Large Hydropower Plants Research Articles

Distinguishing the multiple controls on the decreased sediment flux in the Jialing River basin of the Yangtze River, Southwestern China

Riverine sediment flux is a crucial proxy influencing channel morphology, biogeochemical processes, and riverine ecosystems. However, recent climate change and multiple anthropogenic activities have substantially altered the sediment regimes of the world’s rivers. On a basis of the “multiple double mass curves” method, this study selected the Jialing River (JR) basin as a case study to distinguish the relative impacts of climate change, land-use change, and damming on changes in the runoff and sediment flux over the past 60 years. The results showed that the sediment fluxes in the JR basin drastically decreased by 57–77% from the baseline period (1950s–1984) to the post-change period (1985–2017) mainly due to damming (60–75%), climate change (5–30%), and revegetation (10–20%). The runoff in the JR basin also exhibited a reduction (12–22%) likely because of the joint impacts of a reduction in precipitation and the restoration of vegetation. Although the 2008 Wenchuan Earthquake (M = 7.9) increased the short-term sediment fluxes, its impact on the long-term sediment fluxes in the downstream areas of the JR basin was limited as a result of the buffering effect of the thousands of constructed reservoirs. The decreased sediment fluxes in the JR basin benefit the life expectancy of the Three Gorges Reservoir (the world’s largest hydropower plant), but the reduced runoff can exacerbate water stress. The findings of our study have important implications for better management of water resources, sediment fluxes, and reservoir sedimentation not only for the JR basin, but also for the Three Gorges Reservoir.

Automatic generation control of a large hydropower plant with head‐sensitive forbidden and restricted zones

Head-sensitive forbidden and restricted zones of large hydropower units are challenging the automatic generation control (AGC) as admissible operating zones are discontinuous and variational. This study focuses on the AGC of such a large hydropower plant to ensure the stability, security and timeliness of power grids. A methodology is developed to solve the unit commitment (UC) and load distribution in AGC. This methodology identifies in advance all feasible unit combinations under different water heads and determines admissible operating zones using combinatorial mathematics techniques. A fast strategy that includes the accurate estimation of varying water heads helps to eliminate infeasible unit combinations. Minimising the number of units working in restricted zones and times of unit output passing through forbidden zones is used to optimise the UC, where priority orders of units are introduced to evaluate UC schemes with the same objective value. Finally, a dynamic programming based model is formulated to solve an economic load distribution among operating units. The methodology is applied to the AGC of the Nuozhadu with nine 650 MW units of two different types. Three cases indicate that the number of units working in restricted zones and times of unit output passing through forbidden zones is significantly reduced.

Sizing optimization of exposed steel penstocks supported by ring girders using the combined ANN-GA technique

The design of penstock is a major concern in the implementation of large hydropower plants, where penstock is a large-scale structure. A design procedure incorporating the combined ANN-GA approach was developed for optimizing the exposed penstock supported by ring girders. The objective function considered is the total mass of the penstock to be minimized under the strength requirements. For this purpose, a numerical finite element analysis (FEA) model of a steel exposed penstock supported by ring girders was used to evaluate the equivalent and local stresses on the penstock shell. Parametric analysis was conducted to examine the influence of penstock thickness, ring girders spacing, and sectional size of the T-shaped ring girders on the weight of the penstock and the maximum equivalent stress. Subsequently, an artificial neural network (ANN) was developed by collecting data from the FEA numerical results, before being combined with a genetic algorithm to provide the optimal design of the penstock. The results of the FEA give a detailed distribution of local stresses in the penstock shell. The performance of the trained ANN was illustrated, and its prediction results show good agreement with the FEA numerical results. The results obtained by the ANN-GA approach proved the efficiency of the proposed process in optimizing the exposed penstock supported by ring girders. This process should be a valuable aid for the design of large penstocks.

