缩短户内185～300mm~2电缆终端头搭接时间

1选题理由电缆作为电力系统中重要的传输设备,其电缆终端头搭接质量的好坏是电缆线路能否安全运行的关键,对电力设备的稳定运行有着重要的影响。2010年7～12月期间,桐庐县供电局一次检修班共完成户内电缆终端头搭接工作152个,其中搭接截面积185～300 mm2电缆终端头100个,     

配电柜一次线母排搭接问题的探讨

铜排搭接是配电柜生产中常遇到的问题,简单的主流排和次流排垂直搭接,在一些文件书籍中都涉及到,满搭接也是常规的母排搭接方式。但在实际生产中常遇到在一个主流排上的同一位置搭接相向的两根次流排的情况,那么就出现了半搭接、局部搭接的形式,但搭接多大的尺寸才能满足搭接面的载流量呢?满搭接是不是最好的搭接方式呢?本文对此作了一定说明,并把在实际工作中多年的经验搭接方式介绍给大家,以供大家一起探讨。     

10 kV配电网地电位搭火线夹

<正>1研发背景与功能目标目前用电客户的新建线路与设备或新增专用变压器要想接入电力网并投运使用,通常使用的搭火线装置是铜或者铝并沟线夹来T接;俗称并勾线夹它是一种应用于35 kV及10 kV配网线路搭接、T接使用的一个设备。使用传统的并勾线夹搭火必须将被搭接线路停电,并需要采取相应安全措施由人工登上电杆进行搭接;或采取目前比较成熟可靠的等电位带电搭火方式,而等电位带电搭火需要使用绝缘车与绝缘服并受制于交通和气候条件。鉴于目     

复杂边坡超高脚手架边界三维模拟研究

以福堂水电站边坡处理工程脚手架为例,依托ANSYS计算平台,开发能模拟脚手架与边坡搭接形式、复杂边坡、超高脚手架的计算平台,并比较了传统铰接搭接计算方法与新式模拟摩擦搭接计算方法的异同.填补了脚手架相关规范的空白,对实践具有指导意义.     

低压引线T形线夹的应用

在日常抢修工作中,江苏省邳州市供电公司抢修班员工在处理设备故障时,发现了这样一个现象,故障点集中在T接线头上,搭接的线路接头一边是铜芯电缆,一边是铝芯电缆,铜铝线搭接处氧化后出现了安全隐患。如何才能消除这类安全隐患,一时成了抢修班员工思考的重点。在班组学习会上,一位员工介绍了一种从书上看到的将支导线连接到干导线上的高压用T形线夹:其横部开干线槽,纵部开支线孔,干线槽内壁和支线孔内     

配电网绝缘导线搭接的要领

在新农村电气化建设改造中大量采用架空绝缘导线,使农村电网绝缘化率大幅提高.但在绝缘化配电网实际运行中,线路搭接处经常出现这样那样的问题,绝缘化配电网建设中线路搭接成了关键环节.笔者现根据实际工作经验,谈谈绝缘导线搭接的要领. 1 不能直接用刀剥离主干线绝缘层搭接导线 直接把主干线绝缘层用刀剥掉,把要搭接的导线搭接上去后再用绝缘胶布包裹修复绝缘层.该施工方法简单方便,随时搭接不受任何限制,为工作责任心不强,喜欢偷工减料的施工人员经常采用.     

开关柜局部放电地电波传播特性及试验

高压开关柜是配电系统中的关键设备,是直接面向用户的重要环节。开关柜在长期运行过程中,由于各种客观原因可能会出现电缆搭接处故障、触头故障、绝缘劣化等问题,从而发生局部放电导致开关柜局部温度升高,绝缘水平下降,甚至导致设备爆炸。所以及时发现和掌握开关柜运行状态对保证设备正常运行,减小经济损失有重要意义。     

标准化建设在35kV变电站的应用与实践(续一)

<正>1.5.4高压设备母排绝缘变电站设备安装需要大量使用铝母排。铝母排给施工和运行带来许多便利,虽然铝母排表面刷有相序漆,但起不到绝缘作用,敞露的铝母排如果有异物搭接极易造成接地或短路。城南变对全站所有铝母排加装了绝缘护套,该绝缘护套采用了对应相序色,相比刷相序漆更持久,降低了维护工作量。     

