1. INDUSTRIAL TRAINING REPORT
ON
TITLE: CONTROL AND INSTRUMENTATION OF N.T.P.C,
DADRI
SUBMITTED TO
AMITY SCHOOL OF ENGINEERING AND TECHNOLOGY
BATCH – 2009 - 2013
GUIDED BY: SUBMITTED BY:
MR. NAVDEEP SHARMA SUBARNA PODDAR (A4717009020)
ASSISTANT PROFESSOR (EEE) B.TECH - E&I, SEMESTER 7
ASET, NOIDA ASET, NOIDA
AMITY UNIVERSITY, UTTAR PRADESH

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ACKNOWLEDGEMENT
Any attempt at any level cannot be satisfactorily completed without the support and guidance
of learned people. I would like to express my immense gratitude to PROF. K.M. SONI
(Acting Director, ASET) and PROF. H.P. SINGH (HOD – EEE&EIE) for their constant
support and motivation that has encouraged us to come up with this project.
I also wish to express my deep sense of gratitude to my Faculty Guide MR. NAVDEEP
SHARMA (Assistant professor, ECE) for his able guidance and useful suggestions, which
helped me in completing the project work, on time.
I am also thankful to my industrial guide and mentor MR. A.K. DANG (AGM, N.T.P.C
DADRI) for giving me a privilege to work as a trainee at N.T.P.C DADRI and also for
rendering his whole hearted support at all times for the successful completion of this project.
Last but not the least my hardcore thanks to all the group members, my parents and the
Almighty God without whose blessings it was not possible to commence this project.
Thank you everyone!!!!
SUBARNA PODDAR
(A4717009020)

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CERTIFICATE
This is to certify that Subarna Poddar student of branch electronics and instrumentation IIIrd
Year; Amity University, Noida has successfully completed her industrial training at National
Thermal Power Corporation (NTPC) Dadri for six week from 15th May to 20th June 2012.
She has completed the whole training as per the training report submitted by her. And I have
overviewed her work and checked her report. I have guided her in every possible way I can.
MR. NAVDEEP SHARMA
ASSISTANT PROFESSOR (EEE)
FACULTY GUIDE
ASET, AMITY UNIVERSITY
NOIDA

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ABSTRACT
My project includes the study of basic layout of power plant various cycles and instruments
used in power plant (National Thermal Power Cooperation, Dadri) for producing electricity
and measuring temperature, pressure, flow, level etc. Project report covered a small
description of various cycles at power station like coal cycle, Feed water cycle, Steam cycle,
Condensate cycle. It also includes the study of C & I labs and various process controls such
as load control strategy for pressurized mills, mills temperature control, control of the
combustion system, water pressure control, and also includes the study of various techniques
and instruments used to control processes. It also includes the study of various transducers
which are used to measure pressure, temperature flow etc. such as RTD for temperature
measurements. It also includes how the electricity is transmitted after generation and working
of the switch yard.

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CONTENTS
NAME PAGE No.
Acknowledgement 2
Certificate (faculty guide) 3
Company certificate
Abstract 4
Overview of NTPC 7
NTPC, Dadri (NCPS) 9
Thermal power station (coal based) 11
Coal handling plant (CHP) 11
Main plant 19
Coal cycle 26
Water cycle 29
Rankine cycle 34
Operation of boiler 36
Operation of turbine 39
Auxiliary systems 40
Coal ash 42
Control & monitoring mechanisms (C&I lab) 43
Dadri Switchyard 49
Result 55
Bibliography 56

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LISTS OF FIGURES AND CHARTS
FIGURES
FIG NO. NAME OF THE FIGURE PAGE NO.
Fig 1 Layout of CHP 13
Fig 2 Track hopper at NTPC dadri 14
Fig 3 Wagon Tripler at the plant 15
Fig 4 Stacker / reclaimer in working mode at the coal yard 16
Fig 5 Idler supporting the conveyor 18
Fig 6 Typical diagram of a coal fired thermal power station 20
Fig 7 Coal cycle in power plant 27
Fig 8 PI diagram of scheme of pulveriser with instrumentation 28
Fig 9 Specifications of the coal mills running 28
Fig 10 Condensate cycle and its flow in P.P 30
Fig 11 TDBFP of Unit 5 used in the station 31
Fig 12 Water walls surrounding the boiler (furnace) 31
Fig 13 Unit overview of dadri power plant 33
Fig 14 Rankine cycle 34
Fig 15 Coal-fired power plant steam generator 37
Fig 16 Fire ball formation inside the boiler 38
Fig 17 Arrangement of turbine auxiliaries 39
Fig 18 Ash mount at dadri showing the greenery 42
Fig 19 Typical Bourdon Tube Pressure Gages 44
Fig 20 Capacitive transducer 44
Fig 21 Resistance temperature detector 46
Fig 22 Thermocouple working 46
Fig 23 Venturimeter 48
Fig 24 Single line diagram for power flow 50
Fig 25 Double Main and transfer bus arrangement 50
Fig 26 400kV switchyard single line diagram 53
Fig 27 Transformer at switchyard 55
FLOW CHARTS
CHART NO. NAME OF FLOW CHART PAGE NO.
Graph 1 Growth of NTPC’s capacity & generation 8
Pie chart 1 NTPC’s generation 8
Flow chart 1 Coal to electricity simple flow diagram 11
Flow chart 2 Coal flow in the plant 27
Flow chart 3 Flow diagram of the Water cycle used in plant 29
Flow chart 4 Steam cycle 32
Table 1 Description of all the inlet and outlet temperature of
the turbine supervisory system
33

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CONTROL AND INSTRUMENTATION OF THERMAL
POWER PLANT (DADRI)
OVERVIEW
India’s largest power company, NTPC was set up in 1975 to accelerate power development in
India. NTPC Limited (formerly National Thermal Power Corporation) is the largest
Indian state-owned electric utilities company based in New Delhi, India. NTPC's core
business is engineering, construction and operation of power generating plants and providing
consultancy to power utilities in India and abroad. NTPC is emerging as a diversified power
major with presence in the entire value chain of the power generation business. Apart from
power generation, which is the mainstay of the company, NTPC has already ventured into
consultancy, power trading, ash utilization and coal mining. . NTPC became a Maharatna
company in May, 2010, one of the only four companies to be awarded this status.
The total installed capacity of the company is 39,174 MW (including Joint Ventures) with 16
coal based and 7 gas based stations, located across the country. In addition under JVs, 7
stations are coal based & another station uses naphtha/LNG as fuel. The company has set a
target to have an installed power generating capacity of 1, 28,000 MW by the year 2032. The
capacity will have a diversified fuel mix comprising 56% coal, 16% Gas, 11% Nuclear and
17% Renewable Energy Sources(RES) including hydro. By 2032, non fossil fuel based
generation capacity shall make up nearly 28% of NTPC’s portfolio. NTPC has adopted a
multi-pronged growth strategy which includes capacity addition through green field projects,
expansion of existing stations, joint ventures, subsidiaries and takeover of stations.
India, as a developing country is characterized by increase in demand for electricity and as of
moment the power plants are able to meet only about 60–75% of this demand on an yearly
average. The only way to meet the requirement completely is to achieve a rate of power
capacity addition (implementing power projects) higher than the rate of demand addition.
NTPC strives to achieve this and undoubtedly leads in sharing this burden on the country.
NTPC has been operating its plants at high efficiency levels. Although the company has 19%
of the total national capacity it contributes 29% of total power generation due to its focus on

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high efficiency. NTPC’s share of the total installed capacity of the country was 24.51% and it
generated 29.68% of the power of the country in 2008–09. Every fourth home in India is lit
by NTPC. NTPC's share of the country's total installed capacity is 17.75% and it generated
27.4% of the power generation of the country in year 2010–11.
Graph 1: Growth of NTPC’s capacity & generation
At NTPC, People before Plant Load Factor is the mantra that guides all HR related
policies. NTPC has been awarded No.1, Best Workplace in India among large organizations
and the best PSU for the year 2010, by the Great Places to Work Institute, India Chapter in
collaboration with The Economic Times. The concept of Corporate Social Responsibility
(CSR) is deeply ingrained in NTPC's culture. Through its expansive CSR initiatives, NTPC
strives to develop mutual trust with the communities that surround its power stations.
Pie chart 1: NTPC’s generation

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NTPC, DADRI
NTPC Dadri is model project of NTPC .It is the best project of NTPC, also known as NCPS
(National capital power station) situated 60 km away from Delhi in the District of Gautam
Buddha Nagar, Uttar Pradesh. National Capital Power Station (NCPS) Or NTPC Dadri is
the power project to meet the power demand of National capital region. It has a huge coal-
fired thermal power plant and a gas-fired plant and has a small township located for its
employees. NTPC Dadri is a branch of National Thermal Power Corporation, which is a
public sector now. NTPC Dadri plant and township are property of NTPC ltd and were built
around 1988-1990.
NTPC Dadri is a unique and the only power plant of NTPC group which has both coal based
thermal plant and gas based thermal plant. The National Capital Power Station [NCPS] has
the distinction of being the country's only 3-in-1 project; consisting of Stage-I 840 MW;
Stage-II 490MW of coal based units, 829 MW gas based modules, and a 1,500 MW
H.V.D.C.( high voltage direct current) converter station (under the operational control of
P.G.C.I.L. since October '93). Besides the station has the largest switchyard in the country
with a power handling capacity of 4,500 MW. The station has the unique distinction of
having Asia's first 100 percent dry ash extraction with transit ash storage silos and final
storage place converted to a green ash mound. An Ash Technology park has also been set up
to demonstrate the uses of ash which has become the point of attraction for the visitors.
NTPC Dadri is also planning to set up solar station for renewable power generation. It is
supposed to be completed by the end of 2012.
TOTAL CAPACITY OF DADRI POWER PLANT:-
THERMAL (coal based)
 04 (units) x 210 MW = 840 MW
Stage -1
 Unit 1 210MW
 Unit 2 210MW
 Unit 3 210MW
 Unit 4 210MW
 02 (units) x 490 MW = 980 MW
(Mainly built to supply electricity to commonwealth games)
Stage-2
 Unit 5 490MW
 Unit 6 490MW
Total production of thermal power plant is 1820 MW
GAS
 1 unit = 819 MW
Grand total production of NTPC, Dadri power plant is 2639 MW.

