What is Pelton turbine?

Short Answer:

A Pelton turbine is an impulse-type hydraulic turbine that converts the kinetic energy of a high-velocity water jet into mechanical energy. It is mainly used in high-head and low-discharge hydroelectric power plants. The water jet from a nozzle strikes the spoon-shaped buckets mounted around the runner, causing it to rotate and generate mechanical energy.

This turbine operates under atmospheric pressure, and the energy transfer occurs due to the impulse of water. Pelton turbines are simple, efficient, and suitable for mountainous regions where high heads of water are available.

Detailed Explanation :

Pelton Turbine

The Pelton turbine is one of the most important and commonly used impulse turbines in hydraulic power generation. It was invented by Lester Allan Pelton in the late 19th century. This turbine is designed to work under high head and low discharge conditions, converting the kinetic energy of a high-speed water jet into rotational mechanical energy. The Pelton turbine is widely used in hydroelectric power stations where large heights of water are available, such as in hilly or mountainous regions.

Construction of Pelton Turbine

The main components of a Pelton turbine are:

  1. Nozzle and Spear:
    The nozzle converts the pressure energy of water into a high-velocity jet. A spear or needle inside the nozzle controls the flow of water by adjusting the jet size.
  2. Runner and Buckets:
    The runner is a circular wheel mounted on a shaft. Around its periphery, several double-cupped buckets are fitted. The water jet strikes these buckets tangentially, causing the runner to rotate. The shape of the buckets is designed to split the jet into two equal parts and deflect it almost 180°, maximizing the energy transfer.
  3. Casing:
    The casing encloses the runner and prevents the splashing of water. It also directs the discharged water to the tailrace. The casing does not have to withstand pressure as the Pelton turbine operates under atmospheric pressure.
  4. Brake Nozzle:
    A brake nozzle is used to stop the turbine quickly after the water supply is cut off. It directs a small jet of water onto the back side of the buckets to stop the rotation of the runner.
  5. Shaft:
    The runner is mounted on a shaft that is connected to the generator for producing electricity.

Working Principle of Pelton Turbine

The Pelton turbine works on the impulse principle, where the kinetic energy of a water jet is converted into mechanical energy. The steps involved in the working are:

  1. Water from a high reservoir is brought through a penstock to the nozzle at the turbine’s lower end.
  2. The nozzle converts the pressure energy of water into kinetic energy, producing a high-speed jet.
  3. The water jet strikes the buckets mounted on the runner tangentially.
  4. The impact of the jet exerts an impulse force on the buckets, causing the runner to rotate.
  5. The shape of the bucket deflects the water jet by about 180°, ensuring maximum transfer of momentum.
  6. The water leaves the bucket at very low velocity, and the runner continues to rotate.
  7. The mechanical energy of the runner is then converted into electrical energy using a generator.

Working Conditions

  • Head Range: 150 m to 1800 m
  • Discharge: Low
  • Type of Flow: Tangential flow
  • Type of Energy Conversion: Kinetic energy to mechanical energy

Because of its high efficiency and ability to operate under high head, the Pelton turbine is suitable for power plants located in mountainous areas where large height differences are available.

Velocity Triangles

In a Pelton turbine, the velocity triangle is simple because the water jet strikes the bucket tangentially. The inlet velocity is the jet velocity, and the outlet velocity is in the opposite direction after deflection. The change in momentum of the jet creates an impulse force that rotates the runner.

Energy Conversion and Efficiency

The total energy available at the nozzle exit is the kinetic energy of the water jet, given by

where m is the mass flow rate of water and V is the velocity of the jet.

The hydraulic efficiency of the Pelton turbine depends on how effectively the kinetic energy is transferred to the runner. For maximum efficiency, the velocity of the bucket must be about half the velocity of the water jet:

This ensures optimal energy transfer and minimal energy loss.

The overall efficiency of a Pelton turbine generally ranges between 80% and 90% under good operating conditions.

Advantages of Pelton Turbine

  1. Simple design and easy maintenance.
  2. High efficiency under high-head and low-discharge conditions.
  3. Operates efficiently even with fluctuating water flow.
  4. Requires less space compared to reaction turbines.
  5. Works at atmospheric pressure, reducing casing cost.

Limitations of Pelton Turbine

  1. Not suitable for low-head or high-discharge sites.
  2. Efficiency decreases at part load.
  3. The large head requirement limits its use to mountainous regions.

Applications

  • Used in hydroelectric power stations with high heads and low discharges.
  • Commonly installed in hilly regions such as the Himalayas, Alps, and Andes.
  • Suitable for small-scale hydro plants where high pressure but limited water flow is available.
Conclusion

The Pelton turbine is an efficient and reliable impulse turbine used for converting the kinetic energy of a high-speed water jet into mechanical energy. Its unique bucket design allows maximum energy transfer, making it ideal for high-head applications. Despite its limitation in low-head conditions, the Pelton turbine remains a preferred choice for hydroelectric power generation in mountainous areas due to its high efficiency, simplicity, and durability.