2. ii
ACKNOWLEDGMENT
I am very grateful and thankful to all those who were a
part of this project and helped me towards its smooth
and efficient completion. First of all I am thankful to NAVRATNA COMPANY
NTPC LTD. Mr. Lalit Grover and Mr. A.K.Singh training department (EDC) for
timely arrangement of this training programme.Ms.Fahmida Begum and Mr.
Sushil Srivastava (EDC) contributions regarding paper formalities never be
ignored. I am thankful for first part of this training programme ie.
ELECTRICAL Mr.A.K.Sharma,Mr.M.Z.A.Sidiqque course co-ordinator
(EMD),Ms. Megha Bhardwaj, Mr. K.M.Gupta,Mr. Rakesh Kumar,Mr.Sameer
Kashyap,Mr. Ranjeet Kumar for their kind co-operation.I am also thankful for
second part of this training programme ie. ELECTRONICS Mr.O.P.Solanki ,Mr.
Neeraj Agarwal course co –ordinator(C & I),Mr.Chavi Pant,Mr. Narsingh
Yadav,Mr.Upendra Dubey, Ms.Saba Ansari,Mr. Jeevan Pai,Ms.Megha
Chaurasia for their kind co-operation. Lastly I once again thankful to all above
fellows and others who contributed directly or indirectly during the programme
for their helpful co-operation ,contribution ,co-ordination and knowledge
without which my project would not be a reality.
At last I express my sincere gratitude to HOD Mrs.
Smitha Shrivastav Mam,Lect. Shailja Patwa Mam,Lect. Salil Jain Sir.
ADITI TIWARI
B.E
7 SEM
ELEX
3. iii
HCET JABALPUR
INDEX
Acknowledgement………………………………………………………………………………….ii
List of figures………………………………………………………………………………………vi
List of tables………………………………………………………………………………………vii
I. About the
company…………………………………………………………..…….............1
A. Corporate Vision……………………………………………………………..1
B. Core Values…………………………………………………………………..1
C. Evolution of NTPC…………………………………………………………..3
D. NTPC Group…………………………………………………………………4
II. Introduction to FGUTPP…………………………………………………………5
A. Location………………………………………………………………………5
B. Major Milestones……………………………………………………………..5
C. Installed capacity……………………………………………………………..5
D. Production Inputs…………………………………………………………….5
E. Requirements…………………………………………………………………6
F. Cost of Generation……………………………………………………………6
G. Environmental aspects………………………………………………………6
H. Layout………………………………………………………………………..6
I. Various Cycles in the plant………………………………………………….7
i. Coal
cycle………………………………………..………………………...7
ii. Water
cycle………………………………………………………………….8
iii. Steam
cycle……………………………………….…………………………8
III. Switchyard………………………………………………………………..9
A. Circuit Breaker…………………………………………………………...9
4. iv
B. Lightening Arrester……………………………………………………...11
C. Earthing Switch…………………………………………………………12
D. Bus Bar………………………………………………………………….13
E. Capacitor Voltage Transformer…………………………………………13
F. Wave Trap……………………………………………………………….14
G. PLCC…………………………………………………………………….14
H. Current Transformer…………………………………………………….14
I. Isolator…………………………………………………………………..14
J. Bay………………………………………………………………………15
IV. Generator………………………………………………………………………..18
A. Main Components…………………………………………………………..18
B. Excitation system……………………………………………………………19
C. Generator protection………………………………………………………..19
D. Generator cooling system…………………………………………………..20
E. Cooling specifications of turbogenerators…………………………………21
V. Transformers………………………………….………….…………………….22
A. Transformer accessories…………………………………………………….22
B. Cooling of transformers…………………………………………………….23
C. Main transformers…………………………………………………………..25
i. Generator
transformers…………………………………………………………25
ii. Station
transformers………………….…………………….……………….25
iii. Unit auxiliary
transformers………………………………….……………………..25
iv. Neutral Grounding
Transformer……………………………………….………………..25
VI. DC system………………………………………………………………………27
A. Requirement of DC system…………………………………………………27
B. Description of battery……………………………………………………….27
C. Battery Charger……………………………………………………………..27
D. Capacity test of battery……………………………………………………..28
VII. Switchgear………………………………………………….…………………..29
5. v
A. L.T. switchgear……………………………………………………………..29
B. H.T. switchgear……………………………………………………………...30
VIII. Boiler……………………………………………..……………………………..32
IX. Electrostatic Precipitator (ESP)………………………………………………34
A. Working principle…………………………………………………………..34
B. Description………………………………………………………………….34
C. Parts of ESP…………………………………………………………………34
D. Electrical scheme of ESP……………………………………………………36
E. Variable frequency drive…………………………………………………….36
X. Coal Handling Plant………………………………………………………….39
A. Introduction…………………………………………………………………39
B. Properties of coal…………………………………………………………...39
C. Coal Analysis……………………………………………………………….39
D. Different methods of unloading the coal………………………………….39
E. Various equipments used in CHP………………………………………….40
i. Marshalling
Yard…………………………………….……..…………………….40
ii. Wagon
Tripler……………………………………………………………….40
iii. Paddle
Feeder…………………………………..…………………………...41
iv. Vibrating
feeder……………………………………..…………………………41
v. Transfer
points………………………………….…………………………….41
vi. Flap
gate……………………………….…………………………………42
vii. Conveyors………………………….……………………………….42
viii. Belt protection………………………………………………………42
ix. Primary
crusher…………………………..…………………………………43
x. Secondary
crusher………………………………..……………………………43
6. vi
xi. Cross belt magnetic
separator…………………………………………………………..43
xii. Metal
detector…………………………………..…………………………..43
xiii. Stacker declaimer……………………………………………………44
xiv. Transfer towers………………………………..……………………..45
xv. Tipper…………………………………………..……………………45
xvi. Bunker……………………………………………………………….45
F. Some Special motors of CHP……………………………………………….45
G. Power and Distribution Diagram of CHP………………………………….46
XI. Conclusion…………………………………………………..………………...47
LIST OF FIGURES Pg No.
