study of various systems in 500mw thermal power plant

A

Main Project ReportOn

“STUDY OF VARIOUS SYSTEMS IN 500MW THERMAL POWERPLANT”

Submitted in Fulfillment of the RequirementsFor The Award of the Degree

BACHELOR OF TECHNOLOGY

in

ELECTRICAL AND ELECTRONICS ENGINEERINGby

G.RAVI KUMAR - 116U1A0213

R.TRIVENI - 116U1A0242

I.VENKATESWARLU - 116U1A0217

G.RAJASHEKAR REDDY - 116U1A0216

Under The Esteemed Guidance ofSri. B.V.MURALI PRASAD

A.D.E/EM, Stage-4Dr. NTTPS

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

SREEKAVITHA INSTITUTE OF SCIENCE & TECHNOLOGY

(Approved by AICTE–New Delhi & Affiliated to JNTU-Hyderabad)

KRISHNAPURAM (V), MADHIRA (M), KHAMMAM-507203 (T.S)

MADHIRA (M), KHAMMAM-507203 (T.S)

ACKNOWLEDGEMENT

We would like to express our sincere thanks to external project guides

Mr. B.V.MURALI PRASAD A.D.E/E.M/Stage-4,Dr. NTTPS, for his

magnificent guidance which enlighten us the thing “achievable” from

“inconceivable”.

We render our thanks to Chairman, Mr.P.USHA KIRAN KUMAR

M.Tech who encourage in doing this project.

We are indebted to our beloved Principal, Prof. V. CHINNIAH, Ph.d for

his kind consent in doing the course, project and incitement towards us.

We found immense pleasure in expressing our gratitude to

SRI.G.VENKAT, M.Tech HEAD OF THE DEPARTMENT, department of

electrical engineering, for his timely help throughout the project schedule and

the course of study.

We would like to express our sincere thanks and heart full gratitude to

Mr. R.PRABHAKARA RAO, Chief Engineer/DR.NTTPS, for permitting usto do this project work.

We feel extremely proud to thank all the staff members for their stunning

support during the course of our dissertation work.

Finally, We thank one and all who directly and indirectly helped us to

complete our project successfully.





DECLARATION

We hereby declare that the project report entitled “STUDY OF VARIOUS SYSTEMSIN 500MW THERMAL POWER PLANT” Is done by us, submitted in partial fulfillment of

the requirements for the award of the degree in Bachelor of Technology in Electrical And

Electronics Engineering Jawaharlal Nehru Technological University Hyderabad.

PROJECT ASSOCIATIVES





DATE:

PLACE:

INDEX

NAME OF THE TOPIC PAGE.NO

List of the figures i

List of the tables iii

Abstract iv

Introduction v

About Dr .NTTPS vi

The Process of Power Generation vii

CHAPTER-1GENERALLAYOUT&BASICIDEA

1.1 Introduction 11.2 Fuel & Ash Circuit 21.3 Air and Gas Circuit 21.4 Feed Water And Steam Circuit 21.5 Cooling Water Circuit 31.6 Measurement Parameters In A Thermal Power Plant 4

CHAPTER-2 COALHANDLINGPLANT

2.1 Introduction 72.2 Wagon Unloading System 72.3 Crushing System 8

2.3.1Crusher House 82.3.2Construction & Operation 9

2.4 Conveying System 92.4.1 Stacker Re-Claimer 92.4.2 Conveyor Belt Specification of

Stacker / Re-Claimer 10

CHAPTER-3 ASHHANDLINGPLANT3.1 Types of Plants 113.2 FuelAndAsh Plant 113.3 Air& GasPlant 113.4 Ash Disposal &DustCollection Plant 12

CHAPTER-4ELECTRO-STATICPRECIPITATOR4.1 Introduction 134.2 Precipitator Components 134.3 Theory of Precipitation 144.4 Particle Charging 15

4.4.1 Corona Discharge-Free Electron Generation 15

4.4.2 Ionization of Gas Molecules 16

4.4.3 Charging of Particles 164.4.4 Particle Charging Mechanisms 17

4.5 Electric Field Strength 184.5.1 Particle Collection 18

4.5.2 Particle Removal 19

CHAPTER-5BOILER5.1 Introduction 20

5.2 Boilers Classification 21

5.3 Furnace 22

5.4 Pulverised Fuel System 22

5.5 Fuel Oil System 23

5.6 Boiler Drum 24

5.7 Draft System 25

5.8 Draught Fans 255.8.1 Primary air fan(P.A. fan)or Exhauster fan 265.8.2 Forced draught fan(F.D. fan) 265.8.2 Forced draught fan(F.D. fan) 26

5.9 Economizer 27

5.10 Water Walls 27

5.11 Air-Pre Heaters 27

5.12 Super Heater 28

5.13 Re-Heater 29

5.14 Circulation System 29

5.15 Soot Blower 30

5.16 Start up Devices 31

5.17 Safety Valves 31

5.18 De-Aerator 31

5.19 Boiler Specifications 32

CHAPTER-6STEAM TURBINE

6.1 Introduction 37

6.2 Principal of Operation of Steam Turbine 38

6.3 Description of Steam Turbines 396.3.1 Steam flow 396.3.2 HP Turbine 396.3.3 IP Turbine 406.3.4 LP Turbine 406.3.5 Turbine Driven Boiler Feed Pump 40

6.4 Sectional Arrangement of 500mw Turbine Set 41

CHAPTER-7 GENERATOR7.1 Introduction 427.2 Working Principle 427.3 Stator 437.4 Rotor 447.5 Generator Ratings 45

CHAPTER-8 CONDENSER AND COOLING TOWERS8.1 Introduction 468.2 Condensers Specification Used In Dr.Nttps 468.3 Cooling Towers 47

CHAPTER-9 WATER TREATMENT PLANT9.1 Introduction 48

9.2 D.M. Plant 48

9.3 C.W. Plant 49

9.4 B.C.W. Pump House 49

CHAPTER-10 TRANSFORMERS10.1 Introduction 50

10.1.1 Basic Principle 5010.1.2 Induction Law 51

10.2 Types of Transformer 53

CHAPTER-11 SWITCH YARD

11.1 Introduction 55

11.2 Switch Yard Circuit And Equipments 5511.2.1 Creepage Distance 5611.2.2 Clearence 56

11.2.3 Tasks of The Switch Yard 5611.2.4 Classification of Switchyard 58

11.3 Components In 400kv(EHT) Electrical System 58

11.4 Circuit Breakers 6111.4.1 Classifications of Circuit Breakers 61

11.5 SF6 Circuit Breaker 62

11.5.1 Construction and Operation 62

11.6 Instrument Transformers 6411.6.1 Current Transformers 6411.6.2 Potential Transformers 6511.6.3 Differences Between C.T & P.T 66

11.7 Types of Voltage Transformers 66

11.7.1 Capacitor Voltage Transformers 66

11.8 PLCC 68

11.9SCADA 68

CHAPTER-12 Dr. NTTPS STAGE-4 PLANT START UP PROCEDURE

12.1 Cold Start up Procedure 70

12.2 Shut Down Procedure 71

CONCLUSION 73

REFERENCE 74

i

LIST OF THE FIGURES

NAME OF THE FIGURE PAGE.NO

Figure: 1.1 Layout of 500MW PowerPlant 1

Figure: 1.2 Cross Sectional View of Four Major Part Form A Power Plant 3

Figure:2.1 WagonTripler 8

Figure: 2.2 Stacker / Re-claimer 10

Figure: 3.1 Ash Disposal & Dust Collection 12

Figure: 4.1 Typical Dry Electrostatic Precipitator 15

Figure:5.1 Furnace 22

Figure:5.2 PulverizedFuel System 23

Figure:5.3 Steam Drum 24

Figure:5.4 Economizer 26

Figure:5.6 Pressure Parts 30

Figure:5.7 De-aerator 32

Figure:6.1 Steam Turbine 37

Figure:6.2 Sectional Arrangement of 500mw Turbine Set 41

Figure:7.1 Cross section of Generator 42

Figure:7.2 Stator Frame 43

Figure:7.2 Rotor 44

Figure:8.1 Cooling Tower 47

Figure:10.1 Transformer 50

Figure:10.2 Ideal Transformer. 51

ii

Figure:10.3 Mutual Induction 52

Figure:11.1 Single Line Diagram 57

Figure:11.2 Wave trap 60

Figure:11.3 SF6 Circuit Breakers. 63

Figure:11.4 Line DiagramofCT 64

Figure:11.5 Line DiagramofPT 65

Figure:11.6 Capacitor Voltage Transformer 67

iii

LIST OF THE TABLES

NAME OF THE TABLE PAGE. NO

10.1 Ratings of Different Transformers 54

11.1 Clearence For 400KV Lines 56

iv

ABSTRACT

The development of a country depends mainly on amount of power generation. We

have more established thermal power plants in India. In a thermal power plant, the energy from

the heat of coal is transferred to water to make it as steam.

To meet the variation of fluctuating demands of different consumers from time to

time, the power plants has to optimize their efficiency of its components like boiler, turbine etc.

The study of turbine operation and performance plays a vital role for different working

conditions of power plant. The source stem must be effectively delivered by the boiler to obtain

desired power.

The main the me of this project is to study the operation , maintenance and protection

of power transformer used in stage-IV , Dr.NTTPS

The power generated by generator is synchronized to grid through generator

transformed by stepping of the generator voltage 21KV to 400KV grid voltage in order to meet

the maximum load demand by reading the transmission losses.

v

INTRODUCTION

Electricity is the only form of energy that can be easy to produce, easy to transport,

easy to use and easy to control. So, it is mostly the terminal form of energy for transmission and

distribution. Electricity consumption per capita is the index of living standard of people of a

place or a country.

The basic energy conservation cycle in Thermal Plant is as follows:

CHEMICAL THERMAL STEAM MECHANICAL ELECTRICAL

ENERGY ENERGY ENERGY ENERGY ENERGY

The thermal power plants are the major power generating source in India. Almost 70%

of the total generated electrical power comes from the thermal power plants. Any thermal power

plant is converting the chemical energy of coal or other fuel into electrical energy. The process

involved in this based upon the modified rankine cycle.

Any thermal power plant has three apparatus: Boiler, Turbine, and generator. Its

operation involves the production of the super heated steam in the boiler which rotates the

turbine where the mechanical energy gets converted into electrical energy. The basic raw

materials are coal and water.

The major reasons for the losses in power generation by thermal power plant are mainly

due to the reduction in boiler efficiency and inefficient ash disposal system. In the thermal power

stating major losses are occurred in condenser and it is about 44.3% and boiler losses are 14%

and remaining losses are occurred in turbine and auxiliary systems.So, the plant losses can be

reduced by decreasing the above losses.

vi

ABOUT Dr .NTTPS

In these modern world electrical power plays an important and vital role for development

of any country. the power generation of such electrical power, many generating stations are

installed. There are several types of power stations already in existence they are:

1) Hydel 2) Thermal 3) Nuclear 4) Tidal 5) Wind power stations etc….

In Andhra Pradesh there are different power stations under the management of

APGENCO. The important power stations are as follows:

1. DrNarla Tata Rao Thermal Power Station (Dr.NTTPS), Ibrahimpatnam. (6x210MW,

1x500MW)

2. Rayalaseema Thermal Power Project, Muddanur, Kadapa (5x210 MW)

3. Sri DamodaramSanjeevaiah Thermal Power Project, Krishnapatnam (SDSTPS)

4. Srisailam Right Power House (7x110MW, Hydel)

Among all such types of power stations, the most reliable and uninterrupted power supply

is from Thermal power station. Dr.Narla Tata Rao thermal power station which is the largest

installed capacity in AP GENCO.

Dr.NTTPS is located 16Km away from Vijayawada on the bank of river Krishna at

Ibrahimpatnam village. Dr.NTTPS now has a installed capacity of 1760MW at Generated

voltages of 15.75KV and 21KV. Since the generator is driven by steam turbine as prime mover,

it is called turbo generator. The excitation and protection of such huge capacity drive is very

critical and is quite interesting to study its aspects. It consists of turbine on the front side of as

prime mover and exciter on the back side providing necessary excitation to the generator field.

Dr.NTTPS has become a prestigious power station in the country and bagged many awards and

rewards. The construction of 4 stages of the Dr. Narla Tata Rao thermal power station was

commenced in 1978 and was completed in the year of 2009.

vii

THE PROCESS OF POWER GENERATION

Water from the river enters into demineralization water plant. The hard water is

purified and tend becomes as soft water after removal of impurities in water in D.M.plant. The

purified water flows into low pressure heater of heating water. After LPH the water enters into

the De-aerator and water is supplied to the economizer after passing through the high pressure

heater with help of boiler feed pump.

