Yogesh Report

7/28/2019 Yogesh Report

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BADARPUR

THERMALPOWER

STATION

(A UNIT OF

NTPC)

CONTENTS

BTPS

Submitted by:

YOGESH KUMAR

B.TECH (ELECTICAL ENGG

DEENBANDHU CHHOTU

RAM UNIVERSITY OF

SCIENCE & TECHNOLOGY

MURTHAL,HARYANA.

HARYANA

SUMMER TRAINING REPORT


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Certificate

AcknowledgementTraining at BTPS

1. Introduction

NTPC

Badarpur Thermal Power Station

2. Operation

3. Electrical Maintenance Division-I

HT/LT Switch Gear

HT/LT Motors, Turbine & Boilers Side

CHP/NCHP

4. Electrical Maintenance Division-II

Generator

Transformer & Switchyard

Protection

Lighting

EP


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CERTIFICATE

This is to certify that Yogesh Kumar, student of bachelor of

Technology, ELECTRICAL ENGG., 3rd Year, DCRUST Murthal, Sonipat,

Haryana has successfully completed his industrial Training at

Badarpur Thermal Power Corporation, New Delhi for 25 days from 4th

of July to 29th July 2011. He has completed the whole training as per

the training report submitted by him.

Training Incharge

BTPS/NTPC,

Badarpur,

New Delhi


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ACKNOWLEDGEMENT

With profound respect and gratitude, I take the opportunity toconvey my thanks to complete the training here.

I do extend my heartfelt thanks to Ms. Rachna Singh forproviding me this opportunity to be a part of this esteemedorganisation.

I am extremely grateful to all the technical staff of BTPS / NTPCfor their co-operation and guidance that has helped me a lot duringthe course of training. I have learnt a lot working under them and Iwill always be indebted of them for this value addition in me.

I would also like to thank the training incharge and all the facultymembers of our college, NPTI, Badarpur, for their effort of constantco- operation, which have been a significant factor in theaccomplishment of my industrial training.

YOGESH KUMAR

B.Tech (Electrical Engg.)


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Training at BTPS

I was appointed to do 25 Days training at this esteemedorganization from 5th July to 29th July, 2011. I was assigned to visitvarious division of the plant, which were.

Electrical Maintenance Department -1 (EMD- 1)

Electrical Maintenance Department -2 (EMD- 2)

These 25 Days training was a very educational adventure for me.

It was really amazing to see the plant by yourself and learn howelectricity, which is one of our daily requirements of life, is produced.

This report has been made by my experience at BTPS. Thematerial in this report has been gathered from my textbook, seniorstudent reports and trainers manuals and power journals provided bytraining department. The specification and principles are as learnedby me from the employees of each division of BTPS.

YOGESH KUMAR


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INTRODUCTIONABOUT NTPC

NTPC Limited today is one of the largest companies in India in terms of MarketCapitalization and the single largest player in power sector catering toapproximately 30% of country's power needs. Set up in 1975 by Government ofIndia, today it is a Navratna PSU with a strong workforce of 24,447 powerprofessionals and an annual turnover of Rs.28, 750.7 Crores. The Company has14 coal based and 7 gas based power plants across India with a total installedcapacity of 26,404 MW. Several new projects are underway as the company hasambitious plans of achieving 75,000 MW installed capacity by 2017.

NTPC is providing power at the cheapest average tariff in the country. With itsexperience and expertise in the power sector, NTPC is extending consultancyservices to various organizations in the power business. NTPC has entered into ajoint venture with Alstom, Germany for renovation and modernization of power

plants in India.

NTPC is committed to the environment, generating power at minimalenvironmental cost and preserving the ecology in the vicinity of the plants. It hasundertaken massive afforestation in the vicinity of its plants. Plantations have
http://www.ntpc.co.in/Services_Offered/services_offered.shtmlhttp://www.ntpc.co.in/Services_Offered/services_offered.shtmlhttp://www.ntpc.co.in/aboutus/jointventures.shtmlhttp://www.ntpc.co.in/infocus/environment.shtmlhttp://www.ntpc.co.in/Services_Offered/services_offered.shtmlhttp://www.ntpc.co.in/Services_Offered/services_offered.shtmlhttp://www.ntpc.co.in/aboutus/jointventures.shtmlhttp://www.ntpc.co.in/infocus/environment.shtml


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increased forest area and reduced barren land. The massive afforestation byNTPC in and around its Ramagundam Power station (2100 MW) has contributedreducing the temperature in the areas by about 3c. NTPC has also takenproactive steps for ash utilization. In 1991, it set up Ash Utilization Division tomanage efficient use of the ash produced at its coal stations. This quality of ash

produced is ideal for use in cement, concrete, cellular concrete, building material.

A "Centre for Power Efficiency and Environment Protection (CENPEEP)" has beenestablished in NTPC with the assistance of United States Agency for InternationalDevelopment. (USAID). Cenpeep is efficiency oriented, Eco-friendly and Eco-nurturing initiative - a symbol of NTPC's concern towards environmentalprotection and continued commitment to sustainable power development in India.As a responsible corporate citizen, NTPC is making constant efforts to improve thesocio-economic status of the people affected by its projects. Through itsRehabilitation and Resettlement programmes, the company endeavors toimprove the overall socio-economic status of Project Affected Persons. It was

among the first Public Sector Enterprises to enter into a Memorandum ofUnderstanding (MOU) with the Government in 1987-88.

The development of power in the country was achieved through State ElectricityBoards (SEBS) during the first three decades after independence. The outlay forpower during viii-plan was Rs.34270 crores against Rs.393 crores during the firstplan period. The outlay for power remained 19-20% during all plan periods out oftotal outlay.

