hydal power plant

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


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


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.


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.

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