Which of the following is an example of impulse turbine?

Question

Examoogle · Accepted Answer

Pelton wheel

Explanation: A Pelton wheel is a classic example of an impulse turbine where the entire pressure energy of water is converted into kinetic energy in the nozzle. The resulting high-velocity water jet strikes the buckets of the runner at atmospheric pressure, causing rotation via impulse force.

Working Principle: Water from a high head reservoir passes through a penstock and is accelerated through a nozzle to form a high-velocity jet. This jet strikes the split-buckets of the Pelton runner, converting the kinetic energy into mechanical work by creating an impulse force that turns the wheel. The pressure remains atmospheric throughout the interaction on the runner blades.

Key Formulas: $P = \frac{1}{2} \rho A v^3$ — Power available in the jet; $F = \rho a V (V_w1 + V_w2)$ — Force exerted by jet on buckets

Key Points: Operates under high head and low discharge conditions.; Pressure at inlet and outlet of the runner is atmospheric.; The runner rotates in air, and water flows at atmospheric pressure.

Advantages: High efficiency over a wide range of loads.; Easier maintenance due to atmospheric operation.

Disadvantages: Requires very high head for effective operation.; Large size for a given power output compared to reaction turbines.

Applications: High head hydroelectric power plants.; Small-scale off-grid hydro power generation.

Additional Info: Pelton wheel is specifically designed for high head (usually > 200m).. Francis and Kaplan turbines are reaction turbines, where water pressure drops as it flows through the blades.

Answer: D is correct — The Pelton wheel is the quintessential impulse turbine used for high-head, low-flow applications.

Exam Tip: Always remember: Impulse = Atmospheric pressure on runner blades; Reaction = Pressure drop across runner blades.

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