Hydraulic turbines — define the net (effective) head at runner inlet In hydroelectric practice, the head available at the inlet of the turbine after deducting all losses between headrace and runner is called the net or effective head. State whether this definition is correct.

Introduction:
The concept of head is central to turbine selection and performance prediction. Engineers distinguish between gross head and net (effective) head to account for energy losses in conduits, valves, bends, and entry devices before the water reaches the runner.

Given Data / Assumptions:

• Steady flow of water from headrace to the turbine runner.
• Hydraulic losses occur in penstock, fittings, nozzles, and intake structures.
• Head is measured as energy per unit weight (m of water).

Concept / Approach:
Gross head equals the elevation/energy difference between headrace and tailrace water levels. As water travels through conduits, a portion of the energy is lost to friction and local losses. The head actually available at the runner inlet, after subtracting these losses from gross head, is called net or effective head. This is the head that produces torque and power on the turbine.

Step-by-Step Solution:

Verification / Alternative check:
Power available to the runner (water power) is ρgQ*H_net. Using H_gross in power without subtracting losses overestimates turbine output, demonstrating why H_net is the correct performance basis.

Why Other Options Are Wrong:

• “Incorrect” or intake-limited variants: The definition is standard across impulse and reaction turbines.
• “Only for impulse turbines” or “only when friction is zero”: Net head applies universally; frictionless flow is an idealization where H_net ≈ H_gross.
• “Applies to pumps”: Net head terminology is also used in pumps but the definition here is for turbines and is correct.

Common Pitfalls:
Mixing up net head with effective head at a nozzle exit; neglecting seasonal changes in headrace/tailrace levels; ignoring air vents and valve losses.

Final Answer: