CHAPTER-1

INTRODUCTION

1.1 GENERAL

National Thermal Power Corporation Limited was formed in 1975 to plan,

promote and organize an integrated and efficient development of Central Sector

Power Stations.The Singrauli Super Thermal Power Station was the first of the

series of pithead power stations along with 400kV AC transmission line network. It

is located on the banks of Govind Ballabh Pant Sagar (Rihand Reservoir), about

200km south of Varanasi in the Sonebhadra district of Uttar Pradesh. For coal

transportation, a railway system with rapid loading and unloading facility known

as Merry-Go Round (MGR), continuously hauls coal from the Jayant block of

Singrauli coalfields to the plant site. The rake consists of 30 wagons and will

deliver 1800 MT of coal in each cycle. The average daily consumption of coal is

25,000 MT per day i.e. 8.0 million tonnes per annum considering average calorific

value of 4000 kcal/kg and 7000 hrs of operation in an year for the ultimate

capacity of the plant of 2000 MW having 5 units of 200 MW each and 2 units of

500 MW each.The 5200MW generating units of Stage I are each equipped with

coal-fired, regenerative, re-heat type steam generators with electrostatic

precipitators, each generating 700 tonnes/hr of steam at 138 kg/cm pressure and

535C temperature. The steam generator feeds steam to a condensing, horizontal,

tandem compound 3-cylinder re-heat type turbo generator rotating at 3000 rpm

and each generates 200 MW. Three phase generator transformer of 250 MVA

capacity steps up the generation voltage from 15.75 KV to 400 KV. Cooling water

from the Rihand Reservoir is drawn through an approach channel. It is then

pumped into concrete intake duct by vertical pumps of 15000 m /hr capacity

each. From the ducts, the water is circulated through condensers and is then

discharged into a duct from where it flows into an open channel. This open

channel carries the water for a distance of 6 km to affect sufficient cooling before

it joins back into Rihand Reservoir.

1

The 2500MW generating units of Stage II are each equipped with coal-

fired, regenerative, re-heat type steam generators with electrostatic precipitators,

each generating 1725 tonnes/hr of steam at 178 kg/cm pressure and 540C

temperature. The steam generator feeds steam to a condensing, horizontal,

tandem compound 3-cylinder re-heat type turbo generator rotating at 3000 rpm

and each generates 500 MW. Turbine is a single shaft machine with separate high

pressure (HP), intermediate pressure (IP) and low pressure (LP) parts. The HP part

being a single flow cylinder and the IP and LP parts double flow cylinders. The

individual rotor generator is connected by rigid coupling. The generator is three-

phase, horizontal, 2-pole cylindrical rotor type with a rated output of 588 MVA

and terminal voltage of 21 KV and full load current of 16,200 A. Three single phase

generator transformers of 200 MVA capacity each steps up the generation voltage

from 21 KV to 400 KV.

The circulating water system for cooling the steam in condensers is an

open cycle system utilizing the water from Rihand Reservoir through 2.9 km long

intake channel and pumped through underground RCC duct and the return water

is discharged to the reservoir through 6 km long discharge canal. The intake

channel and the discharge canal are common for both stage I and II units. For

supplying cooling water 6 nos. of vertical pumps each of 27,000 m /hr capacity

have been provided.To reduce the air pollution 220 m high multi-flue stack are

there for better dispersion of the gases emitted by the boilers. There are total four

stacks is SSTPS one for units 1, 2 & 3, second for units 4 & 5 and one each for

units 6 & 7. Electrostatic precipitators are provided between the boiler and stack

in each unit to precipitate the ash content of the flue gases and help in the

reduction of air pollution. The ash so collected is dumped in the ash disposal yard

in the slurry form.

1.2 BRIEF DESCRIPTION OF VARIOUS PLANT IN INDIA

2

NORTHERN & NATIONAL CAPITAL REGION

Details Hy

dro

Coal based Gas/liquid fuel based

Project

(state)

Kolda

m

(Him

achal

Prade

sh)

Singra

uli

(Uttar

Prades

h)

Rihan

d

(Uttar

Prades

h)

Unchah

ar

(Uttar

Pradesh

)

Dadri

(Uttar

Prades

h)

Tanda

(Uttar

Prades

h)

Anta

(Raj-

astha

n)

Auraiy

a

(Uttar

Prades

h)

Dadri

(Uttar

Prades

h)

Fari

d-

aba

d

(Ha

r-

yan

a)

Capaci-

ty(MW)

800 2000 2000 840 840 440 413 652 817 430

Units

Comm-

Ssioned

---- 5x200

+

2x500

2x500 4x210 4x210 4x110 3x88

+

1x14

9

4x112

+

2x102

4x131

+

2x146.

5

2x1

43

+1x

144

Units to

be

commi-

ssioned

4x200 ---- 2x500 ---- ---- ---- ---- ---- ---- ----

Energy

Source

---- Jayant

/

Bina

Amlor

i

North

Karanp

u-

Ra

North

Karan

p-

ura

North

Karan-

pura

HBJ HBJ HBJ HBJ

Water

Source

River

Satluj

Rihan

d

Dam

Rihan

d

Dam

Sharda

Sahaya

k

Canal

Mat

branch

canal/

Hindo

n

River

Saryu

River

Anta

Kota

Right

Canal

Auraiy

a

Etawa

Canal

Hindo

n

River

Gur

gan

Can

al

Benefi-

Ciaries

North

ern

Regio

n

states

&

UT’s

U.P., Uttaranchal, J&K,

H.P., Chandigarh, Rajasthan,

Haryana, Punjab, Delhi

Delhi,

U.P.

