Efficiency and maximum output are the most important two goals to be analyzed in hydraulic turbines. Turbines normally operate in variable head conditions, so the tests to analyze their performance are frequently conducted for a selected number of power plant heads. Usually, they are limited to three heads: low, medium and high. The efficiency of water turbines is often expressed as the weighted average efficiency or arithmetic mean efficiency which is calculated from the results measured in the test heads. For the calculation of efficiency, it is essential to know several parameters such as kinetic and potential energy of water in its position and it is also necessary to know the flow rate entering the turbine. The flow rate of water through the turbine is determined as the volume of water flowing in the unit time and its unit is ㎥/s. The measurement of this quantity is one of the most difficult tasks for water turbine tests.
Measuring methods of flow rate of water turbines mainly include pressure-time method (Gibson), Winter Kennedy method, ultrasonic method and tachometric method. Winter-Kennedy method utilizes the static differential pressure between the outside and the inside of the turbine spiral due to the centrifugal force acting on the curved streams of liquid in the spiral case. This method is accepted as one of the simplest and the most convenient measurement methods of hydraulic power plant measurement technology and it is the most widely used in hydraulic power plants recently. This method is simple in the installation of measurement equipment. In addition, it does not disturb fluid flow and supports real-time measurement. The accuracy is about 1%.
Mun Yong Guk, a section head at the Electric Power System Institute, based on the investigation into the principles of flow measurement for hydraulic power plants and the literature on flow meters, has designed and manufactured a volute differential pressure flow meter and proved its effectiveness through simulations and field application.
The simulation results show that the flow coefficient K was 0.057 and that the accuracy was 0.616%, higher than the standard flow meter.
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