Hydro Power
A generating station which utilizes the potential of energy of water at a
high level for the generation of
electrical; energy is known as hydroelectric station. Hydropower is energy that
comes from the force of moving water. The head of water fall and movement of
water in the form of kinetic or potential is called as Water cycle or
Hydropower cycle. Kinetic energy of water is energy motion and is function of
mass and velocity while potential energy is function of the differences in
level of water between two points. Prior to the widespread availability of
commercial electric power, hydropower was used for irrigation, and operation of
various machines, such as watermills, textile machines, sawmills, dock cranes,
and domestic lifts. A Hydro- electric power station is used to supply
electrical energy to consumers where water resources available.
Mainly the Hydro Power is depends on the rain. The rain defined
as, energy from the sun evaporates water in the earth’s oceans and rivers and
draws it upward as water vapor. When the water vapor reaches the cooler air in
the atmosphere, it condenses and forms clouds. The moisture eventually falls to
the earth as rain or snow, replenishing the water in the oceans and rivers.
The storage of rainy water is completely used
for year or more than a year. The hydro power is depends on the power
requirement can be defined as Base load station and Peak load station. In Base
load station the load requirement is constant through out the year and cost of
the power/unit is comparatively less.
In peak load station is used when the demand of power is more and cost of the
power/unit will be more. The time that a peak plant operates may be many hours
a day or as little as a few hours per year, depending on the condition of the
region's electrical grid The most of the time electricity will be used during
the day hours as the power is required for watermills, textile machines,
sawmills etc. The initial capital cost for the hydro power station is more and
running cost is less.
Hydro plants are more
energy efficient than most thermal power plants, too. That means they waste
less energy to produce electricity. In thermal power plants, a lot of energy is
lost as heat. Hydro plants are about 95 percent efficient at converting the kinetic energy of the moving water
into electricity.
Beginning of Hydropower in India
At that time Gold
mining was small business in
The implement and development of hydropower at
Later it was found that, the original agreement of 1900
between
Hydro
Electric Power Plants
Factors Affecting for
selection of Site for Hydro electric Station:
Amount of water available: Water is the main heart of Hydro power plants. Previous
records of rainfall are studied also minimum and maximum quantity of water available during
the year are estimated. After allowing for losses due to evaporation and
percolation the net volume of water available for
power generation can be determined.
Storage of water: Wide variation of rainfall during
the year makes it necessary to store water for continuous Generation of power
through out year. Intend to provide the sufficient storage for one year or
intend to provide the enough storage so as to useful during the worst dry
periods.
Head of water: The available water head depends
on topography of the area. This is the important factor and it decides the generation of power. low
falls on unregulated streams are subject to wide variations which affect the
net head, and may, in fact, reduce it to ab abnormality low value, uneconomical
for power generation.
Transportation facilities: The site selected for a Hydro
plant should be accessible by rail as well as by road.
Distance of Power site from Power grid: If the power site near to power
grid, the cost of power will be less. If it is far, the cost will be
more.
Types of Hydro Power Plants:
1 .Run-off Plants without Poundage:
As name indicates this type of plant doesn’t store water, the plant uses as
water comes.
2. Run-0ff plants with Poundage: Poundage permits storage of water during the off
–peak period and use of this water during peak periods.
3. Reservoir Plants: A
reservoir plant is that which has reservoir of such size as to permit carrying over storage from wet
season to the next dry season.
4 .Low head plants: In this case
small dam is built across the river to provide the necessary head. In such
plants Francis type of turbines are used.
5. Medium head plants: The fore
bay provided at the beginning of Penstock serves as water reservoir for such
plants. In these plants water is generally carried
out in open canals from reservoir to the Fore bay and then to thepenstock.
6. High head Plant: This plants works above 500mtrs and Pelton wheel
turbines are commonly used. In this plant water is carried out from the main
reservoir by a tunnel up to surge tank and then from the surge tank to
the power house in penstock.
7. Base Load Plants: These
Plants are mainly depending on the nature of load. Is demand is more, this
plants are used regularly and load factor of this plants are high.
8. Peak load Plants: These plants
are mainly used during the peak load. Run-off river plants with pondage can be
used as peak-load plants. reservoir plants with enough storage behind the dam
can be used either as base load or as peak load plants as required.
