Effect of wrap angle on performance of Pump As Turbine (PAT) in both pump and turbine modes

Abstract Pump as turbine (PAT) is used in small hydropower plants to generate electricity for remote hill regions and the integration of other renewable resources. Generally, the efficiency of centrifugal pumps operating in turbine mode is low. To improve efficiency, variables such as wrap angle, blade thickness, and blade count can be optimized for turbine mode; however, such changes may lead to a decrease in PAT performance in pump mode. To explore the effect of wrap angle on PAT performance in pump mode, flow simulations were carried out at conditions with wrap angle and discharge variations between 85°-120° and 8-16 kg/s, respectively. With a decrease in wrap angle in pump mode compared to the rated design condition, both efficiency and head rise were improved at the partial load condition. A design with a 120° wrap angle provided a 5.15 % improvement of efficiency in turbine mode compared with the available empirical relation; however, a minor decrease of 0.5% in pump mode was observed. Such zones with high efficiency in turbine mode with less compromise in pump mode should be identified for PAT.