unit- i - rgmcet · amount of super heater surface installed, as well as the rating of the boiler....
TRANSCRIPT
UNIT- I
A Thermal Power Plant converts the heat energy of coal
into electrical energy.
Coal is burnt in a boiler which converts water into steam.
The expansion of steam in turbine produces mechanical
power which drives the alternator coupled to the turbine.
Thermal Power Plants contribute maximum to the generation
of Power for any country.
Thermal Power Plants constitute 75.43% of the total installed
captive and non-captive power generation in India.
In thermal generating stations coal, oil, natural gas etc. are
employed as primary sources of energy.
Thermal Power plant
General Layout of Thermal Power Station
Diagr am of a typical coal -f ired t hermal
pow er s tation
1. Cooling tower 10. Steam Control valve 19. Superheater
2. Cooling water pump 11. High pressure steam turbine 20. Forced draught (draft) fan
3. transmission line (3-phase) 12. Deaerator 21. Reheater
4. Step-up transformer (3-phase) 13. Feed water heater 22. Combustion air intake
5. Electrical generator (3-phase) 14. Coal conveyor 23. Economiser
6. Low pressure steam turbine 15. Coal hopper 24. Air preheater
7. Condensate pump 16. Coal pulveriser 25. Precipitator
8. Surface condenser 17. Boiler steam drum 26. Induced draught (draft) fan
9. Intermediate pressure steam
turbine 18. Bottom ash hopper 27. Flue gas stack
D i a gr am o f a t y p ical c o al - f ire d
t h e r m al p ow er s tat ion
Main and Auxiliary e q u i p m e n t s
1. Coal handling plant 2. Pulverizing plant 3. Draft fans 4. Boiler 5. Ash handling plant 6. Turbine 7. Condenser 8. Cooling towers and ponds 9. Feed water heater 10. Economiser 11. Superheater and Reheater 12. Air preheater
Coal handling plant
•The function of coal handling plant is automatic feeding of coal to the
boiler furnace.
• A thermal power plant burns enormous amounts of coal.
•A 200MW plant may require around 2000 tons of coal daily
Pulverising plant
In modern thermal power plant , coal is pulverised i.e. ground to dust like size and carried to the furnace in a stream of hot air. Pulverising is a means of exposing a large surface area to the action of oxygen and consequently helping combustion. Pulverising mills are further classified as: 1. Contact mill 2. Ball mill 3. Impact mill
Draft system
• The circulation of air is
caused by a difference in
pressure, known as Draft.
• Draft is a differential
pressure b/w atmosphere
and inside the boiler.
• It is necessary to cause the
flow of gases through boiler
setting
• It may be –
1. Natural draft
2. Mechanical draft
Boiler
Boiler
• A boiler or steam generator is a closed vessel in which water
under pressure, is converted into steam.
• It is one of the major components of a thermal power plant
• Always designed to absorb maximum amount of heat released in
the process of combustion
Boilers are of two types-
1. Fire tube boiler
2. Water tube boiler
Superheater and reheater
Most of the modern boilers are having super heater and reheater arrangement.
Superheater :
Superheater is a component of a steam-generating unit in which steam, after it
has left the boiler drum, is heated above its saturation temperature. The amount
of superheat added to the steam is influenced by the location, arrangement, and
amount of super heater surface installed, as well as the rating of the boiler. The
super heater may consist of one or more stages of tube banks arranged to
effectively transfer heat from the products of combustion. Super heaters are
classified as convection , radiant or combination of these.
Reheater : Some of the heat of superheated steam is used to rotate the turbine where it loses some of its energy.
Reheater is also steam boiler component in which heat is added to this intermediate-pressure steam, which has given up some of its energy in expansion through the high-pressure turbine.
The steam after reheating is used to rotate the second steam turbine where the heat is converted to mechanical energy. This mechanical energy is used to run the alternator, which is coupled to turbine , there by generating electrical energy.
Turbine
Turbine – Full View
Steam turbine
A steam turbine converts heat energy of steam into mechanical energy
and drives the generator. It uses the principle that steam when issuing
from a small opening attains a high velocity. This velocity attained during
expansion depends on the initial and final heat content of the steam. This
difference b/w initial and final heat content represents the heat energy
converted into kinetic energy.
These are of two types :-
Impulse turbine
Reaction turbine
Ash handling plant
The percentage of ash in coal varies from 5% in good quality
coal to about 40% in poor quality coal
Power plants generally use poor quality of coal , thus amount
of ash produced by it is pretty large
A modern 2000MW plant produces about 5000 tons of ash
daily
The stations use some conveyor arrangement to carry ash to
dump sites directly or for carrying and loading it to trucks and
wagons which transport it to the site of disposal
Condenser
Steam after rotating steam turbine comes to condenser. Condenser refers here to the shell and tube heat exchanger (or surface condenser) installed at the outlet of every steam turbine in Thermal power stations of utility companies generally. These condensers are heat exchangers which convert steam from its gaseous to its liquid state, also known as phase transition. In so doing, the latent heat of steam is given out inside the condenser. Where water is in short supply an air cooled condenser is often used. An air cooled condenser is however significantly more expensive and cannot achieve as low a steam turbine backpressure (and therefore less efficient) as a surface condenser. The purpose is to condense the outlet (or exhaust) steam from steam turbine to obtain maximum efficiency and also to get the condensed steam in the form of pure water, otherwise known as condensate, back to steam generator or (boiler) as boiler feed water.
Cooling towers and ponds
o A condenser needs huge quantity of water to condense the steam .
o Typically a 2000MW plant needs about 1500MGallon of water.
oMost plants use a closed cooling system where warm water coming from
condenser is cooled and reused
oSmall plants use spray ponds and medium and large plants use cooling towers.
oCooling tower is a steel or concrete hyperbolic structure having a reservoir at the
base for storage of cooled water
oHeight of the cooling tower may be 150 m or so and diameter at the base is 150 m
Feed water heater
Advantages of heating water before feeding back to the boiler:-
a) Feed water heating improves overall plant efficiency.
b) The dissolved oxygen and carbon dioxide which would
otherwise cause boiler corrosion are removed in feed water
heater
c) Thermal stresses due to cold water entering the boiler drum
are avoided.
d) Quantity of steam produced by the boiler is increased.
e) Some other impurities carried by the steam and condensate,
due to corrosion of boiler and condenser are precipitated
outside the boiler.
Economiser
Flue gases coming out of the boiler carry lot of heat. An economiser extracts a
part of this heat from flue gases and uses it for heating feed water. This use of
economiser results in saving coal consumption and higher boiler efficiency
Economizer
Air preheater
After flue gases leave economiser, some further heat
can be extracted from them and used to heat
incoming heat. Cooling of flue gases by 20 degree
centigrade increases the plant efficiency by 1%.
Air preheaters may be of three types
Plate type
Tubular type
Regenerative type
Electricity by definition is electric current that is used as a power source!
This electric current is generated in a power plant, and then sent out
over a power grid to your homes, and ultimately to your power outlets.
GENERATION STATION
Bulk electrical power is produced by special plants known as
generating station (or) power plants.
To provide cheap, reliable and continous service
Importance of electrical energy 1. Convenient form
Ex. heater
bulb
motor
2.Easy control
3.Greater flexibility
Definition of A Turbo Machine
Turbines are energy developing machines. Turbines convert fluid energy into
mechanical energy. The mechanical energy developed by the turbines is used
in running an electric generator, which is directly connected, to the shaft of the
electrical generator.
