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Special Issue "Hydropower"

A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (31 January 2016)

Special Issue Editors

Guest Editor
Prof. Ånund Killingtveit

Department of Civil and Environmental Engineering, Norwegian University of Science and Technology (NTNU), NO-7491, Trondheim, Norway
Website | E-Mail
Interests: hydrology applied to hydropower planning, design and operation; dam safety; flood control; environmental and social impacts of hydropower; impact of climate change on natural and man-made water systems; interaction between hydropower and other renewable energy technologies, in particular wind and solar; hydropower in cold climate
Guest Editor
Prof. Dr. Juan Ignacio Pérez-Díaz

Department of Hydraulic, Energy and Environmental Engineering, Technical University of Madrid (UPM), c/ Profesor Aranguren s/n 28040 Madrid, Spain
E-Mail
Interests: hydropower scheduling; simulation of hydraulic transients in hydropower plants; control of hydropower plants; provision of load-frequency control by hydropower plants; pumped-storage

Special Issue Information

Dear Colleagues,

Hydropower has been the main source of renewable electrical energy for more than a hundred years, and will continue to be equally, or even more, important in the future, certainly for another 100 years. Though the hydropower of today is a mature technology, there is still room for technological improvements and a need for adaptation to many new challenges: New market conditions, new environmental policies, the water-food-energy-ecosystem nexus, and how to adapt to a changing climate with its impacts on water resources. Hydropower offers significant potential for carbon emission reductions. With 16% of worldwide electricity generation, hydropower today remains the largest source of renewable energy in the electricity sector, and, still, there is a potential to increase global hydropower generation by 200%–300%.

Hydropower planning and operation are closely linked to water resources management, and is in the centre of the “Water-Energy-Food-Ecosystem Nexus”. During hydropower development, one nearly always needs to consider many other users and uses of water, making both planning and operation much more challenging than for other renewables. The sustainability issue is becoming increasingly important, and today it is hardly possible to develop hydropower resources without a thorough discussion and documentation of its long-term sustainability. Situated at the crossroads of two major issues for development, water and energy, hydro reservoirs can often deliver services beyond electricity supply, such as flood control, transport, recreation, and water supply for irrigation, municipal consumption, and industry.

In addition to providing energy and capacity, hydropower offers several other advantages to the grid, such as supporting frequency control, “black start” capability, energy storage, and the capability to balance demand and generation at timescales from seconds to weeks. The rapid development of other renewables, like wind and solar, is creating an increasing demand for energy storage and load balancing, and, here, hydropower is often a perfect companion. We invite papers dealing with the integration of renewables in the grid, and, in particular, the role of hydropower in this process. We would also like to see papers discussing how the existing and ageing hydropower system could be refurbished and extended, for example, by new pumped-storage plants, in order to maximize energy, capacity, and other ancillary services.

To summarize, in this Special Issue on hydropower, we invite authors to submit papers from the full value-chain of hydropower, including resource-mapping, planning, construction, maintenance, and operation. We would like to see papers on novel technology development, use of new materials, new or improved methods for planning including sustainability analysis, the role of hydropower storage and capacity in a grid with increasing share of highly variable generation from wind and solar plants, and on how to develop and operate hydropower plants optimally under the uncertainty brought by climate change.

Prof. Dr. Ånund Killingtveit
Dr. Juan Ignacio Pérez-Díaz
Guest Editors

Manuscript Submission Information

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Keywords

  • hydropower
  • pumped storage
  • power system services
  • sustainability
  • environmental impacts
  • climate change

Published Papers (20 papers)

