Hydroelectric power plants or hydraulic turbines have been widely used as an efficient renewable energy source. Water turbines/hydraulic turbines are prime rotary movers that transform kinetic energy into mechanical energy.
How can we classify hydraulic turbines?
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The hydraulic turbine can be categorised according to the energy at the inlet, the water flow direction, the basic speed and the head at the inlet. All these are explained further below.
Classification of hydraulic turbines
Classification of hydraulic turbines based on the type of energy at the inlet to the turbine
Impulse Turbine
An impulse turbine is a turbine that is powered by high-speed jets of water or steam from a nozzle on to the vanes or buckets attached to a wheel. The efficiency of a hydraulic impulse turbine is very high, for example, Pelton water wheel.
Reaction Turbine
A reaction turbine is a type of turbine which develops torque by responding to a fluid’s pressure or weight. These turbines have relatively less efficiency. Examples of reaction turbine are Francis Turbine, Kaplan and Propeller Turbine, Deriaz Turbine and Tubular Turbine.
Classification of hydraulic turbines based on the direction of flow of water through the runner
Tangential flow:
In this type of hydraulic turbine, the fluids flow through the tangent of the runner. The water jet is tangentially hitting the runner and rotating the turbine, for example, Pelton wheel turbine.
Radial flow turbine:
Water flows radially in this type of turbine e.g. Francis turbine.
Axial flow turbine:
The water flows from the axis of the turbine, for example, Girard, Jonval, Kaplan turbine.
When the water entered the turbine and left, or vice versa with pressure is called mix flow turbine — for example, Modern Francis turbine.
Classification of hydraulic turbines based on the head under which the turbine works:
High Head Turbine:
The turbine is known as the High Head Turbine where water level or reservoirs are in the range of 150 – 2000 meters or even more away from the axis of the turbine, for example, Pelton turbine.
Medium Head Turbine:
If the water level varies between 30 -130 m from the turbine axis, it is known as a medium head turbine, for example, Francis Turbine.
Low Head Turbine:
If the level of water is less than 30 meters from the turbine axis, it is called the low head turbine. To work efficiently, these hydraulic turbines needed a high discharge rate, for example, Kaplan turbine and propeller turbine.
Classification of hydraulic turbines based on the specific speed of the turbine:
Low Specific Speed Turbine:
The turbine is known as low-speed turbine if the specific speed is less than 50 with nozzles, for example, Pelton wheel.
Medium Specific Speed Turbine:
If the specific speed is in between 50 – 250, it is considered as medium-specific speed turbine, for example, Francis turbines.
High Specific Speed Turbine:
If the specific speed of the turbine is above 250 it is known as a high specific speed turbine, for example, Kaplan turbines and Propeller Turbine.