training report

1. 1 | P a g e
National Thermal Power Plant
Kahalgaon
Contents
1. INRODUCTION
1.1 National Thermal Power Corporation
1.2 Installed Capacity
1.3 NTPC Kahalgaon ( Overview )
2. NTPC
2.1 Introduction
2.2 National Thermal Power Corporation Layout
3. Major Areas in NTPC Kahalgaon
3.1 Coal Handling Plant
3.2 Boiler and its Auxiliaries
3.3 Turbine Auxiliaries
3.4 Generator and its auxiliaries
3.5 Switchyard and Transmission Equipments
4. Transformers
5. Turbine

2. 6. Governor
1. INRODUCTION
1.1. National Thermal Power Corporation
NTPC, the largest power Company in India, was setup in 1975 to accelerate
power development in the country. It is among the world’s largest and most
efficient power generation companies. In Forbes list of World’s 2000 Largest
Companies for the year 2007, NTPC occupies 411th
place.
NTPC has installed capacities of 29,394 MW. It has 15 coal based power
stations (23,395 MW), 7 gas based power stations (3,955 MW) and 4 power
stations in Joint Ventures (1,794 MW). The company has power generating
facilities in all major regions of the country. It plans to be a 75,000 MW
company by 2017.
2 | P a g e

3. NTPC has gone beyond the thermal power generation. It has diversified into
hydro power, coal mining, power equipment manufacturing, oil & gas
exploration, power trading & distribution. NTPC is now in the entire power
value chain and is poised to
become an Integrated Power
Major.
NTPC's share on 31 Mar 2008 in
the total installed capacity of the
country was 19.1% and it
contributed 28.50% of the total
power generation of the country
during 2007-08. NTPC has set new
benchmarks for the power industry
both in the area of power plant construction and operations
with its experience and expertise in the power sector, NTPC is extending
consultancy services to various organisations in the power business. It provides
consultancy in the area of power plant constructions and power generation to
3 | P a g e

4. companies in India and abroad.
In November 2004, NTPC came out with its Initial Public Offering (IPO)
consisting of 5.25% as fresh issue and 5.25% as offer for sale by Government of
India. NTPC thus became a listed company with Government holding 89.5% of
the equity share capital and rest held by Institutional Investors and Public. The
issue was a resounding success. NTPC is among the largest five companies in
India in terms of market capitalization.
Recognising its excellent performance and vast potential, Government of the
India has identified NTPC as one of the jewels of Public Sector 'Navratnas'- a
potential global giant. Inspired by its glorious past and vibrant present, NTPC
is well on its way to realise its vision of being "A world class integrated power
major, powering India's growth, with increasing global presence".
1.2. Installed Capacity
An Overview
No Of Plants Capacity MW
NTPC Owned
Coal 15 23395
Gas/Liquid Fuel 7 3955
Total 22 27350
Owned By JVs
Coal & Gas 4 2044
Total 26 29394
Regional Spread of Generating Facilities
4 | P a g e

5. Region Coal Gas Total
Northern 7035 2312 9347
Western 5860 1293 7153
Southern 3600 350 3950
Eastern 6900 - 6900
JVs 564 1480 2044
Tatal 23959 5435 29394
Project Profile
Coal Based Power Stations
Coal based State
Commissioned
Capacity
(MW)
1. Singrauli Uttar Pradesh 2,000
2. Korba Chattisgarh 2,100
3. Ramagundam Andhra Pradesh 2,600
4. Farakka West Bengal 1,600
5. Vindhyachal Madhya Pradesh 3,260
5 | P a g e

6. 6. Rihand Uttar Pradesh 2,000
7. Kahalgaon Bihar 2,340
8. NTCPP Uttar Pradesh 840
9. Talcher Kaniha Orissa 3,000
10. Unchahar Uttar Pradesh 1,050
11. Talcher Thermal Orissa 460
12. Simhadri Andhra Pradesh 1,000
13. Tanda Uttar Pradesh 440
14. Badarpur Delhi 705
15. Sipat Chattisgarh 500
Total (Coal) 23,395
Gas/Liq. Fuel Based Power Stations
Gas based State
Commissioned
Capacity
(MW)
16. Anta Rajasthan 413
17. Auraiya Uttar Pradesh 652
18. Kawas Gujarat 645
19. Dadri Uttar Pradesh 817
20. Jhanor-Gandhar Gujarat 648
21.
Rajiv Gandhi CCPP
Kayamkulam
Kerala 350
22. Faridabad Haryana 430
Total (Gas) 3,955
Power Plants with Joint Ventures
Coal
Based
State Fuel Commissioned
Capacity
6 | P a g e

