Vocational training report

VOCATIONAL TRAINING REPORT
AT
“FARAKKA SUPER THERMAL POWER STATION”
From 25-06-2018 to 24-07-2018
REPORT MADE BY :- 1) ATUL RAJ
2) RISHI BANERJEE
3) ARUP KUMAR MONDAL (of ELECTRICAL ENGINEERING)
INSTITUTE NAME- UNIVERSITY INSTITUTE OF TECHNOLOGY
, BURDWAN UNIVERSITY
(DATE) (INSTRUCTOR SIGNATURE) (HR SIGNATURE)

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DECLARATION
We hereby declare that this is the original work carried
out by us. Whatever we have written inside the report is
what we have learned and understood during 25-06-2018
to 24-07-2018 at FARAKKA SUPER THERMAL POWER
STATION.
SIGNATURE:-
1) …………………………...
2) ……………………………
3) ……………………………

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Index
1) Introduction to NTPC……………………………………………………………………………………………
2) NTPC Farakka at a glance……………………………………………………………………………………..
3) Coal to Electricity………………………………………………………………………………………………….
4) Power plant Familiarization…………………………………....................................................................
i) Coal handling plant (CHP)
ii) 400 KV Switch Yard
iii) Boiler and it‟s auxiliaries
iv) Turbine and it‟s auxiliaries
v) Cooling Tower
vi) Chimney
5) Electrical equipments in power plant…………………………………………………………………….
i) Generator
ii) Transformer
iii) Motor

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1
Introduction to NTPC
NATIONAL THERMAL POWER CORPORATION which is commonly known as NTPC was
set up in the central sector on the 7th
november 1975 in response to widening demand & supply gap
with the main objective of planning, promoting & organizing an integrated development to thermal
power in India. Ever since it‟s inception, NTPC has never looked back and the corporation is treading
steps of success one after the other . The only PSU to achieve the exce- llent rating in respect to MOU
targets signed with govt. of India each year . NTPC is Lighting up one fourth of the nation, NTPC has
an installed capacity of 53,651 MW from it‟s commitment to provide quality power; all NTPC
power stations have been certified for ISO 14001 & OHSAS 18001 by reputed national and
international certifying agencies.The services like engineering, contracts, materials and operation
services have also bagged the ISO 9001 Certification. NTPC Farakka, Kahalgaon, Vindhyachal and
Korba Station have also bagged ISO 14001 Certification. Today NTPC contributes more than 3/5th of
the total power generation in India.
NTPC Limited is the largest thermal power generating company of India. NTPC ranked 317th
in
the „2009 Forbes Global 2000‟ ranking of the world‟s biggest companies.NTPC ranked 25th
in great
places to work in india-moves up from 38th
(2017) to 25th
(2017). Within a span of 43 years , NTPC
has emerged as a truly national power company, with power generating facilities in all the major
regions of the country. Apart from power generation from coal and gas, it has also diversified into
hydro power, coal, mining, power equipment, manufacturing, oil and gas exploration, consultancy in
the area of the power plant construction and generation, power handling, distribution in the form of
joint ventures and various other entities in the India and abroad. NTPC operates from 55 locations in
India, one location in Sri Lanka and 2 locations in Bangladesh.

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NTPC Plants(coal based) and their Capacity:-
Sr. No. COAL BASED(Owned by NTPC) STATE COMMISSIONED CAPACITY(MW)
1. Singrauli Uttar Pradesh 2,000
2. Korba Chhattisgarh 2,600
3. Ramagundam Telangana 2,600
4. Farakka West Bengal 2,100
5. Vindhyachal Madhya Pradesh 4,760
6. Rihand Uttar Pradesh 3,000
7. Kahalgaon Bihar 2,340
8. Dadri Uttar Pradesh 1,820
9. Talcher Kaniha Orissa 3,000
10. Feroze Gandhi, Unchahar Uttar Pradesh 1,550
11. Talcher Thermal Orissa 460
12. Simhadri Andhra Pradesh 2,000
13. Tanda Uttar Pradesh 440
14. Badarpur Delhi 705
15. Sipat Chhattisgarh 2,980
16. Mauda Maharashtra 2,320

