17-01-2013, 04:33 PM
Francis turbines
Francis turbines.ppt (Size: 2.17 MB / Downloads: 131)
TURBINES
Turbines are defined as the hydraulic machines which convert hydraulic energy into mechanical energy.
This mechanical energy is used in running an electric generator which is directly coupled to the shaft of the turbine.
Thus the mechanical energy is converted into electrical energy
Francis turbines
This is the most common turbine type in hydroelectric stations.
The Francis turbine is a radial-flow turbine with water flowing in a radial direction inward over the curved runner blades toward the centre of the turbine
Francis turbines are suitable for hydroelectric systems with water heads between 2 meters to 200 meters, and the efficiency can be over 90%.
Velocity Triangles of Francis turbines
The velocity triangle at inlet and outlet of the Francis turbines are drawn in the same way as incase of inward flow reaction turbine.
As in case of Francis turbine, the discharge is radial at outlet, the velocity of whirl at outletVw2 will be zero.
AXIAL FLOW REACTION TURBINE
If the water parallel to the axis of the rotation of the shaft, the turbine is known as axial flow turbine.
For the axial flow reaction turbine the shaft of the turbine is vertical. The lower end of the shaft is made larger which is known as ‘hub” or boss.
The vanes are fixed on the hub and hence acts as a runner for axial flow reaction turbine.
Propeller Turbine
The vanes are fixed to the hub and they are not adjustable, the runner is known as propeller turbine.
Kaplan Turbine
The vanes on the hub are adjustable the turbine is known as a Kaplan turbine. This turbine is suitable where a large quantity of water at low heads is available.