布仑口水电站冲击式机组柔性电制动技术应用

为保证布仑口水电站机组停机过程中轴承油膜不被破坏,确保机组瓦温运行在安全范围内,解决制动停机问题,文章以新疆布仑口水电站为背景,介绍了冲击式机组柔性电制动技术的工程应用,重点介绍了布仑口电站冲击式机组停机方式、柔性电制动停机原理、电制动主回路接线形式、电制动流程、电制动系统主要设备参数,并对柔性电制动技术的基本思路和工程实现进行探讨。     

电制动停机装置在陈村水电站的应用

陈村水电站于１９８７年开始使用电制动停机装置，到１９９２年投用成功率达９６％以上。是国内全部采用电制动停机且连续正常运行时间最长的电站之一，本文简单介绍了电制动原理，重点介绍了电制动装置在陈村水电站运行情况以及提高电制动可靠性的做法，最后叙述了电制动装置应用的体会和今后值得注意的问题。     

水轮机组电气制动状态下保护误动闭锁方案研究与应用

大型水轮发电机在停机过程中经常采用电气制动方式,通过在发电机机端安装电制动开关,在发电机启动电气制动时通过电制动开关将定子三相短路,与此同时给发电机转子绕组以恒定励磁电流,产生电磁力阻碍转子的旋转,达到制动的目的。而在此过程中,发电机定子绕组的电压、电流及频率与发电机正常运行状态差别很大,发电机-变压器组保护有可能产生误动作。针对此种保护误动作的现象及闭锁方案进行了探讨,并进行了实际优化完善,以提高保护的可靠性。     

水电机组电制动停机技术的应用

总结１９８５年以来《关于推广使用水轮发电机电制动停机技术》的情况，详细列出已有１４个水电厂（站）总容量为４８２５ＭＷ，３２台机组以电制动为正常停机的制动方式在运行，并以实际单一机械制动的事例，说明电制动停机的优越性和明显的经济效益，并指出了运用情况令人不够满意的关键所在，建议基建时应一并考虑的意见理由，以期使电制动停机技术更加普及。     

电制动刀闸拒分导致停机失败缺陷分析

主要是结合生产实际分析某抽水蓄能电厂2号机组发电转停过程中,机组转速降至0,通过监控和现地检查,2号机组电制动刀闸未分开,导致2号机组发电转停机失败。现场检查发现电制动刀闸传动机构中的减速器分位侧轴承磨损、卡涩。经检修处理后,设备恢复正常运行。对电厂同类电制动刀闸拒分等缺陷处理具有借鉴意义。     

莲花水电站电气制动系统设计

莲花水电站装机容量为５５０ＭＷ，为了克服机械制动带来的隐患，对莲花水电站水轮发电机组采用电气制动方案。文中就该电站的电气制动系统的可靠性设计、制动方式设计、电气制动主系统方案设计、电制动控制系统方案设计等方面的内容做了简要论述。     

一例水轮发电机组高转速加闸原因分析及防范措施

对于转动惯量大、阻力矩小的水轮发电机组,为避免长时间惰性停机对轴瓦的损害,一般会同时采用电力制动和机械制动两种方式。但电气制动投入后,对残压信号的影响可能会带来后续机械制动转速接点的误动而造成高转速加闸。通过对某水电站一例高转速加闸事件进行分析,提出了几点防范措施,可对采用单套测速系统进行电制动的水轮发电机组的调试、运行提供有益的借鉴。     

发电机退电制动时转子过电压的分析

分析了隔河岩电厂发电机在退电制动时转子过电压的原因,提出了在制动变压器之前增加一个接触器以解决转子过电压的方法,结果表明,所用方法是可行的。建议将电厂目前的制动方式(恒流方式)改造成柔性制动方式,以便进一步提高机组运行效率。     

电制动技术在50MW水轮发电机组的应用

详细介绍了浙江华电乌溪江水电厂50HW水轮发电机组电气制动技术的系统设计原理、制动程序、控制回路、设备选型、现场试验运行情况等,为电气制动停机技术的应用提供一点经验和方法。     

