Hydropower Generation

7/29/2019 Hydropower Generation

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HYDROPOWER GENERATION

THROUGH RESERVOIR

sUBMITTED BY :-MOHIT AGARWAL

MOHIT BANSALMANISH MUNDRA

MANGAL CHAND


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Principle of Hydropower Generation

Hydropower is generated from the water

flowing in the river or oceans. There are two

water cycles involved in the generation of

electricity. One water cycle is the natural cycleand the other is inside the hydropower

station.


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Water cycle in nature:

In our natural environment there are number of oceansand rivers and then there is sun above them all. Due tosolar energy the surface of the rivers and oceans getheated due to which the water on the surface

evaporates. The evaporated water vapors movetowards the upper layers of the atmosphere wherethey form the clouds. Upon precipitation of clouds rainoccurs. Due to heavy rains large quantities of waterflows through various parts of the earth in the forms of

streams, channels and rivers. All the water from riversis collected back to the oceans, where evaporation ofwater occurs again.
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Water cycle in the hydraulic power

plant

The water in rivers posses two types ofenergies: kinetic energy and potential energy.

The energy of water due to its motion is called

as kinetic energy The energy of water due to its high level is

called as potential energy.

Depending on the type of hydraulic powerplants kinetic and/or potential energy of wateris used to generate electricity.


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The most commonly used method of productionof electricity from hydropower is by dams, whichare constructed across the large rivers.

The large quantities of water from river arediverted by pipelines also called as penstock,towards the main plant where large turbines arelocated.

The water from penstock is allowed to fall on thelarge turbine blades that start rotating. The shaftof the turbine rotates in the electric generatorswhere electricity is generated.

This electricity is then passed to the transformersfrom where it is connected to the main nationalgrid.


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The water leaving the turbine flows back to the

river at the lower levels. In almost all the plants

where water is used to generate electricity, themotion of water is used to rotate the turbine

which generates the electricity in the generators

and the water flows back to the river or ocean.


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Working Principle of Hydroelectric

Power Plant

The water flowing in the river possesses two

type of energy: the kinetic energy due to flow

of water and potential energy due to the

height of water. In hydroelectric power plants

or dams potential energy of water is utilized to

generate electricity.


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The formula for total power that can be generatedfrom water in hydroelectric power plant due to itsheight is given by

P = rhg Where: P is the total power that can be produced in

watts

r- is the flow rate of water measured in cubic meters

per second. h- is called height of water measured in meters. It is

also head of water. It is difference in height betweenthe source of water (from where water is taken) andthe waters outflow (where the water is used to

generate electricity, it is the place near the turbines). g- is the gravity constant 9.81 m/second square


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The formula clearly shows that the total power

that can be generated from the hydroelectric

power plants depends on two major factors: the

flow rate of water or volume of flow of water and

height or head of water.

More the volume of water and more the head ofwater more is the power produced in the

hydroelectric power plant.

To obtain the high head of water the reservoir ofwater should as high as possible and power

generation unit should be as low as possible


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Various Components of

Hydroelectric Power Plants and

their Working

There are eight important components of the

hydroelectric power plant.

All these components and their working have

been described below:


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1) DAM

The dam is the most important component of

hydroelectric power plant. In fact the name

dam is considered to be synonymous to the

hydroelectric power plant. The dam is built

on a large river that has abundant quantity of

water throughout the year. The dam is built at

location where the height of the river issufficiently high so as to get maximum

possible potential energy from water.


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2) Water reservoir

Water reservoir is the place behind the damwhere water is stored. The water in thereservoir is located at the height above the

rest of the dam structure. The height of waterin the reservoir decides how much potentialenergy water possesses. Higher the height ofwater more is its potential energy. The high

position of water in the reservoir also enablesit to move downwards effortlessly due togravity.


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3) 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.

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 wellas kinetic energy.


