Relation between specific speeds of Pelton & Kaplan turbines

Q.  Generally, the value of specific speed of Kaplan turbine is _____________ that of the Pelton turbine.
- Published on 16 Sep 15

a. lower than
b. higher than
c. same as
d. unpredictable

ANSWER: higher than

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    Discussion

  • Pankaj   -Posted on 13 Oct 15
    Specific Speed

    Specific speed (Ns) of a turbine rotating at a speed of 'N' rpm that develops the power of 'P' kW at the heat of 'H' m is given by,

    (Ns) = (N √P) x (H)(5/4)

    The value of specific speed for various turbines depends upon slow, medium and high speed runner.

    Kaplan turbine & Pelton turbine

    - Kaplan turbine is a reaction type turbine and Pelton turbine is an impulse type of turbine.

    - Kaplan turbine has high speed runner than that of Pelton turbine.

    - Therefore, the value of specific speed of Kaplan turbine is higher than that of the Pelton turbine.

    Pelton Turbine: (Ns) = 9 to 35

    Francis Turbine: (Ns) = 50 to 250

    Kaplan Turbine: (Ns) = 250 to 850

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