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Open AccessEditor’s ChoiceArticle Numerical Analysis of the Transient Behaviour of a Variable Speed Pump-Turbine during a Pumping Power Reduction Scenario
Energies 2016, 9(7), 534; https://doi.org/10.3390/en9070534
Received: 10 March 2016 / Revised: 27 June 2016 / Accepted: 27 June 2016 / Published: 12 July 2016
Cited by 8 | PDF Full-text (12490 KB) | HTML Full-text | XML Full-text
Abstract
To achieve the carbon free electricity generation target for 2050, the penetration of renewable energy sources should further increase. To address the impacts of their unpredictable and intermittent characteristics on the future electricity grid, Pumped Hydro Energy Storage (PHES) plants should enhance their
[...] Read more.
To achieve the carbon free electricity generation target for 2050, the penetration of renewable energy sources should further increase. To address the impacts of their unpredictable and intermittent characteristics on the future electricity grid, Pumped Hydro Energy Storage (PHES) plants should enhance their regulation capability by extending their continuous operating range far beyond the optimal normal working range. However, for the time being, the regulation capability of the new generation of PHES, equipped with reversible pump-turbines due to their cost-effectiveness, is limited at part load by instability problems. The aim of this paper is to analyse, during a pumping power reduction scenario, the onset and development of unsteady phenomena leading to unstable behaviour. A 3D transient numerical simulation was carried out on the first stage of a variable-speed two-stage pump-turbine from full load to the unstable operating zone by progressively reducing the speed from 100% to 88% rpm corresponding to a power reduction from full load to about 60% with a ramp rate of 1.5% per s. Two three-dimensional unsteady flow structures affecting the return channel and the wicket gates at the end of the first stage were identified and their evolution in the power regulation scenario was fluid-dynamically and spectrally characterized to determine the fluid-dynamical conditions causing the head drop in the hump zone. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle Hydropower Production in Future Climate Scenarios; the Case for the Zambezi River
Energies 2016, 9(7), 502; https://doi.org/10.3390/en9070502
Received: 29 February 2016 / Revised: 16 June 2016 / Accepted: 21 June 2016 / Published: 30 June 2016
Cited by 3 | PDF Full-text (4129 KB) | HTML Full-text | XML Full-text
Abstract
Climate change remains a threat to water resources projects in southern Africa where impacts resulting from changes in climate are projected to be negative and worse than in most other regions of the world. This work presents an assessment of the impacts of
[...] Read more.
Climate change remains a threat to water resources projects in southern Africa where impacts resulting from changes in climate are projected to be negative and worse than in most other regions of the world. This work presents an assessment of the impacts of climate change on water resources and hydropower production potential in the Zambezi River Basin. Future climate scenarios projected through the five General Circulation Model (GCM) outputs are used as input in the impact assessment. The future projected climate scenarios are downscaled to find local and regional changes, and used in the Hydrologiska Byråns Vattenbalansavdelning (HBV) hydrological model to assess climate change impacts on water resources in the river basin. According to the simulations, air temperature and potential evaporation are projected to increase, while rainfall is projected to decrease. The Zambezi hydropower system is likely to be affected negatively as a result of future climate changes. Increasing air temperature leading to increased evaporation, and reduced rainfall, both contribute to a decrease in resulting river flows and increased reservoir evaporation. Consequently, the decrease in water resources will lead to decreased hydropower production potential, by 9% in 2020s, 18% in 2050s and 28% in 2080s in the hydropower system, for a medium emission scenario, A1B. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle The Influence of Environmental Constraints on the Water Value
Energies 2016, 9(6), 446; https://doi.org/10.3390/en9060446
Received: 29 February 2016 / Revised: 13 May 2016 / Accepted: 6 June 2016 / Published: 9 June 2016
Cited by 1 | PDF Full-text (2821 KB) | HTML Full-text | XML Full-text
Abstract
The establishment of more severe hydrological environmental constraints, usually as seasonal minimum flows (ϕ) and maximum ramping rates (ρ), on hydropower operation is a growing trend. This paper presents a study on the influence of ϕ and ρ on
[...] Read more.
The establishment of more severe hydrological environmental constraints, usually as seasonal minimum flows (ϕ) and maximum ramping rates (ρ), on hydropower operation is a growing trend. This paper presents a study on the influence of ϕ and ρ on the water values (WV) of a real hydropower plant that participates in the Spanish day-ahead electricity market. For this purpose, a master-slave algorithm, based on stochastic dynamic programming (SDP) and deterministic mixed integer linear programming (DMILP), is used on a real hydropower plant. The master module, based on SDP, has a yearly planning period with weekly time steps and considers three state variables: stored water volume in the reservoir at the beginning of each week; weekly water inflow; and average weekly energy price. The slave module, based on DMILP, has a weekly planning period with hourly time steps and considers many features of the hydropower plant operation, such as: start-up costs, evaporation, wear and tear costs, etc. The results indicate that WV of a hydropower plant are very sensitive to the presence of these constraints; ϕ especially during the wettest season and ρ during the driest one. As the severity of ϕ and ρ increase, WV increase and decrease, respectively. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessFeature PaperArticle Hydropower Production in Future Climate Scenarios: The Case for Kwanza River, Angola
