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BACKGROUND
The Francis turbine was developed by James B. Francis, and it is a type of reaction turbine which means that it can only convert a part of the available total head of the fluid into the kinetic energy. These types of turbines have main application in electrical power production which operates in a water head from 40 m to 600 m. This types of turbine when used in the electric generators, they can generate a power output of up to 800 MW.1
The reaction turbine consists of three different types of guide vanes:
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Fixed Guide Vanes (Stay Vanes)
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Adjustable Guide Vanes (Wicket Gates)
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Rotating Blades (Runner Blades)
Apart from these components, the other main components of the Francis turbine are impeller (runner), scroll casing and draft tube. The above-mentioned guide vanes are present between the scroll casing and the impeller which guides the water on to the impeller. Due to the force produced through the fall of water on the impeller, it helps in rotating the impeller shaft.
In the actual experiment facility, the whole of its unit works on a recirculating water system. Its complete set up consists of a sump tank, centrifugal pump set, turbine unit and venturi meter. An electrical dynamometer is used for the loading of the turbine; it is coupled via a V – Belt drive (V ground pulley).2 In a very similar manner to the Pelton wheel, Francis turbine speed remains constant as it is used to drive the alternator.
The main purpose of this experiment is to study the performance of Francis turbine.
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REQUIREMENTS
Materials: Francis Turbine
Optical tachometer
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PROCEDURE
First of all, connect the panel to the source, and make the pump direction in the order of a clockwise direction from the shaft end. After this, fill the sump tank with the clear water for up to 75% of total capacity. Be sure to keep the gate valve in a fully closed position and the guide vanes in a fully opened position. Now, start the pump and slowly open the gate valve until the turbine achieves the desired speed to produce the electricity. When the turbine speed and the voltage becomes constant, switch on the first electrical load switch and adjust the voltage to 200 volts. With switching ON the consecutive load switch one by one, gradually increase the load by keeping the voltage constant. Choose a desired position for the turbine guide vanes and change to this point by using the hand wheel. After this, place the turbine to the no-load condition by slowly switching OFF the load switches one by one and closing the gate valve.
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CONCLUSION
The experiment on the performance of Francis turbine has been discussed. The shaft power produced by the turbine is determined through data from the pony brake, and data readings from the tachometer.
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REFERENCES
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S. M. T. C. E. J. P. L. R Susan-Resiga, “Influence of the velocity field at the inlet of a Francis turbine draft tube on performance over an operating range,” IOP Conference Series: Earth and Environmental Science, vol. 15, no. 3, pp. 95-102, 2003.
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Z. Xin, J. Wu and J. Chang, “Flow field analysis and performance prediction of three-dimensional turbulent flow in francis turbine,” Transactions of the Chinese Society of Agricultural Engineering, vol. 26, no. 3, pp. 118-124, 2010.