Earlier days method – wooden wheel
Overshot Wheel
Had very good efficiency
Could not handle large quantity of water
Undershot Wheel
Low Efficiency
Hydropower to Electric Power
Selection of site
• Location of Dam
• Choice of Dam
• Quantity of water available
• Accessibility of site (cost &type of land)
• Distance from the load center
Classification based on contraction • Runoff river plant without pondage
dam across river
low head
low capacity
• Runoff river plant with pondage
• Valley dam plant large storage capacity
Power plant is located at toe of the dam
• Diversion canal plant
• High Diversion canal plant
Sizes of Hydropower Plants
• Definitions may vary.
• Large plants : capacity >30 MW
• Small Plants : capacity b/w 100 kW to 30 MW
• Micro Plants : capacity up to 100 kW
How Hydropower Works!
• Hydrologic cycle
How Hydropower Works! (ctd…)
• Water from the reservoir flows due to gravity to drive the turbine.
• Turbine is connected to a generator.
• Power generated is transmitted over power lines.
Hydropower to Electric Power
Potential
Energy
Kinetic
Energy
Electrical
Energy
Mechanical
Energy
Electricity
How Hydropower Works
Water from the reservoir
flows due to gravity to
drive the turbine.
Turbine is connected to a
generator.
Power generated is
transmitted over power
lines.
General layout of Hydro-Power Plant
General layout of Hydro-Power Plant
a) Reservoir
Reservoirs ensure supply of water through out the year, by storing water
during rainy season and supplying the same during dry season.
b) Dam
The function of the dam is to increase the reservoir capacity and to increase the
working head of the turbine.
c) Penstock
A pipe between dam and turbine is known as penstock. It will carry the water
from dam to turbine. Penstock is commonly made of steel pipes covered with
RCC.
d) Surge tank/Forebay
When the rate of water flow through the penstock is suddenly decreased, the
pressure inside the penstock will increase suddenly due to water hammer
and thereby damage the penstock.
Surge tank/Forebay is constructed between the dam and turbine. It will act
as a pressure regulator during variable loads.
e) Turbine
Turbines convert the kinetic and potential energy of water into mechanical
energy to produce electric power.
f) Generator and Transformer
Electric generator converts mechanical energy into electrical energy. A step
up transformer will increase the voltage for loss free transmission.
Advantages of hydraulic power plants
Operating cost is very low
Less Maintenance cost and less manpower required
Pollution free
Quick to start and easy to synchronize
Can be used for irrigation and flood control
Long plant life.
Disadvantages of Hydraulic Power Plants
Initial cost of total plant is comparatively high
Power generation depends on availability of water
Cost of transmission is high since most of the plants are in remote areas
Project duration is long.
Advantages and Disadvantages of HPP
1) Hydraulic Efficiency – due to hydraulic losses
Power developed by the runner
Net power supplied at the turbine entrance
SI Unit: kW
Metric Unit : Horse Power/Water Horse Power (W.H.P)
2) Mechanical Efficiency – Due to mechanical losses ( bearing friction)
Power available at the turbine shaft (P)
Power developed by the runner
Efficiencies of Hydraulic Turbines
3) Volumetric Efficiency – due to amt of water slips directly to the tail race
Amount of water striking the runner
Amount of water supplied to the turbine
4) Overall Efficiency
Power available at the turbine shaft (P)
Net power supplied at the turbine entrance
Cont…
Classification of Turbines
Turbines are classified according to several considerations as indicated below.
i) Based on working principle
a) Impulse turbine
b) Reaction turbine
Impulse Turbine: (pressure less)
The pressure of liquid does not change while flowing through the rotor of the
machine. In Impulse Turbines pressure change occur only in the nozzles of
the machine.
One such example of impulse turbine is Pelton Wheel.
Reaction Turbine:
The pressure of liquid changes while it flows through the rotor of the
machine. The change in fluid velocity and reduction in its pressure causes
a reaction on the turbine blades; this is where from the name Reaction
Turbine may have been derived.
Francis and Kaplan Turbines fall in the category of Reaction Turbines.
Cont…
Cont…
ii) Based on working media
a) Hydraulic turbine
b) Steam turbine
c) Gas turbine
d) Wind Turbine
iii) Based on head
Head is the elevation difference of reservoir water level and D/S water level.
a) Very High head turbine (500 m &above) Pelton Turbine
b) High head turbine ( 70-500 m) Francis Turbine (or )Pelton
b) Medium head turbine (15– 70 m) Kaplan (or) Francis Turbine
c) Low head turbine (Below 60 m) Kaplan Turbine
iv) Based on specific speed
Turbines can be classified based on Specific Speed. Specific speed is defined
as the speed in rpm of a geometrically similar turbine, which is identical in
shape, dimensions, blade angles and gate openings with the actual turbine
working under unit head and developing unit power. Specific speed is used to
compare the turbines and is denoted by Ns.
Specific speed Ns = N √P / H5/4
a) Low specific speed (8.5 – 30) - Pelton Turbine
b) Medium specific speed (50 – 340) - Francis Turbine
c) High specific speed (255 – 860) - Kaplan Turbine
Cont…
v) Based on disposition of turbine main shaft
a) Horizontal shaft
b) Vertical shaft
vi) Based on flow through the runner
a) Radial flow
1. Inward
2. Outward
b) Axial flow - Kaplan Turbine
c) Mixed flow - Francis Turbine
d) Tangential flow - Pelton Turbine
Cont…
Pelton Wheel Turbine
Design of Pelton Wheel Turbine
It has a circular disk with cup shaped blades/buckets,
Water jet emerging from a nozzle is tangential to the circumference of the
wheel.
Impulse Turbines
• Uses the velocity of the water to move the runner and discharges to atmospheric pressure.
• The water stream hits each bucket on the runner.
• High head, low flow applications.
• Types : Pelton turbine, Turgo turbine
Pelton Turbine
Turgo Turbine
Reaction
Turbines
• Combined action of pressure and moving water.
• Runner placed directly in the water stream flowing over the blades rather than striking each individually.
• Lower head and higher flows than compared with the impulse turbines.
Working Principle of Pelton Turbine
Water jets emerging strike the buckets at splitter.
Stream flow along the inner curve of the bucket and leave it in the direction
opposite to that of incoming jet.
The high pressure water can be obtained from any water body situated at some height or streams of water flowing down the hills.
The change in momentum (direction as well as speed) of water stream produces an impulse on the blades of the wheel of Pelton Turbine. This impulse generates the torque and rotation in the shaft of Pelton Turbine.
Horizontal shaft - Not more than 2 jets are used and Vertical shaft - Larger no. of jets (upto 6) are used.
Iron/Steel casing to prevent splashing of water and to lead water to the tail
race.
Classification based on contraction • Runoff river plant without pondage
dam across river
low head
low capacity
• Runoff river plant with pondage
• Valley dam plant large storage capacity
Power plant is located at toe of the dam
• Diversion canal plant
• High Diversion canal plant
TECHNOLOGY
Technology
Hydropower
Technology
Impoundment Diversion Pumped
Storage
Impoundment facility
Dam Types
• Arch
• Gravity
• Buttress
• Embankment or Earth
Arch Dams
• Arch shape gives strength
• Less material (cheaper)
• Narrow sites
• Need strong abutments
Concrete Gravity Dams
• Weight holds dam in place
• Lots of concrete (expensive)
Buttress Dams
• Face is held up by a series of supports
• Flat or curved face
Dams Construction
Diversion Facility
• Doesn’t require dam
• Facility channels portion
of river through canal or
penstock
Pumped Storage
• During Storage, water
pumped from lower
reservoir to higher one.
• Water released back to
lower reservoir to generate
electricity.