Figure 1 – NTPC generation growth 1
Figure 2 – NTPC in power sector 2
Figure 3 – NTPC group 4
Figure 4 – Unit overview 7
Figure 5 – Steam flow 8
Figure 6 – SF6 Circuit Breaker 10
Figure 7 – Lightening Arrester 12
Figure 8 – Capacitor Voltage Transformer 13
Figure 9 – Single line diagram of switchyard 17
Figure 10 – Electrical System layout of stage III 31
Figure 11 – Water tube Boiler Schematic Layout 33
Figure 12 – Schematic Diagram of ESP 35
Figure 13 – Electrical scheme of VFD 37
Figure 14 – Two channel arrangement of synchronous motor 37
7. vii
Figure 15 – Forward Conveyor 42
Figure 16 – Return Conveyor 42
Figure 17 – Power distribution diagram of CHP in stage I 46
Figure 18 - Power distribution diagram of CHP in stage II 47
LIST OF TABLES Pg No.
Table I – Specifications of Circuit Breakers 11
Table II – Specifications of earthing switch 12
Table III – Specifications of Turbo generators 19
Table IV – Specifications of GTs 25
Table V – Specifications of STs 26
Table VI – Specifications of UATs 26
Table VII – Specification of NGT 26
Table VIII – Specification of Synchronous Motor 38
8. 1
I. ABOUT THE COMPANY
A. Corporate Vision:
“A world class integrated power major, powering India’s growth, with increasing global
presence”
B. Core Values:
B-Business Ethics
C-Customer Focus
O-Organizational & Professional pride
M-Mutual Respect and Trust
I- Innovation & Speed
T-Total quality for Excellence
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 others. Within a span of 31
years, NTPC has emerged as a truly national power company, with power generating
facilities in all the major regions of the country.
Figure 1. NTPC generation growth
9. 2
NTPC’s core business is engineering, construction and operation of power
generating plants. It also provides consultancy in the area of power plant constructions
and power generation to companies in India and abroad. As on date the installed capacity
of NTPC is 27,904 MW through its 15 coal based (22,895 MW), 7 gas based (3,955
MW) and 4 Joint Venture Projects (1,054 MW). NTPC acquired 50% equity of the SAIL
Power Supply Corporation Ltd. (SPSCL). This JV company operates the captive power
plants of Durgapur (120 MW), Rourkela (120 MW) and Bhilai (74 MW). NTPC also has
28.33% stake in Ratnagiri Gas & Power Private Limited (RGPPL) a joint venture
company between NTPC, GAIL, Indian Financial Institutions and Maharashtra SEB
Holding Co. Ltd.
NTPC’s share on 31 Mar 2007 in the total installed capacity of the country was
20.18% and it contributed 28.50% of the total power generation of the country during
2006-07.
Figure 2. NTPC in power sector
10. 3
C. Evolution of NTPC
NTPC was set up in 1975 with 100% ownership by the
Government of India. In the last 30 years, NTPC has grown into
the largest power utility in India.
In 1997, Government of India granted NTPC status of
“Navratna’ being one of the nine jewels of India, enhancing the
powers to the Board of Directors.
NTPC became a listed company with majority Government
ownership of 89.5%. NTPC becomes third largest by Market
Capitalisation of listed companies
The company rechristened as NTPC Limited in line with its
changing business portfolio and transforms itself from a
thermal power utility to an integrated power utility.
