共查询到20条相似文献，搜索用时 62 毫秒
1.
2.
随着国家电网公司对农村电网改造工程的逐步推进,现今农村电网的供电电压水平过低、频率偏移较大的问题已经基本得到解决,农网的供电质量较十余年前有了较大提升。但与此同时,影响农网配电网络中电能质量的又一重要因素为雷击故障,已然成为了10 kV配电线路中不可忽视的潜在威胁。本文基于湖南某地的10 kV农网配电线路的运行实例,通过分析雷击故障的发生情况,提出相应的防雷策略,以供参考。 相似文献
3.
江西省上犹县是国家级扶贫开发重点县,新一轮农网改造升级工程＂两年攻坚战＂以来,国网江西上犹县供电公司按照省市公司的部署和要求集中力量实施农网改造升级,新增改造10 kV线路37.43 km,配电台区112个,10 kV配电变压器容量14 210 kVA,0.4 kV线路494.54 km,农村用电水平得到了有效提升。 相似文献
4.
福安供电有限公司地处闽东山区,低压供电线路偏长,网架尚不合理;同时也是闽东地区社会用电量最高,高耗能炼钢、电器电机业和造(修)船业是福安的三大用电支柱行业。公司下设18个供电所,截止2006年底,拥有110kV变电站2座;35kV变电站10座;110kV送电线路8km;35kV送电线路192km;10kV配电线路2184km。 相似文献
5.
国网陕西山阳县供电公司十里供电所,位于城乡接合部,全所14名员工管理着辖区170km 10kV线路,379km 0.4kV线路,154台44150kVA配电变压器,服务用电客户19268户。该所着力提升供电优质服务水平,围绕设备故障缺陷发现率、设备检修完好率、设备故障停运率、设备应急抢修效率等开展工作,电网设备维护检修管理水平显著提高,荣获"全国电力行业电网设备维护检修标杆班组"。 相似文献
6.
7.
8.
近几年,10k V配电线路在我国的电网工程建设中的应用愈加普及,为人们的生产生活提供了巨大的便利。然而10kV配电线路受雷电破坏性较大,这在很大程度上影响了配电网的供电可靠性。文章对影响10kV配电线路雷击的因素进行了分析,并对其防雷措施进行了探讨。 相似文献
9.
10.
某供电公司10kV线路运维班负责人满腹牢骚,向他人埋怨有人为了"报复"自己,多次偷偷卸掉其运维班所管辖的某条10kV线路瓷绝缘子螺母,导致该线路多次发生瓷绝缘子脱落造成线路接地故障。笔者听后,深感不解和好奇。询问得知. 相似文献
11.
Relationship between stable carbon isotope discrimination and water use efficiency under regulated deficit irrigation of pear-jujube tree 总被引：2，自引：0，他引：2
Ningbo Cui Taisheng Du Shaozhong Kang Fusheng Li Xiaotao Hu Mixia Wang Zhijun Li 《Agricultural Water Management》2009,96(11):1615-1622
To investigate the relationship between stable carbon isotope discrimination (Δ) of different organs and water use efficiency (WUE) under different water deficit levels, severe, moderate and low water deficit levels were treated at bud burst to leafing, flowering to fruit set, fruit growth and fruit maturation stages of field grown pear-jujube tree, and leaf stable carbon isotope discrimination (ΔL) at different growth stages and fruit stable carbon isotope discrimination (ΔF) at fruit maturation stage were measured. The results indicated that water deficit had significant effect on ΔL at different growth stages and ΔF at fruit maturation stage. As compared with full irrigation, the average ΔL at different growth stages and ΔF at fruit maturation stage were decreased by 1.23% and 2.67% for different water deficit levels, respectively. ΔL and ΔF among different water deficit treatments had significant difference at the same growth stage (P < 0.05). Under different water deficit conditions, significant relationships between the ΔL and WUEi (photosynthesis rate/transpiration rate, Pn/Tr), WUEn (photosynthesis rate/stomatal conductance of CO2, Pn/gs), WUEy (yield/crop water consumption, Y/ETc) and yield, or between the ΔF and WUEy and yield were found, respectively. There were significantly negative correlations of ΔL with WUEi, WUEn, WUEy and yield (P < 0.01) at the fruit maturation stage, or ΔL with WUEi and WUEn (P < 0.01) over whole growth stage, respectively. ΔF was negatively correlated with WUEy, WUEn and yield (P < 0.05), but positively correlated with ETc (P < 0.01) over the whole growth stage. Thus ΔL or ΔF can compare WUEn and WUEy, so the stable carbon isotope discrimination method can be applied to evaluate the water use efficiency of pear-jujube tree under the regulated deficit irrigation. 相似文献
12.