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17. Barh Bihar 1320
18. Bongaigaon Assam 500
19. Kudgi Karnataka 2400
20. Solapur Maharashtra 660
21. Lara Chhattisgarh 800
Total 40,355
Other than this NTPC have many other joint ventures with several other companies of generating
capacity 7,551 MW , Gas based power plants of generating capacity 5,984 MW ,Hydro power plant of
generating capacity 808 MW also NTPC is instaling 50 MW Wind Power project in Rajmol Gujrat .

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2
NTPC Farakka at a glance
Farakka Super Thermal Power Plant is located at Nabarun in Murshidabad district in Indian state
of West Bengal. The power plant is one of the coal based power plants of NTPC. Details of the plant
are as follows.
Address: P.O.-Nabarun (742236) , Dist.- Murshidabad , West Bengal
Approved Capacity: 2100 MW
Installed capacity: 2100 MW
Coal Soure; Rajmahal Coal Fields of ECL ,BCCl, Jharia , Raniganj
Water Source: Farakka feeder canal
Beneficiary States: West Bengal , Bihar, Jharkhand , Orissa , Sikkim, Assam,
Tripura & Damodar valley corporation.
Approved Investment: Stage-I : Rs. 730.93 cr.
Stage-II : Rs. 2453.29 cr.
Unit Sizes: Stage-I: 3*200 MW
Stage-II : 2*500 MW
Stage-III: Expansion of Farakka STPP is approved with the addition of one 500 MW unit.
Units commissioned: Unit-I: 200 MW – January 1986
Unit-II: 200 MW – December 1986
Unit-III: 200MW- August 1987
Unit-IV : 500MW- September 1992
Unit-V: 500MW- February 1994
Unit-VI: 500MW- March 2011

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3
Coal to Electricity
Energy of coal is converted into electricity through following stages.
CC
Basically the conversion of chemical energy to electrical energy is based on the Modified rankine
cycle with reheat and regeneration.
Modified Rankine cycle with reheat and regeneration
In a coal based power plant coal is transported from coal mines to the power plant by railway in
wagons or in a merry-go-round system. Coal is unloaded from the wagons using track hopper or
waggon trippler to a moving underground conveyor belt. Generally Bituminous type coal is used in
thermal power plant because of the fact that it is having high percentage of volatile material, which
helps in proper combustion of the coal. This coal from the mines is of no uniform size. So it is taken
to the Crusher house and crushed to a size of 20mm. From the crusher house the coal is either stored
in yard( generally 30 days coal supply) which serves as coal supply in case of coal supply bottleneck
or to the live storage(8 hours coal supply) in the raw coal bunker in the boiler house. Raw coal from
the raw coal bunker is supplied to the Coal Mills by a Raw Coal Feeder.Feeder is used to control the
supply of coal to mill according to power demand. The Coal Mills or pulverizer pulverizes the coal to
200 mesh size. The powdered coal from the coal mills is carried to the boiler in coal pipes by high
pressure hot air which is supplied by PA fan, the air supplied by the PA fan is having temperature of
35 deg. C. which is made to pass through Air pre heater .In case if we don‟t use APH then there
might be a case where proper combustion of coal will not take place or quinching of flame can take
place. Similarly Secondary air is supplied by FD fan which is made to pass through APH. The
pulverized coal air mixture is burnt in the boiler in the combustion zone. Oil used for ignition energy
Chemical
energy
Thermal
energy
Rotational
energy
Electrical
energy

