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HYDRO ELECTRIC POWER PLANT
INTRODUCTION The energy of water utilized for hydro-power generation may be
kinetic or potential Kinetic energy of water is its energy in motion and is a function of
mass and velocity Potential energy is a function of the difference in water in between
two points Life of hydro power plant is higher than thermal and nuclear
power plants However capital cost for the construction and commissioning is
more than TPS and NPS It requires less man-power Less pollution Unit cost of production of energy is low, because main fuel is water
HYDROLOGY
Precipitation: Water falls from atmosphere to the earth surface by two ways
(i) Liquid precipitation (Rain fall)(ii) Solid precipitation (snow, Hail)
Some part of precipitation is lost due to evaporation, interception and transpiration
Transpiration: Plants absorbing moisture and giving it off to the atmosphere
• Stream flow = precipitation – losses• Surface flow is also known as run-off.Run-off: It is that portion of precipitation which makes its way
towards streams, lakes or oceans
HYDROLOGY
First requirement – Q (discharge) Hydrology deals with occurrence and
distribution of water over and under earth’s surface.
Surface Water Hydrology Ground Water HydrologyWatershed, catchment area or drainage area: length of
the river, size and shape of the area it affects, tributaries, lakes, reservoirs etc.
OBJECTIVES OF HYDROLOGYTo obtain data regarding the stream flow of water that
would be available, To predict the yearly possible flow To calculate the mean annual rainfall in the area under
consideration from a record of the annual rainfall for a number of years, say 25 to 30
To note the frequency of dry years To find maximum rainfall and flood frequency
HYDROGRAPH It is a graphical representation between discharge
and time shows the variation of stream flow in m3/s with
time for a particular river site. The time may be hour, week, month or a year.
The area under hydrograph gives the total volume of flow
Storage: to ensure water availability during deficient
flow and thus increasing the firm capacity Storage also results in more energy production Pondage: Storing water in small ponds near the power
plant as the storage reservoir is away from plant
To meet the power demand fluctuations over a short period of time
SITE SELECTION FOR HYDROPOWER PLANTS Availability of Water: Run-off data for many years
available• Water Storage: for water availability throughout the
year• Head of Water: most economic head, possibility of
constructing a dam to get required head• Geological Investigations: strong foundation,
earthquake frequency is less• Water Pollution: excessive corrosion and damage to
metallic structures
SITE SELECTION FOR HYDROPOWER PLANTS
• Social and Environmental Effects: submergence of areas, effect on biodiversity (e.g. western ghat), cultural and historic aspects
• Access to Site: for transportation of construction material and heavy machinery new railway lines or roads may be needed
• Multipurpose: power generation, irrigation, flood control, navigation, recreation; because initial cost of power plant is high because of civil engineering construction work
CLASSIFICATION OF HYDRO-ELECTRIC PLANTSHydro power plants are classified Based upon (1) Quantity of water available(2) Available Head(3) Nature of load
classification of hydro-electric plants According to water available
A. Run-off River plants Without PondageB. Run-off River plants With PondageC. Reservoir Plants
Run-off river plants without pondage
It doesn’t store water, It uses water as it comes It uses water only when available Generating capacity primarily depending on the rate of
flow of water During rainy season some quantity of water wasted
without using for the generation of power During low run-off periods due to low flow rates , the
generating capacity of plant is low
Run-off river plants with pondage
Usefulness of a run-off river plant is increased by pondage
Pondage permits storage of water during the off-peak periods and use of this water during peak periods
It is cope up by the size of the pondage This plant can be used on parts of the load curve
requirement, within certain limitations It is more useful than a plant without pondage or storage
RESERVOIR PLANTS
Majority of the plants are this type. It permit carrying over storage from wet season to the
next dry season Water is stored behind the Dam and is available to plant
with proper control It has better capacity and can be used through out year It can be used as a base-load plant or peak load plant as
required It can also be used on any portion of the load curve as
required
Classification of hydro-electric plants According to Available Head
a. Low head (2-30m)b. Medium head (30-70m)c. High head (71-500m)
LOW HEAD PLANTS Small dam is built across the river to provide the
necessary head(upto 30m) The excess water is allowed to flow over the dam itself Used turbines: Francis, Propeller or Kaplan turbine No surge tank is required
MEDIUM HEAD PLANTS Forebay is provided at the beginning of penstock serves
as water reservoir for such plants Generally in this plants water carried in open canals from
main reservoir to the forebay and then to the power house through penstock. The forebay itselfs works as a surge tank
Prime mover or Turbines: Francis, Propeller and Kaplan
HIGH HEAD PLANTS All water is carried from the main reservoir by a tunnel
upto the surge tank and then from surge tank to the power house through pen stock
Heads more than 300 m Pelton wheel turbine preferred
Classification of hydro-electric plants According to Nature of load
A. Base load plantsB. Peak load plantsC. Pumped-storage plants for peak loads
BASE LOAD PLANTS
Such loads can take up the load on base portion of the load curve
In this type plants load is almost constant Load factor is high Run-off power plants without pondage can be used as
base load plant Similarly the plants which has storage also work as base
load plants
PEAK-LOAD PLANTS
Run-off river plants with pondage can be used as peak-load plants