Pumped Storage
• Operation : Two pools of Water
• Upper pool – impoundment
• Lower pool – natural lake, river
or storage reservoir
• Advantages :
– Production of peak power
– Can be built anywhere with
reliable supply of water
The Raccoon Mountain project
Sizes of Hydropower Plants
• Definitions may vary.
• Large plants : capacity >30 MW
• Small Plants : capacity b/w 100 kW to 30 MW
• Micro Plants : capacity up to 100 kW
Large Scale Hydropower plant
Small Scale Hydropower Plant
Micro Hydropower Plant
Micro Hydropower Systems
• Many creeks and rivers are permanent, i.e., they never dry up,
and these are the most suitable for micro-hydro power
production • Micro hydro turbine could be a waterwheel
• turbines : Pelton wheel (most common)
• Others : Turgo, Crossflow and various axial flow turbines
Generating Technologies
• Types of Hydro Turbines:
– Impulse turbines
• Pelton Wheel
• Cross Flow Turbines
– Reaction turbines
• Propeller Turbines : Bulb turbine, Straflo, Tube Turbine,
Kaplan Turbine
• Francis Turbines
• Kinetic Turbines
Impulse Turbines
• Uses the velocity of the water to move the runner and
discharges to atmospheric pressure.
• The water stream hits each bucket on the runner. • No suction downside, water flows out through turbine housing
after hitting.
• High head, low flow applications.
• Types : Pelton wheel, Cross Flow
Pelton Wheels
• Nozzles direct forceful
streams of water against a
series of spoon-shaped
buckets mounted around the
edge of a wheel.
• Each bucket reverses the
flow of water and this
impulse spins the turbine.
Pelton Wheels (continued…)
• Suited for high head, low
flow sites.
• The largest units can be up
to 200 MW.
• Can operate with heads as
small as 15 meters and as
high as 1,800 meters.
Cross Flow Turbines
• drum-shaped
• elongated, rectangular-
section nozzle directed
against curved vanes on a
cylindrically shaped runner
• “squirrel cage” blower
• water flows through the
blades twice
Cross Flow Turbines (continued…)
• First pass : water flows from the outside of the
blades to the inside
• Second pass : from the inside back out
• Larger water flows and lower heads than the
Pelton.
Reaction Turbines
• Combined action of pressure and moving
water.
• Runner placed directly in the water stream
flowing over the blades rather than striking
each individually.
• lower head and higher flows than compared
with the impulse turbines.
Propeller Hydropower Turbine
• Runner with three to six blades.
• Water contacts all of the blades constantly.
• Through the pipe, the pressure is constant
• Pitch of the blades - fixed or adjustable
• Scroll case, wicket gates, and a draft tube
• Types: Bulb turbine, Straflo, Tube turbine, Kaplan
Bulb Turbine
• The turbine and generator are a sealed unit placed directly in the water stream.
Others…
• Straflo : The generator is attached directly to the perimeter of
the turbine.
• Tube Turbine : The penstock bends just before or after the
runner, allowing a straight line connection to the generator
• Kaplan : Both the blades and the wicket gates are adjustable,
allowing for a wider range of operation
Kaplan Turbine
• The inlet is a scroll-shaped tube that wraps around the turbine's wicket gate.
• Water is directed tangentially, through the wicket gate, and spirals on to a propeller shaped runner, causing it to spin.
• The outlet is a specially shaped draft tube that helps decelerate the water and recover kinetic energy.
Francis Turbines
• The inlet is spiral shaped.
• Guide vanes direct the water
tangentially to the runner.
• This radial flow acts on the runner
vanes, causing the runner to spin.
• The guide vanes (or wicket gate)
may be adjustable to allow
efficient turbine operation for a
range of water flow conditions.
Francis Turbines (continued…)
• Best suited for sites with
high flows and low to
medium head.
• Efficiency of 90%.
• expensive to design,
manufacture and install,
but operate for decades.
Kinetic Energy Turbines
• Also called free-flow turbines.
• Kinetic energy of flowing water used rather than potential from the head.
• Operate in rivers, man-made channels, tidal waters, or ocean currents.
• Do not require the diversion of water.
• Kinetic systems do not require large civil works.
• Can use existing structures such as bridges, tailraces and channels.
Hydroelectric Power Plants in India
Baspa II Binwa
Continued …
Gaj Nathpa Jakri
Continued…
Rangit Sardar Sarovar
ENVIRONMENTAL IMPACT
Benefits…
• Environmental Benefits of Hydro
• No operational greenhouse gas emissions
• Savings (kg of CO2 per MWh of electricity):
– Coal 1000 kg
– Oil 800 kg
– Gas 400 kg
• No SO2 or NOX
• Non-environmental benefits
– flood control, irrigation, transportation, fisheries and
– tourism.
Disadvantages
• The loss of land under the reservoir.
• Interference with the transport of sediment by the dam.
• Problems associated with the reservoir.
– Climatic and seismic effects.
– Impact on aquatic ecosystems, flora and fauna.
Loss of land
• A large area is taken up in the form of a reservoir in case of large dams.
• This leads to inundation of fertile alluvial rich soil in the flood plains, forests and even mineral deposits and the potential drowning of archeological sites.
• Power per area ratio is evaluated to quantify this impact. Usually ratios lesser than 5 KW per hectare implies that the plant needs more land area than competing renewable resources. However this is only an empirical relation.
Methods to alleviate the negative
impact
• Creation of ecological reserves.
• Limiting dam construction to allow substantial free flowing
water.
• Building sluice gates and passes that help prevent fishes
getting trapped.
Favorable impact
• Enhanced fishing upstream.
• Opportunities for irrigated farming downstream.
• With the flooding of the forest habitat of the Tsetse fly, the
vector of this disease, the problem of Sleeping Sickness has
been substantially reduced.
Technological advancements
• Technology to mitigate the negative environmental impact.
– Construction of fish ways for the passage of fish
through, over, or around the project works of a
hydro power project, such as fish ladders, fish
locks, fish lifts and elevators, and similar physical
contrivances
– Building of screens, barriers, and similar devices
that operate to guide fish to a fish way
Continued…
• Evaluating a new generation of large turbines
– Capable of balancing environmental, technical, operational, and cost considerations
• Developing and demonstrating new tools
– to generate more electricity with less water and greater environmental benefits
– tools to improve how available water is used within hydropower units, plants, and river systems
• Studying the benefits, costs, and overall effectiveness of environmental mitigation practices
UNIT- II
Nuclear (Atomic) Power Plant
Working principle :
A nuclear power plant works in a similar way as a thermal
power plant. The difference between the two is in the fuel they
use to heat the water in the boiler(steam generator).
Inside a nuclear power station, energy is released by nuclear
fission in the core of the reactor.
1 kg of Uranium U235 can produce as much energy as the
burning of 4500 tonnes of high grade variety of coal or 2000
tonnes of oil.
Nuclear chain reaction
Neutrons released in fission trigger the fissions of other nuclei
proton
neutron
U-235 nucleus
Nuclear (Atomic) Power Plant…
Chain Reaction…
Uranium exists as an isotope in the form of U235 which is
unstable.
When the nucleus of an atom of Uranium is split, the neutrons
released hit other atoms and split them in turn. More energy is
released each time another atom splits. This is called a chain
reaction.
Nuclear (Atomic) Power Plant…
Nuclear fission:
Nuclear fission…
Nuclear fission: heavy nuclei split into two smaller parts in order to become more stable
proton
neutron
U-235 nucleus
Kr-92 nucleus
Ba-141 nucleus
energy
Nuclear Fission…
• It is a process of splitting up of nucleus of fissionable material like uranium into two or more fragments with release of enormous
amount of energy. •The nucleus of U235 is bombarded with high energy neutrons
U235+0n1 Ba 141+Kr92+2.50n
1+200 MeV energy.
