NTPC REPORT

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PROJECT REPORT ( N.T.P.C. BADARPUR, NEW DELHI )


INDUSTRIAL TRAINING REPORT
(SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIRMENT OF THE
COURSE OF B.TECH.)

UNDERTAKEN AT


N.T.P.C. BADARPUR, NEW DELHI FROM: 18th JUNE to 11th August, 2007



SUBMITTED TO: SUBMITTED BY:
Mrs. RACHNA SINGH Ashutosh Kumar
N.T.P.C. Badarpur B.Tech 3rd Year
Electrical Engineering
JSS ACADEMY OF TECHNICAL EDUCATION (NOIDA)
TABLE OF CONTENT

Certificate Acknowledgement
Training at BTPS

1. Introduction
¨ NTPC
¨ Badarpur Thermal Power Station
2. Operation
3. Control & Instrumentation
¨ Manometry Lab
¨ Protection and interlock Lab
¨ Automation Lab
¨ Water Treatment Plant
¨ Furnace Safeguard Supervisory System
¨ Electronic Test Lab

4. Electrical Maintenance Division-I
¨ HT/LT Switch Gear
¨ HT/LT Motors, Turbine & Boilers Side
¨ CHP/NCHP

5. Electrical Maintenance Division-II
¨ Generator
¨ Transformer & Switchyard
¨ Protection
¨ Lighting



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¨ EP CERTIFICATE



This is to certify that------------------------- student of Batch Electrical & Electronics
Branch IIIrd Year; Sky line Institute of Engineering & Technology Noida has
successfully completed his industrial training at Badarpur Thermal power station
New Delhi for eight week from 18th June to 11th august 2007
He has completed the whole training as per the training report submitted by him.




Training Incharge
BTPS/NTPC
NEW DELHI




Acknowledgement


With profound respect and gratitude, I take the opportunity to convey my thanks to
complete the training here.

I do extend my heartfelt thanks to Mrs. Rachna Singh for providing me this
opportunity to be a part of this esteemed organization.

I am extremely grateful to all the technical staff of BTPS/NTPC for their co-
operation and guidance that helped me a lot during the course of training. I have
learnt a lot working under them and I will always be indebted of them for this value
addition in me.



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I would also like to thank the training in charge of Skyline Institute of Engineering
& Technology Gr. Noida and all the faculty member of Electrical & Electronics
department for their effort of constant co-operation. Which have been significant
factor in the accomplishment of my industrial training.




Training at BTPS

I was appointed to do eight-week training at this esteemed organization from 18th
June to 11th august 2007. In these eight weeks I was assigned to visit various
division of the plant which were

   1.   Operation
   2.   Control and instrumentation (C&I)
   3.   Electrical maintenance division I (EMD-I)
   4.   Electrical maintenance division II (EMD-II)


This eight-week training was a very educational adventure for me. It was really
amazing to see the plant by your self and learn how electricity, which is one of our
daily requirements of life, is produced.

This report has been made by self-experience at BTPS. The material in this report
has been gathered from my textbooks, senior student report, and trainer manual
provided by training department. The specification & principles are at learned by
me from the employee of each division of BTPS.




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ABOUT NTPC



NTPC Limited is the largest thermal power generating company of India. A public
sector company, it was incorporated in the year 1975 to accelerate power
development in the country as a wholly owned company of the Government of India.
At present, Government of India holds 89.5% of the total equity shares of the
company and FIIs, Domestic Banks, Public and others hold the balance 10.5%.
With in a span of 31 years, NTPC has emerged as a truly national power company,
with power generating facilities in all the major regions of the country.


POWER GENERATION IN INDIA

NTPC‟s core business is engineering, construction and operation of power
generating plants. It also provides consultancy in the area of power plant
constructions and power generation to companies in India and abroad. As on date
the installed capacity of NTPC is 27,904 MW through its 15 coal based (22,895 MW),
7 gas based (3,955 MW) and 4 Joint Venture Projects (1,054 MW). NTPC acquired
50% equity of the SAIL Power Supply Corporation Ltd. (SPSCL). This JV
Company operates the captive power plants of Durgapur (120 MW), Rourkela (120
MW) and Bhilai (74 MW). NTPC also has 28.33% stake in Ratnagiri Gas & Power
Private Limited (RGPPL) a joint venture company between NTPC, GAIL, Indian
Financial Institutions and Maharashtra SEB Co Ltd.
NTPC has set new benchmarks for the power industry both in the area of power
plant construction and operations. Its providing power at the cheapest average tariff
in the country..
NTPC is committed to the environment, generating power at minimal
environmental cost and preserving the ecology in the vicinity of the plants. NTPC
has undertaken massive a forestation in the vicinity of its plants. Plantations have
increased forest area and reduced barren land. The massive a forestation by NTPC
in and around its Ramagundam Power station (2600 MW) have contributed
reducing the temperature in the areas by about 3°c. NTPC has also taken proactive
steps for ash utilization. In 1991, it set up Ash Utilization Division
A "Centre for Power Efficiency and Environment Protection (CENPEEP)" has
been established in NTPC with the assistance of United States Agency for
International Development. (USAID). Cenpeep is efficiency oriented, eco-friendly
and eco-nurturing initiative - a symbol of NTPC's concern towards environmental
protection and continued commitment to sustainable power development in India.
As a responsible corporate citizen, NTPC is making constant efforts to improve the



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socio-economic status of the people affected by its projects. Through its
Rehabilitation and Resettlement programmes, the company endeavors to improve
the overall socio economic status Project Affected Persons.
NTPC was among the first Public Sector Enterprises to enter into a Memorandum
of Understanding (MOU) with the Government in 1987-88. NTPC has been placed
under the 'Excellent category' (the best category) every year since the MOU system
became operative.




Harmony between man and environment is the essence of healthy life and growth.
Therefore, maintenance of ecological balance and a pristine environment has been
of utmost importance to NTPC. It has been taking various measures discussed
below for mitigation of environment pollution due to power generation.

Environment Policy & Environment Management System
Driven by its commitment for sustainable growth of power, NTPC has evolved a
well defined environment management policy and sound environment practices for
minimizing environmental impact arising out of setting up of power plants and
preserving the natural ecology.


National Environment Policy:
At the national level, the Ministry of Environment and Forests had prepared a draft
Environment Policy (NEP) and the Ministry of Power along with NTPC actively
participated in the deliberations of the draft NEP. The NEP 2006 has since been
approved by the Union Cabinet in May 2006.
NTPC Environment Policy:
As early as in November 1995, NTPC brought out a comprehensive document
entitled "NTPC Environment Policy and Environment Management System".
Amongst the guiding principles adopted in the document are company's proactive
approach to environment, optimum utilization of equipment, adoption of latest
technologies and continual environment improvement. The policy also envisages
efficient utilization of resources, thereby minimizing waste, maximizing ash
utilization and providing green belt all around the plant for maintaining ecological
balance.
Environment Management, Occupational Health and Safety Systems:
NTPC has actively gone for adoption of best international practices on environment,
occupational health and safety areas. The organization has pursued the
Environmental Management System (EMS) ISO 14001 and the Occupational Health
and Safety Assessment System OHSAS 18001 at its different establishments. As a
result of pursuing these practices, all NTPC power stations have been certified for
ISO 14001 & OHSAS 18001 by reputed national and international Certifying
Agencies.
Pollution Control systems:



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While deciding the appropriate technology for its projects, NTPC integrates many
environmental provisions into the plant design. In order to ensure that NTPC
comply with all the stipulated environment norms, various state-of-the-art pollution
control systems / devices as discussed below have been installed to control air and
water pollution.



Electrostatic Precipitators:
The ash left behind after combustion of coal is arrested in high efficiency
Electrostatic Precipitators (ESP‟s) and particulate emission is controlled well within
the stipulated norms. The ash collected in the ESP‟s is disposed to Ash Ponds in
slurry form.
Flue Gas Stacks:
Tall Flue Gas Stacks have been provided for wide dispersion of the gaseous
emissions (SOX, NOX etc) into the atmosphere.
Low-NOXBurners:
In gas based NTPC power stations, NOx emissions are controlled by provision of
Low-NOx Burners (dry or wet type) and in coal fired stations, by adopting best
combustion practices.
Neutralisation Pits:
Neutralisation pits have been provided in the Water Treatment Plant (WTP) for pH
correction of the effluents before discharge into Effluent Treatment Plant (ETP) for
further treatment and use.