深厚砂砾石地基墙幕结合防渗体系搭接长度优化研究

目前深厚砂砾石地基墙幕结合防渗体系普遍采用10m的经验搭接长度,针对搭接长度在设计中偏于保守的现状,结合新疆下坂地水利枢纽工程,采用了有限元数值模拟计算和归一化处理的方法,在防渗体系不同深度布置尺寸和搭接长度的情况下,建立有限元数值计算模型,对防渗墙的受力和位移进行研究分析,计算分析出新疆下坂地墙幕结合防渗体系优化搭接长度度值,并总结出墙幕优化搭接长随防渗墙修建深度的变化规律,为深厚砂砾石地基墙幕结合防渗体系的设计和施工提供一定的参考。     

避免设备连接部位发热、烧毁的措施

在配电设备故障处理中，经常遇到设备连接部位发热、烧毁的现象。要解决连接部位发热、烧毁的问题，扎实做到以下几点，可以大大提高设备的安全运行。     

Water productivity in smallholder irrigation schemes in South Africa

This study investigates the productivity and value of water in two smallholder irrigation schemes (Zanyokwe and Thabina) in South Africa. We apply the residual valuation method (RVM), willingness to pay (WTP) and cost-based approaches (CBA) (i.e. accounting costs of operation and maintenance) to evaluate water productivity and values per crop, per farm, and by scheme. In both schemes, water value estimated by the RVM for vegetables (cabbage, tomatoes and butternuts) is greater than water value for dry maize. At the farm and scheme levels, a comparison was made between gross margin per m³ of water, WTP per m³ and accounting cost per m³ to estimate the relative value of water productivity. The active farmers in the Zanyokwe scheme have lower WTP per m³ (R0.03) than the gross margin of output (R0.69). Also, the accounting cost (R0.084) per m³ of water is less than the gross margin. In the Thabina scheme, active farmers are willing to pay (R0.19) per m³ of water. Hence farmers in Thabina are ready to pay as much as three times the proposed costs of O&M (R0.062) per m³ of water used. Both the accounting cost and willingness to pay are less than the gross margin per m³ of water in the Zanyokwe scheme. Our findings indicate that extension and training may be required to improve the productive use of water for those farmers whose returns are insufficient to cover the cost of supply.     

Variation in vineyard evapotranspiration in an arid region of northwest China

Grapevines are extensively grown in the arid region of China, but little information is available on the diurnal, seasonal and interannual variability of vineyard evapotranspiration (ET). To address this question, two vineyards in the arid region of northwest China were taken as an example to study the variation of ET using Bowen ratio-energy balance method in 2005-2008. Results indicate that the Bowen ratio method provided accurate estimate of vineyard ET as the instrument was correctly installed. Irrigation and rainfall increased daily ET by 38 and 175%, respectively, but frost decreased it by 32%. Daily ET had a maximum value of 1.6-3.5 mm/d at the berry development stage, and a minimum value of 0.8-1.7 mm/d at the early and later stages. The total ET was 226-399 mm over the growing season. The ratio of transpiration to evapotranspiration was 0.52 and the modified crop coefficient (K_cm) was 0.71-0.88 (except 2005) over the whole growing stage. Larger interannual difference of ET and K_cm mainly resulted from the difference of irrigation and rainfall between different years.     

Variability in energy partitioning and resistance parameters for a vineyard in northwest China