Simulation of Cracking in High Concrete Gravity Dam Using the Extended Finite Elements by ABAQUS

China's energy demand is growing rapidly and large hydropower plants are becoming more common. This therefore has resulted in the building of many large concrete dams across the country. Significant dam cracking can have major environmental, economic and social consequences. Collapse of High concrete dam may cause serious harm to economic development as well as safety of the people; thereby necessitating the need for research on safety and stability of high concrete dam under high water and seismic conditions. In this paper, the high concrete dam of Longtan was used as an example, using the ABAQUS program based on the extended finite element method to analyze the Longtan Dam under static and dynamic conditions which has been commonly used for the study of crack growth. A numerical prediction of crack propagation in concrete gravity dams is presented. The two-dimensional seismic numerical study was done using acceleration-time records from Koyna earthquake in 1976 Dam concrete cracking range and cracking were discussed during a seismic time. The locations that are easy to generate cracks are illustrated from the analysis and the findings showed that, during seismic activity the Longtan Dam was rather unsafe. The results of the work can provide a valuable guide for the design and operation of the dam system.

Control Methods for Standalone and Grid Connected Micro-Hydro Power Plants With Synthetic Inertia Frequency Support: A Comprehensive Review

The penetration of renewable energy sources on a large scale in conventional electric networks increases exponentially for environmental preservation. However, the increase in RESs leads to some technical problems that include (a) fluctuations in power production, (b) less or no generation units for power balancing, (c) reduced inertia due to RESs decoupling from the conventional grid using converters. Micro-hydro power plants (MHPPs) are emerging as a mature balancing technology and a great alternative to large hydropower plants as they encounter population displacement and many environmental problems. Modern pump storage MHPPs uses a power converter between the grid and machine to control the consumption of power during pumping mode. This power electronic interface loses the ability of the rotating mass of the machine to contribute to the grid inertia by making it independent of the grid frequency. This problem is solved through the control of power converters in such a way that the inertia effect is synthesized termed as synthetic inertia. MHPPs can also be operated in a standalone mode where they are not connected to the grid. This paper reviews control schemes applied in literature for the frequency, voltage, and inertia control, in both the grid-connected and standalone modes. This study starts with the standalone MHPPs, covering the literature review and control structure for voltage and frequency control of standalone MHPPs. Then it presents a detailed operation, control principle, synthetic inertia concepts, and architecture of grid-connected MHPPs. The mathematical formulation of the grid, permanent magnet synchronous generator, synthetic inertia inclusion, and control structures, including direct torque control, virtual synchronous machine, and model predictive control, is also presented. Finally, the paper presents the concluding remarks with the comparative analysis of various control structures to include synthetic inertia, its suitability, and future scope for MHPPs.

Passability of Potamodromous Species through a Fish Lift at a Large Hydropower Plant (Touvedo, Portugal)

River fragmentation by large hydropower plants (LHP) has been recognized as a major threat for potamodromous fish. Fishways have thus been built to partially restore connectivity, with fish lifts representing the most cost-effective type at high head obstacles. This study assessed the effectiveness with which a fish lift in a LHP on the River Lima (Touvedo, Portugal), allows potamodromous fish—Iberian barbel (Luciobarbus bocagei), Northern straight-mouth nase (Pseudochondrostoma duriense) and brown trout (Salmo trutta fario)- to migrate upstream. Most fish (79.5%) used the lift between summer and early-fall. Water temperature was the most significant predictor of both cyprinids’ movements, whereas mean daily flow was more important for trout. Movements differed according to peak-flow magnitude: nase (67.8%) made broader use of the lift in the absence of turbined flow, whereas a relevant proportion of barbel (44.8%) and trout (44.2%) passed when the powerhouse was operating at half (50 m3s−1) and full-load (100 m3s−1), respectively. Size-selectivity found for barbel and trout could reflect electrofishing bias towards smaller sizes. The comparison of daily abundance patterns in the river with fish lift records allowed the assessment of the lift’s efficacy, although biological requirements of target species must be considered. Results are discussed in the context of management strategies, with recommendations for future studies.