A 3-year study was carried out to assess the root biomass production, crop growth rate, yield attributes, canopy temperature
and water-yield relationships in Indian mustard grown under combinations of irrigation and nutrient application for revealing
the dynamic relationship of crop yield (Y) and seasonal evapotranspiration (ET). Three post-sowing irrigation treatments viz. no irrigation (I
1), one irrigation at flowering (I
2) and two irrigations one each at rosette and flowering stage (I
3), three nutrient treatments viz. no fertilizer or manure (F
1), 100% recommended NPK i.e., 60 kg N, 13.1 kg P and 16.6 kg K ha−1 (F
2) and 100% recommended NPK plus farmyard manure @ 10 Mg ha−1 (F
3) were tested in a split-plot design. Root biomass was significantly greater in I
3 than I
2 and I
1, and in F
3 than F
2 and F
1. The I
3 × F
3, I
2 × F
3 and I
3 × F
2 combinations maintained significantly greater crop growth rate, plant height, yield components, ET and crop yield and better
plant water status in terms of canopy temperature, canopy-air temperature difference (CATD) and relative leaf water content
(RLWC). Number of siliqua plant−1 and seeds siliqua−1 were the major contributors to the seed yield. Marginal analysis of water production function was used to establish Y–ET relationship. The elasticity of water production (E
wp) provides a means to assess relative changes in Y and ET, and gives an indication of improvement of Y due to nutrient application. The ET–Y relationships were linear with marginal water use efficiency (WUEm) of 3.09, 4.23 and 3.95 kg ha−1 mm−1 in F
1, F
2 and F
3, respectively, and the corresponding E
wp were 0.63, 0.71 and 0.61. This implies that the scope for improving yield and WUE with 100% NPK was little compared with
100% NPK + farmyard manure. The crop yield was highest in I
3 × F
3 combination, and the similar yield was obtained in I
2 × F
3 and I
3 × F
2 combinations. Application of organic manure along with 100% NPK fertilizers maintained greater crop growth rate, better water
relation in plants, yield attributes and saved one post-sowing irrigation. 相似文献
13.
A study was conducted to determine the relationship between midday measurements of vine water status and daily water use of
grapevines measured with a weighing lysimeter. Water applications to the vines were terminated on August 24th for 9 days and
again on September 14th for 22 days. Daily water use of the vines in the lysimeter (ETLYS) was approximately 40 L vine−1 (5.3 mm) prior to turning the pump off, and it decreased to 22.3 L vine−1 by September 2nd. Pre-dawn leaf water potential (ΨPD) and midday Ψl on August 24th were −0.075 and −0.76 MPa, respectively, with midday Ψl decreasing to −1.28 MPa on September 2nd. Leaf g
s decreased from ~500 to ~200 mmol m−2 s−1 during the two dry-down periods. Midday measurements of g
s and Ψl were significantly correlated with one another (r = 0.96) and both with ETLYS/ETo (r = ~0.9). The decreases in Ψl, g
s, and ETLYS/ETo in this study were also a linear function of the decrease in volumetric soil water content. The results indicate that even
modest water stress can greatly reduce grapevine water use and that short-term measures of vine water status taken at midday
are a reflection of daily grapevine water use. 相似文献
14.
