VOCATIONAL TRAINING REPORT
29/6/2011 – 30/7/2011
NTPC, Badarpur
Aman Samaiyar XA1/EEE/009 1st Year, Electrical and Electronics Engineering Delhi Technological University (formally Delhi College of Engineering)
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ACKNOWLEDGEMENT
After completing the 1 month of industrial training at NTPC, Badarpur, I would like to
thank the concerned engineers of company for their continuous support and step by step
guidance.
I would like to pay my obligation to Mr.G.D. SHARMA, Employee Development
Center, for his valuable suggestions, he gave before commencement of the training &
made me familiar with the HOD‘s of all departments , which guided me on the way of
better learning. I would like to pay my special gratitude to Mr.S.P.VASHIST(DGM) sir of
EMD-I department for allowing me to learn under his highly experienced persona &
providing me in-depth Technical Specification of the electrical machinery. I am thankful to
all HOD‘s, Mr.S.K.MARWAH(DGM – EMD – II) for guiding me to understand turbo-
generators, batteries, switch yards etc and Mr.SHYAMAL BHATTACHARYA(DGM – C&I) for
guiding me to understand the control and instrumentation and other parts of power plants
during project.
- Aman Samaiyar
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TRAINING AT BTPS
I was appointed to do one-month training at this esteemed organization from 29th June to
30th July 2011. In these 34 days I was assigned to visit various division of the plant which
were –
Electrical Maintenance Department – I
Electrical Maintenance Department – II
Control and Instrumentation
This one-month training was a very educational adventure for me. It was really amazing to
see the plant by yourself and learn how electricity, which is one of our daily requirements
of life, is produced.
This report has been made by self-experience at BTPS. The material in this report has
been gathered from my textbooks, senior student report, and trainer manual provided
by training department. The specification & principles are at learned by me from the
employee of each division of BTPS.
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ABOUT THE COMPANY N A T I O N A L T H E R M A L P O W E R C O R P O R A T I O N
NTPC Limited (formerly National
Thermal Power Corporation) is the
largest state-owned power generating
company in India. Forbes Global 2000
for 2010 ranked it 341th in the world.
It is an Indian public sector company
listed on the Bombay Stock Exchange
although at present the Government of
India holds 84.5% (after divestment
the stake by Indian government on 19th October, 2009) of its equity. With a current
generating capacity of 34894 MW, NTPC has embarked on plans to become a 75,000
MW company by 2017. It was founded on November 7, 1975.
NTPC's core business is engineering, construction and operation of power generating
plants and providing consultancy to power utilities in India and abroad.
The total installed capacity of the company is 34894 MW (including JVs) with 15 coal
based and 7 gas based stations, located across the country. In addition under JVs, 5
stations are coal based & another station uses naphtha/LNG as fuel. By 2017, the power
generation portfolio is expected to have a diversified fuel mix with coal based capacity
of around 27,535 MW, 3,955 MW through gas, 1,328 MW through Hydro generation,
about 000 MW from nuclear sources and around 1000 MW from Renewable Energy
Sources (RES). NTPC has adopted a multi-pronged growth strategy which includes
capacity addition through green field projects, expansion of existing stations, joint
ventures, subsidiaries and takeover of stations.
NTPC has been operating its plants at high
efficiency levels. Although the company has
18.79% of the total national capacity it
contributes 28.60% of total power generation
due to its focus on high efficiency. NTPC‘s share
at 31 Mar 2001 of the total installed capacity
of the country was 24.51% and it generated
29.68% of the power of the country in 2008–
09. Every fourth home in India is lit by NTPC. As
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at 31 Mar 2011 NTPC's share of the country's total installed capacity is 17.75% and it
generated 27.4% of the power generation of the country in 2010–11. NTPC is lighting
every third bulb in India. 170.88BU of electricity was produced by its stations in the
financial year 2005–2006. The Net Profit after Tax on March 31, 2006 was INR 58,202
million. Net Profit after Tax for the quarter ended June 30, 2006 was INR 15528 million,
which is 18.65% more than for the same quarter in the previous financial year. 2005).
Pursuant to a special resolution passed by the Shareholders at the Company‘s Annual
General Meeting on September 23, 2005 and the approval of the Central Government
under section 21 of the Companies Act, 1956, the name of the Company "National
Thermal Power Corporation Limited" has been changed to "NTPC Limited" with effect from
October 28, 2005. The primary reason for this is the company's foray into hydro and
nuclear based power generation along with backward integration by coal mining.
(NTPC) is in the 138th position in Fortune 500 in 2009. 10 Indian companies make it to
FT's top 500.
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POWER GENERATION AT BTPS
Stage Unit No. Installed Capacity(MW) Date of Commissioning Status
First 1 95 July 1973 Running
First 2 95 August 1974 Running
First 3 95 March 1975 Running
Second 4 210 December 1978 Running
Second 5 210 December 1981 Running
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NTPC Vindhyanagar
THERMAL POWER PLANTS
A thermal power station is a power plant in which the prime
mover is steam driven. Water is heated, turns into steam and
spins a steam turbine which drives an electrical generator.
After it passes through the turbine, the steam is condensed in
a condenser and recycled to where it was heated; this is
known as a Rankine cycle. The greatest variation in the
design of thermal power stations is due to the different fuel
sources. Some prefer to use the term energy center because such facilities convert forms of
heat energy into electricity. Some thermal power plants also deliver heat energy for
industrial purposes, for district heating, or for desalination of water as well as delivering
electrical power. A large part of human CO2 emissions comes from fossil fueled thermal
power plants; efforts to reduce these outputs are various and widespread.
INTRODUCTORY OVERVIEW | ONE
Almost all coal, nuclear, geothermal, solar, thermal, electric and waste incineration plants,
as well as many natural gas power plants are thermal. Natural gas is frequently
combusted in gas turbines as well as boilers. The waste heat from a gas turbine can be
used to raise steam, in a combined cycle plant that improves overall efficiency. Power
plants burning coal, fuel oil, or natural gas are often called fossil-fuel power plants. Some
biomass-fueled thermal power plants have appeared also. Non-nuclear thermal power
plants, particularly fossil-fueled plants, which do not use co-generation, are sometimes
referred to as conventional power plants.
Commercial electric utility power stations are usually constructed on a large scale and
designed for continuous operation. Electric power plants typically use three-phase
electrical generators to produce alternating current (AC) electric power at a frequency of
50 Hz or 60 Hz. Large companies or institutions may have their own power plants to
supply heating or electricity to their facilities, especially if steam is created anyway for
other purposes. Steam-driven power plants have been used in various large ships, but are
now usually used in large naval ships. Shipboard power plants usually directly couple the
turbine to the ship's propellers through gearboxes. Power plants in such ships also provide
steam to smaller turbines driving electric generators to supply electricity. Shipboard steam
power plants can be either fossil fuel or nuclear. Nuclear marine propulsion is, with few
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exceptions, used only in naval vessels. There have been perhaps about a dozen turbo-
electric ships in which a steam-driven turbine drives an electric generator which powers an
electric motor for propulsion.
Combined heat and power (CH&P) plants, often called co-generation plants, produce both
electric power and heat for process heat, space heating, or process heat. Steam and hot
water lose energy when piped over substantial distance, so carrying heat energy by
steam or hot water is often only worthwhile within a local area, such as a ship, industrial
plant, or district heating of nearby buildings.
HISTORY | TWO
Reciprocating steam engines have been used for mechanical power sources since the 18th
Century, with notable improvements being made by James Watt. The very first commercial
central electrical generating stations in the Pearl Street Station, New York and the Holborn
Viaduct power station, London, in 1882, also used reciprocating steam engines. The
development of the steam turbine allowed larger and more efficient central generating
stations to be built. By 1892 it was considered as an alternative to reciprocating engines.
Turbines offered higher speeds, more compact machinery, and stable speed regulation
allowing for parallel synchronous operation of generators on a common bus. Turbines
entirely replaced reciprocating engines in large central stations after about 1905. The
largest reciprocating engine-generator sets ever built were completed in 1901 for the
Manhattan Elevated Railway. Each of seventeen units weighed about 500 tons and was
rated 6000 kilowatts; a contemporary turbine-set of similar rating would have weighed
about 20% as much.
EFFICIENCY | THREE
The energy efficiency of a conventional thermal power station, considered as salable
energy as a percent of the heating value of the fuel consumed, is typically 33% to 48%.
This efficiency is limited as all heat engines are governed by the laws of thermodynamics.
The rest of the energy must leave the plant in the form of heat. This waste heat can go
through a condenser and be disposed of with cooling water or in cooling towers. If the
waste heat is instead utilized for district heating, it is called co-generation. An important
class of thermal power station are associated with desalination facilities; these are
typically found in desert countries with large supplies of natural gas and in these plants,
freshwater production and electricity are equally important co-products.
A Rankine cycle with a two-stage steam turbine and a single feed water heater.
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A Rankine cycle with a two-stage steam turbine and a single feed water heater.
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Since the efficiency of the plant is fundamentally limited by the ratio of the absolute
temperatures of the steam at turbine input and output, efficiency improvements require
use of higher temperature, and therefore higher pressure, steam. Historically, other
working fluids such as mercury have been used in a mercury vapor turbine power plant,
since these can attain higher temperatures than water at lower working pressures.
However, the obvious hazards of toxicity, high cost, and poor heat transfer properties,
have ruled out mercury as a working fluid.
Above the critical point for water of 705 °F (374 °C) and 3212 psi (22.06 MPa), there is
no phase transition from water to steam, but only a gradual decrease in density. Boiling
does not occur and it is not possible to remove impurities via steam separation. In this case
a super critical steam plant is required to utilize the increased thermodynamic efficiency
by operating at higher temperatures. These plants, also called once-through plants
because boiler water does not circulate multiple times, require additional water
purification steps to ensure that any impurities picked up during the cycle will be removed.
This purification takes the form of high pressure ion exchange units called condensate
polishers between the steam condenser and the feed water heaters. Sub-critical fossil fuel
power plants can achieve 36–40% efficiency. Super critical designs have efficiencies in
the low to mid 40% range, with new "ultra critical" designs using pressures of 4400 psi
(30.3 MPa) and dual stage reheat reaching about 48% efficiency.
Current nuclear power plants operate below the temperatures and pressures that coal-
fired plants do. This limits their thermodynamic efficiency to 30–32%. Some advanced
reactor designs being studied, such as the Very high temperature reactor, advanced gas-
cooled reactor and Super critical water reactor, would operate at temperatures and
pressures similar to current coal plants, producing comparable thermodynamic efficiency.
