Performance Enhancement of Pump as Turbine for Micro Hydropower Plants

Abstract

Growing energy demand and concern for carbon emission is making hydro power development more favorable than conventional power generation resources. But the main limitation in installation of mini/micro hydro power plants (up to 2 MW) is higher initial cost of hydro turbine because smaller capacity turbines are generally not manufactured and it is very difficult, time consuming and costly to develop the site specific turbine correspond to local ecology in low capacity range. In such plants, Pump as turbine (PAT) may become one of the best alternative for fulfilling 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 significant 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 efficiency can be improved at lower cost. In the present study, introduction of small hydro power schemes and PAT is given. The literature review pertaining to PAT is presented. Experimental investigations carried out on pump (Head 15 m, Discharge 1500 lpm) running in turbine mode is presented. Based upon the analysis of data and common theories, several modifications are proposed. In the analysis part, certain parametric studies like effects of rotational speeds, impeller trimming and blade rounding on various parameters like efficiency, power and head was carried out.

The analysis concluded that PAT was found to be performing optimally with 225 mm dia blade rounded impeller in the speed range of 1100-1200 rpm. To improve the part load performance of PAT, guidevenes were designed, fabricated and installed in the casing. The provision of guidevanes with 200 mm dia. impeller showed scope of improvement in the PAT performance. Main and iso efficiency curves were plotted. Finally, Uncertainty as well as statistical analysis of experimental data was done and found to be fit in the criteria.