• The neutrons produced are very fast and can be made to fission other nuclei of U235, thus setting up a chain reaction.
• Out of 2.5 neutrons released one neutron is used to sustain the chain reaction.
1 eV = 1.6X10-19 joule. 1 MeV = 106 eV
Nuclear (Atomic) Power Plant…
Nuclear fission…
U235 splits into two fragments (Ba141 &
K92) of approximately equal size.
About 2.5 neutrons are released. 1
neutron is used to sustain the chain
reaction. 0.9 neutrons is absorbed by
U238 and becomes Pu239. The remaining
0.6 neutrons escapes from the reactor.
The neutrons produced move at a very
high velocity of 1.5 x 107 m/sec and
fission other nucleus of U235. Thus
fission process and release of neutrons
take place continuously throughout the
remaining material.
A large amount of energy(200 Million
electron volts, Mev) is produced.
Note : Moderators are
provided to slow down the
neutrons from the high velocities
but not to absorb them.
Nuclear (Atomic) Power Plant…
Principal parts of a nuclear reactor:
Core : Here the nuclear fission process takes place.
Moderator : This reduces the speed of fast moving neutrons. Most moderators
are graphite, water or heavy water.
Nuclear (Atomic) Power Plant…
Principal parts of a nuclear reactor…
Control rods :
Coolant : They carry the intense heat generated. Water is used as a coolant,
some reactors use liquid sodium as a coolant.
Fuel : The fuel used for nuclear fission is U235 isotope.
Radiation shield : To protect the people working from radiation and
(thermal shielding) radiation fragments.
Control rods limit the number
of fuel atoms that can split.
They are made of boron or
cadmium which absorbs
neutrons
The chain reaction is not slowed down
a huge amount of energy is released very quickly
the rate of fission
increases rapidly
Nuclear bomb
Uncontrolled nuclear reaction
Nuclear reactors
Nuclear power plant: Rate of fission is controlled by artificial means to generate electricity
The Daya Bay
Nuclear Power
Station
Nuclear (Atomic) Power Plant…
Types of Nuclear power plant:
Main two types are :
* Pressurised Water Reactor (PWR)
* Boiling Water Reactor (BWR)
Nuclear (Atomic) Power Plant…
Pressurised Water Reactor
(PWR)
Heat is produced in the reactor due to
nuclear fission and there is a chain
reaction.
The heat generated in the reactor is
carried away by the coolant (water or
heavy water) circulated through the
core.
The purpose of the pressure equalizer
is to maintain a constant pressure of 14
MN/m2. This enables water to carry
more heat from the reactor.
The purpose of the coolant pump is to
pump coolant water under pressure
into the reactor core.
Nuclear (Atomic) Power Plant… Pressurised Water Reactor
(PWR)
The steam generator is a heat exchanger
where the heat from the coolant is
transferred on to the water that circulates
through the steam generator. As the
water passes through the steam generator
it gets converted into steam.
The steam produced in the steam
generator is sent to the turbine. The
turbine blades rotate.
The turbine shaft is coupled to a
generator and electricity is produced.
After the steam performing the work on
the turbine blades by expansion, it comes
out of the turbine as wet steam. This is
converted back into water by circulating
cold water around the condenser tubes.
The feed pump pumps back the
condensed water into the steam
generator.
Schematic diagram of a nuclear power
plant with PWR
control rods
fuel rods
reactor pressure vessel
water (cool)
water (hot)
water (high pressure)
water (low pressure)
coolant out
coolant in steam condenser
steam (low pressure)
turbine
electric power
steam
generator
steam (high pressure)
pump
primary loop secondary loop
generator reactor
core
pump
control rods
reactor pressure vessel
water (cool)
water (hot)
water (high pressure)
water (low pressure)
coolant out
coolant in steam condenser
steam (low pressure)
turbine
electric power
steam
generator
steam (high pressure)
pump
primary loop secondary loop
fuel rods They contain the nuclear fuel:
uranium (U-235)
They are surrounded by a
moderator (water or graphite) to
slow down the neutrons released.
control rods
reactor pressure vessel
water (cool)
water (hot)
water (high pressure)
water (low pressure)
coolant out
coolant in steam condenser
steam (low pressure)
turbine
electric power
steam
generator
steam (high pressure)
pump
primary loop secondary loop
fuel rods
They control the rate of reaction by
moving in and out of the reactor.
Move in: rate of reaction
Move out: rate of reaction
All are moved in: the reactor is
shut down
They are made of boron or
cadmium that can absorb neutrons.
steam
generator
control rods
reactor pressure vessel water (high
pressure)
water (low pressure)
coolant out
coolant in steam condenser
steam (high pressure)
pump
primary loop secondary loop
fuel rods
The steam drives a turbine, which
turns the generator.
Electricity is produced by the
generator.
water (hot)
water (cool)
steam (low pressure) turbine
electric power
generator
control rods
fuel rods
reactor pressure vessel
water (cool)
water (hot)
water (high pressure)
water (low pressure)
coolant out
coolant in steam condenser
steam (low pressure)
turbine
electric power
steam
generator
steam (high pressure)
pump
primary loop secondary loop
Two separate water systems are used to avoid
radioactive substances to reach the turbine.
control rods
reactor pressure vessel water (high
pressure)
water (low pressure)
coolant out
coolant in steam condenser
steam (low pressure)
turbine
electric power
pump
primary loop secondary loop
fuel rods
The energy
released in
fissions heats up
the water around
the reactor.
The water in the
secondary loop
is boiled to
steam.
water (hot)
water (cool)
steam
generator
steam (high pressure)
Nuclear (Atomic) Power Plant…
Boiling Water Reactor
(BWR)
The water is circulated through the
reactor where it converts to water
steam mixture.
The steam gets collected above the
steam separator.
This steam is expanded in the turbine
which turns the turbine shaft.
The expanded steam coming out of the
turbine is condensed and is pumped
back as feed water by the feed water
pump into the reactor core.
Also the down coming recirculation
water from the steam separator is fed
back to the reactor core.
Nuclear (Atomic) Power Plant…
Steam power plant means any plant that uses steam to produce electricity.
E.g. Thermal and Nuclear power plants.
Nuclear (Atomic) Power Plant…
Advantages of Nuclear power plant:
Space required is less when compared with other power plants.
Nuclear power plant is the only source which can meet the increasing demand
of electricity at a reasonable cost.
A nuclear power plant uses much less fuel than a fossil-fuel plant.
1 metric tonne of uranium fuel = 3 million metric tonnes of coal = 12 million
barrels of oil.
Disadvantages of Nuclear power plant:
o Radioactive wastes must be disposed carefully, otherwise it will adversely
affect the health of workers and the environment as a whole.
o Maintenance cost of the plant is high.
Nuclear waste
They are highly radioactive
Many of them have very long half-lives.
Radioactive waste must be stored carefully.
Low level radioactive waste
cooling water pipes, radiation suits, etc.
stored in storage facilities
radioactivity will fall to a safe level after 10 to 50 years.
used nuclear fuel
highly radioactive
embedded in concrete and stored deep underground for several thousand years
High level radioactive waste
Nuclear fusion
Nuclear fusion: light nuclei fuse together to form a heavier nucleus
Nuclear fusion…
Nuclear fusion: light nuclei fuse together to form a heavier nucleus
proton
neutron
helium nucleus
neutron
energy
deuterium nucleus
tritium nucleus
H-2 + H-3 He-4 + n + energy
Videos and Animations
1. 8.
