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Sediment erosion is a crucial issue that affects the reliability of hydraulic turbines operating in sediment laden water. Guide vanes are the prime components for allocating water to produce the useful work, and shape changes due to wear affect the water flow properties. Profile changes can induce wakes, create boundary layer friction, and generate cross flows and leakage flows, all of which eventually deteriorate the performance of turbine. Erosive wear is dependent on the properties of the sand, turbine materials, particle velocity and impact angle. Since these factors vary with the site and the duration of the operation, there is no consistency in erosive wear behavior. This case study discusses sediment erosion in guide vanes in the largest operational hydropower plant in Nepal (Kaligandaki-A (KGA) Hydropower). Observations were combined with computational analysis. Sediment properties and mineral content, the turbine material, the erosion patterns, erosion protection methods, and numerical estimates of erosion have all been addressed. High quartz content, increasing inefficiency of the flushing system, higher sediment load, high impingement velocity, and operation at low guide vane angles were all found to be major contributors to erosive wear in this system. [ABSTRACT FROM AUTHOR]

In high sediment laden river projects or silt affected power stations, the frequency of repair and maintenance of underwater parts is comparatively higher which leads to increase the overall forced outages per year for repair The extent of the major maintenance will depend on the operating condition such as suspended sediment load passing through the turbine and how the machine was loaded during the operation. This paper illustrates the analysis of sediments, effect of sand erosion and maintenance of turbine of Kali Gandaki "A" Hydroelectric Plant (144 MW). The paper also describes the repair methods used for different turbine components to minimize the effects induced by sediment erosion. [ABSTRACT FROM AUTHOR]

Abstract: Kathmandu University (KU) is one of the leading educational institutes in Nepal with a decade long experience with R&D of micro-hydro turbines. With a technical collaboration with Norwegian University of Science and Technology (NTNU), KU has also conducted several studies related to sediment erosion in hydro turbine. In the presented study a new program has been developed to create and optimize the design of Francis runners. The program is also featured to compare erosion in runner blades for different design cases. The final design can be exported to Computational Fluid Dynamics (CFD) and Fluid Structure Interaction (FSI) for further analysis. Parametric survey was carried out with this program to evaluate the relative effect of each design parameter on sediment erosion. Several optimized designs were developed and analyzed with CFD tools to fulfill the desired condition of minimum erosion and maximum efficiency. This paper summaries the problem of sediment erosion of hydro turbines in South Asia region. Some of the important achievements in R&D of hydro turbine and sediment erosion at KU are also presented. The findings of design optimization of Francis turbine for effective reduction in sediment erosion is discussed in details. [Copyright &y& Elsevier]

Nepal is endowed by enormous water resources andpower potential, but not enough energy has been exploited from it. One reason is the deterioration of hydraulic turbines. Research on turbine erosion has shown that sand erodes the turbine material. Only a few researches however, have provided details of the many parameters of sand on the degradation of hydraulic turbines. This paper describes the different parameters of sand and the direct impact of sand on turbine material. The study of sand of the Roshi Khola (river) in Nepal shows that mineral content, size, shape and texture are the most important parameters of sand, with different characteristics and their impact on hydraulic turbines. Different methods like using a sieve analyzer to characterize size, microscopic observation after acid wash technique to characterize mineral content, and image processing to characterize and count particle shape are utilized to characterize sand. Sand samples from 20 stations on the Roshi Khola are used in this study. Most of the sampling locations are proposed hydropower project sites and confluences of tributaries. The erosion tests were carried out on turbine material in a High Velocity Erosion Test Rig at Kathmandu University. It was found that hardness, size, and shape are important parameters concerning their effects on erosion of hydraulic turbines. Even a short river like the Roshi Khola shows different sand characteristics at different locations and that they have different erosion rates. [ABSTRACT FROM AUTHOR]

• Understanding about slurry erosion phenomenon. • The consolidated information of slurry erosion in the hydro-dynamic machinery. • The coatings methods for developing of coatings on the components of turbine. • The materials used in surface modification of hydro-dynamic machinery. The socio-economic development of any country is completely dependent on the energy and the demand for energy is not completely fulfilled from a single source. As a result, renewable sources of energy like solar, wind, and hydro come into the picture. Countries like India and Nepal are naturally gifted with the potential of hydrodynamic energy, where a large number of small and medium hydro-power plants have been installed on the rivers coming from the Himalayas. Most of the hydrodynamic plants are situated in the Himalayan belt and have to deal with the problem of silt erosion in the hydrodynamic machinery. The hydraulic turbine is the heart of any hydropower plant and once it gets damaged due to silt erosion, not only the efficiency of the plant gets affected but it also increases the associated maintenance cost. Over the last two decades, researchers have been continuously working on this problem and focusing extensively to minimize the erosion rates with different materials processed by using surface modification techniques. To prevent the degradation of materials, protective coatings are used, which act as a barrier between the material and the working environment. The current manuscript reviews the performance of modified surfaces, which have been developed by using various surface engineering techniques to combat the slurry erosion failure in hydrodynamic turbines. The deposition of the coating by using different techniques and the evaluation of enhancement in the coating characteristics (mechanical and micro-structural) as well as coating efficiency under different slurry erosion conditions are reported. The effects of different operating parameters such as the angle of impingement, erodent size and shape, and slurry concentration on the performance of coating materials have been studied and discussed in detail. [ABSTRACT FROM AUTHOR]