含多小水电的配电网电压分析与控制策略研究

Low voltages and high power loss are two main problems in distribution network especially in remote area. To solve these problems, typical events of low voltage in distribution network need to be analyzed and identify the similarities. Furthermore, building general optimization model for low voltage in distribution network and proposing improved strategies related to such problems are also necessary. This paper proposes optimization model and strategies against low voltage using Matlab as the main platform with objective functions and several constraints. The particle swarm optimization (PSO) is used to solve the problem. With the open DSS COM interface connected to Matlab, the open DSS are called to calculate distribution network 3-phase power flow repeatedly. Finally, the optimizing strategy, including transformer tap positions and capacitors in each node are obtained. Results from simulations verify the effectiveness and feasibility of the proposed model.

Distributed photovoltaic (PV) in the distribution network accounted for an increasing proportion of the distribution network, and the power quality of the distribution network of the power quality problem is more and more significant. In this paper, the voltage regulation methods for low-voltage distribution networks containing high-penetration PV are investigated. First, the working principles of the four voltage control methods are introduced: energy storage system configuration, regulating the reactive power output of PV inverters, restricting the active power output of PV, adjusting the switching positions of on-load regulator trap changer and distribution network reconfiguration, and then, in combination with the recent related research, the optimization of each method is compared horizontally with its respective concerns and characteristics. The optimization of each method is compared horizontally with the recent studies to find out the focus and characteristics of each method, and the shortcomings of each method are explored. Coordinated voltage control through multiple flexibility resources has become the mainstream voltage regulation scheme, and distribution network voltage regulation is considered from the perspective of flexibility resources. The three types of flexibility resources, namely, source, network, and storage, have been widely used in distribution network voltage regulation. Although load-side resources have become one of the main regulation resources of the new type of power system, the current study introduces less about the participation of load-side flexibility resources in voltage regulation of LV distribution networks and advancing the application of load-side resources in voltage regulation of LV distribution networks is the focus of future research. Then, the important role of load-side flexibility resources in voltage regulation is described in three parts, namely, the important role of load-side resources, the development trend, and the suggestions for promoting the coordination of source-network-load-storage flexibility resources, aiming to promote the application of load-side resources in voltage regulation in LV distribution networks, and the suggestions and programs are proposed for the technological challenges faced by voltage regulation. In the context of today’s new power system emphasizing the interaction of source, network, load, and storage, new technologies and methods for solving voltage problems in LV distribution networks are prospected, with a view to providing certain reference value for the actual operation and optimization of distribution network systems.

This study was conducted to evaluate the impact of seasonal variations (wet and dry season) on the reproductive and productive performance and to do an economic evaluation of hair sheep under Halaieb rangeland conditions and determine which season is the best in grazing areas. A total of 64 multiparous Abou-Delik ewes were bred in two different seasons. During the first season (dry season), a total of 35 ewes, 2-4years of age and 32.02 0.52 kg weight, were bred during May and June, while lambing and lactation took place in the months of November, December and January. On the other hand, during the wet season, 29 ewes, 2-4years age and 31.06 0.57 kg weight, were bred during November and December, whereas lambing and lactation took place in the months of May, June and July. Sheep grazed 8 h daily in the same pastures during the study and then moved back to the barns to receive a sorghum vulgare supplement with a dosage of 250 g per head per day. The results revealed that there were no significant effects of breeding season on conception, lambing and abortion rates. However, the wet season had higher ( ) prolificacy, mortality rates, lambs' weight and lambs born to ewes serviced. Contrariwise, dry-season lambs had a higher ( ) weaning weight. Also, milk yield (mL d ) and number of lambs weaned per lambs born (LW/LB) increased ( ) in the dry season compared to the wet season. No significant differences between the two seasons regarding the biological criteria studied were observed. On the other hand, the flock bred in the dry season generated a higher gross margin than that bred in the wet season. In this context, variable costs of the wet breeding season flock were recorded to be close to the value of the dry breeding season. Hence, it is concluded that the reproductive and productive performance of hair sheep raised in grazing areas in the Halaieb triangle is affected when lambs are born during the dry season because of the higher lamb mortality rate during this period which eliminates any comparative advantage for the good reproductive performance of ewes during the period of feed availability in the wet season. The high lamb mortality rates and low weaning weights in the wet breeding season lessen the economical merits of higher reproductive performance during the seasonal availability of feed in the wet season.