Methods of analysis and risk assessment of accidents of hydraulic structures

Relevance of the research is due to the fact that over the past 10 years severe accidents at large hydropower plants and dams occurred in Russia (SayanoShushenskaya HPP, 2009), USA (Oroville dam, 2018), Brazil (Brumadinho dike, 2019), Colombia (HPP Ituango, 2018) and other countries, the need has arisen to improve the safety programs of the HS and dams. The main method of this important work is to use methods of analysis and assessment of risk accidents of HS and dams. Methods of this important work are to develop modern methodology for analyzing and assessing the risk of accidents of HS and dams. The introduction of the method of analysis and risk assessment in the safety programs of hydraulic structures (dams) in countries that are advanced in the construction of HS (China, Brazil, Canada, USA, Russia, Colombia, Norway, Spain, etc.) shows that in applying risk assessment analysis accidents of HS and dams still a number of difficulties, but this approach is of great benefit in monitoring the safety of HS and dams. The aim of this article is to familiarize and train specialists and hydraulic engineers with modern methods for assessing the safety of HS and dams.

Overall setting and cooperation method for power protection of large hydropower plants

Aiming at solving the operation risk problems caused by the improper protection settings, this paper proposed a new method for the protection setting of the auxiliary power of large hydropower plants. This method applied the idea of setting from LV grade to HV grade, where each type of protection sets the value based on the setting principles and calibrates their sensitivity with their own protection range. This method handled the insufficient sensitivities of protection at the price of sacrificing the lower levels of the protection. Then based on the settings from the dispatch and control center, it vertically conducted the verification of protection setting coordination, preventing the override tripping and expanded scope of accidents. The practical applications indicate that this method could improve the protection setting accuracy of large hydropower plants and limit the operation risks of the auxiliary power within a low level.

2D HYDRODYNAMIC MODELLING FOR IDENTIFICATION OF DEWATERED OR FLOODED STREAM CHANNEL AREAS DOWNSTREAM LARGE HYDROPOWER PLANT

Hydropower is oldest available source for renewable energy generation in Lithuania and the world. However, because of unequal demand of electricity during the day large hydropower plants are adapted to work in hydropeaking regime, which causes rapid water level and discharge fluctuations and has impact on the environment. To assess the extent of this impact in this study 2D numerical hydrodynamic modelling was carried out to reveal the dewatered or flooded stream channel areas at the Nemunas River downstream Kaunas Hydropower Plant. Such estimation of dewatered or flooded areas, considering different operating modes of hydropower plant, was carried out for the first time in Lithuania. It was revealed that largest areas are flooded when Kaunas hydropower plant starts its operation with two and four turbines and accordingly are dewatered when the plant stops such operations. During this study the impact of water level and discharge fluctuations on river ecosystems was not analysed, however the obtained results will be the initial data for more detailed assessment of fish habitats quality under impact of hydropeaking.

Exergy analysis of large and impounded hydropower plants: Case study El Roseires Dam (280 MW)

AbstractNowadays, one of the major and serious worldly concerns is the limitation of energy resources. Sudan, in specific, confronts a critical crisis in fossil fuel resources due to its separation science 2011, and mostly concerning the production of electricity energy. There are many sources of renewable energies in Sudan such as hydropower. Which it is widely used in Sudan, and one example is Elroseires hydropower plant. This research aims to conduct an exergy analysis of the performance of the Elroseires hydropower plant to identify areas for improvement using actual operation data. The exergy efficiency and exergy destruction rate of each unit in the plant were determined independently. The thermodynamic inefficiencies of all units of the plant were quantified for analysis to identify breakthrough points for further energy savings. Results indicated that the lowest exergy destruction rate occurs in August (20.6 MW) despite the lowest production of energy during this period. This outcome is due to the volumetric flow rate being less than those in other months, thereby leading to minimal flow turbulence that result in low exergy destruction. By contrast, the greatest exergy destruction occurs in December (106.1 MW) because of the high volumetric flow rate for the same pipe diameter. Such condition leads to turbulent flow and results in considerable exergy destruction. This study emphasizes that exergy analysis is useful in determining irreversibilities and losses in Elroseires hydropower plant to improve its thermodynamic performance.

