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Hydroelectric Power Plant & Hydroelectric Energy
A hydroelectric power plant or hydropower plant is used to generate electricity from the potential energy of the water at the high-level water. There is a limited source of fossil fuels like coal, petroleum gases, oil, etc. and to avert the pollutions from these fossil fuels, now a day, hydroelectric plants are built in many countries.
The turbine is the main equipment, where the kinetic energy of water is converted into mechanical energy which is further converted to electricity with the help of a generator.
Let’s explore the details of the hydropower plant!
The hydropower plant generates around 24% of the total electricity generated in the world and day by day, it is increasing.
What is Hydroelectric Power Plant or Hydropower Plant?
Hydroelectric Power Plant Definition
A hydroelectric power plant or hydropower plant is defined as a power plant that generates electricity from the water potential energy.
No fuels are required, and it is renewable energy.
The generated electricity is called hydroelectricity.
Potential energy is changed into electricity.
The more the height of the water level and the more the quantity of water, the more power will be generated.
Normally power is produced on large scale.
History of Hydropower
Waterwheels were started to use in ancient time. However, the first industrial hydroelectric power plant was built on the Fox River in 1882 to produce electricity for paper mills.
What is Hydroelectric Energy?
It is the form of energy that is generated or harnessed from water power. It may be from the kinetic energy from the flowing water or it may be from the potential energy stored in a reservoir.
It is also called as hydroelectric power or hydroelectricity. Hence, we understand the hydroelectric power definition.
It is used to generate electricity.
There are many hydroelectric power plants, where hydroelectric energy is used to get electricity.
Hydroelectric Power Plant Diagram
Let’s see a typical diagram to understand the different parts of a hydroelectric power plant.
Hydroelectric Power Plant Parts
A hydroelectric power plant consists of the following parts,
We know that high-level water has potential energy and hydroelectric power plant use it to produce electricity. Now, to create high-level water, a very strong structural barrier is created in the path of river water flow. This barrier is called a dam.
Dams are highly rigid, designed with strong structure.
It helps to stop the water flow.
It stored the water of the river
It stored the water during rain.
It helps to control the flood by storing the water.
It is water-tight
Due to the high water level, high pressure is exerted on the wall.
The dam is able to withstand the high pressure due to and should be able to withstand the pressure exerted by the water on it.
There are different kinds of dams, used for various hydroelectric power plant,
Rock Fill Dam.
The height of water in the dam is called the headrace.
The reservoir means the storage space, where the water is stored. This water is bounded by a dam. Water from the reservoir is supplied to the turbine.
The reservoir is a large area, and during the rainy season, due to heavy rainfall, the water level may exceed the maximum allowable limit.
If the water level exceeds, the stability of the reservoir, as well as the dam, may be reduced.
To avert this problem, the reservoir has few structures so that excess water can be removed from the reservoir.
This structure is called the spillway.
It increases the stability
It reduces excess water.
Spillways can be of two types.
Flow can be controlled here.
Flow is uncontrolled, it means once water level increase, water starts to remove and maintain the maximum level.
It is simply the gate, which helps to control the water flow. Water from the reservoir to be provided to the turbine through a pipe or conduit, namely penstock and this water should be controlled. So, how it can be controlled?
The control gate helps to do it.
It helps to control the amount of water.
If the control gate is fully open, the water flow rate will be maximum.
If the control gate is closed, the water flow will be stopped.
Water from the reservoir to the turbine is by a pipe or conduit, which is known as a penstock. If it is a conduit, then it can be open or closed based on the project site.
Due to very high pressure, this shall be made by RCC (if conduits) and Steel (If pipe) normally.
Sometimes, when the surface is not permitted to put pipes or to made conduits, tunnels are made which also act as a penstock.
Normally, tunnels are used if there is a big barrier like mountains, etc.
Penstocks carry the water to the turbines.
If the water head is less than 30m, then RCC penstocks can be used.
More than 30m or high water head, steel penstocks are used to have suitability over high pressure.
Remember, steel penstocks can be used for all kinds of water head.
The potential energy of the water stored in the reservoir is converted into kinetic energy due to the gravitational flow through the Penstock.
Penstocks have the following components,
air bleed valve or vent pipe,
Penstocks can be two types,
Buried or pressure shaft, or pressure tunnels.
These penstocks are open or exposed.
It is based on the surface or the terrain of the site.
