National thermal power corporation
Published on: Mar 3, 2016
Transcripts - National thermal power corporation
B.TECH 4th YEAR (ELECTRICAL AND ELECTRONICS ENGINEERING),G.L.A.I.T.M
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 the balance 10.5% is held by FIIs, Domestic
Banks, Public and other. Within a span of 32 years, NTPC has
emerged as a truly national power company, with power
generating facilities in all the major regions of the country.
Feroze Gandhi Unchahar Thermal Power Project
conceived as a load center station by the U.P. government for
the benefit of the stage and is stated to have the ultimate
capacity of 1050 MW (5*210 MW) stages of the project
consisting of two units of 210 MW each was implemented by
Unit 1 -21 NOV 1988
Unit 2 -22 MARCH 1989
Unit 3 -27 JAN 1999
Unit 4 -22 OCT 1999
ABOUT STPP UNCHAHAR
Foundation stone was laid by Late Prime Minister Mrs.
Indira Gandhi in June 1981.
First two units of 210 MW were commissioned on
November, 1988 and 22nd
March, 1989 by U.P. Rajya
Vidyut Utpadan Nigam.
FGUTPP was handed over by U.P. Rajya Vidyut Utpadan
Nigam to NTPC in 13th
After take over of FGUTPP from UPRVUN to NTPC, unit-
3, unit-4 and unit-5 were commissioned on 27th
October 1999 and 2006 respectively.
NTPC has been ranked first as per total income in the
power generation, transmission, distribution sector among
India’s top 500 companies for the year 2006 by Dun and
PRINCIPLE OF STEAM POWER PLANT
The working principle of a steam plant is based upon the
Rankine cycle. Generally steam is taken as the working
medium due to its ability to be stable and that it’s readily stable.
The flow of steam in the plant can be very easily be understood
by the flow diagram of the plant. A graph plotted between the
temperature and the entropy would indicate the technical
details of the working by the Rankine cycle.
Plant Flow Diagram(Modified Rankine
AB- Heating of feed water (i.e. sensible heat addition)
BC- Evaporation of water in boiler (i.e. latent heat addition)
CD- Superheating of steam (i.e. heat addition)
DE- Isentropic expansion of steam in HP turbine
EF- Reheating of steam in Reheaters
FH- Isentropic expansion of steam in IP and LP turbine
VARIOUS PATH IN POWER PLANT
1. Coal Cycle:
Railway wagon power house wagon tipplercoal
hopper CHP conveyor belt crusher house conveyor
belt coal stockyard or RC bunker RC feeder pulverised
2. Feed water cycle :
Deaerator boiler feed pump Hp heatereconomiser
Condensate water cycle :
Condenser hot well condensate extraction pump gland
steam cooler LP heater deaerator
1. Steam cycle :
Boiler drum LT SH platen SH final SH HP turbine
reheater IP turbine LP turbine condenser
1. Air Path :
P.A. fan air heater & cold P.A. fan mill furnace
1. Flue gas path :
Furnace reheater economiser air preheater E.S.P.
I.D. fan chimney atmosphere
PLANT LAYOUT AT UNCHAHAR
The fuel used in the thermal power plants in the boiler
furnace is coal. Coal undergoes various processes like
separation, crushing, etc and is then finally moved to the
furnace in the form of pulverised coal.
Coal: It is a mixture of organic chemicals and mineral materials
produced by natural process of growth and decay. The
chemical properties of any coal depend upon the proportions of
different chemicals components present in it. There are four
types of coal:
3. Bituminous Coal
DEMINERALIZE WATER PLANT
Water is required in plant for many purposes like for formation
of steam, for removal of ash, for safety during fire etc. But the
water required for formation of steam should be perfectly
devoid of minerals because if it would be present with the
steam then it will strike the blades of turbine and due to being in
high pressure it produces scars or holes on the turbine blades.
Water is purified in DM plant through a chain of processes as
1. Carbon filter -: Water taken from river is first sent to the
carbon filter for the removal of carbon content in the water.
