Draft Tube in Reaction Turbines: Function, Types, and Efficiency, Slides of Power Electronics

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Prepared By:

ZAINAB ATHER

Definitio n  (^) The draft-tube is a pipe of gradually increasing area which connects the outlet of the runner to the tail race.  (^) One end of the draft tube is connected to the outlet of the runner while the other end is submerged below the level of water in the tail race.

Why it is needed?  (^) If the pressure at the exit of the turbine is lower than the pressure of fluid in the tailrace, a back flow of liquid into the turbine can result in significant damage. By placing a diffusing pipe at the exit of the runner, the pressure head is increased by decreasing the exit velocity, and both the overall efficiency and the output of the turbine can be improved.  (^) Turbines need to have a minimum amount of water to propel them in order to produce enough energy. Without these tubes, the pressure could drop because of lack of water, and in turn, the entire turbine could fail to work and power could be lost.

Functio n  (^) The primary purpose of the draft tube is to monitor the influx of water.  (^) The turbine has something called a "tail race," which is the lowest portion of a dam or construction project where water pools. The tube connects the turbine to this tail race, permitting the turbine to be outside of the water but still have access to the water.  (^) Reduce the velocity of the discharged water to minimize the loss of kinetic energy at the outlet.

Efficienc y  The efficiency of a draft tube is defined as the ratio of actual conversion of kinetic head into pressure head in the draft tube to the kinetic head at the inlet of the draft tube

Types of Draft tube  Conical draft tube

Types of Draft tube  Moody spreading tube

Types of Draft tube  Elbow draft tube with circular inlet and rectangular outlet