The main seasonal characteristics in the tropics include both spatial patterns and temporal parameters of onset, cessation, duration, and the number of wet and dry seasons. Previous studies showed that wet seasons shortened and dry seasons extended with global warming, but the changes in spatial distribution and the number of wet and dry seasons are still unclear. Here, we analyze the climatic characteristics of once wet and dry season a year (annual regime) and twice wet and dry seasons a year (biannual regime), and find that regimes of wet and dry seasons have changed from 1935 to 2014. Across the equator and the Tropic of Cancer and Capricorn, some regions where there used to be an annual regime have become a biannual regime; instead, other regions have shifted from a biannual regime into an annual regime. With seasonal regimes shifting, areas of the biannual regime have expanded at a rate of 31 000 km2/decade. Meanwhile, in annual regime regions, wet seasons have been shortened in 60.3% of regions, with an average of 7 d; the onset dates of wet seasons have been delayed in 64.8%, with an average of 6 d. Besides, wet seasons have become wetter in 51.1% of regions, and dry seasons have become drier in 59.9%. In biannual regime regions, the shortened wet seasons have occurred in 83.7% of regions, with an average shortening of 8 d, and precipitation has decreased in both wet and dry seasons. Moreover, the shorter wet seasons will amplify further by the end of the 21st century. The continuous seasonal changes will threaten agricultural, ecological security, and even human well-being.

Techno-economic evaluation of small hydro power plants in Greece: a complete sensitivity analysis

Poyang Lake is the largest freshwater lake connecting the Yangtze River in China. It undergoes dramatic dynamics from the wet to the dry seasons. A comparison of the hydrological changes between the wet and dry seasons may be useful for understanding the water flows between Poyang Lake and Yangtze River or the river system in the watershed. Gauged measurements and remote sensing datasets were combined to reveal lake area, level and volume changes during 2000–2020, and water exchanges between Poyang Lake and Yangtze River were presented based on the water balance equation. The results showed that in the wet seasons, the lake was usually around 1301.85–3840.24 km2, with an average value of 2800.79 km2. In the dry seasons, the area was around 618.82–2498.70 km2, with an average value of 1242.03 km2. The inundations in the wet seasons were approximately quadruple those in the dry seasons. In summer months, the lake surface tended to be flat, while in winter months, it was inclined, with the angles at around 10′′–16′′. The mean water levels of the wet and dry seasons were separately 13.51 m and 9.06 m, with respective deviations of around 0–2.38 m and 0.38–2.15 m. Monthly lake volume changes were about 7.5–22.64 km3 and 1–5.80 km3 in the wet and dry seasons, respectively. In the wet seasons, the overall contributions of ground runoff, precipitation on the lake surface and lake evaporation were less than the volume flowing into Yangtze River. In the dry seasons, the three contributions decreased by 50%, 50% and 65.75%, respectively. Therefore, lake storages presented a decrease (−7.42 km3/yr) in the wet seasons and an increase (9.39 km3/yr) in the dry seasons. The monthly exchanges between Poyang Lake and Yangtze River were at around −14.22–32.86 km3. Water all flowed from the lake to the river in the wet seasons, and the chance of water flowing from Yangtze River in the dry seasons was only 5.26%.

Vertical distributions of atmospheric black carbon in dry and wet seasons observed at a 356-m meteorological tower in Shenzhen, South China

The spatial rhythm and periodic pattern of fish species was studied in lower and upper streams in Eniong River, Southeastern Nigeria for 12 consecutive months (April, 2019- March, 2020) using standard methods and procedures. A total of 178 individuals of fish species belonging to 14 families and 25 species were recorded in the study. The results revealed species abundance in favour of the lower stream with only two species: Clarias macromystax (Clariidae) and Malapterurus electricus (Malapteruridae) not found in the lower stream. Populations were generally bigger in lower stream 122 (69.32%) than their counterparts in upper stream with 56 (30.68%) samples. The family Cichilidae dominates the lower stream while Clariidae dominates the upper stream. The result of Jaccard Index Similarity of the number of species found between the upper stream and lower stream revealed the value of 0.461˂50%. The overall range of fish sampled falls within (9.7-25.5cmTL) with size structure generally bigger in the wet season than in the dry season. Species had seasonal abundance in the wet season than the dry season. In the wet season, Oreochromis niloticus and Clarias macromystax were the most abundant species in June and September (wet season) while Malapterurus electricus and Citharinus citharus were not found in the wet season. In the dry season, twelve (12) species were completely absent-Hepsetus akawo, Ctenopoma nebulosum, pollimyrus asperses, Marcusens senegaleusis, Ccoptodon zelli, Cclarias gariepinus, Cclarias macromystax, Synodontis obesus, Schilbe mystus, Schilbe uranoscopus and Protopterus annectens and Hemichromis fasciatus. The most abundant species found in both dry and wet seasons were Oreochromis niloticus, Chrysichthys nigrodigitatus and Hemichromis fasciatus. The fish diversity ranges from typical freshwater fishes to brackish species. The greatest dissimilarity between the wet and dry seasons’ samples was generated by Oreochromis niloticus. The study recorded the highest species richness (Margaleaf) and diversity (Shanno-Wiener) in the wet season with 23 species while the lowest with the smallest abundance was observed in the dry season with 13 species. The study recommends low exploitation in the upper stream and in the dry season to enhance species productivity and sustainability in Eniong River, Southeastern Nigeria.

