Hydroelectric Power Plant- Diagram, Working and Types

This article describes the hydroelectric power plant diagram, its working, components, and types. The generation of electrical power using clean and renewable sources has taken center stage because of the increasing average global temperature owing to the indiscriminate use of fossil fuel sources. Hydel power is one of the most important clean and renewable sources of electricity generation.

In a hydroelectric power plant, the energy stored by a flowing water body is converted into electrical energy. This water body is, in most cases, a river with a high volume of water whose flow is controlled to generate the required amount of electricity.

Importance of Hydroelectricity in the contemporary world

Hydroelectricity is one of the most important renewable sources of electricity generation after integrated solar and wind energy. All that is required to set up a hydroelectric power plant is a river descending a steep slope, which can be the top of a hill or a dam that can control the flow of the water. As rivers are common all around the world, the generation of electrical power using the water of these rivers has been one of the most popular methods of electricity generation.

According to the International Hydropower Association, around 15% of the electrical power in the world is generated using hydroelectric power plants. According to the Observer Research Foundation (ORF), hydropower accounted for 12.5% of the total power generation in India. This shows the importance of hydropower in the world. Although fossil fuels have the dominant share in power generation, renewable resources are gaining attention. Therefore, it goes without saying that the share of hydropower is going to rise further.

Layout Diagram and Working Of Hydroelectric Power Plant


The picture shown above is a layout diagram of a Hydroelectric power plant. Let’s understand each component of this hydroelectric power plant in detail.

  • Dam and Reservoir: A Dam is a large and strong barrier that is constructed on top of an elevation like a hill through which the river water descends. The dam restricts and controls the flow of water down the elevation. As the river is obstructed, there is a huge amount of water storage behind the dam, which is known as the reservoir. The dam consists of various gates which are controlled electronically to allow the required amount of water flow. In this way, the stored potential energy within the flowing stream is controlled, which is then utilized to rotate a turbine and generate electricity.
  • Control Gate: Control gates are installed on the dams, which allow the water to flow when kept open. These gates are controlled electronically, which, therefore, allows the flow of water through the penstock to the turbine. If all the gates are opened, maximum water flows through, and thus, a higher demand for power could be met. Control gates are opened completely when water in the reservoir is above the safety factor of the dam.
  • Penstock: Penstock is a passage of pipes through which the water reaches the hydro-turbine after the gates of the dam are opened. The stored potential energy within the water is converted into kinetic energy as it descends the Penstock.
  • Water Turbine: The water turbine or the hydro-turbine is a prime-mover which is coupled to an electric generator. The water flowing down the penstock converts its potential energy into kinetic energy and hits the turbine blades. As a result, it begins to rotate, which in turn causes the generator to rotate and generate the required electricity.
    • The water turbines are of two types – Impulse turbines and Reaction turbines. Impulse turbines are used for large heads, and reaction turbines are used for low and medium heads.

Hydroelectric Turbine (courtesy: General Electric)

  • Generation unit: The generation unit or the generation house consists of a generator which is coupled to the water turbine. As the turbine rotates, the generator begins rotation and generates electricity, which is then taken to the transformer unit to step up the voltage.
  • Transformer: The transformer is used to step up the voltage generated by the generator. The voltage generated has a low magnitude, which is not sufficient for efficient transmission of power. This is because the current flowing through the lines will be more if the transmission voltage is low for the same amount of power being transferred. This will lead to heat loss and voltage drop within the line. Thus, a transformer is employed to step up the voltage to maintain the optimum efficiency of the entire system.
  • Surge tank:  A surge tank is a water storage tank connected between the penstock and the hydro turbine in order to neutralize pressure within the penstock and keep the pressure variance checked. It is a small reservoir that is opened at the top, and the water level within the surge tank rises or falls to maintain adequate pressure within the penstock. When there is a sudden reduction in load demand, the control gates of the dam are closed to reduce the flow of water through the penstock. As a result, the pressure within the penstock rises abruptly. The surge tank checks this rise in pressure by absorbing the excess water within the penstock. When the load demand rises suddenly, the surge tank releases this excess water to meet the demand momentarily.

Types of Hydroelectric power plants

Based on the amount of power demand and the geography of the place, there are three types of hydroelectric power plants.

(1). Conventional plants:

Conventional plants, as the name suggests, generate electricity by conventional methods of storing the water in a reservoir by making a dam. The water is made to flow through the gates of the dam to the penstock of the turbine which rotates a generator. The amount of power generated is directly related to the volume of the water and the water head. Water head can be defined as the difference between the height of water in the reservoir and the level of water outflow.

(2). Pumped storage plant:

The pumped storage plant works like the conventional plant except for the fact that there is a second reservoir constructed at the outflow point of the turbine. This reservoir stores the water, which can be pumped back to the main reservoir during peak load demand. Therefore, the plant can ensure that maximum demand can be met when required.


(3). Run-of-the-river Plant:

In such plants, there is no dam to obstruct the flow of the water, and hence there is no reservoir. Instead, a part of the natural flow of water is diverted through the penstock of the water turbine, which makes the turbine rotate. Thus, the natural thrust of the water in the river is used to run the turbine-generator set, and any overflow of water is passed unused.


Advantages of a Hydroelectric power plant

  • Clean and green source of energy.
  • There is low operational cost as naturally flowing water sources are employed as fuel.
  • Less maintenance is required.
  • Feasible for electricity generation in remote hilly areas where a big power infrastructure can’t be constructed.
  • The plant’s dam is used for irrigation, cleaning of the river bed to avoid silt deposition, etc. Hence, hydropower projects are categorized as multipurpose projects.


  • The initial cost is very high due to the construction of a strong dam.
  • These plants alter the natural habitats of freshwater species in their areas and change the concentration of nutrients, water temperature, and the river’s flow. Downstream river flow suffers a loss of water and silt loads, reducing water quality.
  • The transmission cost from a hydropower plant is significantly high due to its location far from consumers.

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