Energies 2016, 9(5), 363; https://doi.org/10.3390/en9050363
Received: 3 March 2016 / Revised: 27 April 2016 / Accepted: 6 May 2016 / Published: 12 May 2016
PDF Full-text (4171 KB) | HTML Full-text | XML Full-text
Abstract
Climate change is altering hydrological processes with varying degrees in various regions of the world and remains a threat to water resources projects in southern Africa. The likely negative impacts of changes in Africa may be worse than in most other regions of
[...] Read more.
Climate change is altering hydrological processes with varying degrees in various regions of the world and remains a threat to water resources projects in southern Africa. The likely negative impacts of changes in Africa may be worse than in most other regions of the world. This study is an evaluation of the possible impacts of climate change on water resources and hydropower production potential in Kwanza River Basin, Angola. The regional climate data, the basis for future climate scenarios, is used in the hydrological model HBV to assess climate change impacts on water resources in the Kwanza River Basin. Evaluation of changes in hydropower production potential is carried out using an energy model. The simulations show that annual rainfall in 2080 would increase by approximately 16% with increasing inter-annual variability of rainfall and dry season river flow and later onset of the rainy season. The simulation results show that for the Kwanza River Basin the effects as a result of changes in the future climate, in general, will be positive. Consequently, the increase in water resources will lead to increased hydropower production potential in the basin by up to 10%. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle Cavitation Inception in Crossflow Hydro Turbines
Energies 2016, 9(4), 237; https://doi.org/10.3390/en9040237
Received: 19 February 2016 / Revised: 17 March 2016 / Accepted: 21 March 2016 / Published: 24 March 2016
Cited by 7 | PDF Full-text (1123 KB) | HTML Full-text | XML Full-text
Abstract
Cavitation is a common flow phenomena in most hydraulic turbines and has the potential to cause vibration, blade surface damage and performance loss. Despite the fact that crossflow turbines have been used in small-scale hydropower systems for a long time, cavitation has not
[...] Read more.
Cavitation is a common flow phenomena in most hydraulic turbines and has the potential to cause vibration, blade surface damage and performance loss. Despite the fact that crossflow turbines have been used in small-scale hydropower systems for a long time, cavitation has not been studied in these turbines. In this paper, we present the findings of a computational study on cavitation inception in crossflow turbines. Cavitation inception was assessed using three-dimensional (3D) Reynolds-Averaged Navier–Stokes (RANS) computations. A homogeneous, free-surface two-phase flow model was used. Pressure distributions on the blades were examined for different flow rates, heads and impeller speeds to assess cavitation inception. The results showed that cavitation occurs in the second stage of the turbine and was observed on the suction side near the inner edge of the blades. For the particular turbine studied, cavitation always occurred at shaft speeds greater than that, giving the maximum efficiency for each combination of flow rate and head. The implication is that the useful operating range of crossflow turbines is up to and including the maximum efficiency point. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessFeature PaperArticle Measuring the Dynamic Characteristics of a Low Specific Speed Pump—Turbine Model
Energies 2016, 9(3), 199; https://doi.org/10.3390/en9030199
Received: 29 January 2016 / Revised: 4 March 2016 / Accepted: 7 March 2016 / Published: 15 March 2016
Cited by 5 | PDF Full-text (706 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents results from an experiment performed to obtain the dynamic characteristics of a reversible pump-turbine model. The characteristics were measured in an open loop system where the turbine initially was run on low rotational speed before the generator was disconnected allowing
[...] Read more.
This paper presents results from an experiment performed to obtain the dynamic characteristics of a reversible pump-turbine model. The characteristics were measured in an open loop system where the turbine initially was run on low rotational speed before the generator was disconnected allowing the turbine to go towards runaway. The measurements show that the turbine experience damped oscillations in pressure, speed and flow rate around runaway corresponding with presented stability criterion in published literature. Results from the experiment is reproduced by means of transient simulations. A one dimensional analytical turbine model for representation of the pump-turbine is used in the calculations. The simulations show that it is possible to reproduce the physics in the measurement by using a simple analytical model for the pump-turbine as long as the inertia of the water masses in the turbine are modeled correctly. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle Climate Change and Increased Irrigation Demands: What Is Left for Hydropower Generation? Results from Two Semi-Arid Basins
Energies 2016, 9(3), 191; https://doi.org/10.3390/en9030191
Received: 18 December 2015 / Revised: 1 March 2016 / Accepted: 4 March 2016 / Published: 14 March 2016
Cited by 1 | PDF Full-text (3546 KB) | HTML Full-text | XML Full-text
Abstract
In this study, we have modelled the effect of climate change and increased irrigation withdrawals on the available water for hydropower production in two semi-arid river basins, i.e., Kizilirmak (Turkey) and Devoll (Albania), and the role of the reservoirs. The combined effect