Coal Settling Pits / Oil Settling Pits:
In these Pits, coal dust and oil are removed from the effluents emanating from the
Coal Handling Plant (CHP), coal yard and Fuel Oil Handling areas before discharge
into ETP.
DE & DS Systems:
Dust Extraction (DE) and Dust Suppression (DS) systems have been installed in all
coal fired power stations in NTPC to contain and extract the fugitive dust released
in the Coal Handling Plant (CHP).
Cooling Towers:
Cooling Towers have been provided for cooling the hot Condenser cooling water in
closed cycle Condenser Cooling Water (CCW) Systems. This helps in reduction in
thermal pollution and conservation of fresh water.
Ash Dykes & Ash Disposal systems:
Ash ponds have been provided at all coal based stations except Dadri where Dry
Ash Disposal System has been provided. Ash Ponds have been divided into lagoons
and provided with garlanding arrangements for change over of the ash slurry feed
points for even filling of the pond and for effective settlement of the ash particles.
Ash in slurry form is discharged into the lagoons where ash particles get settled
from the slurry and clear effluent water is discharged from the ash pond. The
discharged effluents conform to standards specified by CPCB and the same is
regularly monitored.



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At its Dadri Power Station, NTPC has set up a unique system for dry ash collection
and disposal facility with Ash Mound formation. This has been envisaged for the
first time in Asia which has resulted in progressive development of green belt
besides far less requirement of land and less water requirement as compared to the
wet ash disposal system.
Ash Water Recycling System:
Further, in a number of NTPC stations, as a proactive measure, Ash Water
Recycling System (AWRS) has been provided. In the AWRS, the effluent from ash
pond is circulated back to the station for further ash sluicing to the ash pond. This
helps in savings of fresh water requirements for transportation of ash from the
plant.
The ash water recycling system has already been installed and is in operation at
Ramagundam, Simhadri, Rihand, Talcher Kaniha, Talcher Thermal, Kahalgaon,
Korba and Vindhyachal. The scheme has helped stations to save huge quantity of
fresh water required as make-up water for disposal of ash.
Dry Ash Extraction System (DAES):
Dry ash has much higher utilization potential in ash-based products (such as bricks,
aerated autoclaved concrete blocks, concrete, Portland pozzolana cement, etc.).
DAES has been installed at Unchahar, Dadri, Simhadri, Ramagundam, Singrauli,
Kahalgaon, Farakka, Talcher Thermal, Korba, Vindhyachal, Talcher Kaniha and
BTPS.

Liquid Waste Treatment Plants & Management System:
The objective of industrial liquid effluent treatment plant (ETP) is to discharge
lesser and cleaner effluent from the power plants to meet environmental regulations.
After primary treatment at the source of their generation, the effluents are sent to
the ETP for further treatment. The composite liquid effluent treatment plant has
been designed to treat all liquid effluents which originate within the power station
e.g. Water Treatment Plant (WTP), Condensate Polishing Unit (CPU) effluent, Coal
Handling Plant (CHP) effluent, floor washings, service water drains etc. The scheme
involves collection of various effluents and their appropriate treatment centrally
and re-circulation of the treated effluent for various plant uses.
NTPC has implemented such systems in a number of its power stations such as
Ramagundam, Simhadri, Kayamkulam, Singrauli, Rihand, Vindhyachal, Korba,
Jhanor Gandhar, Faridabad, Farakka, Kahalgaon and Talcher Kaniha. These
plants have helped to control quality and quantity of the effluents discharged from
the stations.

Sewage Treatment Plants & Facilities:
Sewage Treatment Plants (STPs) sewage treatment facilities have been provided at
all NTPC stations to take care of Sewage Effluent from Plant and township areas. In
a number of NTPC projects modern type STPs with Clarifloculators, Mechanical
Agitators, sludge drying beds, Gas Collection Chambers etc have been provided to
improve the effluent quality. The effluent quality is monitored regularly and treated
effluent conforming to the prescribed limit is discharged from the station. At several
stations, treated effluents of STPs are being used for horticulture purpose.



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Environmental Institutional Set-up:
Realizing the importance of protection of the environment with speedy development
of the power sector, the company has constituted different groups at project,
regional and Corporate Centre level to carry out specific environment related
functions. The Environment Management Group, Ash Utilisation Group and Centre
for Power Efficiency & Environment Protection (CENPEEP) function from the
Corporate Centre and initiate measures to mitigate the impact of power project
implementation on the environment and preserve ecology in the vicinity of the
projects. Environment Management and Ash Utilisation Groups established at each
station, look after various environmental issues of the individual station.
Environment Reviews:
To maintain constant vigil on environmental compliance, Environmental Reviews
are carried out at all operating stations and remedial measures have been taken
wherever necessary. As a feedback and follow-up of these Environmental Reviews, a
number of retrofit and up-gradation measures have been undertaken at different
stations.
Such periodic Environmental Reviews and extensive monitoring of the facilities
carried out at all stations have helped in compliance with the environmental norms
and timely renewal of the Air and Water Consents.

Up gradation & retrofitting of Pollution Control Systems:
Waste Management
Various types of wastes such as Municipal or domestic wastes, hazardous wastes,
Bio-Medical wastes get generated in power plant areas, plant hospital and the
townships of projects. The wastes generated are a number of solid and hazardous
wastes like used oils & waste oils, grease, lead acid batteries, other lead bearing
wastes (such as garkets etc.), oil & clarifier sludge, used resin, used photo-chemicals,
asbestos packing, e-waste, metal scrap, C&I wastes, electricial scrap, empty
cylinders (refillable), paper, rubber products, canteen (bio-degradable) wastes,
buidling material wastes, silica gel, glass wool, fused lamps & tubes, fire resistant
fluids etc. These wastes fall either under hazardous wastes category or non-
hazardous wastes category as per classification given in Government of India‟s
notification on Hazardous Wastes (Management and Handling) Rules 1989 (as
amended on 06.01.2000 & 20.05.2003). Handling and management of these wastes in
NTPC stations have been discussed below.

Advanced / Eco-friendly Technologies
NTPC has gained expertise in operation and management of 200 MW and 500 MW
Units installed at different Stations all over the country and is looking ahead for
higher capacity Unit sizes with super critical steam parameters for higher
efficiencies and for associated environmental gains. At Sipat, higher capacity Units
of size of 660 MW and advanced Steam Generators employing super critical steam
parameters have already been implemented as a green field project.
Higher efficiency Combined Cycle Gas Power Plants are already under operation at
all gas-based power projects in NTPC. Advanced clean coal technologies such as



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Integrated Gasification Combined Cycle (IGCC) have higher efficiencies of the
order of 45% as compared to about 38% for conventional plants. NTPC has
initiated a techno-economic study under USDOE / USAID for setting up a
commercial scale demonstration power plant by using IGCC technology. These
plants can use low-grade coals and have higher efficiency as compared to
conventional plants.
With the massive expansion of power generation, there is also growing awareness
among all concerned to keep the pollution under control and preserve the health
and quality of the natural environment in the vicinity of the power stations. NTPC is
committed to provide affordable and sustainable power in increasingly larger
quantity. NTPC is conscious of its role in the national endeavour of mitigating
energy poverty, heralding economic prosperity and thereby contributing towards
India‟s emergence as a major global economy.
Lay out of Employee‟s


Overall Power Generation

                               Unit    1997-98      2006-07      % of increase
Installed Capacity             MW      16,847       26,350       56.40
Generation                     MUs     97,609       1,88,674     93.29
No. of employees               No.     23,585       24,375       3.34
Generation/employee            MUs     4.14         7.74         86.95




The table below shows the detailed operational performance of coal based stations
over the years.
OPERATIONAL PERFORMANCE OF COAL BASED NTPC STATIONS
             Unit 97-98 98-99 99-00 00-01 01-02 02-03 03-04 04-05 05-06 06-07
Generation BU 106.2 109.5 118.7 130.1 133.2 140.86 149.16 159.11 170.88 188.67
PLF          % 75.20 76.60 80.39 81.8 81.1 83.6 84.4 87.51 87.54 89.43
Availability
             % 85.03 89.36 90.06 88.54 81.8 88.7 88.8 91.20 89.91 90.09
Factor



The energy conservation parameters like specific oil consumption and auxiliary
power consumption have also shown considerable improvement over the years.