Reservoir plants with water storage back side dam may be used as either base-load plant or peak load plant as required
Note: Plants used to supply the peak load of the system corresponding to the load at the top portion of the load curve are known as peak-load plants
pumped storage plants for peak-load Water after passing through the turbine stores in tail-race pond, Where it
may fed back to the head water pond Water send from tail-race pond to Head water pond during off-peak
period During peak load period water passes from Head water pond to the
penstock to operate the turbines It can recover 70% of the power by using pumping water By using reversible-turbine-pump unit a turbine can generate power and
a pump while pumping water to storage. The generator is worked as a motor during reverse operation So that efficiency is high The cost of reversible-turbine-pump sets increases It meets peak loads
COMPONENTS OF HYDRO ELECTRIC POWER PLANT
The various components of HPP are as follows:1. Catchment area2. Reservoir3. Dam4. Spillways5. Conduits6. Surge tanks7. Draft tubes8. Power house9. Switchyard for power evacuation
COMPONENTS OF HYDRO ELECTRIC POWER PLANT
Dam Develops a reservoir to store water Builds up head for power generation
Trash Rack: It is provided to stop the entry of debris. Which might damage the gates turbine runners or choking of nozzles of the impulse turbines. It is placed across the intake
Spillway To safeguard the dam when water level in the
reservoir rises
COMPONENTS OF HYDRO ELECTRIC POWER PLANT
Intake Contains trash racks to filter out debris which may
damage the turbineForebay Enlarged body of water just above the intake
INTAKE OR CONTROL GATES
These are the gates built on the inside of the dam. The water from reservoir is released and controlled through these gates. These are called inlet gates because water enters the power generation unit through these gates. When the control gates are opened the water flows due to gravity through the penstock and towards the turbines. The water flowing through the gates possesses potential as well as kinetic energy.
COMPONENTS OF HYDRO ELECTRIC POWER PLANT
Conduits Headrace is a channel which lead the water to the turbine Tailrace is a channel which carries water from the turbine A canal is an open waterway excavated in natural ground
following its contour. A tunnel is a closed channel excavated through an obstruction. A pipeline is a closed conduit supported on the ground. Penstocks are closed conduits for supplying water “under
pressure” from head pond to the turbines.
The Penstock The penstock is the long pipe or the shaft that carries the water
flowing from the reservoir towards the power generation unit, comprised of the turbines and generator. The water in the penstock possesses kinetic energy due to its motion and potential energy due to its height.
The total amount of power generated in the hydroelectric power plant depends on the height of the water reservoir and the amount of water flowing through the penstock. The amount of water flowing through the penstock is controlled by the control gates.
SURGE TANK
A surge tank is a small reservoir in which the water level rises or falls to reduce the pressure swings so that they are not transmitted to the penstock.
Water Hammer Load on the turbine is suddenly reduced Governor closes turbine gates Sudden increase of pressure in the penstockNegative Pressure Load on the generator is suddenly increased Governor opens the turbine gates Tends to cause a vacuum in the penstock When the gates are closed, water level rises in the surge
tank and when the gates are suddenly opened, surge tank provides the initial water supply
Draft TubesThe function of the draft tube is to To reduce the velocity head losses of the water To allow the turbine to be set above the tailrace to
facilitate inspection and maintenance
Tailrace: A tailrace is required to discharge the water leaving the
turbine into the river. The design of the tail race should be such that water has
a free exit.
TYPES OF HYDRAULIC TURBINES
1. According to the head and quantity of water available
a. Low head (2-15m)b. Medium head (16-70m)c. High head (71-500m)d. Very high head (>500m)2. According to the name of the originatora. Francisb. Kaplanc. Pelton
3. According to the nature of working of water on blades
Example:Find out the specific speed of a turbine of 10 MW capacity
working under a head of 500m and having the normal working speed of 300 RPM.
4. According to the direction of flow of watera. Radialb. Axialc. Tangential (Deriaz)5. According to the axis of the turbine
shaft: vertical, horizontal
COMPARISON OF TURBINES
SWITCHYARD
1. Step up transformers2. Instrument transformers3. Transmission lines
POWER HOUSE
POWER HOUSE
1. Hydraulic turbines2. Electric generators3. Governors4. Gate valves5. Relief valves6. Water circulation pumps7. Air ducts8. Switch board and instruments9. Storage batteries10. Cranes
ADVANTAGES OF HYDROELECTRIC ENERGY
1) It is a non-polluting source of energy.2) It has lower operational cost compared to fossil fuel-based generation
plants.3) Can be easily transmitted through wires to long distances.4) Dams made for generation of Hydroelectricity also help in irrigation
projects.
DISADVANTAGES
1) It can be generated only in areas with heavy rainfall and sufficient supply of water.2) Hydel power generation stations are to be located in hilly mountainous terrains where waterfalls as well as ideal sites for dams are located. In a region/country without hills hydel power generation is not possible.3) Loss during transmission is very high, sometimes up to 30%.4) Dams are expensive to build.5) Building a dam affects the environment and wildlife of adjoining areas. Nearby low-lying areas are always under the threat of floods.6) Building of dam causes lot of pollution.7) If rains are scarce, there might not be enough water to turn turbines.
https://www.youtube.com/watch?v=Lx6UfiEU3Q0
http://www.electricalquizzes.com/electric-power-generation/electric-power-generation-mcqs-3