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National Capital Power Station - Coal
The coal-based station mainly meets power requirements of the National Capital Region
[NCR], and the northern grid. With the World Bank funding component, the capital cost of
the units is Rs. 16.69 billion. There are four 210 MW coal based units. The units have a coal-
fired boiler and a steam turbine each. The boiler design is also suitable for 100% operations
with heavy furnace oil firing. For this, three storage tanks, each of capacity 15,000KL,
enough for 10 days continuous oil firing requirements have been provided for the boilers.
Coal Source
The coal is transported from the Piparwar block of mines of the North Karanpura Coalfields
of Bihar, over a distance of about 1,200KM, by the Indian Railways bottom discharge, and
Box 'N' type of wagons. The coal requirement for the four units is 15,000 M.T. each day, 3.67
million tonnes annually. The station has its' own 14 kms. Long rail track from the Dadri
Railway Station, to the site, and a 6 km in-plant track, on electric traction.
National Capital Power Station – Gas
The gas-based station at N.C.P.S. is the country's largest gas power plant. It has two modules;
each module consists of two gas turbines of 130.19 MW, with one waste heat recovery boiler
and one steam turbine of 154.51 MW capacities. The power from this plant is allocated to
Uttar Pradesh, and also to Delhi, Punjab, Jammu and Kashmir, Haryana, Himachal Pradesh
and Rajasthan. The cost of gas based modules is Rs. 9.75 billion. Gas turbines generate
power at an efficiency of about 32% only, and to utilize the rest of this energy, a combined
cycle system is adopted. The waste heat from the gas turbine exhaust is routed through the
waste heat recovery boiler, and the steam thus generated is utilized in a conventional steam
turbine to generate additional power. By this, the overall efficiency of fuel heat utilization
reaches to about 48%.
Gas Source
The source of fuel for this plant is the reserves of South Basin fields in South Tapi and mid
Tapi delta in the Arabian Sea. The natural gas from South Basin off shore fields is
transported through a submarine pipeline to Hazira onshore terminal and then through the
1,700 km Long Hazira- Bijapur pipeline via Shahjanpur and Babrala, to the project. For the
829 MW project, the requirement is 3.00 million cubic meters per day (yearly average). It
would be worthwhile to note that within a short span of less than 7 years, both the coal and
gas based power cycle units/modules have been commissioned in a project. Both the projects
have diverse modern technologies, with the latest process controls.
HVDC
This is a technological accomplishment by NTPC; the system is the first commercial long
distance HVDC link in India, and also the largest in Asia. The basic objective of the HVDC
link is to transmit the generated power efficiently to the northern region, with significant
reduction in transmission losses. It consists of two converter stations - one located at Rihand

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(RhSTPP) acting as a rectifier, and the other at Vidyutnagar (NCPP) as an inverter, involving
a distance of about 900 kms. . These stations are connected by a +/- 500 kV HVDC line for
transmission of 1,500 MW power from Rihand to Vidyutnagar.
THERMAL POWER PLANT (COAL BASED)
Coal based power plant is the safest plant, in terms of fuel as coal is the safest fuel.
Generation of electricity through coal is a long process. First a fall we require fuel. In thermal
power plant required fuel is (for dadri power plant)-
 LDO (Light Diesel Oil) – It’s inferior to diesel. It’s a byproduct of petroleum.
 HFO (Heavy Furnace Oil) – It has a high efficiency in burning. It is very costly and
black in colour. We use this oil very rarely.
 COAL
We start with getting coal to the power plant.
Flow chart 1 : Coal to electricity simple flow diagram
COAL HANDLING PLANT (CHP)
In a power plant we have to be very specific about the property of coal. As coal is the mail
fuel for combustion and electricity generation we have to take proper care about the
specifications and requirement of the type of coal used in the plant.
COAL PROPERTY (Specifications only for dadri power plant)
 Moisture - Air dried-5 to 7%
- Total moisture-10 to 12%
 Ash - Washed coal- below 35-36%

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- Raw coal - above36%
 VM(Volatile matter)- 20-26% (Hydro carbons i.e; ethen etc.)
 Fixed Carbon - 25-27%
 C.V.(Calorific value) - 3600-3800 kcal/kg
COAL GRADE- Decided on UHV (Utilized Heat Value):-
A - Above 6201 Kcal/kg
B - 5601-6200 Kcal/kg
C - 4941-5600 Kcal/kg
D - 4201-4940 Kcal/kg
E - 3361-4200 Kcal/kg
F - 2401-3360 Kcal/kg
G - 1301-2400 Kcal/kg
Ungraded-Below1300 Kcal/kg
India has mostly bituminous coal. Here we basically use Grade E and Grade F coal, which is
then mixed with a coal having high calorific value which is imported from Malaysia.
Density of coal from 0.82 – 0.92 is called washed coal.
COAL TRANSPORTATION SYSTEM
Source of Coal - Piparwar block of North Karanpura coal field of Eastern coal field
Means of transportation - Railway Transportation
Route of Railway - Khalari – Garwa road-Seonnogar-Mughal Sarai-Allahabad-
Kanpur-Aligarh-Dadri-Plant Unloading area
Total distance - 1124 km from khalori to Dadri with electrified track from Seonnogar
Type of wagon- BOBR(Bogy Open Bottom Rapid Discharge Wagon)
Box-N (3 doors on each side)
Box-C (5 doors on each side )
It has its own railway line for coal transportation. Coal required per day is 25,000 MT (Metric
Tons) at NTPC Dadri.
1 Rake = 3500 MT
When 59 wagons are connected in a series then it is called one rake. Each wagon has a
capacity of 60-65 tons. This plant requires about 8-9 rakes per day.
No of wagons/rake - 59 wagons of 60-65 ton capacity
No of rake required/day - 8 to 9
Total cycle time of one rake -Approximately 6 days

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LAYOUT OF CHP
Fig 1: Layout of CHP
Where-
 WT- Wagon Tripler
 T/H – Track Hopper
 P/Feeder – Paddle Feeder
 TP – Turning Point
 GF – Grizzly Feeder
 Cr – Crusher
 S/R – Stacker / Recliamer
Track hopper and Wagon Tripler are the two types of unloading systems used by the plant.
The type of unloading system to be used is determined by the type of wagon in which the
coal is received.

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TRACK HOPPER
Track hopper is used if BOBR type of wagon is received. In this wagon the bottom of the
wagon is opened and all the coal in it is discharged into the track hopper.
Fig 2 : TRACK HOPPER AT NTPC DADRI
Track hopper details –
• Track hopper - 01 no.
• No of hoppers - 66
• Type of hopper- RCC underground
• Length of T/hopper- 201.6m
• Breadth of T/hopper- 6m
• Height of T/hopper - 6.350m
• Capacity of T/hopper- 6000 tons
In BOBR Wagons one rake can be emptied into the track hopper in just 1 hour. When the
coal is discharged through the wagon into the track hopper, then it is collected underground.
Now through paddle feeders this collected coal is transferred to the conveyor belt which
transports the coal to TP.
Paddle feeder used here –
• No of Paddle Feeder - 4
• Type - Rotary type
• Design/rated - 1000 tph/875 tph capacity (tph – ton per hour)
• Travel speed - 2 m/min (approx.)
WAGON TRIPLER
Wagon Tripler is used when BOX type wagons arrive. In wagon Tripler, first the wagon is
pulled by a small machine towards the Tripler and the wagon is separated from rest of the
train. Then the Tripler clamps the wagon from its two sides. These wagons have top open.

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Then the Tripler rotates the wagon at 150o and all the coal falls out of the wagon to the
collector (where the coal is collected). This coal is the send to TP through conveyor belts.
Fig 3 : WAGON TRIPLER AT PLANT
Wagon Tripler details –
1.Wagon Tripler - 12 Tips/hr (guaranteed)
15 Tips/hr (design)
2. Tippling angle - 150º giving 60º angle to the side of wagon
3. Hopper - 04 Nos.
4. Hopper capacity - 02 wagons at a time
5. Mesh size - 350 x 350 mm
6. Platform length - 14.5m
7. Type of wagon handled- 110 Ton
8. Max & minimum dimension of the wagons:-
 Length : 14.1 m to 10.715m
 Width : 3.25m to 3.05 m
 Height : 3.735m to 3.086 m
9. Type of wagon clamping - Gravity
10. Details of Tippler - 02 Nos pinion
11. Motor - 2 x 30 kw slip ring motor
All the coal is collected at TP. From there it goes to the crusher house. In the crusher house
there are GF (Grizzly feeders) and the crushers. The GF separates the coal i.e. it is a vibrating
feeder which separates out coal of different sizes. In the GF the coal below 250 mm directly
falls on the conveyer belt and coal above 250 mm goes to the crusher where it is further
crushed to bring the coal to 200mm size.
Specifications of the crusher house –
• No & make of Crusher- 4 nos. , made in Pennsylvania, USA
• Type & size - Ring granulators, TKKGN-48093
• Main crusher Capacity- 875 tonne/hr each
• Max. coal size - 250 mm before crusher
• Coal size after crusher- 20 mm
• Motor rating - 800hp (597kw)

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 Make - Kirloskar Elect Ltd.
 Power supply - 6.6kv, 30, 58HZ,
 RPM - 743
 Full load ampere - 69 A
 Insulation class - F
• No. of hammers - 60
•
Grizzly feeder specifications –
• No of Vibrating Grizzly Feeder - 4 nos.
• Capacity - 875 ton/hr
• Screen type - BSS 11-244824
• Frequency - 300-1000 rpm
• Stroke angle & - 40º, 0-10º
• Motor - 45 kW, 415v, 30, 58HZ,79 A, 1465rpm
The coal getting out of the crusher house has a size 20 mm. There are four crusher house in
the plant the coal goes through each one of them then it is finally crushed to the size that is
desired. This crushed coal is taken to the stockyard for either stacking or reclaiming. The
crushed coal is stored in the form of stacks in the stock yard for coal. S/R’s are the machines
through which the coal is stocked and then afterwards sent to the bunkers for further
processing. There are two stacker / reclaimer.
Specifications and type of S/R –
• No. - 2
• Model - ASK 650
• Stacking capacity (rated/design) - 1400/1540 tph
• Reclaiming capacity(rated/design) - 1400/1750 tph
• Travel speed - 4.2m/min
• Travel motor - Continuous variable DC motor, 6x10 kw
• Bucket motor Specification - AC squirrel cage motor 90 kw
• Boom conveyor speed - 3m/sec
• Boom conveyor motor Type& rating - Squirrel cage reversible type,75 kw
• Slew speed - 17.5 to 30.48 m/min
• Slew motion motor - DC type 2x14 kw
Fig 4 : Stacker / reclaimer in working mode at the coal yard