Vision:

"To be one of the worlds largest and best power utilities, powering India'sgrowth".

NTPC's vision for the new millennium is inspired by a glorious past, vibrantpresent and a brilliant future.

Mission:

1) Make available reliable and quality power in increasingly large quantitiesat appropriate tariffs, and ensure timely realization of revenues.

2) Speedily plan and implement power projects, with contemporarytechnologies.

3) Implement strategic diversifications in the areas of R&M, Hydro, LNG andnon-conventional and eco-friendly fuels and explore new areas like transmission,information technology etc.
http://www.ntpc.co.in/infocus/ashutilisation.shtmlhttp://www.ntpc.co.in/otherlinks/cenpeep.shtmlhttp://www.ntpc.co.in/aboutus/rrpol.pdfhttp://www.ntpc.co.in/infocus/ashutilisation.shtmlhttp://www.ntpc.co.in/otherlinks/cenpeep.shtmlhttp://www.ntpc.co.in/aboutus/rrpol.pdf


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ABOUT BTPS

Badarpur thermal power station started working in 1973 with a single 95 mw unit.There were 2 more units (95 MW each) installed in next 2 consecutive years. Nowit has total five units with total capacity of 720 MW. Ownership of BTPS wastransferred to NTPC with effect from 01.06.2006 through GOIs GazetteNotification .Given below are the details of unit with the year they are installed.

Address: Badarpur, New Delhi 110 044

Telephone: (STD-011) 26949523Fax: 26949532Installed Capacity 720 MWDerated Capacity 705 MW

Location New Delhi

Coal Source Jharia Coal Fields

Water Source Agra CanalBeneficiary States Delhi

Unit Sizes 3X95 MW2X210 MW

Units Commissioned Unit I- 95 MW - July 1973Unit II- 95 MW August 1974Unit III- 95 MW March 1975Unit IV - 210 MW December 1978Unit V - 210 MW - December 1981


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OPERATIONELECTRICITY FROM COAL

Coal from the coal wagons is unloaded with the help of wagon tipplers in the

C.H.P. this coal is taken to the raw coal bunkers with the help of conveyor belts.

Coal is then transported to bowl mills by coal feeders where it is pulverized and

ground in the powered form.

This crushed coal is taken away to the furnace through coal pipes with the help of

hot and cold mixture P.A fan. This fan takes atmospheric air, a part of which is

sent to pre heaters while a part goes to the mill for temperature control.

Atmospheric air from F.D fan in the air heaters and sent to the furnace as

combustion air.

Water from boiler feed pump passes through economizer and reaches the boiler

drum . Water from the drum passes through the down comers and goes to the

bottom ring header. Water from the bottom ring header is divided to all the four

sides of the furnace. Due to heat density difference the water rises up in the

water wall tubes. This steam and water mixture is again taken to the boiler drum

where the steam is sent to super heaters for super heating. The super heaters are

located inside the furnace and the steam is super heated (540 degree Celsius)

and finally it goes to the turbine.

Fuel gases from the furnace are extracted from the induced draft fan, which

maintains balance draft in the furnace with F.D fan. These fuel gases heat energy

to the various super heaters and finally through air pre heaters and goes to

electrostatic precipitators where the ash particles are extracted. This ash is mixed

with the water to from slurry is pumped to ash period.


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The steam from boiler is conveyed to turbine through the steam pipes and

through stop valve and control valve that automatically regulate the supply of

steam to the turbine. Stop valves and controls valves are located in steam chest

and governor driven from main turbine shaft operates the control valves the

amount used.

Steam from controlled valves enter high pressure cylinder of turbines, where it

passes through the ring of blades fixed to the cylinder wall. These act as nozzles

and direct the steam into a second ring of moving blades mounted on the disc

secured in the turbine shaft. The second ring turns the shaft as a result of force of

steam to the stationary and moving blades together.

MAIN GENERATOR

Maximum continuous KVA rating 24700KVAMaximum continuous KW 210000KWRated terminal voltage 15750VRated Stator current 9050 ARated Power Factor 0.85 lag

Excitation current at MCR Condition 2600 ASlip-ring Voltage at MCR Condition 310 VRated Speed 3000 rpmRated Frequency 50 HzShort circuit ratio 0.49Efficiency at MCR Condition 98.4%Direction of rotation viewed Anti ClockwisePhase Connection Double StarNumber of terminals brought out 9( 6 neutral and 3

phase)


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MAIN TURBINE DAT

Rated output of Turbine 210 MW

Rated speed of turbine 3000 rpm

Rated pressure of steam before emergency 130 kg/cm^2

Stop valve rated live steam temperature 535 degree Celsius

Rated steam temperature after reheat at inlet

to receptor valve

535 degree Celsius

Steam flow at valve wide open condition 670 tons/hour

Rated quantity of circulating water through

condenser

27000 cm/hour

1. For cooling water temperature (degree

Celsius)

24,27,30,33

1.Reheated steam pressure at inlet of

interceptor valve in kg/cm^2 ABS

23,99,24,21,24,49,24

.82

2.Steam flow required for 210 MW in ton/hour 68,645,652,662

3.Rated pressure at exhaust of LP turbine in

mm of Hg

19.9,55.5,65.4,67.7


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THERMAL POWER PLANT

A Thermal Power Station comprises all of the equipment and a subsystem

required to produce electricity by using a steam generating boiler fired with fossilfuels or befouls to drive an electrical generator. Some prefer to use the term

ENERGY CENTER because such facilities convert forms of energy, like nuclear

energy, gravitational potential energy or heat energy (derived from the

combustion of fuel) into electrical energy. However, POWER PLANT is the most

common term in the united state; While POWER STATION prevails in many

Commonwealth countries and especially in the United Kingdom.Such power

stations are most usually constructed on a very large scale and designed for

continuous operation.

