What is the difference between an impulse turbine and a reaction turbine?

Short Answer:

The main difference between an impulse turbine and a reaction turbine lies in how they convert water energy into mechanical energy. An impulse turbine uses the kinetic energy of a water jet to strike the blades and rotate the runner. In contrast, a reaction turbine uses both the pressure energy and kinetic energy of water, where the flow passes over and through the blades, creating movement.

Impulse turbines work with high-head and low-flow water conditions, and their runners operate in air. Reaction turbines are used for low to medium head and high-flow conditions and always operate fully submerged in water.

Detailed Explanation

Difference Between an Impulse Turbine and a Reaction Turbine

Turbines are mechanical devices used in hydroelectric power plants to convert water energy into mechanical energy and then into electrical energy. They are mainly classified into two types based on how water interacts with the blades: impulse turbines and reaction turbines. Understanding their differences is important for selecting the right turbine for a specific hydropower project.

Impulse Turbine

In an impulse turbine, water from a high head is released through nozzles as high-velocity jets. These jets strike the buckets or blades of the turbine runner, causing it to rotate. The entire pressure energy of water is first converted into kinetic energy before it hits the runner.

Key Features:

  • Only kinetic energy is used.
  • Water jet hits the blade in open air.
  • Pressure remains constant over the runner.
  • Example: Pelton turbine.
  • Used for high head (above 300 meters) and low flow conditions.
  • Runner is not submerged in water.

Impulse turbines are simple in construction and easy to maintain. The casing is mainly for controlling the water spray and not for pressure regulation.

Reaction Turbine

A reaction turbine works with both pressure energy and kinetic energy. Water enters the runner at high pressure and flows through curved blades. As the water moves over the blades, it experiences a pressure drop and imparts energy to the runner.

Key Features:

  • Both pressure and velocity changes take place.
  • Water flows over the blades while fully submerged.
  • Pressure changes across the runner.
  • Example: Francis turbine, Kaplan turbine.
  • Suitable for low to medium head (below 300 meters) and high flow conditions.
  • Runner is completely immersed in water.

Reaction turbines are more complex and need a sealed casing to contain the water and maintain pressure. Their efficiency depends greatly on installation accuracy and design.

Summary of Main Differences

  • Energy Conversion: Impulse uses only kinetic energy; reaction uses both kinetic and pressure energy.
  • Water Flow: Impulse has water hitting in air; reaction has water flowing through submerged blades.
  • Pressure Behavior: Impulse pressure stays constant; reaction pressure drops over blades.
  • Head Conditions: Impulse suits high heads; reaction suits low to medium heads.
  • Runner Position: Impulse runner is dry; reaction runner is fully submerged.
Conclusion

The difference between an impulse turbine and a reaction turbine lies in how they use water energy. Impulse turbines work with high-velocity jets and use kinetic energy, while reaction turbines use both pressure and velocity as water flows through the runner blades. Understanding this difference helps engineers choose the right turbine type based on head and flow conditions in civil engineering hydropower projects.