Improving policies and instruments to address cumulative impacts of small hydropower in the Amazon

Small hydropower plants (SHPs) are rapidly sprawling, both globally and across the Amazon's free flowing rivers, threatening provision of ecosystem services, river connectivity, biodiversity conservation, and the livelihoods of indigenous and traditional communities. In Brazil, cumulative impacts of SHPs have been largely neglected in planning and policy instruments. In this perspective article, we highlight current policy challenges and options for assessing the impacts of small hydroelectric plants in the Amazon, which deserve more attention in both academic research and public policies. We review environmental licensing of seven small and one large dam in the Cupari river, a Tapajós tributary, which is being challenged in Federal Courts based on inadequate cumulative impact assessment. We argue for the need of adopting good practices in cross-scale environmental assessment when applying existing or new policy instruments, including: the adoption of Strategic Environmental Assessment in planning for hydropower expansion taking into consideration other plans, programs and policies at regional and Amazon-wide scales; developing integrated environmental assessments considering inventoried SHPs and large hydropower plants; using scientific evidence and technological tools in planning and siting of SHPs; complying with policies that protect human and environmental rights; and strengthening intersectoral dialogue and multi-stakeholder forums and committees.

Modeling and Real-Time Simulation of Large Hydropower Plant

Modeling and Real-Time Simulation of Large Hydropower Plant

Selection of energy matrix sources in Chile using a fuzzy logic decision approach

Chile’s 2050 energy policy ultimate goals are to produce a sustainable model of economic growth respectful of the environment where energy is produced efficiently and reliably. Renewable energy sources are considered the main drive for developing by 2050 at least 70% of the total energy in Chile. This study aims to provide a quantitative analysis for the selection of the most sustainable energy production methods using the compromise ranking method (VIKOR) that uses maximum group utility for the majority and a minimum of individual regret for the opponent. Since all evaluations are provided via intervals, the possible degree theory is used to compare them. Nine major criteria are critically used for this purpose and prioritized using analytical hierarchical process (AHP). Since Chile’s energy production matrix still relies heavily on fossil fuels with major concerns of GHG emissions, all major potential energy sources in Chile are considered including ocean energy in addition to nuclear energy. This study shows that biomasses are the best compromise solution and that traditional and modern nuclear energy plants score consistently better than solar power. Large hydro power plants rank very high but in light of the social opposition present in the country, they might not be easy to build as hoped. Ocean power is far superior to geothermal energy and comparable to wind power and for this reason it should be considered together with nuclear power for the future Chilean energy matrix.

The Role of the Renewable Energy Program in the State of Minas Gerais in the Process of Renewable Sources Expansion

The State of Minas Gerais (MG), in Brazil, has significant potential for the exploration of renewable energy, with emphasis on solar, wind and biomass. Since 2013, the State has created the Renewable Energy Program of Minas Gerais – PMER (in Portuguese), aiming the acceleration of the expansion of these renewable sources in the State’s territory. Nonetheless, the use of renewable sources, excluding large hydropower plants, is still irrelevant in the energy matrix of the State. In this way, the present paper aims to perform an effectiveness analysis of the only instrument of the State Government to expand the number of renewable energy projects, and its contribution to achieve the goals of the energy sector of the Brazilian Nationally Determined Contributions – NDCs. In order to do that, the following parameters has been measured: (1) numbers of projects implemented by the program; (2) policy innovation; (3) job creation; (4) climate change mitigation. It is also briefly discussed the efforts of the Program to address actions that promotes energy storage and the needed infrastructure to supply the energy demand through renewable energy only. There is evidence that the expansion of the renewable energy sources at the regional scope has advanced through incentive policies with clearly defined goals and guidelines. However, the five indicators have shown that the PMER does not attend all the requisites in a satisfactory way to perform as the main state public policy of renewable energy expansion. Therefore, promoting a transformation of the energy sector suggests that a balanced mix of public policies must be implemented in the State.