2. 9. Nuclear power station
3. 10. How a nuclear power plant
works
4. Nuclear Reactor
5. 11.Nuclear power –How it
works
6. How a pressurised water nuclear 12.
reactor works
7. 13. Nuclear power generator
14. Reactor components
1 nuclear fission.swf
2 nuclear react ions.sw f
3 nuclear reactor an activity.swf
5 nuclear reactor w orking.sw f
7-Nuclear pow er plant1.sw f
8 nuclear powerplant2.sw f
12 Nuclear pow er plant3.sw f
Thank You
UNIT- III
SUB-STATIONS
INTRODUCTION
The assembly of apparatus used to change some
characteristic(e.g. Voltage, a.c to d.c, frequency,
power factor etc) of electric supply is called a sub-
station
SITE SELECTION …..
• It should be located at the centre of gravity of
load
• It should be easily operated and maintained
• It should provide safe and reliable arrangement
• It should involve minimum capital cost
CLASSIFICATION OF SUB-STATIONS
Sub-stations
Service requirement
Constructional features
ACCORDING TO SERVICE REQUIREMENT
Transformer sub stations : these are used to change the voltage levels of
supply
switching sub stations: they simply perfome switching operations of power
lines
Power factor sub stations: they improve the power factor of the system by
using synchronous condensers
Frequency sub stations: those sub stations which change supply
frequency
Converting sub stations: those sub stations which change a.c. power to
d.c. power
Industrial sub stations: those sub stations which supply power to industries
Substations are classified as……..
TRANSFORMER SUB-STATIONS Transformer substations are classified into 4 types these are……..
step up substation: the generation voltage is stepped up to high voltage
Primary grid substation: here the voltage level is step down to 66kv from
220kv for secondary transmission
Secondary substation: the voltage level is further step down to 11kv and
these substations are generally outdoor type
Distribution substation: the electric power from 11kv lines is delivered to
distribution substation. These are generally located near consumer
localities…
ACCORDING TO CONSTRUCTIONAL FEATURES
According to constructional features, the sub stations are classified as:
Indoor sub station: these substations can be installed for voltages up to 11kv
Outdoor sub station: for voltages beyond 66kv these type of sub stations can be
installed
Underground sub stations: in thickly populated areas, the space available is less
so we install these type of substations
Pole mounted substations: this is an outdoor substation with equipment installed
overhead on h-pole or 4 pole structure
INDOOR SUBSTATION…..
BLOCK DIAGRAM>>>>>>
pole mounted substation It is a schematic view of pole mounted substation……
POLE MOUNTED SUBSTATION……
UNDERGROUND SUBSTATION…… While designing a underground sub station the following points are to be
followed:
the size of substation should be minimum
There should be reasonable access for both equipment
There should be provision for emergency lights and protection against fire
There should be good ventilation
the transformers,switches,fuses should be air cooled to avoid bringing oil
into premises
Schematic view………
SYMBOLS FOR EQUIPMENT IN SUB STATIONS
EQUIPMENT IN A TRANSFORMER SUB STATION
BUS BARS: various incoming and out going circuits are connected to bus
bars.busbars receive power from incoming circuits and deliver power to out
going circuits.
.
Electric substations are the part of power systems and used for transferring
power from generating points to load centres.some of important components
are…
INSULATORS: insulators serve two purposes
1) they support conductors(busbars)
2) confine the current to the conductors
most commonly used material for manufacture of insulators is
porcelain.
ISOLATING SWITCHES: in sub stations it is often desired to disconnect a
part of system for general maintenance and repairs. this is accomplished by an
isolating switch or isolators.
Circuit breaker: circuit breaker is used for switching during
normal and abnormal conditions. it is used to interrupt short circuit
currents .there are many types of circuit breakers..
1) air blast circuit breaker.
2) oil circuit breaker
3) sf6 circuit breaker
power transformers: these are used to step down or step up a.c. voltages
and to transfer electrical power from one voltage level to another.
Current transformers: current transformer in essentially a
step up transformer which steps down the current to a
known ratio.
voltage transformer: it is essentially a step down transformer and steps down
the voltage to a known ratio.
metering and indicating instruments: there are several metering and indicating
instruments installed in a sub station to maintain watch over the circuit quantities.
in addition to these there may be following equipment in a substation.
1) fuses
2) carrier current equipment
3) sub station auxiliary supplies
BUS BAR ARRANGEMENTS IN A SUBSTATION
Single bus bar system…
Duplicate bus bar system…..
Key diagram of 66/11kv substation
Key diagram of 11/440v indoor substation
GAS INSULATED SUBSTATION
INTRODUCTION…
Gas Insulated substations use sulphur
hexa fluoride(SF6) gas which has
superior dielectric properties. Gas
insulated substations are used where
there is space for providing the
substation is expensive in large cities
and towns
TYPES OF GAS INSULATED
SUBSTATIONS Gas insulated substations are classified according to the
type of configurations as………..
isolated phase module
3-phase common modules
hybrid modules
Compact modules
Highly integrated systems
Isolated-phase module
The individual circuit elements such as a pole of a circuit breaker, a single pole
isolator, one phase assembly of a current transformer etc..are connected together
forms an isolated phase GIS module.
THREE PHASE COMMON MODULE
In this type of module a three phase bay is assembled using the desired number
of three phase elements. This reduces the total number of enclosures to one third.
HYBRID MODULES
It is the combination of isolated phase and three phase common elements is
used to achieve an optimal solution. Hybrid GIS technology has gained
popularity, specially in the medium and low voltage range
COMPACT MODULE
Compact GIS systems are essentially three phase common systems in
which the elements such as three phase circuit breaker, current
transformer etc…. Are placed
HIGHLY INTEGRATED SYSTEM
These are used in outdoor substations .highly integrated substations are
ready to install substations.
SINGLE LINE DIAGRAM
BUS BARS
The high voltage conductor made up of copper
or aluminum is centrally placed in a tabular
metal enclosure. In isolated phase GIS ,coaxial
bus bar are common
Constructional aspects of GIS……..
The main parts of GIS are…….
gas circuit
seals and gaskets
disconnectors
earth switch
Circuit breaker
Current transformer
Plug in joints
Enclosure
Expansion joints
Gas circuit : gas circuit has to maintain the dual purpose
(i.e. arc interruption and insulation). Gas circuit should
maintain the pressure throughout its life period so there
should be no leakages
SEALS AND GASKETS : seals and gaskets are used to
capture the SF6 gas lekages.these are manufactured with
nitrile rubber and viton. These serves sealing purpose
Disconnectors…..
Disconnectors or isolators are used for electrical
isolation of circuit parts.
They are slow acting and operating at off load.
Disconnectors must be carefully designed and tested
to be able to break small charging current without
generating too higher over voltage.
Circuit Breakers…….
Circuit breaker is a metal clad and uses SF6 gas for the purpose of
insulation and fault interruption. The circuit breaker is directly
connected to either current transformers or isolators
Earthing switch……
fast earth switch: these are used to protect the
circuit connected current transformer, voltage
transformer
Maintenance earth switch: these are used for
grounding the high voltage conductors during
maintenance
PLUG IN JOINTS: these are designed in such a way that
they can carry rated full load current uninterruptedly and can
carry heavy transient currents types of plug in joints are
Static joints
Quasi static joints
MAINTENANCE AND INSTALLATION
S.NO 145KV 170KV 245KV
1
Bay width (m) 1.5 2.0 2.0
2 Bay depth 3.3 3.35 3.4
3 Bay height 3.2 3.4 3.4
4 Floor area (sq.m)
4.95 6.7 6.8
5 Volume 15.84 22.78 23.12
6 Weight 3800 5000 5700
Advantages of GIS….
GIS have no risk for fire and explosion due to
leakage of oil.