7. (MW)
23. Durgapur West Bengal Coal 120
24. Rourkela Orissa Coal 120
25. Bhilai Chhattisgarh Coal 324
26. RGPPL Maharastra Naptha/LNG 1480
Total(JV) 2044
Grand Total (Coal + Gas + JV) 29,394
1.3. NTPC Kahalgaon ( Overview )
The area is in Kahalgaon on the bank of River Ganga. In the state of Bihar.
Kahalgaon is one of the major energy sources of India, the place, named after
was once upon a time covered with dense and unnavigable forests and
inhabited by wild animals. The place was considered very treacherous. Just two
generations ago, small holders were tending their parcels of land here, and the
original inhabitants were gathering honey and herbs in the forest. In the late
fifties, a large scale dam banked up the water of the River Ganges. Later, rich
coal deposits spread over an area of 2200 km² in the state of Jharkhand were
discovered that could be used to generate electricity.
The population of Kahalgaon mainly consists of professionals and workers of
these large industrial units and businessmen and employees of other
organizations dealing with the power or coal industry, in addition to staff
members of various government agencies
7 | P a g e

8. Photo 1. National Thermal Power Corporation, Kahalgaon
Mining
All these Industrial developments have only been possible because Mother
earth has blessed this part of the land with mineable reserves of Coal. Northern
Coalfields Limited, the PSU coal major & the highest profit making subsidiary
of Coal giant “Coal India Ltd” is the only feeder to these power, chemical &
cement plants located within the vicinity of Kahalgaon Zone. With many billion
tonnes of coal being mined for the last 35-40 yrs, it still sits on a geographical
reserve of more than 8.7 billion tones, which can be mined for another 35-40
Yrs.
2. NTPC
2.1. Introduction
NTPC full form is National Thermal Power Corporation. The Place is now
known as NTPC Kahalgaon. There is brief detail:-
8 | P a g e

9. 9 | P a g e
Approved Capacity 2340 MW
Installed Capacity 2340 MW
Location Kahalgaon, Bihar
Water Source River Ganga
Fuel Coal
Beneficiary States
State & Union territories of NR, WR, ER,
SR,Uttar Pradesh, Bihar
Fuel requirement
4.1 million tonnes per year for stage I,
6.62 million per year for 2 units of stage II.
3.67 million per year for 3rd
unit of stage II
Sourse of fuel
Rajmahal, Murra, Chuperbita Coal field of
eastern Coal field Ltd.
Total Area 3300 Acres,
Approved
Investment
Rs. 1715 Crore (Stage I), 6330 Crore (Stage
II)
Unit Sizes
Stage - I: 4x 210 MW
Stage -II: 3x 500 MW
Units
Commissioned
Unit -I 200 MW March 1992
Unit -II 200 MW March 1994
Unit -III 200 MW March 1995
Unit -IV 200 MW November 1996
Address: National Thermal Power Corporation,
Kahalgaon

10. 10 | P a g e

11. 2.2. National Thermal Power Corporation Layout
The general layout of thermal power plant consists of mainly four circuits as
shown.
1. Coal and Ash circuit
2. Air and Gas circuit
3. Feed Water and Steam circuit
4. Cooling Water circuit
Coal and Ash Circuit:
In this circuit, the coal from the storage is fed to the boiler through coal
handling equipment for the generation of steam. Ash produced due to
combustion of coal is removed to ash storage through ash-handling system.
Air and Gas Circuit:
Air is supplied to the combustion chamber of the boiler either through forced
draught or induced draught fan or by using both. The dust from the air is
removed before supplying to the combustion chamber. The exhaust gases
carrying sufficient quantity of heat and ash are passed through the air-heater
11 | P a g e

12. where the exhaust heat of the gases is given to the air and then it is passed
through the dust collectors where most of the dust is removed before exhausting
the gases to the atmosphere.
Feed Water and Steam Circuit: The steam generated in the boiler is fed to the
steam prime mover to develop the power. The steam coming out of the prime
mover is condensed in the condenser and then fed to the boiler with the help of
pump. The condensate is heated in the feed-heaters using the steam tapped from
different points of the turbine. The feed heaters may be of mixed type or indirect
heating type. Some of the steam and water are lost passing through different
components of the system; therefore, feed water is supplied from external
source to compensate this loss. The feed water supplied from external source to
compensate the loss. The feed water supplied from external source is passed
through the purifying plant to reduce to reduce dissolve salts to an acceptable
level. This purification is necessary to avoid the scaling of the boiler tubes.
Purification done by DM plants.
Cooling Water Circuit:
The quantity of cooling water required to condense the steam is considerably
high and it is taken from a lake, river or sea. At the Kahalgaon thermal power
plant it is taken from an artificial lake created near the plant. The water is
pumped in by means of pumps and the hot water after condensing the steam is
cooled before sending back into the pond. This is a closed system where the
water goes to the pond and is re circulated back into the power plant. Generally
open systems like rivers are more economical than closed systems.
3. Major Areas in NTPC
3.1.Coal Handling Plant (CHP)
3.1.1. Coal Handling plant layout & Locations of mines
12 | P a g e

