Project Report On

Feroze Gandhi Unchahar Thermal

Power Project

Reporting Officer: Submitted by:

Mr MADHUR KUMAR DGM (TMD) ANSHUMAN SINGH

Mechanical engg.

FGUTPP, Unchahar VIT UNIVERSITY

Rae Bareli (U.P.) CHENNAI (TAMIL NADU)

Acknowledgement

I am very grateful and thankful to all those who were a part of this

project and helped me towards its smooth and efficient completion. I feel

especially thankful to Mr. MADHUR KUMAR DGM (TMD) and Mr G.P.

YADAV, to name a few for their helpful contribution and knowledge

without which my project would not be a reality.

ANSHUMAN SINGH Mechanical Engg.

Third Year

VIT UNIVERSITY CHENNAI (TAMIL NADU)

Contents

1. Introduction

2. Principle of a steam Power Plant

3. Rankine Cycle

4. Various Cycles in Steam Power Plant

5. Coal Handling Plant

6. D M Plant

7. Coal , Water & Steam Cycle

8. Steam Production

9. Turbine

10. Ash Handling Plant

11. Electrostatic Precipitator

12. Variable Frequency Drive

13. Generator

14. Generator Cooling System

15. Switch Yard

16. D C System

17. Conclusion

INTRODUCTION

Electrical energy demand has been rapidly increased in India by the

seventies. This is attributed to greater industrialization and large scale

use of Electrical energy for Agricultural purpose.

The major sources of Electrical energy in India are

fossil fuels (coal, oil and gases) and water. The relative contribution

of thermal plants is 62% ~ 82%. It has been increased during some

resent years only. The central government has set up many thermal

power projects. National Thermal Power Corporation (NTPC) was set

up in 1975 for planning execution of large pithead power station and

associated transmission networks. NTPC has set up six super thermal

power stations having total capacity of 20000 MW at the following

places:-

Singrauli (U.P.)

Korba (M.P.)

Ramagundem (A.P.)

Farakka (W.B.)

Vindhyanchal (M.P.)

Rihand (U.P.)

It has total installed capacity of 39174 MW and has the goal to reach

the capacity of 12 GW. Today it has projects at the following places:-

NORTHERN REGION STATION

Singrauli ------------------ (5*200+2*500) MW

Rihand ---------------------(4*500) MW

Unchahar -------------------(5*210)MW

Tanda-------------------------(4*110)MW

SOUTHERN REGION STATION

Ramgundam ------------------(3*200+4*500)MW

Kayamkulam-------------------(2*155 GT+ 1*120 ST) MW

WESTERN REGION STATION

Korba -----------------------------(3*200+3*500)MW

Vindhyanchal---------------------(6*210+5*500)MW

Kawas ------------------------------(4*106 GT +2*105 ST)MW

EASTERN REGION STATION

Farraka--------------------------(3*200+2*500)MW

Kahalgaon-----------------------(4*210+1*500)MW

Talcher-----------------------------(4*60+2*110)MW

Talcher-Kanhia--------------------(6*500)MW

NATIONAL CAPITAL REGION STATION

Dadri coal -------------------------(4*210)MW

Auta ---------------------------------(3*88 GT+ 1*149 ST)MW

Auriya -------------------------------(4*110 GT +2*106 ST)MW

Faridabad-----------------------------(2*143 GT +1*144 ST) MW

FIROZ GANDHI UNCHAHAR THERMAL

POWER PROJECT (FGUTPP)

foundation stone was laid by Late, Prime Minister Mrs. Indira Gandhi in June 1981.

First two units of 210MW were commissioned on 21stNovember, 1988 and 22

ndMarch, 1989 by U.P. Rajya Vidyut Utpadan Nigam.

FGUTPP was handed over by U.P. Rajya Vidyut Utpadan Nigam to NTPC in 13

th February, 1992.

After take over of FGUTPP from UPRVUN to NTPC, unit-3 & unit-4 were commissioned on 27

th January, 1999 and 22

nd October, 1999.

Station has bagged many awards. NTPC Unchahar stood 9th best power station in the country in terms of PLF in the year 1999-2000

and 2000-2001.

Now third stage (unit-5 & unit-6) is proposed to be of 1210 MW and 1490MW.

Principle of the Steam Power Plant

The working principle of a steam plant is based upon the Rankine

cycle. Generally steam is taken as the working medium due to its ability to

be stable and that its readily stable. The flow of steam in the plant can be

very easily be understood by the flow diagram of the plant. A graph plotted

between the temperature and the entropy would indicate the technical details

of the working by the Rankine cycle. The entropy of a system can be

understood as an index of degradation of energy.

PLANT FLOW DIAGRAM

MODIFIED RANKINE CYCLE

AB- Heating of feed water (i.e. sensible heat addition)

BC- Evaporation of water in boiler (i.e. latent heat addition)

CD- Superheating of steam (i.e. heat addition)

DE- Isentropic expansion of steam in HP turbine

EF- Reheating of steam in Reheaters FH- Isentropic expansion of steam in IP and LP turbine

HA- Condensation of steam in the condenser

Point G-Demarcation between superheated and wet steam

In order to achieve the high efficiency, the following points should be kept

in mind:

The value of useful heat or the temperature of useful heat should be high.

The value of rejected heat or the heat of rejection temperature should be low.

To increase the boiler efficiency (plant efficiency) following methods are

used:

Super heating

Reheating

Feed water heating Efficiency of Rankine cycle without superheating = 27.01%

Efficiency of Rankine cycle with superheating = 44.23%

Efficiency of Rankine cycle with reheating = 46.09%

Efficiency of Rankine cycle with feed water heating = 51.4%

Various Paths or Cycles in power plant

1. Coal Cycle : Railway wagon power house wagon tipplercoal hopper CHP conveyor belt crusher house conveyor belt coal stockyard or RC bunker RC feeder pulverised mill furnace

2. Feed water cycle : DE aerator boiler feed pump HP heater economiser boiler drum

3. Condensate water cycle : Condenser hot well condensate extraction pump gland steam cooler LP heater DE aerator

4. Steam cycle : Boiler drum LT SH platen SH final SH HP turbine Reheater IP turbine LP turbine condenser

5. Air Path :

P.A. fan air heater & cold P.A. fan mill furnace F.D. fan 6. Flue gas path :Furnace Reheater economiser air preheater

E.S.P. I.D. fan chimney atmosphere

Coal Handling Plant

The fuel used in the thermal power plants in the boiler furnace is coal.

Coal undergoes various processes like separation, crushing, etc and is then

finally moved to the furnace in the form of pulverised coal.

Coal: it is a mixture of organic chemicals and mineral materials produced by

natural process of growth and decay. The chemical properties of any coal

depend upon the proportions of different chemicals components present in it.

There are four types of coal:

1. Peat 2. Lignite 3. Bituminous Coal 4. Anthracite

In the plant we use bituminous coal which is one of the most important

varieties of coal, being soft and widely used as fuel. Its approximate

composition is

C = 85%

H = 5%

O2 = 7%

The rest is comprised of sulphur, phosphorus, sodium and other minerals in

traces. Basically the coal used in the plant contains carbon, some volatile

material, moisture and ash. The ash content in the coal is around 30- 40 %.