ABOUT BADARPUR THERMAL POWER STATION


I was assigned to do training in operation division from 18th June 2007 to 23rd June
2007


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ELECTRICITY FROM COAL

Coal from the coal wagons is unloaded with the help of wagon tipplers in the C.H.P.
this coal is taken to the raw coal bunkers with the help of conveyor belts. Coal is
then transported to bowl mills by coal feeders where it is pulverized and ground in
the powered form.

This crushed coal is taken away to the furnace through coal pipes with the help of
hot and cold mixture P.A fan. This fan takes atmospheric air, a part of which is sent
to pre heaters while a part goes to the mill for temperature control. Atmospheric air
from F.D fan in the air heaters and sent to the furnace as combustion air.

Water from boiler feed pump passes through economizer and reaches the boiler
drum . Water from the drum passes through the down comers and goes to the
bottom ring header. Water from the bottom ring header is divided to all the four
sides of the furnace. Due to heat density difference the water rises up in the water
wall tubes. This steam and water mixture is again taken to the boiler drum where
the steam is sent to super heaters for super heating. The super heaters are located
inside the furnace and the steam is super heated (540 degree Celsius) and finally it
goes to the turbine.

Fuel gases from the furnace are extracted from the induced draft fan, which
maintains balance draft in the furnace with F.D fan. These fuel gases heat energy to
the various super heaters and finally through air pre heaters and goes to
electrostatic precipitators where the ash particles are extracted. This ash is mixed
with the water to from slurry is pumped to ash period.

The steam from boiler is conveyed to turbine through the steam pipes and through
stop valve and control valve that automatically regulate the supply of steam to the
turbine. Stop valves and controls valves are located in steam chest and governor
driven from main turbine shaft operates the control valves the amount used.

Steam from controlled valves enter high pressure cylinder of turbines, where it
passes through the ring of blades fixed to the cylinder wall. These act as nozzles and
direct the steam into a second ring of moving blades mounted on the disc secured in
the turbine shaft. The second ring turns the shaft as a result of force of steam. The
stationary and moving blades together.




MAIN GENERATOR
Maximum continuous KVA rating                                24700KVA
Maximum continuous KW                                        210000KW
Rated terminal voltage                                       15750V



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Rated Stator current                                          9050 A
Rated Power Factor                                            0.85 lag
Excitation current at MCR Condition                           2600 A
Slip-ring Voltage at MCR Condition                            310 V
Rated Speed                                                   3000 rpm
Rated Frequency                                               50 Hz
Short circuit ratio                                           0.49
Efficiency at MCR Condition                                   98.4%
Direction of rotation viewed                                  Anti Clockwise
Phase Connection                                              Double Star
Number of terminals brought out                               9( 6 neutral and 3 phase)



MAIN TURBINE DATA

Rated output of Turbine                                      210 MW
Rated speed of turbine                                       3000 rpm
Rated pressure of steam before emergency                     130 kg/cm^2
Stop valve rated live steam temperature                      535 degree Celsius
Rated steam temperature after reheat at inlet to receptor
                                                             535 degree Celsius
valve
Steam flow at valve wide open condition                      670 tons/hour
Rated quantity of circulating water through condenser        27000 cm/hour
1. For cooling water temperature (degree Celsius)            24,27,30,33
1.Reheated steam pressure at inlet of interceptor valve in
                                                             23,99,24,21,24,49,24.82
kg/cm^2 ABS
2.Steam flow required for 210 MW in ton/hour                 68,645,652,662
3.Rated pressure at exhaust of LP turbine in mm of Hg        19.9,55.5,65.4,67.7




THERMAL POWER 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


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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.
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 pulverizer
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

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



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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.
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



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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 stem 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 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



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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 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



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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 modeled 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. Pulverizer

A pulverizer is a device for grinding coal for combustion in a furnace in a fossil fuel
power plant.

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 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.




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12. Economizers
Economizer, or in the UK 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 which is decedents of Green‟s
original design. 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.

14. Precipitator

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-



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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.



C&I



(CONTROL AND INSTRUMENTATION)


I was assigned to do training in control and instrumentation from 25th June 2007 to
14th July 2007

CONTROL AND INSTRUMENTATION

This division basically calibrates various instruments and takes care of any faults
occur in any of the auxiliaries in the plant.

It has following labs:

   1.   MANOMETRY LAB
   2.   PROTECTION AND INTERLOCK LAB
   3.   AUTOMATION LAB
   4.   WATER TREATEMENT LAB
   5.   FURNACE SAFETY SUPERVISORY SYSTEM(FSSS)



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   6. ELECTRONICS TEST LAB


This department is the brain of the plant because from the relays to transmitters
followed by the electronic computation chipsets and recorders and lastly the controlling
circuitry, all fall under this.

5.0 MANOMETRY LAB

5.0.1 TRANSMITTERS
It is used for pressure measurements of gases and liquids, its working principle is that
the input pressure is converted into electrostatic capacitance and from there it is
conditioned and amplified. It gives an output of 4-20 ma DC. It can be mounted on a
pipe or a wall. For liquid or steam measurement transmitters is mounted below main
process piping and for gas measurement transmitter is placed above pipe.

5.0.2 MANOMETER
It‟s a tube which is bent, in U shape. It is filled with a liquid. This device
corresponds to a difference in pressure across the two limbs.




5.0.3 BOURDEN PRESSURE GAUGE
It‟s an oval section tube. Its one end is fixed. It is provided with a pointer to indicate
the pressure on a calibrated scale. It is of 2 types:

(a) Spiral type: for Low pressure measurement.
(b) Helical Type: for High pressure measurement.

5.1 PROTECTION AND INTERLOCK LAB
5.1.1 INTERLOCKING
It is basically interconnecting two or more equipments so that if one equipments
fails other one can perform the tasks. This type of interdependence is also created so
that equipments connected together are started and shut down in the specific
sequence to avoid damage.
For protection of equipments tripping are provided for all the equipments. Tripping
can be considered as the series of instructions connected through OR GATE. When
a fault occurs and any one of the tripping is satisfied a signal is sent to the relay,
which trips the circuit. The main equipments of this lab are relay and circuit
breakers. Some of the instrument uses for protection are:
1. RELAY

It is a protective device. It can detect wrong condition in electrical circuits by



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constantly measuring the electrical quantities flowing under normal and faulty
conditions. Some of the electrical quantities are voltage, current, phase angle and
velocity.
2. FUSES

It is a short piece of metal inserted in the circuit, which melts when heavy current
flows through it and thus breaks the circuit. Usually silver is used as a fuse material
because:
a) The coefficient of expansion of silver is very small. As a result no critical fatigue
occurs and thus the continuous full capacity normal current ratings are assured for
the long time.
b) The conductivity of the silver is unimpaired by the surges of the current that
produces temperatures just near the melting point.
c) Silver fusible elements can be raised from normal operating temperature to
vaporization quicker than any other material because of its comparatively low
specific heat.




5.1.2 MINIATURE CIRCUIT BREAKER

They are used with combination of the control circuits to.
a) Enable the staring of plant and distributors.
b) Protect the circuit in case of a fault.
In consists of current carrying contacts, one movable and other fixed. When a fault
occurs the contacts separate and are is stuck between them. There are three types of

- MANUAL TRIP
- THERMAL TRIP
- SHORT CIRCUIT TRIP


5.1.3 ROTECTION AND INTERLOCK SYSTEM

1. HIGH TENSION CONTROL CIRCUIT

For high tension system the control system are excited by separate D.C supply. For
starting the circuit conditions should be in series with the starting coil of the
equipment to energize it. Because if even a single condition is not true then system
will not start.