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Capacity of the stockyard is 45 days coal i.e. Requirement of 5, 00,000 m3 of coal approx.
Number of coal plies in the stock yard is 4 piles. Length/height of each of the piles is
470m/10m. Minimum to minimum we must have coal of 3 days always in stock.
The conveyor takes the coal from the WT & T/P to the TP then to the crusher house (CH)
then from there it goes to the stock yard for stacking of coal or reclaiming of coal. This
stacking and reclaiming is done through S/R’s. Then from the stock yard through conveyor it
goes to the bunkers where it is stored again and used for the plant in electricity generation.
As this conveyor does a lot of work for transporting the coal so it is not made as one belt. It is
made in forms of small belts which are connected together and a second belt is always kept in
standby as a precaution measure so that if something goes wrong with the first belt they can
switch over to another belt and can smoothly carry on their work of transportation of coal.
There are 14 conveyors in the plant. They are numbered so that their function can be easily
demarcated. Conveyors are made of rubber and more with a speed of 250-300m/min. Motors
employed for conveyors has a capacity of 150 HP. Conveyors have a capacity of carrying
coal at the rate of 400 tons per hour. Few conveyors are double belt, this is done for imp.
Conveyors so that if a belt develops any problem the process is not stalled. The conveyor belt
has a switch after every 25-30 m on both sides so stop the belt in case of emergency. The
conveyors are 1m wide, 3 cm thick and made of chemically treated vulcanized rubber. The
max angular elevation of conveyor is designed such as never to exceed half of the angle of
response and comes out to be around 20 degrees.
Conveyor type and capacity –
• No. of belt conveyor - 16
• Design/rated capacity - 1540 tph/1400 tph
• Conveyor Capacity - 700 - 1400
• Belt speed - 2.6 – 3.36m/sec
• Belt width - 1000 - 1400mm
• Fabric type - Nylon-Nylon/ EP(Polyamide-Synthetic)
• No of plies - 4
• Belt rating - 630 – 1250
• Cover grade - Fire Resistant
• No of belt weigher - 6
• No of metal detector - 4
• No of sampling unit - 4
• No & type of magnetic- 4, suspended type separator (ILMS)
• No of magnetic separator- 2
Some of the basic components which are present in the conveyor are –
Drive Assay - Motor, F.C., G/box, Gear Coup & drive pulley
Pulley - Head pulley, Tail pulley, Snub pulley, Bend pulley & Take-up pulley
Idlers - Carrying Idler, Return Idler, Impact Idler, Self Cleaning Idler ,SA Guide Rollers

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Fig 5 : Idler supporting the conveyor
Conveyor Belt - EP : 1250/4, 1000/4 & 630/4
Gravity Take-up- Take-up pulley, Frame, Rope, Sheave, Counter Wt., Guide channel &
Clamps
Bearings - Spherical Roller Double Row Bearings
Scrapper - Double blade rubber scrapper & V- type scrapper
Chutes - Steel plate chutes provided with polymer & rubber liners
Flap Gates - To discharge coal on the required conveyor (at TPs)
Skirt Board & skirt rubber - Dust suppression system, fire, Extinguisher, Structures,
Walkway & covered Gallery, ILMS MS & MI
For the protection of the belts from any kind of mis-happening we use many systems and
tripping i.e. the belt will stop or trip and would not move further if any kind of problem
arises.
Some of the important tripping are –
1. Sequence tripping – This trips the belt when there is some kind of problem in the
sequence of coal transportation.
2. ZSS (Zero Speed Switch) - It is safety device for motors, i.e., if belt is not moving
and the motor is on the motor may burn. So to protect this switch checks the speed of
the belt and switches off the motor when speed is zero. 2.6 m speed is said to be zero
speed at this point this belt is switched off i.e. it’s at zero speed.
3. BSS (Belt Sway Switch) – when the conveyor belt sways i.e. move in a rapid to-n-
fro motion, then may arise a condition when coal will spill out of the belt or the belt
itself will break down. To avoid this situation there is a belt sway switch, so when the
belt sways it would send an acknowledge and that particular belt is stopped to avoid
any damage to the system.

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4. PCS (Pull Cord Switch) – A cord goes along the length of the conveyor. This cord
works as an emergency brake. It is a manual switch, if anybody detects any problem
such as fire, overloading etc. then the person can pull this cord which acts as a switch
and the belt will stop moving, hence averting the problem.
5. MD (Metal Detector) – As the belt takes coal to the crusher, No metal pieces
should go along with coal. To achieve this objective, we use metal separators. When
coal is dropped to the crusher hoots, the separator drops metal pieces ahead of coal. It
has a magnet and a belt and the belt is moving, the pieces are thrown away. The
capacity of this device is around 50 kg. .The CHP is supposed to transfer 600 tons of
coal/hr, but practically only 300-400 tons coal is transfer. This does not trips the belt
it only sends an acknowledgement to the control room (where all this system is
controlled). It sends a signal when it detects any kind of metal in the coal on the belts
and sends the exact location where it saw the metal. Then this metal is removed either
manually or through the metal detector itself.
6. MVW Spray (for Fire protection) – Medium velocity water spray system for coal
conveyor. The specifications of the MVW spray are –
• Type of system & actuation - Deluge valve operated & MVW spray system
automatic (electrical), remote manual & local manual (mechanical)
• Spray density - 10.2 lph/m2(of floor area + return belt area)
• Min pressure of hydraulically remotest/nearest nozzle - 1.4 bar/3.5 bar
• Discharge time - 30 minutes
• Type of detection system - LHSC & infra red detectors
• Type of spray nozzles
a) For floor protection – Open head up right sprayers with K-79 (Metric)V-1
b) For return belt protection - Open head directional sprayers with K-46
• Water required per zone - Limited to approx 410 m3/hr
• No of zone sprayed at a time - Adjacent two nos.
Coal once stored in bunkers is used in the combustion and production of electricity.
MAIN PLANT
A Thermal Power Station comprises all of the equipment and a subsystem required to
produce electricity by using a steam generating boiler fired with fossil fuels or befouls to
drive an electrical generator. Some prefer to use the term ENERGY CENTER because such
facilities convert forms of energy, like nuclear energy, gravitational potential energy or heat
energy (derived from the combustion of fuel) into electrical energy. However, POWER
PLANT is the most common term in the united state; While POWER STATION prevails in
many Commonwealth countries and especially in the United Kingdom.
Such power stations are most usually constructed on a very large scale and designed for
continuous operation.

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Fig 6 : Typical diagram of a coal fired thermal power station
1. Cooling water pump
2. Three-phase transmission line
3. Step up transformer
4. Electrical Generator
5. Low pressure steam
6. Boiler feed water pump
7. Surface condenser
8. Intermediate pressure steam turbine
9. Steam control valve
10. High pressure steam turbine
11. Deaerator Feed water heater
12. Coal conveyor
13. Coal hopper
14. Coal pulveriser
15. Boiler steam drum
16. Bottom ash hoper
17. Super heater
18. Forced draught(draft) fan
19. Reheater
20. Combustion air intake
21. Economizer
22. Air preheater
23. Precipitator
24. Induced draught(draft) fan
25. Fuel gas stack

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The description of some of the components written above is described as follows:
1. Cooling towers
Cooling Towers are evaporative coolers used for cooling water or other working medium to
near the ambivalent web-bulb air temperature. Cooling tower use evaporation of water to
reject heat from processes such as cooling the circulating water used in oil refineries,
Chemical plants, power plants and building cooling, for example. The tower vary in size from
small roof-top units to very large hyperboloid structures that can be up to 200 meters tall and
100 meters in diameter, or rectangular structure that can be over 40 meters tall and 80 meters
long. Smaller towers are normally factory built, while larger ones are constructed on site.
The primary use of large , industrial cooling tower system is to remove the heat absorbed in
the circulating cooling water systems used in power plants , petroleum refineries,
petrochemical and chemical plants, natural gas processing plants and other industrial facilities
. The absorbed heat is rejected to the atmosphere by the evaporation of some of the cooling
water in mechanical forced-draft or induced draft towers or in natural draft hyperbolic shaped
cooling towers as seen at most nuclear power plants.
2.Three phase transmission line
Three phase electric power is a common method of electric power transmission. It is a type of
polyphase system mainly used to power motors and many other devices. A Three phase
system uses less conductor material to transmit electric power than equivalent single phase,
two phase, or direct current system at the same voltage. In a three phase system, three circuits
reach their instantaneous peak values at different times. Taking one conductor as the
reference, the other two current are delayed in time by one-third and two-third of one cycle of
the electrical current. This delay between “phases” has the effect of giving constant power
transfer over each cycle of the current and also makes it possible to produce a rotating
magnetic field in an electric motor.
At the power station, an electric generator converts mechanical power into a set of electric
currents, one from each electromagnetic coil or winding of the generator. The current are
sinusoidal functions of time, all at the same frequency but offset in time to give different
phases. In a three phase system the phases are spaced equally, giving a phase separation of
one-third one cycle. Generators output at a voltage that ranges from hundreds of volts to
30,000 volts. At the power station, transformers: step-up this voltage to one more suitable for
transmission.
After numerous further conversions in the transmission and distribution network the power is
finally transformed to the standard mains voltage (i.e. the “household” voltage).
The power may already have been split into single phase at this point or it may still be three
phase. Where the step-down is 3 phase, the output of this transformer is usually star
connected with the standard mains voltage being the phase-neutral voltage. Another system
commonly seen in North America is to have a delta connected secondary with a center tap on
one of the windings supplying the ground and neutral. This allows for 240 V three phase as
well as three different single phase voltages( 120 V between two of the phases and neutral ,
208 V between the third phase ( known as a wild leg) and neutral and 240 V between any two
phase) to be available from the same supply.

