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Different Types of Turbines Used in Hydroelectric Power Plants
Water Turbine
In a hydroelectric power plant, a device which is used to convert the energy of falling water into mechanical energy is known as water turbine. There are two types of water turbines used in a hydroelectric power plant viz. −
- Impulse Turbine
- Reaction Turbine
Impulse Turbine
In an impulse turbine, the entire pressure of water is converted into kinetic energy in a nozzle and the velocity of the water jet drives the turbine wheel. Impulse turbines are used for high heads. The pelton wheel is an example of the impulse turbine. It consists of a wheel fitted with elliptical buckets along its periphery. The force of water jet striking the buckets on the wheel drives the turbine. The quantity of water jet falling on the turbine is controlled by a needle placed in the tip of the nozzle and the movement of the needle is controlled by the governor.
When the load on the turbine decreases, the governor pushes the needle into the nozzle and hence decreasing the quantity of water striking the buckets. On the other hand, when the load is increased, the governor pulled out the needle from the nozzle, thereby increasing the quantity of water striking the buckets.
Reaction Turbine
In a reaction turbine, water enters the runner partly with velocity head and partly with pressure energy. Reaction water turbines are mainly used for medium and low heads.
Reaction turbines are also classified into two types viz. −
- Francis Turbine
- Kaplan Turbine
Francis Turbine
The Francis turbine is used for low to medium water heads. The Francis turbine consists of an outer ring of stationary guide blades which are fixed to the turbine casing and an inner ring of moving blades forming the runner. The guide blades are used to control the flow of water to the turbine.
In the Francis turbine, the water flows radially inwards and changes to a downward direction while passing through the runner. When water passes over the rotating blades of the runner, both the velocity and pressure of water are reduced. Consequently, a reaction force is produced which drives the turbine.
Kaplan Turbine
A Kaplan turbine is used for low heads and large quantity of water. The runner of the Kaplan turbine receives water axially instead of radially.
In a Kaplan turbine, water flows radially inwards through the regulating gates all around the sides and then, changing the direction in the runner to axial flow. Consequently, a reaction force is produced which drives the turbine.
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