The main fuel in thermal power stations is the coal . The coal from the mines (major

portion of the coal comes from Thalcheru, Orissa) is brought to the plant mainly through

Railway wagons and the conveyor belt to the main plant and stored in the bunkers. The

controlled amount of coal is sent to the Ball/bowl mills where the coal is crushed into fine

powder. The coal powder is then filtered by using very fine filters (200mesh). The tempered

pressured primary air blown into the mills to carry the coal powder from the mills to the

combustion chamber at all four corners and at 6 levels of each corner of the boiler. Also, the

preheated secondary air blown into the furnace through all four corners for proper combustion of

the fuel. In between the coal elevations in each corners, oil guns in 3 elevations are provided to

inject the fuel oil into the furnace if necessary. Injection of the fuel to the furnace is tangential

and proper combustion of the fuel depends on the time of stay, turbulence and temperature of the

injected fuel air mixture.

By burning of coal in the furnace the flue gases are evolved due to combustion. These

gases heat the water in the economizer. The heated water enters into the drum from there it flows

through down comers and enters into the walls. There the water is evaporated and forms the wet

steam. This wet steam is again supplied to the drum, the water particles separated from the

vapors with the help the stem separators. The boiler drum is made up of carbon steel SA210

Grade C.

The boiler drum contains water at the bottom portion and steam will be in the upper

portion. The bottom portion temperature will higher than that of upper portion. That’s the reason

the thickness of bottom portion of the boiler should be more than the upper portion. The vapor

viii

again flows into the low temperature super heater (LTSH), Intermediate temperature super heater

(ITSH) and High pressure super heater (HTSH) forms super heated steam and supplied to high

pressure turbine.

In this turbine the steam expands after work done, the exhausted steam from this turbine

consists of low temperature and pressure. Such a steam again reheated in re-heaters like LTRH

and HTRH. The heated steam again forms as a super heated steam.

The main steam thus obtained has a temperature of 5400C and at a pressure of 150

KG/cm2. The main steam is allowed to expand through the fixed and moving blades of high

pressure turbine. The expanded steam comes out of HP turbine is called COLD REHEAT

STEAM has a pressure of only 35 Kg/cm2 and temperature 3400c only. Due to high moisture

content in this steam which causes serious erosion of the moving blades and to increase the

enthalpy of the steam, it is reheated in reheaters located in the boiler at constant pressure to the

temperature of 5400c by availing the flue gas heat in the Boiler.

This reheated steam is supplied to the intermediate pressure turbine and to low pressure

turbine. The steam is extracted from HP, IP and LP turbines is blended and is used for the

purpose of heating the feed water in HP, LP heaters and de-aerator. While super heated steam

flows onto the HP, IP & LP turbines. This expands continuously by the expansion of steam, the

velocity changes both in magnitude and direction, this creates change in momentum develops a

centrifugal force, which acts at the periphery of the turbine wheel. So the turbine wheel gets

rotated. This heat energy of steam is converted into mechanical energy.

Since the turbine shaft is coupled to the generator, by the rotation of generator shaft,

electrical power is generated. Such a power is supplied to national grid from there it was

supplied to the place of use. The existed steam from the turbine is cooled in condenser, by

external circulation of raw water. This raw water heats up; such heated water is cooled in the

cooling tower.

STUDY OF VARIOUS SYSTEMS IN 500MW THERMAL POWER PLANT

DEPT OF EEE, SKIT. Page 1

1.1 INTRODUCTION

A control system of station basically works on Rankin Cycle. Steam is produced

in Boiler is exported in prime mover and is condensed in condenser to be fed into the boiler

again. In practice of good number of modifications are affected so as to have heat economy

and to increase the thermal efficiency of plant.

Figure: 1.1 Layout of 500MW PowerPlant



The Narla Tata Rao Thermal Power Station is divided into four main circuits :

1.Fuel and Ash Circuit.

2.Air and Gas Circuit.

3.Feed water and Steam Circuit.

4.Cooling Water Circuit.

1.2 FUEL & ASH CIRCUIT

Fuel from the storage is fed to the boiler through fuel handling device. The fuel used

in NTTPS is coal, which on combustion in the boiler produced the ash. The quantity of

ash produced is approximately 35-40% of coal used. This ash is collected at the back of

the boiler and removed to ash storage tank through ash disposal equipment.

1.3 AIR AND GAS CIRCUIT

Air from the atmosphere is supplied to the combustion chamber of Boiler through the

action of forced draft fan and induced draft fan. The flue gas gases are first pass around the

boiler tubes and super heated tubes in the furnace, next through dust collector (ESP) & then

economizer. Finally, they are exhausted to the atmosphere through fans.

1.4 FEED WATER AND STEAM CIRCUIT

The condensate leaving the condenser is first heated in low pressure (LP) heaters

through extracted steam from the lower pressure extraction of the turbine. Then its goes to

dearator where extra air and non-condensable gases are removed from the hot water to

avoid pitting / oxidation. From deaerator it goes to boiler feed pump which increases the

pressure of the water. From the BFP it passes through the high pressure heaters. A

small part of water and steam is lost while passing through different components therefore

water is added in hot well. This water is called the make up water. Thereafter, feed water

enters into the boiler drum through economizer. In boiler tubes water circulates

because of density difference in lower and higher temperature section of the boiler.

The wet steam passes through superheated. From superheated it goes into the HP turbine

after expanding in the HP turbine. The low pressure steam called the cold reheat steam



(CRH) goes to the reheater (boiler). From reheater it goes to IP turbine and then to the LP

turbine and then exhausted through the condenser into hot well.

1.5 COOLING WATER CIRCUIT

A large quantity of cooling water is required to condense the steam in

condenser and marinating low pressure in it. The water is drawn from reservoir and after

use it is drained into the river.

Figure: 1.2 Cross Sectional View of Four Major Part Form A Power Plant



1.6 MEASUREMENT PARAMETERS IN A THERMAL POWERPLANT

PARAMETERS MEASURING POINTS / LOCATIONS

1. Pressure

Boiler drums.

Turbine 1st stage & turbine throttle.

Primary air line (header)

De-aerator

Furnace.

2. Temperature

Steam at mains super heater inlet and outlet.

High pressure bypass steam.

Auxiliary steam (header).

Feed water at economizer inlet point.

Water at condenser inlet.

De-aerator.

Air pre-heaters.

Primary and secondary air.

Flue gas super heater.

Flue gas re-heater.

Bearings of turbine and generator.



Bearings of FD, ID Fans, and Boiler feed

pumps, condensate pumps, various mills.

3. Flow

High pressure steam.

Feed water inlet.

Condensate.

Heaters drain lines.

Primary and secondary air.

4. Level

Boiler drum.

Condensate tanks.

De-aerators.

Heaters (water line).

Bearings and shafts of ID, FD, PA Fans, Boiler

Feed pumps, condensate pumps.

Turbine and generator shaft & bearings, shells

and casings.

Turbine shaft & casings.

Heated lines.

5. Analyzers

a. Steam

Conductivity saturated and main line steam

Silica of main steam.



Sodium at super heater inlet.

b. Water

Conductivity of makeup water, feed water at

economizer inlet, boiler feed pump inlet, Boiler

drum, condenser, condensate pump discharge.

Silica in feed water at economizer inlet, boiler

drum and condensate pump outlet.

Sodium in condensate, makeup water,

Dematerializes unit outlet.

PH of feed water at Economizer, Boiler drum.

Dissolved oxygen at condensate pump inlet and

boiler feed pump inlet.

Turbidity of condenser outlet.

Hydrazine at economizer.

c. Flue gas

Oxygen in flue gas duct between economizer

and air preheater.

CO2 at air heaters inlet and outlet.

CO at stack.

SO2 at stack.

Nitrogen oxides at stack.

Dust concentration at stack (SPM).



2.1 INTRODUCTION

It can be called the heart of thermal power plant because it provided the fuel for

combustion in boiler. The coal is brought to the NTTPS through rails there are fourteen

tracks in all for transportation of coal through rails. Everyday 6 to 7 trains of coal are

unloaded at NTTPS. Each train consists of 58 wagons and each wagons consists of 60 tones

of coal. The approximate in NTTPS coal required for a 500 MW plant per day= 6720 MT

(approx. if C grade coal is used, Coal calorific value: 4400 Kcal/Kg ). It costs approximate

4.5 crores of rupees per day including transportation expenses. The coal is firstly

unloaded from wagon by wagon triplers, then the coal is being fed through conveyers (1200

tonnes per hour)at a speed of 2.5m/s to crusher house. Their the coal is crushed to a size of

below 50mm then fed to coal bunkers . The whole transportation of coal is through conveyor

belt operated by 3-Ø Induction motor of HT and LT system depending upon the size of the

conveyer.

The coal supply to the bunkers is being fed to mills / pulverized through belt feeders.

In the pulverized the coal is crushed into fine power and the coal power is supplied to boiler

through conveying air by means of primary air fans.

The coal handling plant can broadly be divided into three sections

1) Wagon Unloading System.

2) Crushing System.

3) Conveying System.

2.2 WAGON UNLOADING SYSTEM

It unloads the coal from wagon to hopper. The hopper, which is made of Iron

, is in the form of net so that coal pieces of only equal to and less than 200 mm. size pass

through it. The bigger ones are broken by the workers with the help of hammers. From

the hopper coal pieces fall on the vibrator. It is a mechanical system having two rollers each

at its ends.

The rollers roll with the help of a rope moving on pulley operated by a slip ring

induction motor with specification:



Figure:2.1 Wagon Tripler

Rated Output. :71 KW.

Rated Voltage. : 415 V.

Rated Current. :14.22Amp.

Rated Speed. : 975 rpm.

No. of phases. : 3

Frequency. :50 Hz.

No. of Wagon Tripler : 6

The four rollers place themselves respectively behind the first and the last pair of

wheels of the wagon. When the motor operates the rollers roll in forward direction moving

the wagon towards the “Wagon Table”. On the Wagon table a limit is specified in which

wagon to be has kept otherwise the triple would not be achieved.

2.3 CRUSHING SYSTEM

2.3.1 Crusher HouseIt consists of crushers which are used to crush the coal to 50 mm. size. There are 2

Coal Crushers houses (each crusher house consisting of four crushers) in N.T.T.P.S. The

crushers working in NTTPS are ring granulator.



Basically there are four ways to reduce material size : impact attrition , Shearing and

Compression. Most of the crushers employ a combination of three crushing methods.

Ring granulators crush by compressing accompanied by impact and shearing.The unique

feature of this granulator is the minimum power required for tone for this type of material

to be crushed compared to that of other type of crushers.

2.3.2 Construction & Operation

Secondary crushers are ring type granulators crushing at the rate of 550 TPH/750

TPH for input size of 250 mm. and output size of 50 mm. The crusher is coupled with motor

and gearbox by fluid coupling. Main parts of granulator like break plates, cages, crushing

rings and other internal parts are made of tough manganese (Mn) steel.

The rotor consists of four rows of crushing rings each set having 20 Nos. of toothed

rings and 18 Nos. of plain rings. In CHP Stage 1 & 2 having 64 Nos. of ring

hammers. These rows are hung on a pair of suspension shaft mounted on rotor discs.

Crushers of this type employ the centrifugal force of swinging rings stroking the

coal to produce the crushing action. The coal is admitted at the top and the rings stroke the

coal downward. The coal discharges through grating at the bottom.

2.4 CONVEYING SYSTEM

2.4.1 Stacker Re-Claimer

The stacker re-claimer unit can stack the material on to the pile and reclaim the

stack filed material and fed on to the main line conveyor. While stacking material is being

fed from the main line conveyor via Tripler unit and vibrating feeder on the intermediate

conveyor which feds the boom conveyor of the stacker cum re-claimer. During

reclaiming the material discharged on to the boom conveyor by the buckets fitted to

the bucket wheel body and boom conveyor feeds the material on the main line conveyor

running in the reverse direction.



Figure: 2.2 Stacker / Re-claimer

2.4.2 Conveyor belt Specification of Stacker / Re-claimer

Belt width. : 1400 mm.

Speed. : 2.5m /second.

Schedule of motor : All 3-Ø induction motors.

Bucket wheel motor : 90 KW.