电制动在水轮发电机组停机中的应用

水轮发电机组的容量越大,机组的转动惯量越大,停机所需要的时间就越长.当机组长时间在低转速下运行时,推力瓦的油膜被破坏而导致瓦温升高,润滑油容易变质,严重时会烧毁瓦面.为使机组不要长时间地在低转速下运行,必须对转子施加外力以强迫机组在要求的时间内停转.传统的制动方式是采用压缩空气操作的机械装置对转子进行连续制动,但它只能在较低转速时投入,故延长了停机时间,且制动器易磨损,制动时产生的粉尘还会污染环境等.电制动在较高转速时即可投入,制动时只有电磁功率,无机械磨损,且转矩与转速成反比关系,故可缩短停机时间.不过,机械制动可作电制动失效或机组内部电气事故时的后备制动.     

Call for Papers

正As the eldest and most distributed professional journal of water industry,Water Wastewater Engineering(W WE)gained very wide acceptance from the colleagues working in this field in this country since start publication in 1964.Now it is administrated by the Ministry of Construction of the People’s Republic of China and sponsored by the China Civil Engineering Society etc.     

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。     

SPATIAL AND TEMPORAL WATER QUALITY VARIABILITY IN AQUATIC HABITATS OF A CULTIVATED FLOODPLAIN

The floodplains of lowland rivers contain diverse aquatic habitats that provide valuable ecosystem services but are perturbed when intensively cultivated. Hydrologic, water chemistry and biological (fish) conditions in five aquatic habitats along the Coldwater River, Mississippi, were measured for more than 4 years: the river, two severed meanders that functioned as backwaters, a managed wetland and an ephemeral channel draining cultivated fields. Off‐channel habitats were connected to downstream regions 0.10% to 32% of the dry season and 24% to 67% of the wet season. The median temperatures for the five monitored sites ranged from 18°C to 23°C, the median total solids concentration for all sites was 135 mg L^?1, the median total phosphorus was 0.29 mg L^?1 and the median total nitrogen was 1.56 mg L^?1. Chemical and physical water quality displayed strong seasonal differences between the wet winter/spring and the dry summer/fall periods so that temporal variation consisted of gradual seasonal trends superimposed on strong diurnal variations. All off‐channel habitats exhibited periods of hypoxia and temperatures >30°C during the dry season. Between‐site gradients of water and habitat quality were strongly coupled to water depth and runoff loading. The rehabilitation of one backwater by increasing water depth and diverting agricultural runoff was associated with improved water quality and fish species richness relative to an adjacent untreated backwater. The diversion of polluted runoff and the use of water control structures to maintain greater water depth were observed to be effective management tools, but the former reduces the water supply to habitats that tend to dry up and the latter reduces connectivity. Published in 2011 by John Wiley & Sons, Ltd.     

库水波动下库岸边坡地下水浸润线解析解及误差分析

解析法是库岸边坡地下水浸润线计算中便于实际应用的方法,但该方法须基于若干假定并对潜水运动基本方程线性化后才能求解。针对各假定和线性化过程建立不同的地下水渗流数学模型,用解析法和有限元法解答上述数学模型,分析各误差大小及其规律。结果表明：库岸垂直处理带来的误差要小于方程线性化处理和不考虑非饱和渗流带来的误差,而且它们都随渗透系数变大而减小;在三峡库区库水调度情况下,假定库水位等速变化带来的误差对大多岸坡而言可以忽略;计算库岸边坡地下水浸润线时,解析法只适用于水位变化幅度相比含水层厚度较小,且几何边界规则、岩土结构简单、岩土体渗透性较好时的情况。     

Changes in Summer Irrigated Crop Area and Water Use in Southeastern Turkey from 1993 to 2002: Implications for Current and Future Water Resources

