间的关联作用，将系统运行点向远离临界状态的方向移动，因此可有效预防连锁故障。     

电网复杂性及大停电事故的可靠性研究

从电网连锁故障的近似整体模型的统计分析、动态特点和风险评估入手，探讨了近期关于电网复杂性和连锁故障机理的一些研究进展。众多学者对北美电力可靠性协会（NERC）提供的北美地区15年的事故数据进行分析，发现其事故概率和事故规模近似服从幂指数律，并具有集群特性。学者们提出了多种连锁故障模型来阐释连锁故障的机理。进一步研究发现，电网是一个具有自组织临界特性的网络，其网络演变特性必然导致系统趋向临界状态，而系统临界负荷状态下连锁大停电事故的风险大大增加。要削减和预防电网连锁故障的发生，就需要寻找降低系统风险的作用力，并建立一个综合评估框架来进行分析和研究。     

基于异步迭代的多区域互联系统动态潮流分解协调计算

在全局电网分解协调计算中，为增加各子系统计算的独立性，并减小协调计算对通信系统的要求，提出了一种新的基于异步迭代的互联系统分解协调动态潮流计算方法，这种方法允许每个参与分布式计算的子系统自由选择本系统内的Vθ节点，采用内、外两层迭代的方式求解整个互联系统的动态潮流。以各子系统单独潮流计算作为内层迭代，再利用边界条件构造关于边界节点状态量的不动点迭代格式，通过不断修改各子系统相应外边界节点的等值注入作为外层迭代来统一全网潮流解。所提出的算法经IEEE 9节点试验系统验证，可获得全网动态潮流解。     

基于动态仿真的连锁故障分析

提出一种基于长期动态仿真的电力系统连锁故障模型。该模型不仅考虑了动态过程中机组保护、变压器励磁保护、低频/低压减载、线路过载与短路故障、解列等因素，而且充分考虑了随机因素对这些保护元件的影响，可较为准确、有效地模拟电力系统连锁故障。基于PSS/E，采用蒙特卡罗算法对实际电网予以仿真，结果表明，停电规模 — 频次基本符合幂率分布且存在临界点，当故障规模超过临界点时系统幂尾特性发生变化且停电规模及其概率迅速增大，临界点的提出对预防大停电有参考价值。     

基于广域信息的防连锁过载跳闸保护

连锁过载跳闸是大停电事故的初期表现，防连锁过载跳闸是防止电网大面积停电的重要措施。文中提出了基于广域信息的防连锁过载跳闸保护原理。该原理以重要母线为单元，利用正常运行时存储在广域网调度中心的节点阻抗矩阵中的相关元素估算各支路的过载电流系数，以分析过载支路开断后有无引起连锁跳闸的可能，及时告知调度中心采取防连锁跳闸的措施，以防大面积停电。IEEE 39节点系统的仿真验证了该方法的可行性。     

地下厂房施工过程的三维非线性数值模拟分析

根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。     

Evaluation of freshwater mussel relocation as a conservation and management strategy

The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects.     

基于模型试验的河床砂砾石层基本特性研究

为了经济可靠地确定深厚覆盖层的基本特性参数,以大渡河双江口水电站坝基河床砂砾石层基本特性研究为工程背景,进行大尺寸模型试验,研究河床砂砾石层的旁压模量和动探击数随密度、级配以及上覆压力的变化规律。根据室内模型试验结果,结合现场旁压试验及钻孔试验成果,推断出坝址区河床砂砾石相关层位的密度,并依此进行砂砾石室内力学试验,获得设计所需力学参数。研究成果可为深厚覆盖层基本特性测试提供新的方法。     

基于BP神经网络-马尔科夫链模型的隧道围岩位移预测

在隧道工程施工中,围岩位移预测起着很重要的作用。将BP神经网络-马尔科夫链模型引入到隧道围岩位移预测中来,通过对训练样本的学习,利用BP神经网络实现了对位移时间序列的滚动预测,同时得到了实测值与预测值的相对误差;在此基础上利用马尔科夫链对相对误差进行修正,有效地提高了预测结果的精度。并将该模型应用于某公路隧道拱顶下沉位移时序预测中,结果表明该模型具有精度高、科学可靠的特点,为隧道围岩变形的预测提供了新的途径。     

Short communication. Pipelines as a refuge for freshwater snails

In the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment.     

浙江省水域调查录入系统的设计和应用

浙江省水域调查录入系统将调查数据与电子地图相整合,对分类水域数据进行统计计算,并对输入数据进行合理性和完整性检查,得到调查范围内现有水域的详细数据,实现了水域调查数据输入、计算、统计和查询的数字化管理,提高了工作效率和工作质量,为各地下阶段水域保护规划编制和水域管理工作提供了数据支持。对该系统的设计原则、功能和技术设计等作了介绍。     

基于CT-连续加荷水泥乳化沥青混凝土细观损伤规律研究

利用CT技术对水泥乳化沥青混凝土的细观损伤过程进行实时扫描观测,获得了混凝土试件在连续加荷下的CT图像。通过采用直观分析法、CT数分析法、CT数与损伤变量关系3种方法分析表明,水泥乳化沥青混凝土的破坏过程可分为压密、扩容、裂纹扩展、破坏4个阶段,同时混凝土在受压过程中具有韧性,在极限荷载之前各断面处于压密和微扩容的强化阶段,极限荷载之后混凝土从损伤到破坏发展比较平稳。     

浅谈天湖水电站水轮机运行故障及处理措施

简述天湖水电站投运以来各种故障的表现形式，分析其原因，提出了相应的处理方法及措施，并对合理利用国内外设备提出建议。     

Fish assemblage response to recent mitigation of a channelized warmwater stream

Various designs of low‐head dams are used to rehabilitate streams or forestall upstream channel incision after channelization. We report on the efficacy of using notched sills and grade control structures (GCS) to restore the fish assemblage in Luxapallila Creek, Mississippi. We tested the null hypotheses that habitat variables and species richness, evenness, and assemblage structure would not differ among: (1) a channelized segment with no modifications; (2) a channelized segment mitigated by the installation of sills and GCS; (3) a segment upstream of the installations and undergoing channel incision; and (4) an unaltered segment. Although habitat variables changed, neither species richness, evenness, nor fish assemblage structure differed between mitigated and channelized segments with both exhibiting less richness and different assemblage structures than the unaltered segment. Lack of differences in species richness between the incised and unaltered segments suggest that the GCS may have halted the negative effects of upstream channel incision before species were extirpated. Conspicuous habitat differences between the altered (channelized and mitigated) and unaltered segments were lack of backwaters and canopy coverage and finer substrates in the altered segments. Our results suggest a more comprehensive rehabilitation strategy is required in Luxapallila Creek. Published in 2003 by John Wiley & Sons, Ltd.     

NUMERICAL STUDY OF WAVE EFFECTS ON SURFACE WIND STRESS AND SURFACE MIXING LENGTH BY THREE-DIMENSIONAL CIRCULATION MODELING

1. INTRODUCTION Coastal and continental shelf regions are characterized by intensive interaction between wave and current. These regions are of great economic significance to mankind. Therefore, the modeling of wave and current as well as their mutual int…