Boom Conveyor motor : 70KW.

Intermediate Conveyor Motor : 90 KW.

Boom Housing Motor : 22 KW.

Slewing assembly. : 10 KW.

Travel Motor : 7.5 KW.

Vibrating Feeder. : 2x6 KW.

Total installed power. : 360 KW.



3.1 TYPES OF PLANTS

This plant can be divided into 3 sub plants as follows:-

1) Fuel and Ash Plant.

2) Air and Gas Plant.

3) Ash Disposal and & Dust Collection Plant.

3.2 FUEL AND ASH PLANT

Coal is used as combustion material in NTTPS, In order to get an efficient utilization

of coal mills. The Pulverization also increases the overall efficiency and flexibility of

boilers. However for light up and with stand static load , oil burners are also used. Ash

produced as the result of combustion of coal is connected and removed by ash handling

plant. Ash Handling Plant at NTTPS consists of specially designed bottom ash and fly

ash in electro static precipitator economizer and air pre-heaters hoppers.

3.3 AIR & GAS PLANT

Air from atmosphere is supplied to combustion chamber of boiler through the action

of forced draft fan. In NTTPS there are two FD fans and two ID fans available for draft

system per unit. The air before being supplied to the boiler passes through preheater

where the flue gases heat it. The pre heating of primary air causes improved and

intensified combustion of coal.

The flue gases formed due to combustion of coal first passes round the boiler tubes

and then it passes through the super heater and then through economizer . In re-heater the

temperature of the steam (CRH) coming from the HP turbines heated with increasing the

number of steps of re-heater the efficiency of cycle also increases. In economizer the

heat of flue gases raises the temperature of feed water. Finally the flue gases after passing

through the Electro-Static Precipitator is exhausted through chimney.



3.4 ASH DISPOSAL &DUST COLLECTION PLANT

NTTPS has dry bottom furnace. Ash Handling Plant consists of especially designed

bottom and fly ash system for two pass boiler. The system for all units is identical and

following description is applied to all the units the water compounded bottom ash

hopper receives the bottom ash from the furnace from where it is stores and discharged

through the clinker grinder. Two slurry pumps are provided which is common to the units

& used to make slurry and further transportation to ash dyke through pipe line.

Dry free fly ash is collected into number of 72 fly ash hoppers which are handled

by two independent fly ash system. The ash is removed from fly ash hoppers in dry state

is carries cylos (tubular concrete tank) to the collecting equipment from their it dry ash

collect into to tankers and open trucks.

Figure: 3.1 Ash Disposal &Dust Collection



4.1 INTRODUCTION

As you may know, particulate matter (particles) is one of the industrial air pollution

problems that must be controlled. It's not a problem isolated to a few industries, but pervasive

across a wide variety of industries. That's why the U.S. Environmental Protection Agency

(EPA) has regulated particulate emissions and why industry has responded with various

control devices. Of the major particulate collection devices used today, Electro Static

Precipitators (ESPs) are one of the more frequently used. They can handle large gas volumes

with a wide range of inlet temperatures, pressures, dust volumes, and acid gas conditions.

They can collect a wide range of particle sizes, and they can collect particles in dry and wet

states. For many industries, the collection efficiency can go as high as 99%. ESPs aren't

always the appropriate collection device, but they work because of Electro Static Attraction

(like charges repel; unlike charges attract). Let's see how this law of physics works in an ESP.

4.2 PRECIPITATOR COMPONENTS

All electrostatic precipitators, regardless of their particular designs, contain the

following essential components:

1. Discharge electrodes

2. Collection electrodes

3. High voltage electrical systems

4. Rappers

5. Hoppers

6. Shell

1.Discharge electrodes

These are either small-diameter metal wires that hang vertically (in the electrostatic

precipitator), a number of wires attached together in rigid frames, or a rigid electrode- made



from a single piece of fabricated metal. Discharge electrodes create a strong electrical field

that ionizes flue gas, and this ionization charges particles in the gas.

2. Collection electrodes

These are collect charged particles. Collection electrodes are either flat plates or tubes

with a charge opposite that of the discharge electrodes.

3. High voltage equipment

It provides the electric field between the discharge and collection electrodes used to

charge particles in the ESP.

4. Rappers

These are impart a vibration, or shock, to the electrodes, removing the collected dust.

Rappers remove dust that has accumulated on both collection electrodes and discharge

electrodes. Occasionally, water sprays are used to remove dust from collection electrodes.

5. Hoppers

These are located at the bottom of the precipitator. Hoppers are used to collect and

temporarily store the dust removed during the rapping process.

4.3 THEORY OF PRECIPITATION

Every particle either has or can be given a charge—positive or negative. Let's suppose

we impart a negative charge to all the particles in a gas stream. Then suppose we set up a

grounded plate having a positive charge. What would happen? The negatively charged

particle would migrate to the grounded collection plate and be captured. The particles would

quickly collect on the plate, creating a dust layer. The dust layer would accumulate until we

removed it, which we could do by rapping the plate or by spraying it with a liquid. Charging,

collecting, and removing—that's the basic idea of an ESP, but it gets more complicated. Let's

look at a typical scenario using a common ESP construction.



4.4 PARTICLE CHARGING

Our typical ESP as shown in Figure 4.1 has thin wires called discharge electrodes,

which are evenly spaced between large plates called collection electrodes, which are

grounded. Think of an electrode as something that can conduct or transmit electricity. A

negative, high-voltage, pulsating, direct current is applied to the discharge electrode creating

a negative electric field. You can mentally divide this field into three regions. The field is

strongest right next to the discharge electrode, weaker in the areas between the discharge and

collection electrodes called the inter-electrode region, and weakest near the collection

electrode. The region around the discharge electrode is where the particle charging process

begins.

Figure: 4.1typical Dry Electrostatic Precipitator

4.4.1 Corona Discharge-Free Electron Generation

Several things happen very rapidly (in a matter of a millisecond) in the small area

around the discharge electrode. The applied voltage is increased until it produces a corona

discharge, which can be seen as a luminous blue glow around the discharge electrode. The

free electrons created by the corona are rapidly fleeing the negative electric field, which

repulses them. They move faster and faster away from the discharge electrode. This

acceleration causes them to literally crash into gas molecules, bumping off electrons in the



molecules. As a result of losing an electron (which is negative), the gas molecules become

positively charged, that is, they become positive ions. So, this is the first thing that happens

gas molecules are ionized, and electrons are liberated. All this activity occurs very close to

the discharge electrode. This process continues, creating more and more free electrons and

more positive ions. The name for all this electron generation activity is avalanche

multiplication.

The electrons bump into gas molecules and create additional ionized molecules. The

positive ions, on the other hand, are drawn back toward the negative discharge electrode.

The molecules are hundreds of times bigger than the tiny electrons and move slowly, but they

do pick up speed. In fact, many of them collide right into the metal discharge electrode or the

gas space around the wire causing additional electrons to be knocked off. This is called

secondary emission. So, this is the second thing that happens. We still have positive ions

and a large amount of free electrons.

4.4.2 Ionization of Gas Molecules

As the electrons leave the strong electrical field area around the discharge electrode,

they start slowing down. Now they're in the inter-electrode area where they are still repulsed

by the discharge electrode but to a lesser extent. There are also gas molecules in the inter-

electrode region, but instead of violently colliding with them, the electrons kind of bump up

to them and are captured. This imparts a negative charge to the gas molecules, creating

negative gas ions. This time, because the ions are negative, they too want to move in the

direction opposite the strong negative field. Now we have ionization of gas molecules

happening near the discharge electrode and in the inter-electrode area, but with a big

difference. The ions near the discharge electrode are positive and remain in that area. The

ions in the middle area are negative and move away, along the path of invisible electric field

lines, toward the collection electrode.

4.4.3 Charging of Particles

These negative gas ions play a key role in capturing dust particles. Before the dust

particles can be captured, they must first acquire a negative charge. This is when and where it

happens. The particles are traveling along in the gas stream and encounter negative ions

moving across their path. Actually, what really happens is that the particles get in the way of

the negatively charged gas ions. The gas ions stick to the particles, imparting a negative



charge to them. At first the charge is fairly insignificant as most particles are huge compared

to a gas molecule. But many gas ions can fit on a particle, and they do. Small particles (less

than 1 mm diameter) can absorb “tens” of ions. Large particles (greater than 10 mm) can

absorb "tens of thousands" of ions. Eventually, there are so many ions stuck to the particles,

the particles emit their own negative electrical field. When this happens, the negative field

around the particle repulses the negative gas ions and no additional ions are acquired. This is

called the saturation charge. Now the negatively-charged particles are feeling the inescapable

pull of electrostatic attraction. Bigger particles have a higher saturation charge (more

molecules fit) and consequently are pulled more strongly to the collection plate. In other

words, they move faster than smaller particles. Regardless of size, the particles encounter the

plate and stick, because of adhesive and cohesive forces.

Let's stop here and survey the picture. Gas molecules around the discharge electrode

are positively ionized. Free electrons are racing as fast as they can away from the strong

negative field area around the discharge electrode. The electrons are captured by gas

molecules in the inter-electrode area and impart a negative charge to them. Negative gas ions

meet particles and are captured .And all this happens in the blink of an eye. The net result is

negatively charged particles that are repulsed by the negative electric field around the

discharge electrode and are strongly attracted to the collection plate. They travel toward the

grounded collection plate, bump into it, and stay there.

4.4.4 Particle Charging Mechanisms

Particles are charged by negative gas ions moving toward the collection plate by one

of these two mechanisms: field charging or diffusion charging. In field charging (the

mechanism described above), particles capture negatively charged gas ions as the ions move

toward the grounded collection plate. Diffusion charging, as its name implies, depends on the

random motion of the gas ions to charge particles.

In field charging, as particles enter the electric field, they cause a local dislocation of

the field. Negative gas ions traveling along the electric field lines collide with the suspended

particles and impart a charge to them. The ions will continue to bombard a particle until the

charge on that particle is sufficient to divert the electric lines away from it. This prevents new

ions from colliding with the charged dust particle. When a particle no longer receives an ion

charge, it is said to be saturated. Saturated charged particles then migrate to the collection

electrode and are collected.



Diffusion charging is associated with the random Brownian motion of the negative

gas ions. The random motion is related to the velocity of the gas ions due to thermal effects:

the higher the temperature, the more movement. Negative gas ions collide with the particles

because of their random thermal motion and impart a charge on the particles. Because the

particles are very small (sub-micrometer), they do not cause the electric field to be dislocated,

as in field charging. Thus, diffusion charging is the only mechanism by which these very

small particles become charged. The charged particles then migrate to the collection

electrode.

Each of these two charging mechanisms occurs to some extent, with one dominating

depending on particle size. Field charging dominates for particles with a diameter >1.0

micrometer because particles must be large enough to capture gas ions. Diffusion charging

dominates for particles with a diameter less than 0.1 micrometer. A combination of these two

charging mechanisms occurs for particles ranging between 0.2 and 1.0 micrometer in

diameter.

4.5 ELECTRIC FIELD STRENGTH

In the inter-electrode region, negative gas ions migrate toward the grounded collection

electrode. A space charge, which is a stable concentration of negative gas ions, forms in the

inter-electrode region because of the high electric field applied to the ESP. Increasing the

applied voltage to the discharge electrode will increase the field strength and ion formation

until spark over occurs. Spark over refers to internal sparking between the discharge and

collection electrodes. It is a sudden rush of localized electric current through the gas layer

between the two electrodes. Sparking causes an immediate short-term collapse of the electric

field. For optimum efficiency, the electric field strength should be as high as possible. More

specifically, ESPs should be operated at voltages high enough to cause some sparking, but

not so high that sparking and the collapse of the electric field occur too frequently. The

average spark over rate for optimum precipitator operation is between 50 and 100 sparks per

minute. At this spark rate, the gain in efficiency associated with increased voltage

compensates for decreased gas ionization due to collapse of the electric field.

4.5.1 Particle Collection

When a charged particle reaches the grounded collection electrode, the charge on the

particle is only partially discharged. The charge is slowly leaked to the grounded collection



plate. A portion of the charge is retained and contributes to the inter-molecular adhesive and

cohesive forces that hold the particles onto the plates. Adhesive forces cause the particles to

physically hold on to each other because of their dissimilar surfaces. Newly arrived particles

are held to the collected particles by cohesive forces; particles are attracted and held to each

other molecularly. The dust layer is allowed to build up on the plate to a desired thickness

and then the particle removal cycle is initiated.