NTPC Ltd. Has granted of Maharatna status by Govt. of India.
NTPC Ltd. Has been ranked 7th great place to work in India by
The great places to work institute INDIA and The Economic
times.
1975
1997
2005
TABLE IV
Specificat
ions of
Turbo
Generator
s of stage
I. (gen1,
gen2)
KVA Pf Stator
Voltage
(V)
Stator
Current
(A)
Rotor
Voltage
(V)
Rotor
Current
(A)
Rpm Hz Phase Coolant
247000 0.85 15750 9050 310 2600 3000 50 3 Water
(stator)&
hydrogen
(rotor)
2004
2010
TABLE IV
Specificat
ions of
Turbo
Generator
s of stage
I. (gen1,
gen2)
KVA Pf Stator
Voltage
(V)
Stator
Current
(A)
Rotor
Voltage
(V)
Rotor
Current
(A)
Rpm Hz Phase Coolant
247000 0.85 15750 9050 310 2600 3000 50 3 Water
(stator)&
11. 4
D. NTPC Group
NTPC Limited
Subsidiaries
Joint Ventures
Figure 3. NTPC Group
NTPC Vidyut
Vyapar
Nigam Limited
100%
NTPC Electric
Supply
Co. Limited
100%
Kanti Bijlee
Utpadan
Nigam Limited
64.57%
NTPC Hydro
Limited
100%
Nabinagar
Power
Generating
Company
Pvt.
Limited/
BF-NTPC
Energy
Systems
Limited
NTPC-Alstom
Power
Services Pvt.
Limited/
Utility
Powertech
Ltd. (UPL)
50%
TELK/ICV
PL, NPEL
44.7%
NTPC-SAIL
Power
Company
Pvt.
Limited
50%
NTPC-SAIL
Power
Company
Pvt.
Limited
50
Ratnagiri
Gas &
Power
Private Ltd
29.65%
Meja Urja
Nigam
Private
Limited
50%
NTPC
Tamilnadu
Energy Co.
Limited
50%
Aravali
Power Co.
Pvt. Ltd.
50%
NTPC-
BHEL
Power
Projects
Pvt.
Limited/
PTC India
Limited
8%
12. 5
II. INTRODUCTIONTO NTPC FEROZGANDHI UNCHAHAR
THERMAL POWER PROJECT (FGUTPP)
A. Location
Located on Lucknow Allahabad state highway
35 Km from Raebareli
80 Km from Allahabad
120 Km from Lucknow
B. Major Milestones
Our late Prime Minister Smt. Indira Gandhi laid down the foundation stone on
27TH June 1981.
First two units of 210MW were commissioned on 21stNovember, 1988 and
22ndMarch, 1989 by U.P. Rajya Vidyut Utpadan Nigam.
Unchahar project was taken over by NTPC from UPSEB on 13th Feb,1992
After take over of FGUTPP from UPRVUN to NTPC, unit-3 & unit-4 were
commissioned on 27th January, 1999 and 22nd October, 1999
Now third stage (unit-5) is of 1X 210 MW.
C. Installed Capacity
Stage I = 2 X 210 MW
Stage II = 2 X 210 MW
Stage III = 210 MW
D. Production Inputs
a. Coal Source
Central Coal fields Ltd. ( CCL)
Bharat Cooking Coal Ltd. (BCCL)
b. Water Source
Sharada Sahayak Canal (main)
Dalmau Pump Canal ( from river Ganga)
13. 6
E. Requirements
Coal – 140 tonnes / hr / unit
Water – 700 tonnes/ hr / unit
F. Cost of Generation
Rs. 2.40 / Kwh
G. Environmental Aspects
Water Pollution- Effluents from thermal discharges from condenser, wastes
from coal handling plant, service areas, oil, DM plant, sanitary waste and
effluents from ash pond will be neutralized before being discharged.
Air Pollution- Particulate emission will be limited to 150 mg/Nm3 by
installing high efficiency ESPs.
H. Layout
The main project consists of following areas:
Main plant area consisting of chimney,ESP,Boiler, Control room, turbine,
generator, transformers and switchyard
Ash handling plant consisting of ash handling pump house, ash handling
compressor house, control room, pipeline corridor and ash ponds
Coal handling Plant consisting of track hopper, primary coal yard, primary
crusher, secondary crusher, secondary coal yard, stacker reclaimed, wagon
trippler and connected conveyors.
Circulating water system consisting of CW pumps, associated pipelines and
cooling towers.
Water treatment plant consisting of chlorination plant, pre-treatment plant and
De-mineralized water treatment plant.
14. 7
Figure 4. Unit overview
I. Various Cycles In The Thermal Plant
i. Coal Cycle
C.H.P Plant → Bunker →R.C Feeder → pulverize mill→ Boiler section
R.C. Feeder -It is induction motor driven device, which determine the Quantity of coal
enter in to pulverize mill.
