Comparison of discharge measurements -

Transcription

1 Comparison of discharge measurements - Thermodynamic to US Clamp-On, stationary US and Needle Opening Curve IGHEM 2012 Trondheim, /29 1

2 Comparison of discharge measurements 1. Introduction 2. Thermodynamic method 3. Stationary Ultrasonic System 4. Clamp-On Ultrasonic System 5. Needle Opening Curve 6. Comparison of discharge values 7. Summary 2

3 1. Introduction Finding solutions of doing more cost effective relative efficiency tests, it becomes essential to acquire more experience with different kind of discharge measurements. In this paper the thermodynamic method is used as reference method, compared with Ultrasonic Clamp-On system, Stationary ultrasonic device and Needle opening curve 3

4 2. Thermodynamic method Unit discharge is determined indirectly Measuring plane I: 2 sampling probes Measuring plane II: Frame with 9 temperature sensors and 2 level probes Schematic arrangement of measuring points Vessel at high pressure measuring section 4

5 3. Stationary Ultrasonic system Unit discharge measurement by acoustic transit time method Detection of leakage in the penstock in case of penstock rupture Continuous flow rate measurement in 2 penstocks and in 4 inlet pipes to each turbine 4 planes with 4 paths Single Line Diagram of leakage monitoring 5

6 4. Ultrasonic Clamp-On system Unit discharge measurement by acoustic transit time method 1 plane / 1 path which goes through the center of the cross section Directly after the main inlet valve near to the distributor inlet Problem: Conical measuring section very close to distributor inlet (~1xD) Arrangement of acoustic paths Arrangement of acoustic paths 6

7 5. Needle opening curve Unit discharge can be derived from the needle opening curve With Model Test an accurate needle opening curve can be achieved Accuracy depends on deviation between theoretical design of the needle and the manufactured needle at the prototype Nozzle characteristic w 0,98* 2* g * H Standard flow function with loss factor Q A* w Discharge Q [m3/s] a0 [mm] Determination of discharge by standard flow function Nozzle characteristic derived from Model Test 7

8 6. Comparison of discharge values Ultrasonic Clamp-On to Thermodynamic Significant deviations to the reference measurement (up to -11%) Deviations are not constant and even change their prefix Shape of the efficiency curve could not be reproduced Reasons: Slightly conical part of the penstock Measuring section very close to the distributor inlet Just one path 8

9 6. Comparison of discharge values Stationary Ultrasonic to Thermodynamic Deviations are in an acceptable range (< -1% to reference) Deviations are in the same direction and have the same magnitude Conclusion Shape of the efficiency curve could be reproduced according to the results of the reference measurement For index testing the device delivers acceptable results 9

10 6. Comparison of discharge values Needle opening curve to Thermodynamic Deviations are below 0.9% and have the same magnitude Deviations are higher with lower loads Conclusion Shape of the efficiency curve could be reproduced according to the results of the reference measurement For index testing the device delivers acceptable results 10

11 7. Summary Ultrasonic Clamp-On System (1 plane / 1 path) significant deviations of unit discharge measurement compared to reference method (up to -11%) Shape of efficiency curve could not be reproduced Special care must be taken when using this method (technical restrictions causes by: location and geometry of measuring sections, number of paths) Analysis of velocity profile could reduce the deviations (too expensive for Index testing) 11

12 7. Summary Stationary Ultrasonic System (4 planes / 4 paths) Unit discharge deviations are below - 1.0% Index testing possible due to acceptable results Needle opening curve Unit discharge deviations are below + 0.9% Index testing possible due to acceptable results lowest effort for installation and measurement 12

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