[...] Read more.
In this study, we have modelled the effect of climate change and increased irrigation withdrawals on the available water for hydropower production in two semi-arid river basins, i.e., Kizilirmak (Turkey) and Devoll (Albania), and the role of the reservoirs. The combined effect of climate change and extended irrigation withdrawals will overall lead to reduced runoff in the rivers, according to our simulations. The changes will be most dramatic at Kizilirmak, reducing the water available for hydropower production. The presence of the reservoirs will lead to extended water use/losses due to the provision of regulated flow, enabling larger irrigation withdrawals and increasing the evaporative losses from the reservoir surfaces. Comparing the water consumption losses at Kizilirmak, the irrigation losses are in the range of 2–4 times larger than the gross evaporation losses from reservoir surfaces. The reservoirs at Devoll will improve water availability for hydropower production during low flow periods, and the upstream irrigation represents presently a low risk to the downstream power producers. As the results are sensitive to specific river basin characteristics and the assumptions made, the results cannot be generalized to other river basins without taking these specifics into consideration. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessEditor’s ChoiceArticle Investigation of a High Head Francis Turbine at Runaway Operating Conditions
Energies 2016, 9(3), 149; https://doi.org/10.3390/en9030149
Received: 22 December 2015 / Revised: 5 February 2016 / Accepted: 19 February 2016 / Published: 2 March 2016
Cited by 10 | PDF Full-text (9544 KB) | HTML Full-text | XML Full-text
Abstract
Hydraulic turbines exhibit total load rejection during operation because of high fluctuations in the grid parameters. The generator reaches no-load instantly. Consequently, the turbine runner accelerates to high speed, runaway speed, in seconds. Under common conditions, stable runaway is only reached if after
[...] Read more.
Hydraulic turbines exhibit total load rejection during operation because of high fluctuations in the grid parameters. The generator reaches no-load instantly. Consequently, the turbine runner accelerates to high speed, runaway speed, in seconds. Under common conditions, stable runaway is only reached if after a load rejection, the control and protection mechanisms both fail and the guide vanes cannot be closed. The runner life is affected by the high amplitude pressure loading at the runaway speed. A model Francis turbine was used to investigate the consequences at the runaway condition. Measurements and simulations were performed at three operating points. The numerical simulations were performed using standard k-ε, k-ω shear stress transport (SST) and scale-adaptive simulation (SAS) models. A total of 12.8 million hexahedral mesh elements were created in the complete turbine, from the spiral casing inlet to the draft tube outlet. The experimental and numerical analysis showed that the runner was subjected to an unsteady pressure loading up to three-times the pressure loading observed at the best efficiency point. Investigates of unsteady pressure pulsations at the vaneless space, runner and draft tube are discussed in the paper. Further, unsteady swirling flow in the blade passages was observed that was rotating at a frequency of 4.8-times the runaway runner angular speed. Apart from the unsteady pressure loading, the development pattern of the swirling flow in the runner is discussed in the paper. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle A New Fluctuation Index: Characteristics and Application to Hydro-Wind Systems
Energies 2016, 9(2), 114; https://doi.org/10.3390/en9020114
Received: 25 November 2015 / Revised: 2 January 2016 / Accepted: 25 January 2016 / Published: 18 February 2016
Cited by 3 | PDF Full-text (7197 KB) | HTML Full-text | XML Full-text
Abstract
Hydro-wind system output fluctuations are the primary factors used to assess the effects of hydropower on power companies compensating for wind power intermittency. Considering that most fluctuation indices can only characterize one aspect of fluctuations, namely, the quantitative or contour variations, we present
[...] Read more.
Hydro-wind system output fluctuations are the primary factors used to assess the effects of hydropower on power companies compensating for wind power intermittency. Considering that most fluctuation indices can only characterize one aspect of fluctuations, namely, the quantitative or contour variations, we present a new index that uses the standard deviation (SD) and rotation angle to detect the quantitative variations and contour changes, respectively. Herein, the new index is compared with commonly used indices, specifically, the first-order difference, SD, and Richards-Baker flashiness indices. The results of tests performed using various processes and disposals show that: (1) when dealing with the process by moving average, repeating or overlay disposal, the new index performs comparably to the other indices, while when dealing with the process by zooming disposal, it more fully describes the fluctuation characteristics by taking both quantitative and contour variations into consideration; (2) when the new index is used to characterize the hydro-wind output fluctuations with different resources and capacities, the outcomes coincide with the mechanisms of hydro-wind systems. This study presents a new way to characterize the fluctuation of hydro-wind output. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle Simulation of Wind Speed in the Ventilation Tunnel for Surge Tanks in Transient Processes
Energies 2016, 9(2), 95; https://doi.org/10.3390/en9020095
Received: 8 December 2015 / Revised: 23 January 2016 / Accepted: 26 January 2016 / Published: 3 February 2016
Cited by 2 | PDF Full-text (6658 KB) | HTML Full-text | XML Full-text
Abstract
