What Is Pelton Turbine And How does It work?

What is Pelton Turbine?

The Pelton wheel or Pelton turbine is an impulse type water turbine invented by American inventor Lester Allan Pelton in the 1870s. The Pelton wheel extracts energy from the momentum of the moving water, as opposed to the water’s own weight like the traditional overshot water wheel.

There were many earlier variations of impulse turbines, but they were less efficient than Pelton’s design. The water leaving these wheels was usually still at high speed and carried away much of the dynamic energy brought to the wheels.

Pelton’s paddle geometry was designed so that when the rim was running at half the speed of the water jet, the water exited the wheel at a very low speed. Therefore, his design extracted almost all of the water’s momentum energy – resulting in a very efficient turbine.

Design of Pelton Turbine

The Pelton turbine is built quite simply. A large circular disc is mounted on a type of rotating shaft known as a rotor. Mounted on this circular disc are cup-shaped blades known as buckets that are evenly spaced around the entire wheel.

Generally, the buckets are arranged in pairs around the edge. Nozzles are then placed on the wheel and serve the purpose of introducing water into the turbine.

Nozzles direct powerful, rapid streams of water against a series of spoon-shaped buckets, also known as impulse blades, that are mounted around the outer rim of a drive wheel. When the jet of water hits the blades, the direction of the water velocity is changed to follow the contours of the blades.

The impulse energy of the water jet exerts a torque on the bucket-and-wheel system and turns the wheel. The water jet makes a “U-turn” and emerges on the outside of the bucket, decelerating to a low speed. The impulse of the water jet is transmitted to the wheel and thus to a turbine.

Thus “impulse energy” acts on the turbine. Maximum performance and efficiency are achieved when the speed of the water jet is twice the velocity of the rotating blades.

A very small percentage of the original kinetic energy of the water jet remains in the water, emptying the bucket at the same rate as it is being filled, allowing the high-pressure inlet flow to continue uninterrupted and without wasting energy.

Typically, two buckets are mounted side by side on the wheel, with the water jet split into two equal streams. This balances the side load forces on the wheel and contributes to a smooth and efficient transfer of momentum from the water jet to the turbine wheel.

Since water is almost incompressible, almost all of the available energy is drawn off in the first stage of the hydraulic turbine. “Therefore, unlike gas turbines that work with a compressible fluid, Pelton wheels only have one turbine stage.”

Pelton Turbine is a Tangential flow impulse turbine in which the pressure energy of water is converted into kinetic energy to form high speed water jet and this jet strikes the wheel tangentially to make it rotate. It is also called as Pelton Wheel.

How Does a Pelton Turbine work?

The operation of a Pelton turbine is fairly simple. In this type of turbine, high-speed jets of water emerge from the nozzles that surround the turbine. These nozzles are arranged so the water jet will hit the buckets at splitters, the center of the bucket where the water jet is divided into two streams.

The working of Pelton turbine is as follows:

  • The water is drawn from the high-pressure source through a long pipe called a penstock.
  • The nozzle arrangement at the end of the pressure pipe helps the water to accelerate and it flows out as a high-speed jet at high velocity and discharges at atmospheric pressure.
  • The jet will hit the splitter of the buckets which will distribute the jet into two halves of the bucket and the wheel starts revolving.
  • The kinetic energy of the jet is reduced when it hits the bucket and also due to the spherical shape of buckets the directed jet will change its direction and takes a U-turn and falls into the tailrace.
  • In general, the inlet angle of the jet is between 1o to 3o, after hitting the buckets the deflected jet angle is between 165o to 170o.
  • The water collected in the tailrace should not submerge the Pelton wheel in any case.
  • To generate more power, two Pelton wheels can be arranged to a single shaft or two water jets can be directed at a time to a single Pelton wheel.

Application of Pelton Turbine

Pelton turbine is used in the hydroelectric power plant where the water available at high head i.e. 150 m to 2000 m or even more. In a hydroelectric power plant, it is used to drive the generator attached to it and the generator generates the mechanical energy of the turbine into electrical energy.

Advantages of Pelton Turbine

  • It is easy to maintain.
  • There is no cavitation problem in the Pelton turbine.
  • Pelton turbine has a simple construction.
  • It can work on the high head and low discharge.
  • It is very easy to assemble.
  • The overall efficiency of this turbine is very high.

Disadvantages of Pelton Turbine

  • Pelton Turbine requires a very high head for operation.
  • The efficiency decreases quickly with time.
  • Its turbine size is generally large and hence requires a large space.
  • As it only works in the high head, it is difficult to control vibrations in the operating head.

FAQs.

What is Pelton Turbine?

A Pelton turbine or Pelton wheel is an impulse-type water turbine that is widely used in hydroelectric power plants. These turbines are generally used for sites with a head greater than 300 meters. This type of turbine was developed during the gold rush by American inventor Lester Allan Pelton in the 1870s.

How Does a Pelton Turbine work?

The working principle of the Pelton turbine is simple. When a high-speed water jet injected through a nozzle hits buckets of the Pelton wheel; it induces an impulsive force. This force makes the turbine rotate. The rotating shaft runs a generator and produces electricity.

What is the advantage of Pelton turbine?

Advantages of Pelton Wheel: The Pelton turbine is the most efficient of hydro turbines. It operates with a very flat efficiency curve. Each bucket splits the water jet in half, thus balancing the side-load forces or thrust on the wheel and thus the bearings. It operates on the high head and low discharge.

What type of turbine is Pelton?

A Pelton turbine or Pelton wheel is a type of hydro turbine (specifically an impulse turbine) used frequently in hydroelectric plants. These turbines are generally used for sites with heads greater than 300 meters. This type of turbine was created during the gold rush in 1880 by Lester Pelton.

What is the efficiency of a Pelton turbine?

Pelton turbines can reach up to 95% efficiency, and even on ‘micro-scale systems, 90% peak efficiency is achievable. Also, the efficiency is maintained at a high level even for part-flow rates, mainly because of the low-loss design of the spear-jet.

What is Pelton turbine experiment?

Pelton turbine is an impulse turbine. In an impulse turbine, the energy of water is converted into kinetic energy by making the water flow through one or more nozzles, which are open to the atmosphere. Thus, the water enters the turbine rotor at atmospheric pressure.

Why Pelton turbine is called impulse turbine?

The water in a Pelton turbine moves quickly at high speed, and the turbine extracts energy from the water by slowing the water down, which makes this an impulse turbine.

Why Pelton turbine has low discharge?

Pelton turbine is used for high head for converting hydraulic energy into mechanical energy. In this turbine, the discharge required is comparatively low. Penstock conveys water from head race to distributor fitted with a nozzle. The nozzle converts all the available energy of water into the kinetic energy of the jet.

What is the element of Pelton wheel turbine?

A Pelton turbine consists of a runner, which is a circular disc on the periphery of which a number of buckets are mounted with equal spacing between them. The buckets mounted are either double hemispherical or double ellipsoidal shaped.

How many runners are in Pelton turbine?

Most Pelton turbines use between one to five nozzles. It is possible to mount one, or multiple, Pelton runners onto a single shaft. The efficiency of Pelton turbines often exceeds 90% when the right operating conditions are met.

What is speed ratio of Pelton turbine?

The speed ratio of the Pelton wheel varies between 0.43 to 0.48. The value of the jet ratio is generally taken as 12.

Where do we use Pelton turbine?

Pelton turbines are used for electricity generation in hydraulic power plants. They are suitable for operation when water energy is available at high head and low flow rate. In a Pelton turbine, the energy extracted from the kinetic energy of the water is used for the rotation of the impeller.