Sensitivities are broadly appreciated because of its simplicity and good results in solving voltage problems and congestions in transmission networks. However, since sensitivity calculation is based on a linear approximation of the power flow equations, all decisions commit an intrinsic error that might lead into unexpected results, especially in distribution networks. This paper analyzes the error associated to sensitivities considering a wide range of control variables and proposes a novel formulation to extend the use of sensitivities to manage congestions in active distribution networks. First, a theoretical analysis is performed to study the origin and propagation of errors. Then, numerical results are presented for two types of distribution networks (20 kV and low voltage grids). Finally, a novel formulation is proposed to extend the use of sensitivities to manage congestions, which will allow to reuse previous sensitivity-based methodologies to solve both voltage problems and congestions in active distribution networks.

This study investigates the indoor air quality in coal mining communities during wet and dry seasons in the coal mining belt of Kogi East, Kogi State, Nigeria. The research was conducted at selected coal mining sites, specifically the Ika-Ogboyaga and Okaba mine sites, using a randomized sampling method. Indoor air quality data were collected from fifteen households in Ika and Odele villages within a 500-meter radius of the mining sites. Monitoring was performed using the Gasman autosampler to measure concentrations of nitrogen dioxide (NO₂), sulphur dioxide (SO₂), carbon monoxide (CO), hydrogen sulphide (H₂S), and particulate matter (PM₂.5 and PM₁₀). Data collection spanned 7 days each for the wet season (October 2022) and the dry season (February 2023), with measurements taken thrice daily. Meteorological parameters such as temperature, wind speed, wind direction, and relative humidity were also recorded. The results indicated higher pollutant concentrations during the dry season. For instance, PM₂.5 levels in Ika during the wet season were 45.3±0.25 μg/m³ (morning), 74.6±0.49 μg/m³ (afternoon), and 56.26±0.1 μg/m³ (evening), while dry season values were 48.32±1.74 μg/m³ (morning), 74.12±0.30 μg/m³ (afternoon), and 56.9±0.75 μg/m³ (evening). Similarly, PM₁₀ levels in Ika during the wet season were 73.61±1.44 μg/m³ (morning), 105.53±0.44 μg/m³ (afternoon), and 99.01±0.5 μg/m³ (evening), whereas dry season values were 75.47±0.70 μg/m³ (morning), 102.08±1.48 μg/m³ (afternoon), and 96.98±1.33 μg/m³ (evening). CO concentrations in Ika during the wet season were 4.22±0.22 ppm (morning), 6.13±0.3 ppm (afternoon), and 3.1±0.05 ppm (evening), and during the dry season, they were 5.55±1.74 ppm (morning), 8.11±1.46 ppm (afternoon), and 7.04±1.184 ppm (evening). Meteorological analysis showed that the dry season had higher wind speeds (2-4 m/s) compared to the wet season (0-2 m/s), and lower relative humidity (mean of 51.18%) compared to the wet season (mean of 77.55%). Air Quality Index (AQI) values indicated that PM₂.5 levels in both seasons were unhealthy (155.8-156.4 in the wet season and 151-200 in the dry season), while PM₁₀ levels were moderate (65.5-66.9 in the wet season and 51-100 in the dry season). CO, NO₂, and SO₂ levels generally remained within permissible limits set by the World Health Organization (WHO). Statistical analysis revealed significant seasonal variations in the concentrations of the monitored pollutants, with higher levels typically recorded during the dry season.