Grapevines are extensively grown in the semiarid and arid regions, but little information is available on the variability of energy partitioning and resistance parameters for the vineyard. To address this question, an eddy covariance system was applied to measure energy balance over a vineyard in northwest China during 2005-2006. Result indicated that 2-year average Bowen ratio (β) of vineyard was 1.0, canopy resistance (r_c) 289.3 s m⁻¹, aerodynamic resistance (r_a) 9.7 s m⁻¹ and climatological resistance (r_i) 117 s m⁻¹. This implied that the annual energy was split almost equally between sensible heat and latent heat. Compared to the corresponding values in other ecosystems reported by Wilson et al. [Wilson, K.B., Baldocchi, D.D., Aubinet, M., Berbigier, P., Bernhofer, C., Dolman, H., Falge, E., Field, C., Goldstein, A., Granier, A., Grelle, A., Halldor, T., Hollinger, D., Katul, G., Law, B.E., Lindroth, A., Meyers, T., Moncrieff, J., Monson, R., Oechel, W., Tenhunen, J., Valentini, R., Verma, S., Vesala, T., Wofsy, S., 2002. Energy partitioning between latent and sensible heat flux during the warm season at FLUXNET sites. Water Resource Research 38, 1294-1305.], the vineyard had a higher β, r_c and r_i than deciduous forests, corn and soybean, and grassland. Such difference was mainly attributed to (1) serious water stress in 2005, which resulted in a greater r_c up to 364.4 s m⁻¹; (2) sparse canopy with row spacing of 2.9 m and plant spacing of 1.8 m; (3) warm-dry climate and high attitude (1581 m) along with higher r_i and lower psychrometer (54 Pa K⁻¹) in the arid region of northwest China. These characters of vineyard revealed varying process of energy partitioning and surface resistance, and provided a scientific basis in understanding and modeling water and energy balance for the vineyard in the semiarid and arid regions.     

Phosphorus dynamics in tile-drain flow during storms in the US Midwest

Excess phosphorus (P) in freshwater systems has been associated with eutrophication in agro-ecosystems of the US Midwest and elsewhere. A better understanding of processes regulating both soluble reactive phosphorus (SRP) and total phosphorus (TP) exports to tile-drains is therefore critical to minimize P losses to streams while maintaining crop yield. This paper investigates SRP and TP dynamics at a high temporal resolution during four spring storms in two tile-drains in the US Midwest. Depending on the storm, median concentrations varied between 0.006-0.025 mg/L for SRP and 0.057-0.176 mg/L for TP. For large storms (>6 cm bulk precipitation), for which macropore flow represented between 43 and 50% of total tile-drain flow, SRP transport to tile-drains was primarily regulated by macropore flow. For smaller tile-flow generating events (<3 cm bulk precipitation), for which macropore flow only accounted for 11-17% of total tile-drain flow, SRP transport was primarily regulated by matrix flow. Total P transport to tile-drains was primarily regulated by macropore flow regardless of the storm. Soluble reactive P (0.01-1.83 mg m⁻²/storm) and TP (0.10-8.64 mg m⁻²/storm) export rates were extremely variable and positively significantly correlated to both mean discharge and bulk precipitation. Soluble reactive P accounted for 9.9-15.5% of TP fluxes for small tile-flow generating events (<3 cm bulk precipitation) and for 16.2-22.0% of TP fluxes for large precipitation events (>6 cm bulk precipitation). Although significant variations in tile-flow response to precipitation were observed, no significant differences in SRP and TP concentrations were observed between adjacent tile-drains. Results stress the dominance of particulate P and the importance of macropore flow in P transport to tile-drains in the US Midwest. Although only spring storms are investigated, this study brings critical insight into P dynamics in tile-drains at a critical time of the year for water quality management.     

Effects of salinity on fruit yield and quality of tomato grown in soil-less culture in greenhouses in Mediterranean climatic conditions