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4) The penstock

The penstock is the long pipe or the shaft thatcarries the water flowing from the reservoirtowards the power generation unit that

comprises of the turbines and generator. The water in penstock possesses kinetic

energy due to its motion and potential energydue to its height.

The amount of water flowing through thepenstock is controlled by the control gates.


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5) Water turbines

When water falls on the blades of the turbine the kinetic andpotential energy of water is converted into the rotational motion ofthe blades of the turbine.

Due to rotation of blades the shaft of the turbine also rotates.

The turbine shaft is enclosed inside the generator.

There is large difference in height between the level of turbine andlevel of water in the water reservoir. This difference in height, alsocalled as head of water, decides the total amount of power that canbe generated in the hydroelectric power plant.

The type of turbine used in the hydroelectric power plant depends

on the height of the reservoir, quantity of water and the totalpower generation capacity.


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6) Generators

It is in the generator where the electricity is produced.

The shaft of the water turbine rotates in the generator,which produces alternating current in the coils of thegenerator.

It is the rotation of the shaft inside the generator thatproduces magnetic field which is converted intoelectricity by electromagnetic field induction. Hencethe rotation of the shaft of the turbine is crucial for theproduction of electricity and this is achieved by the

kinetic and potential energy of water. Thus inhydroelectricity power plants potential energy of wateris converted into electricity.


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7) Transformer The electricity generated inside the generator is not of

sufficient voltage.

The transformer converts the alternating current producedfrom within the generator to the high voltage current.

The transformer comprises of two coils: the supply coil andthe outlet coil.

Current is supplied to the supply coil, from where it passesto the outlet coil. The number of turns in the outlet coildecides the voltage of output electricity from the

transformer. If the numbers of turns in outlet coil are double of supply

coil, the voltage produced is also double.


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8) Tailrace

The water that has been used to rotate the turbineblades and turbines shaft leaves the power generationunit entering the pipeline called as the tailrace. Fromhere the water flows into the main river.

The height of water in the tailrace is much below theheight of water in the water reservoir behind the dam.

The potential energy of water in the tailrace has beenused to generate electricity.

The water flowing out from the tail race joins thenatural flow of water.
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Advantages of Hydroelectric Power

Plants

No fuel required : This is the biggest advantageof hydroelectric power plants. They utilises therenewable energy of water for producing power.

Cost of electricty is constant : As thesehydroelectric power plants dont utilize fuel likecoal, oil, natural gas whose cost goes onfluctuate in international market so the cost ofelectricity produce by them is more or less

constant. Moreover the country doesnt have toimport these fuels thus saving lots of localcurrency.


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No air pollution created : As discuss above nofuel consumption for generating electricitydirectly implies that no air pollution will be

created in power generation. Long life : They possess a longer life than

thermal power plants. There were somehydropower plants that were built aboutmore than 50-100 year ago and are stillrunning.


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Low operating cost : For the working of power plant veryless labour is required since most of the operations areautomated, thus have low operating cost. Further , aspower plant become older cost of generating electricitybecome cheaper since initial cost invested in plant is

recovered over long period of operation. Can easily work during high peak daily loads : The daily

demand of power is not constant throughout the day.There will be peak demand of power during night. It is verydifficult to start and stop the thermal or nuclear power

plant on daily basis. The hydroelectric power plants canesily be started and stopped without consuming muchtime.


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Irrigation of farms : Water from dams are alsoused for irrigation of farm lands and producegood yield of crops in the area where there is

scarcity of water or where there is no rainfall. Water sports and gardens : Public recreation

activity can be held in the vicinity of reservoir bydeveloping water parks for water sports and

gardens. Prevent floods : The dams also help to prevent

floods in the area adjoining the large rivers.


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Drawbacks & Disadvantages of

Hydroelectric Power Plants

Disrupts the aquatic ecosystems : The dams leads to largescale destruction of aquatic life. There are chances thatfishes and other aquatic animal may enter the penstockand reach to the turbines where they can be crashed.