1. Cooling water pump

2. Three-phase transmission line

3. Step up transformer

4. Electrical Generator

5. Low pressure steam

6. Boiler feed water pump

7. Surface condenser

8. Intermediate pressure steam turbine

9. Steam control valve

10. High pressure steam turbine

11. Deaerator Feed water heater

12. Coal conveyor

13. Coal hopper

14. Coal pulverizer

15. boiler steam drum

16. Bottom ash hoper

17. Super heater

18. Forced draught(draft) fan

19. Reheater


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20. Combustion air intake

21. Economizer

22. Air preheater

23. Precipitator

24. Induced draught(draft) fan

25. Fuel gas stack

The description of some of the components written above is described as follows:

1.Cooling towers

Cooling Towers are evaporative coolers used for cooling water or other working

medium to near the ambivalent web-bulb air temperature. Cooling tower use

evaporation of water to reject heat from processes such as cooling the circulating

water used in oil refineries, Chemical plants, power plants and building cooling,

for example. The tower vary in size from small roof-top units to very large

hyperboloid structures that can be up to 200 meters tall and 100 meters in

diameter, or rectangular structure that can be over 40 meters tall and 80 meters

long. Smaller towers are normally factory built, while larger ones are constructed

on site.

The primary use of large , industrial cooling tower system is to remove the heat

absorbed in the circulating cooling water systems used in power plants ,

petroleum refineries, petrochemical and chemical plants, natural gas processing

plants and other industrial facilities . The absorbed heat is rejected to the

atmosphere by the evaporation of some of the cooling water in mechanical

forced-draft or induced draft towers or in natural draft hyperbolic shaped cooling

towers as seen at most nuclear power plants.

2.Three phase transmission line

Three phase electric power is a common method of electric power

transmission. It is a type of polyphase system mainly used to power motors and

many other devices. A Three phase system uses less conductor material to


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transmit electric power than equivalent single phase, two phase, or direct current

system at the same voltage. In a three phase system, three circuits reach their

instantaneous peak values at different times. Taking one conductor as the

reference, the other two current are delayed in time by one-third and two-third of

one cycle of the electrical current. This delay between phases has the effect of

giving constant power transfer over each cycle of the current and also makes it

possible to produce a rotating magnetic field in an electric motor.

At the power station, an electric generator converts mechanical power into a set

of electric currents, one from each electromagnetic coil or winding of the

generator. The current are sinusoidal functions of time, all at the same frequency

but offset in time to give different phases. In a three phase system the phases are

spaced equally, giving a phase separation of one-third one cycle. Generators

output at a voltage that ranges from hundreds of volts to 30,000 volts. At the

power station, transformers: step-up this voltage to one more suitable for

transmission.

After numerous further conversions in the transmission and distribution network

the power is finally transformed to the standard mains voltage (i.e. the

household voltage).

The power may already have been split into single phase at this point or it maystill be three phase. Where the step-down is 3 phase, the output of this

transformer is usually star connected with the standard mains voltage being the

phase-neutral voltage. Another system commonly seen in North America is to

have a delta connected secondary with a center tap on one of the windings

supplying the ground and neutral. This allows for 240 V three phase as well as

three different single phase voltages( 120 V between two of the phases and

neutral , 208 V between the third phase ( known as a wild leg) and neutral and

240 V between any two phase) to be available from the same supply.

3.Electrical generator

An Electrical generator is a device that converts kinetic energy to electrical

energy, generally using electromagnetic induction. The task of converting the


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electrical energy into mechanical energy is accomplished by using a motor. The

source of mechanical energy may be a reciprocating or turbine steam engine, ,

water falling through the turbine are made in a variety of sizes ranging from small

1 hp (0.75 kW) units (rare) used as mechanical drives for pumps, compressors

and other shaft driven equipment , to 2,000,000 hp(1,500,000 kW) turbines used

to generate electricity. There are several classifications for modern steam

turbines.

Steam turbines are used in all of our major coal fired power stations to drive the

generators or alternators, which produce electricity. The turbines themselves are

driven by steam generated in Boilers or steam generators as they are

sometimes called.

Electrical power station use large stem turbines driving electric generators to

produce most (about 86%) of the worlds electricity. These centralized stations

are of two types: fossil fuel power plants and nuclear power plants. The turbines

used for electric power generation are most often directly coupled to their-

generators .As the generators must rotate at constant synchronous speeds

according to the frequency of the electric power system, the most common

speeds are 3000 r/min for 50 Hz systems, and 3600 r/min for 60 Hz systems. Most

large nuclear sets rotate at half those speeds, and have a 4-pole generator ratherthan the more common 2-pole one.

Energy in the steam after it leaves the boiler is converted into rotational energy

as it passes through the turbine. The turbine normally consists of several stage

with each stages consisting of a stationary blade (or nozzle) and a rotating blade.

Stationary blades convert the potential energy of the steam into kinetic energy

into forces, caused by pressure drop, which results in the rotation of the turbine

shaft. The turbine shaft is connected to a generator, which produces the electrical

energy.

4.Boiler feed water pump


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A Boiler feed water pump is a specific type of pump used to pump water into a

steam boiler. The water may be freshly supplied or retuning condensation of the

steam produced by the boiler. These pumps are normally high pressure units that

use suction from a condensate return system and can be of the centrifugal pump

type or positive displacement type.

