Runaway speed of runner of Pelton wheel

Q.  What is runaway speed of the runner of Pelton wheel?
- Published on 16 Sep 15

a. maximum unsafe speed of the runner due to sudden increase in load on turbine
b. minimum safe speed of the runner due to sudden increase in load on turbine
c. maximum unsafe speed of the runner due to sudden decrease in load on turbine
d. minimum safe speed of the runner due to sudden decrease in load on turbine

ANSWER: maximum unsafe speed of the runner due to sudden decrease in load on turbine

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    Discussion

  • Pankaj   -Posted on 07 Oct 15
    The maximum speed of turbine at full flow and no load on shaft is called as runaway speed of the turbine. Normally the turbines are designed to survive the mechanical forces of this speed. But this is an unsafe speed which should be avoided while operating turbine such as Pelton wheel.

    Pelton wheel may attend this speed due to sudden decrease in load on turbine. To avoid this situation, deflector is used in hydro-electric system.

    Deflector is hinged to the casing of turbine and used to deflect the jet of water away from striking the blades in case the load on turbine suddenly reduces. It prevents the runner of turbine attaining runaway speed which is unsafe.

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