Properties of Coal

1. Calorific value: the heat evolved when unit amount of coal is burned.

2. Gross calorific value: the heat evolved when all the products of combustion are cooled to the atmospheric temperature.

3. Net calorific value: it is the value obtained when GCV is subtracted by sensible and latent heat of water in the products of combustion.

4. Grindablity: it is the ease with which the coal can be ground to fine sizes. It is measured on the hard grove scale. Coal used here has a

Grindablity index of 55.

Coal analysis

It is done in two ways:

1. Proximate analysis: it gives the behaviour of coal when heated. 2. Ultimate analysis: it tells the elementary composition of coal. it is

useful in determining the air required for combustion and in finding

the weight of combustion products.

Coal Transportation & Handling

Railways are the most commonly used method of coal transportation.

Coal is transported in wagons of capacity 50-56 tonnes. The wagon is

emptied with the use of wagon tippler or track hopper. With the help of

wagon tippler one wagon at a time can be emptied while with the help of

track hopper have the rack can be emptied at a time

Various Equipments Involved

Marshalling Yard: it consist of railway tracks provided to receive the

loaded trains, to unload them and to put them back in formation without

interference between loaded and empty racks.

Wagon Tippler: this consist of tippler structure that supports the wagon during tippling; the hoisting machinery which transmits the motor power

from the driving motor to the tippler structure. It also consists of balance

weight which reduces the load on the motor by balancing a portion of

weight of the structure. To prevent the wagon from falling the tippler is

provided with stopper to fix the angle the tippler rotates the wagon.

Beetle charger: this can be used for placing wagons on to the tippler cradle without the use of locomotive. Hence it avoids unnecessary

investment.

Crusher: these are used to break the received coal from 250mm size to about 20mm size. The crusher consists of fast moving rotor with a

number of hammers mounted on rods. The coal gets crushed by free

impact as it comes in the path of hammers.

Stacker Reclaimer: it is used for stacking and reclaiming coal from the stockyard. The maximum design capacity is 450 metric tonnes per hour.

The stacker reclaimer mainly consist of :

o Bucket wheel

o Boom conveyor While the belt conveyor carrying the coal for the stockyard is in the

same

Direction but the direction of the boom conveyor with respect to the

stacking and reclaiming is in opposite direction.

The stacker reclaimer does the following three functions:

1. travelling (movement in forward and reverse direction)# 2. luffing (up and down movement) 3. slewing (left and right movement) The stacker reclaimer also has two cable reeling drums in which the

reeling action is done by electrical medium and the unreeling is done

mechanically. Great care has to be taken during this operation since any

loop hole can lead to accidental results. During the stocking operation the

coal from the crusher house is diverted towards the stockyard conveyor at

a transfer point. The above conveyor discharges coal to the boom

conveyor through a discharge chute. The boom conveyor running in the

forward direction creates coal stacks

During reclaiming, coal from the stockyard falls on the boom

conveyor with the help of bucket wheel and the boom conveyor during

this period rotates in the reverse direction. The coal from the central

chute falls on the conveyor belts used for transferring the coal from the

stockyard

Advantages:

1. It can operate at full load capacity in bad weather. 2. It is productive at all times as no return journey is to be performed.

The only drawback is that it is expensive.

Magnetic separator: this is an electromagnet placed above t he conveyor to attract magnetic materials and to remove them. Over this

magnet there is a conveyor to transfer these materials to chute

provided for dumping at ground level, hence continuous removal is

possible..

Plough feeders: the plough feeder is normally installed under hoppers for unloading the coal.

Vibrating feeders: it is used for throwing the coal onto the underground conveyor belt from where coal goes to the bunker.

Belt conveyor: this is used for the movement of coal from one place to another. It is made up of nylon fabric with duck weight. For

increasing the holding capacity of belts they are toughened during

movement.

Forward conveyor Return conveyor

Coal cycle in CHP (stage-I)

The coal cycle in CHP in completed under the following steps:

1. The coal is unloaded from wagon tippler and then through conveyor 1A, 1B goes to transfer point-1.

2. Through conveyor 2A, 2B it goes through Cross Belt Suspended Magnet to remove metallic impurities of type ferrous present in the

coal.

3. Then the coal whose present size is 200mm goes to the Primary Crusher House. Here by a rotary breaker the coal is crushed to size

of -150mm. By the centrifugal action of the breaker stones and

other impurities which are not crushable by the breaker are

extracted. If the coal is to be stocked then it goes to the primary

stockyard or it goes to the metal detector. This metal detector

detects both ferrous and non-ferrous impurities.

4. Through conveyor 3A, 3B it goes to the Secondary Crusher House. Here Rotary Granular crusher is used which has hammers attached

to crush the coal. The coal size produced by this crusher is -20mm.

if coal at this stage needs to be stocked then it goes to secondary

stockyard else it is send to stacker reclaimer from where it goes to

the bunkers in the main plant.

Ratings of Equipments used in CHP Conveyor:

Capacity: stage-I 800 tonnes/hr stage-II 1000 tonnes/hr

Speed: 2.3 m/s

Width: 1000 mm

Thickness: 20 mm

Raise of inclination: 12 to 18

Troughing angle: stage-I 20deg stage-II 35deg

Wagon Tippler:

Slip ring induction motor 3, 6.6KV, 71KW, with electromagnetic brakes

Primary Crusher:

Induction motor 3, 6.6KV, 175KW

Secondary Crusher:

Stage-I

Number of crusher: 2

Type of motor: induction motor 3 750KW, 6.6KV Stage-II

Number of crusher: 4

Type of motor: 3 induction motor 450KW, 6.6KV

Stacker Reclaimer (stage-II)

For travelling: 6 induction motors (7.5KW, 415V ac) with brakes.

For luffing: a hydraulic system which is valve operated.

For slewing: 2 dc-shunt motor connected in series.

Boom conveyor:

Stage-I: 37KW, 415 V

Stage-II: 75KW, 415V

Bucket wheel:

Stage-I: 55KW, 415V

Stage-II: 75KW, 415V

Differences between stage I & II CHP

Stage-I Stage-II

Relay logic was used Programmable logic control

circuitry is used

Wagon tippler and track

hopper were added

Manual unloading track hopper

was added

Conveyor capacity:800

tonnes/hr

Conveyor capacity: 1000

tonnes/hr

Two secondary crushers 4 secondary crushers of higher

capacity

6 paddle feeders which are

hydraulic

4 paddle feeders operated

through reduction gear

Cross belt magnetic

separator used

Inline magnetic separator used

Conveyor protection

1. Pull chord: for man and machine safety this protection technique is provided. It is a chord that runs parallel to the conveyor and in case of

emergency it can be pulled as a result of which the conveyor would stop.