Construction and operation

Feed water pumps range in size up to many horsepower and the electric motor is

usually separated from the pump body by some form of mechanical coupling.

Large industrial condensate pumps may also serve as the feed water pump. In

either case, to force the water into the boiler; the pump must generate sufficient

pressure to overcome the steam pressure developed by the boiler. This is usually

accomplished through the use of a centrifugal pump.

Feed water pumps usually run intermittently and are controlled by a float switch

or other similar level-sensing device energizing the pump when it detects a

lowered liquid level in the boiler is substantially increased. Some pumps contain a

two-stage switch. As liquid lowers to the trigger point of the first stage, the pump

is activated. I f the liquid continues to drop (perhaps because the pump has

failed, its supply has been cut off or exhausted, or its discharge is blocked); the

second stage will be triggered. This stage may switch off the boiler equipment

(preventing the boiler from running dry and overheating), trigger an alarm, or

both.

5. Steam-powered pumps

Steam locomotives and the steam engines used on ships and stationary

applications such as power plants also required feed water pumps. In this

situation, though, the pump was often powered using a small steam engine that

ran using the steam produced by the boiler. A means had to be provided, of

course, to put the initial charge of water into the boiler(before steam power was

available to operate the steam-powered feed water pump).the pump was often a


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positive displacement pump that had steam valves and cylinders at one end and

feed water cylinders at the other end; no crankshaft was required.

In thermal plants, the primary purpose of surface condenser is to condense the

exhaust steam from a steam turbine to obtain maximum efficiency and also to

convert the turbine exhaust steam into pure water so that it may be reused in the

steam generator or boiler as boiler feed water. By condensing the exhaust steam

of a turbine at a pressure below atmospheric pressure, the steam pressure drop

between the inlet and exhaust of the turbine is increased, which increases the

amount heat available for conversion to mechanical power. Most of the heat

liberated due to condensation of the exhaust steam is carried away by the cooling

medium (water or air) used by the surface condenser.

6. Control valves

Control valves are valves used within industrial plants and elsewhere to control

operating conditions such as temperature,pressure,flow,and liquid Level by fully

partially opening or closing in response to signals received from controllers that

compares a set point to a process variable whose value is provided by

sensors that monitor changes in such conditions. The opening or closing of control

valves is done by means of electrical, hydraulic or pneumatic systems

7. Deaerator

A Dearator is a device for air removal and used to remove dissolved gases (an

alternate would be the use of water treatment chemicals) from boiler feed water

to make it non-corrosive. A dearator typically includes a vertical domed

deaeration section as the deaeration boiler feed water tank. A Steam generating

boiler requires that the circulating steam, condensate, and feed water should be

devoid of dissolved gases, particularly corrosive ones and dissolved or suspended

solids. The gases will give rise to corrosion of the metal. The solids will deposit on

the heating surfaces giving rise to localized heating and tube ruptures due to

overheating. Under some conditions it may give to stress corrosion cracking.


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Deaerator level and pressure must be controlled by adjusting control valves- the

level by regulating condensate flow and the pressure by regulating steam flow. If

operated properly, most deaerator vendors will guarantee that oxygen in the

deaerated water will not exceed 7 ppb by weight (0.005 cm3/L)

8. Feed water heater

A Feed water heater is a power plant component used to pre-heat water delivered

to a steam generating boiler. Preheating the feed water reduces the irreversible

involved in steam generation and therefore improves the thermodynamic

efficiency of the system.[4] This reduces plant operating costs and also helps to

avoid thermal shock to the boiler metal when the feed water is introduces back

into the steam cycle.

In a steam power (usually modeled as a modified Ranking cycle), feed water

heaters allow the feed water to be brought up to the saturation temperature very

gradually. This minimizes the inevitable irreversibilitys associated with heat

transfer to the working fluid (water). A belt conveyor consists of two pulleys, with

a continuous loop of material- the conveyor Belt that rotates about them. The

pulleys are powered, moving the belt and the material on the belt forward.

Conveyor belts are extensively used to transport industrial and agricultural

material, such as grain, coal, ores etc.

9. Pulverizer

A pulverizer is a device for grinding coal for combustion in a furnace in a fossil

fuel power plant.

10. Boiler Steam Drum

Steam Drums are a regular feature of water tube boilers. It is reservoir of

water/steam at the top end of the water tubes in the water-tube boiler. They store

the steam generated in the water tubes and act as a phase separator for the

steam/water mixture. The difference in densities between hot and cold water

helps in the accumulation of the hotter-water/and saturated steam into steam


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drum. Made from high-grade steel (probably stainless) and its working involves

temperatures 390C and pressure well above 350psi (2.4MPa). The separated

steam is drawn out from the top section of the drum. Saturated steam is drawn

off the top of the drum. The steam will re-enter the furnace in through a super

heater, while the saturated water at the bottom of steam drum flows down to the

mud-drum /feed water drum by down comer tubes accessories include a safety

valve, water level indicator and fuse plug. A steam drum is used in the company

of a mud-drum/feed water drum which is located at a lower level. So that it acts

as a sump for the sludge or sediments which have a tendency to the bottom.

11. Super HeaterA Super heater is a device in a steam engine that heats the steam generated by

the boiler again increasing its thermal energy and decreasing the likelihood that it

will condense inside the engine. Super heaters increase the efficiency of the

steam engine, and were widely adopted. Steam which has been superheated is

logically known as superheated steam; non-superheated steam is called

saturated steam or wet steam; Super heaters were applied to steam

locomotives in quantity from the early 20th century, to most steam vehicles, and

so stationary steam engines including power stations.