Changes in summer irrigated cropland acreage and related water use are estimated from satellite remote sensing and ancillary data in semi-arid Southeastern Turkey where traditionally dry agricultural lands are being rapidly transformed into irrigated fields with the help of water from the Euphrates-Tigris Rivers. An image classification methodology based on thresholding of Landsat NDVI images from the peak summer period reveals that the total area of summer irrigated crops has increased three-fold (from 35,000 ha to over 100,000) in the Harran Plain between 1993 and 2002. Coupled analysis of annual irrigated crop area from remote sensing and potential evapotranspiration based estimates of irrigation water requirements for cotton indicate a corresponding increase in agricultural water use from about 370 million cubic meters to over one billion cubic meters, a volume in accordance with the state estimates. These estimates have important implications for understanding the rapid changes in current agricultural withdrawals in Southeastern Turkey and form a quantitative basis for exploring the changes in future water demands in the region. For example, expansion of irrigated lands have led to a steady decrease in potential evaporation due to increased roughness and decreased humidity deficit in the Harran Plain. Assuming that the changes in future evaporation conditions will be of similar nature, water use for irrigation is expected to decrease over 40 percent in future irrigation sites. Incorporating this decrease in overall planning of the irrigation projects currently under construction should lead to improved management, and by extension, sustainability of water resources in the region.     

Spatio‐temporal variation of gross CO2 and CH4 diffusive emissions from Australian reservoirs and natural aquatic ecosystems,and estimation of net reservoir emissions

Carbon dioxide (CO₂) and methane (CH₄) diffusive emissions were measured during two field surveys in Queensland and Tasmania, Australia, using the floating chamber method. Bubbling and degassing emissions in 2010 were estimated in Koombooloomba Dam reservoir using only inverted funnels and gas concentrations, respectively. A total of 14 reservoirs and 16 rivers and lakes were sampled from 2006 to 2010. Spatial variation was substantial within each water body, as well as between them. The main drivers of diffusive emission variation were physiographic region and climate, with a clear demarcation being observed between diffusive emissions from tropical Queensland and temperate Tasmania, and between the humid West Coast Range (Tasmania) and dry Central Plateau (Tasmania). Higher CO₂ and CH₄ diffusive emissions were observed during the dry season, when long water residence times would promote organic matter degradation. Estimated total gross emissions, including diffusive, bubbling and degassing emissions, for Koombooloomba Dam reservoir were about 1.5 × 10⁶ t CO₂eq km² per year, or 24 × 10⁶ t CO₂eq per year. This corresponds to a plant emission factor of 3.18 kg CO₂eq MWh^?1. Using an estimate of terrestrial emissions derived from literature data for the Tully River catchment area, rough estimated net emissions from the catchment area are about 44 kt CO₂eq per year, or 5.83 kg CO₂eq MWh^?1, which is in the lower range of the studied reservoirs.     

Automated system for removal and pneumatic transport of fly ash from electric precipitator hoppers

A system for removal and pneumatic transport of fly ash is examined, in which air pulses act on batches (pistons) of ash formed in a duct. Studies are made of the effect of several physical parameters on the force required to displace a piston of ash and these serve as a basis for choosing a system for removal and pneumatic transport of ash simultaneously from several hoppers of an electric precipitator. This makes it possible to separate the ash particles according to size without introducing additional components. Formulas are given for calculating the structural and dynamic parameters of this system and measurements of indirect dynamic parameters are used to calculate the input-output characteristics of the system. In order to optimize the system, configurations for summing several ducts into a single transport duct for pneumatic ash transport are proposed. Some variants of dry ash utilization and the advantages of producing of size-separated particles are considered. __________ Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008).     

The flood pulse advantage and the restoration of river-floodplain systems

The ‘flood pulse advantage’ is the amount by which fish yield per unit mean water area is increased by a natural, predictable flood pulse. Evidence for this increase is presented from tropical and temperate fisheries. It is argued that increasing multispecies fish yield by restoring the natural hydrological regime is consistent with increasing production of other trophic levels and with restoration from ecological and aesthetic viewpoints. When applied to a river-floodplain system, this restoration would provide a large, self-sustaining potential for recreation, commercial exploitation, and flood control. An interim ‘natural flood pulse’ restoration approach is proposed for systems modified for navigation. This approach approximates the natural hydrological regime in a river reach and is intended as a first step in the long process of restoring the watershed.