U.P. U.P., Uttaranchal, J&K,

H.P., Chandigarh, Punjab,

Delhi, Haryana, Rajasthan,

Railways

Har

yan

a

:

Table:1.1 Northern & national capital region

PROJECT

(STATE)

KORBA

(CHHATI

VINDHYACHA

L (MADHYA

KAWAS

(GUJRAT)

JHANOR

GANDHAR(G

3

SGARH) PRADESH) UJARAT)

Capacity(

MW)

2100 3260 645 648

Units

commissio

ned

3x200+3x

500

6x200+2x500 4x106+2x11

0.5

3x131+1x255

Units to be

commissio

ned

---- 2x500 ---- -----

Energy

source

Kusmunda

Block

Nigahi HBJ Gandhar Gas

Fields

Water

source

Hasdeo

River

Discharge canal

of Singrauli

Hazira

Branch canal

Narmada

River

Table1.2 Western region

SOUTHERN REGION

Details Coal based Gas/liquid based

4

Project

(state)

Ramagundam

(Andhra Pradesh)

Simhadari

(Andhra Pradesh)

Kayamkulam

(Kerala)

Capacity(MW) 2600 1000 350

Units

commissioned

3x200+3x500 2x500 3x115+1x120

Units to be

commissioned

1x500 ---- ----

Energy source South Godavari Talcher Naphtha

Water source Pochampad Dam Sea water Achankovil River

Beneficiaries Andhra Pradesh,

Tamilnadu, Kerala,

Goa,

Pondichery

Andhra Pradesh Kerala, Tamilnadu

Table1.3 Southern region

EASTERN REGION

5

Details Coal based

Project

(state)

Farakka

(West Bengal)

Khalgaon

(Bihar)

Talcher

Kaniha

(Orissa)

Talcher

Thermal

(Orissa)

Capacity(MW) 1600 2340 3000 460

Units

commissioned

3x200+2x500 4x210 2x500 4x60+2x110

Units to be

commissioned

---- 3x500 4x500 ----

Energy source Rajmahal Rajmahal Talcher Talcher

Water source Farakka Feeder

Canal

Ganga River Samal

Barrage

Bhramani

River

Beneficearies West Bengal, Bihar, Jharkhand, Orissa,

Sikkim,

Assam, Damodar Veally Corporation &

Southern region states.

Orissa

Table1.4 Eastern region

CHAPTER-2

6

PRINCIPLE OF OPERATION

For each process in a vapour power cycle, it is possible to assume a

hypothetical or ideal process which represents the basis intended operation and do

not produce any extraneous effect like heat loss.

1. For steam boiler, this would be a reversible constant pressure heating

process of water to form steam.

2. For turbine, the ideal process would be a reversible adiabatic expansion of

steam.

3. For condenser, it would be a reversible a constant pressure heat rejection as

the steam condenser till it becomes saturated liquid.

4. For pump, the ideal process would be the reversible adiabatic compression

of liquid ending at the initial pressure.

When all the above four cycles are combined, the cycle achieved is called

RANKINE CYCLE. Hence the working of a thermal power plant is based upon

Rankine cycle with some modification.

Flow diagram :

7

Steam Flue Generator gas Wt

Super heater Turbine Fuel Air Evaporator Condenser Outlet Q1

Q2

Inlet Economizer Pump Wp Exhaust gas

Figure:2.1 Rankine cycle

where, Q1 – Heat supplied

Q2 – Heat ejected

Wt – Work obtained form turbine

Wp – Work supplied to pump

Cycle’s efficiency = (Wt – Wp)/Q1

2.1 PROCEDURE

2.1.1 COAL TO STEAM

Coal from the coal wagons is unloaded in the coal handling plant. This

coal is transported upto the raw coal bunkers with the help of belt conveyors. Coal

is transported to bowl mills by coal feeders. The coal is pulverized in the bowl mill,

where it is ground to a powder form. The mill consists of a round metallic table on

which coal particles fall. This table is rotated with the help of a motor. There are

three large steel rollers, which are spaced 120 apart. When there is no coal, these

8

Furnace

rollers do not rotate but when the coal is fed to the table it packs up between the

roller and the table and this forces the roller to rotate. Coal is crushed by the

crushing action between the rollers and the rotating table. This crushed coal is taken

away to the furnace through coal pipes with the help of hot and cold air mixture

from the primary air (P.A.) fan. The P.A. fan takes atmospheric air, a part of which

is sent to the air preheaters for heating while a part goes directly to the mill for

temperature control. Atmospheric air from forced draft (F.D.0 fan is heated in the

air heaters and sent to the furnace as combustion air.

Water from the boiler feed pump passes through economiser and reaches

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

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

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

water wall tubes. Water is partly converted into steam as it rises up in the furnace.

This steam and water mixture is again taken to the boiler drum where the steam is

separated from water. Water follows the same path while steam is sent to the

superheaters for superheating. The superheaters are located inside the furnace and

the steam is superheated (540C) and finally goes to the turbine.

Flue gases from the furnace are extracted by the induced draft (I.D.) fan,

which maintains a balanced draft in the furnace with F.D. fan. These flue gases

emit their heat energy to various superheaters in the plant house and finally pass

through the air preheaters and goes to the electrostatic precipitator where the ash

particles are extracted. Electrostatic precipitators consist of metal plates, which are

electrically charged. Ash particles are attracted to these plates, so that they do not

pass through the chimney to pollute the atmosphere. Regular mechanical hammer

blows cause the accumulation of ash to fall to the bottom of the precipitator where

they are collected in a hopper for disposal. This ash is mixed with water to form

slurry and is pumped to ash dyke.

2.1.2 STEAM TO MECHANICAL POWER

From the boiler, a steam pipe conveys steam to the turbine through a stop

valve (which can be used to shut off steam in an emergency) and through control

valves that automatically regulate the supply of steam to the turbine. Stop valves

and control valves are located in the steam chest and a governor, driven from the

9

main turbine shaft, operates the control valves to regulate the amount of steam used

(this depends upon the speed of the turbine and the amount of electricity required

from the generator).