Disruption in the surrounding areas : The plants and animallife around the rivers thrives due to fresh continous flow ofriver water. But due to construction of dam across the rivermany areas have to be cleared which ultimately leads todistruction of aquatic life. In many cases a lots of trees haveto be cut which not only destroy plants life but also the

animals dependent on them. Even changing the course offlow of water will lead to large scale distruction of plantand animal life.


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Requires large areas : The construction of dam, powergenerating unit, transformer and their connection tonatural grid require large areas of forest. The larger thearea acquired by dam more will be the destruction of

natural ecosystem in surrounding forest. Large scale human displacement : During the running

of the project the main issue that comes is the shiftingand resettlement of the human beings in the nearbyarea of construction site. People are snatched away

from their shelter as well as source of income but arenot getting the proper remuneration and land forresettlement which will lead to large scale revolt andopposition against construction of dams.


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Very high capital cost or investment :Construction of hydroelectric power plantsrequire high initial cost. It also take long time forconstructing a hydropower plant. Lots of

planning, designing, and testing goes on duringconstruction. Each dam is unique in itself so thedesigns cannot be standardized. Construction ofdams require lots of steel, iron, cement which

make the hydroelectric power plant veryexpansive. . Overall, lots of time, money andhuman efforts are invested in the construction ofhydroelectric power plants.


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High quality construction : The quality of materialrequire for construction should be very high since anybreakage in the dam lead to large scale destruction ofhuman, plant, and animal lives.

Site specific : The construction of dams can not bedone at any location. It will only be constructed in areawhere abundant quantity of water is available atsufficient height and throughout the year. A number of

others safety parameters are also have to beconsidered. Construction of dam at inappropiatelocations can cause human casualties.


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Affects on environment : Although hydropower plantsdont emit greenhouse directly but yes they pollute theenvironment indirectly. . Over several years, a numberof vehicles coming to the construction site for loading

and unloading materials also emit greenhouse gasesthat directly affect the sensitive plants and animal lifefound in forests.

Safety of dams : The safety of dam is very crucial as it

affects the lives of millions of people. In these dayswhen terrorists attack are increasing there are greaterconcerns for the safety of large dams.


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A case study of Hydroelectric

Project


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Objective of the project:

Subansiri Lower project is located in Dhemaji and

Lower Subansiri districts in the states of Assam andArunachal Pradesh.

Project is proposed to harness hydro potential of lowerreaches of river Subansiri.

The project envisages harnessing 2000 MW of powerutilizing 100m of maximum gross head by constructionof 133m high concrete gravity dam. Water is led toPowerhouse through 8 no 9.5m diameter headracetunnel. The powerhouse is proposed to house eight

units of 250 MW each. The design energy works out tobe 7421.59 MU. The same shall increase to 7722.90MU considering regulated releases from Subansiriupper and Subansiri Middle projects.


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Project Features

Dam : 133M high dam, 25 L Cumconcrete,

Power House : 285M x 61M x 64M, Foundation

at 35m below river level,

Intake structures : 2 x 4 units at 30 m c/c,

HRT : 8 nos of tunnels of 9.5m dia ,

Turbines/Generators : 8 x 250 MW,

Power Generation

Installed Capacity : 2000 MW

Energy Generation : 7421.59 MU In 90% Dependable

Year

Special Features


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Special Features

Benching for UG

excavation done by high

capacity ripper/Dozer.All aggregate source

from River Bed Material.

Soft rock tunneling for

HRT/Surge tunnel.UG excavation is carried

out by special equipment-

Road Header.

Dam concreting is

carried out by Special

system-Rotec-USA


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The various structures under construction are:

1) HRT INTAKE STRUCTURE

It consists of 2 intakes each having 4 units at 30m c/c.

A shaft is present in front of the gates It has 150mm dia. perforations @ 1.2m c/c. This

arrangement maintains equal water pressure on both the sides of the front wall.