There is increasing pressure to reduce water use and environmental impact associated with open system, soil-less production in simple, plastic greenhouses on the Mediterranean coast. This may force the adoption of re-circulation of nutrient solutions. In south-eastern Spain, irrigation water is mostly from aquifers and has moderate levels of salinity. The adoption of re-circulation using moderately saline water requires detailed information of crop response to salinity, in order to optimise management. The effect of salinity on fruit yield, yield components and fruit quality of tomato grown in soil-less culture in plastic greenhouses in Mediterranean climate conditions was evaluated. Two spring growing periods (experiments 1 and 2) and one long season, autumn to spring growing period (experiment 3) studies were conducted. Two cultivars, ‘Daniela’ (experiment 1) and ‘Boludo’ (experiments 2 and 3), were used. Seven levels of electrical conductivity (EC) in the nutrient solution were compared in experiment 1 (2.5–8.0 dS m⁻¹) and five levels in experiments 2 and 3 (2.5–8.5 dS m⁻¹). Total and marketable yield decreased linearly with increasing salinity above a threshold EC value (EC_t). There were only small effects of climate and cultivar on the EC_t value for yield. Average threshold EC values for total and marketable fruit yield were, respectively, 3.2 and 3.3 dS m⁻¹. The linear reductions of total and marketable yield with EC above EC_t showed significant differences between experiments, the slope varying from 7.2% (autumn to spring period, ‘Boludo’) to 9.9% (spring period, ‘Boludo’) decreases per dS m⁻¹ increase in EC for total yield, and from 8.1% (spring period, ‘Daniela’) to 11.8% (spring period, ‘Boludo’) for marketable yield. The decrease of fresh fruit yield with salinity was mostly due to a linear decrease of the fruit weight of 6.1% per dS m⁻¹ from an EC_t of 3.0 dS m⁻¹ for marketable fruits. Reduction in fruit number with salinity made a smaller relative contribution to reduced yield. Blossom-end rot (BER) increased with increasing salinity. There was a higher incidence of BER with spring grown crops, and ‘Boludo’ was more sensitive than ‘Daniela’. Increasing salinity improved various aspects of fruit quality, such as: (i) proportion of ‘Extra’ fruits (high visual quality), (ii) soluble solids content, and (iii) titratable acidity content. However, salinity decreased fruit size, which is a major determinant of price. An economic analysis indicated that the EC threshold value above which the value of fruit production decreased linearly with increasing salinity was 3.3 dS m⁻¹, which was the same as that for marketable yield. In the economic analysis, the value of increased visual fruit quality was offset by reduced yield and smaller fruit size.     

Sprinkler evaporation losses in alfalfa during solid-set sprinkler irrigation in semiarid areas

Gross sprinkler evaporation losses (SEL_g) can be large and decrease irrigation application efficiency. However, it is not universally established how much of the SEL_g contributes to decrease the crop evapotranspiration during the sprinkler irrigation and how much are the net sprinkler losses (SEL_n). The components of SEL were the wind drift and evaporation losses (WDEL) and the water intercepted by the crop (IL). The gross WDEL (WDEL_g) and evapotranspiration (ET) were measured simultaneously in two alfalfa (Medicago sativa L.) plots, one being irrigated (moist, MT) and the other one not being irrigated (dry, DT). Catch can measurements, mass gains, and losses in the lysimeters and micrometeorological measurements were performed to establish net WDEL (WDEL_n) during the irrigation and net IL (IL_n) after the irrigation as the difference between ET_MT and ET_DT. Also, equations to estimate IL_n and net sprinkler evaporation losses (SEL_n) were developed. IL_n was strongly related to vapor pressure deficit (VPD). SEL_n were 8.3 % of the total applied water. During daytime irrigations, SEL_n was 9.8 % of the irrigation water and slightly less than WDEL_g (10.9 %). During nighttime irrigations, SEL_n were slightly greater than WDEL_g (5.4 and 3.7 %, respectively). SEL_n was mainly a function of wind speed.     

Soil water content and water balance in rainfed fields in Northeast Thailand

Northeast Thailand has a semi-humid tropical climate which is characterized by dry and rainy seasons. In order to stabilize crop production, it may be necessary to develop new water resources, such as soil moisture and groundwater, instead of rainfed resources. This is because rainfed agriculture has already been unsuccessfully tried in many areas of this region. In this study, we investigate the soil water content in rainfed fields in Khon Kaen in Northeast Thailand, where rice and sugarcane were planted, over a 1-year period that contained both dry and rainy seasons, and estimate the actual evapotranspiration (ET_a) using micrometeorological data. In addition, we assess the water balance from the results of the soil water content investigation and the actual evapotranspiration. Although the soil water content at depths above 0.6 m in both the lower and the sloping fields gradually decreased during the dry season, the soil water content at a depth of 1.0 m was under almost constant wet conditions. Two-dimensional profiles of the soil water content demonstrated that at the end of the dry season, the soil layers below a depth of 0.4 m showed a soil water content of more than 0.10-0.15 m³ m⁻³, thus suggesting that water was supplied to the sugarcane from those layers. The range in ET_a rates was almost the same as that in the previous study. The average ET_a rates were 3.7 mm d⁻¹ for the lower field and 4.2 mm d⁻¹ for the sloping field. In the dry season, an upward water flow of 373 mm (equivalent to a flux of 1.9 mm d⁻¹) was estimated from outside the profile. The source of this upward water flow was the sandy clay (SC) layer below a depth of 1 m. It was this soil water supply from the SC layer that allowed the sugarcane to grow without irrigation.     