2. Strong acid cation exchanger-: After passing through the
carbon filter water is sent to the strong acid cation exchanger
which is filled with the concentrated HCL. The acid produces
anions which get combined with the cations present in the
1. Strong base anion exchanger-: After passing though the
two chambers of strong acid cation exchanger water is sent
to the stron base anion exchanger which is filled with the
concentrated NaOH. The base produces cations which get
combined with the anions present in the water.
2. Mixed bed exchanger -: At last water is sent to the chamber
of mixed bed exchanger where the remaining ions are
→ → → →
Boiler drums → Ring Header → Boiler Drum (Steam
chamber) → Super Heater → H.P. Turbine → Reheater → I.
P. Turbine → L.P. Turbine.
Boiler drum consist two chamber water chambers, steam
chamber. Before entering in super heater the steam is going in
to boiler drum, where the boiler drum filtered the moisture and
stored in to water chamber.
The function of super heater is to remove the last traces of
moisture from the saturated steam leaving the water tube
boiler. The temperature is approx 5300
Steam turbine converts the heat energy in to mechanical
energy and drives on initial and final heat content of the steam.
Turbine having number of stage in WHICH the pressure drops
DIAGRAM OF WATER TUBE BOILER
Furnace is placed at the bottom of the most important part
of the thermal plant where steam is generated. The boiler used
at FGUTPP is the water tube boiler type in which, water
circulates in tubes surrounded by fire. Hence it takes up heat
and gets converted into steam. The steam then rises up and
gets collected inside the boiler drum. The boiler is made up of
carbon steel. The temperature of steam that comes out of the
boiler is around 5300
Celsius and its pressure is 120kg/cm2
The type of boiler can be further elaborated as natural
circulation, dry bottom, and tangential fired, radiant heat type
with direct fired pulverised coal system.
Once the steam is produced in the boiler, it gets collected
inside the boiler drum. Boiler drum is a special type of
cylindrical drum like structure which contains a mixture of water
and steam. Steam being lighter gets collected at the top portion
and beneath it we have the water. It is very important to
maintain a safe level of water in the drum since we have two
main types of constraints in this regard. If the steam produced
and collected is more then it can lead to a blast in the boiler
drum else tiny droplets of water can enter the turbine. Hence in
order to keep a check we measure the level by hydrastep.
Hydrastep is based on the difference in the conductivities of
water and steam.
Soot blowers are basically pipe like structures that go
inside the furnace and the boiler for efficient cleaning. Cleaning
is done by the superheated steam which is tapped from the
superheater for the purpose of soot blowing. The pressure is
reduced to 31kg/cm2
at 330 deg Celsius by means of reducing
valve. We mainly have three types of soot blowers:
1. long retraceable soot blower
2. wall blower
3. air reheater
Before sending this steam to the turbine, the steam is again
superheated and then its temperature is around 5800
This increases the efficiency since the temperature is the
measure of energy hence higher temperature higher is the
energy. Hence, during the phenomenon of superheating the
steam which is dry and saturated, is being heated and hence
the temperature of steam again rises.
First the steam from boiler drum enters the low temperature
super heater (LTSH). After LTSH steam enters the platen
superheater and then finally to a high temperature superheater.
The steam which is now produced goes to the HP turbine.
The superheated steam after coming out of the superheater
goes to the turbine. A turbine is a form of an engine running on
steam, which requires a source of high grade energy and a
source of low grade energy. When the fluid flows through the
turbine a part of the energy content is continuously extracted
and continuously converted into useful mechanical work.The
main advantage of using a steam turbine rather than a prime
mover is that the steam in a turbine can be expanded down to a
lower back pressure, thereby making available a greater heat
drop and a larger amount of this heat drop can be converted
into useful mechanical work due to higher efficiency of the
turbine. Therefore a turbine is suitable for driving a generator.
Turbines are of two types:
1. Impulse Turbine
2. Reaction Turbine
However another form called impulse-reaction turbine is also
used which provide benefits of both types. The impulse-
reaction turbine is used here at FGUTPP.
Here three stages of turbine are used:
HP turbine (high pressure)
IP turbine (intermediate pressure)
LP turbine (low pressure)
View Of Steam Turbine
The steam flow in the turbine takes place as follows; the
steam from the superheater first goes to the HP turbine where it
does work and loses its temperature. The steam from HP
turbine is the fed to the reheater where its temperature is
increased pressure remains the same as that from the outlet
from HP turbine. The steam from the reheater is then fed to the
IP turbine and then finally to the LP turbine. The LP turbine is
connected to the generator and the mechanical output from the
turbine is used to drive it.