12. Economizers

Economizer, or in the UK economizer, are mechanical devices intended to

reduce energy consumption, or to perform another useful function like preheating

a fluid. The term economizer is used for other purposes as well. Boiler, power

plant, and heating, ventilating and air conditioning. In boilers, economizer are

heat exchange devices that heat fluids , usually water, up to but not normally

beyond the boiling point of the fluid. Economizers are so named because they can

make use of the enthalpy and improving the boilers efficiency. They are a device

fitted to a boiler which saves energy by using the exhaust gases from the boiler

to preheat the cold water used the fill it (the feed water). Modern day boilers,


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such as those in cold fired power stations, are still fitted with economizer which is

decedents of Greens original design. In this context they are turbines before it is

pumped to the boilers. A common application of economizer is steam power

plants is to capture the waste hit from boiler stack gases (flue gas) and transfer

thus it to the boiler feed water thus lowering the needed energy input , in turn

reducing the firing rates to accomplish the rated boiler output . Economizer lower

stack temperatures which may cause condensation of acidic combustion gases

and serious equipment corrosion damage if care is not taken in their design and

material selection.

13. Air Preheater

Air preheater is a general term to describe any device designed to heat air before

another process (for example, combustion in a boiler). The purpose of the air

preheater is to recover the heat from the boiler flue gas which increases the

thermal efficiency of the boiler by reducing the useful heat lost in the fuel gas. As

a consequence, the flue gases are also sent to the flue gas stack (or chimney) at

a lower temperature allowing simplified design of the ducting and the flue gas

stack. It also allows control over the temperature of gases leaving the stack.

14. Precipitator

An Electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate

device that removes particles from a flowing gas (such As air) using the force of

an induced electrostatic charge. Electrostatic precipitators are highly efficient

filtration devices, and can easily remove fine particulate matter such as dust and

smoke from the air steam.

ESPs continue to be excellent devices for control of many industrial particulate

emissions, including smoke from electricity-generating utilities (coal and oil fired),

salt cake collection from black liquor boilers in pump mills, and catalyst collection

from fluidized bed catalytic crackers from several hundred thousand ACFM in the

largest coal-fired boiler application.


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The original parallel plate-Weighted wire design (described above) has evolved as

more efficient ( and robust) discharge electrode designs were developed, today

focusing on rigid discharge electrodes to which many sharpened spikes are

attached , maximizing corona production. Transformer rectifier systems apply

voltages of 50-100 Kilovolts at relatively high current densities. Modern controls

minimize sparking and prevent arcing, avoiding damage to the components.

Automatic rapping systems and hopper evacuation systems remove the collected

particulate matter while on line allowing ESPs to stay in operation for years at a

time.

15. Fuel gas stack

A Fuel gas stack is a type of chimney, a vertical pipe, channel or similar structure

through which combustion product gases called fuel gases are exhausted to the

outside air. Fuel gases are produced when coal, oil, natural gas, wood or any

other large combustion device. Fuel gas is usually composed of carbon dioxide

(CO2) and water vapor as well as nitrogen and excess oxygen remaining from the

intake combustion air. It also contains a small percentage of pollutants such as

particulates matter, carbon mono oxide, nitrogen oxides and sulfur oxides. The

flue gas stacks are often quite tall, up to 400 meters (1300 feet) or more, so as to

disperse the exhaust pollutants over a greater aria and thereby reduce the

concentration of the pollutants to the levels required by governmental

environmental policies and regulations.

When the fuel gases exhausted from stoves, ovens, fireplaces or other small

sources within residential abodes, restaurants , hotels or other stacks are referred

to as chimneys.


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EMD IElectrical Maintenance division II was assigned to do training in Electrical maintenance division I from 9th

July 2011 to 15th July 2011.

This two week - training in this division were divided as follows.

HT/LT switchgear

HT/LT Motors, Turbine &Boiler side

CHP/NCHP Electrical

EMD 1 is responsible for maintenance of:

1. Boiler side motors

2. Turbine side motors

3. Outside motors

4. Switchgear

5. A.C. MOTORS

INTRODUCTION & PRINCIPLE OF OPERATION:

As in a machine is simply an electric transformer whose magnetic circuit

is separated by an air gap into two relative movable portions, one

carrying the primary and other secondary winding; then the latter is

short circuited or closed through external impedance.

The electromagnetic forces corresponding to the power thus transferred

across the air gap by induction produce relative motion between the

primary and secondary structure.


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1. Boiler side motors: For 1, units 1, 2, 3

1.1D Fans 2 in

no.2.F.D Fans 2 in

no.3.P.A.Fans 2 in

no.4.Mill Fans 3 in

no.5.Ball mill

fans

3 in

no.

6.RC feeders 3 in

no.7.Slag

Crushers

5 in

no.8.DM

Make up Pump

2 in

no.9.PC Feeders 4 in

no.10.Worm

Conveyor

1 in

no.

11.Furnikets4 in

no.

For stage units 1, 2, 3

1.I.D Fans 2 in no.2.F.D Fans 2 in no.

3.P.A Fans 2 in no.4.Bowl

Mills

6 in no.

5.R.C

Feeders

6 in no.

6.Clinker

Grinder

2 in no.


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7.Scrapper 2 in no.8.Seal Air

Fans

2 in no.

9.Hydrazin

e andPhosphorou

s Dozing

2 in no.

1. COAL HANDLING PLANT (C.H.P)

2. NEW COAL HANDLING PLANT (N.C.H.P)

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

1. Wagon Tippler: - 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.2. Conveyor: - 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


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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.