A preliminary study of an alternative controlled drainage strategy in surface drainage ditches: Low-grade weirs 总被引：3，自引：0，他引：3
This study examined hydrological characteristics of low-grade weirs, an alternative controlled drainage strategy in surface drainage ditches. Chemographs of vegetated and clear scraped (control) replicates of weir vs. non-weir treatments were compared to determine differences in time to peak (Tp) and time to base (Tb). Drainage ditches Tp and Tb were affected by both vegetation and weir presence. The order of treatment efficiency for Tp was observed to be: non-vegetated non-weir < vegetated non-weir < non-vegetated weir < vegetated weir. Furthermore, Tb for each ditch was the reverse relationship from Tp where vegetated weir > non-vegetated weir > vegetated non-weir > non-vegetated non-weir. Low-grade weirs increase chemical retention time (vegetated and clear scraped), the average time a molecule of contaminant remains in the system. Future research in water quality improvement and weir management will yield useful information for non-point source pollutant reduction. 相似文献
15.
Expected yield losses as a function of quality and quantity of water applied for irrigation are required to formulate guidelines for the effective utilisation of marginal quality waters. In an experiment conducted during 2004-2006, double-line source sprinklers were used to determine the separate and interactive effects of saline and alkali irrigation waters on wheat (Triticum aestivum L.). The study included three water qualities: groundwater (GW; electrical conductivity of water, ECw 3.5 dS m−1; sodium adsorption ratio, SAR 9.8 mmol L−1; residual sodium carbonate, RSC, nil) available at the site, and two synthesized waters, saline (SW; ECw 9.4 dS m−1, SAR 10.3 mmol L−1; RSC nil) and alkali (AW; ECw 3.7 dS m−1, SAR 15.1 mmol L−1; RSC 9.6 meq. L−1). The depths of applied SW, AW, and GW per irrigation ranged from 0.7 to 3.5 cm; the depths of applied mixtures of GW with either SW (MSW) or AW (MAW) ranged from 3.2 to 5 cm. Thereby, the water applied for post-plant irrigations using either of GW, SW or AW ranged between 15.2 and 34.6 cm and 17.1 and 48.1 cm during 2004-2005 and 2005-2006, respectively and the range was 32.1-37.0 and 53.1-60.0 cm for MSW or MAW. Grain yields, when averaged for two years, ranged between 3.08 and 4.36 Mg ha−1, 2.57 and 3.70 Mg ha−1 and 2.73 and 3.74 Mg ha−1 with various quantities of water applied using GW, SW and AW, respectively, and between 3.47 and 3.75 Mg ha−1 and 3.63 and 3.77 Mg ha−1 for MSW and MAW, respectively. The water production functions developed for the two sets of water quality treatments could be represented as: RY = 0.528 + 0.843(WA/OPE) − 0.359(WA/OPE)2 − 0.027ECw + 0.44 × 10−2(WA/OPE) × ECw for SW (R2 = 0.63); RY = 0.446 + 0.816(OPE/WA) − 0.326(WA/OPE)2 − 0.0124RSC − 0.55 × 10−4(WA/OPE) × RSC for AW (R2 = 0.56). Here, RY, WA and OPE are the relative yields in reference to the maximum yield obtained with GW, water applied for pre- and post-plant irrigations (cm), and open pan evaporation, respectively. Crop yield increased with increasing amount of applied water for all of the irrigation waters but the maximum yields as obtained with GW, could not be attained even with increased quantities of SW and AW. Increased frequency of irrigation with sprinklers reduced the rate of yield decline with increasing salinity in irrigation water. The sodium contents of plants increased with salinity/alkalinity of sprinkled waters as also with their quantities. Simultaneous decrease in potassium contents resulted in remarkable increase in Na:K ratio. 相似文献
16.