9. Pumped storage plants: These
plants are used when quantity of water available for generation is
insufficient. If it is possible to pond at head water and tail water locations
afterpassing through the turbine is
stored in the tail race pond from where it may be pumped back to the Head water
pond.
Achievement
of
In
1947, there were fewer than 300 large dams in
Between 1951 and 2000,
The Indian government has had programs to
promote power generation from renewable sources for the last 25 years, but the
cumulative power generation from these sources is only around 12,000 MW. he
Himachal Pradesh plant’s availability factor—the amount of time a power plant
can produce electricity over a certain period, divided by the amount of time in
the period—for the month of July 2009 was 105.26 percent, with the cumulative
factor for the station at 102.88 percent. This marks the highest factor achieved
by a central sector hydro power station operating in the northern grid.
Large dam
construction has been an important and expensive undertaking for the Indian
government. While dams have enhanced agricultural productivity in
By 2012, the country will see three new projects of 1,000 Mw and
above. These are the Karcham Wantoo project (1,000 Mw) in Himachal Pradesh, the
Tehri pump storage scheme of 1,000 Mw and the 2,000-Mw plant at Subansiri in
Arunachal Pradesh. Post independence we have made lots of progress in Dam and
Water Reservoirs in
Hydro
Power Stations in
In
Graph:
|
Hydro Power station |
Thermal Power Station |
Nuclear Power |
Other |
|
21% |
70% |
4% |
5% |
Thermal power plants are
generating electricity about 70%, 21% by hydroelectric power plants and 4% by
nuclear power plants. Some of the measures announced by; Govt. of India have
already been introduced which
include simplified procedures for transfer of techno-economic clearances,
streamlining of clearance process and introduction of three-stage clearance
approach for development of hydro projects in Central Sector/Joint Ventures,
etc. he Indian government considers hydropower as a renewable economic,
non-polluting and environmentally benign source of energy. Experience of running hydropower
stations in India has shown that even after careful project planning and good
quality control measures from construction to commissioning, unforeseen
problems do occur in service resulting in unplanned outages / low generation
and load shedding etc. This causes disruption toconsumers and reduced cash
generation for the operator.
Major Steps Taken By
1) The hydro-electric potential in
terms of installed capacity
is proposed to be about 148,700 MW out of which a capacity of 30,164 MW (20.3%)
has been developed so far and 13,616 MW (9.2 %) of capacity is under
construction.
2) In addition, 6,782 MW in terms of
installed capacity from small, mini and micro hydro schemes have been assessed.
3) Also, 56 sites for pumped storage
schemes with an aggregate installed capacity of 94,000 MW have been identified.
4) The government expects to harness
its full potential of hydropower by 2027 with a whopping investment of 5,000 billion Rupees.
5) Additionally,
Hydro
Power Generation in the World
The inherent technical, economic and
environmental benefits of hydroelectric power make it an important contributor
to the future world energy mix, particularly in the developing countries. These
countries have a great and ever-intensifying need for power and water supplies
and they also have greatest remaining hydro potential. When highlighted Hydro
Power in world, it was found that hydropower now supplies about 888.8GW or
above 25% of world electricity. Still the construction of large dams are going
on, specially the worlds largest is the Three Gorges Dam
on the third longest river in the world, the
World distribution of hydropower
- Hydropower is the most important and
widely-used renewable source of energy.
- Hydropower represents 25% of total
electricity production.
- There are so many Dams proposed which
are considered to be in list of Largest Dams. Presently the Three Gorges
Dam of China having capacity of 22.5GW generation capacity stands in the
first position and it will complete by the year 2011
Top Seven Countries in Hydropower generation
|
Country |
Annual
hydroelectric |
Generation |
|
585200 |
196.79 |
|
|
369500 |
88.974 |
|
|
363800 |
69.080 |
|
|
250600 |
79.511 |
|
|
167000 |
45.000 |
|
|
140500 |
27.528 |
|
|
115600 |
33.600 |
Top
Future Three Largest Dams Generating Power above 10GW
|
Name |
Capacity
(GW) |
Country |
Construction |
Completion |
|
39 |
2014 |
2025 |
||
|
22.5 |
1994 |
2011 |
||
|
13.050 |
2009 |
2015 |
Dam
A dam is defined as any
impounding structure that is either 25 feet in height, measured from the
downstream toe to the crest, or has a maximum impounding capacity of 50
acre-feet of water. The function of Dam is to provide a head of water to be
utilized in the water turbine. Though many Dams may be built solely to provide
the necessary to the plant a Dam also increases reservoir capacity. Dams
are built of concrete or stone masonary, earth or rock fill. The type and
arrangement depends upon the topography of the site. A masonary dam may be
built in a narrow canyon. An earth dam may be suited for a wide valley. The
type of dams also depends on the foundation conditions, local materials and
transportation available, occurrences of earthquakes and other hazards.
