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Examoogle • User • info@examoogle.com • EE-2024-8821
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Which element of hydroelectric power plant prevents the penstock from water hammer phenomenon?
Valves and Gates
Draft tubes
Spillway
Surge Tank
Surge Tank
A surge tank is a small reservoir or tank connected to the penstock of a hydroelectric power plant. It acts as a pressure buffer, preventing the dangerous pressure rise known as 'water hammer' caused by sudden fluctuations in water velocity when load changes.
A surge tank is a small reservoir or tank connected to the penstock of a hydroelectric power plant. It acts as a pressure buffer, preventing the dangerous pressure rise known as 'water hammer' caused by sudden fluctuations in water velocity when load changes.
P=ρ⋅v⋅a⋅c — where P is the pressure rise, ρ is water density, v is velocity change, and c is wave celerity
ΔH=gL⋅dtdv — head rise due to flow retardation
When a turbine load is suddenly rejected, the governor closes the gates, leading to a sudden stoppage of water flow. Without a surge tank, the momentum of the moving water column would create a massive pressure surge (water hammer) in the penstock, potentially causing it to rupture. The surge tank provides an open surface where the water can rise, absorbing the kinetic energy and converting it into potential energy (head), thereby mitigating the pressure spike.
Water hammer occurs due to sudden change in velocity (Inertia of water)
Surge tanks effectively shorten the length of the penstock subjected to high-pressure waves
Located as close to the powerhouse as possible
Provides immediate supply of water during load acceptance
Protects the penstock from rupture
Stabilizes the turbine speed during sudden load fluctuations
Adds significant construction cost
Requires high topographical elevation for installation
High and medium head hydroelectric power plants
Pumped storage power plants
Draft tubes are used to recover kinetic energy from water leaving the turbine runner.
Spillways are used to discharge excess flood water from the reservoir.
The phenomenon is governed by the relation between the closing time of the valve and the wave propagation time t=c2L.
D is correct — The surge tank acts as a shock absorber to neutralize pressure surges in the penstock during sudden changes in turbine load.
Remember that surge tanks are specifically meant for load rejection, whereas the draft tube is strictly a component of the turbine assembly used for efficiency recovery.