Hydroelectric power plants’ open-type surge tanks may be built in mountains subject to the provision of atmospheric air. Hence, a ventilation tunnel is indispensable. The air flow in the ventilation tunnel is associated with the fluctuation of water-level in the surge tank. There
[...] Read more.
Hydroelectric power plants’ open-type surge tanks may be built in mountains subject to the provision of atmospheric air. Hence, a ventilation tunnel is indispensable. The air flow in the ventilation tunnel is associated with the fluctuation of water-level in the surge tank. There is a great relationship between the wind speed and the safe use and project investment of ventilation tunnels. To obtain the wind speed in a ventilation tunnel for a surge tank during transient processes, this article adopts the one-dimensional numerical simulation method and establishes a mathematical model of a wind speed by assuming the boundary conditions of air discharge for a surge tank. Thereafter, the simulation of wind speed in a ventilation tunnel, for the case of a surge tank during transient processes, is successfully realized. Finally, the effective mechanism of water-level fluctuation in a surge tank and the shape of the ventilation tunnel (including length, sectional area and dip angle) for the wind speed distribution and the change process are discovered. On the basis of comparison between the simulation results of 1D and 3D computational fluid dynamics (CFD), the results indicate that the one-dimensional simulation method as proposed in this article can be used to accurately simulate the wind speed in the ventilation tunnel of a surge tank during transient processes. The wind speed fluctuations can be superimposed by using the low frequency mass wave (i.e., fundamental wave) and the high frequency elastic wave (i.e., harmonic wave). The water-level fluctuation in a surge tank and the sectional area of the ventilation tunnel mainly affect the amplitude of fundamental and harmonic waves. The period of a fundamental wave can be determined from the water-level fluctuations. The length of the ventilation tunnel has an effect on the period and amplitude of harmonic waves, whereas the dip angle influences the amplitude of harmonic waves. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle Efficient Parallelization of the Stochastic Dual Dynamic Programming Algorithm Applied to Hydropower Scheduling
Energies 2015, 8(12), 14287-14297; https://doi.org/10.3390/en81212431
Received: 6 November 2015 / Revised: 4 December 2015 / Accepted: 10 December 2015 / Published: 18 December 2015
Cited by 1 | PDF Full-text (753 KB) | HTML Full-text | XML Full-text
Abstract
Stochastic dual dynamic programming (SDDP) has become a popular algorithm used in practical long-term scheduling of hydropower systems. The SDDP algorithm is computationally demanding, but can be designed to take advantage of parallel processing. This paper presents a novel parallel scheme for the
[...] Read more.
Stochastic dual dynamic programming (SDDP) has become a popular algorithm used in practical long-term scheduling of hydropower systems. The SDDP algorithm is computationally demanding, but can be designed to take advantage of parallel processing. This paper presents a novel parallel scheme for the SDDP algorithm, where the stage-wise synchronization point traditionally used in the backward iteration of the SDDP algorithm is partially relaxed. The proposed scheme was tested on a realistic model of a Norwegian water course, proving that the synchronization point relaxation significantly improves parallel efficiency. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle On the Implementation of Variable Speed in Pump-Turbine Units Providing Primary and Secondary Load-Frequency Control in Generating Mode
Energies 2015, 8(12), 13559-13575; https://doi.org/10.3390/en81212382
Received: 3 September 2015 / Revised: 11 November 2015 / Accepted: 17 November 2015 / Published: 1 December 2015
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Abstract
This paper analyses different control strategies for the speed control loop of a variable-speed pump-turbine unit equipped with a doubly fed induction generator, operating in generating mode in an isolated power system with high penetration of intermittent renewable energy. The control strategies are
[...] Read more.
This paper analyses different control strategies for the speed control loop of a variable-speed pump-turbine unit equipped with a doubly fed induction generator, operating in generating mode in an isolated power system with high penetration of intermittent renewable energy. The control strategies are evaluated and compared to each other in terms of the amount of water discharged through the pump-turbine and of the wicket gates fatigue while providing primary and secondary load-frequency control. The influence of the penstock length and the initial operating point on the performance of each control strategy is studied in detail. For these purposes, several simulations have been performed with a suitable dynamic model of the pumped-storage hydropower plant and the power system. The results of the paper indicate that a proper control strategy would consist in updating the reference speed according to the power generation schedule and keeping it constant within each scheduling period (typically 1 h). Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle Governor Design for a Hydropower Plant with an Upstream Surge Tank by GA-Based Fuzzy Reduced-Order Sliding Mode
Energies 2015, 8(12), 13442-13457; https://doi.org/10.3390/en81212376
Received: 28 August 2015 / Revised: 5 November 2015 / Accepted: 18 November 2015 / Published: 26 November 2015
Cited by 2 | PDF Full-text (8334 KB) | HTML Full-text | XML Full-text
Abstract
This paper investigates governor design by reduced-order sliding mode for a hydropower plant with an upstream surge tank. The governing system is made up of a tunnel, a surge tank, a penstock, a wicket gate and servomechanism, a governor, a hydro-turbine and a