Distribution of herbicides in soil in a simulated drip irrigation system

Summary The behavior of two herbicides (bromacil and napropamide) applied to a Mediterranean red loam soil (hamra) from a point source is presented. Neither herbicide was degraded during the period of the study. Bromacil was only slightly adsorbed by the soil (K _d – 0.1 ml/g; Fig. 1) and was evenly distributed in the soil volume when applied at a constant concentration (Fig. 3). The distribution of napropamide, which was adsorbed by the soil (K _d – 1.2 ml/g; Fig. 1), was restricted to the zone immediately around the emitter (Fig. 3). Application of the herbicides to previously wetted soils increased the vertical and lateral movement of both herbicides (Fig. 4). Leaching of the chemicals was more pronounced for bromacil than for napropamide (Fig. 5). Cycles of irrigation and evaporation at two irrigation frequencies demonstrated that bromacil can be leached quickly from the emitter zone whereas naproparnide will move only slowly into the soil volume (Fig. 8).Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 289-E, 1980 Series     

Evaluating drip irrigation in commercial tea production in Tanzania

This paper evaluates the performance of the first drip irrigation scheme in commercial tea production in Tanzania with a view to making recommendations for improved management and providing data for investment decisions. Uniformity, efficiency and adequacy of irrigation were calculated and the scheduling of irrigation water was reviewed. Operators were interviewed to highlight the main benefits and problems of the system. Investment and recurrent costs of drip and overhead sprinkler systems were quantified and compared. Root development was assessed qualitatively using excavation pits. Irrigation uniformity DU and efficiency ranged between 88 and 95% in the 10 out of 14 irrigation blocks where endline pressures were at least 0.5 bars, and between 77 and 89% in the four blocks were endline pressure was less than 0.5 bars. Scheduling drip irrigation using tensiometers offered potential water savings of 26% in comparison to a water balance schedule, but these are not currently realised. Gross marginal income was very sensitive to tea price and yield. Economically optimal fertilizer rates vary in dependence of tea price and yield and appear to be lower than the current level of 300 kg N ha⁻¹. The higher costs under drip, compared to overhead sprinklers, were mainly for purchase and installation and fertilizer. The costs of labour for applying water and fertilizer were reduced by nearly 50%. At average 2002 tea prices of 1.31 US$ kg⁻¹, drip irrigation would improve the grower’s gross margin if an additional yield of at least 411 kg ha⁻¹ was achieved. The main threats to drip system performance are discussed. Future research efforts should aim at establishing the yield response of tea to water and fertilizer under drip irrigation.     

Nitrate leaching assessment in a long-term experiment under supplementary irrigation in humid Argentina

Applying high rates of nitrogen (N) fertilizer to crops has two major disadvantages: (1) the low N fertilizer use efficiency and (2) the loss of N by leaching, which may cause groundwater nitrate (NO₃⁻) pollution, especially in humid areas.The objectives of this study were to adjust and validate the LEACH-W model simulations with data observed in the field; to quantify nitrate concentrations in the soil solution; to estimate N loss by leaching; and to determine the moments during the year when greatest nitrate transport events occur beyond the rooting profile.A randomized complete block design with four replications was established on a typic Argiudoll. Crop fertilization treatments consisted of three N rates (0, 100, and 200 kg N ha⁻¹) using urea and ammonium nitrate solution (UAN) as the N source. Corn (Zea mays L.) was planted and ceramic soil-water suction samplers were installed to depths of 1, 1.5 and 2 m. Drainage was estimated by the LEACH-W model, which adjusted very well the actual volume of water in the soil profile. Nitrogen losses were statistically analyzed as repeated measure data, using the PROC MIXED procedure.Losses of nitrate-nitrogen (NO₃⁻-N) during the study increased as the rate of N applied increased. At all depths studied, statistically significant higher values were found for 200 N compared to 100 N and 0 N, and for 100 N compared to 0 N (p < 0.001).The greatest NO₃⁻-N losses through leaching occurred during crop growth. Significant differences (p < 0.05) were found between cropping and fallow in the three treatments and depths studied for seasons 4 and 5; these two seasons produced the highest drainage volumes at all depths.