Pressure shaft or pressure tunnels
These are enclosed pipe which is used to provide water to the turbines and these are kept at the lowest possible elevation to avoid the formation of a vacuum.
The design shall be in such a way, that total friction loss shall be less.
It will be supported on the rock or soil.
Based on the project site, sometimes, long penstocks are used. These are small reservoir or tank which is used to stabilize the pressure fluctuations. This surge tank is mainly used to reduce the pressure surges in the pipe or conduit and the name is followed for the same. It is placed between the water reservoir and the powerhouse.
A surge tank is an atmospheric tank, which means it is open.
It is widely used in large or medium hydroelectric power plants.
The surge tank has a free water surface, hence, it reduces the distance between a turbine and free surface and averts water hammer effects.
Reduce load fluctuations.
The surge tank helps to reduce the high-pressure pipe length.
It protects the draining system from high pressure.
Water Turbine or Hydraulic Turbine
The force of falling water from the water reservoir hits the blades of the turbine and the turbine rotates. The kinetic energy of water gained in the penstock is converted into rotational motion as well as mechanical energy.
The flow of water from the Penstock is taken into the water turbine.
The turbine is coupled to a generator.
Since the turbine rotates, the generator also rotates.
Due to the rotation, the generator produces electricity.
There are two types of turbine, in hydroelectric power plants.
Impulse turbines are used normally in high water head applications.
No pressure sealing required around the shaft.
There are many elliptical buckets along its periphery.
Water jet from a nozzle strikes the turbine blades.
The pressure is converted into kinetic energy in the nozzle.
Kinetic energy helps the blades to spin.
The spinning of blades means the turbine rotates.
There are two main reaction turbines are used,
Francis turbines – used for low to medium heads.
Kaplan turbines – used for low heads and large volume
However, based on a few parameters, appropriate turbines shall be selected,
Net head available.
Discharge water quantity.
Discharge flow variation.
A generator is mechanically coupled to the turbine. It is placed in the powerhouse. When the turbine rotates, since, generator shaft is coupled, it will also rotate.
The generator has a rotor and starter.
Due to the rotation of the rotor of the shaft, the magnetic field is created.
The magnetic field produces electricity.
This electricity is distributed through the transmission line, based on requirements.
Power House Auxiliaries
Power house is a station for the generation of power. It houses many equipment as well as auxiliaries.
Components of a typical power house, are
Turbine or Generator hall.
Hydroelectric Power Plant Working Principle
Hydropower Plant Working Procedure
Power generation from the hydroelectric power plant or hydroelectric energy depends on the water flow rate and available water head. Both should be available to generate electricity.
The more the water flow rate and water head, the more power will be generated. The working procedure is as follows,
Step-1 Potential Energy
Water is stored in the reservoir, and it is stopped by a dam. The potential energy in the dam water is high.
Step-2 Kinetic Energy
Water then drops through the penstock after releasing it from the control gate. The fall of water creates a very high pressure as well as kinetic energy. At the end of the penstock, a surge tank is installed to stabilize the fluctuation heads.
Step-3 Rotational Speed
This high-pressure water hits the turbine blades and forces the turbine to spin.
Step-4 Electricity Generation
The generator rotor is connected to the turbine and it also spins and creates a magnetic field and electricity is produced.
This electricity is transferred to the consumers through power grids.
Check a NICE ANIMATED video from Student Energy
Power Energy of a Hydropower Station
The theoretical power available from falling water can be expressed as
Pt = ρ q g h
q: Water flow rate measured in cubic meters per second.
h: Height of water or head of water measured in meters, or the falling of water. It means the height difference between the source of water and the water’s outflow.
g: Gravitational acceleration constant 9.81 m/s2.
Hydroelectric Power Generation Efficiency
Due to different energy losses in various parts of the plants, actual power generation is always a little less than theoretical power generation.
This is expressed, as
Pa = μ ρ q g h
Pa = Actual power available (W)
μ = efficiency (in general in the range 0.75 to 0.95)
Energy from Hydro-power plant
Potential energy is stored and the same is converted into electric power. This energy is calculated, as follows,
W = m g h
W = ρ V g h [As, m = ρ V ]
W = energy (J)
m = mass of water (kg)
V = volume of water (m3)
How Much Electricity Can a Hydroelectric Plant Make?
There are two main factors on which the amount of electricity of a hydropower plant depends,
How Far the Water Falls.
Amount of Water Falling.
How Far the Water Falls
Power production depends on how far the waterfalls. If waterfalls from far, power production will be more.