L.G. Hou H.L. Xiao J.H. Si S.C. Xiao M.X. Zhou Y.G. Yang 《Agricultural Water Management》2010,97(2):351-356
Based on successive observation, fifteen-day evapotranspiration (ETc) of Populus euphratica Oliv forest, in the extreme arid region northwest China, was estimated by application of Bowen ratio-energy balance method (BREB) during the growing season in 2005. During the growing season in 2005, total ETc was 446.96 mm. From the beginning of growing season, the ETc increased gradually, and reached its maximum value of 6.724 mm d−1 in the last fifteen days of June. Hereafter the ETc dropped rapidly, and reached its minimum value of 1.215 mm d−1 at the end of growing season. The variation pattern of crop coefficient (Kc) was similar to that of ETc. From the beginning of growing season, the Kc value increased rapidly, and reached its maximum value of 0.623 in the last fifteen days of June. Afterward, with slowing growth of P. euphratica, the value dropped rapidly to the end of growing season. According to this study, the ETc of P. euphratica forest is affected not only by meteorological factors, but by water content in soil. 相似文献
17.
Impacts of climate variability on reference evapotranspiration over 58 years in the Haihe river basin of north China 总被引：3，自引：0，他引：3
Physically, evaporative demand is driven by net radiation (Rn), vapour pressure (ea), wind speed (u2), and air temperature (Ta), each of which changes over time. By analyzing temporal variations in reference evapotranspiration (ET0), improved understanding of the impacts of climate change on hydrological processes can be obtained. In this study, variations in ET0 over 58 years (1950-2007) at 34 stations in the Haihe river basin of China were analyzed. ET0 was calculated by the FAO Penman-Monteith formula. Calculation of Kendall rank coefficient was done by analyzing the annual and seasonal trends in ET0 derived from its dependent climate variables. Inverse distance weighting (IDW) was used to analyze the spatial variation in annual and seasonal ET0, and in each climate variable. An attribution analysis was performed to quantify the contribution of each input variable to ET0 variation. The results showed that ET0 gradually decreased in the whole basin over the 58 years at a rate of −1.0 mm yr−2, at the same time, Rn, u2 and precipitation also decreased. Changes in ET0 were attributed to the variations in net radiation (−0.9 mm yr−2), vapour pressure (−0.5 mm yr−2), wind speed (−1.3 mm yr−2) and air temperature (1.7 mm yr−2). Looking at all data on a month by month basis, we found that Ta had a positive effect on dET0/dt (the derivative of reference evapotranspiration to time) and Rn and u2 had negative effects on dET0/dt. While changes in air temperature were found to produce a large increase in dET0/dt, changes in other key variables each reduced rates, resulting in an overall negative trend in dET0/dt. 相似文献
18.
