Welcome back to The Mechanical post ! Today we'll see what is hydroelectric power plant , its layout, its components, diagram, advantages and disadvantages. So let's get started.

Hydroelectric power plant - construction and working

Introduction to Hydroelectric power plant

In current times pollution and global warming are increasing at an unprecedented rate. Thus, to curb and control them is the need of the hour. Generally, till now electricity was produced with the help of coal or oil fired steam power plants. These power stations used non renewable fuel to produce power, which caused emission of harmful gases.

However, hydroelectric power plant makes use of renewable energy. This is done by converting the potential energy of water into electrical energy. Thus producing almost zero emission, which is good for us as well as the environment. Now, let's define hydroelectric power plant.

What is a hydroelectric power plant ?

Hydroelectric power plant is defined as "A type of power plant which converts the potential energy of water stored at a height into electrical energy with the help of turbines  and generators."

Construction of hydroelectric power plant 

The Hydroelectric Power Plant is made up of the following components:
  • Reservoir and Dam
  • Control Gate
  • Penstock
  • Surge Tank
  • Water Turbine
  • Draft Tube
  • Generator

Layout of Hydroelectric Power Plant

Given below is the general layout or explanation od each component of the hydroelectric power plant (refer diagram below)

Reservoir and Dam

The dam is constructed on a large river to ensure sufficient water storage at a height and the dam forms a large reservoir behind it. The potential energy stored in water depends upon the height of the water level (also known as water head) the higher the water level the more is the potential energy.

Control valve

The amount of water released in the penstock is controlled by regulating the control valve. During high loads the amount of water supplied is increased whereas while at lesser loads the supply is decreased accordingly.

Surge Tank

A surge tank is a small reservoir or tank fitted between the reservoir and the turbine. The water level in the surge tank rises or falls to reduce the water hammer effect in the penstock. 


A penstock is a long steel pipe reinforced with concrete which delivers water from the reservoir to the turbine. The potential energy of the water stored in the dam is converted into kinetic energy as it flows down through the penstock due to the action of gravity.

 The penstock is usually thicker than normal pipes  to bear the immense pressure exerted by the water. The penstock has a large diameter

Water Turbine

The water turbine is a type of impeller which is coupled directly to an electric generator. Its main function is to convert the kinetic energy of the water into the rotary mechanical energy.

Draft tube

A draft tube is a tube of increasing cross sectional area which is used to carry the water from the exit of the reaction turbine to the tailrace. The smaller end of the draft tube is connected to the exit of the turbine, whereas the other part is submerged into the tailrace. 

The main function of the draft tube is to convert the Kinetic energy of water into pressure energy.


The generator is coupled to the same shaft on which the turbine is mounted on. The generator converts the rotary mechanical energy of the turbine into electrical energy. The produced electricity will be step up or step down  accordingly 
with the help of transformer and later supplied to industries and domestic purpose.


The water after passing over the turbine is then discharged through the tailrace after which the water joins the river.

What is the working principle of hydroelectric power plant ?

The hydroelectric power plant works on the principle of converting the potential energy of the water into electrical energy with the help of various components like the penstock, turbine and the generator.

Diagram of hydroelectric power plant | The Mechanical post
Tennessee Valley Authority; SVG version by Tomia / CC BY-SA

Working of Hydroelectric Power Plant 

The dam is constructed on a large river to ensure sufficient water supply and the dam forms a reservoir behind it. The potential energy stored in water depends upon the height of the water level (also known as water head) the higher the water level the more is the potential energy.

When the control valve is opened, the water from the dam enters the penstock and starts flowing towards the turbine under the influence of gravity. During this process the potential energy of the water is partly converted into kinetic energy.

Total conversion of potential energy into kinetic energy takes place in the nozzle. The surge tank protects the penstock from sudden pressure waves when the control valve is closed suddenly. Thus reducing the water hammer effect.

The  water coming out of the nozzle is directed onto the vanes (blades) of the turbine. This high velocity water jet exerts pressure onto the vanes, thus causing it to rotate. In this way the kinetic energy of the water is converted into mechanical energy.

Since the turbine and the generator shaft's are coupled the rotation of the turbine causes the rotation of the rotor of the generator thus converting this mechanical energy into electrical energy. 

The water is then discharged via the tailrace. The electrical energy produced is supplied to industries and domestic markets. The amount of electricity produced can be controlled by controlling the amount of water entering the turbine.

Fun fact

The world's largest dam and hydroelectric power station is the "Three Georges dam" and is situated in china. It has 34 generators each of which producing 700 MW power. 

When the Three Gorges Dam was built, 39 trillion kilograms of water from the Yangtze River is stored up at a height of 175 meters above sea level. 

According to a report, NASA has calculated that the dam only slows the rotation speed of the earth by 0.06 microseconds. Now that's something interesting isn't it ? do let me know in the comments about it.

Advantages of Hydroelectric Power Plant 

The advantages of Hydroelectric Power Plant are :
  • As mentioned above this type of power generation is clean and green with zero pollution.
  • No fuel cost and thus no fuel transportation problems.
  • No standby losses.
  • No waste disposal problems.
  • Highly reliable.
  • Can be started or stopped in less time.
  • Life of the plant is about 100 years.
  • Almost every dam is fitted with a hydroelectric power plant due to its high efficiency as well as clean energy.
  • Operating cost is low as compared to conventional power plants.
  • Due to the construction of dam the problem of flooding is reduced.
  • The reservoir helps store water which benefits nearby areas especially farmers.

Disadvantages Hydroelectric Power Plant 

The disadvantages of Hydroelectric Power Plant are:
  • The construction cost is very high.
  • Time required for construction of the full setup is much longer as compare to conventional power plants. It usually takes years to setup the hydroelectric power plant.
  • Usually hydroelectric power plants are located in hilly areas, away from the city. Thus they require long transmission lines to supply power to the load. This results in increased transmission losses.
  • The hydroelectric power plant requires large surface area. Thus, people residing in nearby areas are to be relocated.
  • Power generation hugely depends upon the amount of water available in the reservoir. Thus  inadequate rainfall can hinder power generation.
  • Dams cannot be built anywhere. It requires a lot of study as well as resources.
  • Bio diversity is impacted especially fishes due to the the construction of dam.

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Applications of Hydroelectric Power Plant

The applications of Hydroelectric Power Plant are:
  • The primary application of the hydroelectric power plant is to produce electrical energy.
  • The stored water can be used for agricultural purposes.
  • Thermal power plants can be set up in nearby areas.
  • The dam built can be used to prevent floods due to seasonal rain.

That's an overview on Hydro-electric power plant. If you like this post or have any suggestions do let us know in the comments we would love to hear it from you. Do follow The Mechanical post on instagram, facebook and twitter.

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