ASH HANDLING PLANT
1. Ionisation of gases and charging of particles.
2. Migration of particles to respective electrodes.
3. Deposition of particles on the electrodes.
4. Dislodging of particles from the electrodes.
The ESP consist of two sets of electrodes, one in the form
of helical thin wires called emitting electrode which is connected
to -70KV DC and the collecting electrode in grounded.
The following mechanism takes place electrically:
Emitter electrode (E) creates a strong electric field near the
surface and corona discharge takes place.
Positive and negative ions are formed by this discharge.
The positive ions move towards anti positive charge line
electrodes called emitting electrodes and the negative ions
towards collecting electrodes.
During this passage ions collide with ash particles and
adhere to them.
These charged particles stick on the collector curtain which
is the dislodged by the rapping motors which is collected by
For optimum functional efficiency of the precipitator the
supply voltage should be maintained near above the flash over
level between electrodes. This is achieved by the electronic
control. The efficiency of ESP is about 99.95%.
ELECTRICAL MAINTENANCE DEPARTMENT – I (EMD-I)
High Tension/Low Tension Switchgear
Coal handling plant
Squirrel cage motor
Slip ring induction motor
In modern thermal power plant three phase squirrel cage induction motors are used but sometime
double wound motor is used when we need high starting torque e.g. in ball mill.
THREE PHASE INDUCTION MOTOR
Ns (speed) =120f/p
Stator can handle concentrated single layer winding, with each coil occupying one stator slot
The most common type of winding are:
DISTRIBUTED WINDING :
This type of winding is distributed over a number of slots.
DOUBLE LAYER WINDING :
Each stator slot contains sides of two different coils.
SQUIRREL CAGE INDUCTION MOTOR
Squirrel cage and wound cage have same mode of operation. Rotor conductors cut the rotating
stator magnetic field. an emf is induced across the rotor winding, current flows, a rotor magnetic field
is produced which interacts with the stator field causing a turning motion. The rotor does not rotate
at synchronous speed, its speed varies with applied load. The slip speed being just enough to enable
sufficient induced rotor current to produce the power dissipated by the motor load and motor losses.
BEARINGS AND LUBRICATIONS
A good bearing is needed for trouble free operation of motor. Since it is very costly part
of the motor, due care has to be taken by checking it at regular intervals. So lubricating
plays an important role. Two types of lubricating are widely used
Winding is an essential part so it should be insulated. Following types of insulation are
This instrument is used for measuring inside as well as outside diameter of bearing.
This instrument is used for measuring insulation resistance.
It measures the vibration of the motor. It is measured in three dimensions-axial, vertical
Switchgear is one that makes or breaks the electrical circuit.
It is a switching device that opens & closes a circuit that defined as apparatus used
for switching, Lon rolling & protecting the electrical circuit & equipments.
The switchgear equipment is essentially concerned with switching & interrupting
currents either under normal or abnormal operating conditions.
The tubular switch with ordinary fuse is simplest form of switchgear & is used to control
& protect& other equipments in homes, offices etc.
For circuits of higher ratings, a High Rupturing Capacity (H.R.C) fuse in condition with
a switch may serve the purpose of controlling & protecting the circuit.
However such switchgear cannot be used profitably on high voltage system (3.3 KV)
for 2 reasons.
Firstly, when a fuse blows, it takes some time to replace it & consequently there is
interruption of service to customer.
Secondly, the fuse cannot successfully interrupt large currents that result from the High
In order to interrupt heavy fault currents, automatic circuit breakers are used.
There are very few types of circuit breakers in B.P.T.S they are VCB, OCB, and SF6 gas
The most expensive circuit breaker is the SF6 type due to gas.
There are various companies which manufacture these circuit breakers: VOLTAS,
JYOTI, and KIRLOSKAR.
Switchgear includes switches, fuses, circuit breakers, relays & other equipments.
In low tension switch gear thermal over load relays are used whereas in high tension 5
different types of relays are used.
