Impulse Turbine Performance — Definition of Overall Efficiency Evaluate the statement: “The overall efficiency of an impulse turbine is the ratio of the actual power produced by the turbine to the energy actually supplied by the turbine.”

Difficulty: Easy

Correct Answer: No

Explanation:


Introduction:
Efficiency definitions must clearly distinguish between energy supplied to the machine and energy produced by it. This question tests precise terminology for overall efficiency in impulse turbines such as Pelton wheels.


Given Data / Assumptions:

  • Steady operation at rated head and discharge.
  • Neglecting small leakage and windage for the definition.
  • Hydraulic input comes from the water jet or jets impinging on the buckets.


Concept / Approach:
The overall efficiency η_overall is defined as: useful shaft power output divided by the net hydraulic power supplied to the turbine by the water at inlet. The phrase “energy actually supplied by the turbine” is incorrect because the turbine does not supply energy to itself; it receives energy from the fluid. Therefore, the statement must be marked incorrect.



Step-by-Step Solution:
Define P_out = actual shaft power measured at the runner shaft.Define P_in = rho * g * Q * H_net (net head at turbine inlet).Then η_overall = P_out / P_in.The quoted statement misidentifies the denominator as “energy supplied by the turbine,” which is a wording error.


Verification / Alternative check:
Texts present overall efficiency as the product of hydraulic and mechanical efficiencies, both referenced to energy supplied by the water (not by the machine).



Why Other Options Are Wrong:

  • Yes: Accepting the statement would propagate the wording error and confuse input vs output energy roles.


Common Pitfalls:
Mixing “to the turbine” with “by the turbine.” Precision in prepositions is crucial in efficiency definitions.



Final Answer:
No

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