13. 3.1.2. Coal Handling Plant Working
Coal source of plant are Rajmahal, Murra, Chuperbita Coal field of eastern
Coal field Ltd. 14.3 million tonnes of coal are consumed by plant per year. Coal
Reach to the CHP through train.Where the size of coal is Approx. Less than 200
mm. The coal was throw into Track Hopper (These self-cleaning, double rack
and pinion style valves receive material from railroad cars or material reclaimed
from outdoor storage piles by bulldozers. Their purpose is to shut off the
material flow from the hoppers to material handling conveyors below.) From
Track Hopper threw conveyer belts coal reaches to the Crusher House (it is a 6
store building where the coal is cursed into a size of less than 20mm) in
between track hopper and crusher house “SUSPENDED
MAGNETS”,”MAGNETIC DETECTOR” and “MAGNETIC SEPERATORS”
are placed so that only coal pieces reach to the crusher house. Because if
Heavy metal pieces reach to the crusher house they will damage it.Then if Plant
unit need coal threw conveyer belts coal reaches to the coal bunkers of
Unit.Coal Bunkers (they store the coal for a single unit and Supply coal to
furnace threw coal mills when it needs) but when coal bunkers are full then the
coal is stacked in the coal yard using the coal stacker and reclaimer machine
(it is a huge machine used to stack/Reclaim the coal used in the plant they are
always placed in coal yard where coal is stacked, In NTPC SSTPS there are 3
such type of machines are available two for stage-I and one for stage-II. )
In NTPC SSTPS Different types of Electrical machines are used in CHP which
are:
S.No
.
Name Type Ratings
1. Conveyer
motor
Squirrel cage induction motor 6.6 KV / 0.4 KV
2. Plaugh motor Squirrel cage induction motor 6.6 KV
3. Traverse
drive motor
Squirrel cage induction motor 6.6 KV
13 | P a g e

14. 3.2. Boiler & its Auxiliaries
3.2.1. Boiler
“BOILER IS A CLOSED VESSEL IN WHICH STEAM IS GENERATED BY
MEANS OF HEAT ENERGY, BOILER HAVING CAPACITY OF 22.75 LITERS
COMES UNDER BOILER ACT.”
Type of boiler used in NTPC SSTPS in Stage-I and II are Water tube boilers
A water-tube boiler is a type of boiler in which water circulates in tubes heated
externally by the fire. Water-tube boilers are used for high-pressure boilers.
Fuel is burned inside the furnace, creating hot gas which heats up water in the
steam-generating tubes. In smaller boilers, additional generating tubes are
separate in the furnace, while larger utility boilers rely on the water-filled tubes
that make up the walls of the furnace to generate steam.
The heated water then rises into the steam drum. Here, saturated steam is
drawn off the top of the drum. In some services, the steam will renter the
furnace in through a super heater in order to become superheated. Superheated
steam is used in driving turbines. Since water droplets can severely damage
turbine blades, steam is superheated to 730°F (390°C) or higher in order to
ensure that there is no water entrained in the steam.
Cool water at the bottom of the steam drum returns to the feed water drum via
large-bore 'down comer tubes', where it helps pre-heat the feed water supply.
(In 'large utility boilers', the feed water is supplied to the steam drum and the
down comers supply water to the bottom of the water walls). To increase the
economy of the boiler, the exhaust gasses are also used to pre-heat the air
blown into the furnace and warm the feed water supply. Such water-tube boilers
in thermal power station are also called steam generating units.
Properties of fuel
14 | P a g e

15.  FLASH POINT-IT IS A MINIMUM TEMP AT WHICH THE FUEL IS
HEATED TO GIVE OFF INFLAMABLE VAPOUR IN SUFFICIENT
QUANTITY TO IGNITE WHEN BROUGHT IN CONTACT OF FLAME.
 POUR POINT-IT IS A MIN. TEMP AT WHICH OIL CAN HANDLE OR
CAN FLOW EASILY IN PIPE LINE.
 FIRE POINT- IT IS A MIN. TEMP OF FUEL AT WHICH IT STARTS
BURNING WITHOUT EXTERNAL SUPPORT.
 CALORIFIC VALUE-IT IS A HEAT ENERGY LIBERATED BY
COMPLETE COMBUSTION OF UNIT MASS OF FUEL.
• COAL BURNERS
EFFECTIVE UTILISATION OF PULVERISED COAL DEPENDS ON THE
ABILITY OF BURNERS TO PRODUCE UNIFORM MIXING OF COAL
AND AIR.
In NTPC SSTPS(Stage-I and Stage-II ) TANGENTIAL FIRING Method is
used in which from corners tangentially the air and fuel are Passed inside
furnace region where burning takes place as shown in figure.
3.2.2. Boiler Auxiliaries (Stage-I & II)
15 | P a g e

16.  Arrangement of Boiler Aux and various parts at diff. Elevation.
 Role of Air Heaters
• To recycle the heat of exit flue gas back in the combustion process
• Efficient coal combustion and pulverization depends on air heater
performance
• For every 20 deg drop in flue gas exit temp. the boiler efficiency
increased by about 1%.
 Coal Mill
A ball mill is a pulverizer that consists of a horizontal rotating cylinder, up to
three diameters in length, containing a charge of tumbling or cascading steel
balls, pebbles, or rods.
A tube mill is a revolving cylinder of up to five diameters in length used for fine
pulverization of ore, rock, and other such materials; the material, mixed with
water, is fed into the chamber from one end, and passes out the other end as
slime.
ESP (Electrostatic Precipitator )
An electrostatic precipitator (ESP), or electrostatic air cleaner is a
particulate collection 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 that minimally impede the
flow of gases through the device, and can easily remove fine particulate
matter such as dust and smoke from the air stream
16 | P a g e