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is HFO oil. Generally in modern boilers tangential firing system is used i.e. the coal nozzles/ guns
form tangent to a circle. The temperature in fire ball is of the order of 1400 deg.C. The boiler is a
water tube boiler hanging from the top. DM water is converted to steam in the boiler by convection
and radiation energy and steam is separated from water in the boiler Drum. If we don‟t use DM water
in the boiler tubes then it‟ll lead to the overheating of boiler tubes ,as a result of it the tube may get
damaged. The saturated steam from the boiler drum is taken to the Low Temperature Superheater,
Platen Superheater and Final Superheater respectively for superheating. The superheated steam from
the final superheater is taken to the High Pressure Steam Turbine (HPT). In the HPT the steam
pressure is utilized to rotate the turbine and the resultant is rotational energy. In furnace , due to the
combustion Ash is formed . 20% of the ash comes down through hopper which is then sent to the ash
pond and can be utilized for road feeling and other purposes, 80% of the ash formed is fly ash which
is collected by ESP whose electrodes are +vely charged and can be used in cement factory. From the
HPT the out coming steam is taken to the Reheater in the boiler to increase it‟s temperature as the
steam becomes wet at the HPT outlet. After reheating this steam is taken to the Intermediate Pressure
Turbine (IPT) and then to the Low Pressure Turbine (LPT). The outlet of the LPT is sent to the
condenser for condensing back to water by a cooling water system. This condensed water is collected
in the Hotwell and is again sent to the boiler in a closed cycle. The rotational energy imparted to the
turbine by high pressure steam is converted to electrical energy in the Generator.
Coal based Thermal power plant

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4
Power Plant Familiarization
A thermal power station consists of all the equipment‟s and a subsystem required to produce
electricity by using a steam generating boiler fired with fossil fuels or befouls to drive an electric
generator. Some prefer to use the term ENERGY CENTER because such facilities convert form of
energy like nuclear energy, gravitational potential energy or heat energy (derived from the
combustion of fuel) into electrical energy. Following are the major parts of a thermal power plant.
1) Coal handling plant (CHP)
2) 400 KV Switch Yard
3) Boiler and it‟s auxiliaries
4) Turbine and it‟s auxiliaries
5) Cooling Tower
6) Chimney
1 - COAL HANDLING PLANT :
The fuel used in the NTPC farakka thermal power station is coal therefore it is necessary to handle
this fuel carefully and deliver it safely to the site of power plant. A railway siding line is taken into the
power station and coal is delivered to storage yard. Total CHP area is 4.5 SQ km.
MAJOR COMPONENTS
(i)- Wagon Tripler- 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.
(ii)- Conveyer- There are 72 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. 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.
(iii)- 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
(iv)- Metal Separator- 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

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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.
(v)- Crusher- The 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. There are total 8 crusher in the plant.
(vi)- 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. OCHP uses
a technique that crushes the larger of harder substance like metal impurities easing the load on the
magnetic separators.
COAL HANDLING PLANT OF NTPC FARAKKA
MILLING SYSTEM
(i)- 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 13-14m.
(ii)- 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.
(iii)- 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.
(iv)- Worm Conyever- 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.
(v)- Mills Fans- They are of 3 types. They are all in running conditions all the time.
ID Fans- located between the electrostatic precipitator and chimney.
Type-radial Speed-1490 rpm Rating-300KW Voltage- 6.6KV
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
Primary Air Fans- Designed for handling the atmospheric air up to 50 degrees Celsius, 2 in

