Explain Construction and working of Francis Turbine with neat sketch.
1 Answer
Answer :
The main parts of the Francis turbine are: 1) Penstock: It is the large pipe which conveys water from the upstream of the reservoir to the turbine runner. 2) Spiral casing: It is a closed passage whose cross sectional area gradually decreases along the flow direction. Area is maximum at the inlet and nearly zero at the outlet. 3) Guide vanes: These vanes direct the water onto the runner at an angle appropriate to the design. 4) Runner and runner blades: The driving force on the runner is both due to impulse and reaction effect. The number if a runner blade usually varies between 16 to 24. 5) Draft tube: It is gradually expanding tube which discharges the water passing through the runner to the tail race.
Working
1) It is inward mixed flow reaction turbine i.e. Water under the pressure enters the runner from the guide vanestowardsthe centre in the radial direction and discharge out axially. 2) It operates under the medium head and medium discharge. 3) water is brought down to the turbine through the penstock and directed to the guide vanes which direct the water onto the runner at an angle appropriate to the design. 4) In the Francis turbine runner is always full of water.
After doing the work the water is discharge to the trail race through the draft tubes.