Structures that fail to meet these criteria but have the potential to
cause significant property damage or pose a threat to life in the downstream
area are regulated in the same manner as dams. All such structures except
federal dams and those permitted by the Division of Mine Reclamation
and Enforcement must be reviewed, and a stream
construction permit must be issued by this office. Design
criteria, hazard classification information and submittal requirements can be
found in the publication "Design Criteria for Dams and Associated
Structures."
Construction inspections
are performed periodically and during critical stages of work. Upon completion
of construction, the owner submits a notice of completion and as-constructed
drawings. When as-constructed drawings are received, a final inspection is
conducted. If all work is satisfactory, the owner is granted permission to
impound water and the completed dam is placed on the inventory of dams
maintained by the section.
Intended purposes include
providing water for irrigation to a town or city water supply,
improving navigation, creating a reservoir of water to supply industrial uses,
generating hydroelectric power, creating recreation areas
or habitat for fish and wildlife, retaining wet
season flow to minimize downstream flood
risk and containing effluent from industrial sites such as mines or
factories. Some dams can also serve as pedestrian or vehicular bridges across
the river as well. When used in conjunction with intermittent power sources
such as wind or solar, the reservoir can serve as pumped water storage to
facilitate base load dampening in the power grid. Few dams serve all of these
purposes but some multi-purpose dams serve more than one.
Failure of dams:
Water leakage: If there action is not taken at the right time when water leakage is
observed, leads to Dam failure. Proper maintenance is required to maintain the
dam for long life. It is necessary to anticipate any problems and action to be
taken before structure fails
Poor Maintenance: If maintenance is not carried at regular intervals, leading to Dam
failure.
Spillway design error: When river flow
exceeds the storage capacity, the dysfunctional spillway leads to dam failure.
Poor Survey: Dams built on slopes must be properly engineered to avoid issues with
instability or landslide. If it is still continued, leads to Dam Failure.
Material: Building material used for the dam should
be of high quality. Low quality building material leads to dam failure.
Maintenance: Poor maintenance like when water is
overflowing, if the Gates are not worked properly, leads to dam failure.
Foundation: Defects can occur in the foundation supporting the dam.
If this weight is not properly taken into account in the engineering of the
dam, the ground underneath can settle unequally and compromise the foundation
.Similarly, any event causing the movement of a foundation, such as an
earthquake, can also compromise a dam’s foundation. The main cause of concrete
dam failure is a problem with the foundation. High uplift pressures and
uncontrolled foundation seepage can also compromise the dam’s foundation. When
the foundation of an earth fill dam is composed of fine silt, clay, or similar
soft soil,
the whole dam may slide due to water thrust. If seams of fissured rocks, such
as soft clay, or shale exist below the foundation, the side thrust of the water
pressure may shear the whole dam and cause its failure. In such failure the top
of the dam gets cracked and subsides, the lower slopes moves outward and forms
large mud waves near the dam heel.
Seepage failure: Seepage always occurs in the dams.
If the magnitude is within design limits, it may not harm the stability of the
dam. However, if seepage is concentrated or uncontrolled beyond limits, it will
lead to failure of the dam. Following are some of the various types of seepage
failure.
i)
Piping through dam body: When seepage
starts through poor soils in the body of the dam, small channels are formed
which transport material downstream. As more materials are transported
downstream, the channels glow bigger and bigger which could lead to wash out of
dam.
ii)
Piping through foundation: When highly permeable cavities or fissures or
strata of gravel or boorish sand are present in the dam foundation, it may lead to heavy seepage. The concentrated
seepage at high rate will erode soil which
will cause increase flow of water and soil.
As a result, the dam will settle or sink leading to failure. Strength.
Disadvantages:
Human
land Loss: So many poor people are lost their lands as result of
Dams. People who already lost agricultural lands caused major unemployment in
some countries like India etc.