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number and they provide powered coal to burner to firing
Type-Double section radial Rating-300KW Voltage-6.6KV
2- 400 KV SWITCH YARD :
It is a switching station which has the following credits:
(i) Main link between generating plant and Transmission system, which has a large influence on the
security of the supply.
(ii) Step-up and/or Step-down the voltage levels depending upon the Network Node.
(iii) Switching ON/OFF Reactive Power Control devices, which has effect on Quality of power.
SWITCHYARD EQUIPMENTS
(i) Transformers: Transformer transforms the voltage levels from higher to lower level or vice versa,
keeping the power constant. Inter connecting transformer (ICT) are used to connect 400KV
switchyard to 132KV switchyard.
(ii) Circuit breakers: Circuit breakers makes or automatically breaks the electrical circuits under
loaded condition(On load device).
(iii) Isolators: Opens or closes the electrical circuits under No-load conditions(Off load device).
(iv) Instrument transformers : Instrument transformers are used for stepping-down the electrical
parameter (Voltage or Current) to a lower and safe value for Metering and Protection logics.
CTs are single phase oil immersed type.secondary current is generally 1A, but also 5A in certain cases
, we never keep CT secondary as open because a very high voltage will be generated at CT secondary.
The VTS are used at 220KV & above. For lower voltages electromagnetic type transformers are
mostly used. We never short circuit VT secondary because a very high current will flow.
(v) Earth switch: Earth switches are device which are normally used to earth a particular system to
avoid accident, which may happen due to induction on account of live adjoining circuits. These don‟t
handle any appreciable current at all.
(vi) Lightning arrestors: station type “lightening arresters” are provided at the terminals of the
transformers for protection against lightening or any surges developing in the system, the practice is
also to install lightening arresters at the incoming terminals of the line. Shielding of substation from
direct lightening stroke is provided through earth wires located at structures „peaks‟. Recently masts
are also used for the purpose of shielding substation.
Generator transformers and 400 KV bushes gets
connected to each other in One & half breaker
bus system.

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(vii) Circuit Breaker:
Types of breaker in NTPC switchyard
1- 400 KV Air Blast circuit breaker
2- 220kv SF6 Filled circuit breaker
Air Blast 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.
SF6 Filled 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 of 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.
3- BOILER AND IT’S AUXILIARIES:
Water tube boiler is used in the thermal power plant. A water tube boiler is such kind of boiler where
the water is heated inside tubes and the hot gasses surround them. There are many advantages of
water tube boiler due to which these types of boiler are essentially used in large thermal power
station.
(i) Larger heating surface can be achieved by using more numbers of water tubes.
(ii) Due to convectional flow, movement of water is much faster than that of fire tube boiler, hence
rate of heat transfer is high which results into higher efficiency.
(iii) Very high pressure in order of 140 kg/cm2
can be obtained smoothly.
Following are the auxiliaries of a Water tube boiler.

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(i) Boiler Feed 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. 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.
(ii)- Boiler 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.
(iii) ID , FD & PA Fans:
ID , FD & PA Fans together maintains the pressure inside the boiler.
PA FAN- Primary air fan(PA Fan) is used to transport the pulverized coal from mills to the furnace
area. So its main function is the carry the fuel to the furnace for the combustion.
FD FAN- The Forced Draft Fan (FD Fan) is a fundamental part of most boiler systems and is the
element responsible for creating draft inside of the boiler.
ID FAN- A fan is used to extract the air from boiler post combustion via Electrostatic Precipitator to
exhaust through the chimney. This is called ID fan.
(iv) Electrostatic Precipitator(ESP):
The flue gases produced due to combustion of solid pulverized fuel in the furnace contain plenty of
dust particles. When a chimney releases these flue gases in the atmosphere without filtering these dust
particles, the atmosphere may get polluted. Hence, these dust particles need to be removed from the
flue gases as much as possible before these flue gases get discharged to the atmosphere. By removing
the dust particles from flue gases, we can control the air pollution. Electrostatic precipitator does this
work for a furnace system. We install this device in the way of flue gases from the furnace to the
chimney so that the device can filter the flue gases before they enter the chimney.
(v) Reheater:
A reheater is basically a superheater that superheats steam exiting the high-pressure stage of a turbine.
The reheated steam is then sent to the low-pressure stage of the turbine. By reheating steam between
high-pressure and low-pressure turbine it is possible to increase the electrical efficiency of the power
plant cycle beyond 40%.The reheat cycle is used in large power boilers since it is feasible
economically only in larger power plants. Reheater design is very much similar to superheater
design because both operate at high temperature conditions.
(vi) Economiser:
An economiser is a mechanical device which is used as a heat exchanger by preheating a fluid to
reduce energy consumption. In a steam boiler, it is a heat ex-changer device that heats up fluids or
recovers residual heat from the combustion product i.e. flue gases in thermal power plant before being
released through the chimney. Flue gases are the combustion exhaust gases produced at power plants
consist of mostly nitrogen, carbon dioxide, water vapor, soot carbon monoxide etc. Hence, the
economiser in thermal power plants, is used to economise the process of electrical power generation,
as the name of the device is suggestive of. The recovered heat is in turn used to preheat the boiler feed