Pulverize mill - Pulverization means exposing large surface area to the action of oxygen.
Two types of mill are used in the plant.
Ball mill - A ball mill operates normally under suction. A large drum partly filled
with steel balls, is used in this mill. The drum is rotated slowly while coal is fed in to
it. The ball pulverizes the coal by crushing. This type of mill is used in stage -1.
Contact mill - This mill uses impact principle. All the grinding elements and the
primary air fan is mounted on a single shaft. The flow of air carries coal to the
primary stage where it is reduced to a fine granular state by impact with a series of
hammers. This type of mill is used in stage-2.
15. 8
ii. Water Cycle
D.M. Plant → Hot Well → C.E.P. Pump → Low Pressure heater 1,2,3→Derater →
Boiler Feed pump → High pressure Heater 5,6 → Feed Regulating station Economizer
→ Boiler Drum.
Dearater - Feed storage tank of water. To produce sufficient pressure before
feeding to B.F.P. Filter the harmful chemicals.
Feed Regulating Station - Control the quantity of water in to boiler drum.
Economizer - Flue gases coming out of the boilers carry lot of heat. An
economizer extracts a part of this heat from the flue gases and uses it for heat
the feed water.
Drafts System- In forced draft system the fan is installed near the base of the
boiler furnace. This fan forces air through the furnace, economizer, air preheater
and chimney. In an induced draft system, the fan is installed near the base of
Chimney.
iii. Steam Cycle
Boiler drums → Ring Header → Boiler Drum (Steam chamber) → Super Heater → H.P.
Turbine → Reheater → I. P. Turbine → L.P. Turbine
Boiler Drum - 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.
Super Heater - 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 530°C.
Turbine -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 takes place.
Figure 5. Steam flow
16. 9
III. SWITCHYARD
The switch yard is the places from where the electricity is send outside. 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. It has both outdoor and indoor
equipments.
1. Outdoor Equipments
Bus Bar
Lightening Arrester
Wave Trap
Breaker
Capacitor Voltage Transformer
Earthing Rod
Current Transformer
Potential Transformer
Isolators
PLCC
2. Indoor Equipments
Relays
Control Panels
A. Circuit Breaker:
The code for circuit breaker is 52. An electric power system needs some form of
switchgear in order to operate it safely & efficiently under both normal and abnormal
conditions.
Circuit breaker is an arrangement by which we can break the circuit or flow of
current. A circuit breaker in station serves the same purpose as switch but it has many
17. 10
added and complex features. The basic construction of any circuit breaker requires the
separation of contact in an insulating fluid that servers two functions:
It extinguishes the arc drawn between the contacts when circuit breaker opens.
It provides adequate insulation between the contacts and from each contact to
earth.
The insulating fluids commonly used in circuit breakers are:
Compressed air
Oil which produces hydrogen for arc excitation.
Vacuum
Sulphur hexafluoride (SF6 )
There are two makes of Circuit Breakers used at NTPC Unchahar switchyard:
i. SF6 Circuit Breaker – manufactured by ALSTOM
ii. Gas Circuit Breaker – manufactured by CGL
Figure 6. SF6 Circuit Breaker
18. 11
TABLE I
The specifications of the circuit breakers
Specifications ALSTOM Circuit
Breaker
CGL Circuit
Breaker
Type
Rated Voltage
Rated Frequency
Rated Normal Current
Rated Closing Voltage
Rated Opening Voltage
Rated Gas Pressure
Total weight with gas
Gas Weight
Rated Duration of short circuit current
First pole to clear factor
Rated operating pressure
Rated Short-Circuit breaking current
Rated Lightning impulse withstand
voltage
GL 314
245 kV
50 Hz
1600/2500 A
220 V DC
220 V DC
0.85 MPa (abs)
3000 Kg
23.5 Kg
40 kA 3 secs
1.3
15 kg/cm2
-g
40 kA
1050 kV (peak)
200-SFM-40A
245 kV
50 Hz
3150 A
220 V DC
220 V DC
6 Kg/cm2
-g(20° C)
3900 Kg
21 Kg
40 kA 3 secs
5
15 kg/cm2
-g
40 kA
1050 KV (peak)
B. Lightening Arrester
These are provided to combat the effect of over voltages and surges caused due to
lighting strokes on the transmission lines. These are generally provided at the end near
the instrument which we want to protect. The lightening arrestors provide an easy path to
the surge current to the ground thereby not letting the equipments to fail.
It saves the transformer and reactor from over voltage and over currents. We have
to use the lightning arrester both in primary and secondary of transformer and in reactors.