COST OF ELECTRICITY | FOUR
The direct cost of electric energy produced by a thermal power station is the result of cost
of fuel, capital cost for the plant, operator labour, maintenance, and such factors as ash
handling and disposal. Indirect, social or environmental costs such as the economic value of
environmental impacts, or environmental and health effects of the complete fuel cycle and
plant decommissioning, are not usually assigned to generation costs for thermal stations in
utility practice, but may form part of an environmental impact assessment.
BOILER AND STEAM CYCLE | FIVE
In fossil-fueled power plants, steam generator refers to a furnace that burns the fossil fuel
to boil water to generate steam.
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Steam Boiler
In the nuclear plant field, steam generator refers
to a specific type of large heat exchanger used
in a pressurized water reactor (PWR) to
thermally connect the primary (reactor plant) and
secondary (steam plant) systems, which generates
steam. In a nuclear reactor called a boiling water
reactor (BWR), water is boiled to generate steam
directly in the reactor itself and there are no units
called steam generators.
In some industrial settings, there can also be
steam-producing heat exchangers called heat
recovery steam generators (HRSG) which utilize
heat from some industrial process. The steam
generating boiler has to produce steam at the
high purity, pressure and temperature required
for the steam turbine that drives the electrical
generator.
Geothermal plants need no boiler since they use
naturally occurring steam sources. Heat exchangers may be used where the geothermal
steam is very corrosive or contains excessive suspended solids.
A fossil fuel steam generator includes an economizer, a steam drum, and the furnace with
its steam generating tubes and super heater coils. Necessary safety valves are located at
suitable points to avoid excessive boiler pressure. The air and flue gas path equipment
include: forced draft (FD) fan, Air Preheater (AP), boiler furnace, induced draft (ID) fan,
fly ash collectors (electrostatic precipitator or baghouse) and the flue gas stack.
Feed water heating and deaeration | One
The feed water used in the steam boiler is a means of transferring heat energy from the
burning fuel to the mechanical energy of the spinning steam turbine. The total feed water
consists of recirculated condensate water and purified makeup water. Because the metallic
materials it contacts are subject to corrosion at high temperatures and pressures, the
makeup water is highly purified before use. A system of water softeners and ion exchange
demineralizers produces water so pure that it coincidentally becomes an electrical
insulator, with conductivity in the range of 0.3–1.0 microsiemens per centimeter. The
makeup water in a 500 MWe plant amounts to perhaps 20 US gallons per minute (1.25
L/s) to offset the small losses from steam leaks in the system.
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Diagram of boiler feed water deaerator (with vertical, domed aeration section and horizontal water storage
section
The feed water cycle begins with condensate water being pumped out of the condenser
after traveling through the steam turbines. The
condensate flow rate at full load in a 500 MW
plant is about 6,000 US gallons per minute (400
L/s).
The water flows through a series of six or seven
intermediate feed water heaters, heated up at
each point with steam extracted from an
appropriate duct on the turbines and gaining
temperature at each stage. Typically, the
condensate plus the makeup water then flows
through a deaerator that removes dissolved air
from the water, further purifying and reducing
its corrosiveness. The water may be dosed
following this point with hydrazine, a chemical
that removes the remaining oxygen in the
water to below 5 parts per billion (ppb).[vague] It is also dosed with pH control agents
such as ammonia or morpholine to keep the residual acidity low and thus non-corrosive.
Boiler Operation | Two
Once water inside the boiler or steam generator, the process of adding the latent heat of
vaporization or enthalpy is underway. The boiler transfers energy to the water by the
chemical reaction of burning some type of fuel.
The water enters the boiler through a section in the convection pass called the economizer.
From the economizer it passes to the steam drum. Once the water enters the steam drum it
goes down to the lower inlet water wall headers. From the inlet headers the water rises
through the water walls and is eventually turned into steam due to the heat being
generated by the burners located on the front and rear water walls (typically). As the
water is turned into steam/vapor in the water walls, the steam/vapor once again enters
the steam drum. The steam/vapor is passed through a series of steam and water
separators and then dryers inside the steam drum. The steam separators and dryers
remove water droplets from the steam and the cycle through the water walls is repeated.
This process is known as natural circulation.
The boiler furnace auxiliary equipment includes coal feed nozzles and igniter guns, soot
blowers, water lancing and observation ports (in the furnace walls) for observation of the
furnace interior. Furnace explosions due to any accumulation of combustible gases after a
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trip-out are avoided by flushing out such gases from the combustion zone before igniting
the coal.
The steam drum (as well as the super heater coils and headers) have air vents and drains
needed for initial start up. The steam drum has internal devices that removes moisture from
the wet steam entering the drum from the steam generating tubes. The dry steam then
flows into the super heater coils.
Boiler Furnace and Steam Drum | Three
Once water inside the boiler or steam generator, the process of adding the latent heat of
vaporization or enthalpy is underway. The boiler transfers energy to the water by the
chemical reaction of burning some type of fuel.
The water enters the boiler through a section in the convection pass called the economizer.
From the economizer it passes to the steam drum. Once the water enters the steam drum it
goes down to the lower inlet water wall headers. From the inlet headers the water rises
through the water walls and is eventually turned into steam due to the heat being
generated by the burners located on the front and rear water walls (typically). As the
water is turned into steam/vapor in the water walls, the steam/vapor once again enters
the steam drum. The steam/vapor is passed through a series of steam and water
separators and then dryers inside the steam drum. The steam separators and dryers
remove water droplets from the steam and the cycle through the water walls is repeated.
This process is known as natural circulation.
The boiler furnace auxiliary equipment includes coal feed nozzles and igniter guns, soot
blowers, water lancing and observation ports (in the furnace walls) for observation of the
furnace interior. Furnace explosions due to any accumulation of combustible gases after a
trip-out are avoided by flushing out such gases from the combustion zone before igniting
the coal.
The steam drum (as well as the super heater coils and headers) have air vents and drains
needed for initial start up. The steam drum has internal devices that removes moisture from
the wet steam entering the drum from the steam generating tubes. The dry steam then
flows into the super heater coils.
Super Heater | Four
Fossil fuel power plants can have a super heater and/or re-heater section in the steam
generating furnace. In a fossil fuel plant, after the steam is conditioned by the drying
equipment inside the steam drum, it is piped from the upper drum area into tubes inside
an area of the furnace known as the super heater, which has an elaborate set up of
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tubing where the steam vapor picks up more energy from hot flue gases outside the tubing
and its temperature is now superheated above the saturation temperature. The
superheated steam is then piped through the main steam lines to the valves before the
high pressure turbine.
Nuclear-powered steam plants do not have such sections but produce steam at essentially
saturated conditions. Experimental nuclear plants were equipped with fossil-fired super
heaters in an attempt to improve overall plant operating cost.
Steam Condensing | Five
The condenser condenses the steam from the exhaust of the turbine into liquid to allow it to
be pumped. If the condenser can be made cooler, the pressure of the exhaust steam is
reduced and efficiency of the cycle increases.
The surface condenser is a shell and tube heat exchanger in which cooling water is
circulated through the tubes. The exhaust steam from the low pressure turbine enters the
shell where it is cooled and converted to condensate (water) by flowing over the tubes as
shown in the adjacent diagram. Such condensers use steam ejectors or rotary motor-driven
exhausters for continuous removal of air and gases from the steam side to maintain
vacuum.
For best efficiency, the temperature in the condenser must be kept as low as practical in
order to achieve the lowest possible pressure in the condensing steam. Since the condenser
temperature can almost always be kept significantly below 100 °C where the vapor
pressure of water is much less than atmospheric pressure, the condenser generally works
under vacuum. Thus leaks of non-condensible air into the closed loop must be prevented.
Typically the cooling water causes the steam to condense at a temperature of about
35 °C (95 °F) and that creates an absolute pressure in the condenser of about 2–7 kPa
(Template:Convert/in Hg), i.e. a vacuum of about −95 kPa (Template:Convert/in Hg)
relative to atmospheric pressure. The large decrease in volume that occurs when water
vapor condenses to liquid creates the low vacuum that helps pull steam through and
increase the efficiency of the turbines.
The limiting factor is the temperature of the cooling water and that, in turn, is limited by
the prevailing average climatic conditions at the power plant's location (it may be possible
to lower the temperature beyond the turbine limits during winter, causing excessive
condensation in the turbine). Plants operating in hot climates may have to reduce output if
their source of condenser cooling water becomes warmer; unfortunately this usually
coincides with periods of high electrical demand for air conditioning.
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Diagram of a typical water-cooled surface condenser
The condenser generally uses either circulating cooling water from a cooling tower to
reject waste heat to the atmosphere, or once-through water from a river, lake or ocean.
The heat absorbed by the circulating cooling water in the condenser tubes must also be
removed to maintain the ability of the water to cool as it circulates. This is done by
pumping the warm water from the condenser through either natural draft, forced draft or
induced draft cooling towers (as
seen in the image to the right)
that reduce the temperature of
the water by evaporation, by
about 11 to 17 °C (20 to
30 °F)—expelling waste heat to
the atmosphere. The circulation
flow rate of the cooling water in
a 500 MW unit is about 14.2
m³/s (500 ft³/s or 225,000 US
gal/min) at full load.
The condenser tubes are made
of brass or stainless steel to
resist corrosion from either side.
Nevertheless they may become internally fouled during operation by bacteria or algae in
the cooling water or by mineral scaling, all of which inhibit heat transfer and reduce
thermodynamic efficiency. Many plants include an automatic cleaning system that
circulates sponge rubber balls through the tubes to scrub them clean without the need to
take the system off-line.
The cooling water used to condense the steam in the condenser returns to its source without
having been changed other than having been warmed. If the water returns to a local
water body (rather than a circulating cooling tower), it is tempered with cool 'raw' water
to prevent thermal shock when discharged into that body of water.
Another form of condensing system is the air-cooled condenser. The process is similar to
that of a radiator and fan. Exhaust heat from the low pressure section of a steam turbine
runs through the condensing tubes, the tubes are usually finned and ambient air is pushed
through the fins with the help of a large fan. The steam condenses to water to be reused in
the water-steam cycle. Air-cooled condensers typically operate at a higher temperature
than water cooled versions. While saving water, the efficiency of the cycle is reduced
(resulting in more carbon dioxide per megawatt of electricity).
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From the bottom of the condenser, powerful condensate pumps recycle the condensed
steam (water) back to the water/steam cycle.