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water, that will eventually be converted to super-heated steam. Thus, saving on fuel consumption and
economising the process to a large extent, as we are essentially gathering the waste heat and applying
it to, where it is required.
(vii) Air Pre-heater(APH):
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 flue gas. As a consequence, the
flue gases are also conveyed to the chimney at a lower temperature, allowing simplified design of the
conveyance system and the flue gas stack. It also allows control over the temperature of gases leaving
the stack (to meet emissions regulations, for example).It is installed between the economizer and
chimney.In power plant we use APH to heat the primary air and secondary air so that moisture of air
can be removed before entering to the Boiler.
(viii) Superheater:
A superheater is a device used to convert saturated steam or wet steam into superheated steam or dry
steam. There are three types of superheaters used in the modern power plant.
--- Low temperature superheater(LTSH)
--- Platen superheater
--- Final superheater(FSH).
4- TURBINE AND IT’S AUXILIARIES:
Turbine, any of various devices that convert the energy in a stream of fluid into mechanical energy.
The conversion is generally accomplished by passing the fluid through a system of stationary
passages or vanes that alternate with passages consisting of finlike blades attached to a rotor. By
arranging the flow so that a tangential force, or torque, is exerted on the rotor blades, the rotor turns,
and work is extracted. Three stage reaction turbine is used in the power plant, The stages are LP
turbine,IP turbine & HP turbine.
(i) Low pressure(LP) Turbine:
Each LP Turbine (low-pressure turbine) is usually double-flow reaction turbine with about 5-8 stages
(with shrouded blades and with free-standing blades of last 3 stages). LP turbines produce
approximately 60-70% of the gross power output of the power plant unit.
(ii) Intermediate pressure(IP) Turbine:
It is a double flow turbine. The hot reheat from HP turbine goes to the IP turbine. It has total 2×12
stages.
(iii) High pressure(HP) Turbine:
It is a single flow turbine having total 17 stages. The M.S. line at 540 degree c enters the HP turbine
which then gets expanded and goes to the reheater as cold reheat line.
(iv) Condenser:
Condenser uses cooled water to condense the vapours. Cooled water is produced in a cooling tower
and is pumped to condenser. When vapours are brought in contact with cooled water, temperature of
vapours gets reduced as a result vapours gets condensed. In thermal power plants, the purpose of a
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 (referred to as steam condensate) so that it
may be reused in the steam generator or boiler as boiler feed water.
(v) Deaerator:
A deaerator is a device that is widely used for the removal of oxygen and other dissolved gases from
the feedwater to steam-generating boilers.
(vi) 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.

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(vii) Turbine Blades:
A turbine blade is the individual component which makes
up the turbine section of a gas turbine or steam turbine. The
blades are responsible for extracting energy from the high
temperature, high pressure steam.
5- COOLING TOWER:
A cooling tower is a specialized heat
exchanger in which air and water are
brought into direct contact with each other
in order to reduce the water's temperature.
As this occurs, a small volume of water is
evaporated, reducing the temperature of the
water being circulated through the tower.
There are four types of cooling tower
--- Natural draught
--- Mechanical draught
--- Cross flow towers
--- Counter flow towers
In NTPC Farakka Natural draught cooling tower is used.
6- CHIMNEY:
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 vapour 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.Generally diameter of the
chimney at bottom is 7m and at the top is 21m.