2. Belt sways: the sideways movement of the conveyor belt can be quite troublesome and lead to damaging the whole system. When the belt

movement is away from the prescribed zone then after a certain length

this protection would come into action leading to tripping of the

conveyor motor. Belt swaying may also be the result of eccentric loading.

3. Zero speed switches: this protection comes into action when the speed of the conveyor becomes very less than the rated or normal speed no matter

due to any reason. Reason for activation of this protection might be that

the belt might break of the motor may fail etc.

4. Linear heat sensing cable: this protection is for any type of heat related procedures. If by any means the temperature of the conveyor belt

increases beyond a certain limit then this protection comes into action. In

this protection a special temperature sensing type wire runs through the

periphery of the conveyor structure

De mineral (D M) Plant

Introduction

Water is required in plant for many purposes like for formation of steam, for

removal of ash, for safety during fire etc. But the water required for

formation of steam should be perfectly devoid of minerals because if it

would be present with the steam then it will strike the blades of turbine and

due to being in high pressure it produces scars or holes on the turbine blades.

Purification of water

Water is purified in DM plant through a chain of processes as under:-

1. Carbon filter -:Water taken from river is first sent to the carbon filter for the removal of carbon content in the water.

2. Strong acid cation exchanger-: After passing through the carbon filter water is sent to the strong acid cation exchanger which is filled with

the concentrated HCL. The acid produces anions which get combined

with the cations present in the water.

3. Strong base anion exchanger-:After passing though the two chambers of strong acid cation exchanger water is sent to the strong base

anion exchanger which is filled with the concentrated NaOH. The base

produces cations which get combined with the anions present in the

water.

4. Mixed bed exchanger -: At last water is sent to the chamber of mixed bed exchanger where the remaining ions are removed.

Coal, Water & Steam Cycle

COAL CYCLE

C.H.P Plant Bunker R.C Feeder pulverize mill Boiler section

R.C. Feeder -: it is induction motor driven device, which determine the

Quantity of coal enter in to pulverize mill

Pulverize mill: - Pulverization means exposing large surface area to the

action of oxygen. Two types of mill are used in the plant.

Ball mill:- A ball mill operates normally under suction. A large drum partly

filled with steel balls, is used in this mill. The drum is rotated slowly while

coal is fed in to it. The ball pulverizes the coal by crushing. This type of mill

is used in stage -1.

Contact mill:- This mill uses impact principle. All the grinding elements

and the primary air fan is mounted on a single shaft. The flow of air carries

coal to the primary stage where it is reduced to a fine granular state by

impact with a series of hammers. This type of mill is used in stage-2.

WATER CYCLE

D.M. Plant Hot Well C.E.P. Pump Low Pressure heater 1,2,3Derater Boiler Feed pump High pressure Heater 5,6 Feed Regulating station Economizer Boiler Drum.

DERATER:-

. Feed storage tank of water.

. To produce sufficient pressure before feeding to B.F.D.

. Filter the harmful chemicals.

FEED REGULATING STATION:-

. Control the quantity of water in to boiler drum.

ECONOMISER:-

. Flue gases coming out of the boilers carry lot of heat. An economizer

extracts a part of this heat from the flue gases and uses it for heat the feed

water.

DRAFTS SYSTEM:-

. In forced draft system the fan is installed near the base of the boiler

furnace. This fan forces air through the furnace, economizer, air preheater

and chimney.

. In an induced draft system, the fan is installed near the base of Chimney.

STEAM CYCLE Boiler drums Ring Header Boiler Drum (Steam chamber)

Super Heater H.P. Turbine Reheater I. P. Turbine L.P. Turbine.

BOILER DRUM :-

Boiler drum consist two chamber water chambers, steam chamber. Before

entering in super heater the steam is going in to boiler drum, where the

boiler drum filtered the moisture and stored in to water chamber.

SUPER HEATER:-

The function of super heater is to remove the last traces of moisture from the

saturated steam leaving the water tube boiler. The temperature is approx

5300 c.

TURBINE:- Steam turbine converts the heat energy in to mechanical energy and drives

on initial and final heat content of the steam. Turbine having number of

stage in which the pressure drops takes place.

Steam Production

After all the coal is fed to the rc feeder from rc bunker where the coal comes

from the coal handling plant whose size is -20mm. then this coal goes to the

mill for further crushing. The coal is further crushed and takes the form of

talcum powder. This coal is hence called pulverised coal. The coal mills are

HT induction motors. Coal feeders are used to transport the coal from RC

bunker to the mill. The advantages of using pulverised coal are that it is

easily combustible and pulverisation increases the surface area for

combustion and hence the thermal efficiency increases.

In stage-I 4 mills are used which feed 4 elevations out of 6 which run

simultaneously.

In stage-II 2 mills are used which feed 4 elevations out of 6 in the

furnace. The mills employed in stage-I are Bowl type mills. In this type of

mill coal is fed from the bunker to the mill by means of a feeder. The coal

falls on to the mill grinding table and is carried under the grinding rolls

which reduce the coal into pulverised form.

The mills employed in stage-II are ball & tube mills. They operate at a

speed of 17-20 rev/min and in modern power plants they are used as

pressure type mills. The mill drum carrying the ball rotates on the

antifriction bearings. Raw coal is fed inside the drum and it gets crushed.

The ball charge and coal is taken to a certain height and then allowed to fall

down. The coarser particles from both mills are returned by the classifier for

further grinding. From the mills the pulverised coal is then taken to the

furnace by the medium of air which is supplied by the Primary air fan.

Primary air fans are also of 2 types; hot air and cold air type. Hot air fan

contains blast of hot air which removes the moisture from the pulverised

coal and the cold air is simply used for carrying the coal. Primary air fan

motor is a HT motor.

The pulverised coal finally reaches the furnace. It is a 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. The pressure inside the furnace is maintained at -5mm

to 10mm of water column. The air inside the furnace is not sufficient for full

coal burning hence Forced Draught fans are employed for blasting air inside

the furnace at very high pressure. Then to start the firing some oil is also

sprinkled by means of oil igniters.

The method which has been adapted at FGUTPP is the Tangential

Firing of Corner Firing. Here the burners are set at each corner of the

furnace and directed to strike the outside of an imaginary circle in the

furnace which is called the Fire Ball. Since the streams of fuel strike each

other, extremely good mixing is obtained.

Water tube Boiler Schematic Layout

Furnace is placed at the bottom of the most important part of the

thermal plant where steam is generated. The boiler used at FGUTPP is the

water tube boiler type in which, water circulates in tubes surrounded by fire.

Hence it takes up heat and gets converted into steam. The steam then rises

up and gets collected inside the boiler drum. The boiler is made up of carbon

steel. The temperature of steam that comes out of the boiler is around 530

deg Celsius and its pressure is 120kg/cm2. The type of boiler can be further

elaborated as natural circulation, dry bottom, and tangential fired, radiant

heat type with direct fired pulverised coal system.