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3. Electrical generator
An Electrical generator is a device that converts kinetic energy to electrical energy, generally
using electromagnetic induction. The task of converting the electrical energy into mechanical
energy is accomplished by using a motor. The source of mechanical energy may be a
reciprocating or turbine steam engine, , water falling through the turbine are made in a variety
of sizes ranging from small 1 hp (0.75 kW) units (rare) used as mechanical drives for pumps,
compressors and other shaft driven equipment , to 2,000,000 hp(1,500,000 kW) turbines used
to generate electricity. There are several classifications for modern steam turbines.
Steam turbines are used in all of our major coal fired power stations to drive the generators or
alternators, which produce electricity. The turbines themselves are driven by steam generated
in ‘Boilers’ or ‘steam generators’ as they are sometimes called.
Electrical power station use large steam turbines driving electric generators to produce most
(about 86%) of the world’s electricity. These centralized stations are of two types: fossil fuel
power plants and nuclear power plants. The turbines used for electric power generation are
most often directly coupled to their-generators .As the generators must rotate at constant
synchronous speeds according to the frequency of the electric power system, the most
common speeds are 3000 r/min for 50 Hz systems, and 3600 r/min for 60 Hz systems. Most
large nuclear sets rotate at half those speeds, and have a 4-pole generator rather than the more
common 2-pole one.
Energy in the steam after it leaves the boiler is converted into rotational energy as it passes
through the turbine. The turbine normally consists of several stage with each stages
consisting of a stationary blade (or nozzle) and a rotating blade. Stationary blades convert the
potential energy of the steam into kinetic energy into forces, caused by pressure drop, which
results in the rotation of the turbine shaft. The turbine shaft is connected to a generator, which
produces the electrical energy.
4. Boiler feed water pump
A Boiler feed water pump is a specific type of pump used to pump water into a steam boiler.
The water may be freshly supplied or retuning condensation of the steam produced by the
boiler. These pumps are normally high pressure units that use suction from a condensate
return system and can be of the centrifugal pump type or positive displacement type.
Construction and operation
Feed water pumps range in size up to many horsepower and the electric motor is usually
separated from the pump body by some form of mechanical coupling. Large industrial
condensate pumps may also serve as the feed water pump. In either case, to force the water
into the boiler; the pump must generate sufficient pressure to overcome the steam pressure
developed by the boiler. This is usually accomplished through the use of a centrifugal pump.
Feed water pumps usually run intermittently and are controlled by a float switch or other
similar level-sensing device energizing the pump when it detects a lowered liquid level in the

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boiler is substantially increased. Some pumps contain a two-stage switch. As liquid lowers to
the trigger point of the first stage, the pump is activated. I f the liquid continues to drop
(perhaps because the pump has failed, its supply has been cut off or exhausted, or its
discharge is blocked); the second stage will be triggered. This stage may switch off the boiler
equipment (preventing the boiler from running dry and overheating), trigger an alarm, or
both.
5. Steam-powered pumps
Steam locomotives and the steam engines used on ships and stationary applications such as
power plants also required feed water pumps. In this situation, though, the pump was often
powered using a small steam engine that ran using the steam produced by the boiler. A means
had to be provided, of course, to put the initial charge of water into the boiler(before steam
power was available to operate the steam-powered feed water pump).the pump was often a
positive displacement pump that had steam valves and cylinders at one end and feed water
cylinders at the other end; no crankshaft was required.
In thermal plants, the primary purpose of surface condenser is to condense the exhaust steam
from a steam turbine to obtain maximum efficiency and also to convert the turbine exhaust
steam into pure water so that it may be reused in the steam generator or boiler as boiler feed
water. By condensing the exhaust steam of a turbine at a pressure below atmospheric
pressure, the steam pressure drop between the inlet and exhaust of the turbine is increased,
which increases the amount heat available for conversion to mechanical power. Most of the
heat liberated due to condensation of the exhaust steam is carried away by the cooling
medium (water or air) used by the surface condenser.
6. Control valves
Control valves are valves used within industrial plants and elsewhere to control operating
conditions such as temperature,pressure,flow,and liquid Level by fully partially opening or
closing in response to signals received from controllers that compares a “set point” to a
“process variable” whose value is provided by sensors that monitor changes in such
conditions. The opening or closing of control valves is done by means of electrical, hydraulic
or pneumatic systems
7. Deaerator
A Dearator is a device for air removal and used to remove dissolved gases (an alternate
would be the use of water treatment chemicals) from boiler feed water to make it non-
corrosive. A dearator typically includes a vertical domed deaeration section as the deaeration
boiler feed water tank. A Steam generating boiler requires that the circulating steam,
condensate, and feed water should be devoid of dissolved gases, particularly corrosive ones
and dissolved or suspended solids. The gases will give rise to corrosion of the metal. The
solids will deposit on the heating surfaces giving rise to localized heating and tube ruptures

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due to overheating. Under some conditions it may give to stress corrosion cracking.
Deaerator level and pressure must be controlled by adjusting control valves- the level by
regulating condensate flow and the pressure by regulating steam flow. If operated properly,
most deaerator vendors will guarantee that oxygen in the deaerated water will not exceed 7
ppb by weight (0.005 cm3/L).
8. Feed water heater
A Feed water heater is a power plant component used to pre-heat water delivered to a steam
generating boiler. Preheating the feed water reduces the irreversible involved in steam
generation and therefore improves the thermodynamic efficiency of the system.[4] This
reduces plant operating costs and also helps to avoid thermal shock to the boiler metal when
the feed water is introduces back into the steam cycle.
In a steam power (usually modelled as a modified Ranking cycle), feed water heaters allow
the feed water to be brought up to the saturation temperature very gradually. This minimizes
the inevitable irreversibility’s associated with heat transfer to the working fluid (water). A
belt conveyor consists of two pulleys, with a continuous loop of material- the conveyor Belt –
that rotates about them. The pulleys are powered, moving the belt and the material on the belt
forward. Conveyor belts are extensively used to transport industrial and agricultural material,
such as grain, coal, ores etc.
9. Pulveriser
A pulveriser is a device for grinding coal for combustion in a furnace in a fossil fuel power
plant. We have bowl mill here at NTPC, Dadri. It has 3 disc at 1200 angle each with a very
low rpm of about 40-45 rpm. These discs are very hard and easily grind the coal which comes
in between these discs. The coal is pulverized in the bowl mill, where it is grounded 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 rollers do not rotate but when the coal is fed to the
table it packs up between rollers and the table and this forces the rollers to rotate. Coal is
crushed by the crushing actions between the rollers and rotating tables
10. Boiler Steam Drum
Steam Drums are a regular feature of water tube boilers. It is reservoir of water/steam at the
top end of the water tubes in the water-tube boiler. They store the steam generated in the
water tubes and act as a phase separator for the steam/water mixture. The difference in
densities between hot and cold water helps in the accumulation of the “hotter”-water/and
saturated –steam into steam drum. Made from high-grade steel (probably stainless) and its
working involves temperatures 390’C and pressure well above 350psi (2.4MPa). The
separated steam is drawn out from the top section of the drum. Saturated steam is drawn off
the top of the drum. The steam will re-enter the furnace in through a super heater, while the
saturated water at the bottom of steam drum flows down to the mud-drum /feed water drum

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by down comer tubes accessories include a safety valve, water level indicator and fuse plug.
A steam drum is used in the company of a mud-drum/feed water drum which is located at a
lower level. So that it acts as a sump for the sludge or sediments which have a tendency to the
bottom.
11. Super Heater
A Super heater is a device in a steam engine that heats the steam generated by the boiler
again increasing its thermal energy and decreasing the likelihood that it will condense inside
the engine. Super heaters increase the efficiency of the steam engine, and were widely
adopted. Steam which has been superheated is logically known as superheated steam; non-
superheated steam is called saturated steam or wet steam; Super heaters were applied to
steam locomotives in quantity from the early 20th century, to most steam vehicles, and so
stationary steam engines including power stations.
12. Economizers
Economizer, are mechanical devices intended to reduce energy consumption, or to perform
another useful function like preheating a fluid. The term economizer is used for other
purposes as well. Boiler, power plant, and heating, ventilating and air conditioning. In
boilers, economizer are heat exchange devices that heat fluids , usually water, up to but not
normally beyond the boiling point of the fluid. Economizers are so named because they can
make use of the enthalpy and improving the boiler’s efficiency. They are a device fitted to a
boiler which saves energy by using the exhaust gases from the boiler to preheat the cold
water used the fill it (the feed water). Modern day boilers, such as those in cold fired power
stations, are still fitted with economizer. In this context they are turbines before it is pumped
to the boilers. A common application of economizer is steam power plants is to capture the
waste hit from boiler stack gases (flue gas) and transfer thus it to the boiler feed water thus
lowering the needed energy input , in turn reducing the firing rates to accomplish the rated
boiler output . Economizer lower stack temperatures which may cause condensation of acidic
combustion gases and serious equipment corrosion damage if care is not taken in their design
and material selection.
13. Air Preheater
Air preheater is a general term to describe any device designed to heat air before another
process (for example, combustion in a boiler). The purpose of the air preheater is to recover
the heat from the boiler flue gas which increases the thermal efficiency of the boiler by
reducing the useful heat lost in the fuel gas. As a consequence, the flue gases are also sent to
the flue gas stack (or chimney) at a lower temperature allowing simplified design of the
ducting and the flue gas stack. It also allows control over the temperature of gases leaving the
stack.

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14. Precipitator ( ESP)
An Electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate device that
removes particles from a flowing gas (such As air) using the force of an induced electrostatic
charge. Electrostatic precipitators are highly efficient filtration devices, and can easily
remove fine particulate matter such as dust and smoke from the air steam.
ESP’s continue to be excellent devices for control of many industrial particulate emissions,
including smoke from electricity-generating utilities (coal and oil fired), salt cake collection
from black liquor boilers in pump mills, and catalyst collection from fluidized bed catalytic
crackers from several hundred thousand ACFM in the largest coal-fired boiler application.
The original parallel plate-Weighted wire design (described above) has evolved as more
efficient ( and robust) discharge electrode designs were developed, today focusing on rigid
discharge electrodes to which many sharpened spikes are attached , maximizing corona
production. Transformer –rectifier systems apply voltages of 50-100 Kilovolts at relatively
high current densities. Modern controls minimize sparking and prevent arcing, avoiding
damage to the components. Automatic rapping systems and hopper evacuation systems
remove the collected particulate matter while on line allowing ESP’s to stay in operation for
years at a time.
15. Fuel gas stack
A Fuel gas stack is a type of chimney, a vertical pipe, channel or similar structure through
which combustion product gases called fuel gases are exhausted to the outside air. Fuel gases
are produced when coal, oil, natural gas, wood or any other large combustion device. Fuel
gas is usually composed of carbon dioxide (CO2) and water vapor as well as nitrogen and
excess oxygen remaining from the intake combustion air. It also contains a small percentage
of pollutants such as particulates matter, carbon mono oxide, nitrogen oxides and sulfur
oxides. The flue gas stacks are often quite tall, up to 400 meters (1300 feet) or more, so as to
disperse the exhaust pollutants over a greater aria and thereby reduce the concentration of the
pollutants to the levels required by governmental environmental policies and regulations.
When the fuel gases exhausted from stoves, ovens, fireplaces or other small sources within
residential abodes, restaurants , hotels or other stacks are referred to as chimneys.
COAL CYCLE
From the CHP through the conveyor the coal gets into the bunkers. This coal through coal
lines comes to the bowl mills. From the bunker the coal goes to a gravimetric feeder where it
measures the quantity of coal going to the bunkers. From the gravimetric feeders it goes to
the mills. Mills maintains the moisture present in the coal. When the coal is received at the
mills it already has about 8-12 % of moisture in it .the mills dry the coal to 5% of moisture is
left.

