Experimental Study of Francis Turbine with Variable Speed Operation

This study specifically investigates the operating range of a normal Francis turbine through the production of experimental data and characteristic performance curves under both constant and variable rotational speed operating conditions. For the constant speed condition, a specific speed of 204.6 was found for turbine maximum efficiency attained with a guide vane aperture at 60%. The variable speed tests were conducted by keeping the specific speed around 204.6 with the guide vane aperture fixed at 60%. These tests have successfully produced results of turbine maximum efficiency very close to the maximum efficiency for the constant speed condition. The most important contribution of this paper is to report an increase in the operational range of the hydraulic turbine with variable speed operation, particularly when working at a lower flow rate and water head. The results obtained have demonstrated incomplete dynamic similarity between homologous Francis turbines. In other words, the concept of identical hydraulic turbines working with variable speed and producing the same maximum efficiency has been verified. The work also demonstrates an approach to the operation of hydroelectric generating units, aiming at improved compatibility between water availability and the electrical energy supplied to consumers.