It has a round metal cap type structure on the top called CORONA RING, meant
for providing corona losses.
19. 12
A meter is provided which indicates the surface leakage and internal grading current
of arrester.
Green – arrester is healthy
Red – arrester is defective.
In case of red we first de-energize the arrester and then do the operation.
Figure 7. Lightening Arrester
C. Air Break Earthing Switch
These are used to ground the circuit and to discharge the CB when CB is in off
condition.
The code of earthling switch is 5, 6, 7.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.
TABLE II
The specification of earthing switch
Make Type Voltage Current Motor volt
(ac)
Control volt
(dc)
S & S
power
Madras 245 Kv 10 kA 415 volts 220 volts
20. 13
D. Bus Bar
There are three buses viz. two main buses (bus 1 and bus 2 ) and one transfer bus. The
two main buses are further divided into two sections thus giving us a total of five buses.
Bus bars generally are of high conductive aluminum conforming to IS-5082 or
copper of adequate cross section .Bus bar located in air –insulated enclosures &
segregated from all other components .Bus bar is preferably cover with polyurethane.
E. Capacitor Voltage Transformer (CVT)
It is used for three purposes:
Metering
Protection
PLCC
The carrier current equipment can be connected via the capacitor of CVT. Thereby
there is no need of separate coupling capacitor. The reactor connected in series with the
burden is adjusted to such a value that at supply frequency it resonates with the sum of
two capacitors. This eliminates the error. CVT is attached at end of each transmission,
line and buses.
The cvt is used for line voltage measurements on loaded conditions. The basic
construction of a cvt is as follows. Each CVT consists of a coupling capacitor (CC)
which acts as a voltage driver and an Electro Magnetic Unit (EMU) which transforms the
high voltage to standard low voltage. Depending on the system voltage the CC can be a
single or a multi stack unit. 245 kV & 420kV CVTs no normally comprise of 2 units.
The CC and the EMU are individually hermetically sealed to ensure accurate
performance and high reliability.
Figure 8. Capacitor Voltage Transformer
21. 14
The main points of difference between a cvt and a potential transformer is that in
a PT full line voltage is impressed upon the transformer while in cvt line voltage after
standard reduction is applied to the transformer.
F. Wave Trap
It is used in PLCC system to trap frequency higher than 50 Hz. It is lightly inductive
having very less resistance. It is attached at each end of transmission line. It is of
cylindrical shape mounted on top of the transmission line.
G. PLCC ( Power Line Carrier Communication)
In addition to power supply transfer, transmission line is also used for communication
purpose. This is done by PLCC system. Here line conductors itself are used as channel
for carrying information between two end of line.
The PLCC system is used to trap the frequency higher than 50 Hz through high
inductance and low resistance along with a coupling capacitor. The main components of
PLCC are :-
Wave trap
Co-axial cable
CVT
PLCC cabinet
LMU ( Line matching Unit)
H. Current Transformer (CT)
These are used for stepping down AC current from higher value to lower value for
measurement, protection and control. Here N2 gas is used to prevent oil from moisture.
Its secondary winding has 5 cores.
Terminal 1,2,4,5 – protection
3 - Metering
Turns ratio - 800/1
I. Isolator
The isolators can be thought of switches that can either make or break the circuit at the
operator’s wish. The difference of an isolator from a circuit breaker can be realized from
22. 15
the fact that a circuit breaker’s making or breaking of a circuit depends upon certain
predefined conditions while that of the isolator dictates no condition.
It is used as off line line circuit breaker. It is normally used for purpose of isolating a
certain portion when required for maintenance. It operates at 2000 A. In switchyard there
are 3 types of isolators:
Line isolator
Transfer bus isolator
Bus isolator
Sequence of operation while opening / closing a circuit :
While opening: open circuit breaker open isolator close earthing switch (if any)
While closing: ensure circuit breaker is open close isolator open earthing switch
close circuit breaker.
J. Bay
System components connected in a sequence constitute a bay.
The total number of bays is 22. Out of which 3 are spare bays.