2. LOW TENSION CONTROL CIRCUIT

For low tension system the control circuits are directly excited from the 0.415 KV
A.C supply. The same circuit achieves both excitation and tripping. Hence the



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tripping coil is provided for emergency tripping if the interconnection fails.




5.2 AUTOMATION LAB
This lab deals in automating the existing equipment and feeding routes.
Earlier, the old technology dealt with only (DAS) Data Acquisition System and came
to be known as primary systems. The modern technology or the secondary systems
are coupled with (MIS) Management Information System. But this lab universally
applies the pressure measuring instruments as the controlling force. However, the
relays are also provided but they are used only for protection and interlocks.
Once the measured is common i.e. pressure the control circuits can easily be
designed with single chips having multiple applications. Another point is the
universality of the supply, the laws of electronic state that it can be any where
between 12V and 35V in the plant. All the control instruments are excited by 24V
supply (4-20mA) because voltage can be mathematically handled with ease therefore
all control systems use voltage system for computation. The latest technology is the
use of „ETHERNET‟ for control signals. 5.3 PYROMETER LAB
(1) LIQUID IN GLASS THERMOMETER
Mercury in the glass thermometer boils at 340 degree Celsius which limits the range
of temperature that can be measured. It is L shaped thermometer which is designed
to reach all inaccessible places.

(2) ULTRA VIOLET CENSOR
This device is used in furnace and it measures the intensity of ultra violet rays there
and according to the wave generated which directly indicates the temperature in the
furnace.

(3) 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.

(4) 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).
5.4 FURNACE SAFETY AND SUPERVISORY SYSTEM LAB



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This lab has the responsibility of starting fire in the furnace to enable the burning of
coal. For first stage coal burners are in the front and rear of the furnace and for the
second and third stage corner firing is employed. Unburnt coal is removed using
forced draft or induced draft fan. The temperature inside the boiler is 1100 degree
Celsius and its height is 18 to 40 m. It is made up of mild steel. An ultra violet sensor
is employed in furnace to measure the intensity of ultra violet rays inside the
furnace and according to it a signal in the same order of same mV is generated
which directly indicates the temperature of the furnace.
For firing the furnace a 10 KV spark plug is operated for ten seconds over a spray
of diesel fuel and pre-heater air along each of the feeder-mills. The furnace has six
feeder mills each separated by warm air pipes fed from forced draft fans. In first
stage indirect firing is employed that is feeder mills are not fed directly from coal
but are fed from three feeders but are fed from pulverized coalbunkers. The furnace
can operate on the minimum feed from three feeders but under not circumstances
should any one be left out under operation, to prevent creation of pressure different
with in the furnace, which threatens to blast it.

5.5 ELECTRONICS LAB

This lab undertakes the calibration and testing of various cards. It houses various
types of analytical instruments like oscilloscopes, integrated circuits, cards auto
analyzers etc.
Various processes undertaken in this lab are:
1. Transmitter converts mV to mA.
2. Auto analyzer purifies the sample before it is sent to electrodes. It extracts the
magnetic portion.

5.6 ANNUNCIATIN CARDS
They are used to keep any parameter like temperature etc. within limits. It gets a
signal if parameter goes beyond limit. It has a switching transistor connected to
relay that helps in alerting the UCB.




39. Control and Instrumentation Control and Instrumentation
Measuring Instrumentsments

In any process the philosophy of instrumentation should provide a comprehensive
intelligence feed back on the important parameters viz. Temperature, Pressure,
Level and Flow. This Chapter Seeks to provide a basic understanding of the
prevalent instruments used for measuring the above parameters.




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Temperature Measurement

The most important parameter in thermal power plant is temperature and its
measurement plays a vital role in safe operation of the plant. Rise of temperature in
a substance is due to the resultant increase in molecular activity of the substance on
application of heat; which increases the internal energy of the material. Therefore
there exists some property of the substance, which changes with its energy content.
The change may be observed with substance itself or in a subsidiary system in
thermodynamic equilibrium, which is called testing body and the system itself is
called the hot body.

Expansion Thermometer

Solid Rod Thermometers a temperature sensing - Controlling device may be
designed incorporating in its construction the principle that some metals expand
more than others for the same temperature range. Such a device is the thermostat
used with water heaters (Refer Fig. 69).




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Fig No.-69 Rod Type Thermostat



The mercury will occupy a greater fraction of the volume of the container than it
will at a low temperature.
Under normal atmospheric conditions mercury normally boils at a temperature of
(347°C). To extend the range of mercury in glass thermometer beyond this point the
top end of a thermometer bore opens into a bulb which is many times larger in
capacity than the bore. This bulb plus the bore above the mercury, is then filled
with nitrogen or carbon dioxide gas at a sufficiently high pressure to prevent boiling
at the highest temperature to which the thermometer may be used.
Mercury in Steel the range of liquid in glass thermometers although quite large,
does not lend itself to all industrial practices. This fact is obvious by the delicate
nature of glass also the position of the measuring element is not always the best
position to read the result. Types of Hg in Steel Thermometers are:

Bourdon Tube
Most common and simplest type (Refer Fig. 71)

Spiral type
More sensitive and used where compactness is necessary

 Helical Type
Most sensitive and compact. Pointer may be mounted direct on end of helix
Which rotates, thus eliminating backlash and lost motion?
Linkages, which only allow the pointer to operate over a selected range of pressure
to either side of the normal steam pressure. (Refer Fig No.77)

Dewrance Critical Pressure Gauge Measurement of Level


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Direct Methods

'Sight Glass' is used for local indication on closed or open vessels. A sight glass is a
tube of toughened glass connected at both ends through packed unions and vessel.
The liquid level will be the same as that in the vessel. Valves are provided for
isolation and blow down.
"Float with Gauge Post" is normally used to local indication on closed or open
vessels.
"Float Operated Dial" is used for small tanks and congested areas. The float arm is
connected to a quadrant and pinion which rotates the pointer over a scale.




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Bourden Pressure Gauge a Bourdon pressure gauge calibrated in any fact head is
often connected to a tank at or near the datum level.
"Mercury Manometer" is used for remote indication of liquid level. The working
principle is the same as that of a manometer one limp of a U-tube is connected to the
tank, the other being open to atmosphere. The manometer liquid must not mix with
the liquid in the vessel, and where the manometer is at a different level to the vessel,
the static head must be allowed in the design of the manometer.
'Diaphragm Type' is used for remote level indication in open tanks or docks etc. A
pressure change created by the movement of a diaphragm is proportional to a
change in liquid level above the diaphragm. This consists of a cylindrical box with a
rubber or plastic diaphragm across its open end as the level increases .the liquid
pressure on the diaphragm increases and the air inside is compressed. This pressure
is transmitted via a capillary tube to an indicator or recorder incorporating a
pressure
Measuring element.

Sealed Capsule Type The application and principle is the same as for the diaphragm
box. In this type, a capsule filled with an inert gas under a slight pressure is exposed
to the pressure due to the head of liquid and is connected by a capillary to an
indicator. In some cases the capsule is fitted external to the tank and is so arranged
that it can be removed whilst the tank is still full, a spring loaded valve
automatically shutting off the tapping point.
Air Purge System This system provides the simplest means of obtaining an
indication of level, or volume, at a reasonable distance and above or below, the
liquid being measured. The pressure exerted inside an open ended tube below the
surface of a liquid is proportional to the depth of the liquid




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The Measurement of Flow

Two principle measurements are made by flow meters viz. quantity of flow and rate
of flow. 'Quantity of flow' is the quantity of fluid passing a given point in a given
time, i.e. gallons or pounds. „Rate of flow' is the speed of. a fluid passing a given
point at a given instant and is proportional to quantity passing at a given instant, i.e.
gallons per minute or pounds per hour. There are two groups of measuring devices:
-

Positive, or volumetric, which measure flow by transferring a measured quantity of
fluid from the inlet to the outlet.