Water pressure depends on the size of the dam.
If the dam size is more, the water pressure is more.
Water pressure more, means kinetic energy will be more.
Kinetic energy more means turbine rotational motion will increase.
Increase rotational speed means higher power production.
Higher the waterfalls, the higher the power production.
Power production is directly proportional to the water head.
Amount of Water Falling
Power production depends on the amount of water flow. If the water flow rate is more, power production will be more.
The water flow rate depends on the amount of water flow in the river.
If the river is big, the water flow will be more.
More water means more power production.
Power is directly proportional to the water flow rate.
Hydroelectric Power Plant Calculation Examples
Theoretical & Actual Power generation
What will be the power production for a 5 m3/s water flow rate with a waterfall of 90 m? if efficiency is 0.85.
What will be the potential energy if 1000 m3 of water is stored at 80m height from the turbine?
P = (1000 kg/m3) (5 m3/s) (9.81 m/s2) (90 m)
P = 4414500 W
P = 4414.5 kW
Actual power generation
Pa = μ x Pt
Pa = 0.85 x 4414.5 kW
Pa = 3752 kW
Energy in Elevated Water Volume
The potential energy in the water volume shall be as follows,
W = (1000 kg/m3) (1000 m3) (9.81 m/s2) (80 m)
W = 784800000 J/s
W = 784800 kJ/s (1 kW = 3412 J/s)
W = 230 kW
Type of Hydroelectric Power Plants
Based on size or cpacity
Based on the sizes of hydropower plant, it is divided into few categories,
Large Hydropower – Normally its capacity is more than 100 MW and it is connected to power grid for large scale applications.
Medium Hydropower – Normally its capacity ranges from 15-100MW and it may also connect to the power grid for medium-scale applications only.
Small Hydropower – Normally 1-15MW and very small scale application. It can also connect to the power grid.
Mini Hydropower – Normally 100kW -1MW, these are not connected to the power grid, these are very small and used as a standalone system.
Micro Hydropower – 5kW -100kW, very small, used to the power supply in small rural areas.
Pico Hydropower – Below 5kW, used to power supply for the individual house only.
Based on General Feature
It uses potential energy stored in the reservoir.
Heat and water flow rates are the main key parameters for the generation of power.
Maximum hydropower plants are in these categories.
Pumped Storage Plant
This is used to store water so that in case of a low water head, additional water can be fed to the reservoir.
A second reservoir is built near the turbines, and water is stored.
In case, low water in the reservoir, the turbine is connected to the power supply.
Due to the power, the turbine works as a pump.
Water is transferred from the reservoir at a lower elevation to the reservoir at a higher elevation.
It ensures sufficient water head at all the seasons.
River of river plant means; it is based on the river flow.
No dam is built for this kind of plant.
No specific reservoir and it is based on river flow only.
Penstock or canal is made by diversion from the river.
This water is then supplied to the turbines and power generates.
Tide based plant
Tide means daily rise and fall of water level.
It is almost scheduled for all rivers or seas.
This plant can only be installed if the tide is highly predictable.
When the tide comes, the same water head is used to rotate the turbines
Power is generated.
How to Increase the Operating Efficiency of Hydroelectric Power Plant?
To increase the efficiency of hydropower plants, the design should be optimum in terms of all the required parameters. However, there few things that should be taken care of, for maximum efficiency.
Decreasing slippage losses from the reservoir.
Decreasing head loss.
Increasing potential energy even in the offseason.
Continuous water supply.
Reducing water head fluctuations.
Reducing the friction losses in the water transferring system.
Reduction the energy loss in the turbine.
Build a hydropower plant in the mountain regions, where the high head and huge water is available.
Surge tank design hall be optimized.
Proper feasibility study for intake diversion system.
The optimum size of the water transportation system.
Selection of proper turbine.
Project Requirements for Hydroelectric Plants
There are many parameters for building a hydroelectric power plant,
Storage of water
Water head availability
Location of site
Transportation of heavy equipment facilities
Capital cost estimation.
Operating cost estimation.
The water flow rate in different seasons.
Structural design scope.
Installation of penstocks possibilities.
For run-of-run plants, details study water river water flow, seasonal analysis.
In case of tide plants, detail study of tides.
Advantages of Hydroelectric power plant/Hydroelectric energy
Renewable energy source.
The operating cost is less.
The maintenance cost is less.
Pollution is negligible.
The space requirement for power house is very less.