Abstract When the pump turbine does variable speed operation, it can improve the operation efficiency in the turbine mode, and it can improve the automatic frequency adjustment efficiency in the pump ...mode. However, the hydraulic thrust will also change when the speed changes, and the magnitude of the hydraulic thrust is crucial for the safe and stable operation of the unit. The work of this paper is to analyze the changes of the axial hydraulic force and radial force with the change of the speed by numerical simulation method. It is found that the fluctuation of axial hydraulic thrust can reach about 34 t at 398.57rpm speed, 37 t at 412.16rpm speed and 21 t at 428.6rpm speed. the fluctuation of radial force can reach about 13.78 t, 14.4 t and 12.4 t. The purpose of this paper is to use the simulation results to understand the hydraulic thrust characteristics and ensure the stability of the unit to select the appropriate speed range, provide the basis for stable operation of the unit under design conditions.
Vortex is one of typical structures of the unsteady flow inside the hydroturbines, leading to significant pressure fluctuation, prominent vibration of the units, and fatigue of turbine components. In ...order to reveal the complex vortex structures in the hydroturbines, a large amount of advanced methods for vortex identification and visualization have been developed and also are currently being intensively investigated by researchers. In this review, the vortex identification methods are reviewed in great detail with many illustrating examples and quantitative comparisons between different methods. The vortex identification methods are classified based on five different taxonomies. The identification of several typical vortices (e.g. vortex rope in draft tube, Kármán vortex, and inter-blade vortex) in hydroturbines (including reversible pump turbines, Francis turbine, Kaplan turbine etc.) have been shown and discussed. Furthermore, experimental techniques for vortex observation have been also summarized and discussed. This review provides a practical guidance to the researchers for performing vortex identification.
Abstract
Energy is the vital requirements of daily life. It is mainly concerned with production, storage, balance and distribution. Hydropower is a key sources of renewable energy. Regarding the ...storage of hydropower energy, pumped storage comes in the foremost choice. The runner is the main component of pump storage hydropower project. As the energy storage trend is shifting for pump storage hydropower project, the design methodology and operating range of reversible pump turbine play major role. The pump turbine has always compromise in efficiency due to the same machine operating in both turbine and pump mode. Similarly flow instability in the major hurdles in pump turbine. The initial cost for the pumped storage hydropower will certainly be high. Due to this, research trend has been now shifted in possibility of retrofitting of existing hydropower with pumped storage. This is also the true for the study presented here, where the retrofitting of reversible pump turbine in existing hydropower project. The basic dimension for the reversible pump turbine is taken from the existing model Francis Turbine. The blade profile has been changed by increasing blade passage area. Numerical analysis has been performed in both pump mode and turbine mode by at different guide vane angles. Finally the results are discussed with future recommendations.
Abstract The operation conditions of the pump-turbine are changed frequently and are worse than the conventional turbine. The operation stability of the pump-turbine is more focused with the ...incremental unit capacity and the pump-turbine runner diameter. The research of the measurement method for the dynamic stress and the pressure of the model pump-turbine splitter runner blades is performed to evaluate the stress and pressure distribution under the various operation conditions, it is optimized for the turbine mechanical and hydraulic computation, the operation references are provided for the prototype pump-turbine also. In this paper, the measurement positions of the blades are determined based on the hydraulic CFD and mechanical computation, the measurement method of dynamic stress and pressure of model pump turbine-runner splitter blades is studied.
Abstract In order to more accurately evaluate the transition process characteristics of pump turbine in pumped storage power station, this paper summarized a systematic inversion calculation and ...analysis method. Using this inversion calculation method, this paper calculated and analyzed the pressure changes for different load conditions of the same unit, similar conditions of other units in the same hydraulic unit and similar conditions of similar units in other hydraulic units based on the actual measured data of load rejecting test in a pumped storage power station. The inversion calculation results are in good agreement with the experimental measured data, which proves that it is feasible to predict the transient pressure by using this method for inversion calculation.
A full-size converter-fed synchronous machine (CFSM) technology is emerging as the most flexible system for pumped storage plants for efficient operation in a wide range of water flows, which is not ...the case in existing power plants with fixed-speed synchronous machines. This article presents steady-state control strategies to execute the variable speed operation of the pumped storage power plants in both turbine and pump mode using a full-size back-to-back converter. Furthermore, the starting method of the power plant in pump and turbine mode from a standstill is proposed. In addition, the seamless transition of operating modes from the turbine to pump mode and vice versa is presented, which is an essential feature required to adapt to the varying power generation from renewable energy sources like solar and wind. The behavior of the power plant during a voltage dip on ac grid, and the low-voltage ride-through (LVRT) capability in both turbine and pump modes are also presented. The proposed control strategies are experimentally verified with a 100 kVA machine and converter setup with an emulated reversible pump turbine (RPT) and waterways.