Summary A coupled soil-vegetation energy balance model which treats the canopy foliage as one layer and the soil surface as another layer was validated againt a set of field data and compared with a single-layer model of a vegetation canopy. The two-layer model was used to predict the effect of increases in soil surface temperature (T
s
) due to the drying of the soil surface, on the vegetation temperature (T
v
). In the absence of any change in stomatal resistance the impact of soil surface drying on the Crop Water Stress Index (CSWI) calculated from T
v
was predicted. Field data came from a wheat crop growing on a frequently irrigated plot (W) and a plot left un watered (D) until the soil water depletion reached 100 mm. Vegetation and soil surface temperatures were measured by infrared thermometers from tillering to physiological maturity, with meteorological variables recorded simultaneously. Stomatal resistances were measured with a diffusion porometer intensively over five days when the leaf area index was between 5 and 8. The T
v
predicted by the single-layer and the two-layer models accounted for 87% and 88% of the variance of measured values respectively, and both regression lines were close to the 11 relationship. Study of the effect of T
s
on the CWSI with the two-layer model indicated that the CWSI was sensitive to changes in T
s
. The overestimation of crop water stress calculated from the CWSI was predicted to be greater at low leaf area indices and high levels of stomatal resistance. The implications for this bias when using the CWSI for irrigation scheduling are discussed.List of Symbols
C
Sensible heat flux from the soil-vegetation system (W m–2)
-
c
l shade
Mean stomatal conductance of the shaded leaf area (m s–1)
-
c
l sun
Mean stomatal conductance of the sunlit leaf area (m s–1)
-
c
max
Maximum stomatal conductance (m s–1)
-
c
0
Minimum stomatal conductance (m s–1)
-
C
p
Specific heat at constant pressure (J kg–1 °C–1)
-
C
s
Sensible heat flux from the soil (W m–2)
-
C
v
Sensible heat flux from the vegetation (W m–2)
-
c
v
Bulk stomatal conductance of the vegetation (m s–1)
- CWSI
Crop Water Stress Index (dimensionless)
-
e
a
Vapor pressure at the reference height (kPa)
-
e
b
Vapor pressure at the virtual source/sink height of heat exchange (kPa)
-
e
0
*
Saturated vapor pressure at T
0 (kPa)
-
e
s
Vapor pressure at the soil surface (kPa)
-
e
v
*
Saturated vapor pressure at T
v
(kPa)
-
G
Soil heat flux (Wm–2)
- GLAI
Green leaf area index (dimensionless)
- GLAIshade
Green shaded leaf area index (dimensionless)
- GLAIsun
Green sunlit leaf area index (dimensionless)
-
k
Extinction coefficient for photosynthetically active radiation (dimensionless)
-
k
1
Damping exponent for Eq. A 5 (m2 W–1)
- LAI
Leaf area index (dimensionless)
-
LE
Latent heat flux from the soil-vegetation system (W m–2)
-
LE
s
Latent heat flux from the soil (W m–2)
-
LE
v
Latent heat flux from the vegetation (W m–2)
-
p
a
Density of air (kg m–3)
- PARa
Photosynthetically active radiation above the canopy (W m–2)
- PARu
Photosynthetically active radiation under the canopy (W m–2)
-
r
a
Aerodynamic resistance (s m–1)
-
r
b
Heat exchange resistance between the vegetation and the adjacent air boundary layer (s m–1)
-
r
c
Bulk stomatal resistance of the vegetation (s m–1)
-
R
n
Net radiation above the canopy (W m–2)
-
R
s
Net radiation flux at the soil surface (W m–2)
-
r
st
Mean stomatal resistance of leaves in the canopy (s m–1)
-
R
v
Net radiation absorbed by the vegetation (W m–2)
-
r
w
Heat exchange resistance between the soil surface and the boundary layer (s m–1)
-
S
Photosynthetically active radiation on the shaded leaves (W m–2)
-
S
d
Diffuse photosynthetically active radiation (W m –2)
-
S
0
Photosynthetically active radiation on a surface perpendicular to the beams (W m–2)
-
T
a
Air temperature at the reference height (°C)
-
T
b
Temperature at the virtual source/sink height of heat exchange (°C)
-
T
0
Aerodynamic temperature (°C)
-
T
s
Soil surface temperature (°C)
-
T
v
Vegetation temperature (°C)
-
w
0
Single scattering albedo (dimensionless)
-
Psychrometric constant (kPa °C)
-
0
Cosine of solar zenith angle (dimensionless) 相似文献
19.