Failure
of dam: Dam is major storage of water. The dam failure leads,
too many people die and it is like flooding in small towns.
Overflow
of water: Over topping of dam during rainy season leads to vacate
the houses of many people in small towns.
Advantages:
Cheap: If the dam is
maintained properly, a hydroelectric power source is comparatively cheap.
Reliable: Once Dam is
constructed with well design and quality Engineers then dam will be having long
life and reliable. It has no fuel and low escape risk, and as an alternative energy source it is cheaper than
both nuclear and wind power.
Biggest
dam failure:
Banqiao
Shimantan-
The Bangiao Dam was originally designed to pass about 1742 cubic
meters per second through sluice gates and a spillway. The capacity storage
capacity was set at 492 million cubic meters with 375 million cubic meters of
this capacity reserved for flood storage. The height of the dam was at little
over 116 meters. Once the Banqiao and Shimantan Dams were completed many, many
smaller dams were built. Initially the smaller dams were built in the
mountains, but in 1958 Vice Premier Tan Zhenlin decreed that the dam building
should be extended into the plains of
1) On
5 August 1975, Banqiao Reservoir filled to close to maximum capacity. On that
day the reservoir rose to more than two meters above its designed safe
capacity.
2) On
the evening of 7 August Sluice gates were opened, but were found to be partly
blocked with sediment. Banqiao Dam was collapsed, and 500 million cubic meters
of reservoir water surged over the downstream valleys and plains at nearly 50
kilometers per hour. ‘Entire villages and small towns disappeared in an
instant.
3) By
August 8 the Banqiao and Shimantan Dam reservoirs had filled to capacity
because the runoff so far exceeded the rate at which water could be expelled
through their sluice gates. Shortly after midnight (12:30 AM) the water in the
Shimantan Dam reservoir on the
The
floodwaters from the reservoirs and rivers of the
The
vast lake ruptured transport and communications throughout the region, making
many areas inaccessible to disaster relief teams and medical workers. The
pseudonymous Chinese journalist describes the aftermath of the dam bursts:
4)
August 13: Two million people across the district are trapped by the water . In
Runan, 100,000 who were initially submerged but somehow survived are still
floating in the water. In Shangcai, another 600,000 are surrounded by the
flood; 4,000members of Liudayu Brigade in Huabo Commune have stripped the trees
bare and eaten all the leaves. People in the flooded areas who survived had to
face an equally harrowing ordeal. They were trapped and without food for many
days. Many were sick from the contaminated water
5)
August 17: There are still 1.1 million people trapped in the water . . . the
disease morbidity rate has soared. According to incomplete statistics, 1.13
million people have contracted illnesses . . .
6)
August 18: Altogether 880,000 people are surrounded by water in Shangcai and
Xincai. Out of 500,000 people in Runan, 320,000 have now been stricken with
disease, including 33,000 cases of dysentery . . .
Some
two weeks after the disaster, when the flood waters finally began to retreat in
certain areas of
Human
Rights Watch believes that the most likely interpretation of the few and
contradictory statistics available on the death toll from the disaster is that
85,000 were killed by the immediate flood waves from the failed dams, and a
further 145,000 died in the epidemics and famine which struck the area in the
ensuing weeks.
Role of Draft Tube in Hydro
Power Station
The draft tube is of welded steel
construction and consists of a cone and elbow liner. A water and air tight
man-hole access having clear opening with hinged door, bronze hinge
pins, stainless steel bolts and jacking screws has been provided in cone. A test cock and a pressure gauge are provided.
Slots are provided below the manhole for supporting an inspection platform.
When water flows on the turbine there is sudden pressure difference in existing
between water in the turbine and atmosphere. Therefore turbines are completely
enclosed. Hence it is necessary to connect the turbine outlet by means of a
pipe or passage like conic shape up to tail race level. The simplest and
most efficient, turbine draft tube is the conical shaped draft tube. It is usually vertical and is
designed with a truncated cone similar to an inverted ice cream cone. Originally,
turbines were designed without draft tubes. In order to work on the runner,
stop logs were inserted into the tailrace training walls and the discharge pit was pumped
out. It converts a large proportion of the velocity energy rejected from the
runner into useful pressure head i.e. it acts recuperates of pressure of
energy.
