What Is Pelton Turbine And How does It work?

What is Pelton Turbine?

The Pelton wheel, also known as the Pelton turbine, represents a significant development in impulse-type water turbines. It was invented in the 1870s by Lester Allan Pelton, an American engineer. Unlike the traditional overshot water wheel, which relies on the weight of the water, the Pelton wheel is specifically designed to capture energy from the momentum of flowing water.

While earlier impulse turbines did exist, they typically fell short in terms of efficiency. Much of the water used in those designs exited the wheel at high speed, meaning a considerable portion of the energy was simply carried away rather than converted into useful work.

Pelton approached this challenge by carefully shaping the turbine’s paddles. His innovation lay in arranging the rim to move at roughly half the velocity of the incoming water jet. With this configuration, water leaves the wheel at a much lower speed, which means nearly all of its momentum is transferred to the turbine. As a result, Pelton’s design set a new standard for efficiency in water turbines.

Design of Pelton Turbine

The design of a Pelton turbine is straightforward yet highly effective. At its center is a large, circular disc attached to a rotating shaft, called the rotor. Around the perimeter of this disc, you’ll find cup-shaped blades—commonly referred to as buckets—positioned at regular intervals.

In most cases, these buckets are paired along the wheel’s edge. Strategically placed nozzles direct jets of water onto the wheel, introducing the working fluid into the system.

These nozzles are responsible for shooting high-velocity streams of water toward the series of spoon-shaped buckets mounted on the wheel’s rim. As each water jet strikes a bucket, the flow is redirected to match the curved profile of the blade.

This sudden change in the direction of the water’s velocity is what generates the torque that spins the wheel. The water effectively makes a sharp U-turn inside the bucket, losing much of its speed before exiting. This process allows the energy from the water’s impulse to be transferred efficiently to the wheel, and in turn, to the turbine itself.

It’s the impulse energy of the water that powers the turbine. For the best performance, the speed of the incoming water jet should ideally be about twice that of the rotating buckets.

By the time the water leaves the bucket, only a small fraction of its original kinetic energy remains. This efficient exchange ensures that water enters and exits the buckets smoothly, letting the high-pressure flow continue without unnecessary loss of energy.

To further improve performance, two buckets are typically mounted side by side, allowing the water jet to split evenly between them. This arrangement helps balance forces on the wheel and leads to a more stable and efficient transfer of momentum.

Because water is nearly incompressible, almost all of its available energy is extracted in this first stage. This is why, unlike gas turbines—which operate with compressible fluids and often have multiple stages—a Pelton wheel only requires a single turbine stage.

How Does a Pelton Turbine work?

Understanding how a Pelton turbine works isn’t as complicated as it might seem. Essentially, this turbine relies on high-speed jets of water, which shoot out from several nozzles placed around its perimeter.

The positioning of these nozzles is intentional: they direct the water so it strikes the center, or “splitter,” of each bucket on the wheel. When the jet hits this central point, it neatly splits into two streams, ensuring the turbine runs efficiently.

The working of Pelton turbine is as follows:

• Water is supplied from a high-pressure source via a long conduit known as a penstock.
• At the end of this pressure pipe, a specially designed nozzle enables the water to gain speed, so it emerges as a powerful, high-velocity jet at atmospheric pressure.
• This jet strikes the splitter positioned at the center of the Pelton wheel’s buckets, effectively dividing the stream into two and setting the wheel in motion.
• As the jet impacts the bucket, its kinetic energy drops. Thanks to the buckets’ spherical form, the water is redirected sharply—making nearly a U-turn—before it exits and flows down into the tailrace.
• Typically, the jet enters at an angle between 1° and 3°. After contacting the buckets, the water is deflected, leaving at an angle between 165° and 170°.
• It is important to ensure that the tailrace water never rises high enough to submerge the Pelton wheel itself.
• For increased power output, it is possible to either couple two Pelton wheels to a single shaft or direct two water jets onto a single wheel simultaneously.

Application of Pelton Turbine

The Pelton turbine finds its primary application in hydroelectric power plants where water is available at a high head typically ranging from 150 meters up to 2,000 meters or more. Within these plants, the turbine is responsible for turning the generator that is coupled to it. As the Pelton turbine rotates, it converts the energy of the falling water into mechanical energy, which the generator then transforms into electrical energy.

Advantages of Pelton Turbine

• Maintenance is straightforward, requiring minimal effort compared to more complex systems.
• Notably, the Pelton turbine does not encounter cavitation issues, which can be a significant concern in other types of turbines.
• Its design is quite simple, both in concept and in construction.
• The Pelton turbine operates effectively under conditions of high head and low water flow.
• Assembly is uncomplicated, making the setup process quick and manageable.
• Another advantage is its notably high overall efficiency, which sets it apart from many alternatives.

Disadvantages of Pelton Turbine

• The Pelton turbine is designed to operate under conditions of very high water head, making it suitable primarily for sites where such elevations are available.
• Over time, there is a noticeable decline in the efficiency of the Pelton turbine, which can become apparent relatively quickly.
• Due to their typically large physical dimensions, Pelton turbines require a substantial amount of installation space.
• Since the Pelton turbine is restricted to high-head applications, managing vibrations during operation presents a significant challenge.

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