Once the steam is produced in the boiler, it gets collected inside the

boiler drum. Boiler drum is a special type of cylindrical drum like structure

which contains a mixture of water and steam. Steam being lighter gets

collected at the top portion and beneath it we have the water. It is very

important to maintain a safe level of water in the drum since we have two

main types of constraints in this regard. If the steam produced and collected

is more then it can lead to a blast in the boiler drum else tiny droplets of

water can enter the turbine. Hence in order to keep a check we measure the

level by hydrastep. Hydra step is a phenomenon based on the difference in

the conductivities of water and steam.

Since there is great pressure and temperature at the boiler great care

should be taken while going to the site and maintenance.

Since coal is burning in the furnace and then we have water tubes of

the boiler inside hence constant burning of coal produces ash which gets

collected on the water tubes and the start working as insulation, hence its

necessary to blow this soot hence for this purpose we use Soot Blowers.

Soot blowers are basically pipe like structures that go inside the

furnace and the boiler for efficient onload cleaning. Cleaning is done by the

superheated steam which is tapped from the superheater for the purpose of

soot blowing. The pressure is reduced to 31kg/cm2

at 330 deg Celsius by

means of reducing valve. We mainly have three types of soot blowers:

1. long retraceable soot blower 2. wall blower 3. air reheater Before sending this steam to the turbine, the steam is again superheated

and then its temperature is around 580deg Celsius. This increases the

efficiency since the temperature is the measure of energy hence higher

temperature higher is the energy. Hence, during the phenomenon of

superheating the steam which is dry and saturated, is being heated and hence

the temperature of steam again rises.

First the steam from boiler drum enters the low temperature super heater

(LTSH). After LTSH steam enters the platen super heater and then finally to

a high temperature super heater. The steam which is now produced goes to

the HP turbine.

Turbine The superheated steam after coming out of the superheater goes to the

turbine. A turbine is a form of an engine running on steam, which requires a

source of high grade energy and a source of low grade energy. When the

fluid flows through the turbine a part of the energy content is continuously

extracted and continuously converted into useful mechanical work.

The main advantage of using a steam turbine rather than a prime mover is

that the steam in a turbine can be expanded down to a lower back pressure,

thereby making available a greater heat drop and a larger amount of this heat

drop can be converted into useful mechanical work owing to higher

efficiency of the turbine. Therefore a turbine is suitable for driving a

generator.

Turbines are of two types:

1. Impulse Turbine 2. Reaction Turbine

However another form called impulse-reaction turbine is also used which

provide benefits of both types. The impulse-reaction turbine is used here at

FGUTPP.

Here three stages of turbine are used:

HP turbine (high pressure)

IP turbine (intermediate pressure)

LP turbine (low pressure) Steam Flow in the Turbine

A View of the in house Steam Turbine

The steam flow in the turbine takes place as follows; the steam from

the super heater first goes to the HP turbine where it does work and loses its

temperature. The steam from HP turbine is the fed to the reheater where its

temperature is increased pressure remains the same as that from the outlet

from HP turbine. The steam from the reheater is then fed to the IP turbine

and then finally to the LP turbine. The LP turbine is connected to the

generator and the mechanical output from the turbine is used to drive it.

Ash handling plant

The ash produced in the boiler is transported to the ash dump area by means

of ash handling system. It contains bottom ash system, fly ash system and

ash slurry system.

Bottom Ash-: the bottom ash is collected in water troughs employed below

bottom ash hoppers. The ash is continuously transported onto the respective

clinker grinders which reduce lump sizes to fineness. The crushed ash from

the clinker grinder falls into the hopper and from here it is taken to the ash

slurry house.

Fly Ash-: the fly ash also gets collected into the separate hoppers where it

gets mixed with flushing water.

Ash Slurry System-: this is the main system which is responsible for

carrying away the ash slurry.

The bottom ash and the fly ash slurry of the system is sluiced upto ash slurry

pump along the channel with the aid of high pressure water jets located at

suitable intervals along the channel. The ash slurry pump house has the

following specifications. It contains 4 series with 3 pumps each to carry

water upto 6 kilometres. It has got a control room where all the controlling is

done and simultaneously monitoring is also there. The panel consist of

various relays, SF6 circuit breaker and other motor controls. These pumps

are all high tension pumps working on 6.6KV. To maintain the pressure we

also have lp seal pump and hp seal pump which are all driven by 3 induction motors

Ash slurry pump house Ash Slurry Pumps Number of pumps:12

Capacity: 720m3/hr

Speed: 970 rpm

Rating: 6.6KV, 35KW

LP Seal Water Pumps Head: 65m

Capacity: 8.06 lps

Drive HP: 7KW

Speed: 1450rpm

HP Seal Water Pump Head: 156m

Capacity: 5.56lps

Drive HP: 12.87KW

Speed: 2900rpm

Ash slurry pump arrangement

Ma, Mb, Mc: motor driving respective pumps

Pa , Pb , Pc : ash slurry pumps

The ash removing system can also be divided into types i.e., dry ash and wet

ash. Dry ash can be taken out from the hoppers through some openings and

then they are sent to cylos from where they are sent to cement industries.

Wet ash is removed as slurry by the ash slurry pumps

Electrostatic Precipitator (ESP)

The ash content in the Indian coal is of the order of 30 to 40 %. When

coal is fired in the boiler, ashes are liberated and about 80% of ash is carried

along with the flue gases. If this ash is allowed to flow in the atmosphere, it

will cause air pollution and lead to health troubles. Therefore it is necessary

to precipitate the dust from the flue gases and this work is done by the

electrostatic precipitator.

Working principle:

The principle upon which an electrostatic precipitator works is that dust

laden gases are passed into a chamber where the individual particles of dust

are given an electric charge by absorption of free ions from a high voltage

DC ionising field. Electric forces cause a stream of ions to pass from the

discharge electrodes (emitting) to the collecting electrodes and the particles

of ash in the gas are deflected out of the gas stream into the collecting

surfaces where they are retained by electrical attraction. They are removed

by an intermittent blow usually referred to as RAPPING. This causes the ash

to drop into hoppers situated below the electrodes. There are 4 steps that are

involved:

1. Ionisation of gases and charging of particles. 2. Migration of particles to respective electrodes. 3. Deposition of particles on the electrodes. 4. Dislodging of particles from the electrodes.

Description:

The ESP consist of two sets of electrodes, one in the form of helical

thin wires called emitting electrode which is connected to -70KV DC and

the collecting electrode in grounded.

The fundamental parts of ESP consist of:

1. Basing-: the precipitator casing is robustly designed and has an all welded steel construction.

2. Hoppers-: the hoppers are of pyramidal shape. The angle between hopper corner and the horizontal is never less than 55 deg and often more

to ensure easy dust flow. To ensure free flow dry ash into disposal system

the lower portion of hopper are provided with electrical heaters.

3. Collecting system-: the collecting system consists of electrodes which are based on the concept of dimensional stability. They have a flat

uniform surface for uniform charge distribution. These electrodes have

larger area and are grounded, hence have zero potential.

4. Emitting system-: the emitting system consist of emitting or discharging electrodes that are in the front of the helical wires for a non-uniform

distribution to enhance the rate of charging since a non-uniform field is

created.

