Short Answer:

The Pelton wheel is an impulse type hydraulic turbine. It works on the principle of converting the kinetic energy of a high-speed water jet into mechanical energy. In this turbine, the entire pressure energy of water is first changed into kinetic energy before it strikes the wheel buckets. The water jet hits the buckets tangentially, causing the wheel to rotate. Pelton wheels are used for high-head and low-flow water conditions, commonly in hydroelectric power plants located in hilly or mountainous regions.

The Pelton wheel is different from reaction turbines because it works only with the velocity (kinetic) energy of water, not with pressure differences. The water jet, after striking the bucket, loses all its energy and falls away. It is an efficient type of turbine for sites where water pressure is high and discharge is low, ensuring maximum energy conversion from water jets into rotational motion.

Detailed Explanation :

Type of Turbine – Pelton Wheel

The Pelton wheel is classified as an impulse turbine, which is a type of hydraulic turbine that converts the kinetic energy of water into mechanical energy. It was invented by Lester Allan Pelton in the 19th century and is widely used in high-head hydroelectric power plants.

In an impulse turbine like the Pelton wheel, water at high pressure is directed through a nozzle to form a high-velocity jet. This jet strikes the buckets attached to the runner, and the impulse force of the water causes the runner to rotate. The energy conversion in the Pelton wheel occurs entirely due to the impact (impulse) of water jets, not due to any pressure difference across the runner.

Working Principle

The working of the Pelton wheel is based on Newton’s second law of motion, which states that the rate of change of momentum produces a force. In this case, the high-speed water jet hits the bucket, changes direction, and transfers its momentum to the wheel.

The water jet from the nozzle strikes the splitter (center ridge) of the double-cupped bucket, dividing it into two equal streams. The direction of flow is then reversed by nearly 180 degrees. This sudden change in direction causes a strong impulse force, rotating the wheel and driving the shaft connected to an electric generator.

After striking the bucket, the water loses its energy and falls into the tailrace, completing the process. Since the water does not exert any pressure on the buckets while flowing, the Pelton wheel is known as an impulse turbine.

Characteristics of an Impulse Turbine (Pelton Wheel)

1. Energy Conversion:
   The entire potential energy of water is converted into kinetic energy before it reaches the turbine wheel.
2. Flow of Water:
   The water jet strikes the buckets tangentially on the periphery of the runner.
3. Pressure Conditions:
   The pressure of water remains constant while flowing through the runner buckets; only its velocity changes.
4. Use of Nozzle:
   The nozzle converts high-pressure water into a high-speed jet. A spear or needle in the nozzle regulates the flow of water according to load requirements.
5. Casing and Tailrace:
   The casing prevents water from splashing and directs the used water to the tailrace safely.

Why Pelton Wheel is Called an Impulse Turbine

The Pelton wheel is called an impulse turbine because it operates purely on the impulse of water jets. The pressure energy of the water is completely transformed into kinetic energy by the nozzle before striking the turbine buckets. There is no pressure change in the bucket region, and the jet acts as a series of impacts transferring momentum to the wheel.

This is in contrast to reaction turbines (like Francis and Kaplan turbines), where both pressure and velocity changes occur within the runner blades. Therefore, the Pelton wheel belongs to the impulse type, where only kinetic energy is used for power generation.

Applications

• Used in high-head and low-flow hydroelectric plants.
• Commonly installed in mountainous and hilly regions where water pressure is high.
• Ideal for remote power generation and small-scale hydro projects.
• Used in micro-hydro systems due to its high efficiency and simple design.

Advantages of Impulse Turbine (Pelton Wheel)

1. High efficiency at high heads.
2. Simple construction and easy maintenance.
3. Performs efficiently even under fluctuating loads.
4. Long life due to durable material construction.
5. Easy control of water flow using spear mechanism.

Limitations

1. Not suitable for low-head or high-flow conditions.
2. Requires long and strong penstocks to handle high water pressure.
3. Efficiency drops if water jet is not clean or steady.
4. Installation cost is high for penstock and nozzle systems.

Conclusion:

The Pelton wheel is an impulse type turbine, meaning it works on the kinetic energy of water jets rather than on pressure energy. It converts the high-velocity impact of water into rotational energy that drives an electric generator. This type of turbine is best suited for high-head, low-flow conditions and is known for its simplicity, reliability, and high efficiency. Because of these advantages, Pelton wheels continue to be one of the most important impulse turbines used in hydroelectric power generation.