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枕头坝一级水电站位于峡谷地区,接地网布置于各个区域的岩石平均电阻率均较高,整体接地网的面积较小,接地阻抗较大,发生接地故障时地电位升较大;在接地设计时需严格校验人身和设备安全,做好均压隔离措施,以免发生故障时接触跨步电势造成人身伤亡事故和网内电位差破坏二次设备绝缘而造成重大的经济损失。 相似文献
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索风营水电站接地网原设计中虽然已充分利用了电站自然接地体,并用接地干线构成了一个比较完善的均衡电位接地系统,但在2005年3月对厂区接地网工频接地电阻进行测试时实测的接地电阻为0.778Ω,大于0.5Ω的设计要求。为此利用库区水电阻率较低、水位较深的特点,布置了水下立体接地网,并加强了全厂接地网的连接,取得了明显的效果。 相似文献
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广州抽水蓄能电站处于高土壤电阻率地区,一期工程主要机电设备从法国引进,并配套提供电气设备的接地铜材,由中法联合进行接地系统设计,充分利用压力钢管,尾水管,主厂房及主变洞拱顶锚杆等自然接地体,在500kV出线场人工接地沟中置换低土壤电阻率的粘土,人工接地的材料主要使用铜材,本文介绍了接地网的布置,接地计算及优化设计,接地测量及效果。 相似文献
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马迹塘电厂接地网系统为建厂初期建设,所有设备的保护接地、工作接地以及电源零线等均接入该接地网系统,未建立单独的等电位接地网。电气二次屏柜等电位接地,包括开关站、主厂房、中控室及二次屏柜等电位接地反措。结合电厂现场实际情况进行了整改,现已稳定运行1a,取得良好效果。 相似文献
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(一)岩性新安江水电站位于长约800m的铜官峡谷上段.其厂坝区分布的岩层有两种,即千里岗砂岩和乌桐石英砂岩.千里岗砂岩分布,由右岸河床至左岸坝头,约占坝基面积的3/4,位于左岸高程70m以下的岩石呈青灰色,新鲜坚硬完整,高程70m以上为含泥质较多的中粒砂岩,层间常夹细砂岩或砂质页岩,小断层发育,岩石风化破碎较剧烈,缝隙多有夹泥充填.乌桐石英砂岩分布于右岸岸坡约占坝基面积约1/4.石英砂岩质坚而脆,层间普遍夹有软弱的薄层 相似文献
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龙滩水电站在500 kV发生单相接地故障时入地短路电流达26.4 kA,电站所在地区地质电阻率极高,按常规方式进行接地无法满足规程要求。在确保安全的前提条件下,工频接地电位升高按5 000 V控制,利用库区红水河河水与河床浅层电阻率较低(33.3~37.6Ω.m)的有利因素,通过采取在库区上游红水河中敷设大范围库区接地网并与原有接地系统连接等方式,极大地降低了整体接地系统的接地电阻。按此方案实施的龙滩水电工程接地系统电阻实测为0.168Ω,小于0.189Ω,取得了预定的效果。对龙滩水电工程的接地系统现状及要求进行研究、实施及测量等,进行深入的分析和总结。 相似文献
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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。 相似文献
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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. 相似文献
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Samples were taken year-round at eleven sites along the altitudinal profile (2900-1400 m a.s.l.) of the Gunnison River, a 329 km tributary of the Colorado River, to document the distribution of the Plecoptera and to evaluate responses to hypolimnial-release dams in the headwaters and middle reaches. Twenty-two species were present, with the greatest species richness occurring in an unregulated segment upstream of the middle reach dams; average nymphal biomass over the study period (175 organisms, 395 mg dry mass m?2) was also greatest in this segment. Only four species (58 organisms, 48 mg m?2) were present in the tailwaters of the headwater dam and values were greatly reduced (nine species; 35 organisms, 180 mg m?2) below the middle reach dams. The stonefly community recovered ca. 80 km downstream from the last dam (15 species; 244 organisms, 250 mg m?2), apparently in response to natural resetting of environmental conditions corresponding to those above the middle reach dams. At the most downstream site (11) only four species (four organisms, 16 mg m?2) were present. The observed distributional pattern is a classic serial discontinuity in response to hypolimnial stream regulation in a temperate latitude river. 相似文献
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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. 相似文献
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V. K. Konovalov O. V. Yashkin V. V. Ermakov 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2008,42(2):105-109
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.
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Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008). 相似文献
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Peter B. Bayley 《河流研究与利用》1991,6(2):75-86
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. 相似文献