Evaluation of uncertainty in flow and performance parameters in Francis turbine test rig

Abstract

Model tests on hydraulic turbine are essential in hydraulic turbine development and related fields. The methods and technologies used to perform these tests show a constant progress. In addition, due to contractual nature, the demand for model test of turbines is increasing continuously in terms of quantity and accuracy. In this study, in situ calibration of different measuring instruments used in turbine model testing viz. flow meter, measuring tank load cells, calibrator tank load cell, shaft torque transducer, friction torque load cell and speed transducer have been performed and calibration equations have been derived from their calibration curves. The gravimetric approach using the flying start and stop method has been adopted for flow calibration in present study. Type A and Type B uncertainties of weighing balance and flow diverter has been evaluated as per ISO 4185:1980 [5] and JCGM 100: 2008 [13]. As per IEC 60193:1999 [3] performance test on the model has been conducted and efficiency as well as others flow parameters viz. discharge, head, speed and torque have been obtained at 16 different operating points including finding out Type A uncertainty in efficiency measurement. At each operating point, the regression error, Type A and Type B uncertainties are calculated in order to find out total uncertainty of flow and performance parameters. The total uncertainty in flow measurement and efficiency measurement at the best efficiency point has been found out minimum when compared with other operating points. In this paper, a correlation for the estimation of uncertainty in the efficiency measurement has been developed with an error of ± 9%.