Hydroelectric power plant:
Hydroelectric is derived from two word hydro from hydraulic which means energy present in the water and electric is from electrical energy which is produced due to the flow of electrons. Hydro power plant, also called hydropower plant, water power plant is a power generation plant which generates hydroelectricity via water. Generating power from water is cheap because it used renewable source of energy, also environmental form of energy. It is considered a renewable energy source because we can use it again because the water cycle is constantly renewed by the sun the water evaporates from the rivers, ocean etc and come back in form of rain.
The basic process is that when the water flows up to down it has potential energy which is converted in kinetic energy, the water pressure or flow speed impulse the turbine rotation, the hydro energy is the energy generated by water turn the gravitational potential energy and kinetic energy to mechanical energy, then generator is drive by the water turbine rotation in which electrical energy is produced. In power plant production of electricity depends upon on the following factors:
power plant production of factors:
Water level from ground:
When the level of water reservoir is at maximum it will rotate the turbine with maximum speed because it has greater potential energy.
Volume of water:
When the volume of water is less than turbine will not rotate will less water due to which no electric energy will be produce so this is the most important factor of hydroelectric generation.
Efficiency of the turbine:
The electric energy is produce when the turbine rotates.
The demand of electricity varies day by day as well as among season. During summer season the demand of electricity is maximum because air condition, fans etc are used. Hence there is need to store the energy so that it can be used at the time of high electricity demand. Electricity is produced at constant rate in hydroelectric power plant.
History of Hydropower plant:
Nearly 2000 years ago water wheels were used by the Greeks to grind wheat into flour. In the 1700’s, hydropower was used for pumping irrigation water.
In United states in 1882 first operational hydroelectric generating station was invented by Appleton Wisconsin producing 12.5 Kilowatts of power.
The total electrical capacity produce by this hydropower was equivalent to 250 lights. The expansion of hydropower was created by the hydraulic reaction turbine. Due to which about 300 hydroelectric plants were generated within the next 20 years
Niagra Falls was the first American hydropower site developed for a vast quantity of electricity and is still electric power source today. The very first hydroelectric project took place in Northumberland, England in 1878. The electricity produced powered a single lamp. Just four years later, in Appleton Wisconsin, American’s created one of the first hydroelectric plants for wider distribution. The generated power delivered electricity to private and commercial customers.
Working of Hydropower plant:
The working of Hydroelectric power plant require the following parts:
- Water Storage
- Surge tank
- Turbine shaft
Dams have been used to provide a store of water for industrial uses, agriculture, household uses for thousands of years. Majority of the world electrical energy is produce by hydroelectric dams is non-renewable en energy resource. In making dams 2 trillion dollars was spent around the world.
Storage dams are built to provide a reliable source of water; it acts like a barrier that holds back water for short or long periods of time. Small dams, for example, are often built to capture spring runoff, rivers for irrigation purposes or for livestock in the dry summer months. Storage dams are also used for recreation, municipal water supply, irrigation or hydroelectric power generation.
Reservoirs can act to prevent floods downstream by regulating and holding the flow during major flood events. Reservoirs can also be used to balance according to weather condition it can store water when there is heavy rain fall so it save us from floods and releasing more water during droughts or for irrigation use.
Penstocks are like large pipes which are placed with some slope which carries water from storage tank to the turbines. The water flow in the penstock at very high speed, so sudden closing or opening of penstock gates can cause water hammer effect to the penstocks.
It’s essential a very large diameter pipe whose diameter is about 10 meters, built in sections, that conveys water from the source (typically a reservoir) in steel pipes or concrete pipes, and brings it to a hydroelectric powerhouse where the hydro turbines are located. The reservoir is at high elevation than powerhouse. The penstock is typically buried but can be above ground. Sometimes both buried and above ground. The penstock allows for expansion and contraction. The penstock is inspected on a regular basis. There are gates at the top of the penstock and at the bottom of the penstock where it enters in the powerhouse. Diameters of the penstocks vary according to the requirement depending on how much water flow is required for the turbines. Sometimes each turbine has their own penstock. Other times a single penstock will bifurcate for two hydro turbines.
