Experimental and Numerical Investigations on Pump running in Turbine mode for Micro Hydropower Plants

Abstract

Among various renewable energy sources, hydropower is probably the oldest and most reliable source of energy on the earth. In remote communities where it is not economical and practically possible to take the grid connection, stand-alone small hydro systems can be used to fulfill the energy requirement of the local community. Small-scale hydroelectric power systems are emerging as a promising source of renewable energy generation, but they require low cost hydraulic and electric equipments to make them economically feasible. In such plants, pumps can be used in turbine mode considering various advantages associated with the pump e.g. low initial and maintenance cost, ease of availability, proven technology, availability for a wide range of heads and flows etc. newlineThe efficiency of pump as turbines (PATs) is usually lower than the conventional hydro turbines; however, there is substantial decrease in the capital cost of the plant as the pump costs less than one sixth of an equivalent hydro turbine cost. Hydropower plants usually runs at part load for several months in a year due to insufficient water availability for the power generation. Whether power can be generated or not during rest of the months depends on the part load performance of the turbine. The scope of application of PAT can be widened by improving its part load and/or maximum efficiency as well as by improving the life of PAT by cavitation free operation. newlineIn the present study, experimental investigations were carried out on single stage end suction centrifugal pump (rated head: 14 m, rated discharge 1700 LPM) running in turbine mode to optimize its geometric and operational parameters viz. impeller diameter and rotational speed. The experiments were performed in the wide range of speeds varying from 900-1500 rpm with original (and#966;250 mm), 10% trimmed (and#966;225 mm) and 20% trimmed (and#966;200 mm) impellers. The effects of blade rounding were studied in all the cases. Impeller trimming led to improvement in efficiency at part load conditions. The PAT per