4.5.2 Particle Removal

Dust that has accumulated to a certain thickness on the collection electrode is

removed by one of two processes, depending on the type of collection electrode. As described

in greater detail in the next section, collection electrodes in precipitators can be either plates

or tubes, with plates being more common. Tubes are usually cleaned by water sprays, while

plates can be cleaned either by water sprays or a process called rapping.

Rapping is a process whereby deposited, dry particles are dislodged from the

collection plates by sending mechanical impulses, or vibrations, to the plates. Precipitator

plates are rapped periodically while maintaining the continuous flue-gas cleaning process. In

other words, the plates are rapped while the ESP is on-line; the gas flow continues through

the precipitator and the applied voltage remains constant. Plates are rapped when the

accumulated dust layer is relatively thick (0.08 to 1.27 cm or 0.03 to 0.5 in.). This allows the

dust layer to fall off the plates as large aggregate sheets and helps eliminate dust re-

entrainment. Most precipitators have adjustable rappers so that rapper intensity and frequency

can be changed according to the dust concentration in the flue gas. Installations where the

dust concentration is heavy require more frequent rapping.

Dislodged dust falls from the plates into the hopper. The hopper is a single collection

bin with sides sloping approximately 50 to 70 to allow dust to flow freely from the top of

the hopper to the discharge opening. Dust should be removed as soon as possible to avoid

(dust) packing. Packed dust is very difficult to remove. Most hoppers are emptied by some

type of discharge device and then transported by a conveyor.

In a precipitator using liquid sprays to remove accumulated liquid or dust, the sludge

collects in a holding basin at the bottom of the vessel. The sludge is then sent to settling

ponds or lined landfills for proper ultimate disposal.



5.1 INTRODUCTION

A boiler (steam generator) is a closed vessel in which water, under pressure is

converted into steam. It is one of the major components of a thermal power plant. A boiler

is always designed to absorb maximum amount of heat released in process of combustion.

This is transferred to the boiler by all the three modes of heat transfer i.e. conduction,

convection and radiation.

1. Radiation- Which is the transfer of heat from hot body to cold body without medium.

2. Convection- The transfer of heat through a conveying medium, such as air or water.

3. Conduction- The transfer of heat by an actual physical contact. Heat transfer in the

boiler takes place through radiation and convection processes.

There are two types of boiler based upon the construction and the number of the

steam passes they are:

1. Tower type boiler

2. Two pass boiler

1.Tower type boiler

In a tower type boiler the steam parts are mounted inside a single boiler vessel one

above the other. It is simple in construction and has less steam pressure content.

2.Two pass boiler

In a two pass boiler the steam is allowed in two passes it gains a lot of pressure by

entering into the heating elements. Generally a boiler is made up of thousands of tubes called

water walls. These walls are insulated by insulating material and water flows through these

tubes. The height of the boiler is approximately 85-90 meters. The plant efficiency depends

upon the boiler efficiency.

The thermal efficiency of the boiler is defined as the % of the heat input that is

effectively utilized to generate steam



5.2 BOILERS CLASSIFICATION

A)Fire tube boiler -

In this type the products of combustion pass through the tubes which are

surrounded by water. These are economical for low pressure only.

B)Water tube boiler

In this type of boiler water flows inside the tubes and hot gases flow outside the

tubes. These tubes are interconnected to common water channels and to steam outlet.

1. The water tube boilers have many advantages over the fire tube boilers

2. High evaporation capacity due to availability of large heating surface.

3. Better heat transfer to the mass of water.

4. Better efficiency of plant owing to rapid and uniform circulation of water in tubes.

5. Better overall control.

6. Easy removal of scale from inside the tubes.

In NTTPS, Natural circulation, tangentially fired, over hanged type, Water tube

boilers are used. Oil burners are provided between coal burners for initial start up and

flame stabilization. Firstly, light oil (diesel oil) is sprayed for initialization then heavy

oil (high speed diesel oil) is used for stabilization of flame. Pulverized coal is directly fed

from the coal mills to the burners at the four corners of the furnace through coal pipes with

the help of heated air coming from PA fan. Seven nos. of bowl mills of 50MT/hr.

capacity each have been installed for each boiler. The pressure inside boiler is -ve so as

to minimized the pollution and looses & to prevent the accidents outside the boiler.

For ensuring safe operation of boilers, furnace safe guard supervisory system (FSSS)

of combustion engineering USA designed has been installed. This equipment

systematically feed fuel to furnace as per load requirement. The UV flame scanners



installed in each of the four corners of the furnace, scan the flame conditions and in case of

unsafe working conditions trip the boiler and consequently the turbine. Turbine - boiler

interlocks safe guarding the boiler against possibility furnace explosion owing to flame

failure.

5.3 FURNACE

Figure:5.1 furnaceFurnace is primary part of the boiler where the chemical energy available in the

fuel is converted into thermal energy by combustion. Furnace is designed for

efficient and complete combustion. Major factors that assist for efficient combustion

are the temperature inside the furnace and turbulance, which causes rapid mixing of fuel

and air. In modern boilers, water-cooled furnaces are used.

5.4 PULVERISED FUEL SYSTEM

The boiler fuel firing system is tangentially firing system in which the fuel is

introduced from wind nozzle located in the four corners inside the boiler.



Figure:5.2 Pulverized Fuel System

Figure 6.3 Pulverised SystemThe crushed coal from the coal crusher is transferred into the unit coalbunkers where

the coal is stored for feeding into pulverizing mill through rotary feeder. The rotary feeders

feed the coal to pulverize mill at a definite rate. Then coal burners are employed to fire the

pulverized coal along with primary air into furnace. These burners are placed in the corners

of the furnace and they send horizontal streams of air and fuel tangent to an imaginary circle

in the center of the furnace.

5.5 FUEL OIL SYSTEM

The functional requirement of the fuel burning system is to supply a controllable and

uninterrupted flammable furnace input of fuel and air and to continuously ignite and burn

the fuel as rapidly as it is introduced into the furnace. This system provides efficient

conversion of chemical energy of fuel into heat energy. The fuel burning system should

function such that fuel and air input is ignited continuously and immediately upon its entry

into furnace.

The Fuel air (secondary air) provided FD fan, surrounds the fuel nozzles. Since this

air provides covering for the fuel nozzles so it is called as mantle air. Dampers are provided

so that quantity of air can be modulated. Coal burners distribute the fuel and air evenly in

the furnace.

Ignition takes place when the flammable furnace input is heated above the ignition

temperature. No flammable mixture should be allowed to accumulate in the furnace.



Ignition energy is usually supplied in the form of heat. This ignition energy is provided by

oil guns and by igniters.

5.6 BOILER DRUM

The drum is a pressure vessel. Its function is to separate water and steam from

mixture (of steam & water) generated in the furnace walls. It provides water storage for

preventing the saturation of tubes. It also houses the equipment needed for purification of

steam. The steam purification primarily depends on the extent of moisture removal, since

solids in steam are carried by the moisture associated with it. The drum internals reduce

the dissolved solids content of the steam to below the acceptable limit. drum is made up of

two halves of carbon steel plates having thickness of 133 mm.

The top half and bottom half are heated in a plate heating furnace at a very

high temperature and are pressured to form a semi cylindrical shape. The top and

bottom semi cylinders with hemispherical dished ends are fusion welded to form the

boiler drum. The drum is provided with stubs for welding all the connecting tubes

i.e. down comer stubs, riser tubes stubs and super-heater outlet tube stubs.

Boiler drum is located at a height of 70m from ground. The drum is provided

with manholes and manhole covers. Manhole is used for facilitating the maintenance

person to go inside the drum for maintenance.

Figure:5.3 Steam Drum



The drum form the part of boiler circulating system i.e. movement of fluid from the

drum to the combustion zone and back to boiler drum. Feed water is supplied to the drum

from the economizer through feed nozzles. Water from the drum goes to water walls

through six down comers.

Main parts of boiler drum are:-

1. Feed pipe

2. Riser tube

3. Down comer

4. Baffle plate

5. Chemical dosing pipe

6. Turbo separation

7. Screen dryer

8. Drum level gauge

5.7 DRAFT SYSTEM

The combustion process in a furnace can take place only when it receives a steady

flow of air and has the combustion gases continuously removed. Theoretically balanced

draft means keeping furnace pressure equal to atmospheric pressure, but in practice the

furnace is kept slightly below atmospheric pressure. It ensures that there is no egress of air

or hot gas and ash into boiler house.

5.8 DRAUGHT FANS

A fan can be defined as volumetric machine which like pumps moves quantities of

air or gas from one place to another. In doing this it overcomes resistance to flow by

supplying the fluid with the energy necessary for contained motion. The following fans are

used in boiler house.



5.8.1 Primary air fan (P.A. fan) or Exhauster fan

Pulverized coal is directly fed from coal mills to the burners at the four corners of

the furnace through coal pipes with the help of heated air coming from PA fan. Secondly,

this fan also dries the coal. Usually sized for 1500 RPM due to high pressure.

5.8.2 Forced draught fan (F.D. fan)

The combustion process in the furnace can take place only when it receives a steady

flow of air. This air is supplied by FD fan. Thus FD fan takes air from atmosphere at

ambient temperature & so provides additional draught. Its speed varies from 600-

1500RPM.

5.8.3.Induced Draught fan (I.D. fan)

The flue gases coming out of the boiler are passed to the ESP & then dust free gases

are discharged up by the chimney to the atmosphere through the ID fan.

5.9 ECONOMIZER

. Figure:5.4 Economizer



The flue gases coming out of the boiler carry lot of heat. An economizer extracts a

part of this heat from the flue gases and uses it for heating the feed water before it enters into

the steam drum. The use of economizer results in saving fuel consumption and higher boiler

efficiency but needs extra investment. In an economizer, a large number of small diameter

thin walled tubes are placed between two headers. Feed water enters the tubes through the

other. The flue gases flow outside the tubes. Earlier the economizers are introduced mainly to

recover the available heat in the flue gas that leaves the boiler and provision of this additional

heating surface increase the efficiency of the heat generation, saving in fuel consumption,

thus the name economizer christened. In the modern boilers used for power generation feed

water heaters are used to increase the efficiency of the turbine unit and feed water

temperature and hence the relative size of the economizer is less than the earlier units.

5.10 WATER WALLS

The walls of the furnace are made up with the water tubes. These tubes are

connected to the headers and feed water is circulated through them. While water passes

through the tubes, heat is absorbed from the furnace.

Almost all modern power boilers are equipped with water walls. In large boilers,

water walls cover completely the interior surface of the furnace providing practical complete

elimination of exposed refractory surface. Water walls serves as the only means of heating

and evaporating the feed water supplied to the boiler from the economizers. Water walls

usually consist of tangential vertical tubes and are connected to top and bottom of the

headers. These tubes receive water from the boiler drum by means of down comers between

drum and water walls lower header.

5.11 AIR-PRE HEATERS

Air-pre heaters are employed to recover the heat from the flue gases leaving the

economizer and are used to heat the incoming air for combustion. This raises the

temperature of the furnace gases, improves combustion rates an efficiency and lowers the

stack (chimney) temperature, thus improving the overall efficiency of the boiler.

Cooling of flue gases by 20% raises the plant efficiency by 1%.



Figure:5.5 Air Pre-Heater

In NTTPS regenerative type of pre heater is used. They use a cylindrical rotor

made of corrugated steel plate. The rotor is placed in a drum which is divided into two

compartments, i.e. air compartment (primary air coming from primary air fan and

secondary air for air coming from FD fan with +ve pressure) and flue gases (from

economizer with – ive pressure) compartments. To avoid leakage from one compartment

to other seals are provided.

The rotor is fixed on an electrical shaft rotating at a speed of 2 to 4 rpm. As

the rotor rotates the flue gases, are pass through alternatively gas and air zone. The rotor

elements are heated by flue gases in their zone and transfer the heat to air when they are

in air zone. The air temperature required for drying in the case of coal-fired boiler decided

the size of the air heaters.

5.12 SUPER HEATER

Superheated steam is that steam, which contains more heat than the saturated

steam at the same pressure i.e. it, has been heated above the temperature corresponding

to its pressure. This additional heat provides more energy to the turbine and thus the

electrical power output is more.



A super heater is a device which removes the last traces of moisture from the

saturated steam leaving the boiler tubes and also increases its temperature above

the saturation temperature.