Steam from the control valves enters the high pressure cylinder of the

turbine, where it passes through a ring of stationary blades fixed to the cylindrical

wall. These act as nozzles and direct the steam into a second ring of moving blades

mounted on a disc secured to the turbine shaft. This second ring turns the shafts as

a result of the force of the steam. The stationary and moving blades together

constitute a ‘stage’ of the turbine and in practice many stages are necessary, so that

the cylinder contains a number of rings of stationary blades with rings of moving

blades arranged between them. The steam passes through each stage in turn until it

reaches the end of the high pressure cylinder and in its passage some of its heat

energy is changed into mechanical energy. The steam leaving the high pressure

cylinder goes back to the boiler for reheating and returns by a further pipe to the

intermediate pressure cylinder. Here it passes through another series of stationary

and moving blades.Finally, the steam is taken to the low pressure cylinders, each of

which it enters at the center flowing outwards in opposite directions through the

rows of turbine blades – an arrangement known as double flow – to the extremities

of the cylinder. As the steam gives up its heat energy to drive the turbine, its

temperature and pressure fall and it expands. Because of this expansion the blades

are much larger and longer towards the low pressure end of the turbine.

The turbine shaft usually rotates at 3,000 rpm. This speed is determined by

the frequency of the electrical system used in the country. In India, it is the speed at

which a 2- pole generator is driven to generate alternating current at 50 Hz.When as

much energy as possible has been extracted from the steam it is exhausted directly

to the condenser. This runs the length of the low pressure part of the turbine and

may be beneath or on either side of it. The condenser consists of a large vessel

containing some 20,000 tubes, each about 25 mm in diameter. Cold water from the

water source i.e. the Rihand Reservoir is circulated through these tubes and as the

steam from the turbine passes round them it is rapidly condensed into water

condensate. Because water has a much smaller comparative volume than steam, a

vacuum is created in the condenser. This allows the steam pressure to reduce down

to pressure below that of the normal atmosphere and more energy can be utilized.

10

From the condenser, the condensate is pumped through low pressure heaters by the

extraction pump, after which its pressure is raised to boiler pressure by the boiler

feed pump. It is further passed through feed heaters to the economiser and the

boiler for reconversion into steam. The cooling water drawn from the reservoir is

returned directly to the source after use.

2.1.3 MECHANICAL POWER TO ELECTRICITY

The turbine shaft is mechanically coupled to the generator rotor shaft through thrust

bearings. The steam rotates the turbine at 3000 rpm thus the rotor of the generator

also rotates at 3000 rpm. This speed is necessary to generate electricity at a

frequency of 50 Hz with a two pole turbo- generator.The rotor carries the field

winding over it. This field winding is excited by a DC excitation system. The

supply to the excitation system is tapped from the unit auxiliary transformer. The

flux generated by this field current cuts the armature coil. The armature coil is star-

star connected and is induced with three phase emf. The emf is tapped with the help

of slip rings and brushes. This emf is carried over to the generator transformer

through a bus duct. The bus duct is voltage transformer grounded.

The generator transformer has delta connection in the primary side and star

connection in the secondary side. The generator bus supplies electric power per

phase to the three-phase transformer or bank of three single-phase transformers.

These transformers transmit electric power to the switchyard for further

transmission. These transformers also supply the unit auxiliary transformers

required for the working of various electric motors, pumps and other equipments

installed in the unit.

2.1.4 TRANSMISSION

11

The electricity is usually produced in the stator windings of large modern

generators and is fed through terminal connections to one side of a generator

transformer that steps up the voltage to 400KV. From here conductors carry it to a

series of three switches comprising of an isolator, a circuit breaker and another

isolator.

The circuit breaker, which is a heavy- duty switch capable of operating in a

fraction of second, is used to switch off the current flowing to the transmission

lines. Once the current has been interrupted the isolators can be opened. These

isolate the circuit breaker connected to its terminals. Here after the maintenance or

repair work can be carried out safely. From the circuit breakers the current is taken

to the busbar conductors, which run the length of the switching compound – and

then to another circuit breaker with its associated isolators, before being fed to the

Grid. Each generator in a power station has its own transformer, circuit breaker and

associated isolators but the electricity generated is fed into a common set of

busbars. Circuit breakers work like combined switches and fuses but they have

certain special features and are very different from the domestic switch and fuse.

When electrical current is switched off by separating two contacts, an arc is created

between them. At the voltage use in homes, this arc is very small and lasts for a

fraction of a second but at very high voltages used for transmission, the size and

power of the arc is considerable and it must be quickly quenched to prevent

damage. Three phase, four-wire system is used for large power transmission, as it is

cheaper than the single-phase two-wire system that supplies the home. Also power

is generated in a three-phase system.

The center of the power station is the control room. Here the engineers

monitor the output of electricity, supervising and controlling the operation of

generating plant and high voltage switchgear and directing power to the grid system

as required. Instruments on the control panels show the output and the existing

condition of the whole main plant and a miniature diagram indicates the precise

state of the electrical system.

CHAPTER-3

COAL HANDLING PLANT

12

Every thermal power plant is based on steam produced on the expanse of heat

energy produced on combustion of fuel. Fuels used are coal and fuel oil. Coal is

more important as oil is occasionally used. Coal is categorised as follows

depending upon fixed carbon, volatile matter and moisture content:

Anthracite having 86% fixed carbon

Bituminous having 46 to 86% fixed carbon

Lignite having 30% fixed carbon and

Peat having 5 to 10% fixed carbon

Coal from mines is transported to CHP in railway wagons. It is

unloaded in track hoppers. Each project requires transportation of large quantity of

coal mines to the power station site. Each project is established near coal mine

which meets the coal requirements for the span of its entire operational life. For the

purpose each plant has Merry Go-Round (MGR) rail transportation system. The

loading operation of the coal rake takes place while it is moving under the silo at a

present speed of 0.8 Km/hr. the loading time for each wagon is one minute. For

unloading of coal from the wagons an under ground track hopper is provided at the

power station end.

CHP then normally follows three coal paths:

1. Path A – from track hoppers to bunkers.

2. Path B – from track hoppers to stockyard.

3. Path C – from stockyard to bunkers.

Path A

13

Path-B

Path C

Figure: 3.1 coal paths for C.H.P

3.1 PARTS OF CHP

3.1.1 PADDLE FEEDERS

Four nos. of traveling paddle feeders are provided to collect coal from the

track hopper. They travel along the entire length of the hopper and transfer the coal

from the hopper, uniformly to the pair of underground conveyors 1A &1B. The

paddle feeders move to and fro on the rail with the help of 4 nos. of wheel mounted

14

on the supporting structures. The wheels are driven by electric motor of 415V

supply.