Re Heater | Six
Power plant furnaces may have a re heater section containing tubes heated by hot flue
gases outside the tubes. Exhaust steam from the high pressure turbine is rerouted to go
inside the re heater tubes to pickup more energy to go drive intermediate or lower
pressure turbines.
Air Path | Seven
External fans are provided to give sufficient air for combustion. The forced draft fan takes
air from the atmosphere and, first warming it in the air preheater for better combustion,
injects it via the air nozzles on the furnace wall.
The induced draft fan assists the FD fan by drawing out combustible gases from the
furnace, maintaining a slightly negative pressure in the furnace to avoid backfiring through
any opening.
STEAM TURBINE GENERATOR | SIX
The turbine generator consists of a series of steam turbines interconnected to each other
and a generator on a common shaft. There is a high pressure turbine at one end, followed
by an intermediate pressure turbine, two low pressure turbines, and the generator. As
steam moves through the system and loses pressure and thermal energy it expands in
volume, requiring increasing diameter and longer blades at each succeeding stage to
extract the remaining energy. The entire rotating mass may be over 200 metric tons and
100 feet (30 m) long. It is so heavy that it must be kept turning slowly even when shut
down (at 3 rpm) so that the shaft will not bow even slightly and become unbalanced. This
is so important that it is one of only five functions of blackout emergency power batteries
on site. Other functions are emergency lighting, communication, station alarms and
turbogenerator lube oil.
Superheated steam from the boiler is delivered through 14–16-inch (360–410 mm)
diameter piping to the high pressure turbine where it falls in pressure to 600 psi (4.1 MPa)
and to 600 °F (320 °C) in temperature through the stage. It exits via 24–26-inch (610–
660 mm) diameter cold reheat lines and passes back into the boiler where the steam is
reheated in special reheat pendant tubes back to 1,000 °F (500 °C). The hot reheat
steam is conducted to the intermediate pressure turbine where it falls in both temperature
and pressure and exits directly to the long-bladed low pressure turbines and finally exits
to the condenser.
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Rotor of a modern steam turbine, used in a power station
The generator, 30 feet (9 m) long and 12 feet (3.7 m) in diameter, contains a stationary
stator and a spinning rotor, each containing miles of heavy copper conductor - no
permanent magnets here. In operation it generates up to 21,000 amperes at 24,000 volts
AC (504 MWe) as it spins at either 3,000 or 3,600 rpm, synchronized to the power grid.
The rotor spins in a sealed chamber cooled with hydrogen gas, selected because it has the
highest known heat transfer coefficient of any gas and for its low viscosity which reduces
windage losses. This system
requires special handling
during startup, with air in
the chamber first displaced
by carbon dioxide before
filling with hydrogen. This
ensures that the highly
explosive hydrogen–
oxygen environment is not
created.
The power grid frequency
is 60 Hz across North
America and 50 Hz in
Europe, Oceania, Asia
(Korea and parts of Japan
are notable exceptions)
and parts of Africa.
The electricity flows to a
distribution yard where
transformers step the
voltage up to 115, 230,
500 or 765 kV AC as needed for transmission to its destination.
The steam turbine-driven generators have auxiliary systems enabling them to work
satisfactorily and safely. The steam turbine generator being rotating equipment generally
has a heavy, large diameter shaft. The shaft therefore requires not only supports but also
has to be kept in position while running. To minimize the frictional resistance to the rotation,
the shaft has a number of bearings. The bearing shells, in which the shaft rotates, are lined
with a low friction material like Babbitt metal. Oil lubrication is provided to further reduce
the friction between shaft and bearing surface and to limit the heat generated.
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ELECTRICAL MAINTAINANCE DEPARTMENT – I
I was trained under the electrical maintenance department – 1 from 29th June to 9th July.
This department maintains the basic electrical section of the industry. Following things came
under this section of my training –
LT/HT Motors. Turbine and boiler side
LT/HT Switchgear
Coal Handling Plant/New coal Handling Plant(CHP/NCHP) Electrical
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L. T. / H. T. MOTORS T U R B I N E & B O I L E R S I D E M O T O R S
Both high tension and low tension motors are installed in the power plant.
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For Unit – 1, 2, 3
Used in - Quantity
I.D. Fans 2
F.D. Fans 2
P.A. Fans 2
Mill Fans 3
Ball Mill Fans 3
RC Feeders 3
Slag Crusher 5
DM makeup pump 2
PC Feeders 4
Worm Conveyor 1
Furnikets 4
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For Unit – 3, 4
Used in - Quantity
I.D. Fan 2
F.D. Fan 2
P.A. Fan 2
Bowl Mills 6
RC Feeders 6
Clinker Grinder 2
Scrapper 2
Seal Air Fans 2
Hydrazine and Phosphorous Dozing 2
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Electrical Switchgear
L. T. / H. T. SWITCHGEAR
It makes or breaks an electrical circuit.
Isolation | One
A device which breaks an electrical circuit when circuit is switched on to no load. Isolation
is normally used in various ways for purpose of isolating a certain portion when required
for maintenance.
Switching Isolation | Two
It is capable of doing things like interrupting transformer magnetized current, interrupting
line charging current and even
perform load transfer
switching. The main application
of switching isolation is in
connection with transformer
feeders as unit makes it
possible to switch out one
transformer while other is still
on load.
Circuit Breakers |
Three
One which can make or break
the circuit on load and even on
faults is referred to as circuit
breakers. This equipment is the
most important and is heavy duty equipment mainly utilized for protection of various
circuits and operations on load. Normally circuit breakers installed are accompanied by
isolators.
Load Break Switches | Four
These are those interrupting devices which can make or break circuits. These are normally
on same circuit, which are backed by circuit breakers.
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Ear th Switches | Five
Devices which are used normally to earth a particular system, to avoid any accident
happening due to induction on account of live adjoining circuits. These equipment do not
handle any appreciable current at all. Apart from this equipment there are a number of
relays etc. which are used in switchgear.
LOW TENSION SWITCHGEAR | ONE
It is classified in following ways:-
Main Switch | One
Main switch is control equipment which controls or disconnects the main supply. The main
switch for 3 phase supply is available for tha range 32A, 63A, 100A, 200Q, 300A at
500V grade.
Fuses | Two
With Avery high generating capacity of the modern power stations extremely heavy
carnets would flow in the fault and the fuse clearing the fault would be required to
withstand extremely heavy stress in process.
It is used for supplying power to auxiliaries with backup fuse protection. Rotary switch up
to 25A. With fuses, quick break, quick make and double break switch fuses for 63A and
100A, switch fuses for 200A, 400A, 600A, 800A and 1000A are used.
Contractors | Three
AC Contractors are 3 poles suitable for D.O.L Starting of motors and protecting the
connected motors.
Overload Relay | Four
For overload protection, thermal over relay are best suited for this purpose. They operate
due to the action of heat generated by passage of current through relay element.
Air Circuit Breakers | Five
It is seen that use of oil in circuit breaker may cause a fire. So in all circuits breakers at
large capacity air at high pressure is used which is maximum at the time of quick tripping
of contacts. This reduces the possibility of sparking. The pressure may vary from 50-60
kg/cm^2 for high and medium capacity circuit breakers.
HIGH TENSION SWITCHGEAR | TWO
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Classified in following ways –
Minimum Oil Circuit Breaker | One
These use oil as quenching medium. It comprises of simple dead tank row pursuing
projection from it. The moving contracts are carried on an iron arm lifted by a long
insulating tension rod and are closed simultaneously pneumatic operating mechanism by
means of tensions but throw off spring to be provided at mouth of the control the main
current within the controlled device.
Type – HKH 12/1000c
Rated Voltage – 66 KV
Normal Current – 1250A
Frequency – 5Hz
Breaking Capacity –
3.4+ KA Symmetrical
3.4+ KA Asymmetrical
360 MVA Symmetrical
Operating Coils –
CC 220V/DC
FC 220V/DC
Motor Voltage – 220V/DC
Air Circuit Breaker | Two
In this the compressed air pressure around 15 kg per cm2 is used for extinction of arc
caused by flow of air around the moving circuit. The breaker is closed by applying
pressure at lower opening and opened by applying pressure at upper opening. When
contacts operate, the cold air rushes around the movable contacts and blown the arc.
It has the following advantages over OCB : -
Fire hazard due to oil are eliminated.
Operation takes place quickly.
There is less burning of contacts since the duration is short and consistent.
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Facility for frequent operation since the cooling medium is replaced
constantly.
Rated Voltage – 6.6 KV
Current – 630 A
Auxiliary Current – 220V/DC
SF6 Circuit Breaker | Three
This type of circuit breaker is of construction to dead tank bulk oil to circuit breaker but
the principle of current interruption is similar o that of air blast circuit breaker. It simply
employs the arc extinguishing medium namely SF6. the performance of gas . When it is
broken down under an electrical stress. It will quickly reconstitute itself.
Circuit Breaker – HPA
Standard – 1 EC 56
Rated Voltage – 12 KV
Insulation Level – 28/75 KV
Rated Frequency – 50 Hz
Breaking Circuit – 40 KA
Rated Current – 1600 KA
Making Capacity – 110 KA
Rated Short Time Current 1/3 sec – 40 A
Mass Approximation – 185 Kg
Auxiliary Voltage –
Closing Coil – 220V/DC
Opening Coil – 220V/DC
Motor – 220V/DC
SF6 Pressure at 20 Degree Celsius – 0.25 Kg
SF6 Gas Per Pole – 0.25 Kg
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Vacuum Circuit Breaker | Four
It works on the principle that vacuum is used to save the purpose of insulation and it
implies that pr. Of gas at which breakdown voltage independent of pressure. It regards
of insulation and strength, vacuum is superior dielectric medium and is better that all other
medium except air and sulphur which are generally used at high pressure.
Rated Frequency – 50 Hz
Rated Making Current – 10 Peak KA
Rated Voltage – 12 KV
Supply Voltage Closing – 220V/DC
Rated Current - 1250 A
Supply Voltage Tripping – 220V/DC
Insulation Level – IMP 75 KVP
Rated Short Time Current – 3sec – 40 KA
Weight of Breaker – 8Kg
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Coal Handling Plant
C. H. P. / N. C. H. P. C O L D H A N D L I N G P L A N T / N E W C O A L H A N D L I N G P L A N T
COAL HANDLING PLANT | ONE
The old coal handling plant caters to the need of units 2,3,4,5 and 1 whereas the latter
supplies coal to units 4 and V.O.C.H.P. supplies coal to second and third stages in the
advent coal to usable form to
(crushed) form its raw form and send it
to bunkers, from where it is send to
furnace.