The steam is superheated to the highest economical temperature not only to

increase the efficiency but also to have following advantages –

1. Reduction in requirement of steam quantity for a given output of energy owing to

its high internal energy reduces the turbine size.

2. Superheated steam being dry, turbine blades remain dry so the mechanical

resistance to the flow of steam over them is small resulting in high efficiency.

3. No corrosion and pitting at the turbine blades occur owing to dryness of steam.

5.13 RE-HEATER

Re-heaters are provided to raise the temperature of the steam from which part of

energy has already been extracted by HP turbine. This is done so that the steam remains dry

as far as possible through the last stage of the turbine. A re-heater can also be convection,

radiation or combination of both.

5.14 CIRCULATION SYSTEM

In natural circulation system, water delivered to steam generator from header, which

are at a temperature well below the saturation value corresponding to that pressure. After

header, it is delivered to economizer, which heated to above the saturation temperature.

From economizer the water enters the drum and thus joins the circulation system

through down covering water wall tubes. In water wall tubes a part of the water is

converted to steam due to boiler and the mixture flows back to the drum. In the drum,

the steam is separated out through the steam separators and passed to the super heater.

After the super heater when the steam temperature becomes high and pressure upto 175

Kg./cm3 steam is allowed to enter the turbine to convert potential energy to kinetic energy.



Figure:5.6 Pressure Parts

5.15 SOOT BLOWER

The boiler tubes are cleaned with the help of steam by the process called soot

blowing. We are well known that a greater no. of tubes are presented inside the boiler.

Slowly and slowly the fine ash particles are collected on the tube surface and from a layer

this is called soot. Soot is a thermal insulating material.

There are mainly three types of soot blower are used in NTTPS

1. Water wall soot blower

2. Super heater soot blower

3. Air pre heater soot blower



5.16 STARTUP DEVICES

This is provided on each boiler and is operated when the boiler is being lighted up and

to gain or achieve the required values of pressure and temperature and to stabilize the

chemical values of boiler water before changing the system lines or HP/LP bypass even.

Safety valve of the boiler is supposed to close after certain pressure drop. If it is not

closing at a particular pressure, by opening startup vent valve, the pressure can be dropped to

the lower value and safety valve closing is achieved. If the safety valve is allowed to

continuously blow the seat of the safety valve gets damaged and may create a problem in

running the boiler. Startup vent is operated from the control room. It is a puffing type valve.

5.17 SAFETY VALVES

Safety relief equipment is present in any pressurized system, and boilers are no

exception. Boilers have safety valves that can relieve the entire generating capacity of the

boiler if the pressure goes above a limit and are provided in the drum, super heater and re-

heater.

Boilers are high pressure and temperature systems used for generating steam to drive

steam turbine for electricity generation. If due to any reason of malfunction in one of the

controls, the operating pressure goes above the limit and can cause a huge damage. To

prevent such things safety valves are provided in the boilers.

5.18 DE-AERATOR

The function of the de-aerator is to remove dissolved non-condensable gases

and to heat boiler feed water. It consists of a pressure vessel in which the water and steam are

mixed in controlled manner. When this occurs the all non-condensable dissolved gases are

separated and removed and the effluent water may be considered corrosion free from oxygen

or carbon di oxide stand point.

A de-aerator protects the feed pumps, piping, boiler and any other piece of equipment

that is in the boiler feed and return cycle from the effects of corrosive gases i.e., oxygen and

carbon dioxide, to a level where they are no longer a corrosion factor.



Figure:5.7 De-aerator

5.19 BOILER SPECIFICATIONS

PLANT NAME : VIJAYAWADA THERMAL POWER STATION STG-4

PROPOSED FUEL : Sub bituminous coal

FC% 28.7, VM% 28.3, M% 9, Ash%34, S%0.5

Ash fusion Temperature: 1400oc

HHV 4400 Kcal/Kg

Grindability 52 HGI

FUEL BURNING EQUIPMENT:

Main burners Stabilization burners Mills

Type Tilting tangential low NOx XRP 1003

Make &No’s BHEL, 28 BHEL, 12 BHEL, 7

Control Air damper Air damper capacity: 65 t/h

Capacity 65*106 Kcal/h 30.3*10 6Kcal/h motor525 KW

Speed 600RPM

Disposition corners corners system: cold PA



FURNACE:

Type : Balanced draft furnace with fusion welded water walls

Width : 18034mm

Depth : 15797mm

Volume : 14272m3 (as per specification)

Fuel heat I/P : 11981.9*10power6 Kcal/h

BOILER:

Type : Controlled circulation with rifled tubing(cc+)

Pressure : 209Kg/Cm (g)

Drum Design : 178.0Kg/Cm2 (g)- BMCR

Super Heater Outlet : 540 Deg c

SUPER HEATER:

Type H.S. Area (m2)

Stage1: LTSH Horizontal and pendant 10843

Stage 2: SH Division Panellette (tube projected) 1319

Stage3: SH Finish Platen (tube projected) 1330

ATTEMPERATOR:

Type : Spray

No. of Stages : Single

Medium of spray : Feed water



REHEATER:

Type : Front pendant platen

Rear pendant spaced

Total H.S Area m2 : 6298

Control : Burner tilt and Excess air

ECONOMIZER:

Type : Plain tube

Total H.S Area m2 : 19050

No. of blocks : 2

AIR HEATER:

Type : Tri-sector 31.5 VIT 2000

Total H.S area m2 : 86000

No’s : 2

Motor KW : 18.5

BOILER AUXILIARIES SPECIFICATIONS:

Fans Type No’s Flow Pressure Temp Drive Speed Motor Control

M3/s mmwc0C rpm KW

FD Fan Axial 2 218 845 50 motor 990 1025 Blade

FAF pitch

PA Fan Axial 2 156 1320 50 motor 1490 2650 Blade



PAF pitch

ID Fan NDZV 47 2 526 1420 150 motor 580 3000 Inlet

S DOR Damper

SOOT BLOWERS:

Type No’s Medium

Furnace : Wall blowers 88 steam

SH panel : Long retractable 40 steam

SH platen LTSH : Soot blowers

Dust concentration at inlet: 536gm/Nm3

Flue Gas Flow : 519.7Nm3/sec

Combined Efficiency : 99.82% (one field out of service)

PIPE LINES MAIN STEAM HOTREHEAT COLDREHEAT FEEDWATER

Size mm*mm 406.4*42 711.2*40 660*20 508*71

NO.OF 2 2 2 1

Material SA 335P91 SA 335P22 SA106GR.C SA 106GR.C



DETAILS OF THE SAMPLE: SPECIALR COAL SAMPLE

LOAD PARAMETER UNIT 100%TGMCR (500MW)

FUEL ANALYSIS:

Proximate analysis- as fired basis

Moisture % 4.00

Ash % 42.40

Volatile matter % 29.40

Fixed Carbon % 24.20

Ultimate analysis-as fired basis

Carbon in fuel % 34.60

Hydrogen in fuel % 2.60

Sulphur in fuel % 0.40

Nitrogen in fuel % 0.80

Oxygen in fuel % 11.00

Moisture in fuel % 4.00

Mineral matter % 46.60

Gross CV HGI Kcal/Kg 32



6.1 INTRODUCTION

Turbine is a machine in which a shaft is rotated steadily by impact or reaction of

current or stream of working substance (steam, air, water, gases etc) upon blades of a wheel.

It converts the potential or kinetic energy of the working substance into mechanical power by

virtue of dynamic action of working substance. When the working substance is steam it is

called the steam turbine.

Figure:6.1 Steam Turbine



6.2 PRINCIPAL OF OPERATION OF STEAM TURBINE

Working of the steam turbine depends wholly upon the dynamic action of Steam. The

steam is caused to fall in pressure in a passage of nozzle: doe to this fall in pressure a certain

amount of heat energy is converted into mechanical kinetic energy and the steam is set

moving with a greater velocity. The rapidly moving particles of steam, enter the moving part

of the turbine and here suffer a change in direction of motion which gives rose to change of

momentum and therefore to a force. This constitutes the driving force of the machine. The

processor of expansion and direction changing may occur once or a number of times in

succession and may be carried out with difference of detail. The passage of steam through

moving part of the commonly called the blade, may take place in such a manner that the

pressure at the outlet side of the blade is equal to that at the inlet inside. Such a turbine is

broadly termed as impulse turbine. On the other hand the pressure of the steam at outlet from

the moving blade may be less than that at the inlet side of the blades; the drop in pressure

suffered by the steam during its flow through the moving causes a further generation of

kinetic energy within the blades and adds to the propelling force which is applied to the

turbine rotor. Such a turbine is broadly termed as impulse reaction turbine.

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 stages with each stage

consisting of a stationary blade (or nozzle) and a rotating blade. Stationary blades convert

the potential energy of the steam (temperature and pressure) into kinetic energy(velocity) and

direct the flow into the rotating blades. The rotating blades convert the kinetic energy into

forces, caused by pressure drop, which results in the rotation of the turbine shaft. The turbine

shaft is connected to generator, which produces the electricity.

The majority of the steam turbine have, therefore two important elements, or

Sets of such elements . These are (1) the nozzle in which the system expands from high

pressure end a state of comparative rest to a lower pressure end a status of comparatively

rapid motion.

The blade or deflector , in which the steam particles changes its directions and hence

its momentum changes . The blades are attach to the rotating elements are attached to the

stationary part of the turbine which is usually termed the stator, casing or cylinder.



Although the fundamental principles on which all steam turbine operate the same, yet

the methods where by these principles carried into effect very end as a result, certain types of

turbine have come into existence.

1. Simple impulse steam turbine.

2. The pressure compounded impulse turbine.

3. Simple velocity compounded impulse turbine.

4. Pressure-velocity compounded turbine.

5. Pure reaction turbine.

6. Impulse reaction turbine.

6.3 DESCRIPTION OF STEAM TURBINES

6.3.1 Steam flow

500 MW steam turbine is a tandem compound machine with HP, IP & LP parts. The

HP part is single flow cylinder and HP & LP parts are double flow cylinders. The individual

turbine rotors and generator rotor are rigidly coupled. The HP cylinder has a throttle

control. Main steam is admitted before blending by two combined main stop and control

valves. The HP turbine exhaust (CRH) leading to reheated have tow swing check valves that

prevent back flow of hot steam from reheated, into HP turbine. The steam coming from

reheated called HRH is passed to turbine via two combined stop and control valves. The IP

turbine exhausts directly goes to LP turbine by cross ground pipes.

6.3.2 HP Turbine

The HP casing is a barrel type casing without axial joint. Because of its rotation

symmetry the barrel type casing remain constant in shape and leak proof during quick change

in temperature. The inner casing too is cylinder in shape as horizontal joint flange are

relieved by higher pressure arising outside and this can kept small. Due to this reason barrel

type casing are especially suitable for quick start up and loading.The HP turbine consists of

25 reaction stages. The moving and stationary blades are inserted into appropriately shapes

into inner casing and the shaft to reduce leakage losses at blade tips.



6.3.3 IP Turbine

The IP part of turbine is of double flow construction. The casing of IP turbine is split

horizontally and is of double shell construction. The double flow inner casing is supported

kinematiccally in the outer casing. The steam from HP turbine after reheating enters the inner

casing from above and below through two inlet nozzles. The centre flows compensates the

axial thrust and prevent steam inlet temperature affecting brackets, bearing etc. The

arrangements of inner casing confines high steam inlet condition to admission branch of

casing, while the joints of outer casing is subjected only to lower pressure and temperature at

the exhaust of inner casing. The pressure in outer casing relieves the joint of inner casing so

that this joint is to be sealed only against resulting differential pressure.

The IP turbine consists of 20 reaction stages per flow. The moving and stationary

blades are inserted in appropriately shaped grooves in shaft and inner casing.

6.3.4 LP Turbine

The casing of double flow type LP turbine is of three shell design. The shells are

axially split and have rigidly welded construction. The outer casing consist of the front and

rear walls , the lateral longitudinal support bearing and upper part.

The outer casing is supported by the ends of longitudinal beams on the base plates of

foundation. The double flow inner casing consist of outer shell and inner shell. The inner

shell is attached to outer shell with provision of free thermal movement. Steam admitted to

LP turbine from IP turbine flows into the inner casing from both sides through steam inlet

nozzles.

