What is Pelton wheel?

Short Answer:

A Pelton wheel is an impulse-type hydraulic turbine used to generate electricity from high-head and low-flow water sources. It converts the kinetic energy of a high-velocity water jet into mechanical energy by striking the curved buckets fixed around the wheel.

In a Pelton wheel, water is directed through a nozzle that converts water pressure into a jet. This jet hits the buckets on the wheel’s rim, causing it to rotate. The Pelton wheel is highly efficient for high-head applications and is commonly used in mountain regions for hydroelectric power generation.

Detailed Explanation :

Pelton Wheel

The Pelton wheel is one of the most important and widely used impulse turbines in hydroelectric power plants. It was invented by Lester Allan Pelton in the late 19th century. The turbine is designed to efficiently convert the kinetic energy of water into mechanical energy under high-head and low-discharge conditions.

In this turbine, water strikes the wheel’s buckets in the form of one or more high-speed jets from nozzles. The wheel rotates due to the impact of these jets, and this mechanical energy is used to drive a generator to produce electricity. Because the Pelton wheel works purely on the impulse principle, the water pressure remains constant throughout the process.

Construction of Pelton Wheel

The Pelton wheel consists of the following main parts:

  1. Nozzle and Spear:
    The nozzle is a small opening at the end of the penstock that converts high-pressure water into a high-velocity jet. A spear (conical needle) is fitted inside the nozzle to control the flow rate of water entering the turbine. By adjusting the spear, the velocity and quantity of water can be controlled according to load requirements.
  2. Runner and Buckets:
    The runner is the main rotating part of the turbine, consisting of several cup-shaped buckets mounted around its rim. Each bucket is divided into two symmetrical halves by a central ridge called the splitter. When the jet of water strikes the splitter, it divides into two equal streams and flows along the inner curved surfaces, changing direction by almost 180°. This change in direction transfers momentum to the bucket, causing the runner to rotate.
  3. Casing:
    The casing is a protective cover that surrounds the runner and prevents splashing of water. It also protects the runner and collects the discharged water, directing it toward the tailrace (exit).
  4. Brake Nozzle:
    A small nozzle known as a brake nozzle is used to stop the runner quickly when the turbine needs to be shut down. It directs a jet of water on the back side of the buckets, bringing the wheel to rest.
  5. Shaft and Bearings:
    The runner is mounted on a shaft supported by bearings. The shaft transfers mechanical energy from the turbine to the generator.

Working of Pelton Wheel

The working of the Pelton wheel is based on Newton’s Second Law of Motion, which states that the rate of change of momentum of a fluid is equal to the force exerted on it.

The working process can be explained as follows:

  1. Water Supply:
    Water from a high reservoir is carried to the turbine through a large pipe known as a penstock.
  2. Conversion of Pressure Energy to Kinetic Energy:
    As the water flows through the nozzle, its pressure energy is completely converted into kinetic energy, forming a high-velocity jet.
  3. Jet Strikes Buckets:
    The high-speed jet strikes the splitter of a bucket mounted on the runner. The jet divides into two equal parts and flows along the inner curved surfaces of the bucket.
  4. Change in Direction:
    The water jet changes its direction by nearly 180° after striking the bucket. This change in momentum applies a force on the bucket, causing the runner to rotate.
  5. Power Generation:
    The runner shaft is connected to a generator. As the runner rotates, the mechanical energy of rotation is converted into electrical energy by the generator.
  6. Discharge of Water:
    After striking the bucket, the water loses most of its energy and falls into the tailrace at atmospheric pressure.

The pressure throughout the process remains constant; only the velocity of the water changes.

Working Principle

The Pelton wheel works on the impulse principle, which means that all the pressure energy of water is converted into kinetic energy before striking the turbine blades. The wheel extracts energy from the momentum of moving water, not from pressure difference. The high-velocity water jet strikes the bucket tangentially, producing torque and rotation of the wheel.

Advantages of Pelton Wheel

  • High efficiency (up to 90%) under high-head and low-flow conditions.
  • Simple construction and easy maintenance.
  • Operates efficiently even with fluctuating water flow.
  • Less wear and tear because there is no direct contact with the runner casing.
  • Suitable for mountainous regions with steep slopes.

Disadvantages of Pelton Wheel

  • Not suitable for low-head, high-discharge applications.
  • Large installation space is required for penstock and accessories.
  • Efficiency decreases if water contains sand or impurities.
  • Speed regulation is difficult under rapidly changing loads.

Applications of Pelton Wheel

  • Used in hydroelectric power plants located in mountainous or hilly regions where the water head is high (above 300 meters).
  • Commonly used in small and medium hydroelectric power projects with low flow rates.
  • Applied in remote or off-grid areas to produce electricity using natural water streams.

Operating Conditions

  • Head Range: Above 300 meters (high head).
  • Discharge: Low (small flow rate).
  • Efficiency: Around 85% to 90%.
  • Type of Flow: Tangential flow (the jet strikes the wheel tangentially).

Importance of Pelton Wheel in Hydropower Plants

The Pelton wheel plays a crucial role in hydropower generation due to its high efficiency and reliability under extreme conditions. It is one of the most efficient turbines for converting the energy of high-head water sources into electricity. The turbine’s simple design, ability to handle high heads, and long service life make it ideal for remote and mountainous power stations.

The Pelton wheel also provides stable performance and requires less maintenance compared to other types of turbines, making it a preferred choice in many hydroelectric projects worldwide.

Conclusion :

The Pelton wheel is an impulse-type hydraulic turbine that works efficiently under high-head and low-flow conditions. It converts the kinetic energy of a high-velocity water jet into mechanical energy, which is then used to generate electricity. The wheel’s simple construction, high efficiency, and durability make it one of the most effective and reliable turbines for hydroelectric power generation.

With proper maintenance and design, Pelton wheels can operate for decades, providing clean and renewable energy from natural water sources.