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Hydro Electric Power plants

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Hydro Electric Power plants

Classification of Hydroelectric Power Plants

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Diesel power plants

Water is found in enormous amount in the Earth. About 70% of the Earth is under the water surface. For the electric power generation water flowing from a higher level to a lower level is passed through turbine. The energy of water used for power generation may be kinetic energy or potential energy. Water from rain is collected in lakes and reservoirs at high altitudes. Dams are constructed across the flowing steams. After the power generation the water is let out into the river which finally ends at the sea. The water after power generation is free from pollutants and can be used for drinking and agricultural purposes.

Types of hydro-power plants

Based on head, the hydro power plants are classified as follows:


Low head plants

< 15 m

Medium head plants

15 – 70 m

High head plants

71 – 250 m

Very high head plants

More than 250m

Layout of a Hydro Electric power plant


Main components of Hydro- Electric Power plants

The main components of a typical hydro electric power plant are the following.

  1. Dam
  2. Reservoir
  3. Fore bay
  4. Water conduit system
  5. Tailrace
  6. Surge tank
  7. Trash rack
  8. Turbine
  9. Power house
  10. Spillway

1. Dam or barrage

A dam or barrage is constructed to provide a head of a water to be utilized in the water turbines. A dam is constructed across the river and serves as a very important component in the most of the high and medium head hydropower plants. In order to attain ease of pumping dams are built at the top of the hills. The main factors considered during the construction of dams are safety and economy apart from these, material availability, environmental degradation etc are also considered.


2. Reservoir

The reservoir is used to store water for power generation and irrigation purposes. The water is mainly stores during the rainy season. The water required for the power generation determines the capacity of the reservoir.

3. Fore bay

Fore bay is a regulating reservoir used to store water temporarily when the load on the turbine is reduced and provide water when load has increased.

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4. Water- conduit system

A water conduit system carries water from the reservoir to the turbine through pipes. These pipes are called as penstock. These can be laid above ground or underground.

5. Tail race

Water discharged into the tail race after passing through the turbine. It carries the water back to the river. Tail race may be an open channel or a tunnel depending on upon the power house location.

6. Surge tank

It acts as pressure release valve of the water conduit system. It is an additional storage space provided near the turbine to control the pressure variation of the penstock and prevent water hammer effect during sudden pressure variation.

7. Trash rack.

It is provided to stop the entry of debris, which might damage the gates and turbine runner. It is placed across the intake.

8. Turbine

Turbine converts the kinetic and potential energy of the water into mechanical energy. Turbine is attached to the shaft of the alternator. Thus the mechanical energy of the turbine is converted into electrical energy. The commonly used turbines are Francis turbine, Kaplan turbine, Propeller turbine and Pelton turbine. Normally water turbines rotate on the vertical axis.

9. Power house

Turbine, Alternator and various control systems are present in the power house. It is normally located near the foot of the dam. It may be under ground or open type. The location of the power house is based on the maximum possible head at the turbine.

10. Spill way

When the water level rises beyond the permissible levels in the reservoir, spillway discharges the excess of water and acts as safety valve of reservoir. If the excess of water is not discharged, the water level raises and starts flowing over the dam. This phenomenon is known as overtopping.

Advantages of hydro power.

  1. Non polluting
  2. The efficiency of the hydroelectric power plants are higher than thermal power plant.
  3. Hydro electric power plants have very long life.
  4. Less and easy maintenance
  5. Power production cost is small.
  6. Quick start and shut down are possible.
  7. More flexibility in operation and control.
  8. Water after electricity production can be used for irrigation and drinking purposes.

Draw backs.

  1. High initial cost.
  2. Long construction period.
  3. Large portion of area is submerged under water due to the construction of dams and reservoirs and leads to environmental and social problems.

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