Define the gross (total) head for turbines Gross head between headrace and tailrace is obtained by what relation between their water surface levels?
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Asum
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Bdifference
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Cproduct
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Dratio
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Eaverage
Answer
Correct Answer: difference
Explanation
Introduction:Before accounting for conduit and entry losses, engineers begin with the gross or total head available from a site. This head reflects the vertical energy difference driving the hydropower installation.Given Data / Assumptions:
- Steady water levels at headrace and tailrace.
- Neglecting velocity heads for a basic definition (or considered small).
Concept / Approach:Gross head H_gross is the elevation (energy) difference between the upstream headrace water level and the downstream tailrace water level. It is a site attribute, independent of penstock routing. The net head used for power calculations is obtained after subtracting hydraulic losses.Step-by-Step Solution:
Measure z_headrace and z_tailrace relative to the same datumForm H_gross = z_headrace − z_tailraceLater compute H_net = H_gross − h_losses for turbine powerVerification / Alternative check:Bernoulli’s equation between headrace and tailrace simplifies to the difference in piezometric heads when velocities are small and pressures are hydrostatic.
Why Other Options Are Wrong:
- Sum/product/ratio/average: have no physical meaning for head definition.
Common Pitfalls:Confusing gross head with rated head at the turbine inlet; forgetting that tailrace levels rise during floods, reducing gross head.
Final Answer:
difference