6.3.5 Turbine Driven Boiler Feed Pump

Turbine driven BFP uses a turbine of 14 stage connected to condenser Turbine is

coupled with a main pump having an engage /disengage unit called power pack unit using oil

pressure for above function. Between turbine and booster pump gear assembly is present. In

500 MW unit , there are two TDBFPs present in addition to a MDBFP. TDBFPs have a big

LCP (Local control panel) having facility for all operations of TDBFP from local. Motor

driven BFP (MDBFP) is used for startup operations of an unit.



6.4 SECTIONAL ARRANGEMENT OF 500MW TURBINE SET

Figure:6.2 Sectional Arrangement of 500mw Turbine Set



7.1 INTRODUCTION

In electricity generation, an electric generator is a device that converts mechanical

energy to electrical energy. A generator forces electrons in the windings to flow through the

external electrical circuit. Generators produce almost all of the electricity used by people.

They supply the electrical power that runs machines in factories, provide lighting and operate

appliances at home. There are two types of generators – alternating current (AC) generators

and direct current (DC) generators. The source of the mechanical energy may be a

reciprocating or turbine steam engine, water falling on a turbine, wind turbine or any other

source of mechanical energy.

Figure:7.1 Cross section of Generator

7.2 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 rotating part called

rotor. The stator housed the armature windings. The rotor houses the field winding to which

the D.C voltage is supplied from permanent magnet exciter.

When the rotor is rotated, the lines of magnetic flux cut through the stator windings.

This induces an electromagnetic force (e.m.f) in the stator windings. The magnitude of the

generated e.m.f is given by following expression:

E=4.44* *f*t



The main parts of a turbo generator are STATOR and ROTOR

7.3 STATOR

A)Stator Frame

The stator frame is a welded steel frame construction, which gives sufficient and

necessary rigidity to minimize the vibrations and to withstand the thermal gas pressure.

Heavy end shields enclose the ends of the frame and form mounting of generator bearing and

radial shaft seals stator body.

Figure:7.2 Stator Frame

Stator body is a robust totally enclosed gas fabricated structure.

Designed mechanically to withstand high internal pressure of explosion of oxygen.

Air mixture of hydrogen gas coolers are housed longitudinally inside stator body.

The end shields are made in two halves for ease in assembly.

B)Stator core

Made up of segmental, varnished insulated bushings of CRGO silicon steel

laminations.

Built in several packets separated by steel spacers for radial cooling of the core by

Hydrogen.

Core is held firmly by means of Heavy non-magnetic steel press rings bolted

thoroughly with ends of core bars.



C)Stator Winding

Three phase double layer short chorded bar type windings with two parallel paths.

Each coil consists of gas insulated solid and hollow copper conductors.

The elementary conductors are Roebel transposed in the slot portion to minimize eddy

losses.

Coils are held in the slots firmly by fibrous wedges.

7.4 ROTOR

The rotor shaft is a forged from one single piece from Chromium, Nickel,

Molybdenum and Vanadium steel.

It under goes all types of series of mechanical tests to ensure any internal flaws.

Rotor is dynamically balanced to a high degree of accuracy.

Figure:7.2 Rotor

A)Field Windings

Field windings are made up of hard driven silver bearing copper.

It is held in position against centrifugal forces by means of duralumin wedges in the

slot portion.

Over hanging portion is held by the non-magnetic steel retaining ring

Several ventilation ducts are milled on the slots for hydrogen gas cooling of the rotor.



B)Terminal bushing

Porcelain insulators are used to insulate the terminal bars from the stator

body

Terminal bushings are situated in the lower part of the stator casing (slip

ring side).

Sealing is provided between bushings and stator body to avoid possibility

of leakage of hydrogen gas.

Three phase and six neutral bushings are available.

7.5 GENERATOR RATINGS

Power : 500 mw

voltage : 21000v

current : 16200a

power factor : 0.85 lag

phase : 3 phase

frequency : 50 hz

winding : y-y

cooling type : hydrogen and purified primary water



8.1 INTRODUCTION

Exhaust steam from the L.P turbine enters into the condenser, where it condenses into

water by exchanging its heat energy into the cooling water. Cold water from the river, water

from the cooling tower is circulated through the tubes in the condenser and as the steam in

the condenser passes around them it is rapidly condensed into water. Because the water has a

much smaller comparative volume than steam, a vacuum is created in the condenser. This

allows the steam to reduce down in pressure below that of normal atmosphere and more

energy can be utilized. For this reason it is the largest and most important of the heat

exchanger in the power station.

8.2 CONDENSERS SPECIFICATION USED IN DR.NTTPS

In Dr.NTTPS surface type condensers are used, which are completely welded

construction and consists of two paths called A&B, Which are interconnected by a bypass

pipe. Each condenser path has an separate inlet and outlet for cooling water. This

arrangement allows cleaning of one of the condensers while the turbo set is operating with 50

to 60% load.

Both the condensers are supported on springs to allow for expansion along the height.

End covers of water boxes are detachable for facilitating repairs and replacement of the

cooling tubes.

There is a provision for adding make up water in condenser. The upper limits of

parameters for make up water are as follows.

Pressure : 5kg/cm2(abs).

Temperature : 400C

Quantity : 30 Tonnes per hour.



8.3 COOLING TOWERS

Cooling towers are heat removal devices used to transfer waste heat to the atmoshere.

Cooling towers may either use the evaporation of water to remove process heat and cool the

working fluid to near the wet bulb air temperature, in the case of closed circuit dry cooling

towers, rely solely on air to cool the working fluid to near the dry-bulb air temperature.

Figure:8.1 Cooling Tower

Common applications include the circulating water used in oil refineries,

petrochemical and other chemical plants, thermal power stations for cooling buildings. The

main types of cooling towers are natural draft and induced draft cooling towers. The

classification is based on the type of air induction into the tower.



9.1 INTRODUCTION

The principle problem in high pressure boiler is to control corrosion and steam

quality. Internal corrosion costs power station crores of rupees in repair without strict control

impurities in steam also form deposit over turbine blades and nozzles. The impurities

present in water are as follows

1) Un-dissolved and suspended solid materials.

2) Dissolved slats and minerals.

3) Dissolved gases

4) Other minerals ( oil, acid etc.).

5). a) Turbidity & Sediment.

b) Silica.

c) Micro Biological.

d) Sodium & Potassium Salt.

e) Dissolved Sales Minerals.

6). a) O2gas.

b) CO2 gas.

9.2 D.M. PLANT

In this plant process water is fed from all these dissolved salts. This plant consists of

two streams each stream with activated carbon filter, weak acid , cation exchanger and mixed

bed exchanger. The filter water to DM plant through 250 dia. header from where a heater top

off has been taken to softening plant. Two filtered water booster pumps are provided on

filtered water line for meeting the pressure requirement in DM Plant.

Sodium Sulphate solution of required strength is dosed into different filtered

water by mean of dosing pump to neutralize chlorine prior to activated carbon filter. When

water passed an activated carbon filter will remove residual chlorine from water. Provision

is made for back washing the activated carbon filter. When pressure drop across filter

exceeds a prescribed limit from the activated carbon filter the works acid cation unit. The

deception water the weak base anion exchanger unit water then enters de-gasified unit where

free CO2 is scrubbed out of water by upward counter flow of low pr. air flow through

degasified lower and degassed water is pumped to strong base exchanger ( anion exchanger).



Arrangement for dosing ammonia solution into de-mineralized water after mixed bed

unit has been provided p+1 correction before water is taken in de-condensate transfer pump

the DM water to unit condenser as make up.

9.3 C.W. PLANT

Circulating water pump house has pumps for condensing the steam for condenser.

Five pumps are used for condensing Unit No.1 & 2 and after condensing this water is

discharged back into the river. Each pump has capacity of 8275 /Hr, and pressure about

1.94 Kg./ . Three seal water pump are used for sealing circulating water pump shaft at pr.

4.5 kg./ .

Two pump for unit 1 & 2 with one standby is used for supplying raw water to

chlrofied chemical dosing is tone between and chlorified water is taken through main line.

From main line water passes through filter bed to filter the water. Chlorified water is pumped

to 42 m elevation by two pumps of capacity 270 M3/Inch at discharge pressure of 6.9

Kg./ . At 42 M elevation the water is stored in tank and used for cooling the oil coolers

and returned back to river. Oil coolers are situated on ground and there are no. of tress for

each unit.

9.4 B.C.W. PUMP HOUSE

Filter water after demineralization is used for bearing cooling from BCW pump

house after passing through strainer and heat exchanger it enters at 30-32oC and leave

exchanger at 38oC. The raw water used in ash handling plant and remaining quantity is

stored in sumps of BCW Pump House. From here the water is pumped to CW Pump by

TWS (Traveling water screens) pumps are run by motors of 90 KW and has a capacity of 240

Cum/hr/pump at pressure of 5 kg/cm2. BCW here stand for water used for cooling oil used

for cooling the bearing. In CW pump house water is discharged from nozzle and impinged for

traveling water screens for cleaning it.



10.1INTRODUCTION

Transformers come in a range of sizes from a thumbnail-sized coupling transformer

hidden inside a stage microphone to huge units weighing hundreds of tons used

to interconnect portions of national power grids. All operate with the same basic

principles, although the range of designs is wide. While new technologies have eliminated

the need for transformers in some electronic circuits, transformers are still found in nearly

all electronic devices designed for household ("mains") voltage. Transformers are

essential for high voltage power transmission, which makes long distance transmission

economically practical.

Figure:10.1 Transformer

10.1.1 Basic Principle

The transformer is based on two principles: firstly, that an electric current can

produce a magnetic field (electromagnetism) and secondly that a changing magnetic field



within a coil of wire induces a voltage across the ends of the coil (electromagnetic

induction).

Changing the current in the primary coil changes the magnetic flux that is

developed. The changing magnetic flux induces a voltage in the secondary coil.

Figure:10.2 Ideal Transformer.

An ideal transformer is shown in the adjacent figure; Current passing through the

primary coil creates a magnetic field. The primary and secondary coils are

wrapped around a core of very high magnetic permeability, such as iron, so that most of

the magnetic flux passes through both primary and secondary coils.

10.1.2 Induction law

The voltage induced across the secondary coil may be calculated from

Faraday's law of induction, which states that, where VS is the instantaneous voltage, NS

is the number of turns in the secondary coil and Φ equals the magnetic flux through

one turn of the coil. If the turns of the coil are oriented perpendicular to the magnetic

field lines, the flux is the product of the magnetic field strength and the area A

through which it cuts. The area is constant, being equal to the cross-sectional area of

the transformer core, whereas the magnetic field varies with time according to the

excitation of the primary.



Figure:10.3 Mutual Induction

Since the same magnetic flux passes through both the primary and secondary coils

in an ideal transformer, the instantaneous voltage across the primary winding equals

Taking the ratio of the two equations for VS and VP gives the basic equation for stepping

up or stepping down the voltage Ideal power equation The ideal transformer as a circuit

element.

If the secondary coil is attached to a load that allows current to flow, electrical

power is transmitted from the primary circuit to the secondary circuit. Ideally, the

transformer is perfectly efficient; all the incoming energy is transformed from the

primary circuit to the magnetic field and into the secondary circuit. If this condition is

met, the incoming electric power must equal the outgoing power.

Giving the ideal transformer equation Transformers are efficient so this formula is

a reasonable approximation. If the voltage is increased, then the current is decreased by the

same factor. If an impedance ZS is attached across the terminals of the secondary coil, it

appears to

the primary circuit to have an impedance of ZS = (VS/IS).



10.2 TYPES OF TRANSFORMER

The different types of transformers present in the 4th stage of Dr. NTTPS are:

1. Generator transformers

2. Station transformers

3. Unit transformers

4. Unit auxiliary and station auxiliary transformers

5. LT transformers.

1. Generator Transformer

The main purpose of this transformer is to step up the generated voltage from 21KV to

400KV so as to synchronize this voltage to grid voltage.

2. Station Transformer

The main purpose of this transformer is to receive power from grid. If there is any

problem occurred or trips in unit the power is taken from grid. Here we use two station

transformers there are station transformer-6 and station transformer-7.

3 Unit Transformer (2Nos)

The main purpose of this transformer is to tap the power from generated power i.e., from

Isolated Phase Bus Duct for11KV unit auxiliaries like ID fans, PA fans, CW pumps and

MDBFP etc.

4 Unit auxiliary and Station auxiliary transformers

The main purpose of unit auxiliary and station auxiliary transformers are for

supplying power to 3.3KV HT drives i.e. FD fans, Mill motors, BCW pumps and ACW

pump and etc.

