Performance Evaluation of Centrifugal Pump-As-Turbine For Micro Hydro Applications

Abstract

The Philippines is entirely dependent on imported hydropower (HP) system parts, specifically the turbine and generator. The use of a centrifugal pump as a turbine is a good option for the HP system due to its low cost and wide availability in the market. The performance of the centrifugal pump-as-turbine was evaluated under the following conditions: (1) different head setting, (2) different configurations of the draft tube, and (3) a match with an AC generator. A 75x75mm end suction, non-self-priming centrifugal pump was used in this study. The head settings used were 0.28 kg/cm2 to 0.84 kg/cm2 (pressure gauge reading). A prony brake dynamometer was fabricated to measure the torque at the shaft of the pump-as-turbine. The configurations of the draft tube used include: (a) conical angles - 0°, 4°, and 6°, and (b) draft tube lengths – 0.4572 m, 0.9144 m, and 1.3716 m. A 900W AC generator was matched with the pump–as–turbine and tested at different pressure and load settings. Results showed that the centrifugal pump could operate in turbine mode without any mechanical modifications. The highest mechanical efficiency obtained was 83.60% and was attained at a pressure setting of 0.70 kg/cm2. The highest shaft power of 1.02 kW that was attained at 0.84 kg/cm2 pressure setting. Based on the results, in terms of shaft power, the best draft tube configuration has a conical angle of 4° and a length of 1.3716 m. Meanwhile, in terms of efficiency, the best draft tube configuration is 4° conical angle and 0.4572 m length. The generator speed of 4000 rpm was obtained at a pressure setting of 0.84 kg/cm2. On the other hand, a generator speed of 3800 rpm was obtained at a pressure setting of 0.63 kg/cm2. It could be observed that the maximum power (515 W) obtained during the actual run was way below the expected output (847 W). The system efficiencies as well as the electrical power output could improve if the belt slippage is reduced. It is recommended to conduct more testing to be able to determine the full potential of the pump-as-turbine.