Measurement of the jet deflector torque for model Pelton turbine and associated uncertainties in test rig development

Abstract

Hydraulic turbines play an important role in stabilizing electrical grids due to their fast response times. Comparative to other hydraulic turbines, a jet deflector of a Pelton turbine enables rapid response for load reduction. However, jet deflectors are subjected to high forces, torques and the splashing water impinges on the runner and elements within the casing. Thus, the design of the jet deflector is important. The analytical calculations are complex due to the splashing and backscattering of the deviated jet. Though the prediction of forces and deflector torque based on the impulse–momentum equation is feasible, but results are not sufficiently accurate, and thus measurements are required. Subject of this study is a test rig equipped with the physical model of a Pelton turbine injector with deflector control and a high-quality torque transducer for precise measurement. Calibration of instruments used, and uncertainty analysis of the test rig has been carried out. The overall uncertainty of the torque resulted in ±1.58%. The experimental results are compared with the analytical results to verify the primary data. It is observed that as the deflector initiates its action, the torque undergoes an increasing trend. At a deflection angle of 12°, the torque reaches its maximum value, and subsequently, upon achieving complete deflection, the torque is observed to attain its minimum magnitude. The empirical relationship of the deflector torque uncertainty has been developed using the regression analysis of the evaluated uncertainty data.