Increasing water productivity of irrigated crops under limited water supply at field scale 总被引：1，自引：0，他引：1
Borkhar district is located in an arid to semi-arid region in Iran and regularly faces widespread drought. Given current water scarcity, the limited available water should be used as efficient and productive as possible. To explore on-farm strategies which result in higher economic gains and water productivity (WP), a physically based agrohydrological model, Soil Water Atmosphere Plant (SWAP), was calibrated and validated using intensive measured data at eight selected farmer fields (wheat, fodder maize, sunflower and sugar beet) in the Borkhar district, Iran during the agricultural year 2004-2005. The WP values for the main crops were computed using the SWAP simulated water balance components, i.e. transpiration T, evapotranspiration ET, irrigation I, and the marketable yield YM in terms in terms of YMT−1, YM ET−1 and YM I−1.The average WP, expressed as $ T−1 (US $ m−3) was 0.19 for wheat, 0.5 for fodder maize, 0.06 for sunflower and 0.38 for sugar beet. This indicated that fodder maize provides the highest economic benefit in the Borkhar irrigation district. Soil evaporation caused the average WP values, expressed as YM ET−1 (kg m−3), to be significantly lower than the average WP, expressed as YMT−1, i.e. about 27% for wheat, 11% for fodder maize, 12% for sunflower and 0.18 for sugar beet. Furthermore, due to percolation from root zone and stored moisture content in the root zone, the average WP values, expressed as YMI−1 (kg m−3), had a 24-42% reduction as compared with WP, expressed as YM ET−1.The results indicated that during the limited water supply period, on-farm strategies like deficit irrigation scheduling and reduction of the cultivated area can result in higher economic gains. Improved irrigation practices in terms of irrigation timing and amount, increased WP in terms of YMI−1 (kg m−3) by a factor of 1.5 for wheat and maize, 1.3 for sunflower and 1.1 for sugar beet. Under water shortage conditions, reduction of the cultivated area yielded higher water productivity values as compared to deficit irrigation. 相似文献
20.
Soil salinity related to physical soil characteristics and irrigation management in four Mediterranean irrigation districts 总被引：1，自引：0，他引：1
R. Aragüés V. UrdanozM. Çetin C. KirdaH. Daghari W. LtifiM. Lahlou A. Douaik 《Agricultural Water Management》2011,98(6):959-966
Irrigated agriculture is threatened by soil salinity in numerous arid and semiarid areas of the Mediterranean basin. The objective of this work was to quantify soil salinity through electromagnetic induction (EMI) techniques and relate it to the physical characteristics and irrigation management of four Mediterranean irrigation districts located in Morocco, Spain, Tunisia and Turkey. The volume and salinity of the main water inputs (irrigation and precipitation) and outputs (crop evapotranspiration and drainage) were measured or estimated in each district. Soil salinity (ECe) maps were obtained through electromagnetic induction surveys (ECa readings) and district-specific ECa-ECe calibrations. Gravimetric soil water content (WC) and soil saturation percentage (SP) were also measured in the soil calibration samples. The ECa-ECe calibration equations were highly significant (P < 0.001) in all districts. ECa was not significantly correlated (P > 0.1) with WC, and was only significantly correlated (P < 0.1) with soil texture (estimated by SP) in Spain. Hence, ECa mainly depended upon ECe, so that the maps developed could be used effectively to assess soil salinity and its spatial variability. The surface-weighted average ECe values were low to moderate, and ranked the districts in the order: Tunisia (3.4 dS m−1) > Morocco (2.2 dS m−1) > Spain (1.4 dS m−1) > Turkey (0.45 dS m−1). Soil salinity was mainly affected by irrigation water salinity and irrigation efficiency. Drainage water salinity at the exit of each district was mostly affected by soil salinity and irrigation efficiency, with values very high in Tunisia (9.0 dS m−1), high in Spain (4.6 dS m−1), moderate in Morocco (estimated at 2.6 dS m−1), and low in Turkey (1.4 dS m−1). Salt loads in drainage waters, calculated from their salinity (ECdw) and volume (Q), were highest in Tunisia (very high Q and very high ECdw), intermediate in Turkey (extremely high Q and low ECdw) and lowest in Spain (very low Q and high ECdw) (there were no Q data for Morocco). Reduction of these high drainage volumes through sound irrigation management would be the most efficient way to control the off-site salt-pollution caused by these Mediterranean irrigation districts. 相似文献