In the wet season, a large portion of the Amazon region constitutes one of the most pristine continental areas, with very low concentrations of atmospheric trace gases and aerosol particles. However, land use change modifies the biosphere-atmosphere interactions in such a way that key processes that maintain the functioning of Amazonia are substantially altered. This study presents a comparison between aerosol properties observed at a preserved forest site in Central Amazonia (TT34 North of Manaus) and at a heavily biomass burning impacted site in south-western Amazonia (PVH, close to Porto Velho). Amazonian aerosols were characterized in detail, including aerosol size distributions, aerosol light absorption and scattering, optical depth and aerosol inorganic and organic composition, among other properties. The central Amazonia site (TT34) showed low aerosol concentrations (PM2.5 of 1.3 +/- 0.7 microg m(-3) and 3.4 +/- 2.0 microg m(-3) in the wet and dry seasons, respectively), with a median particle number concentration of 220 cm(-3) in the wet season and 2200 cm(-3) in the dry season. At the impacted site (PVH), aerosol loadings were one order of magnitude higher (PM2.5 of 10.2 +/- 9.0 microg m(-3) and 33.0 +/- 36.0 microg m(-3) in the wet and dry seasons, respectively). The aerosol number concentration at the impacted site ranged from 680 cm(-3) in the wet season up to 20 000 cm(-3) in the dry season. An aerosol chemical speciation monitor (ACSM) was deployed in 2013 at both sites, and it shows that organic aerosol account to 81% to the non-refractory PM1 aerosol loading at TT34, while biomass burning aerosols at PVH shows a 93% content of organic particles. Three years of filter-based elemental composition measurements shows that sulphate at the impacted site decreases, on average, from 12% of PM2.5 mass during the wet season to 5% in the dry season. This result corroborates the ACSM finding that the biomass burning contributed overwhelmingly to the organic fine mode aerosol during the dry season in this region. Aerosol light scattering and absorption coefficients at the TT34 site were low during the wet season, increasing by a factor of 5, approximately, in the dry season due to long range transport of biomass burning aerosols reaching the forest site in the dry season. Aerosol single scattering albedo (SSA) ranged from 0.84 in the wet season up to 0.91 in the dry. At the PVH site, aerosol scattering coefficients were 3-5 times higher in comparison to the TT34 site, an indication of strong regional background pollution, even in the wet season. Aerosol absorption coefficients at PVH were about 1.4 times higher than at the forest site. Ground-based SSA at PVH was around 0.92 year round, showing the dominance of scattering aerosol particles over absorption, even for biomass burning aerosols. Remote sensing observations from six AERONET sites and from MODIS since 1999, provide a regional and temporal overview. Aerosol Optical Depth (AOD) at 550 nm of less than 0.1 is characteristic of natural conditions over Amazonia. At the perturbed PVH site, AOD550 values greater than 4 were frequently observed in the dry season. Combined analysis of MODIS and CERES showed that the mean direct radiative forcing of aerosols at the top of the atmosphere (TOA) during the biomass burning season was -5.6 +/- 1.7 W m(-2), averaged over whole Amazon Basin. For high AOD (larger than 1) the maximum daily direct aerosol radiative forcing at the TOA was as high as -20 W m(-2) locally. This change in the radiation balance caused increases in the diffuse radiation flux, with an increase of Net Ecosystem Exchange (NEE) of 18-29% for high AOD. From this analysis, it is clear that land use change in Amazonia shows alterations of many atmospheric properties, and these changes are affecting the functioning of the Amazonian ecosystem in significant ways.

Wet and dry season rates of photosynthesis and stomatal conductance were compared for upper canopy leaves of six species of tropical semi-deciduous forest trees. Photosynthetic rates showed no clear relationship to leaf form (simple/ compound), specific leaf area, or seasonality (evergreen/deciduous). Photosynthetic rates for three of five evergreen species were similar in wet and dry seasons. The rates (in ,mol m-2 sec-') were 14.5 (wet season) and 15.5 (dry season) for Didymopanax morototoni, 13.8 (wet season) and 12.2 (dry season) for Ficus obtusifolia, and 10.4 (wet season) and 10.2 (dry season) for Luehea seemannii. In the dry season, stomatal conductance for all five evergreen species was half or less than in the wet season, except in Didymopanax, for which conductance was high in both seasons. For Anacardium excelsum and Cecropia longipes, photosynthetic rates in the dry season (4.71 and 6.38 ,mol m-2 sec-', respectively) were lower than in the wet season (8.62 and 12.4 umol m-2 sec-'). For these species, the lower photosynthetic rates in the dry season were observed at internal CO2 concentrations (Cl) as high or higher than wet season Cl, suggesting that photosynthetic activity was reduced by water stress. Pseudobombax septenatum, a dry season deciduous species, sometimes showed low levels of photosynthesis and stomatal conductance as well as low C, levels, suggesting that stomatal closure restricted photosynthetic activity. Higher stomatal conductance was associated with higher rates of photosynthesis among species and between seasons.