3. Zero Speed Switch:-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.

4. Metal Separators: - 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

5. Crusher: - 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.

6. Rotatory Breaker: - 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.


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MILLING SYSTEM

1. RC Bunker: - Raw coal is fed directly to these bunkers. These are 3

in no. per boiler. 4 & tons of coal are fed in 1 hr. the depth of bunkers

is 10m.

2. RC Feeder: - 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.

3. Ball Mill: - 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.

4. Classifier:- 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.

5. Cyclone Separators: - It separates the pulverized coal from

carrying medium. The mixture of pulverized coal vapour caters the

cyclone separators.


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6. The Tturniket: - It serves to transport pulverized coal from cyclone

separators to pulverized coal bunker or to worm conveyors. There are 4

turnikets per boiler.

7. Worm Conveyor: - 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.

8. Mills Fans: - It is of 3 types:

Six in all and are running condition all the time.

(a) ID Fans: - Located between electrostatic precipitator and

chimney.

Type-radical

Speed-1490 rpm

Rating-300 KW

Voltage-6.6 KV

Lubrication-by oil

(b) FD Fans: - Designed to handle secondary air for boiler. 2 in number

and provide ignition of coal.

Type-axial

Speed-990 rpm

Rating-440 KW

Voltage-6.6 KV

(c)Primary Air Fans: - Designed for handling the atmospheric air up to

50 degrees Celsius, 2 in number. And they transfer the powered coal to

burners to firing.


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NCHP

1. Wagon Tippler:-

Motor Specification

(i) H.P 75 HP

(ii) Voltage 415, 3 phase

(iii) Speed 1480 rpm

(iv) Frequency 50 Hz

(v) Current rating 102 A

2. Coal feed to plant:-

Feeder motor specification

(i) Horse power 15 HP

(ii) Voltage 415V,3 phase

(iii) Speed 1480 rpm

(iv) Frequency 50 Hz

3. Conveyors:-

10A, 10B

11A, 11B

12A, 12B

13A, 13B

14A, 14B

15A, 15B

16A, 16B

17A, 17B

18A, 18B

4. Transfer Point 6


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5. Breaker House

6. Rejection House

7. Reclaim House

8. Transfer Point 7

9. Crusher House

10. 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 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 100mmsq of hammer are rejected via conveyors 18A,18B to the rejection house

. Extra coal is to sent to the reclaim hopper via conveyor 16. From

breaker house coal is taken to the TP7 via Conveyor 13A, 13B.

Conveyor 17A, 17B also supplies coal from reclaim hopper, From TP7

coal is taken by conveyors 14A, 14B to crusher house whose function is

to render the size of coal to 20mm sq. now the conveyor labors are

present whose function is to recognize and remove any stones moving

in the conveyors . In crusher before it enters the crusher. After being

crushed, if any metal is still present it is taken care of by metal

detectors employed in conveyor 10.


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SWITCH GEAR-It makes or breaks an electrical circuit.

1. Isolation: - 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.

2. Switching Isolation: - 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.

3. Circuit Breakers: - 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

4. Load Break Switches: - These are those interrupting devices which

can make or break circuits. These are normally on same circuit, which

are backed by circuit breakers.

5. Earth Switches: - 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 equipments do not handle any

appreciable current at all. Apart from this equipment there are a

number of relays etc. which are used in switchgear.

LT Switchgear : It is classified in following ways:-


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1. Main Switch:- 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.

2. Fuses: - 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.

3. Contractors: - AC Contractors are 3 poles suitable for D.O.L Starting

of motors and protecting the connected motors.

4. Overload Relay: - 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.

5. Air Circuit Breakers: - 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.

HT SWITCH GEAR:-

1. Minimum oil Circuit Breaker: - 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


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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 Asymmetrical360 MVA Symmetrical

Operating Coils-CC 220 V/DC

FC 220V/DC

Motor Voltage-220 V/DC

2. Air Circuit Breaker: - In this the compressed air pressure around 15

kg per cm^2 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:-

i. Fire hazard due to oil are eliminated.

ii. Operation takes place quickly.

iii. There is less burning of contacts since the duration is short and

consistent.

iv. Facility for frequent operation since the cooling medium is

replaced constantly.

Rated Voltage-6.6 KV

Current-630 A


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Auxiliary current-220 V/DC

3. SF6 Circuit Breaker: - 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 Breakers-HPA

Standard-1 EC 56

Rated Voltage-12 KV

Insulation Level-28/75 KV

Rated Frequency-50 Hz

Breaking Current-40 KA

Rated Current-1600 A

Making Capacity-110 KA

Rated Short Time Current 1/3s -40 A

Mass Approximation-185 KG

Auxiliary Voltage

Closing Coil-220 V/DC

Opening Coil-220 V/DC

Motor-220 V/DC

SF6 Pressure at 20 Degree Celsius-0.25 KG

SF6 Gas Per pole-0.25 KG

4. Vacuum Circuit Breaker: - 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


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better that all other medium except air and sulphur which are generally

used at high pressure.

Rated frequency-50 Hz

Rated making Current-10 Peak KA

Rated Voltage-12 KV

Supply Voltage Closing-220 V/DC

Rated Current-1250 A

Supply Voltage Tripping-220 V/DC

Insulation Level-IMP 75 KVP

Rated Short Time Current-40 KA (3 SEC)

Weight of Breaker-8 KG


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EMD IIElectrical Maintenance division III was assigned to do training in Electrical maintenancedivision II from 15th July 2010 to 29th July 2011. This two weekof training in this division were divided as follows.

Generator & Transformer

Switchyard

Protection

Lighting


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Generator and Auxiliaries

The transformation of mechanical energy into electrical energy is

carried out by the Generator.