Bay 1 250 MVA 15.75/242 kV Generator transformer – 1
Bay 2 Spare 40 MVA 220/7.1 kV Station Transformer- 3
Bay 3 40 MVA 220/7.1 KV Station Transformer - 1
Bay 4 40 MVA 220/7.1 KV Station Transformer - 2
Bay 6 250 MVA 15.75/242 KV Generator Transformer -2
Bay 7 220 Kv (Chin hut) Luck now Feeder - 1
Bay 8 220 KV Luck now Feeder -2
Bay 9 Bus couplets 220 KV
Bay 10 220 KV Fateful Feeder - 1
Bay 11 220 KV Fateful Feeder - 2
Bay 12 220 KV by Pass Breaker
Bay 13 210 MW Generators -3
Bay 14 40 MVA 220/6.9 KV Station Transformer - 3
Bay 16 210 Mw Generators - 3
Bay 17 220 KV Transfer Bus Coupler- 2
23. 16
Bay 19 220 KV Kanpur Feeders - 1
Bay 20 220 KV Kanpur Feeders - 2
Bay 21 220 KV Kanpur Feeders - 3
Bay 22 220 KV Kanpur Feeders - 4
25. 18
IV. GENERATOR
The transformation of mechanical energy into electrical energy is carried out by the
generator. The generator also called the alternator is based upon the principle of
electromagnetic induction. The stator houses the armature windings and the rotor houses
the field windings. The alternator is a doubly excited system and the field is excited from
dc supply whereas the output received from the alternator is ac. When the rotor is
energised the flux lines emitted by it are cut by the stator windings which induces an emf
in them given by
E = 4.44 f Φ N
Where f frequency in Hz
Φ field strength in webers/m2
N speed of rotor in rpm
Turbo generators run at a very high speed hence the no. of poles are generally two or
four and have a cylindrical rotor construction with small diameter and long axial length.
A. Main components
The main components of a generator are the rotor and stator.
Rotor
The electrical rotor is the most difficult part of the generator to design. It is an
electromagnet and to give it the required strength of magnetic field a large current is
required to flow through it. The rotor is a cast steel ingot and is further forged and
machined.
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. Rotor has hollow conductors with slots to provide for circulation of the cooling
gas.
Rotor balancing: The rotor must then be completely tested for mechanical balance
which eans that a check is made to see if it will run up to normal speed without vibration.
Stator
Stator frame: It is the heaviest load to be transported. The major part is the stator core.
This comprises an inner frame and an outer frame. The outer frame is a rigid fabricated
structure of welded steel plate. In large generator the outer casing is done in two parts.
26. 19
Stator core: it is the heaviest part and is built from a large no. of thin steel plates or
punching.
Stator windings: It is of lap type and employs direct water cooled bar type winding. The
stator winding bar is made from glass lapped elementary conductor and hollow
conductors. The main insulation is applied by means of mica tape which is wrapped and
is compounded with the help of a silicon epoxy compound.
TABLE III
Specifications of Turbo Generators
KVA Pf Stator
Voltage
(V)
Stator
Current
(A)
Rotor
Voltage
(V)
Rotor
Current
(A)
Rpm Hz Phase Coolant
247000 0.85 15750 9050 310 2600 3000 50 3 Water
(stator)&
hydrogen
(rotor)
B. Excitation System
Static Excitation System-The generators in stage -1(u-1&u-2) have this
excitation system. Static excitation system has slip ring and carbon brush
arrangement. It consists of step down transformer, converter and AVR (automatic
voltage regulator).
Brushless Excitation System –The generators in stage -2(U-3, U-4& &U- 5)
have this excitation system. It has two exciters, one is main exciter and other is
pilot exciter.
C. Generator Protection
Stator Protection- The neutral of star connected winding is connected to primary
of neutral grounding transformer, so that earth fault current is limited by over
voltage relay.
Differential Protection- In case of phase-to-phase fault generator is protected by
longitudinal differential relay.
27. 20
Rotor Protection-Rotor winding may be damaged by earth faults or open circuits.
The field is biased by a dc voltage, which causes current to flow through the relay
for an earth fault anywhere on the field system.
Over Speed Protection –Mechanically over speed device that is usually in the
form of centrifugally operated rings mounted on the rotor shaft, which fly out and
close the stop valves if the speed of the set increase more than 10%.
Over Voltage Protection – It is provided with an over voltage relay. The relay is
usually induction pattern. The relay open the main circuit break and the field
switch if the over voltage persists.
Seal Oil System –Hydrogen in the generator is under very high pressure. There is
a possibility of this hydrogen to come out of gaps, which is very hazardous. So,
seal oil is used to seal the gaps so that hydrogen doesn’t come out.
Lubrication Oil System –Turbine lubrication-oil system seeks to provide proper
lubrication of turbo generator bearings and operation of barring gear. Pumps are
used to circulate lubrication-oil inside the generator. The oil of the lubrication
and the governing system is cooled in the oil coolers. The cooling medium for
these coolers is circulating water.
D. Generator Cooling System
Turbo generator is provided with an efficient cooling system to avoid excessive
heating and consequent wear and tear of its main components during operation. The
two main systems employed for cooling are water cooling system and hydrogen
cooling system.
Hydrogen cooling system: Hydrogen is used as a cooling medium in large capacity
generator in view of the following feature of hydrogen. When hydrogen is used as a
coolant the temperature gradient between the surface to be cooled and the coolant is
greatly reduced. This is because of the high coefficient of heat transfer of hydrogen.