They generate no noise and have no radio
interference.
The maintenance of GIS is free.
It offers solutions,
-Industrial areas where space and
pollution problems .
-Mountain areas where ice and snow are
major problems.
Disadvantages of GIS…….
Gas insulations tend to be much more
expensive than air insulated installations with
the same ratings.
Care should be taken that no dust particles
enter into the live compartments which results
in flash over.
When fault occurs internally the diagnosis of
the fault and rectifying takes very long time.
UNIT- IV
INTRODUCTION
• The electrical energy generated at generating stations
• It is Conveyed to the consumers through a network
of transmission and distribution system.
POWER SYSTEM
GS
11KV
PRIMARY
GRID SS
SECONDARY
SS
HT-CONSUMERS
DISTRIBUTION
SS
SECONDARY
SS
DISTRIBUTION
SS
HT-CONSUMERS
Fig.1
VOLTAGES USED IN INDIA
• Generation : 3.3KV, 6.6KV, 11KV, 33KV
• Transmission : 110KV, 132KV, 220KV, 400KV
• High voltage distribution : 3.3KV, 6.6KV,11KV
• Low voltage distribution :
• AC : 400V between phases, 230V to Neutral
• DC : 3Wire, 2x220V.
DISTRIBUTION SYSTEM
• The conductor system by which Electrical energy is
conveyed from a bulk power source (sub-station) to the
consumer is called Distribution system.
Primary distribution
Secondary distribution
Distribution
DISTRIBUTION SYSTEMS
REQUIREMENTS OF GOOD DISTRIBUTION SYSTEM
• The declared consumer voltage should be within the prescribed limits i.e., + 5%
• High reliability
• Maximum efficiency
• Non overloading of distribution lines
• High insulation resistance of the system
• Economical
• The conductor system through which the power is
distributed between secondary transmission sub-station
to the primary distribution sub-station.
• Primary distribution voltages are 3.3KV, 6.6KV, 11KV
PRIMARY DISTRIBUTION SYSTEM
SECONDARY DISTRIBUTION SYSTEM
• The conductor system through which the power is distributed
between primary distribution sub-stations to the consumer.
• Secondary distribution voltages are - AC 400V line to line,
230V line to phase DC 3Wire, 2 x 220V.
Feeder A
D
B
C Feeder
Service mains
Service mains Service mains
Service mains
11KV/0.4KV
SS
FEEDERS
• The conductors which connects substations to the areas
served by these stations.
• No tapings are taken from the feeders to feed the consumers
• Feeders are mainly designed on the basis of its current
carrying capacity
DISTRIBUTORS
• The conductors from which numerous tapings are taken for supplying the power to the consumers
• Current flowing through the distributor lines are not constant.
• Distributor lines are mainly designed on basis of
voltage drop
SERVICE MAINS
• The conductor which connect the consumer terminal to the
distributors.
Type of current
Construction
Service
No of wires
Scheme of connection
CLASSIFICATION OF DISTRIBUTION SYSTEMS
• The distribution systems are classified on the basis of
BASED ON TYPE OF CURRENT:
• A.C. distribution System
• D.C. distribution System
FEEDER
LOADS
SUB
STATION
FEEDER
AC DISTRIBUTION
11KV/0.4KV
DISTRIBUTOR
Fig.1
FEEDER
LOADS
SUB
STATION
FEEDER
DC DISTRIBUTION
DISTRIBUTOR
Fig.2
BASED ON CONSTRUCTION:
• Over head distribution system
• Under ground distribution system
11KV/0.4KV
OVER HEAD DISTRIBUTION SYSTEM
Fig.3
Ground level
Fig.4
BASED ON SERVICE:
• General Lighting and Power distribution
system
• Industrial Power distribution system
• Railways distribution system
• Street Lighting distribution system
BASED ON NO.OF WIRES:
• Two Wire distribution System
• Three Wire distribution System
• Four Wire Distribution System
BASED ON SCHEME OF CONNECTION:
• Radial distribution System
• Ring distribution System
• Parallel distribution system
• Inter connected distribution system
SS PRIMARY
RING
LOADS
DTR
DTR
DTR
Q
O
P
S
R
M N
F
L
RING DISTRIBUTION SYSTEM
Fig.5
INTER
CONNECTED
SYSTEM
S2
S1
DTR
DTR
DTR
11KV/0.4KV
DTR
FEEDER
LOADS DISTRIBUTOR
Fig.6
• In this system, separate feeder radiate from a single substation and feed the
distributors at one end only.
Radial system:
• RADIAL DISTRIBUTION SYSTEM
33/11KV
SS
LOADS
11KV/400V D.T/F
11KV/400V D.T/F
FEEDER
FEEDER
LOADS
DISTRIBUTORS
A
B
C
FEEDER
FIG.1
Advantages of radial system
• Simple in construction
• Switching equipment is less
• Low investment cost
• Simple protective relaying
Disadvantages of radial system
• Lack of security of supply
• Over loading of the distributor end nearest to the feeding point
• Series voltage fluctuation affects the end consumer
• Not suitable for long distances
RING DISTRIBUTION SYSTEM
• It is a closed loop circuit from the substations bus bars, make a loop through the
area to be served and returns to the substation
• The distributors are tapped from different points through distribution transformer
SS PRIMARY
RING
LOADS
DTR
DTR
DTR
Q
O
P
S
R
M N
F
L
RING DISTRIBUTION SYSTEM
FIG.2
Advantages of ring distribution system:
• Less voltage fluctuations at consumer’s terminals
• More reliability as compared to radial system
• Easy maintenance
• Low voltage drop
• Both consumer is fed through two feeders
INTER CONNECTED DISTRIBUTION SYSTEM
• The feeder ring is energized by two or more generating
stations (or) substations. it is called inter connected system
INTER
CONNECTED
SYSTEM
S2
S1
DTR
DTR
DTR
11KV/0.4KV
DTR
FEEDER
LOADS DISTRIBUTOR
INTER CONNECTED DISTRIBUTION SYSTEM
FIG.3
Advantages:
• Increase in service stability
• More efficiency of the system
• Feeding any area during peak load period from more no. of generating stations is possible
COMPARISON BETWEEN RADIAL AND
RING DISTRIBUTION SYSTEM
RADIALDISTRRIBUTION
• More voltage drop
• Not reliable
• Not economical system
• Consumer is fed by a simple distributor
• No provision distributor for interconnect or
RING DISTRIBUTION
• Less voltage drop
• More reliability
• More economical
• Consumer in fed through two or more distributor
• Possibility of inter connection to rise the potential
TABLE NO.1
DISTRIBUTORS
• The conductors from which numerous tapings
are taken for supplying the power to the consumers is called
distributors
CLASSIFICATION OF DISTRIBUTORS
Distributor
Loading
Feeding
Concentrated loading
Uniformly distributed loading
At unequal
voltage
Fed at one end
only
Fed at both ends At equal
voltage
Fed at center
Fed at any point on ring
distributor Fig.1
CLASSIFICATION BASED ON LOADING
• Concentrated loading distributors
• Uniformly distributed loading distributors
CONCENTRATE LOADING OF DISTRIBUTOR
• The distributor is connected to the supply at one or both ends and loads are taken at different points along the length of the distributor.
I1 I2 I3 I4
F I1 r1
D C B A I2 r2 I3 r3
I4 r4
V1
CONCENTRATED LOADING OF DISTRIBUTOR
Fig.2
UNIFORM DISRIBUTED LOADING DISTRIBUTOR
• The distributor is connected to the supply at one or
both ends.
• Loads are taken uniformly at different equal distant points
along the length of the distributor.
