A STUDY OF SEDIMENT TRANSPORT AND ITS IMPACT ON HYDRO-TURBINE IN HYDROPOWER PROJECT

Abstract

Hydropower, being a clean renewable source of energy, must be developed on priority basis as the total reserve of fossil fuel of the world is depleting at faster rate with increase in energy demands. In India, most of the potential for hydropower generation lies in the Himalayan region. From the experience of operating hydropower stations in Himalayan region, it is found that they suffer a severe problem of erosion of hydro-turbine parts due to sediment transported with water. The problem in hydropower plants due to sediment starts from headwork to powerhouse. This problem becomes more severe in case of run-of-river hydropower plants. The prime reason for prior stated problems is that rivers carry a lot of sediment with them during monsoon season in Himalayan region. In this study, a case of Chilla hydropower plant, a run-of-river scheme of a Himalayan river system, is considered. Using the data obtained from Pashulok barrage, the intake site for withdrawing water from river Ganges into the power channel of Chilla hydropower plant, temporal variation of river discharge and silt concentration after silt ejector is analyzed for monsoon period and a rising limb is observed till mid august and a recession limb there onwards. On the basis of findings, a relationship between silt concentration and river discharge has been observed for the considered plant. This observed relationship is of the form of hysteresis loop having year to year variability as well as within the year variability. Different techniques, which can be adopted, have been discussed like selecting different soil erosion and transport models for establishing relationship between river discharge and silt concentration after silt ejector. Different turbine erosion models were compared and a suitable model of turbine erosion estimation for the site is fitted. The fitted model is verified for estimating turbine erosion satisfactorily within the range of turbine erosion for the site. An attempt has been made to suggest an approach for practically linking the combined effect of the silt transport and discharge with turbine erosion. A relationship of river discharge, silt concentration and turbine erosion is found out, which is recommended to be used during operation period of the Chilla hydropower plant. This relationship is comprised of two relationships. From first relationship, silt concentration can be approximately computed knowing the river discharge. Second relationship computes turbine erosion using calculated value of silt concentration from first relationship as an input. This approach is proposed to be having better understanding of hydro-turbine problems and its causes. iv