Report

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.


Page 24

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


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


Page 25

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


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


Page 26

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.


Page 27

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.


Page 28

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


Page 29

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


Page 30

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


Page 31

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.


Page 32

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


Page 33

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.


Page 34

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


Page 35

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


Page 36

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


Page 37

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


Page 38

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


Page 39

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


Page 40

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


Page 41

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


Page 42

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


Page 43

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


Page 44

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


Page 45

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



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



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


Page 46

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.


Page 47

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


Page 48

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.


Page 49

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


Page 50

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.


Page 51

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


Page 52

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.


Page 53

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.


Page 54

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


Page 55

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


Page 56

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.


Page 57

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.


Page 58

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


Page 59

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.


Page 60

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.


Page 61

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


Page 62

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


Page 63

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


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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