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# Francis Turbine Working Principle

## Francis Turbine

### The main parts of a Francis Turbine are

• Penstock: That is a large size conduit that conveys water upstream of the dam/reservoir before the turbine runner.
• Spiral/scroll casing: This constitutes a closed passage whose cross-sectional space gradually decreases along each flow direction; some area is maximum at the inlet including nearly zero at any exit.
• Guide vanes/wicket gates: Certain vanes direct the water above the runner at an angle appropriate so the design. Each motion to them is given by means regarding a handwheel either automatically with a governor.
• Governing mechanism: This changes the position of one guide blade/vanes to affect a variation in water flow rate during the load conditions next to the turbine change.
• Runner and runner blades: Special driving force on the runner is both due to impulse further reaction effects. A unique number of runner blades usually ranges between 16 to 24.
• Draft tube: A gradually expanding tube discharges water, passing within the runner, into the tailrace.

#### Velocity Diagram also Work Done like Francis Turbine

Some work done per second at the runner with water is

=pav1[Vw1u1+-Vw2u2]

pQ[Vw1u1+-Vw2u2]

(As av1 = Q)

Where,

Vw1= Velocity of whirl at the inlet

Vw2 = Velocity of whirl at an outlet

u1 = Tangential velocity at inlet

= πD1N/60,

Where,

D1 = Outer diameter of the runner

u2 = Tangential velocity at the outlet

= πD2N/60,

Where,

D2 = Inner diameter of a runner,

N = Speed of turbine in RPM

The work is done per second per unit weight of water per second

(pQ[Vw1u1+-Vw2u2]) / pQg

=(1/g)[Vw1u1+-Vw2u2]

+ve sign acts taken if angle β exists as an acute angle.

If β is an obtuse angle then the –ve sign is taken.

If β = 90o, then and work done per second per unit weight of water per second is

=(1/g)[Vw1u1]