[...] Read more.
This paper investigates governor design by reduced-order sliding mode for a hydropower plant with an upstream surge tank. The governing system is made up of a tunnel, a surge tank, a penstock, a wicket gate and servomechanism, a governor, a hydro-turbine and a grid. Concerning the components of the governing system, their mathematic models are established. Then, these models are interconnected to simulate the governing system. From the viewpoint of state space in modern control theory, the governing system is partially observed, which challenges the governor design. By introducing an additional state variable, the control method of reduced-order sliding mode is proposed, where the governor design is based on a reduced-order governing system. Since the governor is applied to the original governing system, the system stability is analyzed by means of the small gain theorem. An genetic algorithm is employed to search a group of parameters of the predefined sliding surface, and a fuzzy inference system is utilized to decrease the chattering problem. Some numerical simulations are illustrated to verify the feasibility and robustness of the control method. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle Linear Modeling and Regulation Quality Analysis for Hydro-Turbine Governing System with an Open Tailrace Channel
Energies 2015, 8(10), 11702-11717; https://doi.org/10.3390/en81011702
Received: 5 September 2015 / Revised: 3 October 2015 / Accepted: 13 October 2015 / Published: 19 October 2015
Cited by 6 | PDF Full-text (738 KB) | HTML Full-text | XML Full-text
Abstract
On the basis of the state–space method (SSM), a novel linear mathematical model of the unsteady flow for the tailrace system with an open channel is proposed. This novel model is an elastic linearized model of water hammer. The validity of the model
[...] Read more.
On the basis of the state–space method (SSM), a novel linear mathematical model of the unsteady flow for the tailrace system with an open channel is proposed. This novel model is an elastic linearized model of water hammer. The validity of the model has been verified by several examples of numerical simulation, which are based on a finite difference technique. Then, the complete mathematical model for the hydro-turbine governing system of hydropower station with an open tailrace channel, which is used for simulating the transient process of the hydro-turbine governing system under load disturbance, is established by combining the models of hydro-turbine, generator, governor and open tailrace channel. Finally, according to the complete model, the regulation quality for hydro-turbine governing system with an open tailrace channel under load disturbance is studied, and the effects of open tailrace channel and tailrace surge tank on regulation quality are analyzed. The results indicate that: The open tailrace channel has a strong influence on the regulation quality by observing the water level fluctuations in tailrace surge tank. The surge shows a piecewise periodical change along with the variation in the length of an open channel. The open tailrace channel can be used to improve the regulation quality of hydro-turbine governing system. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle Peak Operation of Cascaded Hydropower Plants Serving Multiple Provinces
Energies 2015, 8(10), 11295-11314; https://doi.org/10.3390/en81011295
Received: 18 May 2015 / Revised: 28 August 2015 / Accepted: 8 October 2015 / Published: 13 October 2015
Cited by 5 | PDF Full-text (891 KB) | HTML Full-text | XML Full-text
Abstract
The bulk hydropower transmission via trans-provincial and trans-regional power networks in China provides great operational flexibility to dispatch power resources between multiple power grids. This is very beneficial to alleviate the tremendous peak load pressure of most provincial power grids. This study places
[...] Read more.
The bulk hydropower transmission via trans-provincial and trans-regional power networks in China provides great operational flexibility to dispatch power resources between multiple power grids. This is very beneficial to alleviate the tremendous peak load pressure of most provincial power grids. This study places the focus on peak operations of cascaded hydropower plants serving multiple provinces under a regional connected AC/DC network. The objective is to respond to peak loads of multiple provincial power grids simultaneously. A two-stage search method is developed for this problem. In the first stage, a load reconstruction strategy is proposed to combine multiple load curves of power grids into a total load curve. The purpose is to deal with different load features in load magnitudes, peaks and valleys. A mutative-scale optimization method is then used to determine the generation schedules of hydropower plants. In the second stage, an exterior point search method is established to allocate the generation among multiple receiving power grids. This method produces an initial solution using the load shedding algorithm, and further improves it by iteratively coordinating the generation among different power grids. The proposed method was implemented to the operations of cascaded hydropower plants on Xin-Fu River and another on Hongshui River. The optimization results in two cases satisfied the peak demands of receiving provincial power grids. Moreover, the maximum load difference between peak and valley decreased 12.67% and 11.32% in Shanghai Power Grid (SHPG) and Zhejiang Power Grid (ZJPG), exceeding by 4.85% and 6.72% those of the current operational method, respectively. The advantage of the proposed method in alleviating peak-shaving pressure is demonstrated. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle Failures during Load-Frequency Control Maneuvers in an Upgraded Hydropower Plant: Causes, Identification of Causes and Solution Proposals
Energies 2015, 8(10), 10584-10604; https://doi.org/10.3390/en81010584