17. • INDUCED DRAUGHT FAN
 Made by: BHEL
 Type :3 phase Squirrel cage induction motor
 Stator connection : Y (star)
17 | P a g e

18.  Operated at Freq.: 50 Hz
 Voltage: 6600V
 Current: 138.5 A
 Power: 1300 KW
 P.f. : 0.85
 Efficiency: 95.5
 Rotor speed:744 rpm
 Weight: 13700 Kg
 Lubricant: Greave servogem-2
 Max Wdg. Temp.:48°C
• FORCED DARUGHT FAN
 Made By: BHEL
 Type: 3 phase Squirrel cage induction motor
 Stator connection : Y (star)
 Operated at Freq.: 50 Hz
 Voltage: 6600V
 Current: 84.5 A
 Power: 800 KW
18 | P a g e

19.  P.f. : 0.875
 Efficiency: 94.8
 Rotor speed:1490 rpm
 Lubricant: Greave servogem-2
 Max Wdg. Temp.:48°C
• PRIMARY AIR FAN
 Made By: BHEL
 Type: 3 phase Squirrel cage induction motor
 Stator connection : Y (star)
 Operated at Freq.: 50 Hz
 Voltage: 6600V
 Current: 84.5 A
 Power:1400 KW
 P.f. : 0.87
 Efficiency: 96.3
 Rotor speed:1493 rpm
 Lubricant: Greave servogem-2
 Max Wdg. Temp.:48°C
 FLY ASH COMPOSITION(BY WEIGHT)
19 | P a g e

20.  AL2O3- 20-25%
 CAO - 01.0%
 FE2O3+FE3O4- 0 5-8%
 K2O- 02.0%
 MGO - 00.7%
 MNO - 00.02%
 NA2O - 00.24%
 TIO2- 0.7-1.5%
 SILICA- 64.78%
 Ash Utilization
Ash utilization is one of the key concerns at NTPC. The Ash Utilization
Division, set up in 1991, strives to derive maximum usage from the vast
quantities of ash produced at its coal-based stations. The division proactively
formulates policy, plans and programme for ash utilization. It further monitors
the progress in these areas and works at developing new fields of ash
utilization.
As the emphasis on gainful utilization of ash grew, the usage over the years also
increased. From 0.3 million tonnes in 1991-1992, the level of utilization during
2006-07 stood at over 20.76 million tonnes.
NTPC has adopted user friendly policy guidelines on ash utilisation. These
include actions identified for:
20 | P a g e

21. (i) Ash Collection & Storage System
(ii) Facilities & Incentives to users
(iii) Direct Department Activities
(iv) Administrative & Financial aspects.
3.3. Turbine Auxiliaries
Figure shown below gives the perfect representation of the arrangement of
turbine auxiliaries. For proper function of turbine the auxiliaries are arranged
at different location peeping the view of easy installation, proper operation and
maintenance and technical requirement.
21 | P a g e

22. 22 | P a g e
TurbineAuxiliaries

23.  Condensate system
This comprise of
 Condensate pumps – 3 per Unit of 50% capacity each located near
the condenser Hot well.
 L.P. Heater – Normally 4 in number with no. 1 located at the
upper part of the condenser and No. 2,3,and 4 around 4m level.
 Deaerator – one per unit located around 18’M’ level in CD bay.
 Feed Water system
The main equipment coming under this system are
 Boiler feed pump - 3 per Unit of 50% capacity each located 0 ‘M’
level in the T.G. bay.
 High Pressure Heater – Normally three in number and located
near TG bay.
 Drip Pumps – Generally two in number of 100% capacity each
situated beneath the LP heater.
 Turbine Lub. Oil System –
It consist of main oil pump (M.O.P) ,Starting Oil Pump (S.O.P.) AC stand
by oil pumps and emergency DC oil pump and jacking oil pump (JOP)
(one at each Unit).
23 | P a g e

24.  Auxiliary Steam System
The main 16 ata header runs parallel to BC bay at the level of around 18
‘M’.
3.4. Generator and its Auxiliaries
 Constructional Features
Stator frame
1. Stator Components
2. Stator Core
3. Stator windings
4. Bushings
1. Stator Frame
Totally enclosed gas tight fabricated structure made of high quality mild
steel. and
It houses the stator core and Hydrogen coolers
24 | P a g e

25. 2. Stator Core
 The entire core is laminated to minimize magnetic and eddy current
losses
 Each laminations is made up of cold rolled high quality silicon steel
25 | P a g e