3.1.2 BELT CONVEYOR SYSTEM

The belting system is designed for conveyor capacity of 1200T/hr and belt

speed of 2.6metre/sec. The belt is of cotton fabric with rubber covers of adequate

strength having width of 1400mm.

3.1.3 MAGNETIC SEPARATORS

This is an electromagnet placed above the conveyor to attract magnetic

materials. Over this magnet there is one conveyor to transfer these materials to

chute provided for dumping at ground level. Because of this, continuous removal is

possible and it is also not necessary to stop the electric supply to the magnetic

separators for removal of separated material.

3.1.4 STACKER AND RECLAIMER

Two nos. of traveling stacker/reclaimer each capable of both stacking and

reclaiming are installed which operate on rail tracks running for adequate length to

cover the entire coal storage yard. The belt of the stacker/reclaimer is mounted on a

cantilever boom and has a capacity of 1200T/hr for both stacking and reclaiming.

The boom can revolve about the center of the receiving hopper and

discharge/reclaim materials on/from both sides of the track anywhere between 28

meters radius of the boom. These units work in conjunction with the conveyor 9A

& 9B.

3.1.5 CRUSHER HOUSE

The plant has four nos. of crushers each capable of crushing coal of 200mm

size at the rate of 600T/hr. the crusher with hammer tips is symmetrical in size and

shape on either side. In case of wearing out of one side, the other can be used by

turning over the tips. These crushers are placed in the crusher house, which have

special strong foundations to bear the vibrations due to running of the crushers.

15

3.1.6 VIBRATING FEEDER

The vibrating feeder is used for throwing the coal on the underground

conveyor belt from where coal goes to the bunker. Coal from the stockyard, with

the help of bulldozer, is taken to the vibrating feeder via reclaimer hopper and

underground conveyor belt. In case the bunker requirement is more than the

capacity of crusher or stacker reclaimer, then with the help of bulldozer the coal is

sent to the bunker from the stockyard, through these feeders.

CHAPTER-4

MILLS

16

These are basically coal pulverizing mills. Thermal power stations use pulverized

coal firing system. In this the coal is reduced to fineness such that 70 to 80% passes

through a 200 mesh sieve. This fine powdered coal is called pulverized coal and is

carried forward to the burner by air through pipes.

Advantage of pulverized coal firing system:–

1. Efficient utilization of low grade and cheap coal.

2. Flexibility in firing.

3. Ability to meet fluctuating load.

4. Better reaction to automatic control.

5. High efficiency of boiler.

6. Easy complete combustion.

The only disadvantage being its high initial cost.

4.1 BOWL MILL

The most widely used mills are bowl mills. Even SSTPS uses these kinds of

mills. Bowl mill is a medium speed mill with 30 rpm speed. It pulverizes coal to a

size of 200 microns with a purity of 600 micron. Bowl mills are available in

varying capacities ranging from 1.7 to 100 tons per hour.A 200 MW unit uses 6

mills of 32 tons per hour capacity, out of which 4-5 run at a time and one is in

stand-by condition for emergency. A 500 MW unit uses 8 mills of 60 tons per hour

capacity, out of which 6-7 run at a time.

4.1.1 CONSTRUCTION

Bowl mill has a bowl covered with bull rings. It is mounted on a gear called

worm gear and bearings assembly. This assembly is held in a casing filled with

lubricating oil along with cooling arrangements. Worm gear is coupled to helical

gear shaft which is in turn coupled to AC motors.A bowl mill has three grinding

rollers each weighing three tons. There is a 3mm clearance between bowl and roller

and both are at an angle of 22o to each other. A spring mechanism with 25 kg/cm2

tension is used to maintain the clearance. Rollers are free to rotate about their

axis.The mill has five openings at the top. Out of these, one is inlet of gravimetric

feeder and rest four is outlet openings to each corner of furnace. There are

classifiers around openings and scrapers around the bowl.

17

4.1.2 WORKING

Coal is fed into mill through Gravimetric feeder. When the A.C. supply is

switched on the bowl rotate and due to centrifugal force, the coal moves in the

outward direction. As the coal come between grinder and bowl, it gets pulverized.

The unwanted material is removed through scrapers. The pulverized coal is then

carried to burners by primary air through outlet openings. The heavier particles, as

they rise, collide with classifiers and fall back in mill for further grind. Sealing air

is provided through seal air fan to avoid deposition of coal dust in bearings and

spring mechanism.

4.1.3 SPECIFICATIONS

1.Air flow/mill 60 T/hr.

2.Air temp. at mill inlet 260° C.

3.Mill outlet temperature 77° C.

4.Coal flow/mill 36 T/hr.

5.Fineness of coal Milled 70 % through 200 mesh

6.Primary air pressure inlet 650 mmwcl.

7.Primary air pressure outlet 244 mmwcl.

CHAPTER-5

DRAFT FANS

18

Like water circulation, air circulation is equally important in boilers. It helps in

complete combustion of fuel and removal of flue gases and ash from furnace. It

also helps in maintaining furnace’s pressure below atmospheric pressure.Draft fans

are used for fulfilling the above requirements. There are three types of draft fans

used:-

5.1 FD FAN (FORCED DRAFT)

FD fan is located prior to furnace. It forces air to flow through furnace via

pre-heater. This air helps in complete combustion of fuel. FD fan is an axial fan and

has Pitch Control i.e. the pressure of forced air is controlled by rotating the blades

of fan using oil control.

FD fan is run by an A.C. motor at 1490 rpm. A.C. motor used is 3 phases,

squirrel cage induction motor that takes 6600V, 84.5A, 800KW supply. It is 94.5%

efficient.

5.1.1 Specification

Fan

1.Type & size Axial Reaction API 18/11.

2.Orientation Horizontal.

3.Medium handled Air.

4.Location Ground level.

5.No. of fans/boiler 2

6.Capacity 105 m3/sec.

7.Temp of medium 50° C.

8.Speed 740 rpm.

Motor

1,Type Squirrel cage induction motor

2.Rated power 1100 KW.

3.Rated voltage 6.6 KV.

19

4.Rated frequency 50 Hz.