The thermal conductivity of hydrogen is 7 times that of air and hence good heat
conduction is possible. While using hydrogen it eliminates oxygen in the chamber
and hence prevents the formation corrosive acids therefore lengthens the life of
insulation. As hydrogen is a non-supporter of combustion hence risk of fire is
28. 21
eliminated. The density of hydrogen is 1/14th times of air hence circulation is also
easier.
The cooling system mainly comprises of a gas control stand, a driver, hydrogen
control panel, gas purity measuring instrument and an indicating instrument, valves
and the sealing system. A great care should be taken so that no oxygen enters the
cooling system because hydrogen forms an explosive mixture with air. The purity of
hydrogen is maintained as high as 98%.to produce hydrogen in such large quantities
a separate plant called the hydrogen plant is also maintained.
Water cooling system: Turbogenerators require water cooling arrangement. The
stator winding is cooled by circulation of demineralised water through hollow
conductors. The system is designed to maintain a constant rate of cooling water flow
to the stator winding at a nominal temperature of 40 deg Celsius.
E. Cooling Specifications Of Turbogenerators At FGUTPP
Stage-I:
Water as well as hydrogen cooling is present in stage-I turbo generators with
following specifications:
Rotor cooling: Hydrogen gas pressure: 3.5 Kg/cm2, Purity: 98%
Stator cooling: Water pressure: 3.5 Kg/cm2, Rate of flow of water: 130 m3/hr
Stage-II & III:
Only hydrogen cooling is used for both stator and rotor cooling.
Rotor cooling: Hydrogen gas pressure: 3.5 Kg/cm2, Purity: 98%
Stator cooling: Hydrogen gas pressure: 2.0 Kg/cm2, Purity: 98%
29. 22
V. TRANSFORMERS
The transformer is a device that transfers electrical energy from one electrical circuit to
another through the medium of magnetic field and without the change of frequency. It is
an electromagnetic energy conversion device, since the energy received by the primary is
first converted to magnetic and is then reconverted to electrical energy in the secondary.
Thus these windings are not connected electrically but coupled magnetically. Its
efficiency is in the range of 97 to 98 %.
A. Transformeraccessories
Conservator: with the variation of temperature there is a corresponding variation
in the volume of oil due to expansion and contraction of oil caused by the
temperature change. To account for this, an expansion vessel called the
conservator is connected to the outside atmosphere through a dehydrating
breather to keep the air in the conservator dry. An oil gauge shows the level of oil
in the conservator.
Breather: it is provided to prevent the contamination of oil in the conservator by
the moisture present in the outside air entering the conservator. The outside air is
drawn into the conservator every time the transformer cools down which results
in the contraction of the volume occupied by the oil in the conservator. The
breather contains a desiccators usually Silica gel which has the property of
absorbing moisture from the air. After sometime silica gel gets saturated and then
it changes it colour from purple to pink indicating that it has become saturated
and hence needs to be replaced or regenerated.
Relief vent: In case of severe internal fault in the transformer, the pressure may
be built to a very high level which may result in the explosion in the tank. Hence
to avoid such condition a relief vent is provided with a bakelite diaphragm which
breaks beyond certain pressure and releases the pressure.
Bushings: they consist of concentric porcelain discs which are used for insulation
and bringing out the terminals of the windings from the tank.
Buchcholtz relay: this is a protection scheme for the transformer to protect of
against anticipated faults. It is applicable to the oil immersed transformer and
depends on the fact that transformer breakdowns are always preceded by violent
30. 23
generation of gas which might occur due to sparking or arcing. It consist of two
mercury relayed switches one for a danger alarm and the second for tripping the
transformer.
Temperature indicators: transformers are provided with two temperature
indicators that indicate the temperature of the winding and that of the oil in the
transformer for an oil filled transformer. The temperature indicators are also
protective in nature whereby the first create an alarm and then trip the respective
transformer in case the temperature of the respective parts rises beyond a certain
value.
Tap changers: these are also provided and are mounted on the transformer. In
case some kind of load fluctuations the taps can be changed or adjusted as per the
need. There are two types of tap changers on load tap changer and off load tap
changer.
B. Cooling Of Transformers
Heat is produced in the transformers due to the current flowing in the conductors of the
windings and on account of the eddy current in the core and also because of the
hysteresis loss. In small dry type transformers the heat is directly dissipated to the
atmosphere. In oil immersed systems oil serves as the medium for transferring the heat
produced. Because of the difference in the temperatures of the parts of the transformers
circulating currents are set. On account of these circulating currents hot oil is moved to
the cooler region namely the heat exchanger and the cooler oil is forced towards the hot
region. The heat exchangers generally consist of radiators with fins which might be
provided with forced or natural type air circulation for removal of heat.
