Performance Analysis of a Pump-as-Turbine Under Cavitating Conditions

Market liberalization in the power sector has led to the emergence of micro-hydropower schemes that are dependent on the use of a pump-as-turbine in applications that were not suitable as potential hydropower sites in earlier years. As a result, there has been an accelerated adoption of pump-as-turbine technology due to the economic advantages it presents in comparison to the conventional turbines in the micro-hydropower space. The performance of these machines under cavitation conditions, however, is not well understood as there is a deficiency of knowledge in literature focused on their turbine mode of operation. In hydraulic machines, cavitation is a common occurrence which needs to be understood to safeguard them and prolong their operation life. The overall purpose of this study is to investigate the effects of cavitation on the performance of a pump-as-turbine system over its entire operating range. At various operating speeds, the cavitating region is identified experimentally while monitoring the effects this has on the power produced by the machine. Results indicate that the occurrence of cavitation coincides with zero power output from the machine implying that cavitation-free operation also ensures that the machine serves its purpose without the need of drawing more power from the grid.