5 LT Transformers

There are different types of LT transformers connected to the station transformers or

unit auxiliary transformers they are 2MVA and 1.6MVA transformers. These transformers

are known as service transformers, which are used to supply power to 415volts LT motors of

LT station axuliarys like ESPs AHP , CHP, PTP ,Switch yard.



The ratings of the above transformers are as follows:

TABLE -1

10.1 Ratings of Different Transformers

GT

(03no)

ST-7

(01no)

ST-6

(01no)

UT

(02no)

UAT

(02no)

SAT

(02no)

LTTransformers

(10+6no)

Type ofcooling

ONAN/ONAF/OFAF

ONAN/ONAF/OFAF

ONAN/ONAF/OFAF

ONAN/ONAF

ONAN/ONAF

ONAN/ONAF

ONAN

Rating

MVA

124.2/165.6/207

48/

64/

80

30/

40/

50

20/

25

10/

12.5

10/12.5 1600KVA/2000KVA

No loadvoltage(HV)KV

400/√3 400 220 21 11 11 11

No loadvoltage(LV) KV

21 11.5 -

11.5

LV1&LV2

11.5 11.5 3.6 3.6 0.433

HV linecurrent

Amps

537.8/

717.1/

896.3

115.5 131.22 549.86/

687.32

524.86/

656.08

524.86/

656.08

84/105

LV linecurrent

Amps

5914.2/

7885.7/

9857.1

2008.2 -

2008.2

LV1&LV2

2510.22 1004.09/

1255.11

1603.75/

2004.69

1603.75/

2004.69

2133.4/

2666.75

Phase 1 3 3 3 3 3 3



11.1 INTRODUCTION

A 400kv switch yard shall be provided for evacuation of power generated in the

500MW generation plant through two numbers parallel buses and two(2) double circuit

400kv transmission lines to Nunna, sattenapalli and malkaram by making LILO arrangement

of existing 400kv nunna to Srisailam double circuit line. The start up power for the plant shall

be drawn from 200kv existing switch yard of Vijayawada thermal power station(Dr.NTTPS)

through 220/11.5kv station transformer which was extension in the existing 220kv switch

yard.

The existing 220kv switch yard is having two main and one transfer bus arrangement

it will be added with two new bays one will be for 220/11.5kv station transformer and other

for 400/220kv ICT(Inter Connecting Transformer ).The new 400kv switch yard shall have

one and half breaker(1 1 2) switching scheme and four CT method, the enclosed main single

line diagram shows the arrangement of circuits.

11.2 SWITCH YARD CIRCUIT AD EQUIPMENTS

The 400kv switch yard shall have for six diameter bays and nine circuits as the

following:

1) Inter connecting Transformer –one(1)

2) Generator Transformer –one(1)

3) Line feeders –six(6)

4) Tie bays-six(6)

5) Station Transformer –one(1)

6) 420kv circuit breaker, disconnector, current Transformer and capacitor voltages

transformers (Instrument Transformers)

7) Power line carries communication (PLCC) system, wave trap etc….

8) 360kv lighting arrestors

9) Bus Bar materials and accessories ,insulators

10) Switch yard (SRP) relay and control panel, Computer – based SCADA system (for

control metering and synchronizing)



11) Backup control panel for control of switch yard equipments.

11.2.1 Creepage Distance

Considering the location of switchyard,the creepage distance of 25mm/KV shall be

provided for the following equipment:

Circuit breakers,

Bus post insulators,isolaters and lighting Arrestors,

Insulators strings and transformer bushings,

Current and voltage Transformers

11.2.2 Clearence

In line with the recommended insulation level above,the following minimum

clearences are proposed for 400kV.

TABLE -2

11.1 Clearence For 400KV Lines

S.NO Clearence Distance

1. Phase to Phase 4100mm

2. Phase to width 3500mm

3. Live part to ground 8000mm

4. Section Clearence 6500mm

11.2.3 Tasks of The Switch Yard

Protection of trasmissoin system (to isolate false networks from the healthy network)

Controlling the exchange of power i.e., to control the power transmission to load

points as for requirements.

Maintanance of system frequency with in targeted limits. This can be done by raising

lowering of generation or load shedding.

Determination of power transfer through transmission lines.

Fault analysis and subsequent improvements.

Communication via power line carrier communications for the purpose of network

monitoring,controlling and protection.


DEPT OF EEE, SKIT. Page 57Figure:11.1 Single Line Diagram



11.2.4 Classification of Switchyard

In our project we studied about three types Switchgears.

Switchgear at 400KV level (EHT system)

Station Switchgear at 11KV/3.3KV level(HT systems)

Station auxillaries Switchgear at 415KV level(LT systems)

11.3 COMPONENTS IN 400KV(EHT) ELECTRICAL SYSTEM

A)Bus Bars

Bus bars are connecting bars to which a member of incoming or outgoing circuits are

connected. The choice of the bus scheme for a substation depends upon the degree of

reliability and economic justification. The degree of reliability is evaluated by determining

the continuity of service and possible faults. The bus bar can be of QUAD MOOSE ACSR

for 220KV AND TABULAR HALLOW ALLUMINIUM pipes for 440KV systems

according to standard mentionised A1 pipes (ips) of 4 inches dia’’ in size.

B)Bus Structures

IPBD-Isolated Phase Bus Duct-21KV

SPBS-Segregated Phase Bus Duct-11KV&13.3KV

NSPBD-Non-Segregated Phase Bus Duct-415V

C)BusBar Arrangement in 400KV Switch Yard

The choice of bus bar scheme for a switchyard depends upon the degree of reliability

and economic justification. The degree of reliability is evaluated by determining the

continuity of service and possible faults.

D)One&Half Breaker With 4 CTs Method

Generally the 400KV substations are provided with one&half breaker arrangement. In

breaker half scheme five CT’s&4CT’s method will be adopted for protection. It is important

for 400KV substations where higher flexibility is required. Cost is higher for this

arrangement.



Bus bar protection schemes should be

Completely reliable

Absolutely stable for heavy through faults

Selectivity

Accurate and fast operating

For feeder both bus&opposite tie breaker CT will be summated and connected to the

relay(CT1&CT4 for feeder-1,CT2&CT3 for feeder-2)

Bus side CT’s will be utilized for bus bar protection.

E)Double Bus Bar With Tie Bus

This system has additional flexibility for operation. We can take shut down on a

breaker without interrupting the transmission line. It is used for critical 220/400KV

substations.

F)Isolators

An isolator disconnects two electrical circuits in power system networks. They are

three types:

1.Horizontal rotating center break type

2.Horizontal rotating double break type

3.Vertical pantograph type.

Isolators at 400KV switch yard are HCB(Horizontal center break) type these are

disconnecting switches which can be used for disconnecting the circuit under no load

conditions either electrically or manually. They are generally installed along with the circuit

breaker. An isolator can be open after tripping of the circuit breaker and vice-versa. After

opening the isolator,the earth switch should be closed to discharge the trapped electrical

charges to the ground while doing maintenance works etc.

G)Wave Traps

Wave trap is used to trap high(carrier communication) frequency signal of the order

of KHz from entering the switch yard. It allows only power signals i.e.,50HZ.



Figure:11.2 Wave trap

H)Lightening Arresters(Surge Arresters)

Lightening arrestors are the instruments that are used in the incoming feeders so that

to prevent the high voltage entering the main station. This high voltage is very dangerous to

the instruments used in the substation. Even the instruments are very costly, so to prevent

any damage lightening arrestors are used. The lightening arrestors do not let the

lightening to fall on the station. If some lightening occurs the arrestors pull the lightening

and ground it to the earth. In any substation the main important is of protection which is

firstly done by these lightening arrestors. The lightening arrestors are grounded to the earth

so that it can pull the lightening to the ground. Lightening arrestor has Non-linear

resistance(Phase to ground) and offer low resistance to high voltages and high resistances to

normal voltages

These arresters are gapless,consisting of Metal Oxide elements(ZnO,CoO,MnO and

BiO2) with contact plates between discs held rigidly by tie rod assembly in series. ZnO

arresters superior V/I characteristics and higher energy absorption levels. These are having

specials type of characteristics. They offer high resistance for normal frequency and low

resistance for high frequency currents. The V/I characteristics is given by I=kVn,where n is

above 40. For normal voltages,leakage current is low.

Surge monitor is connected in series with the arrester (in the earth lead). It houses

pulse counter and ammeter associated with zener diodes. The discharge counter records the

number of operations the surge arresters performed. The ammeter scale is classified into two

states:



The slightly non-linear green band-this is operating region for grading current under

normal phase to ground voltage and indicates a healthy arrester.

A highly non linear red band-this indicates pollution on external housing or

deterioration of blocks at normal phase to ground voltage.

I)Earthing

In EHT switch yard earthing observation is one of the important aspect. The

resistance should be maintained below 0.5Ohm in the EHT stations(above 220KV), below

1.0 Ohm in 132KV substations and below 5.0 Ohm in 33KV substations.

11.4 CIRCUIT BREAKERS

These are the devices for switching ON/OFF during normal conditions and also

current interrupting devices during abnormal conditions such as earth faults or short circuits

etc. Basically, a circuit breaker is an isolated chamber and comprises a set of fixed and

movable contacts. As soon as the moving contact separates from the fixed contact, a heavy

arc is drawn between fixed and moving contacts. It is necessary to quench he arc as soon as

possible i.e., all the factors contributing towards the maintenance of the arc must be

eliminated by the insertion of high resistance or grading capacitors. The arc can also be

extinguished by the use of a suitable medium such as Transformer oil,vaccum,air,sf6 gas etc.

11.4.1 Classifications of circuit breakers

A)Based on voltage

Low voltage circuit breaker-<1KV

Medium voltage circuit breaker-1KV to 52KV

High /Extra High voltage circuit breaker -66KV to 765KV

Ultra High voltage circuit breaker ->765KV

B)Based on interrupting medium

Air Break Circuit Breaker(ACB)

Air Blast Circuit Breaker(ABCB)

Bulk Oil Circuit Breaker(BOCB)

Minimum Oil Circuit Breaker(MOCB)

SF6 Circuit Breaker(GCB)



Vaccum Circuit Breaker(VCB)

In this switch yard SF6 circuit breakers are used because of high voltages 400Kv.

11.5 SF6 CIRCUIT BREAKER

Sulphur hexa fluoride is used for the arc quenching. It is a heavy non inflammable,

nontoxic and colorless gas with a high dielectric strength which is about 2.5 times that of air.

Electro negativity is the best property of the gas. This is to the maintained at a pressure of

6.67kg/ &8.5 kg/ .

SF6 circuit breaker type SFM makes full use of arc quenching and electrical

insulating characteristics of SF6 gas. In the circuit breaker puffed by the puffer cylinder

extinguishes the arc. Makes the breaker operation very simple with low breaking noise. The

pneumatic operating mechanism ,which operated by air pressure for opening and spring force

for closing is very simple and reliable.

The moving contact system is connected to operating mechanism. Housed

mechanism housing . the operating mechanism uses compressed spring for opening and

compressed spring force for closing. Since compressed spring is required for opening/ closing

operation. The mechanism is simple and reliable. The pole units sealed off from the

atmosphere contamination& therefore deterioration of SF6 gas&erosion of contacts is little.

11.5.1 Construction and Operation

A tropical single pole of the breaker consists of interrupting unit

a. Support unit

b. Mechanism Housing

A)Opening Operation

Opening is affected by pulling the piston rod, puffer cylinder, moving main contact,

moving arc contact and the nozzle. After the moving contact wipe the stationary contact an

arc is generated. During downward movement the gas in puffer chamber builds up and high

pressure through the nozzle and qunenches the arc.



Figure:11.3 Sf6 Circuit Breakers.

B)Closing Operation

In closing operation,piston rod is pulled up and the parts move in the reverse

direction of operating operation. Also SF6 gas is taken into puffer chamber.



11.6 INSTRUMENT TRANSFORMERS

Instrument transformers like voltage and current transformers have low VA rating

used for protection and measurement purpose in electrical circuits. Where as Power-

Transformers are rated for high KVA ratings and are used for transmission of high electrical

energy(order of KVA, MVA ) from one voltage level to another voltage leve

The Main Tasks of Instrument Transformers are

To transform current or voltage from usually high values to a value easily to handle

for relays and instruments.

To insulate the metering circuit from the primary high voltage system.

To provide possibilities of standardizing the instruments and relays to a few rated

currents and voltages.