Major components –
Wagon Tippler | One
Wagons from the coal yard come to
the tippler and are emptied here. The
process is performed by a slip –ring
motor of rating: 55 KW, 415V, 1480
RPM. This motor turns the wagon by
135 degrees and coal falls directly on the conveyor through vibrators. Tippler has raised
lower system which enables is to switch off motor when required till is wagon back to its
original position. It is titled by weight balancing principle. The motor lowers the hanging
balancing weights, which in turn tilts the conveyor. Estimate of the weight of the conveyor is
made through hydraulic weighing machine.
Conveyor | Two
There are 14 conveyors in the plant. They are numbered so that their function can be
easily demarcated. Conveyors are made of rubber and more with a speed of 250-
300m/min. Motors employed for conveyors has a capacity of 150 HP. Conveyors have a
capacity of carrying coal at the rate of 400 tons per hour. Few conveyors are double belt,
this is done for imp. Conveyors so that if a belt develops any problem the process is not
stalled. The conveyor belt has a switch after every 25-30 m on both sides so stop the belt
in case of emergency. The conveyors are 1m wide, 3 cm thick and made of chemically
treated vulcanized rubber. The max angular elevation of conveyor is designed such as
never to exceed half of the angle of response and comes out to be around 20 degrees.
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Crusher House
Zero Speed Switch | Three
It is safety device for motors, i.e., if belt is not moving and the motor is on the motor may
burn. So to protect this switch checks the speed of the belt and switches off the motor
when speed is zero.
Metal Separators | Four
As the belt takes coal to the crusher, No metal pieces should go along with coal. To
achieve this objective, we use metal separators. When coal is dropped to the crusher
hoots, the separator drops metal pieces ahead of coal. It has a magnet and a belt and
the belt is moving, the pieces are thrown away. The capacity of this device is around 50
kg. .The CHP is supposed to transfer 600 tons of coal/hr, but practically only 300-400
tons coal is transfer.
Crusher | Five
Both the plants use TATA crushers powered by
BHEL. Motors. The crusher is of ring type and
motor ratings are 400 HP, 606 KV. Crusher is
designed to crush the pieces to 20 mm size i.e.
practically considered as the optimum size of
transfer via conveyor.
Rotatory Breaker | Six
OCHP employs mesh type of filters and allows
particles of 20mm size to go directly to RC
bunker, larger particles are sent to crushes. This leads to frequent clogging. NCHP uses a
technique that crushes the larger of harder substance like metal impurities easing the load
on the magnetic separators.
MILLING SYSTEM | TWO
RC Bunker | One
Raw coal is fed directly to these bunkers. These are 3 in no. per boiler. 4 & ½ tons of coal
are fed in 1 hr. the depth of bunkers is 10m.
RC Feeder | Two
It transports pre crust coal from raw coal bunker to mill. The quantity of raw coal fed in
mill can be controlled by speed control of aviator drive controlling damper and aviator
change.
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Ball Mill | Three
The ball mill crushes the raw coal to a certain height and then allows it to fall down. Due
to impact of ball on coal and attraction as per the particles move over each other as well
as over the Armor lines, the coal gets crushed. Large particles are broken by impact and
full grinding is done by attraction. The Drying and grinding option takes place
simultaneously inside the mill.
Classifier | Four
It is an equipment which serves separation of fine pulverized coal particles medium from
coarse medium. The pulverized coal along with the carrying medium strikes the impact
plate through the lower part. Large particles are then transferred to the ball mill.
Cyclone Separators | Five
It separates the pulverized coal from carrying medium. The mixture of pulverized coal
vapour caters the cyclone separators.
The Turniket | Six
It serves to transport pulverized coal from cyclone separators to pulverized coal bunker or
to worm conveyors. There are 4 turnikets per boiler.
Worm Conveyor | Seven
It is equipment used to distribute the pulverized coal from bunker of one system to bunker
of other system. It can be operated in both directions.
Mill Fans | Eight
It is of three types. Six in all are in running condition all the time.
ID Fans | One
Located between electrostatic precipitators and chimney.
Type – Radial
Speed – 1490 rpm
Rating – 300 KW
Voltage – 6.6 KV
Lubrication – by Oil
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FD Fans | Two
Designed to handle secondary air for boiler. 2 in number and provide ignition of coal.
Type – axial
Speed – 990rpm
Rating – 440 KW
Voltage – 6.6 KV
Primary Air Fans | Three
Designed for handling the atmospheric air up to 50 degrees Celsius, 2 in number.
And they transfer the powered coal to burners to firing.
Type – Double Suction Radial
Rating – 300 KW
Voltage – 6.6 KV
Lubrication – by Oil
Type of Operation – Continuous
Bowl Mill | Nine
One of the most advanced designs of coal pulverizes presently manufactured.
Motor Specification – Squirrel Caged Induction Motor
Rating – 340 KW
Voltage – 6600 KV
Current – 41.7 A
Speed – 980 rpm
Frequency – 50Hz
No load current – 15-16 A
NEW COAL HANDLING PLANT | THREE
WAGON TIPPLER
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Motor specification –
Horse power - 75 HP
Voltage - 415, 3 phase
Speed - 1480 rpm
Frequency - 50 Hz
Current Rating - 102 A
COAL FEED TO PLANT
Feed Motor Specification –
Horse Power - 15 HP
Voltage - 415V, 3 phase
Speed - 1480 rpm
Frequency - 50Hz
CONVEYORS
10A, 10B
11A, 11B
12A, 12B
13A, 13B
14A, 14B
15A, 15B
16A, 16B
17A, 17B
18A, 18B
TRANSFER POINT 6
BREAKER HOUSE
REJECTION HOUSE
RECLAIM HOUSE
TRANSFER POINT 7
CRUSHER HOUSE
EXIT
The coal arrives in wagons via railways and is tippled by the wagon tipplers into
the hoppers. If coal is oversized (>400 mm sq) then it is broken manually so that it
passes the hopper mesh. From the hopper mesh it is taken to the transfer point TP6
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by conveyor 12A ,12B which takes the coal to the breaker house , which renders the
coal size to be 100mm sq. the stones which are not able to pass through the 100mm
sq of hammer are rejected via conveyors 18A,18B to the rejection house . Extra
coal is to sent to the reclaim hopper via conveyor 16. From breaker house coal is
taken to the TP7 via Conveyor 13A, 13B. Conveyor 17A, 17B also supplies coal
from reclaim hopper, From TP7 coal is taken by conveyors 14A, 14B to crusher
house whose function is to render the size of coal to 20mm sq. now the conveyor
labors are present whose function is to recognize and remove any stones moving in
the conveyors . In crusher before it enters the crusher. After being crushed, if any
metal is still present it is taken care of by metal detectors employed in conveyor 10.
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ELECTRICAL MAINTAINENCE DEPARTMENT – II
I was trained under the electrical maintenance department – 2 from 9th July to 18th July.
This department maintains the basic electrical section of the industry. Following things came
under this section of my training –
Generator and Transformer
Switchyard
Lightening
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GENERATOR AND AUXILIARIES
The transformation of mechanical energy into electrical energy is carried out by the
Generator. This Chapter seeks to provide basic understanding about the working
principles and development of Generator.
WORKING PRINCIPLE | ONE
The A.C. Generator or alternator is based upon the principle of electromagnetic
induction and consists generally of a stationary part called stator and a rotating part
called rotor. The stator housed the armature windings. The rotor houses the field
windings. D.C. voltage is applied to the field windings through slip rings. When the rotor is
rotated, the lines of magnetic flux (viz magnetic field) cut through the stator windings. This
induces an electromagnetic force (e.m.f.) in the stator windings. The magnitude of this e.m.f.
is given by the following expression.
E = 4.44 /O FN volts
0 = Strength of magnetic field in Weber‘s
F = Frequency in cycles per second or hertz
N = Number of turns in a coil of stator winding
F = Frequency = Pn/120, where P = nos. of plates, n = revolutions per
second of rotor
From the expression it is clear that for the same frequency, number of poles increases with
decrease in speed and vice versa. Therefore, low speed hydro turbine drives generators
have 14 to 20 poles where as high speed steam turbine driven generators have generally
2 poles. Pole rotors are used in low speed generators, because the cost advantage as well
as easier, construction.
DEVELOPMENT | TWO
The first A.C. Generator concept was enunciated by Michael Faraday in 1831. In 1889 Sir
Charles A. Parsons developed the first AC turbo-generator. Although slow speed AC
generators have been built for some time, it was not long before that the high-speed
generators made its impact.
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Steam Turbo Generator
Development contained until, in 1922, the increased use of solid forgings and improved
techniques permitted an increase in generator rating to 20MW at 300rpm. Up to the out
break of second world war, in 1939, most large generator;- were of the order of 30 to
50 MW at 3000 rpm.
During the war, the development and installation of power plants was delayed and in
order to catch up with the delay in plant
installation, a large number of 30 MW
and 60 MW at 3000 rpm units were
constructed during the years immediately
following the war. The changes in design
in this period were relatively small.
In any development programme the.
Costs of material and labour involved in
manufacturing and erection must be a
basic consideration. Coupled very closely
with these considerations is the
restriction is size and weight imposed
by transport limitations. Development of
suitable insulating materials for large turbo-generators is one of the most important tasks
and need continues watch as size and ratings of machines increase. The present trend is
the use only class "B" and higher grade materials and extensive work has gone into
compositions of mica; glass and asbestos with appropriate bonding material. An
insulation to meet the stresses in generator slots must follow very closely the thermal
expansion of the insulated conductor without cracking or any plastic deformation.
Insulation for rotor is subjected to lower dielectric stress but must withstand high dynamic
stresses and the newly developed epoxy resins, glass and/or asbestos molded in resin
and other synthetic resins are finding wide applications.
GENERATOR COMPONENT | THREE
Rotor | One
The electrical rotor is the most difficult part of the generator to design. It revolves in most
modern generators at a speed of 3,000 revolutions per minute. The problem of
guaranteeing the dynamic strength and operating stability of such a rotor is complicated
by the fact that a massive non-uniform shaft subjected to a multiplicity of differential
stresses must operate in oil lubricated sleeve bearings supported by a structure
mounted on foundations all of which possess complex dynamic be behavior peculiar to
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themselves. It is also an electromagnet and to give it the necessary magnetic strength the
windings must carry a fairly high current. The passage of the current through the windings
generates heat but the temperature must not be allowed to become so high, otherwise
difficulties will be experienced with insulation. To keep the temperature down, the cross
section of the conductor could not be increased but this would introduce another problems.