Working Principle

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 Webers.

F = Frequency in cycles per second or Hertz.N = Number of turns in a coil of stator winding

F = Frequency = Pn/120

Where P = Number of poles

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.


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Generator component

Rotor :

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

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, bodyand 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


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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 forinspection. Slots are then machined for

windings and ventilation.

Rotor winding:

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:

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


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circumference at each

end.

Stator:

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 ofgirder 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 thedouble frequency vibrations inherent in 2 pole generators. The end 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:

a)There is an increase in core stacking factor with improvement in lamination coldRolling and in cold buildings techniques.

b) 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 Windings: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


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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 withblocks 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 :

The 200/210 MW Generator is provided with an efficient cooling

system to avoid excessive heating and consequent wear and tear of its

main components during operation.

Rotor Cooling System

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

inherent advantage of eliminating the deformation of copper due to

varying temperatures.

Hydrogen Cooling System


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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 thegenerator 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 of

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 thetimes.

Provide indication to the operator about the condition of the gas insidethe machine i.e. its pressure, temperature and purity.

Continuous circulation of gas inside the machine 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 SystemThe 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 demineralised water (DM water) through hollow conductors.

The cooling water used for cooling stator winding calls for the use ofvery 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 values. The system is designed to

maintain a constant rate of cooling water flow to the stator winding at


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a nominal inlet water temperature of 40 deg.C.


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Rating of 95 MW Generator

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 connection - 3 phase

Rating of 210 MW Generator

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 V

Speed - 3000 rpm

Power factor - 0.85

Frequency - 50 Hz

Hydrogen - 3.5 Kg/cm2

Stator wdg connection - 3 phase star connection

Insulation class - B

TRANFORMER


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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 worlds electrical power has passed

trough a series of transformer by the time it reaches the consumer.

Rating of transformerManufactured by Bharat heavy electrical limited

No load voltage (hv) - 229 KV

No load Voltage (lv) -10.5 KV

Line current (hv) - 315.2 A

Line current (lv) - 873.2 A

Temp rise - 45 Celsius

Oil quantity -40180 lit

Weight of oil -34985 KgTotal weight - 147725 Kg

Core & winding - 84325 Kg

Phase - 3

Frequency - 50 Hz


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LIGHTING

Lighting includes both artificial light sources such as lamps and natural

illumination of interiors from daylight. Lighting represents a major component of

energy consumption, accounting for a significant part of all energy consumed

worldwide. Artificial lighting is most commonly provided today by electric lights,

but gas lighting, candles or oil lamps were used in the past, and still are used in

certain situations. Proper lighting can enhance task performance or aesthetics;

while there can be energy wastage and adverse health effects of lighting

220 KV SWITCHYARD

BUS BARS: The arrangement in the 220kV switchyard comprises of a 220kVdouble bus bar system, with a bus coupler and a by pass bus. With thisarrangement it is possible to take out any one breaker for maintenance withoutinterruption of supply. In the eventuality of a bus bar or a circuit breaker fault theperiod for which supply is interrupted is the time taken to transfer the feedersfrom the faulty bus to the healthy one or replacing the faulty circuit breaker bythe 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 themaintenance shall be transferred to the other bus by closing one bus isolator andopening the other. The bus coupler shall be tripped and the earthing switchclosed. After the maintenance work is over, the earthing switch must be openedbefore the respective bus bar is energized.

For maintenance of the by-pass bus, it should be ensured that by-pass breaker isopen and all the by pass isolators of various bays are open.

220KV CIRCUIT BREAKERS:There are two types of 220kV breakers being usedin BTPS switchyard: Air blast ciruit breaker

SF6 circuit breaker

These breakers operate with sequential isolators and suitable for three-phaseauto-reclosing facility. These breakers can be operated from the switch yard
http://en.wikipedia.org/wiki/Light_sourcehttp://en.wikipedia.org/wiki/Daylighthttp://en.wikipedia.org/wiki/Electric_lighthttp://en.wikipedia.org/wiki/Gas_lightinghttp://en.wikipedia.org/wiki/Candlehttp://en.wikipedia.org/wiki/Oil_lamphttp://en.wikipedia.org/wiki/Light_pollution#Effects_on_human_health_and_psychologyhttp://en.wikipedia.org/wiki/Light_sourcehttp://en.wikipedia.org/wiki/Daylighthttp://en.wikipedia.org/wiki/Electric_lighthttp://en.wikipedia.org/wiki/Gas_lightinghttp://en.wikipedia.org/wiki/Candlehttp://en.wikipedia.org/wiki/Oil_lamphttp://en.wikipedia.org/wiki/Light_pollution#Effects_on_human_health_and_psychology


49/60

control board. In case of failure, emergency manual handles are provided in thecontrol kiosk.

Feeder breaker: When it is required to maintain either a line or a generator or atransformer 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: the main purpose of the by pass breaker is to facilitatemaintenance/repair of other 220 kV breakers without the necessity of tripping outthe associated circuit.

Bus coupler breaker: The two bus bars can be kept coupled through buscouplers. The by pass breaker cannot act as a substitute for bus coupler breakerwhen the bus coupler breaker is being maintained. If buses I and II are paralleledby means of bus coupler and by pass breaker then in order to maintain the buscoupler breaker all feeders must be transferred to one bus depending upon the

prevalent load.