THE EQUIPMENTS THAT NORMALLY FALL IN THIS
Isolator cannot operate unless breaker is open
Bus 1 and bus 2 isolators cannot be closed simultaneously
The interlock can be bypass in the event of closing of bus coupler breaker.
No isolator can operate when the corresponding earth switch is on
Switching isolator is capable of:
Interrupting charging current
Interrupting transformer magnetizing current
Load transformer switching. Its main application is in connection with the transformer feeder as the unit
makes it possible to switch gear one transformer while the other is still on load.
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.
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
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.
Low Tension SWITCHGEAR
Main switch is control equipment which controls or disconnects the main supply. The main
switch for 3 phase supply is available for the range 32A, 63A, 100A, 200Q, 300A at 500V
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. 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.
AC Contractors are 3 poles suitable for D.O.L Starting of motors and protecting the
For overload protection, thermal overload relay are best suited for this purpose. They
operate due to the action of heat generated by passage of current through relay
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 50-60kg/cm^2
for high and medium capacity circuit breakers.
Contactors used in ntpc
Thermal overload relay
MINIMUM OIL CIRCUIT BREAKER
These use oil as quenching medium.
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
SF6 CIRCUIT BREAKER
The principle of current interruption is similar to that of air blast
circuit breaker. It simply employs the arc extinguishing medium namely
SF6. When it is broken down under an electrical stress, it will quickly
VACUUM CIRCUIT BREAKER
It works on the principle that vacuum is used to save the purpose of
insulation and. In 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.
ELECTRICAL MAINTENANCE DEPARTMENT –II
The generator works on the principle of
electromagnetic induction. There are two
components stator and rotor. The rotor is
the moving part and the stator is the stationary
part. The rotor, which has a field winding, is
given a excitation through a set of 3000rpm to
give the required frequency of HZ. The rotor is
cooled by Hydrogen gas, which is locally
manufactured by the plant and has high heat
carrying capacity of low density. If oxygen and
hydrogen get mixed then they will form very
high explosive and to prevent their combining in
any way there is seal oil system. The stator
cooling is done by de-mineralized (DM) water
through hollow conductors. Water is fed by one
end by Teflon tube. A boiler and a turbine are
coupled to electric generators. Steam from the
boiler is fed to the turbine through the
connecting pipe. Steam drives the turbine rotor.
The turbine rotor drives the generator rotor
which turns the electromagnet within the coil
of wire conductors.
Carbon dioxide is provided from the top and oil
is provided from bottom to the generator. With
the help of carbon dioxide the oil is drained out
to the oil tank.
RATINGS OF THE GENERATORS USED
Turbo generator 100MW
TURBO GENERATOR 210 MW
The 100 MW generator generates 10.75 KV and
210 MW generates 15.75 KV. The voltage is
stepped up to 220 KV with the help of generator
transformer and is connected to the grid.
The voltage is stepped down to 6.6 KV with the
help of UNIT AUXILLARY TRANSFORMER (UAT) and
this voltage is used to drive the HT motors. The
voltage is further stepped down to 415 V and then
to 220 V and this voltage is used to drive Lt Motors.
TURBO GENERATOR 210MW
MAKE BHEL, Haridwar
CAPACITY 247,000 KVA
POWER 210,000 KW
STATOR VOLTAGE 15,750 V
STATOR CURRENT 9050 A
SPEED 5000 rpm
POWER FACTOR 0.85
FREQUENCY 50 HZ
EXCITATION 310 V
GAS PRESSURE 3.5 kg/cm
It is a static machine which increases or
decreases the AC voltage without changing
the frequency of the supply.
It is a device that:
Transfer electric power from one circuit
It accomplishes this by electromagnetic
In this the two electric circuits are in mutual
inductive influence of each other.