In order to make room for the large conductors, body and this would cause mechanical
weakness. The problem is really to get the maximum amount of copper into the windings
without reducing the mechanical strength. With good design and great care in construction
this can be achieved. The rotor is a cast steel ingot, and it is further forged and machined.
Very often a hole is bored through the centre of the rotor axially from one end of the
other for inspection. Slots are then machined for windings and ventilation.
Rotor Winding | Two
Silver bearing copper is used for the winding with mica as the insulation between
conductors. A mechanically strong insulator such as micanite is used for lining the slots.
Later designs of windings for large rotor incorporate combination of hollow
conductors with slots or holes arranged to provide for circulation of the cooling gas
through the actual conductors. When rotating at high speed. Centrifugal force tries to lift
the windings out of the slots and they are contained by wedges. The end rings are secured
to a turned recess in the rotor body, by shrinking or screwing and supported at the other
end by fittings carried by the rotor body. The two ends of windings are connected to slip
rings, usually made of forged steel, and mounted on insulated sleeves.
Rotor Balancing | Three
When completed the rotor must be tested for mechanical balance, which means that a
check is made to see if it will run up to normal speed without vibration. To do this it would
have to be uniform about its central axis and it is most unlikely that this will be so to the
degree necessary for perfect balance. Arrangements are therefore made in all designs to
fix adjustable balance weights around the circumference at each end.
Stator | Three
Stator frame: The stator is the heaviest load to be transported. The major part of this load
is the stator core. This comprises an inner frame and outer frame. The outer frame is a
rigid fabricated structure of welded steel plates, within this shell is a fixed cage of girder
built circular and axial ribs. The ribs divide the yoke in the compartments through which
hydrogen flows into radial ducts in the stator core and circulate through the gas coolers
housed in the frame. The inner cage is usually fixed in to the yoke by an arrangement of
springs to dampen the double frequency vibrations inherent in 2 pole generators. The end
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shields of hydrogen cooled generators must be strong enough to carry shaft seals. In large
generators the frame is constructed as two separate parts. The fabricated inner cage is
inserted in the outer frame after the stator core has been constructed and the winding
completed. Stator core: The stator core is built up from a large number of 'punching" or
sections of thin steel plates. The use of cold rolled grain-oriented steel can contribute to
reduction in the weight of stator core for two main reasons:
There is an increase in core stacking factor with improvement in lamination
cold rolling and in cold buildings techniques.
The advantage can be taken of the high magnetic permeance of grain-
oriented steels of work the stator core at comparatively high magnetic
saturation without fear or excessive iron loss of two heavy a demand for
excitation ampere turns from the generator rotor.
Stator Winding | Four
Each stator conductor must be capable of carrying the rated current without
overheating. The insulation must be sufficient to prevent leakage currents flowing between
the phases to earth. Windings for the stator are made up from copper strips wound with
insulated tape which is impregnated with varnish, dried under vacuum and hot pressed to
form a solid insulation bar. These bars are then place in the stator slots and held in with
wedges to form the complete winding which is connected together at each end of the core
forming the end turns. These end turns are rigidly braced and packed with blocks of
insulation material to withstand the heavy forces which might result from a short circuit or
other fault conditions. The generator terminals are usually arranged below the stator. On
recent generators (210 MW) the windings are made up from copper tubes instead of
strips through which water is circulated for cooling purposes. The water is fed to the
windings through plastic tubes.
GENERATOR COOLING SYSTEM | FOUR
Rotor Cooling System | One
The rotor is cooled by means of gap pick-up cooling, wherein the hydrogen gas in the air
gap is sucked through the scoops on the rotor wedges and is directed to flow along the
ventilating canals milled on the sides of the rotor coil, to the bottom of the slot where it
takes a turn and comes out on the similar canal milled on the other side of the rotor coil to
the hot zone of the rotor. Due to the rotation of the rotor, a positive suction as well as
discharge is created due to which a certain quantity of gas flows and cools the rotor. This
method of cooling gives uniform distribution of temperature. Also, this method has an
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Air inlets for cooling
inherent advantage of eliminating the deformation of copper due to varying
temperatures.
Hydrogen Cooling System | Two
Hydrogen is used as a cooling medium in large capacity generator in view of its high heat
carrying capacity and low density. But in view of its forming an explosive mixture with
oxygen, proper arrangement for filling, purging and maintaining its purity inside the
generator have to be made. Also, in order to prevent escape of hydrogen from the
generator casing, shaft sealing system is used to provide oil sealing.
The hydrogen cooling system mainly comprises of a gas control stand, a drier, an liquid
level indicator, hydrogen control panel, gas purity measuring and indicating instruments.
The system is capable performing the following functions –
Filling in and purging of hydrogen safely without bringing in contact with air.
Maintaining the gas pressure inside the machine at the desired value at all the times.
Provide indication to the operator about the condition of the gas inside the
machine i.e. its pressure, temperature and purity.
Continuous circulation of gas inside the machine through a drier in order to remove any
water vapour that may be present in it.
Indication of liquid level in the generator and alarm in case of high level.
Stator Cooling System | Three
The stator winding is cooled by distillate which is fed from one end of the machine by
Teflon tube and flows through the upper bar and returns back through the lower bar of
another slot.
Turbo generators require water cooling
arrangement over and above the usual hydrogen
cooling arrangement. The stator winding is cooled
in this system by circulating demineralized water
(DM water) through hollow conductors. The cooling
water used for cooling stator winding calls for the
use of very high quality of cooling water. For this
purpose DM water of proper specific resistance is
selected. Generator is to be loaded within a very
short period if the specific resistance of the cooling DM water goes beyond certain preset
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values. The system is designed to maintain a constant rate of cooling water flow to the
stator winding at a nominal inlet water temperature of 40 deg C.
RATING OF GENERATORS IN NTPC | FIVE
95 MW Generator | One
Manufacture by Bharat heavy electrical Limited (BHEL).
Capacity - 117500 KVA
Voltage - 10500V
Speed - 3000 rpm
Hydrogen - 2.5 Kg/cm2
Power Factor - 0.85 (lagging)
Stator Current - 6475 A
Frequency - 50 Hz
Stator wdg conn - 3 phase
210 MW Generator | Two
Manufacture by Bharat heavy electrical Limited (BHEL).
Capacity - 247000 KVA
Voltage (stator) - 15750 V
Current (stator) - 9050 A
Voltage (rotor) - 310 V
Current (rotor) - 2600 A
Speed - 3000 rpm
Power Factor - 0.85
Frequency - 50 Hz
Hydrogen - 3.5 Kg/cm2
Stator wdg conn - 3 phase stator connection
Insulation Class - B
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TRANSFORMER
A transformer is a device that transfers electrical energy from one circuit to another by
magnetic coupling with out requiring relative motion between its parts. It usually comprises
two or more coupled windings, and in most cases, a core to concentrate magnetic flux. An
alternating voltage applied to one winding creates a time-varying magnetic flux in the
core, which includes a voltage in the other windings. Varying the relative number of turns
between primary and secondary windings determines the ratio of the input and output
voltages, thus transforming the voltage by stepping it up or down between circuits. By
transforming electrical power to a high-voltage,_low-current form and back again, the
transformer greatly reduces energy losses and so enables the economic transmission of
power over long distances. It has thus shape the electricity supply industry, permitting
generation to be located remotely from point of demand. All but a fraction of the world‘s
electrical power has passed trough a series of transformer by the time it reaches the
consumer.
BASIC PRINCIPLES | ONE
The principles of the transformer are illustrated by consideration of a hypothetical ideal
transformer consisting of two windings of zero resistance around a core of negligible
reluctance. A voltage applied to the primary winding causes a current, which develops a
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magneto motive force (MMF) in the core. The current required to create the MMF is termed
the magnetizing current; in the ideal transformer it is considered to be negligible, although
its presence is still required to drive flux around the magnetic circuit of the core.
An electromotive force (MMF) is induced across each winding, an effect known as mutual
inductance. In accordance with faraday‘s law of induction, the EMFs are proportional to
the rate of change of flux. The primary EMF, acting as it does in opposition to the primary
voltage, is sometimes termed the back EMF‖.
ENERGY LOSSES | TWO
An ideal transformer would have no energy losses and would have no energy losses, and
would therefore be 100% efficient. Despite the transformer being amongst the most
efficient of electrical machines with ex the most efficient of electrical machines with
experimental models using superconducting windings achieving efficiency of 99.85%,
energy is dissipated in the windings, core, and surrounding structures. Larger transformers
are generally more efficient, and those rated for electricity distribution usually perform
better than 95%. A small transformer such as plug-in ―power brick‖ used for low-power
consumer electronics may be less than 85% efficient.
Transformer losses are attributable to several causes and may be differentiated between
those originated in the windings, sometimes termed copper loss, and those arising from the
magnetic circuit, sometimes termed iron loss. The losses vary with load current, and may
furthermore be expressed as ―no load‖ or ―full load‖ loss, or at an intermediate loading.
Winding resistance dominates load losses contribute to over 99% of the no-load loss can
be significant, meaning that even an idle transformer constitutes a drain on an electrical
supply, and lending impetus to development of low-loss transformers.
Losses in the transformer arise from:
Winding resistance | One
Current flowing through the windings causes resistive heating of the conductors.
At higher frequencies, skin effect and proximity effect create additional winding
resistance and losses.
Hysteresis losses | Two
Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis
within the core. For a given core material, the loss is proportional to the frequency, and is
a function of the peak flux density to which it is subjected.
Eddy current | Three
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Power Transformer
Ferromagnetic materials are also good conductors, and a solid core made from such a
material also constitutes a single short-circuited turn trough out its entire length. Eddy
currents therefore circulate with in a core in a plane normal to the flux, and are
responsible for resistive heating of the core material. The eddy current loss is a complex
function of the square of supply frequency and inverse square of the material thickness.
Magnetostriction | Four
Magnetic flux in a ferromagnetic
material, such as the core, causes
it to physically expand and
contract slightly with each cycle of
the magnetic field, an effect
known as magnetostriction. This
produces the buzzing sound
commonly associated with
transformers, and in turn causes
losses due to frictional heating in
susceptible cores.