Penstock
Penstocks are open or closed conduits which carry water
to the turbines in hydro power stations. Penstock
is generally made of reinforced concrete or steel. Concrete penstocks
are suitable for low heads less then 30mtrs.The steel penstocks are designed
for any head. The thickness of penstocks increases with head or water pressure.
When the distance from the forebay to the power house is short separate penstocks are used for
each turbine. In high head dams, the penstocks are provided with penstock gates
or butterfly valves and air valves. The penstocks gates are fixed to initial of
penstocks, and flow of water is controlled by operating penstock gates. In high
head power plants the butterfly valve and air valve are provided in the power
houses. Air valve maintains the air pressure inside the penstock equal to
atmospheric pressure. When water runs out of penstock faster then it enters, a vacuum created which may cause the
penstock to collapse. Under such circumstances, air valve opens and admits the air in the penstock
to maintain inside equal to the outside pressure. If the butterfly suddenly
opens and water enters with high pressure there will be chances of penstock
collapse. Hence there is a water pressure valve fixed before the butterfly
valve, which maintains the water pressure at the both sides of penstocks
by bypassing butterfly valve.
Before operating the butterfly valve, this water pressure valve operates and
fills up the water at the other side of penstock. The setting of system is such
that the butterfly valve operates, when the water pressure at the both sides of
penstocks are equal.
There are two types of penstocks in which
are mainly used for power generation
Low Pressure Penstocks: The low pressure type consists of a
canal commonly flume or a pipe.
High Pressure Penstocks: The high pressure consists of steel pipes which
can take water under pressure.
Water Turbines:
Water
turbines are used to convert the energy water of falling water into mechanical
energy. A water turbine is a rotary engine that takes
energy from moving water. Water turbines were developed in the nineteenth century and were
widely used for industrial power prior to electrical grids.
Now they are mostly used for electric power
generation. They harness a clean and renewable energy
source. Flowing water is directed on to the blades of a turbine runner,
creating a force on the blades. Since the runner is spinning, the force acts
through a distance (force acting through a distance is the definition of work).
In this way, energy is transferred from the water flow to the turbine.
The
principal types of turbines are:
1)
Impulse turbine
2)
Reaction Turbine
Impulse
turbines: These types of turbines are mainly used in high head plants. In this
turbine the entire pressure of water is converted into kinetic energy in a
nozzle and the velocity of the jet drives the blades of turbine. The nozzle
consist of a needle, and quantity of water jet falling on the turbine is
controlled this needle placed in the tip of the nozzle. If the load on the
turbine decreases, the governor pushes the needle into the nozzle, thereby
reducing the quantity of water striking the turbine.
Newton's second law describes the transfer of
energy for impulse turbines.
Impulse
turbines are most often used in very high (>300m/984 ft) head
applications.
Power
The power
available in a stream of water is;
where:
- P = power (J/s or watts)
- η = turbine efficiency
- ρ = density of water (kg/m³)
- g = acceleration of gravity (9.81
m/s²)
- h = head (m). For still water, this is
the difference in height between the inlet and outlet surfaces. Moving
water has an additional component added to account for the kinetic energy
of the flow. The total head equals the pressure head plus velocity head.
=
flow rate (m³/s)
Examples
of Impulse turbines are:
Reaction
Turbine:
Examples
of reaction turbines are:
1)
Francis turbine
2)
Kaplan turbine
Reaction turbines are mainly for low and
medium head plants. In reaction turbine the water enters the runner partly with
pressure energy and partly with velocity head. Most water turbines in use are
reaction turbines and are used in low (<30m/98 ft) and medium
(30-300m/98–984 ft)head applications. In reaction turbine pressure drop occurs
in both fixed and moving blades. In this turbine the runner blades changed with
respect to guide vane opening. As the sudden decrease of load takes place, the
guide vane limit decreases according to that runner blade closes.
Spillways
Spillways may be considered a sort of
safety valve for a Dam. Passage for surplus water over or around a dam when the
reservoir itself is full. Spillways are particularly important safety features
for earth dams, protecting the dam and its foundation from erosion. They may
lead over the dam or a portion of it or along a channel around the dam or a
conduit through it. There are times when the river flow exceeds the storage
capacity of the reservoir. Such a situation arises during the heavy rain fall
in the catchments area. In order to discharge the surplus water from the
storage reservoir into the river on the downstream side of dam, spillways are
used. Spillways are constructed f concrete piers on the top of the dam. Gate
are provided between piers and surplus water is discharged over the crest of
the dam by the opening these gates.