26. 3. Stator Winding
 The stator has a three phase, double layer, short pitched and bar type
windings having two parallel paths.
 Each slot accommodates two bars.
 Each bar consists of solid as well as hollow conductors with cooling
water passing through the hallow space.
 In the straight slot portion the strands are transposed by 360 0
to reduce
the eddy losses.
 Bar is taped with several layers of thermosetting epoxy mica tape.
 To prevent corona discharges between insulation and the wall of the
slot, the slot portion is coated with semi conducting varnish.
4. Bushings
26 | P a g e

27. Three phases and six neutral terminals are brought out from the
stator frame through bushings which are capable of withstanding high
voltage and provided with gas tight joint.
The conductor of the bushing is made of high conductivity copper tube
on which silver plated terminal plates are brazed at both ends.
Rotor
It comprises of the fallowing components
 Rotor shaft
 Rotor windings
 Retaining ring
 Fans
 Slip rings
 Rotor Shaft
The main constituents are chromium, molybdenum, nickel and vanadium
On 2/3 of its circumference approximately, the rotor body is provided
with longitudinal slots to accommodate field windings
 Rotor windings
The conductors are made of hard drawn silver bearing copper.
Exhibits high creep resistance so that coil deformations due to thermal
cycling.
27 | P a g e

28. The individual turns are insulated from each other by layer of glass
laminates.
 Retaining Ring
The overhang portion of field winding is held by non magnetic steel
forging of retaining ring against centrifugal forces.
To reduce stray losses , the retaining rings are made of non
magnetic, steel and cold worked, resulting high mechanical
strength.
 Rotor Fan
28 | P a g e

29. The generator cooling gas is circulated by two single stage axial
flow propeller type fans. These Fan hubs are made of alloy steel.
 Slip rings
The slip rings consist of helically grooved alloy steel rings shrunk
on rotor body shaft and insulated from it.
The slip rings are provided with inclined holes for self ventilation
 Generator Parameters
o Generator Volume : 56 cu m
o CO2 reqd for expelling H2 at standstill : 120 cu m
o CO2 reqd for expelling H2 under rolling : 160 cu m
o H2 filling quantity at standstill : 300 cu m
o H2 filling quantity under Standstill : 336cum
o Nominal pressure of hydrogen : 3.0 ksc
o Permissible variations : +/-0.2 ksc
o Hydrogen purity : 99 %
o Purity of H2 (minimum) : 97 %
o Max temp of Cold gas : 44 deg c
Max moisture content in generator casing : 15 mg/m3 of H2
o Gas flow per Cooler : 7.5 m3/sec
29 | P a g e

30. o Heat Load :528 KW
o Cooling water flow per cooler :87.5m3/sec
o No of H2 coolers :4
o Pressure Drop through cooler :17.5mmwcl
o Minimum Temp of cooling water :13deg C
to maintain min 20 deg c cold gas
 Cooling of Generator
Hydrogen cooling: - Stator core, Rotor core and winding
 Generator Hydrogen Cooling Circuit
 Seal oil system
30 | P a g e
Cold Gas
Hot Gas

31. The locations where the rotor shaft passes through the stator casing are
provided with radial seal rings.
The gap between the seal ring and the shaft is sealed with seal oil.
To ensure effective sealing seal oil pressure in the annular gap is
maintained at a higher level than the gas pressure within the generator
casing.
31 | P a g e

32.  Seal Oil Operation
Seal oil supplied to the shaft seals is drained from both air & H2 sides.
The air side seal oil is directly returned to SOT via a float valve. The oil
drained from H2 side of the shaft seal is discharged into generator
prechambers. The prechambers permit the escape of entrained gas
bubbles and deforming of the oil. Oil from prechambers flow to IOT & a
float valve maintains the oil level in IOT excess oil is returned back to
SOST.IOT act as a gas barrier preventing the ingress of H2 to SOT.
 Excitation System
32 | P a g e

33. Static excitation system is used in mainly 200MW Generator set. The AC
power is trapped off from generator terminal. Stepped down and rectified
by fully controlled thyristor bridge and then feed to generator field as
excitation power. to control the generator output voltage. A high control
speed is achieved by using an inertia free control and power electronics
system. Any deviation in generator terminal voltage is sensed by error
detector and causes the voltage regulator to advance or retard the firing
angle of thyristor there by controlling the field excitation.
The Static Excitation System Consists of:
 Rectifier Transformer
 Thyristor Converter
 Automatic voltage Regulator
 Field Flashing Circuit
 Field Breaker and Field Discharge Equipment
33 | P a g e

34. 2 Pole 3000 RPM Hydrogen / Hydrogen and Water cooled Turbo-
generators
The Hydrogen and water cooled machines (THDF type) are offered with
the stator winding directly water-cooled and the rotor winding directly
cooled with Hydrogen. The stator core has a leaf spring suspension. The
machines are with Micalastic system of impregnation and the bearings are
mounted on end shields. The stator overhang is with a support ring. A
magnetic shunt traps the end leakage flux. These machines are provided
34 | P a g e