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5
Electrical Equipments In Power Plant
1- GENERATOR: A generator is a device which converts mechanical energy into electrical
energy.At NTPC Farakka there are two types of generator, for 200MW set the generator terminal
voltage is 15.75KV and for 500MW set the generator terminal voltage is 21KV.
Generator Components- This deals with the two main components of the Generator viz. Rotor, its
winding , stator, its frame, core & windings and cooling system.
(i) Rotor:
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 rpm. 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
them. 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 therotor axially from
one end of the other for inspection. Slots are then machined for windings and ventilation
(ii) 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.
(iii) Stator:
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.

P a g e | 18
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.
(iv) Stator Winding:
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
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.
(v) 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.
Hydrogen Cooling - Hydrogen is used as a cooling medium for rotor in large capacity generator in
view of its high heat carrying capacity and low density. But in view of it‟s 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.
The system is capable of performing the following functions:
I). Filling in and purging of hydrogen safely without bringing in contact with air
II). Maintaining the gas pressure inside the machine at the desired value at all the times.
III). Provide indication to the operator about the condition of the gas inside the machine i.e. its
pressure, temperature and purity.
IV). Continuous circulation of gas inside the machine through a drier in order to remove any water
vapor that may be present in it.
V). Indication of liquid level in the generator and alarm in case of high level.

Stator Cooling System- The stator winding is cooled by distillate. 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 400C.
(vi) Excitation System:
Excitation system is used to control the generator terminal voltage as per the demand.Two types of
excitation system are used in the power plant,
a) Static Excitation: At NTPC Farakka this type of excitation system is used for 200MW generator
set. In this type of system the output from the generator terminal is converted to 575 volts using an
excitation transformer, Then the output from ET is feed to the thyristor bank to convert the AC power
into DC. The DC power is then feed to the field winding through brushes,sliprings and field
breaker.Initially when the plant is not in running condition then the power is taken by Field flashing
circuit which consists of a FF contactor , a thyristor bank and a step down transformer.

P a g e | 19
b) Brushless Excitation: This type
of system is used for 500 MW
generator set. It consists of a
permanent magnet generator which is
mechanically coupled with the main
exciter(a synchronous generator)
.Field winding of Main Exciter is
feed from the permanent magnet
generator through a thyristor circuit.
From Main Exciter the power is feed
to the field winding through a
rotating diode circuit , coupled with
main exciter and rotor of the
generator.
2-TRANSFORMER:
A transformer is a device that transfers electrical energy from one circuit to another by magnetic
coupling without 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.In a power plant several types of transformer are used ,
those are-
Generator Transformer(GT): Power transformers are the backbone of the large grid. The power is
generated at the low voltage level and has to be carried to far away load centers. Typically the power
is generated at the Pit heads i.e power source like coal, water. It is uneconomical carry the bulk power
at low voltage levels. Depending upon the requirement the voltage level is stepped upto the
transmission level i.e 220 or 400kV. At higher voltages the transmission losses are less. Similarly at
the remote end the voltage is stepped down the distribution level. To accomplish the task Power
transformers are installed and act as bi-directional element in the system.At NTPC Farakka for
200MW set GT of rating 200MVA is used where as in case of 500MW set for each phase 200MVA
single phase GT is used. If we‟ll use a single GT of rating 600MVA in case of 500MW set ,then the
size of GT will be huge as a result of it transportation and maintainance will be difficult. All these
transformers are star- star connected transformers with neutral solidly grounded.Each of these
transformers are provided with lightning arrestor to protect the transformer from lightning stroke. A
third winding called tertiary winding at much lower voltage i.e 33kV, is also provide and is connected
in delta to facilitate the flow of third harmonic current to reduce the distortion in the output voltage.
To reduce the overall size of the transformer, the transformer is provided with Oil forced and Air
forced type cooling at its 100% rating. However, to save the energy, the cooling system is controlled
by the temperature of the winding. The transformers are also equipped with On Load Tap Changer to
meet the change in voltage variation.