Inferential, which measures the velocity of the flow and the volume passed is
inferred, it being equal to the velocity times the cross sectional area of the flow. The
inferential type is the most widely used.




Measurement of Fluid Flow through Pipes:

"The Rotating Impeller Type" is a positive type device which is used for medium
quantity flow measurement i.e., petroleum and other commercial liquids. It consists
of
Two fluted rotors mounted in a liquid tight case fluid flow and transmitted to a
counter.
Rotating Oscillating Piston Type This is also a positive type device and is used for
measuring low and medium quantity flows, e.g. domestic water supplies. This
consists of a brass meter body into which is fitted a machined brass working



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chamber and cover, containing a piston made of ebonite. This piston acts as a
moving chamber and transfers a definite volume of fluid from the inlet to the outlet
for each cycle.
Helical Vane Type For larger rates of flow, a helical vane is mounted centrally in the
body of the meter. The helix chamber may be vertical or horizontal and is geared to
a counter. Usually of pipe sizes 3" to 10" Typical example is the Kent Torrent Meter.
Turbine Type this like the helical Vane type is a inference type of device used for
large flows with the minimum of pressure drop. This consists of a turbine or drum
revolving in upright bearings, retaining at the top by a collar. Water enters the
drum
from the top and leaves tangentially casings to rotate at a speed dependent upon the
quantity of water passed. The cross sectional area of the meter throughout is equal
to
the area of the inlet and outlet pipes and is commonly used on direct supply water
mains,
Combination Meters this is used for widely fluctuating flows. It consists of a larger
meter (helical, turbine or fan) in the main with a small rotary meter or suitable type
in a
bypass. Flow is directed into either the main or bypass according to the quantity of
flow
by an automatic valve. By this means flows of 45 to 40,000 gallons per hour can be
measured.

Measurement of Fluid Flow through Open Channels:
The Weir If a fluid is allowed to flow over a square weir of notch, The height of the
liquid above the still of the weir, or the bottom of the notch will be a measure of the
rate of flow.




A formula relates the rate of flow to the height and is dependent upon the design of
the
Venturi Flumes The head loss caused by the weir flow meter is considerable and its
construction is sometimes complicated, therefore the flume is sometimes used. The
principle is same as that of venture except that the rate of flow is proportional to the
depth of the liquid in the upstream section. It consists of a local contraction in the
cross
section of flow through a channel in the shape of a venturi. It is only necessary to
measure the depth of the upstream section which is a measure of the rate of flow.
This
may be done by pressure tapping at the datum point or by a float in an adjacent
level


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chamber.
Pressure Difference Flow meters These are the most widely used type of flow meter
since they are capable of measuring the flow of all industrial fluids passing through
pipes. They consists of a primary element inserted in the pipeline which generates a
differential pressure, ^he magnitude of which is proportional to the square of the
rate of flow and a secondary element which measures this differential pressure and
translates it into terms of flow. (Refer fig. 79).




Fig. No-79 Pressure Differential Flow meters




Primary elements Bernoulli's theorem states that the quantity of fluid or gas flowing
is proportional to the square root of the differential pressure. There are four
principal types of primary elements (or restrictions) as enumerate below:
Venturi; This is generally used for medium and high quantity fluid flow and it
consists of two hollow truncated cones, the smaller diameters of which are
connected together by a short length of parallel pipe, the smallest diameter of the
tube formed by this length of parallel pipe is known as the throat section and the
lower of the two pressures, (the throat, or downstream pressure) is measured here.
Orifice Plate This is the oldest and most common form of pressure differential
device. In its simplest form it consists of a thin metal plate with a central hold
clamped between two pipe flanges. In the metering of dirty fluids or fluids
containing solids the hole is placed so that its lower edge coincides with the inside
bottom of the pipe. (Refer Fig.80) It is essential that the leading edge of the hole is
absolutely sharp rounding or burring would have a very marked effect on the flow.




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Fig No.-80 Typical Orifice Plate Pressure Tapping




EMD I


Electrical Maintenance division I


I was assigned to do training in Electrical maintenance division I from 17th July
2007 to 28th July 2007.

This two week of training in this division were divided as follows.




· 17th to 19th July 2007- HT/LT switchgear
· 21st to 24th July 2007 - HT/LT Motors, Turbine &Boiler side
· 26th to 28th July 2007- CHP/NCHP Electrical




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Electrical maintenance division 1

It is responsible for maintenance of:

1. Boiler side motors
2. Turbine side motors
3. Outside motors
4. Switchgear


1. Boiler side motors:


For 1, units 1, 2, 3

1.1D Fans                                         2 in no.
2.F.D Fans                                        2 in no.
3.P.A.Fans                                        2 in no.
4.Mill Fans                                       3 in no.
5.Ball mill fans                                  3 in no.
6.RC feeders                                      3 in no.
7.Slag Crushers                                   5 in no.
8.DM Make up Pump                                 2 in no.
9.PC Feeders                                      4 in no.
10.Worm Conveyor                                  1 in no.
11.Furnikets                                      4 in no.




For stage units 1, 2, 3

1.I.D Fans                                   2 in no.
2.F.D Fans                                   2 in no.
3.P.A Fans                                   2 in no.
4.Bowl Mills                                 6 in no.


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5.R.C Feeders                               6 in no.
6.Clinker Grinder                           2 in no.
7.Scrapper                                  2 in no.
8.Seal Air Fans                             2 in no.
9.Hydrazine and Phosphorous Dozing          2 in no.
                                            2/3 in no.

1. COAL HANDLING PLANT (C.H.P)
2. NEW COAL HANDLING PLANT (N.C.H.P)
The old coal handling plant caters to the need of units 2,3,4,5 and 1 whereas the
latter supplies coal to units 4 and V.O.C.H.P. supplies coal to second and third
stages in the advent coal to usable form to (crushed) form its raw form and send it
to bunkers, from where it is send to furnace.

Major Components

1. Wagon Tippler: - Wagons from the coal yard come to the tippler and are emptied
here. The process is performed by a slip –ring motor of rating: 55 KW, 415V, 1480
RPM. This motor turns the wagon by 135 degrees and coal falls directly on the
conveyor through vibrators. Tippler has raised lower system which enables is to
switch off motor when required till is wagon back to its original position. It is titled
by weight balancing principle. The motor lowers the hanging balancing weights,
which in turn tilts the conveyor. Estimate of the weight of the conveyor is made
through hydraulic weighing machine.
2. Conveyor: - 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.

3. 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.

4. Metal Separators: - 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
5. Crusher: - Both the plants use TATA crushers powered by BHEL. Motors. The



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crusher is of ring type and motor ratings are 400 HP, 606 KV. Crusher is designed
to crush the pieces to 20 mm size i.e. practically considered as the optimum size of
transfer via conveyor.

6. Rotatory Breaker: - OCHP employs mesh type of filters and allows particles of
20mm size to go directly to RC bunker, larger particles are sent to crushes. This
leads to frequent clogging. NCHP uses a technique that crushes the larger of harder
substance like metal impurities easing the load on the magnetic separators.
MILLING SYSTEM

1. RC Bunker: - Raw coal is fed directly to these bunkers. These are 3 in no. per
boiler. 4 & ½ tons of coal are fed in 1 hr. the depth of bunkers is 10m.

2. RC Feeder: - It transports pre crust coal from raw coal bunker to mill. The
quantity of raw coal fed in mill can be controlled by speed control of aviator drive
controlling damper and aviator change.

3. Ball Mill: - The ball mill crushes the raw coal to a certain height and then allows
it to fall down. Due to impact of ball on coal and attraction as per the particles move
over each other as well as over the Armor lines, the coal gets crushed. Large
particles are broken by impact and full grinding is done by attraction. The Drying
and grinding option takes place simultaneously inside the mill.

4. Classifier:- It is an equipment which serves separation of fine pulverized coal
particles medium from coarse medium. The pulverized coal along with the carrying
medium strikes the impact plate through the lower part. Large particles are then
transferred to the ball mill.

