CAM CORRELATION ANALYSIS USING ACOUSTIC DISCHARGE MEASUREMENT
The low head hydro power plant in Wettingen, Switzerland, is in operation since 1933 and no effective cam optimization has been carried out up to now. The goal of the measuring campaign was to provide data enabling an economic study for a retrofit and upgrade project of the plant and the measurement of the efficiency improvement of turbines after refurbishment. The contribution discusses cam tests using the acoustic transit time method in the intake for discharge measurements. A cam correlation analysis and an efficiency test of the installed Kaplan turbines were performed as a first measurement campaign showing the actual status. While one turbine operated at optimum cam, the other two turbines operated off-cam. After rehabilitation works, based on the recommendations of the first measurements, a second measurement campaign was performed. The results showed the expected efficiency increase due to overhaul of the regulating mechanics (connection between the piston stroke in the machine hall and the regulating ring / guide vane stem at the turbine) of the governor. With the set of data from the second measurement campaign an optimization study for the operation of the three Kaplan units were conducted. Especially the transition zone from one to two and from two to three machine operation could be optimized due to the knowledge of the individual efficiency curves.
Discharge Measurement in a Short Intake with a Converging Section — a Case Study
In the context of a planned retrofit and upgrade of the hydropower plant Wettingen, operated by the Elektrizitätswerke Zürich, three intakes were equipped with acoustic transit time flow measuring devices. Since the flow meters are installed in a converging section, downstream of a pier, it became necessary to perform numerical flow simulations in order to weight the acoustic path velocities for a quantitative flow rate evaluation. With the flow rate available and performing additional site measurements, cam test could be performed with the turbines. While one turbine operated at optimum cam, the other two turbines operated off-cam. Accordingly a substantial improvement potential could be identified.
Analyse und Fehleroptimierung der mehrpfadigen akustischen Durchflussmessung in Wasserkraftanlagen
III Abstract The exact knowledge of the discharge in hydro power plants is of major importance for field acceptance tests, for continuous efficiency monitoring, for water manage¬ ment and accounting of the gross hydraulic energy, for leak detection in pipes and for the calibration of secondarv discharge measurement devices. The acoustic discharge measurement (ADM) bases on the superposition of the pro¬ pagation velocity of an acoustic signal with the fluid velocity. With the measure¬ ment of the transit time of a downstream and upstream propagated signal the mean flow velocity can be derived between transducers which are mounted at the pipe wall with a angle of 30 to 60 degrees to the mean flow. Additional laterally shifted transducer pairs increase the measurement accuracy. The aim of this work is the analysis of the major error sources and the improvement of the measurement accuracy for a given number of transducers. In practical use it is assumed that the signal propagates along a straight line ("acou¬ stic path") between the two transducers. In reality the ray path is slightly bent due to the varying flow and sound velocities in the pipe. In the first part of this thesis, calculations based on methods using geometrical acoustics have proven, that with exception of the very rare case of very high air bubble concentrations paired with a strong variation of bubble diameter along the acoustic piath the measurement error due to the bend ing of the ray path can indeed be neglected. The multipath ADM consists typically of 4 to 8 acoustic paths (8 or 16 transducers) arranged in one or two measuring planes. In general, the measured path readings are summed up using a quadrature integration method according to Gauss-|acobi to evaluate discharge in each of the measuring planes. Inherent to this method is a systematic error of about ±0.15%. In this thesis, a modified quadrature formula is presented which almost fully eliminates all svstemafic errors. A further part of this thesis is dedicated to the detailed analysis of the three major sources of errors ot the multipath ADM, including an error depending on the velocity profile ("integration error"), an error resulting from the transducer protrusion into the pipe ("protrusion error"), and a geometrical error, which can pri¬ marily be attributed to an imprecise positioning of the transducers in the measuring section ("installation error"). To investigate the integration error, a software program based on a triangulation rou¬ tine was developed. With this program scattered velocity data m circular pipes may be interpolated and integrated, which is basis for the numerical simulation of the ADM including the calculation of the measuring error as a I unction of the mounting angle. Divided into the groups "single bends", "double bends", "vanes" and "contrac¬ ting cones" integration errors ot about 20 velocity records from different sources were computed and compared to measured data trom held and laboratory measu¬ rements. Based on the results of the simulation calculations guide lines for an opti-The exact knowledge of the discharge in hydro power plants is of major importance for field acceptance tests, for continuous efficiency monitoring, for water manage¬ ment and accounting of the gross hydraulic energy, for leak detection in pipes and for the calibration of secondarv discharge measurement devices. The acoustic discharge measurement (ADM) bases on the superposition of the pro¬ pagation velocity of an acoustic signal with the fluid velocity. With the measure¬ ment of the transit time of a downstream and upstream propagated signal the mean flow velocity can be derived between transducers which are mounted at the pipe wall with a angle of 30 to 60 degrees to the mean flow. Additional laterally shifted transducer pairs increase the measurement accuracy. The aim of this work is the analysis of the major error sources and the improvement of the measurement accuracy for a given number of transducers. In practical use it is assumed that the signal propagates along a straight line ("acou¬ stic path") between the two transducers. In reality the ray path is slightly bent due to the varying flow and sound velocities in the pipe. In the first part of this thesis, calculations based on methods using geometrical acoustics have proven, that with exception of the very rare case of very high air bubble concentrations paired with a strong variation of bubble diameter along the acoustic piath the measurement error due to the bend ing of the ray path can indeed be neglected. The multipath ADM consists typically of 4 to 8 acoustic paths (8 or 16 transducers) arranged in one or two measuring planes. In general, the measured path readings are summed up using a quadrature integration method according to Gauss-|acobi to evaluate discharge in each of the measuring planes. Inherent to this method is a systematic error of about ±0.15%. In this thesis, a modified quadrature formula is presented which almost fully eliminates all svstemafic errors. A further part of this thesis is dedicated to the detailed analysis of the three major sources of errors ot the multipath ADM, including an error depending on the velocity profile ("integration error"), an error resulting from the transducer protrusion into the pipe ("protrusion error"), and a geometrical error, which can pri¬ marily be attributed to an imprecise positioning of the transducers in the measuring section ("installation error"). To investigate the integration error, a software program based on a triangulation rou¬ tine was developed. With this program scattered velocity data m circular pipes may be interpolated and integrated, which is basis for the numerical simulation of the ADM including the calculation of the measuring error as a I unction of the mounting angle. Divided into the groups "single bends", "double bends", "vanes" and "contrac¬ ting cones" integration errors ot about 20 velocity records from different sources were computed and compared to measured data trom held and laboratory measu¬ rements. Based on the results of the simulation calculations guide lines for an opti-