11.6.1 Current Transformers

These transformers are used for protective relaying & metering purpose, current

transformers are used for supplying the current to the indicating instrument(Ammeter,Watt

meter etc),recording instruments (energy meters etc) and protective relays. The current

transformers are designed to provide standard secondary current output of 1A/5A when rated

current flows through the primary. The current transformer is ideally a short circuited

transformer where the secondary terminal voltage is zero and the magnetizing current is

negligible. The current transformers should not the left with their secondary open. The

equation which gives current transformation in proportion to the primary and secondary turns

is given by =

Figure:11.4 Line Diagram of CT



The two classes of current transformers(CTs) are protective transformers used in

current circuits in protection systems employing secondary relays and control systems.

Current transformers for indicating and metering purpose should have a minimum

error at their rated normal value. These CTs should have low current multiple of

saturation and high accuracy.

CTs for metering instruments shall be able to transform the current at an acceptable

degree of accuracy for the secondary side from 10% to 120% of the rated current.

However under fault conditions,the secondary reflected current should not be very

high so as to damage the instrument normally ISF is 5. CTs for protection should have

the accuracy between the rated current up to the maximum desired secondary current

under fault conditions.

11.6.2 Potential Transformers

The potential transformers are used to supply the voltage to various protection

schemes,windings of power direction relays etc,are of single phase or three phase design. The

secondary voltage of these transformer is 110V. The primary of VT is connected directly to

power circuit between phase and ground depending upon rated voltage and application. The

VA ratings of voltage transformer is lesser as compared with that of power transformers.

Figure:11.5 Line Diagram of PT



There are two types of constructions.

Electromagnetic P.T in which primary and secondary are wound on magnetic core

like in usual transformer.

Capacitor in which the primary voltage is applied to a series capacitor group. The

voltage across one of the capacitor is taken to auxiliary VT. The secondary of

auxiliary V.T is taken for the measurement of protection.

11.6.3 Differences between C.T & P.T

The P.T may be considered as ‘parallel’ transformer with its secondary winding

operating nearly under open circuit conditions whereas the current transformer may

be thought ass a ‘series’ transformer under virtual short circuit conditions. Thus the

secondary windind of a P.T can be open-circuited without any damage being caused

to the operator or to the transformer.

The primary winding current in a C.T is independent of the secondary winding circuit

conditions while the primary winding current in P.T certainly depends upon the

secondary circuit burden.

In a potential transformer, full line voltage is impressed upon its terminals whereas a

C.T carries the full line current.

Under normal operation the line voltage is nearly constant and, therefore the flux the

flux density and hence the exciting current of a potential transformer varies only over

a restricted range whereas the primary winding current and excitation of a C.T vary

over wide limits in normal operation.

11.7 TYPES OF VOLTAGE TRANSFORMERS

There are two types of voltage transformers

1. Electromagnetic voltage transformers(EMVT)

2. Capacitive voltage transformers(CVT)

11.7.1 Capacitor voltage transformers

The capacitor voltage transformer consists of the capacitive voltage divider and an

inductive medium voltage circuit. The inductive part is immersed in mineral oil and

hermitically sealed with air /nitrogen cushion in side a steel tank. One, two or three capacitor



units are mounted on the tank. They consist of condenser stack with paper oil as dielectric

under mineral oil with nitrogen gas cushion. AT 132KV and above,capacitor voltage

transformer(CVT) are more economical than the electromagnetic voltage transformers,

capacitor voltage transformer convert transmission class voltage to standardized low and

easily measurable values , which are used for metering , protection and control of the high

voltage system. As such , the need for accurate and reliable voltage transformation is

essential. Additionally, Capacitor voltage transformers serve as coupling capacitors for

coupling high frequency power line carrier signal to the transmission line.

Figure:11.6 Capacitor Voltage Transformer

The performance of CVT is not much difference with that of conventional

electromagnetic VTs at steady state condition. However it’s performance is affected by the

supply frequency , switching transients magnitude of connected burden etc. The capacitors

can be connected in series act like potential dividers provided the current becomes relatively

larger and ratio error and phase error introduced. Compensation is carried out by ‘tuning’.

The reactor connected in series with burden is adjusted to such a valve that at supply



frequency it resonates with the sum of 2 capacitors. This eliminates the error. The

construction of capacitor type VT depends on form of capacitor voltage divider. Generally

H.V capacitors are enclosed in porcelain housing. A large metal sheet box at the base

encloses the tuning coil intermediate transformer.

11.8 PLCC

In the 400KV switch yard of 500MW unit they are two types of PLCC systems are in

services.

Carrier communication system along with protection where the power lines are being

used for communication with wave traps to filter/ block the high frequency signals

entering into the switch yard.

The superior system then the existing one where the OFC cable is used for carrier

communication and carry protection signals from one substation to another.

11.9 SCADA (SUPERVISORY CONTROL AND DATA ACQUISITION SYSTEM)

The switchyard control and protection consists of SCADA system for 400Kv and

220Kv for its control & monitoring system. The disturbance recording and event recording

which shall be a part of SCADA system. The controls of switch yard breakers and isolators

for the various bays viz, lines, station transformer, etc shall be through SCADA from CRT

located in main control room. However breaker closing and tripping should also be possible

from a backup single switch yard control panel, which shall be located in the switch yard

control room and shall also have mimic of switch yard. Miniature switches for breaker,

indications, metering and annunciation shall also be provided on this panel. All essential

metering shall be displayed on the CRT. Switch yard protection relay panels, PLCC panels ,

switch yard battery, DCDBs&ACDB and necessary,RTUs for interfacing with SCADA

system shall be housed in a separate relay room in the switch yard. Two nos SCADA CRTs

shall be located in main control room. The numerical protective relays in switch yard room

shall be connected SCADA by means of RTU located in switch yard relay room.

The control and interlocking scheme suitable for one and half breaker-switching

scheme shall be provided . Line bays shall be provided with single phase and three phase auto

reclosing feature. All the necessary relays, trip relays auxiliary relays shall be provided

provisions shall be made to accord higher reclosing priority to main breakers, or to issue



reclosing commend to both breakers simultaneously. Rapid reclosing& delayed reclosing

features shall be provided. All conditions requiring blocking auto reclosure shall be

considered. Live line-dead bus closing and dead line –live bus closing facilities shall be

provided using dedicated relays for this purpose. Indicating lamps for fulfillments of the

permissive condition shall be provided. Synchronizing facility shall be provided for all lines

in SCADA. In check in synchronizing position, the synchronizing criteria shall be fulfill as

indicating by the closing permissive provided by check synchronizing relay. In manual mode,

closure is possible only if either the line or the bus is dead. It shall not be possible to close in

manual mode if both line and bus are live. Control and indication shall be provided for each

of the breaker and isolator.



12.1 COLD STARTUP PROCEDURE

Conditions

Cold startup when Turbine shaft /casing temp<150deg.C

Warm startup when Turbine shaft/ casing temp>150deg.C and <350deg.C

Hot startup when Turbine shaft/ casing temp>350deg.C

1) Charge ST-7 and ST-6 transformers and all 11KV, 3.3KV, 440v buses.

2) Charge cooling water system (Raw water, Clarified and DM water).

3) Charge ACW/CW and DMCW systems and compressor/A.C systems.

4) Ensure seal oil/H 2/Primary water system.

5) Ensure main turbine and TDBFPS barring gear.

6) Fill the drum by taking MDBFP into service and ensured closing of Ring Header

drains.

7) Through ID/FD/BCW/CEP/HFO/LDO systems and ensure L.T PRDS, FOPH from

stg-3 PRDS.

8) Ensure no water is coming from CRH pot drain.

9) Maintain air flow greater than 650tph.

10) Purge the boiler, Light up with LDO and ensure opening of all turbine side drains to

UFT.

11) Close boiler side vents at 2kgs and drain at 5kgs.

12) MS line/PRDS/Seal steam lines charging.

13) Condenser vacuum pulling and charging HP-LP bypass system.

1 4) Ensure no hammering of lines and observe HP bypass downstream temp.

15) Reset turbine trip and open main turbine stop valves.

16) Turbine rolling, Soaking and fulfilling TSE criteria.

17) Take one PA fan, Mill B and maintain proper O2 %.

18) Keep turbine speed 3000RPM and synchronize unit.

19) Close turbine side all drains/HP-LP bypass and observe all turbovisory parameters.



20) To load the machine above 100MW observe IP turbine front/rear diff temp.

21) At 120MW load charge UT’s and LP Heaters.

22) Take second mill and CEP, charge CDBFP’s from PRDS and keep them in soaking

(1500rpm).

23) Before taking third mill into service observe SH outlet temperature.

24) At 210MW load charge de-aerator and change PRDS from MS to CRH.

25) At 220MW load take one TDBFP and second PA fan into service.

26) Take fourth mill into service observe SH outlet temps.

27) At 300MW load charge HP heaters after warming up.

28) Take 5th mill into service and keep 3000rpm for 2nd TDBFP.

29) Cut off oil support and load second TDBFP.

30) Parallel TDBFP’s, keep drum level in auto and MDBFP as standby.

31) Take 6th mill (if needed 7th mill also) raise the load to 500MW.

32) Keep all remaining H.T drives in standby mode and turbine side keep in SLC mode.

12.2 SHUT DOWN PROCEDURE

1) Inform to load dispatch centre, CHP, MCR, chief chemists and also all maintenance

wings.

2) Start reducing load gradually, by taking out mills one by one and maintaining proper

air flow.

3) Take MDBFP into service.

4) Below 350MW take oil support.

5) Maintain drum level by MDBFP/TDBFP and trip other TDBFP.

6) At load <250MW cut off HP heaters.



7) Monitor SH/HPBP downstream temps.

8) Maintain drum level by MDBFP and trip 2nd TDBFP.

9) Cut off extraction to de-aerator.

10) De-parallel PA fans and trip one PA fan

11) Further reduce load by cutting off mills and monitor draught, O2, air flow SH temp,

etc...

12) Monitor HPBP downstream temp, turbovisory parameters.

13) Change over PRDS from CRH to MS and cut off extractions to LP heaters.

14) Keep HP/LP bypass in manual and ensure LP bypass spray in auto.

15) Hand trip the turbine hold HP bypass (close on spray isolation valves).

16) Ensure starting of AOP at 2850rpm, JOP at 510rpm.

17)Cut off last mill, trip 2nd PA fan and maintain seal steam temperature.

18)Take out HFO guns boiler trips on loss of all fuel.

19)Depending upon the requirement cool the boiler with prescribed airflow or boxed it

up

20)Ensure opening of gate valve gearing at210rpm and keep turbine under barring gear.

21)Kill vacuum (off vacuum pumps, open vacuum breaker and close seal steam isolation

valve).

22)At drum pr 7kgs trip one BCW pump at 5kgs open boiler side drains and at 2kgs open

boiler side vents.

23)At suction manifold temp <95deg, Trip 2nd BCW pump drain the boiler if required.



CONCLUSION

Here in this project we experienced the efficient working of a thermal power plant and

generation of electricity in it. It is a complex structure involving a number of stages working

simultaneously for the production of electricity.

The most important and the necessary parts of the thermal plant are boiler, turbine,

condenser and generator. The efficiency of a thermal plant depends upon the effective

working of these parts.

In this we learnt about the whole process of power generation by the co-ordination of

various auxiliary systems. We saw that the major losses in are mainly due to steam leaks in

boiler tubes and condenser. The effective transfer of steam from boiler to condenser and

reuse it as feed water greatly improves the efficiency of a power plant

Thus, I conclude that the working of a thermal power plant does not entirely rely upon

the boiler and generator but, the co-ordination of various systems together get the efficient

generation.



REFERENCES

1. A Course in Power Plant Engineering:-S.C.Arora, S.Domkundwar Dhanapat Rai & Co.2001

2. Thermal Engineering:-R.S.Khurmi, S.Chand Publisher

3. Steam Turbine Operation & Maintenance:-B.H.E.L. Haridwar

4. Operation and Maintenance Manuals:-APGENCO, Dr. NTTPS

5. Electrical Power by-J.B.Gupta

6. Power System by

-V.K.Mehta

G.Rajashekar Reddy

Mobile:9908553685

9492312221

E-Mail: [email protected]

Facebook: facebook.com/Rajashekar.Reddy.H

Twitter: Twitter.com/Raji4H

G,Ravi Kumar

Mobile No: 8331918229

7396224600

E-Mail: [email protected]

Facebook: facebook.com/innocent.RaviKumar

study of various systems in 500mw thermal power plant

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