Surge tanks are the most common means of protecting against excessive water hammer pressure. These are vertical columns of water with the water surface exposed to the atmosphere. They are generally used in the penstock upstream of the turbine, but as close to the turbine as circumstances allow. They have also been used in draft tube tunnels. If the top of the tank is closed to the atmosphere to create a surge chamber, these are called accumulators, but are seldom used in hydropower designs.
It is used as a large reservoir or a pipe which is placed in a vertical position to extend the water supply. We can often see surge tanks in medium or large plants.This tank is installed on large pipelines so that when the pressure is exceeded due to the water hammer it can stop it and also supplies water when there is a negative pressure in the pipelines when the valve opens. A simple tank placed vertically above ground and made of concrete is capable of things we can’t imagine.
Hydraulic electric turbine, a device which can convert the hydraulic energy into the mechanical energy when the water fall on blades of turbine which again convert this mechanical energy into the electrical energy by connecting generator to the shaft of turbine. The hydroelectric turbine design consists of:
- Wicket gate
Power output factors:
- Head of pressure which is the height of water from the turbine
- Flow rate of the turbine
This work on the principal that when the circular blades will strike by the water coming from penstock with high pressure it will rotate the shaft that is connected with the propellers provided at the center and it causes generator to produce electrical power.
Francis turbine is the mostly preferred hydraulic turbine. It contributes about 60% of the global hydro power capacity. Mainly because it can efficiently convert wide range of operating condition. In francis turbine the head is 45 to 400 meters and flow rate is 10 to 700. Most important of francis turbine is its runner which is faded with complex shape blades. In runner water enter horizontally and leaves vertically. Drain the course to flow water glide with the runner blade. Francis turbine are specially shaped have foil shaped so when water will flow over it low pressure will be created at one side and high pressure on the other side. This will result in lift force. It has bucket kind of shape so water will hit and create impulse force. Both the lift force and impulse force make the runner to rotate. So francis turbine is not pure reaction turbine.
Ftotal = Freaction + Fimpulse
When water will rotates the turbine both the kinetic energy and pressure energy will be come down. This is also called mix flow turbine. The runner shaft is connected with generator for electricity production. This arrangement is faded in spiral casing flow enter in the inlet nozzle. Flow rate of water get reduced over long link of casing since water is drawn into the runner but decrasing area of the spiral casing will make sure that water enter to the runner region at uniform velocity. Stay vanes and guide vanes are faded at the entrance of the runner. The basic purpose of it is to convert one part of the pressure energy to kinetic energy.
Kaplan turbine is suitable for power extraction when water energy is available at low head and high flow rate which means they are suitable for operation when water is stored in big reservoir at relatively shallow altitude. Low head is about to 2 to 25m. High flow rate is 70 to 800. In Kaplan turbine flow of water is enter through spiral casing almost at uniform velocity throughout the perimeter which decrease the area of casing make sure that flow is entered through center portion. Water after passing guide vanes passes over the runner. Finally it leaves through the draft tube. Most important part of the Kaplan turbine is its runner cross section of runner blade will have a curve shape. When water will flows over it will induce a lift force due to airfoil effect. The runner will rotate by the Tangential component of lift force. This rotation is transfer to generator for electricity production. Kaplan turbine are axial flow machine where absolute velocity of flow is parallel to axis of turbine. Water is precisely pass through the runner blade with the help of shroud. Guide vanes is to control the flow of water. This can meet for varying power domain. Blades of Kaplan turbine are designed to operate under a wide range of operating condition. A rotating blade experience relative velocity of flow. The fundamental thing in the blade design is relative velocity of fluid flow should be at optimum angle of attack at all across sections. Inclination of relative velocity increases as removed from rotor tip due increase in blade velocity. There should be continuous twist in blade from the rotor tip. So that at every cross section the angle of attack is optimum. With varying flow condition relative velocity changes drastically. Kaplan turbine are adjustable when flow rate is high relative velocity of flow will be more axial so blades should pitch vertically.
Types of Hydro Turbines:
The type of hydropower turbine selected for a project although same principles apply to all turbines is based on the height of standing water referred to as “head” and the flow, or volume of water, at the site their specific designs sufficiently to merit separate description. Other deciding factors include how deep the turbine must be set means the height of reservoir and turbine, efficiency, and cost.