UNIFORM DISTRIBUTED LOADING
A B
VA VB
Fig.3
CLASSIFICATION BASED ON FEEDING ENDS
• Fed at one end only
• Fed at both ends with equal voltages
• Fed at both end with un equal voltages
• Fed at centre of the distributor
• Fed at any point on the ring distributor
DISTRIBUTER FED AT ONE END: • The distributor is connected to the supply at one end and loads
are taken at different points along the length of the distributor
• The current flowing in different sections of the distributor away from the feeding point goes on decreasing
• The voltages across the loads away from the feeding point goes on decreasing
• Continuity of supply is interrupted in case of fault on the feeder
DISTRIBUTER FED AT ONE END:
I1 I2 I3 I4
F
I1 r1
D C B A
I2 r2 I3 r3 I4 r4
V1
Fig.4
DISTRIBUTOR FED AT BOTH ENDS:
• The distributor is connected to the supply mains at both ends . • The loads are taped-off at different points along the length.
• Continuity of supply is maintained even any fault occurs
on any section of the distributor
• Cross sectional area of the conductor required is lesser
than single fed distributor
• Continuity of supply is maintained even any fault occurs
on any fed point
ADVANTAGES
•The load voltage reaches maximum at the other feeding point
• The load voltage decreases as we move away from any
feeding point
DISADVANTAGE
• Middle point at minimum potential
• The distributor can be imagined to be cut into two at the
middle point
V1
L
i i i i i i i i i i i i
A B
V2
V1=V2
Distributor Fed At Both Ends With Equal Voltages
Fig.5
P L/2
i i i i i i
B P
V2
V1 = V2
L/2
i i i i i i
A
V1
X
Distributor imagined to be cut into two equal parts
Fig.6
FED AT BOTH ENDS AT DIFFERENT VOLTAGES
L
i i i i i i i i i i i i
A B
V1 V2
x
P
DX
Fig.7
DISTRIBUTER FED AT THE CENTRE
The distributor is fed at The centre through supply mains
• The distributor is equivalent to two single fed distributors with a common feeding point
• Distributor is equivalent to two single fed distributor of length equal to half of the total length
DISTRIBUTOR FED AT THE CENTRE :
L
i i i i i i i i i i i i
A B
Fig.8
RING MAIN DISTRIBUTOR FED AT ANY POINT
• The distributor is equivalent to a straight distributor with equal voltages.
• The distributor ring may be fed at one (or) more points
DISTRIBUTION RING
FEEDERS
I1
I2
I3 A
B
C
RING DISTRIBUTOR FED AT ANY POINT
Fig.9
DISTRIBUTION
RING
FEEDERS
I1
I2
I3 A
B
C
AC DISTRIBUTION
Fig.2
AC DISTRIBUTION
• A.C distribution is widely used in the world
• A.C distribution used for domestic consumer supply
• A.C distribution is used for all industrial consumer supply
DISTRIBUTION
RING
FEEDERS
I1
I2
I3 A
B
C
DC DISTRIBUTION
Fig.3
w.r.t. VS
w.r.t VL 1
Power factor
vectorically simple arithmetic Addition & subtraction of V&I
R, L, C only R Drop in distributor
due to
AC DC CRITERIA
DIFFERENCES BETWEEN AC & DC
DISTRIBUTION TABLE.1
AC DISTRIBUTION VOLTAGES
• A.C –HT distribution voltage is 11KV
• A.C –LT 3 Phase distribution voltage is 400V
• A.C -LT 1 Phase distribution voltage is 230V
In AC distribution calculations, p.f. of various load currents have to be
considered.
The p.f. of load currents may be given W.r.t receiving or sending end
voltage, W.r.t to load voltage itself
Methods of solving AC distribution
MODEL PROBLEM
• Consider ac distributor ABC having load current I1 and I2 at B
and C with power factor cosФ1 & cosФ 2 respectively
• Let R1 +JX1 be the impedance of the section AB
and R2+JX2 be the impedance of the section BC
Fig.1
From figure Current flowing in section BC=I2 (ampere)
Voltage drop in section BC=I2Z2=I2(R2+JX2)
Voltage at B=voltage drop between BC +Voltage at C =Vc+I2(R2+JX2)
Current in section AB=I1+I2
Voltage at A=Voltage at B+Voltage drop in section AB VA=VB(I1+I2)(R1+jX1)
VECTOR DIAGRAMS W.R.T TO RECEIVING END Case 1:
Case 2: VECTOR DIAGRAMS W.R.T TO LOAD POINT
Fig.2
Fig.3
PROBLEM-1
• A single phase AC distributor is shown in figure.1. Calculate
the total voltage drop. The resistance and reactance are
0.25ohm and 0.125ohm for 1000m for to and fro.
B F A C
I1=100A
0.707 lag I3=80 A
0.8 Lag
I2=120A
UPF
100 m 150 m 150 m
FIG.1
GIVEN DATA
• Resistance of the distributor ,R=0.25 Ώ
• Reactance of the distributor ,X=0.125 Ώ
• Length of the distributor to and fro ,
L=1000m
SOLUTION
Resistance per metre = resistance of the distributor length of the distributor = R L = 0.25/1000 = 0.25×10-3Ώ
• Reactance per metre = reactance of the distributor
length of the distributor
=X
L
=0.125/1000
=0.125 × 10-3 Ώ
• Impedance of the section FA,
Z = impedence per metre × length of the section
=Z/m × l
=(0.25 × 10-3+j 0.125 ×10-3) ×100
=(25+j12.5 )×10-3 Ώ
• Impedence of the section AB,
Z2= impedence per metre × length of the section
=(0.25 × 10-3+j 0.125 ×10-3) ×150
=(37.5+j18.75) 10-3 Ώ
• Impedance of the section BC,
Z3=(0.25 × 10-3+j 0.125 ×10-3) ×150
=(37.5+j18.75) 10-3 Ώ
• Current flowing in the section FA,
=I1+I2+I3
=100 45°+120 0°+80 36.86°
= (254.7-j118.7)Amp
• Current flowing in the section AB,
=I1+I2
=120 0°+80(0.8-j0.6)
=(184-j48)Amp
Current flowing in the section BC,
= I3
= 80(0.8 -j0.6)
= (64-j48)Amp
• Voltage drop in section FA,
=Current flowing in section FA ×impedance of the section FA
=(254.7-j118.7)(25+j12.5 )× 10-3
=(7.851+j 0.22) volt
• Voltage drop in the section AB,
=current flowing in the section AB× impedence of the section
AB
=(184-j48) ×(37.5+j18.75) × 10-3
=(7.8+j1.65)Volt
Voltage drop in section BC=Current in section BC x
impedance of the section BC
=(64-j48) (37.5+ j 18.75)x 10-3
= 3.3-j0.6
• Total voltage drop in the distributor
=voltage drop in section FA+ voltage drop in section AB
+voltage drop in section BC
=(7.851+j0.22)+(7.8+j1.65)+(3.3-j0.6)
=18.951+j1.27
=19Volts
UNIT- V
ECONOMIC ASPECTS OF POWER GENERATION
Load Curves The curve showing the variation of load on the power station with respect to
(w.r.t) time is known as a load curve.
Importance of Load Curve
The Daily Load Curve gives the information of load on the power station during different running hours of the day.
The number of unit’s generation per day is found from the area under the daily Load Curve.
Average load is found from the Load Curve.
Average load= [Area (KWh) under daily load curve/24 hours]
The maximum demand of the station on that day is found from the highest point of the daily Load Curve.
The size and the number of generating units can be determined from the load curve.
This Load Curve helps to determine the operation schedule of the station. In that case when all the units or the less units needs to running is found.
