Hydraulics and Fluid Mechanics in ME
If V1 and V2 are the velocities of water at inlet and outlet of the draft tube respectively, then the efficiency of a draft tube is

V1² / (V1² - V2²)
(V­1 - V2) / V1
(V­1² - V2²) / V1²
V1 / (V1 - V2)

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Hydraulics and Fluid Mechanics in ME
Runaway speed of a hydraulic turbine is

The speed corresponding to maximum overload permissible
Full load speed
The speed if the turbine runner is allowed to revolve freely without load and with the wicket gates wide open
The speed at which turbine runner will be damaged

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