Impacts of small cascaded hydropower plants on river discharge in a basin in Southern China

AbstractThe run‐off volume altered by the construction of hydropower plants affects ecohydrological processes in catchments. Although the impacts of large hydropower plants have been well documented in the literature, few studies have been conducted on the impacts of small cascaded hydropower plants (SCHPs). To evaluate the impacts of SCHPs on river flow, we chose a representative basin affected by hydropower projects and, to a lesser degree, by other human activities, that is, the Qiuxiang River basin in Southern China. The observed river discharge and climate data during the period of 1958–2016 were investigated. The datasets were divided into a low‐impact period and a high‐impact period based on the number of SCHPs and the capacities of the reservoirs. The daily river discharge alteration was assessed by applying the Indicators of Hydrologic Alteration. To separate the impact of the SCHPs on the local river discharge from that of climate‐related precipitation, the back‐propagation neural network was used to simulate the monthly average river discharge process. An abnormal result was found: Unlike large reservoirs in large watersheds, the SCHPs regulated the flows during the flood season but were not able to mitigate the droughts during the dry season due to their limited storage and the commonly occurring inappropriate interregulations of the SCHPs. The SCHPs also reduced the annual average river discharge in the research basin. The contribution of the SCHPs to the river discharge changes was 85.37%, much higher than the contributions of climate change (13.43%) and other human activities (1.20%). The results demonstrated that the impacts of the SCHPs were different from those of large dams and reservoirs that regulate floods and relieve droughts. It is necessary to raise the awareness of the impacts of these river barriers.

Full-size converter operation of hydro power generators: a state-of-the-art review of motivations, solutions, and design implications

This paper reviews motivations and solutions for variable-speed operation in large hydro power plants with a special emphasis on full-size converter operated synchronous generators. First, the established concepts of conventional pumped storage power plants are briefly described. Then, the implemented applications with use of power converters and synchronous machines in hydro power plants, their power ratings, power converter topologies used, and the experiences obtained during operation are reviewed. Concerning its state-of-the-art position in variable-speed pumped storage power plants, the variable-speed capability offered by doubly-fed induction machines is also briefly described, including the power range that can be achieved in pumping mode as well as the power converter ratings of existing power plants. Following this comprehensive analysis, this paper identifies the requirements of today’s power converters and synchronous machines for utilization in large pumped storage power plants as full-size converter operated synchronous generators. It analyzes the design implications on the electric machines driven by such converters, and investigates the advantages of the additional possibilities given by the full-size converter operation that may outweigh the added cost, system complexity, and power loss.

Optimization Model for the Short-Term Operation of Hydropower Plants Transmitting Power to Multiple Power Grids via HVDC Transmission Lines

Long-distance and large-capacity hydropower transmission from large hydropower plants in southwestern China to load centers is an important and effective measure for the accommodation of large-scale hydropower in China. However, the load demands of the receiving-end power grids are not fully considered in the conventional power transmission mode, which has greatly affected their enthusiasm for the absorption of trans-regional hydro energy. In order to make full use of the peak shaving capability of the hydropower plants, this paper develops an optimization model for determining the hourly generation scheduling of the hydropower plants transmitting electric power to several power grids via high voltage direct current (HVDC) transmission lines. A large-capacity and highly complex multi-unit hydropower system, the Xiluodu plant in China, is taken as the case study. In the proposed model, minimizing the peak-valley differences of multiple receiving-end power grids is adopted as the objective to alleviate the peak shaving pressure of the receiving-end power grids. In addition to the traditional hydraulic constraints, the operation constraints of individual units and HVDC power transmission limits are well considered. The study focuses mainly on modeling the stair-like power transmission curve constraint which is discrete and nonlinear and has been rarely considered in previous studies. This constraint is then linearized through limiting the logical relations between multiple binary integer variables. Case studies demonstrate that the proposed model has high computational efficiency, and the peak-valley differences of the two receiving-end power grids, i.e., Zhejiang Power Grid and Guangdong Power Grid, are decreased by 15.2% and 7.33%, respectively. Moreover, frequent conversion of HVDC converter equipment can also be avoided, which makes the obtained generation schedule more executable.