Mechanical losses | Five
In addition to magnetostriction, the
alternating magnetic field causes
fluctuating electromagnetic field between primary and secondary windings. These incite
vibration with in near by metal work, adding to the buzzing noise, and consuming a small
amount of power.
Stray losses | Six
Leakage inductance is by itself loss less, since energy supplied to its magnetic fields is
returned to the supply with the next half-cycle. However, any leakage flux that intercepts
nearby conductive material such as the transformers support structure will give rise to
eddy currents and be converted to heat.
COOLING SYSTEMS | THREE
Large power transformers may be equipped with cooling fans, oil pumps or water-cooler
heat exchangers design to remove heat. Power used to operate the cooling system is
typically considered part of the losses of the transformer.
RATING | FOUR
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Manufactured by Bharat heavy electrical limited.
No Load Voltage (hv) - 229 KV
Line Current - 315.2 A
Temperature Rise - 45 deg Celsius
Oil Quantity - 40180 L
Weight of Oil - 34985 Kg
Total Weight - 147725 Kg
Core and Winding - 84325 Kg
Phase - 3
Frequency - 50 Hz
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Switchyard
220 KV SWITCHYARD
BUS BARS | ONE
The arrangement in the 220kV switchyard comprises of a 220kV double bus bar system,
with a bus coupler and a bypass bus. With this arrangement it is possible to take out any
one breaker for maintenance without interruption of supply. In the eventuality of a bus bar
or a circuit breaker fault the period for which supply is interrupted is the time taken to
transfer the feeders from
the faulty bus to the healthy
one or replacing the faulty
circuit breaker by the by-
pass breaker. It is only in the
case of a line fault that
supply cannot be restored
to the feeder until the fault
is rectified.
For maintenance of a
particular bus all feeders
connected to the bus
requiring the maintenance
shall be transferred to the
other bus by closing one bus isolator and opening the other. The bus coupler shall be
tripped and the earthing switch closed. After the maintenance work is over, the earthing
switch must be opened before the respective bus bar is energized.
For maintenance of the by-pass bus, it should be ensured that by-pass breaker is open
and all the bypass isolators of various bays are open.
220 KV CIRCUIT BREAKER | TWO
There are two types of 220kV breakers being used in BTPS switchyard:
Air blast circuit breaker
SF6 circuit breaker
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These breakers operate with sequential isolators and suitable for three-phase auto-
reclosing facility. These breakers can be operated from the switch yard control board. In
case of failure, emergency manual handles are provided in the control kiosk.
Feeder breaker | One
When it is required to maintain either a line or a generator or a transformer breaker, the
feeder is transferred to the by-pass breaker. The earthing switches on isolators must be
earthed before maintaining the breaker.
By-pass breaker | Two
The main purpose of the bypass breaker is to facilitate maintenance/repair of other 220
kV breakers without the necessity of tripping out the associated circuit.
Bus coupler breaker | Three
The two bus bars can be kept coupled through bus couplers. The by pass breaker cannot
act as a substitute for bus coupler breaker when the bus coupler breaker is being
maintained. If buses I and II are paralleled by means of bus coupler and by pass breaker
then in order to maintain the bus coupler breaker all feeders must be transferred to one
bus depending upon the prevalent load.
RATINGS OF CIRCUIT BREAKERS | THREE
Air Blast Circuit Breaker | BHEL
Volts - 220 KV
Amperes - 1200 A
Breaking Capacity -
Symmetrical - 26.31 KA
Equivalent - 10000 MVA
Asymmetrical - 32.1 KA
Making Capacity - peak 67.1 KA
Short Circuit Time - 3 sec 26.3 KA
Closing Coil Voltage - 220 V DC
Tripping Coil Voltage - 220 V DC
Working Pressure -
Max - 28.1 Kg/cm2-g
Min - 26.0 Kg/cm2-g
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Lockout Pressure - 21.1 Kg/cm2-g
Air Blast Circuit Breaker | ABB
Volts - 245 KV
Amperes - 1200 A
Breaking Capacity -
Symmetrical - 31.5 KA
Asymmetrical - 38.4 KA
Short Circuit Time - 3 sec 31.5 KA
Closing Coil Voltage - 220 V DC
Tripling Coil Voltage - 220 V DC
RIL at 50 Hz - 480 KV
VI Impulse - 1.2/50 s 1050 KV per sec
U Switching Impulse - first pole to clear 1.3
Mass - 1830 Kg
Working Pressure - Max 27.31 kg/cm2-g
Air Blast Circuit Breaker | BHEL
Volts - 245 KV
Amperes - 2000 A
Short Circuit Time - 3 sec 26.3 KA
Closing Coil Voltage - 220 V DC
Tripping Coil Voltage - 220 V DC
Working Gas Pressure - 6.1 Kg/cm2-g at 20OC
Rated Frequency and Voltage for auxiliary - 415 AC 50 Hz
Total Weight of Gas - 3900 Kg
Rated operating scheme - O-0.3sec-CO-3 min.-CO
Rated lightening impulse withstands voltage - 1050 KVp
Rated short circuit breaking current - 40 KA
Rated operating pressure - 15 kg/cm2-g
First pole to clear factor - 1.3
Rated duration of short circuit current - 40 kA for 3 sec
Rated line charging breaking current - 125 A
Gas weight - 21 Kg
ISOLATORS | FOUR
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Outdoor Isolator Switch
These are single break, single pole isolators supplied by M/s. Hvelm limited, Madras.
These are pneumatically operated at a pressure of 15 kg/cm2. These isolators and
earthing switches are interlocked with each other and with the circuit breakers to prevent
mal-operation. No interlocking arrangements are provided for the bus earthing switches.
Main Bus Isolators | One
To maintain the main bus isolators the corresponding bus has to be shut down by
transferring loads to other bus, bus earthed and circuit breaker and isolator opened, after
transferring the requisite feeder on to the
bypass breaker and the earthing switches
are closed.
Bypass Isolator | Two
To maintain the by-pass isolators the by-
pass bus has to be shut down, isolators
opened and the earthing switches are
closed.
Feeder Isolators | Three
When the feeder is working on bus I or
bus II, the earthing switches on both sides of the isolator are closed after opening the
breaker and isolators and shutting down the feeder.
PT Isolators | Four
The corresponding bus must be shut down and earthing switches on the isolator closed for
maintenance.
PNEUMATIC SYSTEM | FIVE
This system consists of seven compressors with one spare air compressor. All the seven
compressors are connected to two wet air cylinders, which are coupled to each other. This
wet air is dried through an air drier and fed into six dry cylinders divided into a two
groups each having three dry cylinders. The dry air through these two groups is passed
through two separate air drier for further dryness of air up to a dew point of - C. The
dried air from these two dryers is fed into two separate dry cylinders which feed dry air
into pressure reducers. From these pressure reducers the pressurized dry air is supplied to
air blast circuit breakers. High pressure and low-pressure alarms are arranged on the
pressure gauges and any mal-operation noticed must be rectified immediately.
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POWER LINE COMMUNICATION EQUIPMENT | SIX
To maintain the power line carrier communication equipment like wave trap or coupling
capacitor the conditions would be same as those of maintaining the concerned feeder
isolator. Depending upon whether inter-circuit coupling or phase to ground coupling is used
either both the circuits or the single circuit must be shut down along with the feeder
isolator.
220KV CURRENT TRANSFORMERS | SEVEN
The 220kV single phase 4 core current transformers supplied by Hindustan Brown Broveri
Ltd. (Baroda). The transformation ratio 1200-600/1/1/1/1 amps are used in Tie in
transformer, generator and transmission line bays and bus coupler bay. The secondary
windings of these CTs are connected to protection and measurement circuits.
220KV POTENTIAL TRANSFORMERS | EIGHT
These single phase potential transformers supplied by HE(I) Ltd., Bhopal are connected to
220kV buses. These are required for measurement and protection purposes. The main PTs
are of ratio 22000/53/110/53 volts and the auxiliary PTs are of ratio 62.5/63.5 volts.
The auxiliary PTs will operate in conjunction with the main PT to provide one more
secondary winding. Consequent by the combined set of main and auxiliary PTs will
provide to secondary winding each of 110/53 voltage ratings.
LIGHTING ARRESTORS | NINE
These have been supplied by M/s. W.S. insulators of India Ltd. (Madras). These are
installed for protection of transformers and other electrical equipments against voltage
surges.
One set of lighting arrestors have been provided on each power transformers, tie in
transformers and to the bus PTs.
The 195kV, 10000 amps single pole heavy duty station class SVS type self supporting L.A.
comprises of one metal top and metal base, having mobile arc, pressure relief and a
transfer device. The mobile arc gap assembly consists of a permanent ceramic ring
magnet, radially magnetized, m series with air gap. Thus it provides a constant magnetic
field in the air gap which is always preset at full strength regardless of the current of the
discharge, when lighting wave discharges through it, the spark discharge takes place in
the annular space, causing an arc at right angles to the magnetic field. This field forces the
arc to spin around the gap electrode surfaces. Pressure relief device is provided to take
care of the gas formed at the time of short circuit when the arrestor is damaged. When
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the diaphragm bursts due to a gas pressure, the ionized gases come out and are vented
through the exhaust ports. The gas from the top of the unit is deflected downward and that
from the bottom is deflected upward. The gas steams meet and transfer the fault current is
from inside the arrestor to the outside in less than half cycle of fault current.
220KV LINES | TEN
all the feeders from the 220 kV bus bars are shown in the diagram on the previous page.
All the metering and protection should normally be connected only to the bus VT supplies.
However when necessary CVTs can be used for metering and protection.
Bus - 1 Bus - 2
Gen – Tr - 1 Gen – Tr - 2
Gen – Tr - 3 Gen – Tr - 4
Gen – Tr - 5 IP Line I
IP Line II Mehrauli Line II
Mehrauli Line I Ballabgarh Line II
Ballabgarh Line I Noida Line
Alwar Line Okhla Line II
Okhla Line I Stn Tr – 2
Stn Tr - 1 Bus Coupler
Stn Tr - 3 By Pass Bay
SYNCHRONISING | ELEVEN
Synchronizing facility with check feature has been provided for all 220KV breakers.
Whenever a breaker is proposed to be closed, its synchronizing switch should be unlocked
and synchronizing check relay by pass switch is in circuit position. It is ensured that voltage
and frequency of the incoming and running supplies are nearly same, and the red ‗out of
synchronism lamp is not continuously on. After the breaker has been closed, its
synchronizing switch should be returned to off position and locked.
