The ability to accurately control hydro turbine flow and improve turbine efficiency requires the ability to measure water flow through the turbine. The subject of turbine efficiency has been a long time industry concern, and foresighted individuals and companies have been interested in and working toward developing and improving methods that would enable plant operators to best determine the optimum turbine flow and achieve the highest efficiency. Additionally, hydroelectric station operators have recently seen a new demand for more accurate and real-time turbine flow measurement to meet station operating requirements, such as mandated station minimum flows and water management discharge requirements. This study reviews currently used and accepted methodologies, and discusses available real-time turbine flow measurement options.
The ASME Hydraulic Turbines and Pump-Turbines Performance Test Codes (ASME PTC 18-2002) and the International Standard (IEC 60041 or IEC 41) Field Acceptance Tests are used to determine the hydraulic performance of hydraulic turbines, storage pumps, and pump-turbines and to identify industry-approved direct methods used for flow measurement during absolute turbine efficiency acceptance testing. These methods include current meter, pressure-time, ultrasonic (transit-time), venture meter, dye dilution, volumetric, and thermodynamic testing. The various types of direct and indirect flow measurement are discussed.
Hydro facilities are unique, and the use of some testing methods is not feasible at various stations due to plant or intake configurations. Some methods such as salt dilution and pitot devices are currently not used because they are no longer economically feasible. Methods such as salt velocity, dye dilution and current meter testing are not acceptable for real-time flow measurement. Indirect methods such as Winter-Kennedy taps and Unit Rating tables provide relative comparative flows, but do not provide absolute flow values.
This review focused on available real-time electronic monitoring methods such as magnetic flow meters and acoustic metering including: acoustic (time-of-flight), acoustic scintillation, and Doppler methods. The principles of particle image velocimetry were also reviewed.
The hydroelectric industry is continuing to perform comparative testing of various flow measuring methodologies. This study also included an informal survey to poll a number of utilities regarding their flow testing techniques, the frequency of flow testing, and current or potential interest in real-time flow monitoring.
Keywords:Turbine flow meter, hydro testing, Acoustic, transit-time, Magnetic flow meter, Winter-Kennedy, acoustic scintillation, Doppler, salt velocity, dye dilution, current meter, Pitot tube, weir, flume.