2. NTPC Limited was established, as a Public
Sector Power utility by Government of India in the
year 1975 at a time when the country was reeling
2
Reporting Officer:-
Madhur Kumar (AGM BMD)
P.S. Pandey (Mn. BMD)
NTPC Unchahar
Submitted by:-
Vivek Kushwaha
B.Tech. ME, 2nd
year
Roll no. : 1336340123
Ambalika Institute of Management and
Technology-Lucknow
3. under acute shortage of power and other players in
the field were not able to cope up with the situation.
NTPC Limited, true to the exaction, played a key
role in the development of the sector and has
emerged as the largest power utility, lighting every
fourth bulb in the country, powering the growth of
the country was the prime motto and the vision had
been to make available power in plenty.
NTPC has installed capacity of 39174 MW. It has 16
coal-based power stations, 7 gas based power
stations and 7 power stations in Joint Ventures. The
company has power generating facilities in all major
regions of the country. NTPC has gone beyond the
thermal power generation. It has diversified into
hydropower, coal mining, power equipment
manufacturing, oil & gas exploration, power trading
& distribution. NTPC is now in the entire power
value chain and is poised to become an Integrated
Power Major.
Presently Govt. of India has declared NTPC
Maharatna status.
3
4. Sr.No. Owned by NTPC No. of Plant
01. Coal Based Project 16
02. Gas Based Project 7
03. Joint Venture 7
4
5. “The foundation stone of this project was laid by
late Smt. India Gandhi, Ex Prime Minister of
India on 27.06.81. National Thermal Power Corp.
has taken over the Feroze Gandhi Unchahar
Thermal Power Project from UPRVUN Ltd.
having the capacity of 420 MW at a Plant Load
Factor (PLF) of about 18% w.e.f. 13.2.92, now it is
a 1050 MW power plant with PLF of more than
95% “
5
6. Location
The site is located in the Raibareli district of
Uttar Pradesh State, at latitude of 25°15'N and
a longitude of 81°19'E. It is bounded by
villages Khanpur, Faridpur and Khaliqupur
Khurd and is at a distance of approximately 3
kms from Mustafabad (present name:
Unchahar) town on the Allahabad-Rae-Bareli
BG section of Northern Railways.
Approach
-Unchahar is situated at Lucknow Allahabad
State Highway (NB-24B)
-40 Km from Raebareli
-85 Km from Allahabad.
-120 Km from Lucknow
-130 Km from Kanpur
Plant
Configuration
-Stage I Unit I: 210 MW November 1988 Unit
II: 210 MW March, 1989
-Stage II Unit III: 210 MW January 1999 Unit
IV: 210 MW October 1999
-Stage III- Unit V: 210 MW September 2006
Land Area
-Stage-I: 1953.0 acres, Stage-II: 250.70
acres
Coal Sources
-Central Coal Field Limited (CCL)
-Bharat Cocking Coal Limited (BCCL)
Water Sources
-Sharda Sahayak Canal (Main Source)
-Dalmau Pump Canal (From River Ganga)
(During closure of Sharda Sahayak canal)
6
7. Power
Evacuation
(220 KV)
-Unchahar Raebareli Line –1 , 2 & 3 (PGCIL)
-Unchahar Fatehpur- Line –1 & 2 (UPPCL)
-Unchahar Kanpur Line – 1,2,3 & 4 (PGCIL)
Beneficiary
States
Uttar Pradesh, Uttaranchal, Haryana,
Himachal Pradesh, J&K, Punjab, Chandigarh,
Rajasthan, Delhi & NVVN
Certifications
ISO 1901:2000, ISO 14001, OHSAS
18001, SA 8000:2001 & 5 S
Recent
Features
CII EXIM Business Excellence Award 2007
Asian Power Plant of the year – 2006
Swarna Shakti Award for the best Hospital
management 2008-09
2nd
in NTPC & 3rd
in all INDIA RANKING
on PLF basis up to March 2010
Swarna Shakti Award for the best operational
performance in the year 2011
Power line Award for 2012
DL Shah Award for the Quality Management
7
8. 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,
Mr. P.S. Pandey Mr. Sanjay Kumar to name a few for their
helpful contribution and knowledge without which my project
would not be a reality.