5. Rapping mechanism-: the Rapping mechanism is a process which is employed to hammer out the ash particles which get precipitated on the

respective plates. Hence in order to hammer out those particles rapping

motors are employed which hammer at the rate of 2 to 3 cycles per

minute. Various motors are employed and are called collecting rapping

motor and emitting rapping motor.

6. Insulators-: these are also employed for support since ESP is hung with the help of these insulators.

7. Transformer Rectifier-: a transformer rectifier is employed which steps up the voltage to 70KV and then it is rectified to -70 KV and is given to

the emitting electrode

Diagram of basic construction of ESP

Electrical scheme of ESP The following mechanism takes place electrically:

Emitter electrode (E) creates a strong electric field near the surface and corona discharge takes place.

Positive and negative ions are formed by this discharge.

The positive ions move towards anti positive charge line electrodes called emitting electrodes and the negative ions towards collecting

electrodes.

During this passage ions collide with ash particles and adhere to them.

These charged particles stick on the collector curtain which is the dislodged by the rapping motors which is collected by the hoppers.

For optimum functional efficiency of the precipitator the supply

voltage should be maintained near above the flash over level between

electrodes. This is achieved by the electronic control. The efficiency of ESP

is about 99.95%. The ESP is divided into 4 passes called A, B, C, D and has

various fields per pass.

In stage-I we have 7 fields per pass and hence the total no. of fields is

28 whereas in stage-II we have have 8 fields per pass and hence the total no.

of fields is 32.

Variable frequency drive

From the electrostatic precipitator, the flue gases are sucked. It is a

type of fan and is called Induced draft fan. It sucks the flue gases from the

ESP and then transfers them to the chimney. In stage-I an IM is employed

for this purpose but the speed control of that motor is not possible.

Sometimes the amount of flue gases coming out is small and other times it is

large but since no speed control is possible hence the flow of flue gases

become a tedious task. However in stage-II the speed control is possible

since here we have variable frequency drive. The motor which is employed

here are synchronous motor.

Using variable frequency drive voltage is compensated at low frequencies,

the torque at low speeds is improved. To obtain the voltage boost, we require

a controlled converter as well as a controlled inverter. The electrical scheme

is shown below

The above panel is a variable frequency drive panel. First the three phase

supply from transformer is fed to the controlled rectifier which the ac to dc.

The advantage of using a controlled rectifier is that the average value of the

output can be controlled by varying the firing angle. Then its output is fed to

the inverter which is a type of load commutated inverter. Before passing it to

the inverter a reactor is also employed in between this reduces the ripples.

The inverter then converts dc to ac and the ac is fed to the synchronous

motor. The speed of synchronous motor is fixed and is given by 120 f / p.

since the only thing variable in the expression is the frequency which is

directly proportional to the speed. Hence the inverter varies the frequency

and hence controls the speed of the motor. The controlled rectifier in the

circuit is used for voltage control while the load commutated inverter is used

for frequency variation

Two channel arrangement for synchronous motor

The stator of the synchronous motor is given supply using two channels. Normally the motor works on both channels but under

some faulty conditions on any one of the channels the other channel can

continue working since the motor is required for continuous operation

Hence the

frequency is varied from 0.5 Hz to 47.5Hz. When both channels operate the

motor moves at 575rpm and when one channel is in operation the maximum

speed is 475rpm. The power and current ratings in case of both the channels

is 1414KW & 420Amp. In case only one channel is working then the power

is 635KW and current is 380Amp

Ratings of synchronous motor Frame: IDQ 4134

KW rating: 1414KW

KVA rating: 1646

Power factor: 0.9 (lead)

Speed: 575

Stator voltage: 2 X 1200 V

Excitation voltage: 170 V dc

Insulation class: F

Phase: 2 X 3

Connection: double star

Stator amps: 2 X 396

Excitation amps: 64 dc

Degree of protection: IP54

Duty: continuous

Weight: 19,000 Kgs

Advantages of Variable Frequency Drive

1. Speed control is fine as the frequency is varied from 0.5Hz to 47.5 Hz. 2. Very low starting current as motor starts on reduced voltage. 3. Power consumption is low.

Motor life is improved

Generator

The transformation of mechanical energy into electrical energy is carried

out by the generator. The generator also called the alternator is based

upon the principle of electromagnetic induction and consist of a

stationary part called the stator and a rotatory part called rotor. The stator

houses the armature windings and the rotor houses the field windings.

The alternator is a doubly excited system and the field is excited from dc

supply whereas the output received from the alternator is ac. When the

rotor is energised the flux lines emitted by it are cut by the stator

windings which induces an emf in them given by

E = 4.44 f N

Where f frequency in Hz field strength in webers/m2 N speed of rotor in rpm

Turbo generators run at a very high speed hence the no. of poles are

generally two and have a cylindrical rotor construction with small

diameter and long axial length.

Generator main components The main components of a generator are the rotor and stator.

Rotor: the electrical rotor is the most difficult part of the generator to design. It

is an electromagnet and to give it the required strength of magnetic field

a large current is required to flow through it. The rotor is a cast steel

ingot and is further forged and machined.

Rotor winding: silver bearing copper is used for the winding with mica

as the insulation between conductors. A mechanically strong insulator

such as micanite is used for lining the slots. Rotor has hollow conductors

with slots to provide for circulation of the cooling gas.

Rotor balancing: the rotor must then be completely tested for

mechanical balance which means that a check is made to see if it will run

up to normal speed without vibration.

STATOR

Stator frame: it is the heaviest load to be transported. The major part is

the stator core. This comprises an inner frame and an outer frame. The

outer frame is a rigid fabricated structure of welded steel plate. In large

generator the outer casing is done in two parts.

Stator core: it is the heaviest part and is built from a large no. of thin steel

plates or punching.

Stator windings: it is of lap type and employs direct water cooled bar

type winding. The stator winding bar is made from glass lapped

elementary conductor and hollow conductors. The main insulation is

applied by means of mica tape which is wrapped and is compounded with

the help of a silicon epoxy compound.

Excitation system The electric power generator requires direct current excited magnets for

its field systems. The excitation system must be reliable, stable in

operation and must respond quickly to excitation current requirements.