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CHP (coal handling plant) Bunkers (9 nos.)
Gravimetric-Feeders Mills (Pulveriser) Furnace
Flow chart 2 : Coal flow in the plant
From there the coal is sent to the pulveriser. Pulveriser has 3 discs placed from 120o angle at
each other. These discs are very hard and it grinds the coal further to size of 200 wire mesh.
This finely powdered coal is then mixed with primary air (PA). The primary air dries the coal
as well as helps the coal to be transported from mills to the furnace. We get primary air
through PA Fans. These fans take in the atmospheric air and then heats this air and then pass
it through the pulverised coal. The primary air temperature is maintained < 900C .
We have 9 coal mills of which only 6 run at the same time.
Fig 7 : Coal cycle in power plant
This coal burns in about 1-3 seconds inside the furnace. The fire ball created inside the
furnace due to the burning of coal has a temperature of about 16000C. After burning the coal
we get bottom ash and fly ash. The bottom ash settles down at the bottom of the furnace into
the hopper from where it is removed at time intervals. The bottom ash is also called wet ash
as it is has a little moisture in it. And the fly ash travels to the ESP (Electro Static
Precipitator) where it is settled down with the help of charge and the transported for further

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use. Fly ash is called the dry ash which is used in making cement, construction work, ash
mount etc.
In mills there are various kinds of control and measurement systems. Through all these
systems we control the flow of ail into the mills , pressure difference in the mills, temperature
of the air going in the mill as well as the normal temperature of the mill.
Fig 8 : PI diagram of scheme of pulveriser with instrumentation
Venturi is used here to determine the flow of air into the mills. The PA passes through venturi
first and then it goes to the mills where it is mixed with coal and transported to the furnace.
Seal air fan is used so that the coal in the mills does not leak out or come out of the mills.
Seal air fan creates a pressure at the bottom of the mill through the use of pressurised air so
that the crushed coal remains inside the mills. PDT (pressure difference transducer)
measures the pressure difference in the mills. The PDT reading should not be zero, it should
always have some kind of value i.e. there must be always a pressure present inside the mills
to make sure they continue working smoothly.

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Fig 9 : Specifications of the coal mills running
WATER CYCLE
Water is a very important component in the working of the power plant. Water cycle is
basically a closed loop cycle here i.e. we here use the water again and again in the process.
We do not use normal water we use DM Water (De-Mineralized water), the water which does
not contain any kind of minerals or cations and anions. This DM Water is very expensive and
hard to produce so we do not waste this water we cool this water and use it again in the
process.

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Flow chart 3 : Flow diagram of the Water cycle used in plant
The water after treatment i.e. removing all the impurities, minerals, cations and anions from
the DM Plant comes to the condenser. The heat which is present in the water coming from
DM plant and the water (steam) coming from the turbines after rotating the turbine is
collected in the condenser. Condenser is a shell type system where the heated water is cooled
by passing cold water in the shell and the heated water inside the chamber gets cooled down
due to the passing of the cold water. After the condenser cools of the steam and water and it
converts it into cooled water it goes to the hot well. All the cooled water is collected here.

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Fig 10 : Condensate cycle and its flow in P.P
CEP (Condensate extraction pump), extracts the water from the hot well and send it to drain
cooler. In the drain cooler the water is again cooled and the temperature further reduces. At
drain cooler all the water gets collected and mixed there. After drain cooler it goes to GSC
(Gland Steam Cooler) where it measures the water content and if there is any loss in the
amount of water then the make –up water is added to it (make-up water is also DM Water).
From GSC it goes to the LPH (low pressure heaters). The water passes from 3 LPH. In LPH
the water is lightly heated to make it useful for further transportation. From LHP it goes to
CPU (condensate polishing unit), here the quality of water is further improved so it becomes
fit for using. From CPU it goes to the D/A (De-aerator). As the name suggest de-aerator
removes all the air content in the water. We use DM Water in the plants as we do not want
any minerals to get deposited in the pipes, turbines blades, or the shaft and cause corrosion or
other harmful hazards. So the quality of water is thoroughly checked and controlled at every
step of the cycle. From de-aerator it goes to BFP (boiler feed pump). BFP is considered as the
heart of the plant as it supplies water to all the parts of the power plant. So BFP takes up to
3.5 – 4 MW of power supply. It consumes most of the energy in its running. There are two
types of BFP’s.
 MDBFP (Motor driven Boiler feed pump) – This BFP does not have a turbine in it ,
it just uses the electricity generated by the plant to run itself . It takes up to 3.5 MW. It
also sends the water to the boiler drum.
 TDBFP (Turbine driven boiler feed pump) – this BFP uses its own turbine (a small
turbine is fitted inside it) to first produce its own electricity for running and the energy

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produced is then consumed by the BFP itself to send the water to the parts of the plant
where it is required , mostly to the boiler drum.
Fig 11 : TDBFP of Unit 5 used in the station
For each running unit we require 2 BFP’s for their proper functioning. After the water which
is pumped from BFP’s, the water is pumped to HPH (high pressure heater). There are two
HP’s which are connected in parallel to each other. They are connected in parallel so that it
could be used even if there is a problem with one of them, we do not have to shut down the
whole system. The HPH’s connected in parallel even gives a better heating. Then it goes to
the FRS (Feed regulating system). Here all the heated water is collected and stored, it is
basically a type of sink. From FRS it goes to the Economizer. They are a device fitted to a
boiler which saves energy by using the exhaust gases from the boiler to preheat the cold
water used the fill it (the feed water). Then it goes to the boiler for storage. Boiler is divided
into two halves. The lower half is filled with water and its upper half is used to store the
steam produced and then it is transported from there to other parts of the power plant. Boiler
drum of the 210MW boiler is situated at 52 m and the boiler drum of the 590MW is situated
at 75 m height from the ground. From the boiler drum the water comes down through down
comer lines (many lines) till the base of the boiler or furnace. At the base of the boiler all the
water coming down is collected at the ring header. From the ring header the water flows
through the water walls surrounding the boiler.
Fig 12 : Water walls surrounding the boiler (furnace)
The coal burning in the furnace heats up the water flowing in the water walls. The water gets
heated up and is converted into the steam. This steam is then again goes the boiler drum. The

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water and steam does not mix in the boiler drum, they are stored in separate compartments
inside the boiler drum. Now the water is converted into steam. The temperature of the steam
is 348oC. Now this steam moves forward. From here the steam cycle starts.
Flow chart 4 : Steam cycle
Now this steam from the boiler drum goes to the LTSH (low temperature super heater).the
temperature of steam is increased to 400oC. It is a primary super heater. From there the stem
moves towards the Planten Heater. Here the temperature of the steam is further raised to
5100C. The steam goes to the Final Super Heater. Here the temperature is finally 5400C. Then
this super heated steam goes to the HPT (High pressure turbine). This steam rotates the HPT,
the steam pressure is 170 Ksi and temperature is 5400C while entering into the HPT. The
HPT has 17 rotating blades and its size is also small i.e. it has only one half. The steam
rotates the HPT, and then it again goes through the Cold Reheat Line (CRH Line) to the Re-
Heater. In Re heater the heat and the pressure lost by the steam while rotating the HPT, is
again regained i.e. the temperature is again raised to 5400C. The steam temperature entering
the Re Heater is 3340C. From Re Heater it travels through Hot Reheat Line (HRH Line) and
goes to the IPT (Intermediate pressure turbine). This steam rotates the IPT. The size of IPT is
greater than the HPT. It has 2 stages; it has 12 x 2 rotating blades. From IPT it goes to the
LPT (low pressure turbine). LPT has 6 x 2 rotating blades and it is even larger than the IPT.
Now this used up steam is then again goes to the condenser. Hence water cycle is again
started there.

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Table 1 : Description of all the inlet and outlet temperature of the turbine supervisory
system
Fig 13 : Unit overview of dadri power plant

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Rankine cycle
The steam turbine works on rankine cycle, the Rankine cycle is a thermodynamic cycle
which converts heat into work. The heat is supplied externally to a closed loop, which usually
uses steam as the working fluid. A Rankine cycle describes a model of the operation of steam
heat engines most commonly found in power generation plants. Common heat sources for
power plants using the Rankine cycle are coal, natural gas, oil, and nuclear.The Rankine
cycle is sometimes referred to as a practical Carnot cycle as, when an efficient turbine is
used, the TS diagram will begin to resemble the Carnot cycle. The main difference is that a
pump is used to pressurize liquid instead of gas. This requires about 100 times less energy
than that compressing a gas in a compressor
Fig 14 : Rankine cycle
The working fluid in a Rankine cycle follows a closed loop and is re-used constantly. The
water vapor often seen billowing from power stations is generated by the cooling systems

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(not from the closed loop Rankine power cycle) and represents the waste heat that could not
be converted to useful work. Note that steam is invisible until it comes in contact with cool,
saturated air, at which point it condenses and forms the white billowy clouds, seen leaving
cooling towers. While many substances could be used in the Rankine cycle, water is usually
the fluid of choice due to its favorable properties, such as nontoxic and unreactive chemistry,
abundance, and low cost, as well as its thermodynamic properties.
One of the principal advantages it holds over other cycles is that during the compression
stage relatively little work is required to drive the pump, due to the working fluid being in its
liquid phase at this point. By condensing the fluid to liquid, the work required by the pump
will only consume approximately 1% to 3% of the turbine power and so give a much higher
efficiency for a real cycle. The benefit of this is lost somewhat due to the lower heat addition
temperature. Gas turbines, for instance, have turbine entry temperatures approaching 1500°C.
Nonetheless, the efficiencies of steam cycles and gas turbines are fairly well matched.
Processes in rankine cycle:
Ts diagram of a typical Rankine cycle operating between pressures of 0.06bar & 50bar
There are four processes in the Rankine cycle, each changing the state of the working fluid.
These states are identified by number in the diagram to the right.
 Process 1-2: The working fluid is pumped from low to high pressure, as the fluid is a
liquid at this stage the pump requires little input energy.
 Process 2-3: The high pressure liquid enters a boiler where it is heated at constant
pressure by an external heat source to become a dry saturated vapor.
 Process 3-4: The dry saturated vapor expands through a turbine, generating power.
This decreases the temperature and pressure of the vapor, and some condensation may
occur.
 Process 4-1: The wet vapor then enters a condenser where it is cooled at a constant
pressure and temperature to become a saturated liquid. The pressure and temperature