It works on FARADAY’S LAW
OF ELECTROMAGNETIC INDUCTION (self
or mutual induction depending on the type of
COOLING OF TRANSFORMERS
OF LARGE MVA
As size of transformer becomes large, the rate of the oil circulating becomes insufficient to
dissipate all the heat produced & artificial means of increasing the circulation by electric
pumps. In very large transformers, special coolers with water circulation may have to be
TYPES OF COOLING:
Air Natural (AN)
Air Forced (AF)
Oil immersed cooling
Oil Natural Air Natural (ONAN)
Oil Natural Air Forced (ONAF)
Oil Forced Air Natural (OFAN)
Oil Forced Air Forced (OFAF)
Oil immersed Water cooling
Oil Natural Water Forced (ONWF)
Oil Forced Water Forced (OFWF)
MAIN PARTS OF TRANSFORMER
1. Secondary Winding
2. Primary Winding.
3. Oil Level
6. Drain Cock
7. Cooling Tubes.
8. Transformer Oil.
9. Earth Point
10. Explosion Vent
11. Temperature Gauge.
12. Buchholz Relay
13. Secondary Terminal
14. Primary Terminal
(125MVA UNIT-I & UNIT-III)
TYPE OF COOLING OFB
TEMP OF OIL 45^C
TEMP WINDING 60^C
KV (no load) HV-233 KVA
LINE AMPERES HV-310 A
FREQUENCY 50 HZ
IMPEDANCE VOLTAGE 15%
VECTOR GROUP Y DELTA
INSULATION LEVEL HV-900 KV
CORE AND WINDING WEIGHT 110500 Kg
WEIGHT OF OIL 37200 Kg
TOTAL WEIGHT 188500 Kg
OIL QUANTITY 43900 lit
(166 MVA UNIT-IV)
TYPE OF COOLING ON/OB/OFB
TEMP OF OIL 45C
TEMP WINDING 60C
VOLTS AT NO LOAD HV-236000
LINE AMPERES HV-587 A
FREQUENCY 50 HZ
IMPEDANCE VOLTAGE 15.55%
VECTOR GROUP Y DELTA
CORE AND WINDING WEIGHT 138800 Kg
WEIGHT OF OIL 37850 Kg
TOTAL WEIGHT 234000 Kg
OIL QUANTITY 42500 lit
GUARANTEED MAX TEMP 45C
UNIT AUXILIARY TRANSFORMER (UAT)
Unit I & V- 12.5 MVA
The UAT draws its input from the main bus-ducts. The total KVA
capacity of UAT required can be determined by assuming 0.85
power factor & 90% efficiency for total auxiliary motor load. It is
safe & desirable to provide about 20% excess capacity then
circulated to provide for miscellaneous auxiliaries & possible
increase in auxiliary.
It is required to feed power to the auxiliaries during startups. This
transformer is normally rated for initial auxiliary load requirements
of the unit in typical cases; this load is of the order of 60% of the
load at full generating capacity. It is provided with on load tap
change to cater to the fluctuating voltage of the grid.
NEUTRAL GROUNDED TRANSFORMER
This transformer is connected with supply coming out of UAT in
stage-2. This is used to ground the excess voltage if occurs in the
secondary of UAT in spite of rated voltage.
As we know that electrical energy can’t be stored like cells, so what we generate should be consumed
instantaneously. But as the load is not constants therefore we generate electricity according to need i.e.
the generation depends upon load. The yard is the places from where the electricity is send outside. It
has both outdoor and indoor equipments.
CAPACITATIVE VOLTAGE TRANSFORMER
Normally un-galvanized mild steel flats are used for earthling. Separate earthing electrodes
are provided to earth the lightening arrestor whereas the other equipments are earthed by
connecting their earth leads to the rid/ser of the ground mar.
It is essentially a step up transformer which step down the current to a known ratio. It is a type
of instrument transformer designed to provide a current in its secondary winding proportional
to the alternating current flowing in its primary.
It is essentially a step down transformer and it step downs the voltage to a known ratio.
Relay is a sensing device that makes your circuit ON or OFF. They detect the abnormal
conditions in the electrical circuits by continuously measuring the electrical quantities, which
are different under normal and faulty conditions, like current, voltage frequency. Having
detected the fault the relay operates to complete the trip circuit, which results in the opening
of the circuit breakers and disconnect the faulty circuit.
There are different types of relays:
Numerical relay etc.
AIR BREAK EARTHING SWITCH
The work of this equipment comes into picture when we want to shut down the supply for
maintenance purpose. This help to neutralize the system from induced voltage from extra high
voltage. This induced power is up to 2KV in case of 400 KV lines.