5. Cyclone Separators: - It separates the pulverized coal from carrying medium. The
mixture of pulverized coal vapour caters the cyclone separators.

6. The Tturniket: - It serves to transport pulverized coal from cyclone separators to
pulverized coal bunker or to worm conveyors. There are 4 turnikets per boiler.

7. Worm Conveyor: - It is equipment used to distribute the pulverized coal from
bunker of one system to bunker of other system. It can be operated in both
directions.



8. Mills Fans: - It is of 3 types:
Six in all and are running condition all the time.
(a) ID Fans: - Located between electrostatic precipitator and chimney.
Type-radical
Speed-1490 rpm
Rating-300 KW



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Voltage-6.6 KV
Lubrication-by oil

(b) FD Fans: - Designed to handle secondary air for boiler. 2 in number and provide
ignition of coal.

Type-axial
Speed-990 rpm
Rating-440 KW
Voltage-6.6 KV

(c)Primary Air Fans: - Designed for handling the atmospheric air up to 50 degrees
Celsius, 2 in number

And they transfer the powered coal to burners to firing.

Type-Double suction radial
Rating-300 KW
Voltage-6.6 KV
Lubrication-by oil
Type of operation-continuous

9. Bowl Mill: - One of the most advanced designs of coal pulverizes presently
manufactured.

Motor specification –squirrel cage induction motor
Rating-340 KW
Voltage-6600KV
Curreen-41.7A
Speed-980 rpm
Frequency-50 Hz
No-load current-15-16 A

NCHP

1. Wagon Tippler:-

Motor Specification
(i) H.P 75 HP
(ii) Voltage 415, 3 phase
(iii) Speed 1480 rpm
(iv) Frequency 50 Hz
(v) Current rating 102 A

2. Coal feed to plant:-




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Feeder motor specification

(i) Horse power 15 HP
(ii) Voltage 415V,3 phase
(iii) Speed 1480 rpm
(iv) Frequency 50 Hz



3. Conveyors:-
10A, 10B
11A, 11B
12A, 12B
13A, 13B
14A, 14B
15A, 15B
16A, 16B
17A, 17B
18A, 18B

4. Transfer Point 6

5. Breaker House

6. Rejection House

7. Reclaim House

8. Transfer Point 7

9. Crusher House

10. Exit

The coal arrives in wagons via railways and is tippled by the wagon tipplers into the
hoppers. If coal is oversized (>400 mm sq) then it is broken manually so that it
passes the hopper mesh. From the hopper mesh it is taken to the transfer point TP6
by conveyor 12A ,12B which takes the coal to the breaker house , which renders the
coal size to be 100mm sq. the stones which are not able to pass through the 100mm
sq of hammer are rejected via conveyors 18A,18B to the rejection house . Extra coal
is to sent to the reclaim hopper via conveyor 16. From breaker house coal is taken to
the TP7 via Conveyor 13A, 13B. Conveyor 17A, 17B also supplies coal from reclaim
hopper, From TP7 coal is taken by conveyors 14A, 14B to crusher house whose
function is to render the size of coal to 20mm sq. now the conveyor labors are
present whose function is to recognize and remove any stones moving in the
conveyors . In crusher before it enters the crusher. After being crushed, if any metal



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is still present it is taken care of by metal detectors employed in conveyor 10.

SWITCH GEAR-

It makes or breaks an electrical circuit.

1. Isolation: - A device which breaks an electrical circuit when circuit is switched on
to no load. Isolation is normally used in various ways for purpose of isolating a
certain portion when required for maintenance.

2. Switching Isolation: - It is capable of doing things like interrupting transformer
magnetized current, interrupting line charging current and even perform load
transfer switching. The main application of switching isolation is in connection with
transformer feeders as unit makes it possible to switch out one transformer while
other is still on load.

3. Circuit Breakers: - One which can make or break the circuit on load and even on
faults is referred to as circuit breakers. This equipment is the most important and is
heavy duty equipment mainly utilized for protection of various circuits and
operations on load. Normally circuit breakers installed are accompanied by
isolators

4. Load Break Switches: - These are those interrupting devices which can make or
break circuits. These are normally on same circuit, which are backed by circuit
breakers.

5. Earth Switches: - Devices which are used normally to earth a particular system,
to avoid any accident happening due to induction on account of live adjoining
circuits. These equipments do not handle any appreciable current at all. Apart from
this equipment there are a number of relays etc. which are used in switchgear.

LT Switchgear

It is classified in following ways:-

1. Main Switch:- Main switch is control equipment which controls or disconnects
the main supply. The main switch for 3 phase supply is available for tha range 32A,
63A, 100A, 200Q, 300A at 500V grade.

2. Fuses: - With Avery high generating capacity of the modern power stations
extremely heavy carnets would flow in the fault and the fuse clearing the fault would
be required to withstand extremely heavy stress in process.
It is used for supplying power to auxiliaries with backup fuse protection. Rotary
switch up to 25A. With fuses, quick break, quick make and double break switch
fuses for 63A and 100A, switch fuses for 200A, 400A, 600A, 800A and 1000A are
used.



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3. Contractors: - AC Contractors are 3 poles suitable for D.O.L Starting of motors
and protecting the connected motors.

4. Overload Relay: - For overload protection, thermal over relay are best suited for
this purpose. They operate due to the action of heat generated by passage of current
through relay element.

5. Air Circuit Breakers: - It is seen that use of oil in circuit breaker may cause a fire.
So in all circuits breakers at large capacity air at high pressure is used which is
maximum at the time of quick tripping of contacts. This reduces the possibility of
sparking. The pressure may vary from 50-60 kg/cm^2 for high and medium
capacity circuit breakers.


HT SWITCH GEAR:-

1. Minimum oil Circuit Breaker: - These use oil as quenching medium. It comprises
of simple dead tank row pursuing projection from it. The moving contracts are
carried on an iron arm lifted by a long insulating tension rod and are closed
simultaneously pneumatic operating mechanism by means of tensions but throw off
spring to be provided at mouth of the control the main current within the controlled
device.

Type-HKH 12/1000c
· Rated Voltage-66 KV
· Normal Current-1250A
· Frequency-5Hz
· Breaking Capacity-3.4+KA Symmetrical
· 3.4+KA Asymmetrical
· 360 MVA Symmetrical
· Operating Coils-CC 220 V/DC
§ FC 220V/DC
· Motor Voltage-220 V/DC

2. Air Circuit Breaker: - In this the compressed air pressure around 15 kg per cm^2
is used for extinction of arc caused by flow of air around the moving circuit . The
breaker is closed by applying pressure at lower opening and opened by applying
pressure at upper opening. When contacts operate, the cold air rushes around the
movable contacts and blown the arc.

It has the following advantages over OCB:-

i. Fire hazard due to oil are eliminated.
ii. Operation takes place quickly.



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iii. There is less burning of contacts since the duration is short and consistent.
iv. Facility for frequent operation since the cooling medium is replaced constantly.
Rated Voltage-6.6 KV
Current-630 A
Auxiliary current-220 V/DC

3. SF6 Circuit Breaker: - This type of circuit breaker is of construction to dead tank
bulk oil to circuit breaker but the principle of current interruption is similar o that
of air blast circuit breaker. It simply employs the arc extinguishing medium namely
SF6. the performance of gas . When it is broken down under an electrical stress. It
will quickly reconstitute itself

· Circuit Breakers-HPA
· Standard-1 EC 56
· Rated Voltage-12 KV
· Insulation Level-28/75 KV
· Rated Frequency-50 Hz
· Breaking Current-40 KA
· Rated Current-1600 A
· Making Capacity-110 KA
· Rated Short Time Current 1/3s -40 A
· Mass Approximation-185 KG
· Auxiliary Voltage
§ Closing Coil-220 V/DC
§ Opening Coil-220 V/DC
· Motor-220 V/DC
· SF6 Pressure at 20 Degree Celsius-0.25 KG
· SF6 Gas Per pole-0.25 KG




4. Vacuum Circuit Breaker: - It works on the principle that vacuum is used to save
the purpose of insulation and it implies that pr. Of gas at which breakdown voltage
independent of pressure. It regards of insulation and strength, vacuum is superior
dielectric medium and is better that all other medium except air and sulphur which
are generally used at high pressure.
· Rated frequency-50 Hz
· Rated making Current-10 Peak KA
· Rated Voltage-12 KV
· Supply Voltage Closing-220 V/DC
· Rated Current-1250 A
· Supply Voltage Tripping-220 V/DC
· Insulation Level-IMP 75 KVP



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· Rated Short Time Current-40 KA (3 SEC)
· Weight of Breaker-8 KG




EMD II


Electrical Maintenance division II


I was assigned to do training in Electrical maintenance division II from 31st July
2007 to 11th August 2007.
This two week of training in this division were divided as follows.