35. with multistage compressors and vertical coolers on turbine end. These
can be offered with either brushless /static type of excitation systems
The (THW) type machines have the stator winding directly cooled by water
whereas the rotor winding is directly cooled by Hydrogen by gap pick up
method. The stator core is mounted resiliently on flexible core bars. Resin
rich thermo-reactive insulation is used for the stator winding and top
ripple springs are placed in the stator slots. These machines are also
characterized by enclosed type slip rings with forced ventilation. Two axial
fans are provided on rotor and four Hydrogen coolers are provided for
systematic ventilation. These are offered with static excitation system
Generator Rating:
KW 500,000
Power Factor 0.85 lagging
KVA 588,000
Stator Voltage 21,000
Stator Ampere 16,200
Rotor Voltage 340
Rotor Ampere 4040
Rpm 3000
Hz 50
Phase 3
Connection Y Y
Coolant Water & Hydrogen
Gas Pressure 4 Bar
Insulation Class B
Type TG-HH-0500-2
Make BHEL- Haridwar
3.5. Switchyard & Transmission Equipments
35 | P a g e

36. An electric power system is composed of high –voltage transmission lines
that feed power to a medium voltage (MV) network by means of substations.
In NTPC Kahalgaon these MV networks generally operated at voltages
between 15.7 KV to 22.0 KV. In turn they supply thousands of independent
low voltage system that function between 220V to 600V.
Switchyard and transmission equipments are:
Substations
Substations are used throughout an electrical system. Starting with the
generating station , a substation raises the medium-voltage generated by the
Synchronous generator to the high-voltage needed to transmit the energy
economically.
The high transmission-line voltage is then reduced in those substations
located close to the power consuming center. The electrical equipment in
such distribution substation is similar to that found in substation associated
with generating plant.
Substations Equipments
 Transformers
 Circuit breakers
 Surge arresters
 Current Limiting Reactor
 Isolators
 Instrument transformers
 Relay and protection devices
36 | P a g e

37.  Transformers
Generator Transformer:
GT-(1,2,3,4,)
Rating
Maker: BHEL Bhopal
Cooling method: OFWF
Vector group: YNd11
KVA rating: 250
KV (no load):
HV: 400
LV: 15.75
Line Ampere:
HV: 360.9
LV: 9164.6
No. of phases: 3
Frequency: 50Hz
Independent volt: 14.41
37 | P a g e

38. Top oil Temp. rise
(above 50C ambient): 35C
Mean Wdgs Temp Rise:40 C
Generator Transformer:
GT-(5)
Rating
Maker: ABB
Cooling method: OFAF
Vector group: YNd11
Frequency: 50Hz
KVA rating: 250
KV (no load):
HV: 250
LV: 250
Line Ampere:
HV: 343.66
LV: 9164.28
No. of phases: 3
38 | P a g e

39. Frequency: 50Hz
Independent volt: 14.41
Top oil Temp. rise
(above 50C ambient): 35C
Mean Wdgs Temp Rise:40 C
UST-3A
Maker: BBL Bombay
KVA – 1600
Voltage at No load
HV: 6600V
LV: 433V
Ampere
HV: 140A
LV: 2133A
Phase: 3
Frequency: 50Hz
UTA-2A
39 | P a g e

40. Maker: Hackbridge Hewittic andEasun Ltd.
KVA – 1600
Voltage at No load
HV: 6600V
LV: 433V
Ampere
HV: 140A
LV: 2133A
Phase: 3
Frequency: 50Hz
 Circuit breakers
A circuit breaker is an automatically-operated electrical switch designed to
protect an electrical circuit from damage caused by overload or short
circuit. Unlike a fuse, which operates once and then has to be replaced, a
circuit breaker can be reset (either manually or automatically) to resume
normal operation. Circuit breakers are made in varying sizes, from small
devices that protect an individual household appliance up to large
switchgear designed to protect high voltage circuits feeding an entire city.
Circuit Breaker Operation
All circuit breakers have common features in their operation, although details
vary substantially depending on the voltage class, current rating and type of
the circuit breaker.
40 | P a g e

41. The circuit breaker must detect a fault condition; in low-voltage circuit
breakers this is usually done within the breaker enclosure. Circuit breakers
for large currents or high voltages are usually arranged with pilot devices to
sense a fault current and to operate the trip opening mechanism. The trip
solenoid that releases the latch is usually energized by a separate battery,
although some high-voltage circuit breakers are self-contained with current
transformers, protection relays, and an internal control power source.
Once a fault is detected, contacts within the circuit breaker must open to
interrupt the circuit; some mechanically stored energy within the breaker is
used to separate the contacts, although some of the energy required may be
obtained from the fault current itself. The stored energy may be in the form of
springs or compressed air. Small circuit breakers may be manually operated;
larger units have solenoids to trip the mechanism, and electric motors to
restore energy to the springs.
The circuit breaker contacts must carry the load current without excessive
heating, and must also withstand the heat of the arc produced when
interrupting the circuit. Contacts are made of copper or copper alloys, silver
alloys, and other materials. Service life of the contacts is limited by the
erosion due to interrupting the arc. Miniature circuit breakers are usually
discarded when the contacts are worn, but power circuit breakers and high-
voltage circuit breakers have replaceable contacts.
When a current is interrupted, an arc is generated - this arc must be
contained, cooled, and extinguished in a controlled way, so that the gap
between the contacts can again withstand the voltage in the circuit. Different
circuit breakers use vacuum, air, insulating gas, or oil as the medium in
which the arc forms. Different techniques are used to extinguish the arc
including:
 Lengthening of the arc
 Intensive cooling (in jet chambers)
 Division into partial arcs
 Zero point quenching
 Connecting capacitors in parallel with contacts in DC circuits
41 | P a g e