The impulse turbine generally uses the velocity of the water to move the runner mean that there is only kinetic energy available at the inlet of the turbine and discharges to atmospheric pressure. The water stream hits each bucket on the runner peloton wheel is an example of impulse turbine. The down side of the turbine has no suction and the water flows out the bottom of the turbine housing after hitting the runner. An impulse turbine is generally suitable for high head in which water strike the turbine at high speed.
In a reaction turbine, the blades sit in a much larger volume of fluid the kinetic energy and pressure energy is available at the inlet of the turbine and turn around as the fluid flows past them. A reaction turbine doesn’t change the direction of the fluid its example is Francis turbine and Kaplan turbine flow as drastically as an impulse turbine: it simply spins as the fluid pushes through and past its blades.
Generation of Power:
In nature, energy cannot be created or destroyed, but its form can change in hydropower plant water energy is converted into electrical energy. In generating electricity, no new energy is created. Actually one form of energy which is mechanical energy is converted to another form like electrical energy. To generate electricity, water must be in motion. When water is in moving form it has kinetic energy.
The dam is made at certain height to create falling water. Also controls the flow of water through valves. The theory is to build a dam on a large river we will select such a place which will between two mountains so that we can easily block the flow of water in the reservoir usually such place is selected for the water reservoir which is at certain height that has a large drop in elevation. The dam stores lots of water behind it in the reservoir three gorges dam is world largest dam that has huge reservoir to store water. Near the bottom of the dam wall there is the water intake nozzle which will cause the water to flow at high pressure so that turbine rotates at high speed.
The water flow from the water reservoir in penstock there is also valve in the penstock with the help of which we can stop the flow of water.
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The force of falling water pushes the blades of turbine to rotate.
Water turbine is same like windmill except water turbine use water to rotate the blades while wind mill use wind to rotate the blades. The turbine converts the kinetic and potential energy of falling water on propellers into mechanical energy. At the end of the penstock there is a turbine propeller, when the water fall on the propeller at will start rotation. The propeller is than connected with the shaft when the propeller rotates the shaft will also rotate.
Generator is Connected by shaft and gears to the turbine so when the turbine rotates it causes the generator to rotate also which will converts the mechanical energy from the turbine into electric energy with the help of generator. Generators in hydropower plants work just like the generators in other types of power plants.. When flowing water turns blades in a turbine, turbine shaft rotation convert hydel energy into mechanical energy. The turbine turns the generator rotor which will convert the energy produced by the shaft rotation mechanical energy is converted into electrical energy. Since water is the initial source of energy, we call this hydropower or hydroelectric power for short.
Electric power transmission and distribution:
Electricity is supplied to our homes by the Power lines that are connected to the generator. A single large power plant can generate enough electricity 2 giga watts to supply a couple of hundred thousand homes.
|Mega watt||Volt Ampere|
The generator produce voltage is about 20-22 KV. The voltage from the power station is transfer to the substation where step-up transformer the voltage to transmit it large distance. The voltage is supplied in power lines. When the voltage is increased the current losses will be decrease. In step transformer 12000V is step-up to 240000V. It increase the voltage about 10 times. Now this voltage is transmitted to other substation where step-down transformer is located through high voltage transmission lines. The transmission lines are:
- 765 KV
- 500 KV
- 345 KV
- 230 KV
- 138 KV
If a large factory came in way of these high transmission lines which require large power rating can also get voltage line directly from these transmission lines. These transmission lines supply voltage to the substation where the voltage is step down to 11KV which is further step down by the transformers that are located in our streets, cities to 220V.
Types of Hydro Power Plant
There are three main types of hydro plants.
The most common type of hydroelectric power plant is an impoundment facility which uses a dam to create a large reservoir of water. An impoundment facility, typically a large hydropower system, in impoundment facilities a large dam is made to store water coming from river, lake, ocean in a reservoir. Water released from the reservoir flows through penstock on turbine where propeller rotates when water fall on it which in turn activates a generator to produce electricity. The water maintains constant reservoir level to meet changing electricity needs in summer season we release water from the reservoir because the water level increase in summer.
