Energy Available at the Inlet of the Turbine

• Impulse turbine: The energy available at the inlet of the turbine is kinetic energy. A jet of water impacts on the turbine blades mounted on the shaft and results into shaft rotation at high speed. Impulse turbine works on the principle of impulse-momentum equation. The change in momentum of water produces impulse on the blades of turbine, which acts as torque for rotation of turbine shaft. Example: Pelton turbine.
• Reaction turbines: Produce back thrust or reaction on the blade due to the difference in pressure at inlet and outlet of the turbine. Pressure at the inlet of the reaction turbine is more than that of the outlet as reverse of the impulse turbine in which pressure remains constant at inlet and outlet of the turbine. Example: Francis turbine and Kaplan turbine.

Direction of Flow of Water

• Tangential flow turbine: The turbine, in which water flows along the tangent of the runner, is known as tangential flow turbine. Example: Pelton turbine.
• Radial flow turbine: The turbine, in which water flows in radial direction inward or outward, is known as radial flow turbine.
• Axial flow turbine: The turbine, in which water flows through the runners along the axis of turbine, is known as axial flow turbine. Example: Kaplan turbine.
• Mixed flow turbine: The turbine, in which water flows through the runner in radial direction but leaves the turbine in axial direction, is known as mixed flow turbine. Example: Francis turbine.

Head

• High head turbine (Head > 180 m). Example: Pelton Turbine.
• Medium head turbine (60 < Head < 150 m). Example: Francis turbine.
• Low head turbine (30 < head < 60 m). Example: Kaplan turbine.

Specific Speed of the Turbine

• Low specific speed turbine (10 − 35). Example: Pelton turbine.
• Medium specific speed turbine (60 − 300). Example: Francis turbine.
• High specific speed turbine (300 − 1,000). Example: Kaplan turbine.