Trends in an increased dependence towards hydropower energy utilization—a short review

Over the past few decades, fossil fuels replacements have shown leaps and bounds of progressions. Hence, various nations have initiated the adoption of biomass energy, solar energy, wind energy and hydropower energy. Yet, these currently developing technologies have constantly faced dual pressure from both the economic growth and environmental protection. Hydropower has become a key candidate for considerable utilization in various countries due to its numerous social, economic and environmental benefits. In this paper, a short review was carried out to analyse the development of various hydropower plants and compare its utilization over the conventional fossil fuels. The main setback for the adoption of this technology is that large hydropower plant demands for huge deforestation. This would direly result in the destruction of critical ecosystems, migration of large population at downstream and other catastrophic outcomes such as flash floods and landslides. However, this singular setback could be alleviated with the utilization of small or micro hydropower plant. This technology, in particular, was found to have minimal destruction effects to the environment and is able to produce affordable energy to the rural areas as it has proven in many countries.

Numerical and Experimental Investigation of the Cavitating Flow Within Venturi Tube

Hydrodynamic cavitation represents complex physical phenomenon undesirably affecting operation as well as lifespan of many hydraulic machines from small valves to the large hydro power plants. On the other hand, the same phenomenon and its concomitants such as pressure pulsations can be exploited in many positive ways. One of them which seems to be very promising and perspective is the cavitation utilization for reduction of the microorganisms such as cyanobacteria within large bulks of water. Mutual effect of the swirl induced by the upstream mounted generator and flow constriction in converging–diverging nozzle has been experimentally investigated. The analysis of the hydraulic losses in the wide range of the cavitation regimes has been done as well as the investigation of the pipe wall acceleration induced by the fluctuations of the cavitating structures. The dynamics of the cavitation was studied using the proper orthogonal decomposition (POD) of the captured video records. The main scope of this paper is numerical investigation complementing the experimental results. The multiphase simulations were carried out using the OpenFOAM 1606+ and its interPhaseChangeFoam solver. The present study focuses on computational fluid dynamics results of the cavitating velocity field within the nozzle and analysis of the loss coefficient within the nozzle. The results of the numerical analysis were utilized for the further discussion of the experimental results.

An MILP-based model for short-term peak shaving operation of pumped-storage hydropower plants serving multiple power grids

China's power grids have constructed many large pumped-storage hydropower plants (PSHPs) to relieve their increasing peak shaving pressure. Unlike PSHPs in a single power grid, the PSHPs directly operated by the dispatch center of regional power grids are required to simultaneously provide peak regulation services for several subordinate provincial power grids. This makes the daily operation of these PSHPs very challenging for both system operators and researchers. Hence, this paper develops a Mixed-integer linear programming (MILP) based model for determining the optimal hourly scheduling of PSHPs serving several provincial power grids. The objective is to minimize the peak-valley difference of the residual load series of each power grid. The performance of individual units in the model will be considered, as well as the head effect for each unit in both generating mode and pumping mode. The study focuses mainly on the linearization of the commonly-used nonlinear objective function, constraints on the operation status of units, and turbine performance curves. These nonlinearities are then linearized with the aid of binary integer variables. The optimization results obtained from two real-world case studies are used to demonstrate that the proposed model is computationally efficient and shows good performance in relieving the peak regulation pressure of each power grid.