Pump turbines play a quite important role of peak-valley shifting in the grid, and the hump margin is a critical criterion related to the safety and stability of operation in pump mode. Aiming at ...investigating the influence of runner outlet setting angle distribution on hump performance of a pump turbine, three runners with different linear distributions of setting angle at outlet were proposed, and the corresponding hump performance comparison was analyzed numerically through the SST k-ω turbulent model. The numerical result shows that, compared to the experiment, the relative errors of all simulated performances (energy characteristic, torque characteristic, and efficiency) were within 3%. Moreover, it was found that setting angle distribution modes could lead to a remarkably different performance in the hump region and, for the runner whose setting angle at shroud was 10° larger than that at hub, the hump safety margin could be increased from 4% to 4.5%. Thereafter, the corresponding mechanisms including energy input and hydraulic loss were investigated through the Euler head theory and the entropy method, respectively. It was found that hydraulic loss distribution played a more important role than the input energy on controlling hump performance. Moreover, for the runner with the largest hump margin, the hydraulic loss was distributed more evenly in the decreasing discharge direction, contributing to the elimination of hump performance. In addition, hydraulic loss distribution was calculated through local entropy production rate (LEPR) method. For all proposed runners, when the pump turbine entered the hump region from a normal operation point, the hydraulic loss was mainly concentrated in vaneless areas and guide/stay vane channels, while the runner with a large setting angle at shroud could better control the hydraulic loss distribution in both the spatial location and the discharge varying direction, increasing the hump margin. The design method presented in our paper is more likely to be applied in engineering applications.
Pump as Turbine (PAT) is an effective alternative of power generation for small hydropower system. Since the characteristic curves under turbine mode are not supplied by manufacturer of pumps, the ...theoretical model for energy performance of centrifugal turbomachinery under pump and turbine modes is proposed by means of detailed modeling of losses inside hydraulic machinery. Based on the theoretical model, a flowrate-based iteration method is proposed to determine the best efficiency point (BEP) under turbine mode. In order to validate the accuracy of established theoretical model, case studies are carried out under three centrifugal pumps, with the specific speed varied from 103 to 187, and the predicted results by theoretical model are compared with experimental measurements and numerical simulations. It is found that the average relative variations for prediction of pump head and efficiency are 6.12% and 5.51%, respectively, and they are 5.40% and 3.63% for turbine head and efficiency, which is of sufficient accuracy for engineering practice. The predicted BEP under turbine mode is also of great accuracy, with relative variation of 1.28% on average. In addition, the PAT performance as well as losses under pump and turbine modes have been analyzed in detail.
•Theoretical model of energy performance prediction for pump as turbine is proposed.•Flowrate-based iteration method of best efficiency point (BEP) determination is proposed.•Three pumps with specific speed of 103, 131 and 187 are investigated.•Losses of centrifugal pump and PAT under various flow rates are analyzed.
S-shaped characteristics on the performance curves of pump-turbines in turbine mode promote instability problems in associated transient processes, e.g., difficulties in synchronizing with power grid ...in turbine start-ups, unstable performance in turbine load rejections, etc. The present paper presents and discusses relative studies on the S-shaped characteristics, which have been carried out by various investigators. Studies include system instability analysis, experimental and numerical investigations on the flow mechanism of pump-turbines, studies on the influencing geometric and operating parameters of the unit, and precautions and countermeasures to improve the S-shaped characteristics and instability problems in associated transient processes.
Abstract In order to test the performance of pump turbine, it is necessary to collect and analyze the performance indexes such as energy characteristics, stability performance, cavitation performance ...and force characteristics of the unit through the pump turbine model test test system. however, the current test systems all use manual operation based on the standard specification requirements to handle the data collection and analysis of the test, and the accuracy of the data relies on human experience and the efficiency is not high. The method described in this paper uses emerging computer test technology means such as big data technology, noise and image recognition technology to automatically and efficiently complete the test data test, and quickly complete the test test, while the test results are more accurate.