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Relay Wiring Schematics
Synchronizing check relay SKE prevents closing of a breaker when incoming and running
supplies are out of synchronism. This relay has to be bypassed when closing a breaker one
side of, which is dead.
ANNUNCIATION SYSTEM | TWELVE
All ―breaker tripped‖ alarms have been classed as emergency alarms. Whenever a
breaker trips, the ―breaker tripped‖ facia/flashes and a separate buzzer sounds to draw
immediate attention of operator to tripping of a breaker. Whenever an alarm initiating
contact closes, the corresponding facia of that alarm starts flashing. Simultaneously, the
bell /buzzer starts ringing. Ringing of buzzer stops automatically after a preset time.
Flashing continues unit accepts push button pressed, whereupon facia becomes steadily
lighted if the initiating contact is still closed. Facial lamps should be tested for operation
regularly by pressing ―lamp test‖ button, provided separately for each control panel.
PROTECTION AND RELAYS USED IN MAIN CIRCUIT BOARD | THIRTEEN
High Speed Biased Differential Relay | One
The DMH type relay provides high speed biased differential protection for two or three
winding transformers. The relay is
immune to high inrush current and
has a high degree of stability
against through faults. It requires a
max of two cycles operating time
for current above twice relay rated
current. Instantaneous over current
protection clears heavy internal
faults immediately. This relay is
available in two forms. Firstly for
use with time Cts, the ratios of line
which are matched to the load
current to give zero differential current under normal working conditions. Secondly with
tapped interposing transformers for use with standard line current transformers of any
ratio.
Directional inverse time overcurrent and ear th fault relays | Two
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The CDD type relays are applied for directional or earth fault protection of ring mains,
parallel transformers or parallel feeders with the time graded principle. It is induction disc
type relay with induction cup used to add directional feature.
Instantaneous voltage relay | Three
The type VAG relay is an instantaneous protection against abnormal voltage conditions
such as over voltage, under voltage or no voltage in AC and DC circuits and for definite
time operation when used with a timer. It is an attracted armature type relay.
Auxiliary relays | Four
The VAA/CAA type auxiliary relays are applied for control alarm, indication and other
auxiliary duties in AC or DC systems. CAA is a current operated and VAA is a voltage
operated relay.. it is attracted armature type.
High speed tripping relays | Five
This VAJH type relay is employed with a high speed tripping duties where a number of
simultaneous switching operations are required. This is a fast operating multi contact
attracted armature relay.
Definite time delay relay | Six
This VAT type relay is used in auto reclosing and control schemes and to provide a definite
time feature for instantaneous protective relay. It is an Electro mechanical definite time
relay. It has two pair of contacts. The shorter time setting is provided by a passing contact
and longer time setting by the final contact.
Trip circuit supervision relay | Seven
This VAX relay is applied for after closing or continuous supervision of the trip circuit of
circuit breakers. They detect the following conditions –
Failure of trip relay
Open circuit of trip coil
Failure of mechanism to complete the tripping operation
Instantaneous over current and ear th fault relay | Eight
An instantaneous phase or earth fault protection and for definite time operation when
used with a timer. It is a CAG 12/12G standard attracted armature relay with adjustable
settings. It may be a single pole or triple pole relay.
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Inverse time over current and ear th fault relay | Nine
This CDG 11-type relay is applied for selective phase and earth fault protection in time
graded systems for AC machines. Transformers, feeders etc. this is a non-directional relay
with a definite minimum time which has an adjustable inverse time/current characteristics.
It may be a single pole or triple pole relay.
Fuse failure relay | Ten
This VAP type relay is used to detect the failure or inadvertent removal of voltage
transformer sec. fuses and to prevent incorrect tripping of circuit breaker. It is three units,
instantaneous attracted armature type relay the coil of each unit connected across one of
the VTs. The secondary fuses under healthy conditions, the coil is SC by fuses and can‘t be
energized. But one or more fuses blow the coil is energized and relay operates.
Instantaneous high stability circulating current relay | Eleven
It is used to serve the following three purposes –
Differential protection of Ac machines , reactors auto transformers and bus bars.
Balanced and restricted earth fault protection of generator of generator and
transformer windings.
Transverse differential protection of generators and parallel feeders.
This CAG type relay is a standard attracted armature relay. In circulating current
protection schemes, the sudden and often asymmetrical growth of the system current
during external fault conditions can cause the protection current transformers to go into
saturation, resulting in high unbalance current to insure stability under these conditions.
The modern practice is to use a voltage operated high impedance relay, set to operate at
a voltage slightly higher than that developed by CT under max fault conditions. Hence this
type of relay is used with a stabilizing resistor.
Local breaker back up relay | Twelve
This is a CTIG type three phase or two phase earth fault instantaneous over current unit
intended for use with a time delay unit to give back up protection in the event of a circuit
breaker failure.
Poly-phase directional relay | Thir teen
The PGD relay is a high speed induction cup unit used to give directional properties to
three phase IDMT over-current relays, for the protection of parallel feeders, inter
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connected networks and parallel transformers against phase to phase and three phase
faults. Owing to low sensitivity on phase to earth faults the relay is used with discretion on
solidly earthed systems.
Auto reclose relay | Four teen
Five types of auto reclose relays are available –
VAR21
Giving one reclosure. The dead time and reclaim time are adjustable form 5 to 25
secs. If the circuit breaker reopens during reclaim time, it remains open and locked
out.
VAR41B
Is a single shot scheme for air blast circuit breakers. Reclaim time is fixed at
between 15 to 20 secs. Dead time adjustment is from 0.1 to 1.0 sec of which first
300 millisec will be circuit breaker opening time.
VAR42
Giving four reclosure. It is precision timed from 0 to 60 sec. it can be set for max
four enclosures at min intervals of 10 sec and instantaneous protection can be
suppressed after the first reclosure so that persistent faults are referred to time
graded protection.
VAR 71
Giving single shot medium speed reclosure with alarm and lockout for circuit
breaker. This allows up to 10 faults clearance before initiating an alarm. The alarm
is followed by lockout if selected no. of faults clearances exceed. If the circuit
breaker reopens during reclaim time, it remains open and locked out. It offers delay
in reclosing sequence. Instantaneous lockout on low current earth fault and
suppressing instantaneous protection during reclamation time.
VAR 81
Is a single shot high-speed reclosure with alarm and lockout for circuit breaker This
allows up to 10 faults clearance before initiating an alarm.
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CONTROL AND INSTRUMENTATION
I was trained under the control and instrumentation department from 18th July to 27th
July. This division basically calibrates various instruments and takes care of any faults
occur in any of the auxiliaries in the plant. This department is the brain of the plant
because from the relays to transmitters followed by the electronic computation chipsets
and recorders and lastly the controlling circuitry, all fall under this. Instrumentation can be
well defined as a technology of using instruments to measure and control the physical and
chemical properties of a material.
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LABS
Control and instrumentation has following labs –
Manometry Lab
Protection and Interlocks Lab
Automation Lab
Electronics Lab
Water Treatment Plant
Furnace Safety and Supervisory System Lab
MANOMETRY LAB | ONE
Transmitters- Transmitter is used for pressure measurements of gases and liquids, its
working principle is that the input pressure is converted into electrostatic capacitance
and from there it is conditioned and amplified. It gives an output of 4-20 ma DC. It can
be mounted on a pipe or a wall. For liquid or steam measurement transmitters is
mounted below main process piping and for gas measurement transmitter is placed
above pipe.
Manometer- It‘s a tube which is bent, in U shape. It is filled with a liquid. This device
corresponds to a difference in pressure across the two limbs.
Bourden Pressure Gauge- It‘s an oval section tube. Its one end is fixed. It is provided
with a pointer to indicate the pressure on a calibrated scale. It is of two types : (a)
Spiral type : for low pressure measurement and (b) Helical type : for high pressure
measurement.
PROTECTION AND INTERLOCK LAB | TWO
Interlocking- It is basically interconnecting two or more equipments so that if one
equipments fails other one can perform the tasks. This type of interdependence is also
created so that equipments connected together are started and shut down in the
specific sequence to avoid damage. For protection of equipments tripping are
provided for all the equipments. Tripping can be considered as the series of instructions
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Thermal Trip Circuit Breaker
connected through OR GATE. When the main equipments of this lab are relay and
circuit breakers. Some of the instrument uses for protection are: 1. RELAY It is a
protective device. It can detect wrong condition in electrical circuits by constantly
measuring the electrical quantities flowing under normal and faulty conditions. Some of
the electrical quantities are voltage, current, phase angle and velocity. 2. FUSES It is a
short piece of metal inserted in the circuit, which melts when heavy current flows
through it and thus breaks the circuit. Usually silver is used as a fuse material because:
a) The coefficient of expansion of silver is very small. As a result no critical fatigue
occurs and thus the continuous full capacity normal current ratings are assured for the
long time. b) The conductivity of the silver is unimpaired by the surges of the current
that produces temperatures just near the melting point. c) Silver fusible elements can be
raised from normal operating temperature to vaporization quicker than any other
material because of its comparatively low specific heat.
Miniature Circuit Breaker- They are used with combination of the control circuits to. a)
Enable the staring of plant and distributors. b) Protect the circuit in case of a fault. In
consists of current carrying contacts, one movable
and other fixed. When a fault occurs the contacts
separate and are is stuck between them. There
are three types of –MANUAL TRIP - THERMAL TRIP
- SHORT CIRCUIT TRIP.
Protection and Interlock System- 1. HIGH
TENSION CONTROL CIRCUIT For high tension
system the control system are excited by separate
D.C supply. For starting the circuit conditions should
be in series with the starting coil of the equipment
to energize it. Because if even a single condition
is not true then system will not start. 2. LOW TENSION CONTROL CIRCUIT For low
tension system the control circuits are directly excited from the 0.415 KV A.C supply.
The same circuit achieves both excitation and tripping. Hence the tripping coil is
provided for emergency tripping if the interconnection fails.
AUTOMATION LAB | THREE
This lab deals in automating the existing equipment and feeding routes. Earlier, the old
technology dealt with only (DAS) Data Acquisition System and came to be known as
primary systems. The modern technology or the secondary systems are coupled with (MIS)
Management Information System. But this lab universally applies the pressure measuring
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instruments as the controlling force. However, the relays are also provided but they are
used only for protection and interlocks.
PYROMETRY LAB | FOUR
Liquid in glass thermometer - Mercury in the glass thermometer boils at 340 degree
Celsius which limits the range of temperature that can be measured. It is L shaped
thermometer which is designed to reach all inaccessible places.