With the development of the economy and the improvement of people’s living standards, energy has become an increasingly indispensable substance. The large-scale development and utilization of fossil energy has caused problems of energy crisis and environmental pollution. In order to solve these two problems, it is necessary to develop and utilize renewable energy sources, and access distributed power sources in the distribution network to form an active distribution network. The active distribution network contains a large number of distributed power sources, energy storage units and reactive power compensation equipment. Although it provides more convenience for voltage and reactive power regulation of the distribution network, the intermittent and volatility of renewable energy sources will also be Its voltage has a big impact. In order to solve the voltage dip and overvoltage problem of active distribution network, a new active distribution network voltage control strategy is proposed by using model prediction control technology. Inaccurate system modeling is reduced by establishing active distribution bus voltages, distributed power supplies, and energy storage device prediction models. With the minimum adjustment cost as the control target, the second-order cone relaxation method is used to optimize the action behavior of each control device. Finally, the IEEE33 node simulation example is built on the matlab simulation platform. The results show that the proposed voltage control strategy has good control effect and robustness.

Leafhoppers constitute one of the largest groups of pests causing damage to crops worldwide. Edge grasses, which are border crops (also known as border grasses), contain diverse plant species and maintain large populations of leafhoppers during the tropical dry and wet seasons. However, little is known about the diversity of leafhoppers on these grasses. The objective of this study was to characterize the diversity of leafhoppers on maize and on surrounding border grasses during the dry and wet seasons. Leafhopper adults were collected with a sweep net from border grasses during the dry season, when maize is absent. During the wet, maize-growing season, leafhoppers were collected in both the maize fields and their surrounding edge grasses. A highly diverse (H' = 1.97 ± 2.03) leafhopper population was seen on the edge grasses during the dry season, and during the wet season, leafhopper diversity was higher in the edge grasses (H'= 1.79 ± 1.72) than in the maize fields themselves (H'= 1.67 ± 1.12). Throughout the wet season, the most abundant leafhopper species in border grasses were Stirellus bicolor (Van Duzee) (Hemiptera: Cicadellidae), Graminella sonora (Ball) (Hemiptera: Cicadellidae), and Balclutha incisa (Matsumura) (Hemiptera: Cicadellidae), whereas Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae) was the most abundant species in maize fields. All of these species were from the subfamily Deltocephalinae. Canonical Component Analysis showed that leafhopper abundance of Sibovia compta (Fowler) (Hemiptera: Cicadellidae), Graphocephala aurolineata (Fowler) (Hemiptera: Cicadellidae), D. maidis, and S. bicolor was associated with abiotic factors such as relative humidity, soil moisture, temperature, and pluvial precipitation. Nevertheless, for most leafhopper species, abundances were not significantly correlated with the abiotic variables measured.

Spatio–temporal variation in Chlorophyll, Nutrients and Primary Productivity of some selected sampling stations in Lagos lagoon were investigated using conventional method from November 2019 to July 2020, in order to compare the result with data from satellite image using MODIS Aqua. Global Positioning Receiver was used to capture the geographic coordinates of the sampling stations. Water sampling was carried out monthly using standard methods during wet and dry seasons. The observed data were subjected to statistical analysis using Microsoft Excel and SPSS version 20. In wet season, the highest mean value for Chlorophyll a (1.15±0.02 µg/L) was recorded in Ofin while the lowest values (0.06±0.01 µg/L) was observed in Okobaba. During the dry season, the highest mean value (0.75±0.10 µg/L) was in Ofin while the lowest mean value (0.27±0.0.08 µg/L) was recorded in Ibeshe. The MODIS satellite variation in chlorophyll-a showed that the highest value of highest recorded value (1.37±0.00 µg/L) was in wet season (Ijede) while the lowest value (0.12±0.01 µg/L) was observed in dry season (Okobaba). The highest transparency value (0.97±0.01 mg/L) was recorded in dry season (Ofin) while the lowest value (0.35±0.25 mg/L) was recorded in wet season (Oworonsoki). The highest mean value of Surface Sea temperature was recorded in the dry season of Apapa (30.28±1.15oC) while the lowest mean value (26.41±1.15oC) was observed in Okobaba in the wet season. The chlorophyll-a concentration analyzed using standard method and MODIS satellite, in both dry and wet seasons in the sampled stations differ greatly from one another in terms of the mean concentration. The primary productivity of Lagos Lagoon was relatively low, with no significant spatial variations between sampling stations. The results of sea surface temperature, transparency and chlorophyll ‘a’ estimation from the MODIS revealed that the values were positively correlated with laboratory result with r2-value of 0.67, 0.80 and 0.77. This indicates that MODIS data and laboratory results generated for Lagos Lagoon were positively related.