42. Finally, once the fault condition has been cleared, the contacts must again be
closed to restore power to the interrupted circuit.
In NTPC SSTPS Type of High-voltage circuit breakers used are given below:
• Air blast Circuit Breaker
• SF6 Circuit Breaker
Air Blast circuit Breaker
These circuit breakers interrupt the circuit by blowing compressed air at
supersonic speed across the opening contact. Compressed air is stored in
reservoirs at a pressure of about 27-31 Kg/cm2
and is replenished by
compressor located in the substation. The most powerful circuit breakers
can typically open short-circuit current of 40KA at a line Voltage of 765KV
in a matter of 3 to 6 cycles on a 60Hz line.
42 | P a g e

43. Characteristics of SF6 circuit breakers:
• Simplicity of the interrupting chamber which does not need an auxiliary
breaking chamber
• Autonomy provided by the puffer technique
• The possibility to obtain the highest performance, up to 63 kA, with a
reduced number of interrupting chambers
• Short break time of 2 to 2.5 cycles
• High electrical endurance, allowing at least 25 years of operation
without reconditioning
• Possible compact solutions when used for GIS or hybrid switchgear
• Integrated closing resistors or synchronized operations to reduce
switching over-voltages
• Reliability and availability
• Low noise levels.
The reduction in the number of interrupting chambers per pole has led to a
considerable simplification of circuit breakers as well as the number of parts
and seals required. As a direct consequence, the reliability of circuit breakers
improved, as verified later on by CIGRE surveys.
43 | P a g e

44.  Lightning Arrester
The purpose of lightning arrester is to limit the over voltage that may occur
across transformers and other electrical apparatus due either to lightning or
switching surges. The upper end of the arrester is connected to the line or
terminal that has to be protected, while the lower end is solidly connected to
ground.
Ideally a lightning arrester clips any voltage in excess of a specified
maximum, by permitting a large current, if needed be, to be diverted to
ground. In this way the arrestor absorbs energy from the incoming surge.
So the E-I characteristics of an ideal surge arrester is therefore, a
horizontal line whose level corresponds to the maximum permissible surge
voltage. In practice, the E-I characteristics slopes upward but is still
considered to be reasonably Flat.
 Current-Limiting Reactor
The MV bus in the NTPC SSTPS usually energized several feeder, which
carry power to regional load centers surrounding the substation. If so
happens that the output impedance of the MV bus is usually very low.
44 | P a g e

45. Consequently, If the short circuit should occur on one of the feeders, The
resulting short-Circuit current could be disastrous.
 Isolators
Circuit-Isolator
Circuit-Isolator provides three-pole, group-operated, visible-air-gap
isolation in distribution substations. The Circuit-Isolator II can be used to
interrupt low-level charging currents associated with substation buswork
and circuit-breaker bushings, as well as other low-voltage currents
commonly present in substations.
Benefits
 Ideal for isolating transformers, circuit breakers, and other substation
equipment for repair and maintenance.
 Each disconnect is factory-assembled and adjusted for easy installation.
 Can be custom engineered for mounting on almost any customer-
supplied structure.
45 | P a g e

46. Fig: Circuit Isolator
 Instrument transformers
Current Transformer
A current transformer (CT) is a type of instrument
transformer designed to provide a current in its secondary
46 | P a g e

47. winding proportional to the alternating current flowing in its primary. They
are commonly used in metering and protective relaying in the electrical
power industry where they facilitate the safe measurement of large currents,
often in the presence of high voltages. The current transformer safely
isolates measurement and control circuitry from the high voltages typically
present on the circuit being measured.
Capacitor Voltage Transformer
A capacitor voltage transformer (CVT) is a transformer used in power
systems to step-down extra high voltage signals and provide low voltage
signals either for measurement or to operate a protective relay. In its most
basic form the device consists of three parts: two capacitors across which
the voltage signal is split, an inductive element used to tune the device to the
supply frequency and a transformer used to isolate and further step-down
the voltage for the instrumentation or protective relay. The device has at
least four terminals, a high-voltage terminal for connection to the high
voltage signal, a ground terminal and at least one set of secondary terminals
for connection to the instrumentation or protective relay. CVTs are typically
single-phase devices used for measuring voltages in excess of one hundred
kilovolts where the use of voltage transformers would be uneconomical. In
practice the first capacitor, C1, is often replaced by a stack of capacitors
connected in
series. This results in a
large voltage drop
across the stack of
capacitors that
replaced the first capacitor
and a comparatively
small voltage drop
across the second
capacitor, C2, and hence the secondary terminals.
47 | P a g e