Based on the excitation systems the type of excitations can be:

Normal excitation

Brushless excitation Normal excitation: normal dc supply is given to the field winding of the

alternator. After the rotor is excited and stator winding is given ac supply,

then magnetic locking is created. But it was found that dc excitation

could not meet the demands of large capacity turbo generators because

they employed brushes for making external contacts. The other

disadvantage of dc exciter is that commutator may be satisfactory during

steady state but during load fluctuations, there is risk of flash over at the

commutator. To correct this fault the brush less excitation was

introduced. The normal excitation system is used in stage-I whose ratings

are given below:

KW rating: 210,000

KVA rating: 247,000

Rated terminal voltage: 15.75 KV

Rated stator current: 9050 Amps

Rated power factor: 0.85 lag

Excitation current: 2000 Amps

Excitation voltage: 310 V

Rated speed: 3000 rpm

Rated frequency: 50 Hz

Connection: double star

Rotor cooling hydrogen pressure: 3.5 Kg/cm2

Hydrogen purity: 98 %

Stator cooling water pressure: 3.5 Kg/cm2

No. of poles: 2

Insulation class: B

Rotor type: cylindrical type

Brush less excitation system: this system gained favour because it was possible to use 2 or 4 pole

revolving field type machine possessing all the robust associated with the

generator. Commutator and dc brush gear were eliminated. A pilot exciter is

necessary part of this system. This is a permanent magnet generator. The

following scheme is employed

This is present in stage-II where an arrangement is there in which a

pilot exciter drives the main exciter whose output first passes through the

automatic voltage regulator which is then fed to the rotating diode wheel

which converts the ac to dc and then it is coupled to the rotor of the main

generator which gets dc excitation. In this arrangement no brushes are

used and hence no sparking occurs therefore no wear and tear takes place,

hence the maintenance cost is reduced.

Ratings of turbo generator stage- II

KW rating: 210,000

KVA rating: 247,000

Rated terminal voltage: 15.75 KV

Rated stator current: 9054 Amps

Rated power factor: 0.85 lag

Excitation current: 2080 Amps

Excitation voltage: 270 V

Rated speed: 3000 rpm

Rated frequency: 50 Hz

Connection: double star

Insulation class: F

Gas pressure: 8 bars

Ratings of permanent magnet generator

KW rating: 5

KVA rating: 8

Terminal voltage: 220 V

Speed: 3000 rpm

Coolant: air

Connection type: double star

Rated current: 26 Amps

Phase: 3

Power factor: 0.6 lag

Insulation class: F

Frequency: 150 Hz

Generator cooling system

Turbo generator is provided with an efficient cooling system to avoid

excessive heating and consequent wear and tear of its main components

during operation. The two main systems employed for cooling are water

cooling system and hydrogen cooling system.

Hydrogen cooling system: Hydrogen is used as a cooling medium in large capacity generator in

view of the following feature of hydrogen. When hydrogen is used as a

coolant the temperature gradient between the surface to be cooled and the

coolant is greatly reduced. This is because of the high coefficient of heat

transfer of hydrogen.

The thermal conductivity of hydrogen is 7 times that of air and hence

good heat conduction is possible. While using hydrogen it eliminates

oxygen in the chamber and hence prevents the formation corrosive acids

therefore lengthens the life of insulation. As hydrogen is a non-supporter

of combustion hence risk of fire is eliminated. The density of hydrogen is

1/14th times of air hence circulation is also easier.

The cooling system mainly comprises of a gas control stand, a driver,

hydrogen control panel, gas purity measuring instrument and an

indicating instrument, valves and the sealing system. A great care should

be taken so that no oxygen enters the cooling system because hydrogen

forms an explosive mixture with air. The purity of hydrogen be

maintained as high as 98%.to produce hydrogen in such large quantities a

separate plant called the hydrogen plant is also maintained.

Water cooling system: Turbo generators require water cooling arrangement. The stator

winding is cooled by circulation of demineralised water through hollow

conductors. The system is designed to maintain a constant rate of cooling

water flow to the stator winding at a nominal temperature of 40 deg

Celsius.

Generator sealing system: seals are employs to prevent leakage of hydrogen from the stator at the point of rotor exit.

Cooling specifications of turbo generators at FGUTPP

Stage-I: water as well as hydrogen cooling is present in stage-I turbo generators

with following specifications:

Rotor cooling

Hydrogen gas pressure: 3.5 Kg/cm2

Purity: 98%

Stator cooling

Water pressure: 3.5 Kg/cm2

Rate of flow of water: 130 m3/hr

Stage-II: only hydrogen cooling is used for both stator and rotor cooling.

Rotor cooling

Hydrogen gas pressure: 3.5 Kg/cm2

Purity: 98%

Stator cooling

Hydrogen gas pressure: 2.0 Kg/cm2

Purity: 98%

Switch yard

If we see to the electrical side of a thermal power station, the first thing

that will come to our mind is the switchyard. The main components here

apart from the transformers

comprise what is known as the

switchgear. If we talk in simple

language, switchgear is one

which makes or breaks a circuit.

This definition straight away

does not attract much curiosity

nor does it show the enormous

linking required in designing a

switchgear. Numerous problems

are encountered in erection,

testing and commissioning of the

switchgear and various

precautions are to be taken for

proper operation maintenance.

The main components of

switchyard are:

Transformers

Generator transformer

Unit auxiliary transformer

Station transformer

Lighting arrestor

Isolators

Current transformers

Circuit breakers

Earth switches

Capacitated voltage transformers

Wave traps

Using all of the above equipments after the generation stage i.e., after the

generation has generated an output voltage of 15.75KV all these equipments

are employed for safe and economic self consumption and transmission.

A view of the Switch Yard

Hence before this power is fed or transmitted to the other cities some

precautionary measures are taken.

Transformers The transformer is a device that transfers electrical energy from one

electrical circuit to another through the medium of magnetic field and

without the change of frequency. It is an electromagnetic energy

conversion device, since the energy received by the primary is first

converted to magnetic and is then reconverted to electrical energy in the

secondary. Thus these windings are not connected electrically but

coupled magnetically. Its efficiency is in the range of 97 to 98 %.

TYPES OF TRANSFORMERS

1. GENERATOR TRANSFORMER:- This is a step up transformer. This transformer gets its

primary supply from generator and its secondary supplies the switchyard

from where it is transmitted to grid. This transformer is oil cooled. The

primary of this transformer is connected in star. The secondary is connected

in delta. These are four in number.

2. STATION TRANSFORMER:- This transformer has almost the same rating as the

generator transformer. Its primary is connected in delta and secondary in

star. It is a step down transformer. These are four in number.

3. UNIT AUXILLARY TRANSFORMER:- It is a step down transformer .The primary receives from

generator and secondary supplies a 6.6 KV bus. This is oil cooled. These are

8 in number.

4. NEUTRAL GROUNDED TRANSFORMER:- This transformer is connected with supply coming out of

UAT in stage 2. This is used to ground to excess voltage, if occurs in the

secondary of UAT in spite of rated voltage.

Transformer accessories Conservator: with the variation of temperature there is a corresponding variation in the volume of oil due to expansion and

contraction of oil caused by the temperature change. To account for this, an

expansion vessel called the conservator is connected to the outside

atmosphere through a dehydrating breather to keep the air in the conservator

dry. An oil gauge shows the level of oil in the conservator.

Breather: it is provided to prevent the contamination of oil in the conservator by the moisture present in the outside air entering the

conservator. The outside air is drawn into the conservator every

time the transformer cools down which results in the contraction of

the volume occupied by the oil in the conservator. The breather

contains a desiccator usually Silica gel which has the property of

absorbing moisture from the air. After sometime silica gel gets

saturated and then it changes it colour from purple to pink

indicating that it has become saturated and hence needs to be

replaced or regenerated.