5.Lubricating system Grease lubrication.

6.No. of phases 3

7.Bearing type hydrodynamic ring assisted bearing

8.Speed 1480 rpm.

5.2 ID FAN (INDUCED DRAFT)

ID fan, induces a draft that helps in removal of flue gases from the furnace.

It also causes the flue gases to flow through ESP and then out of chimney and

ESP.ID fan is an axial fan made of croton steel. It is driven by 3 phase squirrel cage

induction motor at 744 rpm. Motor uses 6600V, 138.5A, 1300KW supply and is

95.5% efficient. ID fan has Inlet Guide Vane control pressure.

5.2.1 Specification

Fan

1.Type & size Axial Impulse AN 28e6.

2.Orientation Horizontal.

3.Medium handled Flue gas.

4.No. of fans/boiler 2

5.Capacity 225 m3/sec.

6.Temperature of medium 136° C.

7.Speed 740 rpm.

.

Motor

1.Type Squirrel cage induction motor

2.Rated power 1100 KW.

3.Rated voltage 6.6 KV.

4.Rated frequency 50 Hz.

5.Lubricating system Forced oil lubrication.

6.No. of phases 3

7.Bearing type hydrodynamic ring assisted bearing

8.Speed 740 rpm.

20

5.3 PA FAN (PRIMARY AIR)

PA fan supplies primary air that carries the pulverized coal from mills to

furnace. Primary air passes to mills through 2 different ducts. One duct carries air

1st to pre-heater and then to mills while the other carries directly to mills. Air

through pre-heater is hot air while other is cold air. Hot air helps in removal of

moisture content from pulverized coal. PA fan is a radial fan runs at 1480 rpm by

an A.C. motor and has Inlet Guide Vane control.

5.3.1 Specification:-

Fan

1.Type & size Single suction, Radial fan.

2.Orientation Horizontal.

3.Medium handled Air.

4.No. of fans/boiler 2

5.Capacity 75 m3/sec.

6.Temp of medium 50° C.

7.Lubricating system Forced oil lubrication.

.

Motor

1.Type 3-phase, air cooled, Squirrel cage

Induction motor.

2.Rated power 1250 KW.

3.Rated voltage 6.6 KV.

4.Rated frequency 50 Hz.

5.Lubricating system Grease lubrication.

6.No. of phases 3

7.Speed 1480 rpm.

21

CHAPTER-6CHAPTER-6

BOILER

22

Boiler can simply defined as the device where any liquid is boiled or Boiler may be

defined as a device that is used to transfer heat energy being produced by burning

of fuel to liquid, generally water, contended in it to cause its vaporization.Boiler, in

simple terms, can be called “Steam Generator”.

The following are factors essential for the efficient combustion usually

referred as “The three T’s”.

a) Time – It will take a definite time to heat the fuel to its ignition

temperature and having ignited, it will also take time to burn.

b) Temperature – A fuel will not burn until it reaches its ignition

temperature.

c) Turbulence – Turbulence is introduced to achieve a rapid relative

motion between the air and fuel particles.

6.1 SPECIFICATIONS

Following are the specifications of the main boiler used at Singrauli Super

Thermal Power Station for (200) MW:

1.Type: Natural circulation, Dry bottom,

Tangentially fired, balanced draft,

Radiant Reheat type with direct fired

pulverized coal system.

2.Manufacturer: BHEL

3 .Nominal rating 210 MW

4. Peak loading (without HP heaters) 229 MW

5.Rated speed 3000 rpm

6.Main steam flow at full load

(with HP heater in service) 630 tons per hour

7.Main steam pressure /temperature

at full load 147.1 kg/cm2 535° C.

8.Condenser pressure 76 mm Hg CW inlet

temperature 33°

9.Designed fuel: Indian Bituminous coal

10.Furnace type: Fusion welded

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11.Drum:

Material Carbon Steel

Overall length 15.700 mtr

Designed pressure 176 Kg/cm2

Designed metal temp. 354 o C

Fig 6.1 Arrangement of boiler auxiliaries

6.2BOILER AUXILIARIES

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Efficiency of a system is of most concerned. Thus it is very important to

maintain a system as efficient as possible. Boiler auxiliaries help in improving

boiler’s efficiency. Following are the important auxiliaries used

6.2.1Economizer: Its purpose is to preheat feed water before it is introduced

into boiler drum by recovering heat from flue gases leaving the furnace.

6.2.2Super Heater: It increases the temperature of steam to super heated

region.

6.2.3Reheater: It is used for heat addition and increase the temperature of

steam coming from high pressure turbine to 540o.

6.2.4Soot Blower: It blows off the ash deposited on the water wall surface. It

uses steam for blowing purpose.

6.2.5Air Preheater: It pre-heats the air entering the furnace by recovering heat

from flue gases in order to ease the combustion process.

6.2.6Draft Fans: They handle the supply of air and the pressure of furnace.

6.2.7Oil Guns: They are used to spray oil to raise the temperature of furnace

to ignition temperature of fuel.

6.2.8Wind Box: It distributes the excess air uniformly through out furnace.

CHAPTER-7

25

GENERATOR AND TURBINE

7.1 Generator

The 200 MW generator is a 3-phase, horizontally mounted 2-pole

cylindrical rotor type, synchronous machine driven by steam turbine. The stator

windings are cooled by de-mineralized water flowing through the hollow conductor

while the rotor winding is cooled by hydrogen gas. Fans mounted on the generator

rotor facilitate the circulation of the H2 inside the machine requiring cooling. 4

coolers mounted inside the machine cool the H2 gas.The generator winding is

insulated by epoxy thermo- setting type insulation. It is provided with static

excitation system. 2 H2 driers are provided to facilitate moisture removal. H2 is

circulated through them via the fans in dry condition. Normally one drier is kept in

service and other is in standby. Liquid Level Detectors (LLDs) are provided to

indicate liquid in the generator casing, to indicate whether oil is leaking or water. It

can be drained through drain valves. H2 gas purity is to be maintained at more than

99%.

