Hydroelectric Power Plant – Layout, Principle and Working

  • Post author:
  • Post category:Power Plant
  • Reading time:22 mins read
Hydroelectric Power Plant | There are six types of components used in the schematic arrangement of the hydroelectric power plant. They are dam and reservoir, control gate, pen-stock, water turbine, surge tank and generator.

Dam and Reservoir

The dam is constructed on a large river or lake in hilly areas to ensure sufficient water storage at height. The dam forms a large reservoir behind it. The height of water level in the reservoir determines how much of potential energy is stored in it.

Control Gate

Water from the reservoir is allowed to flow through the pen-stock to the water turbine. Control gate is used to control the amount of water released in the pen-stock. When the control gate is fully opened, huge amount of water is released through the pen-stock.


A pen-stock is a huge steel pipe which carries water from the reservoir to the water turbine. Potential energy of the water is converted into kinetic energy as it flows down through the pen-stock.

Water Turbine

The water turbine is taken the water from the pen-stock. The electric generator is mechanically coupled with the water turbine. Kinetic energy of the water drives the water turbine and consequently the electric generator gets driven. There are two main types of water turbine. The following are,
1.Impulse turbine and 2. Reaction turbine.
Impulse water turbines are used for large head power plants and reaction water turbines are used for low and medium head power plants.

Surge Tank

Surge tanks are usually provided in high or medium head plants when considerably long pen-stock is required. The surge tank is also called a small reservoir or tank which is open at the top. It is fitted between the power house and the reservoir.
hydroelectric power plant, hydro power generation, working of hydro power plant @electrical2z
Hydroelectric Power Plant – Surge Tank
The water level in the surge tank rises or falls to reduce the pressure swings in the pen-stock. When there is sudden reduction in load on the water turbine, the governor closes the gates of the water turbine to reduce the water flow. This causes pressure to increase abnormally in the pen-stock.
This is prevented by using a surge reservoir, in which the water level rises to reduce the pressure. Also the surge tank provides excess water needed when the gates are suddenly opened to meet the increased load demand.


The electric generator is mounted in the power house and it is mechanically coupled with shaft to the turbine. When the water turbine blades are rotated, it drives the electric generator and electricity is generated which is then stepped up with the help of a transformer for the transformation purpose.

Types of Hydroelectric Power Plants

Conventional Plants

The dammed water is used to the conventional plants for the potential energy. The energy extracted depends on the volume and head of the water. The difference between the water outflow level and height of water level in the reservoir is called as water level or water head.

Pumped Storage Plant

In pumped storage plant, a second reservoir is constructed near the water outflow from the water turbine. When the demand of electricity is low, the water from lower reservoir is pumped into the main reservoir. This is to ensure sufficient amount of water available in the main reservoir to meet the peak loads.

Run of River Plant

In this type of method, no dam is constructed and, hence, reservoir is absent. The river is diverted through a pen-stock or canal to the water turbine. Thus, only the water flowing from the river is available for the generation. And due to absence of river, any oversupply of water is passed unused.
hydro power plant, hydroelectric power plant, hydro power generation, working of hydro power plant @electrical2z
Hydro Power Plant vs Other Plants
Advantages of a hydroelectric power plant
  • In this power plant, no fuel is required as kinetic energy of water is converted into electricity energy.
  • Neat and clean source of energy generation.
  • Very low running charges. water is available with free of cost. Comparatively less maintenance is required and has longer life.
  • Serves other purposes too, such as irrigation.
Disadvantages of a hydroelectric power plant
  • Cost of dam construction is very high.
  • Transmission cost is high – as hydroelectric power plants are located in hilly areas which are quite away from the consumers.
Comparison of Hydroelectric Power Plant with Thermal and Nuclear Power Plant
Hydroelectric Plant
Located where large reservoirs or dams can be created like in hilly areas.
Located where water and coal and transportation facilities are adequate.
Located in isolated areas
away from population.
Initial cost pretty high
due to large dam construction.
Initial cost is lower than
Nuclear and hydroelectric power plant.
Initial cost is highest as cost of reactor construction is very high.
Practically nil as no fuel is required.
Running cost is higher than nuclear and hydro power plant due to amount of coal required.
Cost of running is low as
very very less amount of
fuel is required.
Water is source of power which is not a dependable quantity.
Coal is source of power.
So limited quantity is available.
Uranium is fuel source
along with platinum rods.
So sufficient quantity is
No cost for fuel transportation.
Cost of fuel transportation
is maximum due to large
demand for coal.
Cost of fuel transportation is
minimum due to small quantity required.
Most environment friendly.
Least environment friendly.
Better friend of environment than steam power plant.
Around 85% efficient.
25% overall efficiency.
More efficient than steam
Maintenance cost is
quite low.
Maintenance cost is very
Maintenance cost is the
highest as highly skilled
workers are required.
No standby losses.
Maximum standby losses as boiler still keep running even though turbine is not.
Less standby losses.
Final Word
Hope you understand this article about the Hydroelectric Power Plant. In case of any doubt please comment below. Please follow our website for future updates. Thank you for visiting our website @Electrical2z.

Leave a Reply