Relief vent: In case of severe internal fault in the transformer, the pressure may be built to a very high level which may result in the

explosion in the tank. Hence to avoid such condition a relief vent is

provided with a bakelite diaphragm which breaks beyond certain

pressure and releases the pressure.

Bushings: they consist of concentric porcelain discs which are used for insulation and bringing out the terminals of the windings

from the tank.

Bucholz relay: this is a protection scheme for the transformer to protect of against anticipated faults. It is applicable to the oil

immersed transformer and depends on the fact that transformer

breakdowns are always preceded by violent generation of gas

which might occur due to sparking or arcing. It consist of two

mercury relayed switches one for a danger alarm and the second

for tripping the transformer.

Temperature indicators: transformers are provided with two temperature indicators that indicate the temperature of the winding

and that of the oil in the transformer for an oil filled transformer.

The temperature indicators are also protective in nature whereby

the first create an alarm and then tripp the respective transformer in

case the temperature of the respective parts rises beyond a certain

value.

Tap changers: these are also provided and are mounted on the transformer. In case some kind of load fluctuations the taps can be

changed or adjusted as per the need. There are two types of tap

changers On load tap changer and Off load tap changer.

Cooling of transformers Heat is produced in the transformers due to the current flowing in the

conductors of the windings and on account of the eddy current in the core

and also because of the hysteresis loss. In small dry type transformers the

heat is directly dissipated to the atmosphere. In oil immersed systems oil

serves as the medium for transferring the heat produced. Because of the

difference in the temperatures of the parts of the transformers circulating

currents are set. On account of these circulating currents hot oil is moved to

the cooler region namely the heat exchanger and the cooler oil is forced

towards the hot region. The heat exchangers generally consist of radiators

with fins which might be provided with forced or natural type air circulation

for removal of heat.

The oil in oil immersed transformers may also be of forced or natural

circulation type. The oil used for cooling is silicone oil or a mixture of

naphthalene and paraffin. When forced oil circulation is used then pumps are

used for the circulation of the oil. The oil forced air forced type cooling is

used in large transformers of very high KVA rating.

Major transformers used in the plant Generator transformer: the generator is connected is connected to this

transformer by means of isolated bus ducts. It is used to step up the

generated voltage from 15.75KV to 220KV for the purpose of transmission.

Though high voltage transmission definitely requires better insulation but it

also has the following advantages requires less conductor material and less

transmission losses hence higher efficiency. The transformer is generally

ofaf type cooled and provides off load tap changing on the HV side. It has an

elaborate cooling system consisting of oil pumps and cooling fans. At

FGUTPP there are four generator transformers (GT). GT-I & GT-II

comprise stage-I while GT-III & GT-IV comprise stage-II. The oil used in

transformers of stage-I is mineral oil which is a mixture of naphthalene and

paraffin while in stage-II we use silicone oil.

SPECIFICATIONS:-

GENERATOR TRANSFORMER (GT-1 & GT-2):-

KV : 15.75/242

MVA : 250

Phase : 3

Hz : 50

Connection : Y d 11 Type of cooling : OFAF/ ONAF / ONAN

Rated HV & IV (MVA) : 250/150/100

Rated LV (MVA) : 250/150/100

No load voltage HV (KVA) : 242

No load voltage IV (KVA) : -----

No load voltage LV (KVA) : 15.75

Line current HV (Amps) : 597.14/358.29/238.86

Line current IV (Amps) : -------

Line current LV (Amps) : 9175.15/5505.09/3670.66

Temp rise oil (0 C) :50

0C

Temp rise winding (0 C) : 60/55/55

0C

POTENTITAL TRANSFORMER

Type of cooling : ONAN

KVA : 100

Phase : 3

Hz : 50

No load voltage HV (Volts) : 6600

No load voltage LV (Volts) : 433

Line current HV (Amps) : 87.53

Line current LV (Amps) : 133.5

Temp rise oil (0 C) :50

0C

Temp rise winding (0 C) : 55

0C

NEUTRAL GROUNDED TRANSFORMER

Type of cooling : ONAF /ONAN

KVA : 1150

Phase : 3

Hz : 50

No load voltage HV (Volts) : 6600

No load voltage LV (Volts) : 250

Line current HV (Amps) : 105.9

Line current LV (Amps) : 2655.8

Temp rise oil (0 C) :50

0C

Temp rise winding (0 C) : 55

0C

Details of generator transformer at NTPC, Unchahar

GT # 1,2 (BHEL) GT# 3,4 (CGL)

MVA 250 250

Type of cooling OFAF OFAF

Phases 3 3

No load KV (HV) 15.75 15.75

No load KV (LV) 242 237

Frequency 50 Hz 50 Hz

HV current 597A 609A

LV current 9175A 9164A

Vector group YND11 YND11

Tap changer off load off load

Temperature rise oil 50deg Celsius 50deg Celsius

Temperature rise winding 60deg Celsius 55deg Celsius

Oil in litres 57700 3680

Two other types of transformer namely the Unit Auxiliary transformer

and the station transformer both being used to run the station auxiliaries and

support the colonial loads. Both these transformers have natural oil

circulation and forced air circulation for their cooling.

A Lightening Arrestor

Lighting Arrestors These are provided to combat the effect of

over voltages and surges caused due to lighting

strokes on the transmission lines. These are

generally provided at the end near the

instrument which we want to protect. The

lightening arrestors provide an easy path to the

surge current to the ground thereby not letting

the equipments to fail. The arrestor come

generally in two types i.e., dry and oil filled

type. The dry type consists of zinc oxide filled

insulator relays while the oil filled arrestor is

similar to a high tension bushing.

Isolators These are devices used for isolation of an

instrument that is being used in the network or

currently working mesh. The isolator works by

disconnecting the device terminals from the

network thereby no current flows through the

device or the load also gets cut-off. The isolators

can be thought of switches that can either make or

break the circuit at the operators wish. The difference of an isolator from a circuit breaker can

be realized from the fact that a circuit breakers making or breaking of a circuit depends upon

certain predefined conditions while that of the

isolator dictates no condition.

A three phase isolator

Circuit Breaker A circuit breaker can make or

break a

circuit depending upon its rating. If

the current flowing through the

circuit breaker in operation

exceeds the rated capacity it tripps

results in disconnection of the load.

With the advancement of

technology quite many options are

available to be used a circuit

breakers. The classification of

circuit breaker is done upon the

methods used for quenching the

arc. That is when the circuit

breaker connects or disconnects the

load the current density at that

point of contact rises to high

leading to an arc which might

result to flash-over in case it is not

quenched or extinguished quickly.

The methods used for arc quenching are:

Sf6 method

Air blast method

Oil quenched An outdoor circuit breaker

Vacuum method The circuit breakers used at FGUTPP are of the type of SF6 or the air blast

type.