The cooling water system consists of 2x100% duty AC motor driven

pumps, 2x100% duty water coolers, 2x100% duty mechanical filters, 1x100% duty

magnetic filter, expansion tank, polishing unit and ejector system. The stator water

pump drive the water through coolers, filters and winding and finally discharges

into the expansion tank situated at a height of about 5m above the TG floor. It is

maintained at a vacuum of about 250mm Hg by using water ejectors. A gas trap is

provided in the system to detect any traces of hydrogen gas leaking into the stator

water system. To prevent leakage of hydrogen from generator housing, ring type

seals are provided at the both ends of the generator. The seal ring is free to adjust

its position according to shaft position.

7.1.1 SPECIFICATIONS

Maximum Continuous KVA rating ~~ 235300 KVA

Rated Terminal Voltage ~~ 15750 V

Rated Stator Current ~~ 9050 A

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Rated Power Factor ~~ 0.85 lag

Excitation Voltage at MCR condition ~~ 310 V

Excitation Voltage at MCR condition ~~ 2600 A

Excitation voltage at no load ~~ 102 V

Excitation current at no load ~~ 917 A

Rated speed ~~ 3000 rpm

Rated frequency ~~ 50 c/s

Efficiency at MCR condition ~~ 98.49%

Short circuit ratio ~~ 0.49

Direction of rotation from slip ring ~~ Anti clockwise

Phase connection ~~ Double star

No. of terminals brought out ~~ 9(6 neutral, 3 phase)

Generator gas volume ~~ 56 m 3

Nominal pressure of H2 ~~ 3.5 Kg/cm 2

Nominal temp of cold gas ~~ 40 0 C (Alarm)

Purity of hydrogen ~~ > 97% (min)

Relative humidity of H2 ~~ 60 %

Hot gas temp ~~ 75 0C

Stator water flow

1. Normal ~~ 27 + 3 m 3 / hr

2. Alarm ~~ 21 m 3 / hr

3. Trip ~~ 13 m 3 / hr

Stator water conductivity

1. Normal ~~ < 5.0 µ mho/ cm

2. High ~~ 13.3 µ mho/ cm

3. Trip ~~ 13 m 3 / hr

Stator water expansion tank volume ~~ 200-300 mm wcl

Nominal consumption of cooling water

1. At 35 0C ~~ 95 m 3 / hr

2. At 37 0C ~~ 110 m 3 / hr

3. At 40 0C ~~ 130 m 3 / hr

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Seal oil outlet temperature

1. Normal ~~ 40 0C

2. Alarm ~~ 65 0C

Safety Valve release (AC seal oil pump) ~~ 9 Kg/cm 2

0Safety Valve release (DC seal oil pump) ~~ 9 Kg/cm 2

7.1.2 GENERATOR PROTECTION

The core of an electrical power system is generator. During operating conditions

certain components of the generator are subjected to increase stress and therefore,

could fail, referred to as faults. It can be internal fault or external fault depending

upon whether they are inside or outside of the machine. The machine with fault

must be tripped immediately. The corrective measures against generator’s abnormal

operation are taken care by stubborn system.

7.1.3TASK OF THE PROTECTIVE SYSTEM:

Detect abnormal condition or defect.

Limit its scope by switching to isolate the defect.

Alarm the operating staff.

Unload and/or trip the machine immediately.

7.1.4 PROTECTIVE DEVICES

The choice of protective equipment for the generator should

precisely understand the type of fault and do the necessary preventive measures for

avoiding it.

Electrical protection

Differential protection:

Earth fault protection:

Stator earth fault

Rotor earth fault

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Stator Inter turn fault

Over voltage

Generator Transformer Protections

Buchholz Protection

Winding Temperature High

Oil Temperature High

Fire Protection

Bus Bar Protection

7.2 TURBINE

A steam turbine has two main parts viz. the cylinder and the rotor. The

cylinder (stator) is a cast iron or steel housing usually divided at the horizontal

centerline. Its halves are bolted together for easy access. The cylinder contains

fixed blades, vanes and nozzles that direct steam into moving blades carried by

the rotor. Each fixed blade set is mounted in diaphragms located in front of

each disc on the rotor, or directly in the casing. A disc and diaphragm together

make a turbine stage. Steam turbine can have many stages. The rotor is a

rotating shaft that carries the moving blades on the outer edges of either

drums or discs. The blades rotate as the rotor rotates. The rotor of a large

steam turbine consists of high, intermediate and low pressure sections.

In a multiple stage turbine, steam at a high pressure and high temperature

enters the first row of fixed blades or nozzles through an inlet valve or valves. As

the steam passes through the fixed blades or nozzles it expands and its velocity

increases. The high velocity jet of steam strikes the first set of moving blades. The

kinetic energy of the steam changes into mechanical energy, causing the shaft to

rotate. The steam then enters the next set of fixed blades and strikes the next row of

moving blades. As the steam flows through the turbine, its pressure and

temperature decreases, while its volume increases. The decrease in pressure and

temperature occurs as the steam transmits energy to the shaft and performs work.

After passing through the last turbine stage, the steam exhausts into the condenser

or process steam system.Large turbines use both impulse and reaction types. These

combination turbines have impulse blades at the high pressure end and reaction

29

blades at the low pressure end. The blade length and size increases throughout the

turbine to use the expanding steam efficiently. Blade rows require seals to prevent

steam leakage where the pressure drops. Seals for impulse blades are provided

between the rotor and the diaphragm to stop leakage past the nozzle. Seals for

reaction blades are provided at the tips of both the fixed and moving blades.In stage

I, condensing, tandem reheat, impulse type turbine is installed. The HP cylinder has

12 stages, IP cylinder has 11 stages and LP cylinder has 42 stages. The HP and IP

parts are single flow cylinders and the LP part has double flow cylinder.In stage II,

3 cylinder, reheat, reaction type turbine is installed. The HP cylinder has 18 stages,

IP cylinder has 142 stages and LP cylinder has 62 stages. The HP part is a

single- flow cylinder and the IP and LP parts are double flow cylinders.

