Hydraulic Turbines: Introduction and Classification

Hydraulic turbines are Machines that convert hydraulic energy into mechanical energy. The mechanical energy is used in running an electric generator directly coupled to the turbine’s shaft. The generator generates electric power, sometimes known as hydroelectric power. In general, a water turbine consists of a wheel called a runner, provided with specially designed blades or buckets. The water processes considerable hydraulic energy when it strikes the runner and causes it to rotate. Hydraulic turbines use the potential energy and kinetic energy of water and turn the rotor by the dynamic action of water.

Classification of Hydraulic turbines:

1) Based on the type of energy at the inlet to the turbine:

• Impulse or velocity Turbine: The energy is in the form of kinetic form. e.g: Pelton wheel turbine, Turgo-impulse wheel turbine, Banki turbine, Jonval turbine.
• Reaction or pressure Turbine: The energy is in Kinetic and Pressure form. e.g., Francis turbine, Kaplan turbine, Fourneyron turbine, Thompson turbine, Propeller turbine.

2) Based on the direction of flow of water through the runner:

• Tangential flow: water flows in a direction tangential to the rotational path, i.e., Perpendicular to both axial and radial directions.
• Radial outward flows, e.g., Forneyron turbine.
• Axial flow: Water flows parallel to the axis of the turbine. e.g: Girard, Jonval, Kalpan turbine.
• Mixed flow: Water enters radially at the outer periphery and leaves axially. e.g., Modern Francis turbine.

3) Based on the head under which turbine works:

• High head, impulse turbine. e.g., Pelton turbine.
• Medium head, reaction turbine. e.g., Francis turbine.
• Low head, reaction turbine. e.g., Kaplan turbine, propeller turbine.

4) Based on the specific speed of the turbine:

• Low specific speed, impulse turbine. e.g., Pelton wheel.
• Medium specific speed, reaction turbine. e.g., Francis wheel.
• High specific speed, reaction turbine. e.g., Kaplan and Propeller turbine.

5) Based on the name of the originator:

• Impulse turbine – Pelton wheel, Girard, Banki turbine.
• Reaction turbine – Forneyron, Jonval, Francis, Dubs, Deriaze, Thomson Kaplan, Barker, Moody, Nagler, Bell.