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of the condenser is fixed by the temperature of the cooling coils as the fluid is
undergoing a phase-change.
Modification in rankine cycle(Reheat cycle)
In this cycle steam is extracted from a suitable point in the turbine and reheated generally to
the original temperature by flue gases. Reheating is generally used when the pressure is high
say above 100 kg/cm2.
o It advantages:
o It increases dryness fraction of steam at exhaust so that blade erosion due to
impact of water particles is reduced.
o It increases thermal efficiency.
o It increases the work done per kg of steam and this results in reduced size of
boiler.
o Its disadvantages:
o Cost of plant is increased due to reheater and its long connection.
o It increases condenser capacity due to incresed dryness fraction.
OPERATION OF BOILER
The boiler is a rectangular furnace about 50 ft (15 m) on a side and 130 ft (40 m) tall. Its
walls are made of a web of high pressure steel tubes about 2.3 inches (60 mm) in diameter.
Pulverized coal is air-blown into the furnace from fuel nozzles at the four corners and it
rapidly burns, forming a large fireball at the center. The thermal radiation of the fireball heats
the water that circulates through the boiler tubes near the boiler perimeter. The water
circulation rate in the boiler is three to four times the throughput and is typically driven by
pumps. As the water in the boiler circulates it absorbs heat and changes into steam at 700 °F
(370 °C) and 22.1 MPa. It is separated from the water inside a drum at the top of the furnace.
The saturated steam is introduced into superheat pendant tubes that hang in the hottest part of
the combustion gases as they exit the furnace. Here the steam is superheated to 1,000 °F (540
°C) to prepare it for the turbine. The steam generating boiler has to produce steam at the high
purity, pressure and temperature required for the steam turbine that drives the electrical
generator. The generator includes the economizer, the steam drum, the chemical dosing
equipment, and the furnace with its steam generating tubes and the superheater coils.
Necessary safety valves are located at suitable points to avoid excessive boiler pressure. The
air and flue gas path equipment include: forced draft (FD) fan, air preheater (APH), boiler
furnace, induced draft (ID) fan, fly ash collectors (electrostatic precipitator or baghouse) and
the flue gas stack.

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Fig 15 : Coal-fired power plant steam generator
 Boiler Furnace and Steam Drum
Once water inside the boiler or steam generator, the process of adding the latent heat of
vaporization or enthalpy is underway. The boiler transfers energy to the water by the
chemical reaction of burning some type of fuel.The water enters the boiler through a section
in the convection pass called the economizer. From the economizer it passes to the steam
drum. Once the water enters the steam drum it goes down the down comers to the lower inlet
water wall headers. From the inlet headers the water rises through the water walls and is
eventually turned into steam due to the heat being generated by the burners located on the
front and rear water walls (typically). As the water is turned into steam/vapour in the water
walls, the steam/vapor once again enters the steam drum.
 Fuel Preparation System
In coal-fired power stations, the raw feed coal from the coal storage area is first crushed into
small pieces and then conveyed to the coal feed hoppers at the boilers. The coal is next
pulverized into a very fine powder. The pulverizers may be ball mills, rotating drum grinders,
or other types of grinders. Some power stations burn fuel oil rather than coal. The oil must
kept warm (above its pour point) in the fuel oil storage tanks to prevent the oil from
congealing and becoming un-pumpable. The oil is usually heated to about 100°C before
being pumped through the furnace fuel oil spray nozzles.

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Fig 16 : Fire ball formation inside the boiler
 Fuel Firing System and Ignite System
From the pulverized coal bin, coal is blown by hot air through the furnace coal burners at an
angle which imparts a swirling motion to the powdered coal to enhance mixing of the coal
powder with the incoming preheated combustion air and thus to enhance the combustion.To
provide sufficient combustion temperature in the furnace before igniting the powdered coal,
the furnace temperature is raised by first burning some light fuel oil or processed natural gas
(by using auxiliary burners and igniters provide for that purpose).
 Air Path
External fans are provided to give sufficient air for combustion. The forced draft fan takes air
from the atmosphere and, first warming it in the air preheater for better combustion, injects it
via the air nozzles on the furnace wall.The induced draft fan assists the FD fan by drawing
out combustible gases from the furnace, maintaining a slightly negative pressure in the
furnace to avoid backfiring through any opening. At the furnace outlet, and before the furnace
gases are handled by the ID fan, fine dust carried by the outlet gases is removed to avoid
atmospheric pollution. This is an environmental limitation prescribed by law, and
additionally minimizes erosion of the ID fan.
 Fly Ash Collection
Fly ash is captured and removed from the flue gas by electrostatic precipitators or fabric bag
filters (or sometimes both) located at the outlet of the furnace and before the induced draft
fan. The fly ash is periodically removed from the collection hoppers below the precipitators
or bag filters. Generally, the fly ash is pneumatically transported to storage silos for
subsequent transport by trucks or railroad cars.

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 Bottom Ash Collection and Disposal
At the bottom of every boiler, a hopper has been provided for collection of the bottom ash
from the bottom of the furnace. This hopper is always filled with water to quench the ash and
clinkers falling down from the furnace. Some arrangement is included to crush the clinkers
and for conveying the crushed clinkers and bottom ash to a storage site.
OPERATION OF TURBINE
Steam turbines are used in all of our major coal fired power stations to drive the generators or
alternators, which produce electricity. The turbines themselves are driven by steam generated
in 'Boilers' or 'Steam Generators' as they are sometimes called. Energy in the steam after it
leaves the boiler is converted into rotational energy as it passes through the turbine. The
turbine normally consists of several stages with each stage consisting of a stationary blade
(or nozzle) and a rotating blade. Stationary blades convert the potential energy of the steam
(temperature and pressure) into kinetic energy (velocity) and direct the flow onto the rotating
blades. The rotating blades convert the kinetic energy into forces, caused by pressure drop,
which results in the rotation of the turbine shaft. The turbine shaft is connected to a generator,
which produces the electrical energy. The rotational speed is 3000 rpm for Indian System
(50 Hz) systems and 3600 for American (60 Hz) systems. In a typical larger power stations,
the steam turbines are split into three separate stages, the first being the High Pressure (HP),
the second the Intermediate Pressure (IP) and the third the Low Pressure (LP) stage, where
high, intermediate and low describe the pressure of the steam. After the steam has passed
through the HP stage, it is returned to the boiler to be re-heated to its original temperature
although the pressure remains greatly reduced. The reheated steam then passes through the IP
stage.
Fig 17 : Arrangement of turbine auxiliaries

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Auxiliary systems
Boiler make-up water treatment plant and storage
Since there is continuous withdrawal of steam and continuous return of condensate to the
boiler, losses due to blowdown and leakages have to be made up to maintain a desired water
level in the boiler steam drum. For this, continuous make-up water is added to the boiler
water system. Impurities in the raw water input to the plant generally consist of calcium and
magnesium salts which impart hardness to the water. Hardness in the make-up water to the
boiler will form deposits on the tube water surfaces which will lead to overheating and failure
of the tubes. Thus, the salts have to be removed from the water, and that is done by a water
demineralising treatment plant (DM). A DM plant generally consists of cation, anion, and
mixed bed exchangers. Any ions in the final water from this process consist essentially of
hydrogen ions and hydroxide ions, which recombine to form pure water. Very pure DM water
becomes highly corrosive once it absorbs oxygen from the atmosphere because of its very
high affinity for oxygen.
The capacity of the DM plant is dictated by the type and quantity of salts in the raw water
input. However, some storage is essential as the DM plant may be down for maintenance. For
this purpose, a storage tank is installed from which DM water is continuously withdrawn for
boiler make-up. The storage tank for DM water is made from materials not affected by
corrosive water, such as PVC. The piping and valves are generally of stainless steel.
Sometimes, a steam blanketing arrangement or stainless steel doughnut float is provided on
top of the water in the tank to avoid contact with air. DM water make-up is generally added at
the steam space of the surface condenser (i.e., the vacuum side). This arrangement not only
sprays the water but also DM water gets deaerated, with the dissolved gases being removed
by a de-aerator through an ejector attached to the condenser.
Fuel preparation system
In coal-fired power stations, the raw feed coal from the coal storage area is first crushed into
small pieces and then conveyed to the coal feed hoppers at the boilers. The coal is next
pulverized into a very fine powder. The pulverizers may be ball mills, rotating drum grinders,
or other types of grinders.
Some power stations burn fuel oil rather than coal. The oil must kept warm (above its pour
point) in the fuel oil storage tanks to prevent the oil from congealing and becoming
unpumpable. The oil is usually heated to about 100 °C before being pumped through the
furnace fuel oil spray nozzles.
Boilers in some power stations use processed natural gas as their main fuel. Other power
stations may use processed natural gas as auxiliary fuel in the event that their main fuel
supply (coal or oil) is interrupted. In such cases, separate gas burners are provided on the
boiler furnaces.

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Barring gear
Barring gear (or "turning gear") is the mechanism provided to rotate the turbine generator
shaft at a very low speed after unit stoppages. Once the unit is "tripped" (i.e., the steam inlet
valve is closed), the turbine coasts down towards standstill. When it stops completely, there is
a tendency for the turbine shaft to deflect or bend if allowed to remain in one position too
long. This is because the heat inside the turbine casing tends to concentrate in the top half of
the casing, making the top half portion of the shaft hotter than the bottom half. The shaft
therefore could warp or bend by millionths of inches.
This small shaft deflection, only detectable by eccentricity meters, would be enough to cause
damaging vibrations to the entire steam turbine generator unit when it is restarted. The shaft
is therefore automatically turned at low speed (about one percent rated speed) by the barring
gear until it has cooled sufficiently to permit a complete stop.
Oil system
An auxiliary oil system pump is used to supply oil at the start-up of the steam turbine
generator. It supplies the hydraulic oil system required for steam turbine's main inlet steam
stop valve, the governing control valves, the bearing and seal oil systems, the relevant
hydraulic relays and other mechanisms.
At a preset speed of the turbine during start-ups, a pump driven by the turbine main shaft
takes over the functions of the auxiliary system.
Generator cooling
While small generators may be cooled by air drawn through filters at the inlet, larger units
generally require special cooling arrangements. Hydrogen gas cooling, in an oil-sealed
casing, is used because it has the highest known heat transfer coefficient of any gas and for its
low viscosity which reduces windage losses. This system requires special handling during
start-up, with air in the generator enclosure first displaced by carbon dioxide before filling
with hydrogen. This ensures that the highly flammable hydrogen does not mix with oxygen in
the air.
The hydrogen pressure inside the casing is maintained slightly higher than atmospheric
pressure to avoid outside air ingress. The hydrogen must be sealed against outward leakage
where the shaft emerges from the casing. Mechanical seals around the shaft are installed with
a very small annular gap to avoid rubbing between the shaft and the seals. Seal oil is used to
prevent the hydrogen gas leakage to atmosphere.
The generator also uses water cooling. Since the generator coils are at a potential of about 22
kV, an insulating barrier such as Teflon is used to interconnect the water line and the
generator high voltage windings. Demineralized water of low conductivity is used.
Generator high voltage system
The generator voltage for modern utility-connected generators ranges from 11 kV in smaller
units to 22 kV in larger units. The generator high voltage leads are normally large aluminium
channels because of their high current as compared to the cables used in smaller machines.
They are enclosed in well-grounded aluminum bus ducts and are supported on suitable
insulators. The generator high voltage leads are connected to step-up transformers for