CHAPTER-8CHAPTER-8

30

ELECTROSTATIC PRECIPITATORELECTROSTATIC PRECIPITATOR

Indian coal contains about 30% of ash. The hourly consumption of coal of a

200 MW unit is about 110 tons. With this, the hourly production of ash will be 33

tons. If such large amount of ash is discharge in atmosphere, it will create heavy air

pollution thereby resulting health hazards. Hence it is necessary to precipitate dust

and ash of the flue gases.

Precipitation of ash has another advantage too. It protects the wear and erosion of

ID fan.

To achieve the above objectives, Electrostatic Precipitator (ESP) is used. As

they are efficient in precipitating particle form submicron to large size they are

preferred to mechanical precipitation.

8.1 CONSTRUCTION

An ESP has series of collecting and emitting electrons in a chamber

collecting electrodes are steal plates while emitting electrodes are thin wire of

2.5mm diameter and helical form. Entire ESP is a hanging structure hence the

electrodes are hung on shock bars in an alternative manner.

It has a series of rapping hammer mounted on a single shaft device by a

motor with the help of a gear box at a speed of 1.2 rpm. At the inlet of the chamber

there are distributor screens that distributes the gas uniformly through out the

chamber.

There are transformer and rectifiers located at the roof of chamber. Hopper

and flushing system form the base of chamber.

8.2 WORKING

Flue gases enter the chamber through distributor screen and get uniformly

distributed. High voltage of about 40 to 70 KV form the transformer is fed to

rectifier. Here ac is converted to dc. The negative polarity of this dc is applied

across the emitting electrode while the positive polarity is applied across the

collecting electrodes. This high voltage produces corona effect negative (–ve) ions

from emitting electrode move to collecting electrode. During their motion, they

collide with ash particles and transfer their charge. On gaining this charge, ash

31

particles too move to collecting electrode and stock to them. Similar is the case

with positive (+ve) ions that moves in opposite direction.

The rapping hammers hit the shock bars periodically and dislodge the collected

dust from it. This dust fall into hopper and passes to flushing system. Here it is

mixed with water to form slurry which is passed to AHP. Efficiency of ESP is

approximately 99.8%.

CHAPTER-9

32

ROLE OF TRANSFORMERSROLE OF TRANSFORMERS

After the electricity is generated by the turbogenerators of Unit-1 to 5 (generating

15.75KV) & Unit 6 & 7(generating 21 KV),it is sent to the Generating

Transformer(G.T.) and Unit-Auxiliary Transformer(U.A.T.) at the same time.

9.1 Generating Transformer

Steps–up this voltage of 15.75/21 KV to a higher voltage of 400 KV (hence,

working as a step-up Transformer).This voltage of 400 KV is then transmitted to

switchyard.

Figure9.1 generating transformer (G.T)

9.2 Unit-Auxiliary Transformer (U.A.T.)

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Steps-down this voltage of 15.75/21 KV to a comparatively lower voltage

of 6.9 KV which is required to run the auxiliaries of the Main Plant such as I.D.

Fan, P.A. Fan, F.D. Fan and other auxiliary motors. Each unit has its own separate

G.T. & U.A.T.

Figure9.2 Unit auxiliary transformer(U.A.T)

9.3 STATION TRANSFORMER

There is one more Transformer known as station transformer used only for

initializing the start-up of the station (Main Plant).It is very beneficial during

emergency situations such as tripping of Units, shut-down etc.

It gets the supply in its primary from 132 KV switchyard, steps-down it to 6.6

KV which is used for starting various equipments & devices used in the Main

Power Plant.

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Figure9.3 Station transformer(S.T.)

9.4RATINGS

9.4.1 GENERATING TRANSFORMER

Type of cooling: O.F.W.F.

Rating H.V.(MVA): 200

Rating L.V.(MVA): 200

No-load Voltage (KV):

H.V. 400/√3

L.V. 21

Line current(Amps.):

H.V. 866.0

L.V. 9523.8

Temperature rise(°C):

Oil 50

Windings 60

Phase: 1

35

Frequency (Hz): 50

Connection symbol: YND11

Makers Serial No: 60046

Electrical Specification No: 600626

Year of manufacture: 1985

Core & winding(Kg.): 123050

Weight of Oil(Kg.): 27500

Total weight (Kg.): 179500

Oil quantity(l.): 29540

Transport weight(Kg.): 138000

Untanking weight(Kg.): 12000

9.4.2 UNIT AUXILIARY TRANSFORMER

Rating (KVA): 12000/16000

Cooling: Method ONAN/ONAF

% 75/100

KV (At no load):

H.V. 15.75

L.V. 6.9

Amperes:

H.V. 439.8/586.53

L.V. 1004.1/1338.8

Phases: H.V. & L.V. Three

Vector group: H.V. & L.V. DY ∩1

Temp.rise (˚C):

Tap oil 40

Winding 50

Total Mass(Kg.): 37700

Untanking Mass(Kg.): 19200

36

Mass of Oil(Kg.): 7100

Volume of Oil(l.): 8250

Transport Mass with Oil(Kg.): 30000

Manufacture’s Serial No: 37893

Year of manufacture: 1982

Frequency(Hz): 50

9.4.3 STATION TRANSFORMER

Rating(KVA): 19000/25000/31500

Amperes:

H.V. 83.1/109.3/137.8

L.V. 1589.8/2091.8/2635.7

KV at no-load:

H.V. 132

L.V. 6.9

Phases: H.V. & L.V. 3

Vector group: H.V. & L.V. YNY∩O

Temp. rise(°C):

Tap Oil 40

Winding 55

Frequency(Hz): 50

Total Mass(Kg.): 63000

Untanking Mass(Kg.): 29000

Mass of Oil(Kg.): 17000

Volume of Oil(l.): 19600

Transport Mass with Oil(Kg.): 47000

Insulation level(KVp):

H.V./H.V.N. 550/170

L.V. 60

Cooling Methods: ONAN/ONAF/OFAF

% 60/80/100

Manufacture’s Serial No: 37899

37

Year of manufacture: 1980

CHAPTER-10

38

POWER TRANSMISSION

Figure10.1 Switchyard

10.1 SWITCHYARDSWITCHYARD

Switchyard is considered as the HEART of the Power Plant. Power

generated can be worthful only if it is successfully transmitted and received by its

consumers. Switchyard plays a very important role as a buffer between the

generation and transmission. It is a junction, which carries the generated power to

its destination (i.e. consumers). Switchyard is basically a yard or an open area

where many different kinds of equipments are located (isolator, circuit breaker

etc…), responsible for connecting & disconnecting the transmission line as per

requirement (e.g. any fault condition). Power transmission is done at a higher

39

voltage. (Higher transmission voltage reduces transmission losses). Therefore, the

power generated by the Turbogenerator of 1 to 5 units is 15.75KV and of 6&7 units

is 21KV which is further stepped-up to 400KV by the Generating transformer &

then transmitted to switchyard.