48. Transformer:
Photo: Transformer
TURBINE
There are three turbines for each generator. These are meant to extract maximum heat energy
from the steam so as to achieve maximum efficiency. These turbines are named as:
a) High pressure turbine (HP Turbine)
48 | P a g e

49. b) Intermediate pressure turbine (IP Turbine)
c) Low pressure turbine (LP Turbine)
• Steam comes into the HP turbine from boiler through the main steam line (MSL).the
initial temperature and pressure of this steam is 540⁰C and 170 atm respectively. Each
turbine consists of several stages and one stage is made up of one rotor blade and one
stator blade.
• For 500 MW, HP turbine consists of 6 stages. Final temperature and pressure after
passing through all the stages of HP turbine becomes 345⁰C and 45 atm respectively.
• Steam comes out of HP turbine and goes back to reheater in boiler through cold
reheating line. Steam is then reheated in reheater and is fed to intermediate pressure
turbine through hot reheating line (HRH). Initial temperature and pressure of steam in
IP turbine is 540⁰C and 40 atm respectively.
• Steam then passes through various stages and then the used steam is again fed back to
boiler at reduced temperature and pressure.
• Finally steam is fed to the LP turbine and steam is then passed to the condenser where
it is converted back to water.
• At the bottom of the condenser there is a hot well where water collects.
• There are three condensate extract pumps (CEP) out of which two work at a time and
extract the water from the hot well.
49 | P a g e

50. • Steam coming out of the various outlets combine at one place in drain cooler where
the temperature and pressure of various steams comes to a common level.
• Now water need to be fed into the boiler but before that it needs some preheating.
• There are three low pressure heaters (LP Heaters) and two high pressure heaters (HP
Heaters)
• The heating elements in these heaters is steam coming out of various stages of the IP
Turbine and LP Turbine.
• From HP Heater, the water goes to economizer.
• From economizer heated water goes to the boiler drum. Boiler drum contains water
and steam both.
• Boiler drum is at a height of 90 meter. Steam being lighter collects at the top of the
boiler drum and water flows to the bottom ring header.
• Because of high potential energy, water from boiler drum goes down in the boiler,
gets heated, its temperature rises and attains enough kinetic energy to reach back to
the boiler drum.
• Steam from the boiler drum passes through superheater and attains a high temperature
of 540⁰C at 170 atm pressure and goes to the HP turbine.
50 | P a g e

51. Governor
The widespread use of electric clocks, the need for satisfactory operation of power stations
running in parallel and the relation between system frequency and the speed of the motors has
led to the requirement of close regulation of power system frequency. Control of system
frequency and load depends upon the governors of the prime-movers. Fig.1 shows the basic
characteristics of a governor. It is seen that with a given setting there is a definite relationship
between turbine speed and the load being carried by the turbine. If the load carried by the
turbine increases the speed decreases. In order to keep the speed same the governor setting by
changing the spring tension in the fly-ball type of governor will be resorted to and the
characteristics of the governor will be indicated by the dotted line. In practice the change in
characteristics is obtained by remotely operating the governor control motor from the control
room. A turbine can be adjusted to carry any given load at a desired speed. If constant
frequency is required the operator can adjust the speed of the turbine by changing the
governor characteristics as and when desired.
Speed governing system
Fig. 2 shows the schematic diagram of a speed governing system which controls the real
power flow in the power system. The speed governing system consists of the following parts:
1. Speed governor: this is a fly-ball type of speed governor and constitutes the heart of
the system as it senses the change in speed or frequency. With the increase in speed
the fly-balls move outwards and the point B on linkage mechanism moves downwards
and vice-versa.
51 | P a g e

52. 2. Linkage mechanism: ABC and CDE are the rigid links pivoted at B and D
respectively. The mechanism provides a movement to the control valve in the
proportion to change in speed. Link 4(l4) provides a feedback from the steam valve
movement.
Fig.2 Turbine Speed governing system
3. Hydraulic Amplifier: This consists of the main piston and the pilot valve. Low power
level pilot valve movement is converted into high power level piston valve movement
which is necessary to open or close the steam valve against high pressure steam.
4. Speed changer: The speed changer provides a steady state power output setting for
the turbine. The downward movement of the speed changer opens the upper pilot
valve so that more steam is admitted to the turbine under steady condition. The
reverse happens when the speed changer moves upward.
52 | P a g e

53. BOILER
• Boiler is a long column where coal is fired to produce heat and to convert water into
superheated steam.
• In NTPC – Kahalgaon, the height of the boiler is 90 meter.
• In the boiler section there are ten elevations which are meant for coal input. Coal is
pulverized in the form of fine powders and fed into the boiler at different elevations.
• Oil is sprayed in between these elevations to ignite the coal powders and to allow the
heat to sustain for the maximum time in the boiler.
• There are numerous fine tubes inside the boiler through which water flows. This water
while flowing through the tubes extracts heat from the boiler and gets converted to
steam at suitable temperature and pressure.
• Maximum temperature is available at the topmost part of the flame. Due to this reason
the boiler drum is located at the top (90 meter height).
53 | P a g e