RATINGS OF CIRCUIT BREAKERS:

1. AIR BLAST CIRCUIT BREAKER (BHEL)

Volts: 220 kV

Amperes: 1200A

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: 220V DC

Tripping coil voltage: 220V DC

Working pressure: Max. 28.1 kg/cm2-g

Min. 26.0 kg/cm2

-gLockout pressure: 21.1 kg/cm2-g

2. AIR BLAST CIRCUIT BREAKER (ABB)

Volts: 245 kV

Amperes: 1200A


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Breaking capacity: symmetrical 31.5 kA

Asymmetrical 38.4 kA


Closing coil voltage: 220V DCTripping coil voltage: 220V DC

RIL at 50 Hz: 480 kV

VI impulse: 1.2/50s 1050 kV per sec.

U switching impulse: first pole to clear 1.3

Mass: 1830 Kg

Working pressure: max. 27.31 kg/cm2-g

3. AIR BLAST CIRCUIT BREAKER (BHEL)

Volts: 245 kV

Amperes: 2000A


Closing coil voltage: 220V DC

Tripping coil voltage: 220V DC

Working gas pressure: 6.1 kg/cm2-g at 200c

Rated frequency and voltage for auxiliary: 415AC 50Hz

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: 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


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with the circuit breakers to prevent mal-operation. No interlocking arrangements

are provided for the bus earthing switches.

Main bus isolators: to maintain the main bus isolators the corresponding bushas 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 by

pass breaker and the earthing switches are closed.

By pass isolator: 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: 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: The corresponding bus must be shut down and earthing switches

on the isolator closed for maintenance.

PNEUMATIC SYSTEM: 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 -70C. 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.

POWER LINE COMMUNICATION EQUIPMENT: To maintain the power line

carrier communication equipment like wave trap or coupling capacitor the


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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: 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: 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: 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


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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 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 isdeflected 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: 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

1. Gen-Tr-1 1. Gen-Tr-2

2. Gen-Tr-3 2. Gen-Tr-4

3. Gen-Tr-5 3. IP line I

4. IP line I 4. Mehrauli line II

5. Mehrauli line I 5. Ballabgarh line II

6. Ballabgarh line I 6. Noida line

7. Alwar line 7. Okhla line-1I

8. Okhla line-1 8. Stn Tr-2

9. Stn Tr-1 9. Bus coupler

10. Stn Tr-3 10. By pass bay


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SYNCHRONISING: 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 andfrequency 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.

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: 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

1. High speed biased differential relay: 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.


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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.

2. Directional inverse time over current and earth fault relays: 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.

3. Instantaneous voltage relay: 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.

4. Auxiliary relays: 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.

5. High speed tripping relays: 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.

6. Definite time delay relay: 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.


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7. Trip circuit supervision relay: this VAX relay is applied for after closing or

continuous supervision of the trip circuit of circuit breakers. They detect the

following conditions:

a) Failure of trip relayb) Open circuit of trip coil

c) Failure of mechanism to complete the tripping operation

8. Instantaneous over current and earth fault relay: 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.

9. Inverse time over current and earth fault relay: 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.

10. Fuse failure relay: 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 cant be

energized. But one or more fuses blow the coil is energized and relay operates.

11. Instantaneous high stability circulating current relay: it is used to

serve the following three purposes

a) Differential protection of Ac machines , reactors auto transformers and bus

bars

b) Balanced and restricted earth fault protection of generator of generator and

transformer windings

c) Transverse differential protection of generators and parallel feeders.


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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 protectioncurrent 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.

12. Local breaker back up relay: 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.

13. Poly-phase directional relay: 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 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.

14. Auto reclose relay: five types of auto reclose relays are available

a) 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.

b) 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.


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c) VAR 42 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.d) 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.

e) Var81 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.

REACTANCE DISTANCE SCHEME: this scheme consists of the following relays,

XCG22-3 for phase to phase and 3 for phase to ground, YCG17, mho starting unit

one in each place, VAT51 along with timing unit for zone 2 and 3, 86-X aux.

tripping relay and 30G, H, and J for 1 st, 2nd and 3rd. Zone indication VAA51, CAG12

and VAA31.

Theses schemes provide three zone phase and earth fault protection using

reactance relays type XCG22 and also starting relays YCG17. They are applicable

to important line sections where high values of arc resistance would otherwise

effect the accuracy of measurement and where high speed tripping is essential.

High-speed protection is provided for phase and earth faults on 80-90% of the line

section and faults on the remaining section are cleared in second zone, time. The

third zone provides backup protection after further time interval.

Each mho starting unit Y3 and its auxiliary Y3 X is associated with one phase and

operates for all faults involving this phase. Each reactance unit X is connected to

measure phase or earth fault distance, but is prevented from operating by short

circuit across the polarizing coils

LINE FAULT

DETECTORS Y3

EARTH FAULT

DETECTORS 64


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The principle of distance scheme is shown in the above block diagram

Under the phase fault conditions, the Y3 X units unblock the appropriate X1

reactance units, which initiate tripping immediately for faults within their setting.

Operation of the earth auxiliary relay 64 in conjunction with the Y3 X units selects

the appropriate reactance units for measurement of earth faults. The reach of

reactance units is extended by the timer, 2 after successive intervals to cover

ZONE

TIMING 2

EARTH FAULT

REACTANCE

UNITS X2

RANGE

EXTENSION 2X2X

PHASE FAULT

REACTANCE UN

X1

TRIPPING AND

INDICATION 30

DETECTOR

AUXILIARIES

Y3X

TRIP REINFORCI

86X


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faults in zone 2 and 3. Discrimination is not affected by changing faults, for

example a zone 2 earth fault which develops into a double phase to earth fault

will be cleared correctly by the X1 (phase fault) units in zone 2 time. In the rare

event of two faults occurring simultaneously at different points on the line; thescheme will measure to a distance approx. half way.

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Yogesh Report