Pumped storage facilities
Pumped storage facilities are also known as peak load plants. Peak loads plants are those types of plants which supply the power plant during the peak hours. There are two types of load duration one is base load duration and other is peak load duration. In peak duration the hours generally rises from base value to high value. During the high values in pump power plants we have two reservoirs upper reservoir and lower reservoir. During the peak hours of the load the penstock valve open the upper reservoir and the water from the upper reservoir flow to the power plant which is situated at lower place. In this power plant there is reversible turbine during the peak hours this turbine work as generator turbine and generate the electrical power. This electrical power is transmitted to the substation from where it is transmitted to our homes through transmission lines. The water which came from the upper reservoir is store in the lower reservoir. During the off peak loads the reversible turbine behaves like motor pump which will again raise the lower reservoir water to upper reservoir water. This process will work in cycle to generate electrical power.
- Run-of-river facilitiesrely more on natural water flow rates we have no reservoir to store water, diverting just a portion of river water through turbines. The water at the top is known as head water and the water at the bottom is known as tail water. So the upper elevation is head water and the lower elevation is tail water. Difference in the height is known as head pressure. The pondage area will store small portion of water and divert it to the power station. We have weir which will change the flow characteristics of the river. As it has no reservoir the amount of electricity depending upon the season in summer as water flow is large so maximum electricity will be generated. In the winter season the water is frozen and the water level in the rivers will drop and no electricity will be generated. The trash rack will stop the rubbish to go to power station. Sluice gate is for emergency to stop water. The water through penstock come to the turbine in volute casing and then it will drop to the bottom the water will exit through draft tube. In volute casing we have a turbine.Since run-of-river hydro is subject to natural water variability, it is more intermittent than dammed hydro.
Energy generated by dam calculation:
To calculate the generation of the dam we must know the following factors:
Height of the dam:
Let suppose that the water reservoir is 20 feet high means that water falls from 20 feet on the turbine.
Amount of water flowing:
We will calculate the water flow rate in cubic feet per second let suppose that water flow rate is 500 cubic feet per second.
Efficiency is the conversion of power of falling water into electric power. It is 60 to 65 % for older power plants. While for newer power plants, well operated plants this might be as high as 80 to 90%.
Power of the Dam
Power= (Dam heigh×flow rate×efficiency)/11.8
The electric power will be in kilowatts. The 11.8 value convert feet and seconds into kilowatts. By assuming the above values we will calculate the power of dam:
Power= (Dam heigh×flow rate×efficiency)/11.8
So in one hour 678 kilowatts power is generated now to calculate the total power generated in year:
To calculate total power generated in year, we multiply the power from our dam by the number of hours in a year.
Electric Energy = 678 kilowatts x 24 hours per day x 365 days per year
Electrical energy= 5939280 kilowatt hours.
Now we will calculate that how many people is served from this energy. Now let suppose that every person use about 3,000 kilowatt-hours energy.
People served= (Electrical energy)/(energy per person)
Which is approximately equal to 1980. Thus 1980 people will be served from this power plant.
SIZES OF HYDROELECTRIC POWER PLANTS
According to the power requirement and size the hydropower is divided into the following types.
Large hydropower range is from 10 to 30 megawatts (MW).
The small hydropower range is from 1 to 100KW are called micro hydro power plant. Mini hydro power range is from 100KW to 1MW.
Hydropower relies on the water cycle
Hydropower works on water cycle. The water cycle has three steps:
- Solar energy sun heats water on the surface of lakes, rivers, and oceans, which causes the water to evaporate.
- Water vapor condenses into clouds and falls as precipitation rain and snow.
- The water come down in form of rains and snow fall which empty into oceans and lakes
- The water will evaporates and the water cycle will start again.
Seasonal variations in precipitation and long-term changes in precipitation patterns, such as droughts, can have large effects on the availability of hydropower production.
Advantages of a hydroelectric power plant:
- No fuel is required as potential energy is stored in water this energy is converted in kinetic energy and mechanical energy for electricity generation.
- Neat and clean source of energy.
- Hydro energy is available free of cost
- No pollutant are released by the hydroelectric power plant
- Comparatively less maintenance is required and has longer life
- Serves other purposes too such as irrigation
- Reliability of hydroelectric power plant is more.
- It has longer life.
- Less man power is required for operation of plant.
Site Selection of hydroelectric power station:
- Availability of water
- Geological structure
- Type of land
- Transportation facilities