Vivek Kushwaha
B.Tech.( ME)
AIMT - Lucknow
8
9. CONTENTS
1. Introduction
2. Principle of a steam Power Plant
3. Coal & Steam Cycle (Boiler)
4. D M Plant
5. Turbine
6. Coal Handling Plant
7. Electrostatic Precipitator
8. Variable Frequency Drive
9. Ash Handling Plant
10. Generator
11. Switch Yard
12. Conclusion
---------------------------
9
10. 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.
It has total installed capacity of 39174 MW.
-----------------------------------
10
11. 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 it’s 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.
11
12. 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
12
13. 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 is 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%
------------------------------
13
14. COAL & STEAM CYCLE (BOILER)
Various Paths or Cycles in power plant
1. Coal Cycle:
Railway wagon wagon tippler coal hopper CHP
conveyor belt crusher house conveyor belt coal
stockyard or RC bunker RC feeder pulverised mill
furnace
2. Feed water cycle:
Deaerator boiler feed pump HP heater economiser
boiler drum
3. Condensate water cycle:
Condenser hot well condensate extraction pump
gland steam cooler LP heater deaerator
4. Steam cycle:
Boiler drum LT SH platen SH final SH HP
turbine re heater 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 re heater economiser air pre heater
E.S.P. I.D. fan chimney atmosphere
14
15. 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 are mounted on a
15
16. 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.
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 5400
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.
16
17. 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 classifier for further grinding returns the
coarser particles from both mills. 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 that 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
17
18. 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 540 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. Hydrastep 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
18
19. 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 piped like structures that go inside
the furnace and the boiler for efficient on load 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 31 kg/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 preheater
19
20. 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 superheater and then finally to a high temperature
superheater. The steam which is now produced goes to the
HP turbine.
---------------------
20
21. 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
21
22. A View of the in house Steam Turbine
The steam flow in the turbine takes place as follows; the
steam from the superheater 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.
-----------------------
22
23. DEMINERALISE WATER 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.
23
24. --------------------------
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
24
25. 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.
25
27. 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
27
28. 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.
28
29. The only drawback is that it is expensive.
• Magnetic separator: this is an electromagnet placed above
the 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.
29
30. 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 uncrushable
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 3Φ, 6.6KV, 71KW, with
electromagnetic brakes
Primary Crusher:
Induction motor 3Φ, 6.6KV, 175KW
Secondary Crusher:
30
31. Stage-I
Number of crusher: 2
Type of motor: induction motor 3Φ 750KW, 6.6KV
Stage-II
Number of crusher: 4
Type of motor: 3Φ 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
31
32. 6 paddle feeders
which are hydraulic
4 paddle feeders operated
through reducxtion 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 switch: 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.
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.
----------------------
32
33. 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.
33
34. 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 pyramidical 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
34
35. 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:
35
36. • 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.
------------------------------
36
37. 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
37
38. 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 varying the firing angle can control
the average value of the output. 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
38
39. 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
---------------------------
39
40. GENERATOR
The generator carries out the transformation of mechanical
energy into electrical energy. 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 Φ N
Where f frequency in Hz
Φ 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
40
41. 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
upto 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:
41
42. 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
42
43. 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
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 is 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
43
44. 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 is
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.
--------------------------
44
45. 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
45
A view of the Switch Yard
46. 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
• Capacitive 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. 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 %.
46
47. 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:
47
48. 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 desiccators
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:
48
49. 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 trip 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 hyterisis
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
49
50. 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.
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.
50
51. Both these transformers have natural oil circulation and
forced air circulation for their cooling.
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 comes
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
51
52. 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
operator’s wish. The
difference of an isolator
from a circuit breaker can
be realized from the fact
that a circuit breaker’s
making or breaking of a circuit depends upon certain
predefined conditions while that of the isolator dictate no
condition.
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 trips 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
52
53. to an arc which might result to flash-over incase 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.
CapacitiveVoltage 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
53
54. 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.
---------------------------------
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.
54
55. 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.
----------------------------------
55
