Hydraulic Turbines

1. A hydraulic turbine is a machine which converts the pressure and kinetic energy of water called hydraulic energy into mechanical energy.
2. These are also called as water turbines.
3. The mechanical energy of turbine is further converted into electric energy by an electric generator which is directly coupled to the shaft of hydraulic turbine.
4. The electrical power generated is known as hydro-electric power.
5. Hydraulic turbines are efficient.
6. These have low wear and tear and ease of maintenance.
7. However their capital cost is high with long gestation period due to the requirement of constructing the dam across the river and laying the long pipe lines.

Basic Classification of Hydraulic Turbines :

Basically the hydraulic turbines are classified as impulse and reaction turbines.

1. An impulse turbine, as the name suggests, works on the principal of impulse.
2. In these turbines, the head or pressure energy of water is first converted into kinetic energy by means of a nozzle or set of nozzles kept close to the runner.
3. This high velocity jet produced by nozzle is allowed to impinge on the set of buckets fixed on the outer periphery of the wheel or runner.
4. The direction of jet is changed by buckets.
5. The change of momentum of water causes the wheel to rotate, thus produces mechanical energy.
6. It should be noted that the pressure of water is atmospheric and remains constant while passing over the runner.
7. Examples of important impulse turbines are pelton wheel, Girard turbine, Turgo turbine etc.

Reaction turbines :

1. In these turbines, a part of pressure energy is first converted into kinetic energy before supplied to runner.
2. Therefore, the water enters the runner having partly the pressure energy and partly the kinetic energy and both these energies are reduced simultaneously while passing over the runner and produce mechanical energy.
3. Hence, these turbines work on the principle of impulse-reaction.
4. The runner of these turbines being under pressure above atmospheric, it requires the blades of turbine to run in closed passages which are completely filled with water in all conditions.
5. Examples of reaction turbine are Francis, Kaplan and Propeller turbines.