Surge tank is for the protection of

Question

Examoogle · Accepted Answer

Penstock

Explanation: A surge tank is a small reservoir or tank placed at the end of the penstock or near the turbine to protect the penstock from 'water hammer' pressure effects. It acts as a pressure relief mechanism by absorbing sudden surges of water or providing water during load demand fluctuations.

Working Principle: When the turbine load suddenly decreases, the governor closes the gates, causing a rapid stoppage of water flow. This creates high-pressure waves (water hammer) that could burst the penstock; the surge tank provides a relief path, allowing the water level to rise in the tank instead of hitting the penstock walls. Conversely, during sudden load increases, the surge tank supplies the initial surge of water, preventing negative pressure (cavitation) in the penstock.

Key Formulas: $h_w = \frac{L \cdot v}{g \cdot t}$ — approximate pressure head rise due to water hammer ($L$=length, $v$=velocity, $t$=closing time); $P = \rho \cdot g \cdot Q \cdot H$ — power output relation where surge tank maintains steady $H$

Key Points: Prevents water hammer effect in long penstocks.; Improves turbine speed regulation by acting as a supplementary water source.; Usually placed as close to the powerhouse as possible.; Essential in high-head and medium-head hydro power plants.

Advantages: Protects penstock from bursting due to pressure surges; Provides quick response to load changes; Prevents penstock collapse under negative pressure

Disadvantages: High initial construction cost; Requires significant maintenance and structural monitoring

Applications: Hydroelectric power stations with long pressure conduits; Pumped storage systems

Additional Info: Water hammer is the phenomenon of pressure oscillation caused by the rapid change in water velocity.. Option A (Dam) is a storage structure, not a protection device for flow conduits. Option B (Spillways) are safety valves for dams, not penstocks.

Answer: C is correct — The surge tank is specifically designed to mitigate water hammer pressure waves within the penstock during rapid flow changes.

Exam Tip: Always remember that in hydroelectric questions, 'Penstock' relates to fluid pressure regulation via surge tanks, while 'Governor' relates to mechanical speed control.

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