Experimental and Numerical Investigations on Pump as Turbine for Micro Hydropower Plants

Abstract

The main limitation in installation of mini/micro hydropower plants (up to 2 MW) is higher initial cost of hydro turbine because the turbine manufactures do not manu- facture the turbines in smaller capacities and it is very di cult, time consuming and costly to develop the site speci c turbine correspond to local ecology in low capacity range. In such plants, Pump as turbine (PAT) may become one of the best alternative for ful lling the energy demand and providing the electricity in remote and rural areas considering various advantages associated with pump e.g. ease of availability, mass production, proven technology, low initial and maintenance cost etc. The efficiency of PAT may be lower than the conventional hydro turbines but there may be signi cant reduction in the capital cost of the plant as the centrifugal pump costs less than one sixth of the equivalent hydro turbine cost. The applications of PAT may be widened if its effciency can be improved at lower cost. In the present study, introduction of small hydropower plant and PAT are given. The literature review pertaining to PAT is presented. The computational uid dynamics analysis of piping system along with two di fferent reducers to decide its size and lo- cation is presented. The experimental investigations carried out on pump (head: 15 m, discharge: 1750 lit/min) running in turbine mode at di fferent rotational speeds at Institute of Technology, Nirma University, Ahmedabad are presented. Two modi ca- tions proposed to improve the performance of PAT at low cost are discussed. In the rst modi fication, the pump impeller of 250 mm dia. was replaced by impeller of 200 mm dia. which lead to increase in power output by 7-38 % and PAT efficiency by 3-18 % at di erent speeds. In the second modi cation, the 250 mm dia. impeller blades were trimmed from the edges and bullet shape was given which lead to increase in power output by 13-33 % and PAT efficiency by 4-15 % at di fferent speeds.