There are two types of Spillways:
Controlled spillway
In this type Gates are provided to regularize the flow of water. When water is
overflowing the dam, gate are mainly used to control the pressure of water.
Uncontrolled spillway
In this type, gates are not provided. When the water rises above the ''crest''
of the spillway it begins to be released from the reservoir. The rate of
discharge is controlled only by the depth of water within the reservoir. All of
the storage volume in the reservoir above the spillway crest can be used only
for the temporary storage of floodwater, and cannot be used as water supply
storage because it is normally empty.
Role
of Hydro Electric Stations in Power Industry
In Power industry, three types of power
plants exist: the first one being Thermal (Fossil fuel powered), the other is
Nuclear Power plant (Energy released in fission reaction). The third one is
Hydro-Electric plant where power is generated from
the generator coupled with the turbine- turbine being rotated by water energy.
All types of power stations are linked together by HV/EHV transmission lines.
Power generated must be used as soon as it is generated. Thus, it is obvious
that at any time the power demand must by equal to generation. However, power
demand not often remains constant. It varies with time of day and in seasons.
Thus generation is needed to be
adjusted all through.
Thermal power plants are put into service throughout the day though the
generation capacity may to some extent vary. Nuclear plants supply the base
loads and hydro electric plants can be utilized to
take care of the flexibilities in
the generation and demand. Its power output can be altered very quickly. Hydro
electric plants can also be utilized as reserve capacity plants.
In some hydel power stations the dam is constructed only for irrigation
purpose. Power should be generated whenever water demand increased by farmers in irrigation
dams. Irrigation can be remarkably improved by routing the canals in the
downstream of the hydel plants. Draught and flood both can be effectively
controlled utilizing the dam
water and discharge water of hydel plants.
Though hydro-electric power can effectively serve major share in power generation still the
role played by it cannot be fully evaluated by the share of hydro power in the
overall production alone.
Apart from purely power generating aspect, hydel stations have most commendable
effect on environmental control and much lower man-power requirement.
Hydel-elecric power doesn’t pollute the atmosphere and the unit cost of
production of energy is obviously low as the main’ fuel’ is only water.
However, the hydel generation is to some extent dependent on weather
variations.
Pelton
wheel
A Pelton wheel, also called a Pelton
turbine, is one of the most efficient types of water turbines. It was invented
by Lester Allan Pelton (1829-1908) in the 1870s, and is an impulse machine,
meaning that it uses
The Pelton wheel turbine is a tangential
flow impulse turbine, water flows along the tangent to the path of the runner.
Studying the high head plants the Pelton turbines are designed. The Pelton
turbines are available in various sizes. Depending on that number of nozzles
decided. Nozzles are arranged around the wheel such that the water jet
emerging from a nozzle is tangential to the circumference of the wheel of
Pelton Turbine. Accordingly Nozzles direct forceful streams of water against a
series of spoon-shaped buckets mounted around theedge of a wheel. Each bucket reverses the flow
of water, leaving it with diminished energy. The resulting impulse spins the
turbine. The buckets are mounted in pairs, to keep the forces on the wheel
balanced, as well as to ensure smooth, efficient momentum transfer of the fluid
jet to the wheel. The Pelton wheel is most efficient in high head applications.
For a constant water flow rate from the nozzles the speed of turbine changes with
changing loads on it. For quality hydroelectricity generation the turbine should rotate at a constant
speed. To keep the speed constant despite the changing loads on the turbine
water flow rate through the nozzles is changed. To stop the striking water jet to the turbine blades when load decreased on the turbine, the servo
controlled spear valves are used in jets. In sudden reduction of load jets are
made to stop by deflector plates so that over speed of turbine should not take.
Low
head Power Plants
In this case a small dam is built across
the river to provide the necessary head. The excess water is allowed to flow
over the dam itself. In such plants Francis, Propeller or Kaplan types of
turbines are used. Also no surge tank is required. These plants are constructed
where the water head available less then 30mtrs. The production of electricity
will be less due to low head.
Medium Head Hydro Power
Plants
Mainly forebay provided before the
Penstock, acts as water reservoir for medium head plants. In this plants mainly
water is carried through main reservoir to forebay and then to the penstock.
The forebay acts as surge tank for these plants. The turbines used will be
Francis type of the steel encased variety.