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connecting to a high voltage electrical substation (usually in the range of 115 kV to 765 kV)
for further transmission by the local power grid.
The necessary protection and metering devices are included for the high voltage leads. Thus,
the steam turbine generator and the transformer form one unit. Smaller units,may share a
common generator step-up transformer with individual circuit breakers to connect the
generators to a common bus.
Monitoring and alarm system
Most of the power plant operational controls are automatic. However, at times, manual
intervention may be required. Thus, the plant is provided with monitors and alarm systems
that alert the plant operators when certain operating parameters are seriously deviating from
their normal range.
Coal Ash
Coal ash in Dadri Plant has been successfully used in the following applications.
 LAND FILLS
 ROAD EMBANKMENTS
 ROAD CONSTRUCTION
 PORTLAND POZZOLONA CEMENT
 BUILDING PRODUCTS
 CONCRETE
Use of Dadri ash in above applications have resulted in saving in terms of money,
conservation of natural resources viz land, lime stone, coal, sand, energy, land and water
apart from reduction in CO2 emission and thus environment. NTPC - A trend setter in the
country has set up 100 % dry ash extraction cum disposal in the form of Ash Mound at NTPC
Dadri. Ash mound has come out as the most viable alternative for ash disposal in an
economic friendly way by minimum use of land and water. Ash from dadri power plant is
send to –
 Aditya Birla cement
 Abujha cement
 Bricks construction factory
 Road construction
Fig 18 : Ash mount at dadri showing the greenery

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Features of Ash Mound
 Ash mound covers area of 375 acres.
 Ultimate height 55 meters.
 Side slope 1:4 with haulage road at 15 m interval.
 Top most flat area 140 acres.
 Capacity of ash storage 53 million cum.
 Sufficient for running 840 MW for 40 years.
 Side slopes covered with green grass and plantations of trees.
 Beautiful green spot in the vicinity of power house.
Benefits of Ash Mound
 Less requirement of land only 1/3rd land requirement as compared to wet disposal
system.
 375 acres of land is required as compared to 1000 acres for installed capacity of 840
MW at Dadri.
 Only 1/50th water required in comparison to wet system
 Eliminates leaching effect.
 Separate storage of fly ash (PFA) and furnace bottom ash (FBA).
 Facilitates large scale utilization at later stage.
 The green ash mound can be used as a useful piece of land.
CONTROL AND MONITORING MECHANISMS ( C&I LAB)
There are basically two types of Problems faced in a Power Plant
 Metallurgical
 Mechanical
Mechanical Problem can be related to Turbines that’s the max speed permissible for a turbine
is 3000rpm , so speed should be monitored and maintained at that level Metallurgical
Problem can be view as the max Inlet Temperature for Turbine is 1060oC so temperature
should be below the limit. Monitoring of all the parameters is necessary for the safety of both,
Employees and Machines
So the Parameters to be monitored are:
 Speed
 Temperature
 Current
 Voltage
 Pressure
 Eccentricity
 Flow of Gases
 Vaccum Pressure

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 Valves
 Level
 Vibration
PRESSURE MONITORING
Pressure can be monitored by three types of basic mechanisms
 Switches
 Gauges
 Transmitter type
FOR GAUGES
For gauges we use Bourdon tubes. The Bourdon Tube is a non liquid pressure measurement
device. It is widely used in applications where inexpensive static pressure measurements are
needed. A typical Bourdon tube contains a curved tube that is open to external pressure input
on one end and is coupled mechanically to an indicating needle on the other end, as
shown schematically below
Fig 19 : Typical Bourdon Tube Pressure Gages
FOR TRANSMITTER TYPES
Transmitter types use transducers (electrical toelectrical normally) they are used where
continuous monitoring is required normally capacitive transducers are used.
Fig 20 : Capacitive transducer

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FOR SWITCHES
Pressure switches are used and they can be used for digital means of monitoring as
switch being ON is referred as high and being OFF is as low. All the monitored data is
converted to either Current or Voltage parameter.
The Plant standard for current and voltage are asunder
Voltage : 0 – 10 Volts range
Current : 4 – 20 milliAmperes
We use 4mA as the lower value so as to check for disturbances and wire breaks.Accuracy of
such systems is very high .ACCURACY: + - 0.1 %The whole system used is SCADA based.
Programmable Logic Circuits ( PLCs) are used in the process as they are the heard of
Instrumentation. Hence PLC selection depends upon the Criticality of the Process
ABSOLUTE PRESSURE CALIBRATION
We learnt to calibrate absolute pressure measurement gauges. There is absolute calibration
set installed, where on the one side we put the gauge to be calibrated and on the other side is
the measuring or calibrating unit which calibrates it as per our requirements . it caliberates in
terms of weight in kgs. We can calibrate upto 0-200kgs (its range).
DIFFERENTIAL PRESSURE CALIBRATION
Here we have a separate calibration unit and control units. The control unit have three valves
one for the input of the calibration unit and the other two for the measuring the differential
pressure of the gauge. The calibration unit consists of input valves from the control unit and
knobs to set pressure and calibrate weight according to it.
VACCUM PRESSURE CALIBRATION
It consists of very sophisticated instruments and they are very delicate. It uses mercury (Hg)
in the measurement of the vaccum pressure. It is computer based and the machinery is placed
in a sealed area
TEMPERATURE MONITORING
We can use Thermocouples or RTDs for temperature monitoring Normally RTDs are used
for low temperatures. Thermocouple selection depends upon two factors:
 Temperature Range
 Accuracy Required
Normally used Thermocouple is K Type Thermocouple, Chromel (Nickel-Chromium Alloy) /
Alumel (Nickel-Aluminum Alloy). This is the most commonly used general purpose
thermocouple. It is inexpensive and, owing to its popularity, available in a wide variety of
probes. They are available in the −200 °C to +1200 °C range. Sensitivity is approximately
41µV/°C.

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RTD (RESISTANCE TEMPERATURE DETECTOR)
It performs the function of thermocouple basically but the difference is of a resistance. In this
due to the change in the resistance the temperature difference is measured. In this lab, also the
measuring devices can be calibrated in the oil bath or just boiling water (for low range
devices) and in small furnace (for high range devices).
Fig 21 : Resistance temperature detector
RTDs are also used but not in protection systems due to vibrational errors. We pass a
constant current through the RTD. So that if R changes then the Voltage also changes RTDs
used in Industries are Pt100 and Pt1000.
Pt 100 : 0C – 100 Ω( 1 Ω = 2.5C )
Pt 1000 : 0C - 1000Ω
Pt 1000 is used for higher accuracy the gauges used for Temperature measurements are
mercury filled Temperature gauges. For Analog medium thermocouples are used and for
Digital medium Switches are used which are basically mercury switches.
THERMOCOUPLES
This device is based on SEEBACK and PELTIER effect. It comprises of two junctions at
different temperature. Then the emf is induced in the circuit due to the flow of electrons. This
is an important part in the plant.
Fig 21 : Thermocouple working

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RTD CALIBRATION / THERMOCOUPLE CALIBRATION
In NCPS, the calibration instruments used are of FLUKE instruments. It is used for the
standard calibration of both RTD’s and thermocouples. Calibration is done at a interval of
one year (1yr). Every calibration of the temperature measurement instruments needs
calibration certificate after 1yr. all the calibration data is digitalized and is on constant check
with the FLUKE instruments through internet and only after registering all the data with the
FLUKE services we are able to get the certificate and the calibration is fully completed.
TEMPERATURE SWITCH CALIBRATION
We have calibration unit, output testing unit, mercury probes and the testing switch.
Calibration unit has a temperature setter which has arrange of 2500C. Calibration unit is also
attached with the mercury probe. As we increase the set temperature the mercury in probe
expands accordingly in the probe. The mercury probe connects the calibrating unit and the
testing switch. At ted testing switch end the mercury probe is connected with bellows. When
the mercury expands in the probe it creates pressure in the bellows and the bellows in turn
activates the switch (the testing switch). This output of the switch is taken to the testing or the
output testing unit. This testing unit confirms calibration or it any mis-calibration is there it
corrects it. It gives a beep sound when the switch is properly calibrated.
FLOW MEASUREMENT
Flow measurement does not signify much and is measured just for metering purposes and for
monitoring the processes.
ROTAMETERS
A Rota meter is a device that measures the flow rate of liquid or gas in a closed tube. It is
occasionally misspelled as 'rotameter'.It belongs to a class of meters called variable area
meters, which measure flow rate by allowing the cross sectional area the fluid travels through
to vary, causing some measurable effect. A rotameter consists of a tapered tube, typically
made of glass, with a float inside that is pushed up by flow and pulled down by gravity. At a
higher flow rate more area (between the float and the tube)is needed to accommodate the
flow, so the float rises. Floats are made in many different shapes, with spheres and spherical
ellipses being the most common. The float is shaped so that it rotates axially as the fluid
passes. This allows you to tell if the float is stuck since it will only rotate if it is not. For
Digital measurements Flap system is used. For Analog measurements we can use the
following methods :
 Flowmeters
 Venurimeters / Orifice meters
 Turbines

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 Mass flow meters ( oil level )
 Ultrasonic Flow meters
 Magnetic Flow meter ( water level )
Selection of flow meter depends upon the purpose, accuracy and liquid to be measured so
different types of meters used.
Turbine type is the simplest of all. They work on the principle that on each rotation of the
turbine a pulse is generated and that pulse is counted to get the flow rate.
VENTURIMETERS
Fig 23 : Venturimeter
Referring to the diagram, using Bernoulli's equation in the special case of incompressible
fluids (such as the approximation of a water jet).
The theoretical pressure drop at the constriction would be given by (ρ/2) (v 22- v 12) .
And we know that rate of flow is given by:
Flow = k √ (D.P)
Where –
D.P – Differential Pressure or the Pressure Drop.
CONTROL VALVES
A valve is a device that regulates the flow of substances (gases, fluidized solids, slurries, or
liquids) by opening, closing, or partially obstructing various passageways. Valves are
technically pipefittings, but usually are discussed separately. Valves are used in a variety of
applications including industrial, military, commercial, residential, transportation. Plumbing
valves are the most obvious in everyday life, but many more are used. Some valves are driven
by pressure only; they are mainly used for safety purposes in steam engines and domestic
heating or cooking appliances. Others are used in a controlled way, like in Otto cycle engines
driven by a camshaft, where they play a major role in engine cycle control.
Many valves are controlled manually with a handle attached to the valve stem. If the handle
is turned a quarter of a full turn (90°) between operating positions, the valve is called a
quarter-turn valve. Butterfly valves, ball valves, and plug valves are often quarter-turn valves.
Valves can also be controlled by devices called actuators attached to the stem. They can be
electromechanical actuators such as an electric motor or solenoid, pneumatic actuators which