Switchyards can be of 400KV, 200KV&132KV.

In SSTPS there are two interconnected switchyards:-

(i) 400KV SWITCHYARD

(ii) 132KV SWITCHYARD

10.1.1 400KV SWITCHYARD

There are on total 21 bays in this switchyard.

(A bay is basically a way for the incoming power from generator as well as

outgoing power for distribution).

7 for unit Generating Transformer.

7 for various distribution lines such as:

Lucknow line;

Allahabad #1 line;

Anpara line;

Allahabad #2 line;

Rihand #1 line;

VSTPP line;

Rihand #2 line;

2 for Bus coupler.

2 for TBC.

2 for ICT.

1 for the Bus Section.

There are on total 6 buses in 400KV switchyard.

Bus-1

Bus-2

Bus-3

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Bus-4

There are two transfer buses:

Transfer bus-1

Transfer bus-2

Transfer buses are kept spare and remain idle and are used only for emergency

purposes.

Bus-1 & Bus-3, Bus-2 & Bus-4; both are joined together by bus section (1 & 2)

respectively.

10.1.2 132KV SWITCHYARD:

There are 15 bays in 132KV switchyard.

4 for Station Transformer.

4 for C.W. Transformer.

2 for Colony Transformer.

2 for I.C.T.

1 for S-V-R line.

1 for Pipri line.

1 for Bus Coupler.

10.2 SWITCHYARD EQUIPMENTS

10.2.1 LIGHTENING ARRESTOR:

It is a protective device, which protects the costly equipments such as overhead

lines, poles or towers, transformer etc. against lightening. As the name suggests it

arrests the lightening of very high voltage (crores of KV) and dump it into the

ground. It works on the principle of easy path for the flow of current.L.A. is

connected in parallel with the line with its lower end connected and the upper end

projected above the pole of tower.

41

10.2.2 LIGHTENING MOST:

It is present at the highest point, at the topmost tower of the switchyard and is

connected together by wires forming a web. The reason for its presence at the

topmost point is to grasp the lightening before it can come, fall and damage the

costly equipments present in the switchyard.

10.2.3. WAVE TRAP:

It is equipment used to trap the high carrier frequency of 500 KHz and above and

allow the flow of power frequency (50 Hz). High frequencies also get generated

due to capacitance to earth in long transmission lines. The basic principle of wave

trap is that it has low inductance (2 Henry) & negligible resistance, thus it offers

high impedance to carrier frequency whereas very low impedance to power

frequency hence allowing it to flow in the station.

10.2.4. CIRCUIT BREAKER:

It is an automatic controlling switch used in power house, substation & workshop

as well as in power transmission during any unwanted condition (any fault

condition-earth fault, over-current, flashover, single phasing,).

During such condition it cuts down the supply automatically by electromagnetic

action or thermal action. It can be used in off-load as well as on-load condition.

When a circuit breaker is operated by sending an impulse through relay, C.B.

contact is made or broken accordingly. During

this making and breaking, an arc is produced which has to be quenched; this is done

by air, oil, SF6 gas etc….

Depending on the medium being used C.B.s can be categorized into various

types.In SSTPS for 400 KV/132 KV switchyard only 4 main types are being used:-

ABCB (Air operated circuit breaker):- operated as well as arc quenched

through air.

Air operated SF6 circuit breaker:- operated through air but arc quenching

done through SF6 gas.

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MOCB (Minimum oil circuit breaker):-operated through spring action but

arc quenching done through oil (Aerosol fluid oil).

Hydraulic operated SF6 circuit breaker:- operated through hydraulic oil

and arc quenching done through SF6 gas.

Hydraulic operated SF6 circuit breaker is the most efficient due to following

reasons:-

1. Less maintenance.

2. Arc quenching capability of SF6 gas is more effective than air.

3. Heat transfer capacity is better in this C.B.

10.2.5. ISOLATOR:

An isolator is also a switching device used to disconnect the line. As the name

suggests it isolate the line from the supply. It is always used in OFF-LOAD

condition. Whenever any fault occurs in the equipments present in the line, in order

to remove the fault or replace the device first of all supply is disconnected. But

even after the disconnection of the supply, the line remains in charged mode so

before working on the device (to remove fault) isolator should be made open.

Depending on the structure there are mainly two types of isolators:-

Pantagraph isolator.

Centre-break isolator (also known as Sequential isolator).

Pantagraph is generally used in buses whereas Centre-break (Sequential) is

used in line.

Isolators may be operated in air (pneumatic), electrically or even manually.

10.2.6. P.T (Potential Transformer):

This Transformer is connected in parallel with the line with one end earthed. It is

only used for voltage measurement by stepping-down the voltage to the required

measurable value.

10.2.7. C.T (Current Transformer):

43

This Transformer is used for basically two major functions: -

Metering which means current measurement.

Protection such as over current protection, overload earth fault protection,

Bus-bar protection, Bus differential protection.

NOTE:-Secondary of the C.T should be kept shorted because (when secondary is

kept open) even the presence of a very small voltage in the primary of C.T will

prove to be harmful as it will start working as a step-up Transformer & will

increase the voltage to such a high value that primary would not be able to bear it &

will get burned.

CHAPTER-11

44

CONCLUSION

The entire system configuration study helped me understand the following.

1.Use of instrument in power plant.

2.The various instrument available for industry.

3.various cables and specified use.

REFERENCES

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1.www.ntpc.co.in

2.Power plant familiarization by Poonam khurana

3.Power system engineering by A.Chakrabarti

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