Received: 25 June 2015 / Revised: 7 September 2015 / Accepted: 15 September 2015 / Published: 24 September 2015
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Abstract
The objective of this paper is to investigate the cause of several unexpected high amplitude oscillations that occurred in the surge tank water level of a real hydropower plant during secondary load-frequency control (LFC) maneuvers, after the replacement of the turbine runner, and
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The objective of this paper is to investigate the cause of several unexpected high amplitude oscillations that occurred in the surge tank water level of a real hydropower plant during secondary load-frequency control (LFC) maneuvers, after the replacement of the turbine runner, and to propose solutions that allow the power plant to continue providing secondary LFC in a safe and reliable manner. For this purpose, a simulation model has been developed and calibrated from data gathered during several on-site tests. Two different solutions are proposed in order to cope with the observed problem: using a state-dependent load change rate limiter or modifying the hydro turbine governor gains; the turbine governor remains the same as before the runner replacement. The proposed solutions are tested against a set of realistic secondary LFC signals by means of simulations and compared to each other as a function of the probability that the surge tank water level descends below a minimum safe level and the quality of the secondary LFC response. The results presented in the paper demonstrate the validity of the methodology proposed to determine the state-dependent ramp limit, as well as its effectiveness to prevent the surge tank drawdown and to provide clear insight into the trade-off between response quality and power plant safety. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle A Mathematical Model and Its Application for Hydro Power Units under Different Operating Conditions
Energies 2015, 8(9), 10260-10275; https://doi.org/10.3390/en80910260
Received: 9 June 2015 / Revised: 1 September 2015 / Accepted: 10 September 2015 / Published: 17 September 2015
Cited by 23 | PDF Full-text (1093 KB) | HTML Full-text | XML Full-text | Correction
Abstract
This paper presents a mathematical model of hydro power units, especially the governor system model for different operating conditions, based on the basic version of the software TOPSYS. The mathematical model consists of eight turbine equations, one generator equation, and one governor equation,
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This paper presents a mathematical model of hydro power units, especially the governor system model for different operating conditions, based on the basic version of the software TOPSYS. The mathematical model consists of eight turbine equations, one generator equation, and one governor equation, which are solved for ten unknown variables. The generator and governor equations, which are different under various operating conditions, are presented and discussed in detail. All the essential non-linear factors in the governor system (dead-zone, saturation, rate limiting, and backlash) are also considered. Case studies are conducted based on one Swedish hydro power plant (HPP) and three Chinese plants. The simulation and on-site measurements are compared for start-up, no-load operation, normal operation, and load rejection in different control modes (frequency, opening, and power feedback). The main error in each simulation is also discussed in detail. As a result, the model application is proved trustworthy for simulating different physical quantities of the unit (e.g., guide vane opening, active power, rotation speed, and pressures at volute and draft tube). The model has already been applied effectively in consultant analyses and scientific studies. Full article
(This article belongs to the Special Issue Hydropower)
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Open AccessArticle Numerical Analysis on the Stability of Hydraulic Fracture Propagation
Energies 2015, 8(9), 9860-9877; https://doi.org/10.3390/en8099860
Received: 23 June 2015 / Revised: 13 August 2015 / Accepted: 25 August 2015 / Published: 11 September 2015
Cited by 10 | PDF Full-text (957 KB) | HTML Full-text | XML Full-text
Abstract
The formation of dense spacing fracture network is crucial to the hydraulic fracturing treatment of unconventional reservoir. However, one difficulty for fracturing treatment is the lack of clear understanding on the nature of fracture complexity created during the treatment. In this paper, fracture
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The formation of dense spacing fracture network is crucial to the hydraulic fracturing treatment of unconventional reservoir. However, one difficulty for fracturing treatment is the lack of clear understanding on the nature of fracture complexity created during the treatment. In this paper, fracture propagation is numerically investigated to find the conditions needed for the stable propagation of complex fracture network. Firstly, starting from a parallel fracture system, the stability of fracture propagation is analyzed and a dimensionless number M is obtained. Then, by developing a hydraulic fracturing simulation model based on displacement discontinuity method, the propagation of parallel fractures is simulated and a clear relation between M and the stability of parallel fractures is obtained. Finally, the investigation on parallel fractures is extended to complex fracture networks. The propagation of complex fracture networks is simulated and the results show that the effects of M on complex fracture networks is the same to that of parallel fractures. The clear relation between M and fracture propagation stability is important for the optimization of hydraulic fracturing operation. Full article
(This article belongs to the Special Issue Hydropower)
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Review