Ultra violet censor- This device is used in furnace and it measures the intensity of ultra
violet rays there and according to the wave generated which directly indicates the
temperature in the furnace.
Thermocouples - This device is based on SEEBACK and PELTIER effect. It comprises of
two junctions at different temperature. Then the emf is induced in the circuit due to the
flow of electrons. This is an important part in the plant.
RTD (Resistance temperature detector) - It performs the function of thermocouple
basically but the difference is of a resistance. In this due to the change in the resistance
the temperature difference is measured. In this lab, also the measuring devices can be
calibrated in the oil bath or just boiling water (for low range devices) and in small
furnace (for high range devices).
FURNACE SAFETY AND SUPERVISORY SYSTEM LAB |FIVE
This lab has the responsibility of starting fire in the furnace to enable the burning of coal.
For first stage coal burners are in the front and rear of the furnace and for the second
and third stage corner firing is employed. Unburnt coal is removed using forced draft or
induced draft fan. The temperature inside the boiler is 1100 degree Celsius and its height
is 18 to 40 m. It is made up of mild steel. An ultra violet sensor is employed in furnace to
measure the intensity of ultra violet rays inside the furnace and according to it a signal in
the same order of same mV is generated which directly indicates the temperature of the
furnace. For firing the furnace a 10 KV spark plug is operated for ten seconds over a
spray of diesel fuel and pre-heater air along each of the feeder-mills. The furnace has six
feeder mills each separated by warm air pipes fed from forced draft fans. In first stage
indirect firing is employed that is feeder mills are not fed directly from coal but are fed
from three feeders but are fed from pulverized coalbunkers. The furnace can operate on
the minimum feed from three feeders but under not circumstances should any one be left
out under operation, to prevent creation of pressure different with in the furnace, which
threatens to blast it.
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ELECTRONICS LAB | SIX
This lab undertakes the calibration and testing of various cards. It houses various types of
analytical instruments like oscilloscopes, integrated circuits, cards auto analyzers etc.
Various processes undertaken in this lab are: 1. Transmitter converts mV to mA. 2. Auto
analyzer purifies the sample before it is sent to electrodes. It extracts the magnetic
portion.
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CONTROL SYSTEM STRUCTURE
The primary requirement to be fulfilled by any control system architecture is that it be
capable of being organized and implemented on true process-oriented lines. In other
words, the control system structure should map on to the hierarchy process structure. BHEL‘s
PROCONTROL P®, a microprocessor based intelligent remote multiplexing system, meets
this requirement completely.
SYSTEM OVERVIEW | ONE
The control and automation system used here is a micro based intelligent multiplexing
system. This system, designed on a modular basis, allows to tighten the scope of control
hardware to the particular control strategy and operating requirements of the process
Regardless of the type and extent of process to control provides system uniformity and
integrity for –
Signal conditioning and transmission
Modulating controls
CONTROL AND MONITORING MECHANISMS | TWO
There are basically two types of Problems faced in a Power Plant.
Metallurgical
Mechanical
Mechanical Problem can be related to Turbines that is the max speed permissible for a
turbine is 3000 rpm, so speed should be monitored and maintained at that level
Metallurgical Problem can be view as the max Inlet Temperature for Turbile is 1060 oC so
temperature should be below the limit. Monitoring of all the parameters is necessary for
the safety of both –
Employees
Machines
So the Parameters to be monitored are –
Speed
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Typical Bourdon Tube Pressure Gage
Temperature
Current
Voltage
Pressure
Eccentricity
Flow of Gases
Vacuum Pressure
Valves
Level
Vibration
PRESSURE MONITORING | THREE
Pressure can be monitored by three types of basic mechanisms –
Switches
Gauges
Transmitter type
For gauges we use Bourden tubes : The Bourdon Tube is a non liquid pressure
measurement device. It is widely used in applications where inexpensive static pressure
measurements are needed.
A typical Bourdon tube contains a curved
tube that is open to external pressure input
on one end and is coupled mechanically to
an indicating needle on the other end, as
shown schematically below.
For Switches pressure switches are used and
they can be used for digital means of
monitoring as switch being ON is referred
as high and being OFF is as low. All the monitored data is converted to either Current or
Voltage parameter.
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The Plant standard for current and voltage are as under –
Voltage : 0 – 10 Volts range
Current : 4 – 20 milliAmperes
We use 4mA as the lower value so as to check for disturbances and wire breaks.
Accuracy of such systems is very high .
ACCURACY : + - 0.1 %
The whole system used is SCADA based.
Programmable Logic Circuits ( PLCs) are used in the process as they are the heard of
Instrumentation.
TEMPERATURE MONITORING | FOUR
We can use Thermocouples or RTDs for temperature monitoring.
Normally RTDs are used for low temperatures.
Thermocouple selection depends upon two factors –
Temperature Range
Accuracy Required
Normally used Thermocouple is K Type Thermocouple - Chromel (Nickel-Chromium Alloy)
/ Alumel (Nickel-Aluminium Alloy)
This is the most commonly used general purpose thermocouple. It is inexpensive and, owing
to its popularity, available in a wide variety of probes. They are available in the −200 °C
to +1200 °C range. Sensitivity is approximately 41 μV/°C. RTDs are also used but not in
protection systems due to vibrational errors.
We pass a constant current through the RTD. So that if R changes then the Voltage also
changes.
RTDs used in Industries are Pt100 and Pt1000.
Pt100 : 00C – 100 Ω ( 1 Ω = 2.50C )
Pt1000 : 00C - 1000Ω
Pt1000 is used for higher accuracy.
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The gauges used for Temperature measurements are mercury filled Temperature gauges.
For Analog medium thermocouples are used. And for Digital medium Switches are used
which are basically mercury switches.
FLOW MEASUREMENT | FIVE
Flow measurement does not signify much and is measured just for metering purposes and
for monitoring the processes.
Rotameters | One
A Rotameter is a device that measures the flow rate of liquid or gas in a closed tube. It is
occasionally misspelled as 'rotometer'. It belongs to a class of meters called variable area
meters, which measure flow rate by allowing the cross sectional area the fluid travels
through to vary, causing some measurable effect. A rotameter consists of a tapered tube,
typically made of glass, with a float inside that is pushed up by flow and pulled down by
gravity. At a higher flow rate more area (between the float and the tube) is needed to
accommodate the flow, so the float rises. Floats are made in many different shapes, with
spheres and spherical ellipses being the most common. The float is shaped so that it
rotates axially as the fluid passes. This allows you to tell if the float is stuck since it will
only rotate if it is not.
For Digital measurements Flap system is used.
For Analog measurements we can use the following methods –
Flowmeters
Venurimeters / Orifice meters
Turbines
Massflow meters ( oil level )
Ultrasonic Flow meters
Magnetic Flow meter (water level)
Selection of flow meter depends upon the purpose , accuracy and liquid to be measured
so different types of meters used. Turbine type are the simplest of all. They work on the
principle that on each rotation of the turbine a pulse is generated and that pulse is
counted to get the flow rate.
Venturimeters | Two
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Referring to the diagram, using Bernoulli's equation in the special case of incompressible
fluids (such as the approximation of a water jet), the theoretical pressure drop at the
constriction would be given by (ρ/2)(v22 - v1
2).
And we know that rate of flow is given by
Flow = k √ (D.P)
Where DP is Differential Presure or the Pressure
Drop.
CONTROL VALVES | SIX
A valve is a device that regulates the flow of substances (either gases, fluidized solids,
slurries, or liquids) by opening, closing, or partially obstructing various passageways.
Valves are technically pipe fittings, but usually are discussed separately.
Valves are used in a variety of applications including industrial, military, commercial,
residential, transportation. Plumbing valves are the most obvious in everyday life, but
many more are used.
Some valves are driven by pressure only, they are mainly used for safety purposes in
steam engines and domestic heating or cooking appliances. Others are used in a
controlled way, like in Otto cycle engines driven by a camshaft, where they play a major
role in engine cycle control.
Many valves are controlled manually with a handle attached to the valve stem. If the
handle is turned a quarter of a full turn (90°) between operating positions, the valve is
called a quarterturn valve. Butterfly valves, ball valves, and plug valves are often
quarter-turn valves. Valves can also be controlled by devices called actuators attached to
the stem. They can be electromechanical actuators such as an electric motor or solenoid,
pneumatic actuators which are controlled by air pressure, or hydraulic actuators which
are controlled by the pressure of a liquid such as oil or water.
So there are basically three types of valves that are used in power industries besides the
handle valves. They are –
Pneumatic Valves – they are air or gas controlled which is compressed to turn or
move them.
Hydraulic valves – they utilize oil in place of Air as oil has better compression.
Motorized valves – these valves are controlled by electric motors.
Venturimeter
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FURNACE SAFEGUARD SUPERVISORY SYSTEM | SEVEN
FSSS is also called as Burner Management System (BMS). It is a microprocessor based
programmable logic controller of proven design incorporating all protection facilities
required for such system. Main objective of FSSS is to ensure safety of the boiler.
The 95 MW boilers are indirect type boilers. Fire takes place in front and in rear side.
That‘s why its called front and rear type boiler.
The 210 MW boilers are direct type boilers (which means that HSD is in direct contact
with coal) firing takes place from the corner. Thus it is also known as corner type boiler.
Igniter System | One
Igniter system is an automatic system, it takes the charge from 110kv and this spark is
brought in front of the oil guns, which spray aerated HSD on the coal for coal combustion.
There is a 5 minute delay cycle before igniting, this is to evacuate or burn the HSD. This
method is known as PURGING.
Pressure Switch | Two
Pressure switches are the devices that make or break a circuit. When pressure is applied ,
the switch under the switch gets pressed which is attached to a relay that makes or break
the circuit. Time delay can also be included in sensing the pressure with the help of
pressure valves.
Examples of pressure valves –
Manual valves (tap)
Motorized valves (actuator) – works on motor action
Pneumatic valve (actuator) _ works due to pressure of compressed air
Hydraulic valve
VOCATIONAL TRAINING REPORT
Page 64
CONCLUSION
The training was organized by NTPC Badarpur training department from 29th June to 28th
July 2011 in following departments –
EMD – I
EMD – II
C & I
I am thankful to all the operational and maintenance staff of BTPS. Without their co-
operation the training would not be successful.
Report Submitted.
Aman Samaiyar
1st Year Student
Electrical and Electronics Engineering
Delhi Technological University
(formally Delhi College of Engineering)
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