Load Duration Curve
• When the load elements of a load curve are arranged in the order of descending magnitudes, the curve thus obtained is called a load duration curve.
Important Terms and Factors
• Connected load : • It is the sum of continuous ratings of all the equipments connected to supply
system.
• Maximum demand: • It is the greatest demand of load on the power station during a given period.
• Demand factor: • It is the ratio of maximum demand on the power station to its connected load.
• Diversity factor: • The ratio of the sum of individual maximum demands to the maximum demand on
power station is known as diversity factor
• Reserve Capacity • Plant Capacity – Maximum demand
• Average load: • The average of loads occurring on the power station in a given period (day or
month or year) is known as average load or average demand.
• Load factor: • The ratio of average load to the maximum demand during a given period is known
as load factor.
•Plant capacity factor: • It is the ratio of actual energy produced to the maximum possible
energy that could have been produced during a given period
• Plant use factor • It is ratio of kWh generated to the product of plant capacity and the number of
hours for which the plant was in operation
Suppose a plant having installed capacity of 20 MW produces annual output of
7·35 × 106 kWh and remains in operation for 2190 hours in a year. Then,
•Utilisation factor • it is the ratio of maximum demand to plant capacity.
• Base load • The unvarying load which occurs almost the whole day on the station is
known as base load.
• Peak load • The various peak demands of load over and above the base load of the station is
known as peak load.
UNIT- VI
Economics of Power Generation
The art of determining the per unit (i.e., one kWh) cost of production of electrical energy is known as economics of power generation.
This economics of power generation can be used two types
1. Interest: The cost of use of money is known as interest.
2. Depreciation: The decrease in the value of the power plant equipment and building due to constant use is known as depreciation.
Cost of electrical energy :
This cost of electrical energy can be divided in to 3 types
I. Fixed cost
II. Semi-fixed cost
III. Running or operating cost
I. Fixed cost: It is the cost which is independent of maximum demand and units generated.
II. Semi-fixed cost: It is the cost which depends upon maximum demand but is independent of units generated.
III. Running cost: It is the cost which depends only upon the number of units generated.
Expression for cost of electrical energy
The overall annual cost of electrical energy generated by a power station can be expressed in two farms.
(i) Three part form.
(ii) (ii) Two part form.
Three part form:
In this method, the overall annual cost of electrical energy generated is divided into three parts viz fixed cost, semi-fixed cost and running cost i.e.
Total annual cost of energy = Fixed cost + Semi-fixed cost + Running cost
= Constant + Proportional to max. demand + Proportional to kWh generated.
= Rs ( a + b kW + c kWh) where a = annual fixed cost independent of maximum demand
and energy output. It is on account of the costs mentioned in Art. 4.2.
b = constant which when multiplied by maximum kW demand on the station gives the annual semi-fixed cost.
c = a constant which when multiplied by kWh output per annum gives the annual running cost.
(ii) Two part form: It is sometimes convenient to give the annual
cost of energy in two part form. In this case, the annual cost of energy is divided into two parts viz., a fixed sum per kW of maximum demand plus a running charge per unit of energy. The expression for the annual cost of energy then becomes :
Total annual cost of energy = Rs. (A kW + B kWh) where A = a constant which when multiplied by maximum
kW demand on the station gives the annual cost of the first part.
B = a constant which when multiplied by the annual kWh generated gives the annual running cost. It is interesting to see here that two-part form is a simplification of three-part form.
TARRIF
The rate at which electrical energy is supplied to a consumer is known as tariff.
Objectives of tariff:
(i) Recovery of cost of producing electrical energy at the power station.
(ii) (ii) Recovery of cost on the capital investment in transmission and distribution systems.
(iii) (iii) Recovery of cost of operation and maintenance of supply of electrical energy e.g., metering equipment, billing etc.
(iv) (iv) A suitable profit on the capital investment.
Desirable characteristics of a tariff
(i) Proper return :
The tariff should be such that it ensures the proper return from each consumer. In other words, the total receipts from the consumers must be equal to the cost of producing and supplying electrical energy plus reasonable profit. This will enable the electric supply company to ensure continuous and reliable service to the consumers.
(ii) Fairness : The tariff must be fair so that different types of consumers are satisfied
with the rate of charge of electrical energy. Thus a big consumer should be charged at a lower rate than a small consumer. It is because increased energy consumption spreads the fixed charges over a greater number of units, thus reducing the overall cost of producing electrical energy. Similarly, a consumer whose load conditions do not deviate much from the ideal (i.e., nonvariable) should be charged at a lower* rate than the one whose load conditions change appreciably from the ideal.
(iii) Simplicity :
The tariff should be simple so that an ordinary consumer can easily understand it. A complicated tariff may cause an opposition from the public which is generally distrustful of supply companies.
(iv) Reasonable profit :
The profit element in the tariff should be reasonable. An electric supply company is a public utility company and generally enjoys the benefits of monopoly. Therefore, the investment is relatively safe due to non-competition in the market. This calls for the profit to be restricted to 8% or so per annum.
(v) Attractive :
The tariff should be attractive so that a large number of consumers are encouraged to use electrical energy. Efforts should be made to fix the tariff in such a way so that consumers can pay easily.
Types of tariff Simple tariff:
When there is a fixed rate per unit of energy consumed, it is called a simple tariff or uniform rate tariff.
Disadvantages:
(i) There is no discrimination between different types of consumers since every consumer has to pay equitably for the fixed* charges.
(ii) The cost per unit delivered is high.
(iii) It does not encourage the use of electricity.
Flat rate tariff:
When different types of consumers are charged at different uniform per unit rates, it is called a flat rate tariff.
Disadvantages:
(i) Since the flat rate tariff varies according to the way the supply is used,
separate meters are required for lighting load, power load etc. This makes the application of such a tariff expensive and complicated.
(ii) A particular class of consumers is charged at the same rate irrespective of the magnitude of energy consumed. However, a big consumer should be charged at a lower rate as in his case the fixed charges per unit are reduced.
Block rate tariff: When a given block of energy is charged at a
specified rate and the succeeding blocks of energy are charged at progressively reduced rates, it is called a block rate tariff.
Two-part tariff: When the rate of electrical energy is charged on the
basis of maximum demand of the consumer and the units consumed, it is called a two-part tariff.
Total charges = Rs (b × kW + c × kWh) where, b = charge per kW of maximum demand c = charge per kWh of energy consumed This type of
tariff is mostly applicable to industrial consumers who have appreciable maximum demand.
Advantages (i) It is easily understood by the consumers.
(ii) It recovers the fixed charges which depend upon the maximum demand of the consumer but are independent of the units consumed. Disadvantages
(i) The consumer has to pay the fixed charges irrespective of the fact whether he has consumed or not consumed the electrical energy.
(ii) (ii) There is always error in assessing the maximum demand of the consumer.
Maximum demand tariff
it is similar to two-part tariff with the only difference that the maximum demand is actually measured by installing maximum demand meter in the premises of the consumer. This removes the objection of two-part tariff where the maximum demand is assessed merely on the basis of the rateable value.
Power factor tariff
The tariff in which power factor of the consumer’s load is taken into consideration is known as power factor tariff.
a. kVA maximum demand tariff
b. Sliding scale tariff
c. kW and kVAR tariff
Three-part tariff: When the total charge to be made from the consumer is
split into three parts viz., fixed charge, semi-fixed charge and running charge, it is known as a three-part tariff. i.e.,
Total charge = Rs (a + b × kW + c × kWh)
where a = fixed charge made during each billing period. It includes interest and depreciation on the cost of secondary distribution and labour cost of collecting revenues,
b = charge per kW of maximum demand,
c = charge per kWh of energy consumed.