Francis Turbines : Parts, Working, Advantages and Disadvantages
Francis turbine is from the reaction turbine class of hydraulic turbine. It is name after its inventor James Francis.
It was the first turbine with the radial flow, water enter the turbine radially and leave axially.
High pressure water entering the turbine strike the blades of turbine and reaction of which blades of turbine rotates.
Francis Turbine Parts
Spiral / scroll casing
Guide vanes / wicket gates
Runner and Runner blades
Working of Francis turbine
|Francis Turbine Working
Blades are mounted on the runner. Design of the blade is like a thin air foil so when water flow over it low pressure is created at one point and high pressure is created on other sideand motion take place from high pressure to low pressure. Lower side of the blade is like a bucket which use the impulse forces of water in the rotation.
|Francis Turbine Blades
If water flow rate change then governing mechanism came into use and change the angle of attack of water on to the blade so the turbine can work properly. After the water passes the blades it enter the draft tube whose continuous increase in area decrease the velocity of the water.
|Francis Turbine Draft Tube
Advantages of Francis turbine
- Easy control on changing head
- Size of runner and generator is small
- Small change in efficiency over time
- The operating head can be utilized even when the variation in the tail water level is relatively large when compared to total head
Disadvantages of Francis turbine
- Unclean water can create wear
- Inspection method is very difficult
- Cavitation is an ever present danger
- Water hammer effect can create some problems
- Head 50% lower can have harmful effect on the efficiency as well as cavitation danger became more serious