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· 31st to 2nd August 2007- Generator
· 4th August 2007 - Transformer &switchyard
· 7th August 2007 - protection
· 9th August2007 - Lightning
· 11th August 2007 - EP




Generator and Auxiliaries Generator and Auxiliaries
Generator Fundamentals Fundamentals

The transformation of mechanical energy into electrical energy is carried out by the
Generator. This Chapter seeks to provide basic understanding about the working
principles and development of Generator.

Working Principle

The A.C. Generator or alternator is based upon the principle of electromagnetic
induction and consists generally of a stationary part called stator and a rotating
part called rotor. The stator housed the armature windings. The rotor houses the
field windings. D.C. voltage is applied to the field windings through slip rings. When
the rotor is rotated, the lines of magnetic flux (viz magnetic field) cut through the
stator windings. This induces an electromagnetic force (e.m.f.) in the stator windings.
The magnitude of this e.m.f. is given by the following expression.

E = 4.44 /O FN volts
0 = Strength of magnetic field in Weber‟s.
F = Frequency in cycles per second or Hertz.
N = Number of turns in a coil of stator winding
F = Frequency = Pn/120
Where P = Number of poles
n = revolutions per second of rotor.

From the expression it is clear that for the same frequency, number of poles
increases with decrease in speed and vice versa. Therefore, low speed hydro turbine
drives generators have 14 to 20 poles where as high speed steam turbine driven
generators have generally 2 poles. Pole rotors are used in low speed generators,
because the cost advantage as well as easier construction.




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Development

The first A.C. Generator concept was enunciated by Michael Faraday in 1831. In
1889 Sir Charles A. Parsons developed the first AC turbo-generator. Although slow
speed AC generators have been built for some time, it was not long before that the
high-speed generators made its impact.
Development contained until, in 1922, the increased use of solid forgings and
improved techniques permitted an increase in generator rating to 20MW at 300rpm.
Up to the out break of second world war, in 1939, most large generator;- were of the
order of 30 to 50 MW at 3000 rpm.
During the war, the development and installation of power plants was delayed and
in order to catch up with the delay in plant installation, a large number of 30 MW
and 60 MW at 3000 rpm units were constructed during the years immediately
following the war. The changes in design in this period were relatively small.
In any development programme the. Costs of material and labour involved in
manufacturing and erection must be a basic consideration. Coupled very closely
with
these considerations is the restriction is size and weight imposed by transport
limitations.

Development of suitable insulating materials for large turbo-generators is one of the
most important tasks and need continues watch as size and ratings of machines
increase. The present trend is the use only class "B" and higher grade materials and
extensive work has gone into compositions of mica; glass and asbestos with
appropriate bonding material. An insulation to meet the stresses in generator slots
must
follow very closely the thermal expansion of the insulated conductor without
cracking or
any plastic deformation. Insulation for rotor is subjected to lower dielectric stress
but
must withstand high dynamic stresses and the newly developed epoxy resins, glass
and/or asbestos molded in resin and other synthetic resins are finding wide
applications.


Generator component
This Chapter deals with the two main components of the Generator viz. Rotor, its
winding & balancing and stator, its frame, core & windings.

Rotor




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The electrical rotor is the most difficult part of the generator to design. It revolves in
most modern generators at a speed of 3,000 revolutions per minute. The problem of
guaranteeing the dynamic strength and operating stability of such a rotor is
complicated
by the fact that a massive non-uniform shaft subjected to a multiplicity of
differential
stresses must operate in oil lubricated sleeve bearings supported by a structure
mounted on foundations all of which possess complex dynamic be behavior peculiar
to
themselves. It is also an electromagnet and to give it the necessary magnetic strength
the windings must carry a fairly high current. The passage of the current through
the
windings generates heat but the temperature must not be allowed to become so high,
otherwise difficulties will be experienced with insulation. To keep the temperature
down,
the cross section of the conductor could not be increased but this would introduce
another problems. In order to make room for the large conductors, body and this
would
cause mechanical weakness. The problem is really to get the maximum amount of
copper into the windings without reducing the mechanical strength. With good
design
and great care in construction this can be achieved. The rotor is a cast steel ingot,
and
it is further forged and machined. Very often a hole is bored through the centre of
the
rotor axially from one end of the other for inspection. Slots are then machined for
windings and ventilation.

Rotor winding

Silver bearing copper is used for the winding with mica as the insulation between
conductors. A mechanically strong insulator such as micanite is used for lining the
slots. Later designs of windings for large rotor incorporate combination of hollow
conductors with slots or holes arranged to provide for circulation of the cooling gas
through the actual conductors. When rotating at high speed. Centrifugal force tries
to lift
the windings out of the slots and they are contained by wedges. The end rings are
secured to a turned recess in the rotor body, by shrinking or screwing and
supported at
the other end by fittings carried by the rotor body. The two ends of windings are


connected to slip rings, usually made of forged steel, and mounted on insulated
sleeves.

Rotor balancing



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When completed the rotor must be tested for mechanical balance, which means that
a
check is made to see if it will run up to normal speed without vibration. To do this it
would have to be uniform about its central axis and it is most unlikely that this
will be so to the degree necessary for perfect balance. Arrangements are therefore
made in all designs to fix adjustable balance weights around the circumference at
each
end.

Stator

Stator frame: The stator is the heaviest load to be transported. The major part of
this load is the stator core. This comprises an inner frame and outer frame. The
outer frame is a rigid fabricated structure of welded steel plates, within this shell is a
fixed cage of girder built circular and axial ribs. The ribs divide the yoke in the
compartments through which hydrogen flows into radial ducts in the stator core
and circulate through the gas coolers housed in the frame. The inner cage is usually
fixed in to the yoke by an arrangement of springs to dampen the double frequency
vibrations inherent in 2 pole generators. The end shields of hydrogen cooled
generators must be strong enough to carry shaft seals. In large generators the frame
is constructed as two separate parts. The fabricated inner cage is inserted in the
outer frame after the stator core has been constructed and the winding completed.
Stator core: The stator core is built up from a large number of 'punching" or
sections of thin steel plates. The use of cold rolled grain-oriented steel can contribute
to reduction in the weight of stator core for two main reasons:

a) There is an increase in core stacking factor with improvement in lamination cold
Rolling and in cold buildings techniques.

b) The advantage can be taken of the high magnetic permeance of grain-oriented
steels of work the stator core at comparatively high magnetic saturation without
fear or excessive iron loss of two heavy a demand for excitation ampere turns
from the generator rotor.




Stator Windings

Each stator conductor must be capable of carrying the rated current without
overheating. The insulation must be sufficient to prevent leakage currents flowing
between the phases to earth. Windings for the stator are made up from copper
strips wound with insulated tape which is impregnated with varnish, dried under
vacuum and hot pressed to form a solid insulation bar. These bars are then place in
the stator slots and held in with wedges to form the complete winding which is



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connected together at each end of the core forming the end turns. These end turns
are rigidly braced and packed with blocks of insulation material to withstand the
heavy forces which might result from a short circuit or other fault conditions. The
generator terminals are usually arranged below the stator. On recent generators
(210 MW) the windings are made up from copper tubes instead of strips through
which water is circulated for cooling purposes. The water is fed to the windings
through plastic tubes.