50. 50 | P a g e
are controlled by air pressure, or hydraulic actuators which are controlled by the pressure of a
liquid such as oil or water. So there are basically three types of valves that are used in power
industries besides the handle valves. They are –
 Pneumatic Valves – they are air or gas controlled which is compressed to turn or
move them
 Hydraulic valves – they utilize oil in place of Air as oil has better compression
 Motorized valves – these valves are controlled by electric motors
PCB CALIBRATION
In a power plant we also use different kinds of PCB’s (Printed Circuit Board). Before
calibration we put the PCB’s in a ultrasonic cleaner, to clean any kind of dirt or soot
contained in a PCB. Cleaning PCB before calibrating is a very important task. The ultrasonic
cleaner uses propylene. The cleaner produces ultrasonic waves and the propylene combined
effect cleans the PCB effectively then it s calibrated.
For PCB testing we use function generator, CRO (cathode ray oscilloscope) , multimeter , IC-
Tester (computer based) , variable resistance box, variable DC – AC supply box & LCR
tester.
DADRI SWITCHYARD
A Switchyard or Substation, consisting of large breakers and towers, is usually located in an
area close to the plant. The substation is used as the distribution center where:
 electrical power is supplied to the plant from the outside, and
 electrical power is sent from the plant
Often there are at least 2 main Buses. Very high voltages (typically 220,000 or 345,000 volts)
are present. Gas and oil circuit breakers are used. The gas (e.g. sulfur hexaflouride) or oil is
used to extinguish the arc caused when a breaker is opened, either by a control switch or due
to a fault. Manually or motor operated disconnects are provided on either side of the breaker
to allow the breaker to be electrically isolated so that maintenance work can be performed.
SUB-STATION EQUIPMENTS
1. Bus-bar
2. Circuit Breaker
3. Earth Switch
4. Inter Connecting Transformer (I.C.T.)
5. Current Transformer (C.T)
6. Capacitive Voltage Transformer (C.V.T.)
7. Lightning Arrester
8. Protection Relay
10. Power Line Carrier Communication (PLCC)

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Fig 24: Single line diagram for power flow
Fig 25 : Double Main and transfer bus arrangement
CIRCUIT BREAKER
Types of breakers operational at NTPC Dadri Switchyard –
 ABCB (Air blast circuit breaker) – This is connected in line of the transmission.
Here air is used as a medium for circuit breaking and insulation of the circuit. Air
pressure of 60 kcs (kilo centimetre square) is maintained in the breaker. The working
condition of the breaker is 30 kcs , but it is maintains high as air is the only quenching
medium. If the pressure drops to 29 kcs an alarm is sounded in the control room of the
switchyard and if the pressure further drops to 28 kcs , the breaker automatically

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breaks the circuit and do not allow the transmission or stops the electricity
transmission.
SPECIFICATION OF AIR BLAST CIRCUIT BREAKER
 Hydraulic breakers (with SF6) - This breaker uses the pressure of oil to break the
circuit. It uses sulphur floro phosphate (SF6) , as a quenching medium. The pressure
is maintained at 350 ksc, and its working condition is 310 ksc. It gives a alarm at
270ksc and it breaks the circuit connection and the transmission of electricity at
262ksc.
SPECIFICATIONS OF HYDRAULIC BREAKER WITH SF6
 Spring charge breaker – It has a D.C Motor and a spring attached to this motor. The
D.C motor keeps the spring in tension (or charge). When there is any fault the tension
on the spring is released i.e. the spring gets discharged and hits the plunger which in
turn switches off the circuit hence breaking the transmission of electricity.

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INTERCONNECTING TRANSFORMER (ICT)
Power transformers are the backbone of the large grid. The power is generated at the low
voltage level and has to be carried to far away load centres. Typically the power is generated
at the Pit heads i.e power source like coal, water. It is uneconomical carry the bulk power at
low voltage levels. Depending upon the requirement the voltage level is stepped up to the
transmission level i.e 220 or 400kV. At higher voltages the transmission losses are less.
Similarly at the remote end the voltage is stepped down the distribution level. To accomplish
that ask Power transformers are installed and act as bi-directional element in the system. At
NTPC Dadri this task is carried out by bank of Single Phase 400/220kVInterconnecting
transformers. Autotransformers are used when transformation ratio is between 1 and 2 and
above 315MVA, due to size and weight constraints all the transformers are single phases.
Three such single phase transformers are installed three phases to make One bank of
transformer. Three banks of transformers are installed to evacuate power from the
220kVswitchyard generated by 4X 210MW thermal Units. All these transformers are star-
star connected transformers with neutral solidly grounded. A third winding called tertiary
winding at much lower voltage i.e 33kV,is also provide and is connected in delta to facilitate
the flow of third harmonic current to reduce the distortion in the output voltage. To reduce
the overall size of the transformer, the transformer is provided with Oil forced and Air forced
type cooling at its 100% rating. However, to save the energy, the cooling system is controlled
by the temperature of the winding. The transformers are also equipped with On Load Tap
Changer to meet thechange in voltage variation. Typically the Tap changer provides variation
between ±10% of the nominal voltage i.e. 400kV with a variation of 0.5% at each tap.
SPECIFICATIONS OF ICT

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Fig 26 :400kV switchyard single line diagram
PROTECTION RELAYS
Relay is a device that detects the fault mostly in the high voltage circuits and initiates the
operation of the circuit breaker to isolate the defective section from the rest of the circuit.
Whenever fault occurs on the power system, the relay detects that fault and closes the trip
coil circuit. This results in the opening of the circuit breaker, which disconnects the faulty
circuit. Thus the relay ensures the safety of the circuit equipment from damage, which
the fault may cause.
PURPOSE OF PROTECTIVE RELAYING
The capital investment involved in a power system for the generation, transmission and
distribution of electrical power is so great that the proper precautions must be taken to ensure
that the equipment not only operates as nearly as possible to peak efficiency, but also that it is
protected from accidents. The normal path of the electric current is from the power source
through copper conductors in the generators, transformers and transmission lines to the
load and it is confined to this path by insulation. The insulation however may be broken-
down, either by the effect of temperature and age or by a physical accident, so that the current
then follows an abnormal path generally known as a short circuit or fault. Whenever this
occur the destructive capabilities of the enormous energy in the power system may cause
expensive damage to the equipment, severe drop in the voltage and loss of revenue due to
interruption of service. Such faults may be made in frequent by good design of the power
apparatus and lines and the provision of protective devices, such as surge diverters and

55. 55 | P a g e
ground fault neutralizers, but a certain number will occur inevitably due to lightening and
unforeseen accidental conditions. The purpose of protective relays and relaying systems is
to operate correct circuit breaker so as to disconnect only the faulty equipment from the
system as quickly as possible, thus minimizing the trouble and damage caused by faults
when they do occurs. With all other equipment it is only possible to mitigate the effects of
short circuit by disconnecting the equipment as quickly as possible, so that the destructive
effects of the energy into the fault may be minimized.
UNDER VOLTAGE RELAY
Under voltage protection is provide for AC circuits, bus bar, transformer, motor, rectifier etc.
Such protection is given by means of under voltage relay. The relay coil is energized by
voltage to be measured either directly or via a voltage transformer.
OVER CURRENT RELAY
If a short circuit occurs the circuit impedance is reduced to a low value and therefore a fault is
accompanied by a large current, Over current protection is that protection in which the relay
pickup when the magnitude of current exceeds the pickup level. The basic element in over
current protection is an over current relay. The over current relays are connected to the
system normally by means of CTs.
EARTH FAULT RELAY
Earth fault protection responds to single line to ground fault and double line to ground faults.
The current coil of the earth fault relay is connected either in neutral to ground relay CT
circuit. Core balance Ct’s are used for earth fault protection.
DIFFERENTIAL RELAY
Differential protection responds to vector difference between two or more similar quantities.
In circulating current differential protections CTs are connected on either side of the
protected equipments. During the internal faults the difference of secondary current flow
through the relay coil. Differential protection is used for protection of large transformer,
generator, motors feeders and bus bars.
TRANSFORMERS
A Transformer is a static electric device that transfers electrical energy from one circuit to
another through inductively coupled electrical conductors. The transfer of energy from one
circuit to another takes place without any change in the frequency.
The Transformer is based on two principles: firstly that an electric current can produce a
magnetic field (electromagnetism) and secondly that a changing magnetic field within a coil
of wire induces a voltage across the end of the coil (electromagnetic induction).
An Ideal Transformer should have the following properties:-
 There should be no losses either in the electric circuit or in the magnetic circuit.
 The whole of the magnetic flux is confined to magnetic circuit so that there is no leakage
flux.

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Transformers are some of the most efficient electrical machines which are able to transfer
99.75% of their input power to their output. Transformers come in a range of sizes from a
thumbnail sized coupling transformer hidden inside a stage microphone to huge units
weighing hundreds of tons.
FIG 27: Transformer at switchyard
RESULT
I learnt about the working of the power plant. Its working and all the instruments and cycles
used there. I learnt about the efforts put in by the employees from coal handling to generation
and distribution of electricity. Generation of electricity is a very interesting and complex
process. It includes people from almost every field. I studied and learnt about the basic layout
of power plant various cycles and instruments used in power plant (National Thermal Power
Cooperation, Dadri) for producing electricity and measuring temperature, pressure, flow,
level etc. I covered the cycles at power station like coal cycle, Feed water cycle, Steam cycle,
Condensate cycle. I also studied and worked at C&I labs and various process controls such as
load control strategy for pressurized mills, mills temperature control, control of the
combustion system, water pressure control, and also includes the study of various techniques
and instruments used to control processes. It also studied the various types of transducers
which are used to measure pressure, temperature flow etc. such as RTD for temperature
measurements, bourdon tubes for pressure etc. I learnt how the electricity is transmitted after
generation and working of the switch yard.

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BIBLIOGRAPHY
The material to make this report was consulted from various magazines and networking sites.
They are the following:
The websites consulted are:
 http://www.google.com/
 http://www.wikepedia.org/
 http://ntpc.co.in/
 http://ntpc/dadri/powerplant.co.in/
 http://www.scribd.com/doc/37664516/NTPC-dadri-thermal-report
 http://www.forbes.com
 http://www.bseindia.com
 http://electronics.howstuffworks.com/gadgets/
The magazines consulted are:
 Electronics for You
 NTPC report
 NTPC news flash
 Chip