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A Pelton wheel is a tangential flow impulse turbine.

This type of turbine is designed so that the water jet strikes the buckets tangentially to the wheel, and the impulse from the water jet drives the wheel

The undershot water wheels are those in which the wheel runs entirely by the impulse of water.

In an undershot water wheel, water flows under the wheel, and the movement is driven primarily by the velocity (impulse) of the water hitting the paddles or blades of the wheel.

The hydraulic efficiency of an impulse turbine is maximum when the velocity of the wheel is one-half of the jet velocity.

This condition ensures the optimal transfer of energy from the jet to the turbine wheel

The Kaplan turbine is not an impulse turbine; it is a reaction turbine.

Impulse turbines, such as the Pelton wheel, Turgo turbine, and Girard turbine, operate by converting the kinetic energy of a jet of water into mechanical energy. In contrast, reaction turbines like the Kaplan turbine operate by developing pressure and kinetic energy simultaneously in the water as it passes through the turbine.

In a reaction turbine, the draft tube is used to increase the head of water by an amount equal to the height of the runner outlet above the tail race.

Explanation: The draft tube allows the turbine to operate with the outlet of the runner positioned above the tail race, thereby converting the kinetic energy of the water exiting the turbine into pressure energy as it flows down through the draft tube. This increases the effective head and improves the efficiency of the turbine.

In a Kaplan turbine runner, the number of blades is generally between 4 to 8.

This range provides a balance between efficiency and operational stability for the turbine

The runaway speed of a hydraulic turbine is the speed at which the turbine will run freely without load.

Explanation: This speed is also referred to as the no-load speed or free-running speed, and it is the speed at which the turbine operates without any mechanical load. It is important for ensuring the turbine can safely handle situations where it might be operating without any load applied.

The flow ratio of a Francis turbine is defined as the ratio of the theoretical velocity of jet to the velocity of flow at inlet.

Explanation: The flow ratio helps in understanding the relationship between the theoretical velocity of the jet (based on the potential energy of the water) and the actual velocity of the water entering the turbine. This ratio is crucial for designing and analyzing the turbine’s performance.

The correct statement is:

In an impulse turbine, the pressure of the flowing water remains unchanged and is equal to atmospheric pressure.

Explanation: In an impulse turbine, the water is directed onto the turbine blades or buckets as a high-velocity jet, and the pressure of the water remains at atmospheric pressure. The energy conversion happens through the kinetic energy of the jet.

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