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二次回路可以监测电力系统的运行状况,同时反馈信号给工作人员,对电路设备进行控制和维护。继电保护二次电路的可靠性直接影响电力设备的安全运行。提高继电保护二次回路可靠性对继电保护装置的安全运行十分重要。文章通过分析继电保护二次回路不可靠的原因,阐述了提高继电保护二次回路可靠性的对策,希望对有关人士有所帮助。 相似文献
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电力系统的安全可靠性是确保电力正常运行十分重要的部分,继电保护能够确保设备安全,防止出现大面积停电等提高系统安全可靠性的重要措施。如何确保继电保护二次回路的安全性是继电保护关键技术,文章研究继电保护二次回路常见隐患,分析二次回路故障对系统运行的影响,研究二次回路隐患排查与处理策略,提出二次回路隐患防范的措施。 相似文献
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在县级电网继电保护装置的运行管理中,由于专业人员业务技术水平低,缺乏必要的测试设备,继电保护整定方案不能及时更改,以及电网结构造成的一些缺陷等原因,使继电保护装置误动作事故时有发生。现将继电保护装置误动作的主要原因归纳如下,以供继电保护专职人员和调度运行管理人员参考。 1、保护装置错误结线造成的误动作。在新建、改建或扩建工程中,由于图纸画错、工作疏忽或交接试验项 相似文献
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在电力系统实际运行过程中,继电保护二次回路自身的稳定性和安全性极为重要,需要工作人员对其投入更多的关注和重视,利用在线状态检测技术对继电保护相关二次回路的稳定使用提供保障。本文针对继电保护相关二次回路具体监测的必要性进行简单阐述,对交流二次回路在线的具体状态检测进行分析,提出继电保护有关二次回路状态方面的检测技术。 相似文献
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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
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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