Generator Cooling System

The 200/210 MW Generator is provided with an efficient cooling system to avoid
excessive heating and consequent wear and tear of its main components during
operation. This Chapter deals with the rotor-hydrogen cooling system and stator
water cooling system along with the shaft sealing and bearing cooling systems.

Rotor Cooling System

The rotor is cooled by means of gap pick-up cooling, wherein the hydrogen gas in
the
air gap is sucked through the scoops on the rotor wedges and is directed to flow
along
the ventilating canals milled on the sides of the rotor coil, to the bottom of the slot
where
it takes a turn and comes out on the similar canal milled on the other side of the
rotor
coil to the hot zone of the rotor. Due to the rotation of the rotor, a positive suction as
well as discharge is created due to which a certain quantity of gas flows and cools
the
rotor. This method of cooling gives uniform distribution of temperature. Also, this
method has an inherent advantage of eliminating the deformation of copper due to
varying temperatures.


Hydrogen Cooling System

Hydrogen is used as a cooling medium in large capacity generator in view of its high
heat carrying capacity and low density. But in view of its forming an explosive
mixture with oxygen, proper arrangement for filling, purging and maintaining its
purity inside the generator have to be made. Also, in order to prevent escape of
hydrogen from the generator casing, shaft sealing system is used to provide oil
sealing.

The hydrogen cooling system mainly comprises of a gas control stand, a drier, an
liquid level indicator, hydrogen control panel, gas purity measuring and indicating
instruments,



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The system is capable of performing the following functions :


 Filling in and purging of hydrogen safely without bringing in contact with air.
 Maintaining the gas pressure inside the machine at the desired value at all the
times.
 Provide indication to the operator about the condition of the gas inside the
machine i.e. its pressure, temperature and purity.
 Continuous circulation of gas inside the machine through a drier in order to
remove any water vapour that may be present in it.
 Indication of liquid level in the generator and alarm in case of high level.

Stator Cooling System

The stator winding is cooled by distillate. Which is fed from one end of the machine
by Teflon tube and flows through the upper bar and returns back through the lower
bar of another slot?
Turbo generators require water cooling arrangement over and above the usual
hydrogen cooling arrangement. The stator winding is cooled in this system by
circulating demineralised water (DM water) through hollow conductors. The
cooling water used for cooling stator winding calls for the use of very high quality of
cooling water. For this purpose DM water of proper specific resistance is selected.
Generator is to be loaded within a very short period if the specific resistance of the
cooling DM water goes beyond certain preset values. The system is designed to
maintain a constant rate of cooling water flow to the stator winding at a nominal
inlet water temperature of 40 deg.C.




Rating of 95 MW Generator

Manufacture by Bharat heavy electrical Limited (BHEL)


Capacity - 117500 KVA
Voltage - 10500V
Speed - 3000 rpm
Hydrogen - 2.5 Kg/cm2
Power factor - 0.85 (lagging)
Stator current - 6475 A
Frequency - 50 Hz
Stator wdg connection - 3 phase




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Rating of 210 MW Generator

Capacity - 247000 KVA
Voltage (stator) - 15750 V
Current (stator) - 9050 A
Voltage (rotor) - 310 V
Current (rotor) - 2600 V
Speed - 3000 rpm
Power factor - 0.85
Frequency - 50 Hz
Hydrogen - 3.5 Kg/cm2
Stator wdg connection - 3 phase star connection
Insulation class - B




TRANFORMER


A transformer is a device that transfers electrical energy from one circuit to another
by magnetic coupling with out requiring relative motion between its parts. It usually
comprises two or more coupled windings, and in most cases, a core to concentrate
magnetic flux. An alternating voltage applied to one winding creates a time-varying
magnetic flux in the core, which includes a voltage in the other windings. Varying
the relative number of turns between primary and secondary windings determines
the ratio of the input and output voltages, thus transforming the voltage by stepping
it up or down between circuits. By transforming electrical power to a high-
voltage,_low-current form and back again, the transformer greatly reduces energy
losses and so enables the economic transmission of power over long distances. It has
thus shape the electricity supply industry, permitting generation to be located
remotely from point of demand. All but a fraction of the world‟s electrical power
has passed trough a series of transformer by the time it reaches the consumer.

Basic principles


                           The principles of the transformer are illustrated by
consideration of a hypothetical ideal transformer consisting of two windings of zero
resistance around a core of negligible reluctance. A voltage applied to the primary
winding causes a current, which develops a magneto motive force (MMF) in the core.
The current required to create the MMF is termed the magnetizing current; in the
ideal transformer it is considered to be negligible, although its presence is still
required to drive flux around the magnetic circuit of the core. An electromotive
force (MMF) is induced across each winding, an effect known as mutual inductance.
In accordance with faraday‟s law of induction, the EMFs are proportional to the
rate of change of flux. The primary EMF, acting as it does in opposition to the


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primary voltage, is sometimes termed the back EMF”. Energy losses An ideal
transformer would have no energy losses and would have no energy losses, and
would therefore be 100% efficient. Despite the transformer being amongst the most
efficient of electrical machines with ex the most efficient of electrical machines with
experimental models using superconducting windings achieving efficiency of
99.85%, energy is dissipated in the windings, core, and surrounding structures.
Larger transformers are generally more efficient, and those rated for electricity
distribution usually perform better than 95%. A small transformer such as plug-in
“power brick” used for low-power consumer electronics may be less than 85%
efficient. Transformer losses are attributable to several causes and may be
differentiated between those originated in the windings, some times termed copper
loss, and those arising from the magnetic circuit, sometimes termed iron loss. The
losses vary with load current, and may furthermore be expressed as “no load” or
“full load” loss, or at an intermediate loading. Winding resistance dominates load
losses contribute to over 99% of the no-load loss can be significant, meaning that
even an idle transformer constitutes a drain on an electrical supply, and lending
impetus to development of low-loss transformers. Losses in the transformer arise
from: Winding resistance Current flowing trough the windings causes resistive
heating of the conductors. At higher frequencies, skin effect and proximity effect
create additional winding resistance and losses. Hysteresis losses Each time the
magnetic field is reversed, a small amount of energy is lost due to hysteresis within
the core. For a given core material, the loss is proportional to the frequency, and is a
function of the peak flux density to which it is subjected. Eddy current
Ferromagnetic materials are also good conductors, and a solid core made from such
a material also constitutes a single short-circuited turn trough out its entire length.
Eddy currents therefore circulate with in a core in a plane normal to the flux, and
are responsible for resistive heating of the core material. The eddy current loss is a
complex function of the square of supply frequency and inverse square of the
material thickness. Magnetostriction Magnetic flux in a ferromagnetic material,
such as the core, causes it to physically expand and contract slightly with each cycle
of the magnetic field, an effect known as magnetostriction. This produces the
buzzing sound commonly associated with transformers, and in turn causes losses
due to frictional heating in susceptible cores. Mechanical losses In addition to
magnetostriction, the alternating magnetic field causes fluctuating electromagnetic
field between primary and secondary windings. These incite vibration with in near
by metal work, adding to the buzzing noise, and consuming a small amount of
power. Stray losses Leakage inductance is by itself loss less, since energy supplied to
its magnetic fields is returned to the supply with the next half-cycle. However, any
leakage flux that intercepts nearby conductive material such as the transformers
support structure will give rise to eddy currents and be converted to heat. Cooling
system Large power transformers may be equipped with cooling fans, oil pumps or
water-cooler heat exchangers design to remove heat. Power used to operate the
cooling system is typically considered part of the losses of the transformer




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Rating of transformer
Manufactured by Bharat heavy electrical limited
No load voltage (hv) - 229 KV
No load Voltage (lv) -10.5 KV
Line current (hv) - 315.2 A
Line current (lv) - 873.2 A
Temp rise - 45 Celsius
Oil quantity -40180 lit
Weight of oil -34985 Kg
Total weight - 147725 Kg
Core & winding - 84325 Kg
Phase - 3
Frequency - 50 Hz




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posted:9/14/2011
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Description: NTPC REPORT