Pumped Storage Hydro Power
Plants
In these plants mainly water is pumped
back for more generation of power. Pumped-storage hydroelectricity is a type of
hydroelectric power generation used by some power plants for load balancing. The
method stores energy in the form of water pumped from a lower elevation
reservoir to a higher elevation. Low-cost off-peak electric power is used to
run the pumps.. These plants are used when amount of water available for
generation of power is otherwise inadequate. If it is possible to pond at
head water and tail water locations water after passing through the turbine is
stored in the tail race pond where it may be pumped back to head water pond.
The pumping back from tail race pond to the head water pond is done during
off-peak period. During peak load period water is drawn from the head water
pond through the penstock to operate the turbines.
Although the losses of the pumping process makes the plant a net consumer of
energy overall, the system increases revenue by selling more electricity during
periods of peak demand, when electricity prices are highest. Pumped storage is
the largest-capacity form of grid energy storage now available. Such plants can
recover almost 70% of the power used in pumping the water. A recent development
in this field is the use of reversible turbine-pump unit. Such unit can be used
as a turbine while generating power and as pumping water to storage. The
generator in this case works as motor during reverse operation. The efficiency
in such a case is high and is almost the same in both the operations. With the
use of reversible – turbine- pump sets additional capital investment on pump
and its motor can be saved and the scheme can be worked more economically. Such
plants can be operated only in interconnected systems where other generating
plants (steam, hydro etc.) are also available.
A pumped-storage plant has two reservoirs
Upper reservoir - Like a conventional hydropower plant, a
dam creates a reservoir. The water in this reservoir flows through the
hydropower plant to create electricity. Using a reversible turbine, the
plant can pump water back to the upperreservoir. This is done in off-peak
hours. Essentially, the second reservoir refills the upper reservoir. By
pumping water back to the upper reservoir, the plant has more water to generate
electricity during periods of peak consumption.
Lower
reservoir - Water exiting the hydropower plant flows into a lower
reservoir rather than re-entering the river and flowing downstream.
High Head power plant
Mainly in these plants pressure tunnel is
provided before the surge tank, which inturn connected to penstock. A pressure tunnel
is taken off from the reservoir and water brought to the valve house (not shown
in picture) at the start of the penstocks. The penstocks are huge
steel pipes which take large quantity of water from the valve house to the
power house. The valve house contains main sluice gates and in addition automatic
isolating valves which come into operation when the penstock bursts, cutting
further supply of water. Surge tank is an open tank and is built just in between the beginning of the penstocks and the valve house. In
absence of surge tank, the water hammer can damage the fixed gates. InMajority of dams Sluice gates are provided. The
sluice gates are opened when dam level is below level and there
is shortage water for irrigation. Normally the high head plants are 500 meters
above and for heads above 500 meters Pelton wheels are used.
Spiral Casing
The spiral casing and stay ring are
fabricated from steel plates. The spiral casing is of logarithmic form and
circular cross section for maintaining a constant
velocity through its passage. The plates are gradually reduced in thickness to suit hydraulic load. The spiral casing has
been made in different number segments which are welded to each other and with
stay ring at site. Stay ring is made in two parts, joined by machined flanges
and fasteners and steel welded. The top cover and runner envelop are attached
to stay ring flanges. Before 1849, in old turbines spiral casing was not there
and water was directly following in the centre of the runner and was radially
flowing outwards. At that time the American Engineer, James B. Francis, set out to improve upon the
design of the few hydraulic turbines operating at the time in
All investigations of
this Engineer proved that water to enter the runner from the outside and to flow
inward through the radial blades. Afterwards the design was improved so that
the water was turned from a radial to an axial path within the
runner, rather than outside it. Looking at the result it was found that the
water pressure can be controlled and turbine was named as Francis. Mainly Francis turbines are
comes under Reaction turbines. The reaction turbines designed as per velocity
and the pressure of the water. Water pressure in the penstock is more and
directly hitting on the runner may damage the runner blades. The reaction
turbines controls the flow of water equally maintains the turbine speed.