P a g e | 20
200MVA
GENERATOR
TRANSFORMER
Unit Auxiliary Transformer (UAT)
The UAT draws its input from the main bus duct connecting generator to the generator transformer. It
is used for the working of large devices such as boilers, heavy motors etc. The total kVA capacity of
UAT required can be determined by assuming 0.85 power factor and 0.9 efficiency for total auxiliary
motor load. For large units, it has become necessary to use more than one auxiliary transformer. The
maximum short circuit currents on auxiliary bus should be limited with in the maximum switch gear
rating available. The maximum permissible voltage dip while starting the largest single auxiliary
motor, usually boiler feed pump, shall remain within acceptable limits.Each GT is provided with two
UAT‟s.UAT decreases the voltage level to 6.6KV to run the plant drives.
Station Transformer (ST)
Station transformer is used to feed the power to the auxiliaries during the start up. This transformer
normally rated for the initial auxiliary load requirements of unit. In physical cases this load is of order
of 60% of the load at full generating capacity. It is also provided with on load tap changer to cater to
the fluctuating voltage of the grid.This transformer steps down the voltage level from 33KV to
6.6KV.
Connection
diagram of
GT,UAT,S
T and TT

P a g e | 21
COOLING OF TRANSFORMER
Heat is produced in the winding due to the current flowing in the conductors (I^2*R) and in the core
on account of eddy currents and hysteresis losses. In small dry type transformer heat is dissipated
directly to the atmosphere. In oil immersed transformer heat is dissipated by THERMO SIPHON
ACTION. The purpose of using oil is:-
1. Cooling: Provides a better cooling and helps in exchanging heat
2. Insulation: A non-conductor of electricity so good insulator. The oil used is such that its flash
point is pretty high so that it doesn‟t have any possibility to catch fire. The oil serves as the medium
for transferring the heat produced inside the transformer to the outside transformer
There are various types of cooling:-
1. AN – Air Natural
2. ON – Oil Natural
3. AF – Air forced
4. OF – Oil forced
5. ONAF – Oil natural Air forced
6. OFAN - Oil forced Air natural
7. OFAF – Oil forced Air forced
TRANSFORMER ACCESSORIES
Conservator:
With the variation of temperature there is corresponding variation in the oil volume.To account for
this an expansion vessel called conservator is added to the transformer with a connecting pipe to the
main tank. It is also used to store the oil and make-up of the oil in case of leakage.
Breather:
In conservator the moisture from the oil is excluded from the oil through breather it is a silica gel
column, which absorbs the moisture in air before it enters the conservator air surface.
Radiator:
This a chamber connected to the transformer to provide cooling of the oil. It has got fans attached to it
to provide better cooling.
Buchholz Relay:
Buchholz relay in transformer is an oil container housed the connecting pipe from main tank to
conservator tank. It has mainly two elements. The upper element consists of a float. The float is
attached to a hinge in such a way that it can move up and down depending upon the oil level in
theBuchholz relay Container. Buchholz relay is used for the protection of transformers from the faults
occurring inside the transformer. Short circuit faults such as inter turn faults, incipient winding faults,
and core faults may occur due to the impulse breakdown of the insulating oil or simply the
transformer oil.It is a mechanical relay.
Bushing:
When an energized conductor is near any material at earth potential, it can cause very high field
strengths to be formed, especially where the field linesare forced to curve sharply around the earthed
material. The bushing controls the shape and strength of the field and reduces the electrical stresses in
the insulating material.
Transformer Core:
In all types of transformer construction, the central iron core is constructed from of a highly
permeable material made from thin silicon steel laminations. These thin laminations are assembled
together to provide the required magnetic path with the minimum of magnetic losses.

P a g e | 22
3-MOTOR :
Most of the motors in power plant are squirrel cage induction motor , DC motors are also used in few
cases. Induction motor of 6.6KV voltage rating are used in the plant to operate ID Fan,FD Fan,PA
Fan, Mill , CW pump etc. DC Motors of 415V rating are used to operate DC seal oil pump(for
Generator, BFP etc.) , DC Jacking oil pump for turbine etc.

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