Capacitative Voltage Transformer (cvt)

The cvt is used for line voltage measurements on loaded

conditions. The basic construction of a cvt is as follows. Each CVT

consists of a coupling capacitor (CC) which acts as a voltage driver and

an Electro Magnetic Unit (EMU) which transforms the high voltage to

standard low voltage. Depending on the system voltage the CC can be a

single or a multi stack unit. 245 kV & 420kV CVTs no normally

comprise of 2 units. The CC and the EMU are individually hermetically

sealed to ensure accurate performance and high reliability.

The main points of difference between a cvt and a potential transformer

is that in a PT full line voltage is impressed upon the transformer while

in cvt line voltage after standard reduction is applied to the transformer.

Switchyard control room

the switchyard control room or the

MCC as it is commonly known here at FGUTPP, unchahar. The control

room contains an array of relays and circuit breaker that are used for the

protection of man and machinery leading to uninterrupted and efficient

working of the plant. The MCC continuously monitors 24x7 the state of

working of the generated energy its conversion through generator

transformers, supply of power to station auxiliary bus-bars and the

distribution of generated power to various load centres. The FGUTPP caters

to the energy needs of the cities of Lucknow, Kanpur and Fatehpur through

eight transmission lines. A plan for extension of energy to Rae-Barelli is also

going on.

D.C. System

INTRODUCTION:

Dc system is generally used for control and protection

operation. Ac supply is not fully dependable. To maintain constant supply in

case of power failure we use de supply.

Dc system consists of a battery charger. These are the

mode of energy storage.

CHARGING EQUIPMENTS:-

The battery charging equipment comprises

of trickle charger, quick charger, battery panel, main distribution board and

switch control and signaling board.

CHARGING EQUATION:-

In battery Pbo2 used as positive plate and Pb

as negative plate.

Discharging process

Pbo2 + H2 + H2So4 PbSo4+2H2o (+ive)

Pb + So4 PbSo4 (- ive)

Charging process

PbSo4 +2 H2o+ So4 Pbo2+2H2So4 (+ive)

PbSo4 + H2 Pb + H2So4 (- ive)

BATTERY CHARGER

Battery charger normally operates in two modes

1. Float charging: it is a constant voltage mode and works as a trickle charger.

2. Boost charging: it is a constant current mode and works as quick charger.

TRICKLE CHARGER:-

This charger is fed from three- phase ac supply

and gives a dc- stabilized output at rated full load current. The variation of

the dc output voltage ids limited to +/-1% for 0 to 100% load variation and

simultaneously ac voltage variation of +/-10% of frequency variation of +/-

5% from 50 Hz. The rectification is obtained full bridge converted silicon

rectifier. Stack comprising of three SCR and three diode with the surge

suppression RC network connected across each SCR and diode.

WORKING:- The circuit on phase control principle. The SCR is three

terminal device anode, cathode & gate. The main load current by anode &

cathode. The characteristic of scar is block the forward voltage when gate

current is reaches to specify can control the instant, at which the SCR goes

into conduction or triggers. Once the SCR is triggered it remains in

conduction till anode current reaches to zero or reverse voltage is applied to

it. Thus changing the instant firing can control the output voltage of Rectifier

Bridge. The potentiometers are used for adjusting the output voltage. It

senses the load current. The signal proportional to this load current to this

load current is fed to the controller. In event of load of load current

exceeding rated the full load current. This inherent protection is provided in

float charger apart from the back protection provided by HRC fuses.

The auxiliary transformers TR2-4 supply synchronizing voltages to UJT

circuit of the controller. The transformer TR-5 is power supply transformer

for controller. The diode D4 is freewheeling diode that conducts when the

load is inductive. The stored energy then flows through D4 instead of SCR.

A filter circuit comprising of choke and condenser is connected in the output

to limit the ripple contents to normal value.

QUICK CHARGER:-

The charger is fed from 3phase AC supply and gives a

DC stabilized output current at rated full load current. The output current of

the charger shall remain stabilized with in +/- 2% for 0 to 100% of load

variation for AC input voltage +/- 10% from 415 volts and frequency

variation +/- 5% from 50 Hz. The rectification is obtained by using a full

wave bridge connected silicon rectifier stack comprising of three SCR and

3diode with RC surge suppression network across each SCR and diode.

Solid state SCR controller adjusts the triggering angle of SCR and maintains

the current constant.

WORKING OF SYSTEM:-

Normally the trickle charger will float the

batteries at 2.16 volt/cell with in a stabilization of +/- 1% of floating voltage.

The trickle charge will supply trickle charging current require for the

batteries and will also de continuous load require. During this time the

trickle charger and the batteries are across the DC load terminal. When there

is a power failure the battery readily meets the various dc loads. When the

power resumes the battery has to be recharged for which the quick charger is

put on and operated in a constant current mode so that the require constant

current for recharging current can be set. It is advisable to set the constant

current from 30% to 100% of the maximum boost charging current and once

the current is set. The same shell remains constant within the 1/-20% the

higher current during the initial operation of recharging can be set after the

gassing occurs; the required lower can also be set. Whatever are the current

set they remain constant within +/-2% for boosting the battery, charger

supply to the battery is connected through a double pole dc contactor/1 of

battery panel, which can be energized by push button pb 1 of battery panel

the load is connected to battery through a single dc contactor to of battery

panel. This contactor isolates load from the battery during boost charging

of the battery, thereby preventing the excessive dc voltage (about 307)

appearing across the load sw1 one poke on/off dc switches provided to

bypass the dc contactor to if quick charger is to operated as electrical charger

as the contactor to reenergized when the charger is switched on. In the event

off the failure of ac during boost charging to maintain the continuity of

battery voltage across the load. The battery tapped diode (MR-3) provided.

SPECIFICATION OF BATTERY CHARGER:-

Make : ICA Mumbai

Type of rectifier : Diode rectifier

Rated output current : 40 Amp.

Out put voltage range : 24 V

BATTERY CELLS:-

MAKE: EXIDE MUMBAI

TYPE: LEAD ACID AUTOMATIC

UNITS VOLTAGE AMPERE

HOURS

USAGE

1st & 2

nd 220

26

-26

1400

400

150

LT switchgear &

Protection

C & I control

3rd

& 4th

220

26

-26

900

2000

4000

LT switchgear &

Protection

C & I control

1st & 2

nd 400

400

350

250

UPS stage 1

3rd

& 4th

400 800 UPS stage 2

1st & 2

nd 3

rd &4

th

220 400 CW & switchyard

switchgear

Conclusion

On completion of my vocational training at Feroze Gandhi Unchahar

Thermal Power Project, Unchahar I have come to know about how the very

necessity of our lives nowadays i.e., electricity is generated. What all

processes are needed to generate and run the plant on a 24x7 basis.

NTPC Unchahar is one the plants in India to be under highest load

factor for the maximum duration of time and that to operating at highest

plant efficiencies. This plant is an example in terms of working efficiency

and management of resources to all other thermal plants in our country. The

operating plf of the NTPC as compared to the rest of country is the highest

with 87.54% the highest since its inception.

The training gave me an opportunity to clear my concepts from practical

point of view with the availability of machinery of such large rating.