There are 2 gates i.e. Bulk Head and Service Gate. In the upstream side there is a

DPT (differential pressure tube) which measures the pressure difference between

the reservoir head and the pressure head in the tunnel. In the downstream side

there is another pipe to record the water level. In addition to this, there is also a

air vent pipe between the gates to remove any trapped air between gates.


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2)Head Race Tunnel (HRT)

Nos : 08

Size & shape : 9.5M dia, Horse Shoe Shape

Lengths : 608.00 to 1168.82m

Total Length : 7128 Rm

Design Discharge : 322.4Cumecs

The tunnels are at a slope of 1 in 250 and 1 in 100.The excavated diaof the tunnel is 11 m.

To Stabilize the rock in upper part of the structure Shotcrete of150mm thick, Rock Anchor/rock bolt of 32mm dia 5m length @1.5m staggered ,Rib Support of ISMB250 @ 1m Spacing areprovided.

In the finished structure 600mm of high performance RCC lining is

provided (M25,A 40)/(M60,A20).Lining of the upper curved part istermed as OVERT and lower part is termed as INVERT. A Steelstructure(Steel Shutter) termed as GANTRY is used as Formwork forConcrete Lining.

ROCK BOLT


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ROCK BOLT:

Drilling is done by Tamrock/Ro-bolt of desired length and thenresin is inserted into the drilled

holes. Anchor rod is insertedgiving a slow rotationalmovement. This punctures theresin capsule and the part ofanchor rod dipped in resin getsfixed in rock mass. This part is

known as fixed length. In thefree zone, there are two PVCpipes, one reaches almost tothe fixed part and another inthe end part of it. Thereinforced element is stressedimmediately after installation by

providing torque or jacking.After stressing the free length, itis grouted through the longerPVC pipe until it comes out fromthe other pipe.

3) Pressure Shafts


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)

Number : 08

Shape : Circular

Diameter : 9.5 / 8 / 7 m

Lengths : 220 M to 266 m(Including Steel Lined Portion of 220m)

Length (Upper Part) : 472.15m

Length (Vertical Part) : 383.20m

Length (Lower Part : 967.57m

HRT is followed by UHPS (Upper horizontal pressure shaft), verticaldip of 48m in VPS (Vertical pressure shaft) and LHPS (Lowerhorizontal pressure shaft). The pressure shafts have Ferrule lining

of 25mm.The width of the steel liner varies from 2 to 3m. They arejoined by welding and ultrasound test is done to check any airtrapping, sludge deposition has taken place at the joint.Thediameter of these pressure shafts goes on reducing as waterreaches the turbine.

5) SURGE TUNNEL


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5) SURGE TUNNEL

ADITS >>

Nos : 03

Size & shape : 9M D-Shaped

Total Length : 1562.386

Surge Tunnels >>

Nos : 08

Size & shape : 9.5M dia, Horse Shoe Shape

Lengths : 390 to 450m Total Length : 3395.00m

Surge Shafts >>

Nos : 08

Size & shape : 9.5M dia, Circular Length : 9.6 to 11.6m

Total Length : 81.3m

The concept of surge tunnel is introduced so as to absorb the surgecreated due to water hammer pressure in the HRT.


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There are 8 number of tunnels of 11m dia.(Excavation dia) and

9.5m(Finished dia) at a slope of 1:10.The length of tunnel varies from

390m in ST-8 to 450m in ST-1. The total length of the adit is 1.5 km which

provides access to 8 tunnels. The excavation is done using the samemachineries as in HRT .Surge tunnels are meant for absorbing the huge

pressure generated in the main tunnel at the time of the sudden closure

of the inlet gate at the power house site.

6) TAIL RACE CHANNEL

Length : 206M

Width : 35M

Tail race channel has been proposed to be built up at the downstream sideof the Subansiri River in the Power House. These tunnels will take the

water from the power house to the river at the downstream side and are

built at EL 76.

Documents

Hydropower Generation