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Open AccessEditor’s ChoiceReview Experimental and Numerical Studies of a High-Head Francis Turbine: A Review of the Francis-99 Test Case
Energies 2016, 9(2), 74; https://doi.org/10.3390/en9020074
Received: 9 November 2015 / Revised: 11 January 2016 / Accepted: 18 January 2016 / Published: 26 January 2016
Cited by 14 | PDF Full-text (9983 KB) | HTML Full-text | XML Full-text
Abstract
Hydraulic turbines are widely used to meet real-time electricity demands. Computational fluid dynamic (CFD) techniques have played an important role in the design and development of such turbines. The simulation of a complete turbine requires substantial computational resources. A specific approach that is
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Hydraulic turbines are widely used to meet real-time electricity demands. Computational fluid dynamic (CFD) techniques have played an important role in the design and development of such turbines. The simulation of a complete turbine requires substantial computational resources. A specific approach that is applied to investigate the flow field of one turbine may not work for another turbine. A series of Francis-99 workshops have been planned to discuss and explore the CFD techniques applied within the field of hydropower with application to high-head Francis turbines. The first workshop was held in December 2014 at the Norwegian University of Science and Technology, Norway. The steady-state measurements were conducted on a model Francis turbine. Three operating points, part load, best efficiency point, and high load, were investigated. The complete geometry, meshing, and experimental data concerning the hydraulic efficiency, pressure, and velocity were provided to the academic and industrial research groups. Various researchers have conducted extensive numerical studies on the high-head Francis turbine, and the obtained results were presented during the workshop. This paper discusses the presented numerical results and the important outcome of the extensive numerical studies on the Francis turbine. The use of a wall function assuming equilibrium between the production and dissipation of turbulence is widely used in the simulation of hydraulic turbines. The boundary layer of hydraulic turbines is not fully developed because of the continuously-changing geometry and large pressure gradients. There is a need to develop wall functions that enable the estimation of viscous losses under boundary development for accurate simulations. Improved simulations and results enable reliable estimation of the blade loading. Numerical investigations on leakage flow through the labyrinth seals were conducted. The volumetric efficiency and losses in the seals were determined. The seal leakage losses formulated through analytical techniques are sufficient. Full article
(This article belongs to the Special Issue Hydropower)
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Other

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Open AccessCorrection Correction: Yang, W.; Yang, J.; Guo, W.; Zeng, W.; Wang, C.; Saarinen, L.; Norrlund, P. A Mathematical Model and Its Application for Hydro Power Units under Different Operating Conditions. Energies 2015, 8, 10260–10275
Energies 2016, 9(6), 477; https://doi.org/10.3390/en9060477
Received: 23 May 2016 / Accepted: 30 May 2016 / Published: 22 June 2016
PDF Full-text (390 KB) | HTML Full-text | XML Full-text
Abstract
The authors wish to make the following corrections to the published paper [1].[...] Full article
(This article belongs to the Special Issue Hydropower)
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