Surge tank
Surge tank is additional storage for near to turbine, usually provided in
high head plants. A surge tank is located near the beginning of the conduit (penstock). When turbine
is running at a steady load, there are no surges in the flow of
water through the conduit i.e. the quantity of water flowing in the conduit is
just sufficient to meet the turbine requirements. As the load on the turbine
decreases or during load rejection by the turbine the surge tank provides space
for holding water. Similarly when load on turbine increases it furnishes additional water. Thus the
conduit (penstock) prevented from bursts. Hence, a surge tank over comes the
abnormal pressure in the conduit when load on the turbine
falls and acts as a reservoir during increase of load on the turbine. Several designs
of surge tanks have been adopted in power stations, the important
considerations being the amount of water to be stored, the amount of pressure
to be release off and the separate space available at the site of construction.
Guide Bearing
The Guide bearing is of pivoted pad type
with self contained oil bath lubrication. It consists of Babbitt lined pads
arranged along the outer circumference of skirt of the shaft. Each pad is
adjustable by means of studs. The pads remain pivoted against the spherical end
of studs. The bearing housing is of split construction and is secured on the
upper side of to cover by studs. Four dowels are used for locating bearing
housing on top cover. In stationary condition, the pads are kept immersed in
oil bath up to a level slightly above the centre line of bearing. Rotation of
shaft induces centrifugal force, due to which oil flows through the holes in
shaft collar and rises along the journal surface, thus lubricating the pads.
The oil returns through the pipe line bearing body and is led to the oil sump
by gravity.
The oil cooled in the
oil sump which is directly placed on turbine top cover and cooling is carried
out by main turbine discharge. The oil after passing through the tank flows
back into the bearing through a pipe line provided on bottom ring.
This above article
explained as per practically observed in Kaplan Turbine. Normally in all type
of turbines same type of guide bearing followed.
An eight-km deep underground tunnel next
to one of
Through the tunnel, scientists will lower
a string of instruments for setting up an underground seismic observatory, which
will collect data to help understand the complex geophysical processes leading
to an earthquake.
“Koyna is the only place in the world for
this experiment as quakes
are happening within a small area of 20x30 km and even within that 600 sq km,
they are concentrated within a core area of 5 sq km,” Harsh Gupta, who
successfully predicted Koyna dam’s potential to trigger earthquake more than
three decades ago told Deccan
Herald on the sidelines of the 98th Indian Science Congress here.
The first step on this Rs 350-crore experiment would
be taken on Friday with
An international workshop will be
organised in March. Later, scientists will go to the site to decide the
tunnel’s exact location.Once the observatory is in place, the researchers will
record hundreds of tiny quakes with magnitude one and more every year besides
four to five quakes of magnitude 2 and at least five to six quakes of magnitude
3 and above. They also hope to get at least one magnitude 4 or 5 quake once in
every two years.
The experiment has been initially planned
for five years involving a large number of institutions and universities.There
will be enough number of earthquakes to generate data on the stress build up
and how the rock behaves under stress condition. This will help understand the
physics of earthquake, using which a prediction model can be developed.
“With fresh information, our approach to
earthquake prediction will be closer to reality,” said Gupta who had once
forecast on quakes in the north-east and raised red flags on Koyna.Even though
deep boreholes were dug to install underground
observatories in Kobe (Japan) and Chi Chi (Taiwan), those tunnels were dug at the
boundaries of tectonic plates and did not yield much information.
The experiments can neither be
conducted at the 1,300-km-long San Andreas fault in California nor in the
Himalayan range as there is no way to find out the exact region where the
stress is being built up.
Water to be released from Gorur Dam
New food and civil supplies minister
V Somanna decided to release water for planting the seeds
and standing crops in Hassan, Mandya and Tumkur districts from February week by utilizing the 13.12 tmcft of water from Gorur
Dam. It was decided on 19th Jan-2011 in an advisory committee on the Hemavathi
irrigation project headed by V Somanna and also attended by legislators and officials of
irrigation departmentof the Hemavathi Project.
V Somaana also said 1.905tmcft of water
would be used for drinking water and also directed Kaveri Neeravari Nigama
Managing Director M A Sadiq for submitting report on the rehabilitation
measures required for families in 10villages in the Hemavathi basin adversely affected by seepage of water from irrigation
canals.
The Hemavathi River
impounded behind the Gorur Dam, which is situated about 12km from Hassan to
Arakalagud. Hemavathi Reservoir is also a pilgrim spot, owing to the notable
temples located near the site. The water-level is being maintained at 2922 ft.
The present storage in the reservoir is 37.103 tmcft.