The oil in oil immersed transformers may also be of forced or natural circulation
type. The oil used for cooling is silicone oil or a mixture of naphthalene and paraffin.
When forced oil circulation is used then pumps are used for the circulation of the oil. The
oil forced air forced type cooling is used in large transformers of very high KVA rating.
i. Simple Cooling
AN: Natural cooling by atmospheric circulation, without any special devices. The
transformer core and coils are open all round to the air. This method is confined to very
small units at a few kV at low voltages.
31. 24
AB: In this case the cooling is improved by an air blast, directed by suitable trucking and
produced
By a fan.
ON: The great majority of transformers are oil-immersed with natural cooling, i.e. the
heat developed
In the cores and coils is passed to the oil and thence to the tank walls, from which it is
dissipated.
The advantages over air-cooling include freedom from the possibility of dust clogging
the cooling
Ducts, or of moisture affecting the insulation, and the design for higher voltages is
greatly improved.
OB: In this method the cooling of an ON-type transformer is improved by air blast over
the
Outside of the tank.
OFN: The oil is circulated by pump to natural air coolers.
OFB: For large transformers artificial cooling may be used. The OFB method comprises
a forced
Circulation of the oil to a refrigerator, where it is cooled by air-blast.
OW: An oil-immersed transformer of this type is cooled by the circulation of water in
cooling
Tubes situated at the top of the tank but below oil-level.
OFW: Similar to OFB, except that the refrigerator employs water instead of air blast for
cooling
The oil, which is circulated by pump from the transformer to the cooler.
ii. Mixed Cooling
ON/OB: As ON, but with alternative additional air-blast cooling. ON/OFN, ON/OFB,
ON/OFW,
ON/OB/OFB, ON/OW/OFW: Alternative cooling conditions in accordance with the
methods indicated.
A transformer may have two or three ratings when more than one method of cooling is
provided. For an ON/OB arrangement these ratings are approximately in the ratio 1/1.5;
for ON/OB/OFB in the ratio 1/1.5/2.
32. 25
C. Main Transformers —
i. Generator Transformer: -- This is a step up transformer. This supply gets its
primary supply from generator and its secondary supplies the switchyard from
where it is transmitted to grid. This transformer is oil cooled. The primary of this
transformer is connected in star. The secondary is connected in delta. These are
five in number.
ii. Station Transformer: --This transformer has almost the same rating as the
generator transformer. Its primary is connected in delta and secondary in star. It is
a step down transformer. These are 4 in number.
iii. Unit Auxiliary Transformer: -- This is a step down transformer. The primary
receives from generator and secondary supplies a 6.6 KV bus. This is oil cooled.
These are 10 in number.
iv. 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.
TABLE IV
Specifications of GTs
TA
33. 26
TABLE V
Specifications of STs
TABLE VI
Specifications UATs
TABLE VII
Neural grounded transformer (NGT)
KVA Phase Hz Type of
cooling
No
load
voltage
(volts)
No
load
voltage
LV
(volts)
Line
current
HV (A)
Line
Current
LV (A)
Temp
Rise
of Oil
(°C)
Temp
rise
Winding
1150 3 50 ONAF/ONAN 6600 250 105.9 2655.8 50 55
34. 27
VI. D.C SYSTEM
A. Requirement Of Dc System
There are some auxiliaries which need to run even when the ac supply fails such as seal
oil pumps, the scanner system, valve control, lights, etc. So we require the DC system.
All the circuit breakers in the power plant operate on DC. The DC system
comprises of batteries, chargers, and control circuit to maintain a continuous supply for
the DC feeders.
There are five units in unchahar power plant and in each unit separate battery
rooms are made from which we have 220V as well as 24V DC supply
B. Description of battery:
Capacity = 220 V (1400 AH) / 24 V (400 AH)
Per unit cell = 2.2 V
Battery plate:
Positive terminal = PbO2
Negative terminal = Pb
Electrolyte = H2SO4
Reactions occurring in the battery:
1. At the time of charging:
At positive plate –
PbSO4 + SO4 + 2H2O -> PbO2 + 2H2O
At negative plate –
PbSO4 + H2 -> Pb + H2S
2. At the time of Discharging:
At positive plate –
PbO2 + H2 + H2SO4 -> PbSO4 + 2 H2O
At negative plate –
Pb + SO4 -> PbSO4
C. Battery charger
Battery charger normally operates in two modes.
35. 28
Float charging: It is constant voltage mode and works as a trickle charger.
Boost charging: It is constant current mode and works as a quick charger.
Trickles Charger – It operates at 220V. It is used for continuous charging of the battery.
Full time battery is charged by the trickle charger and remains in float condition.
Quick charger – It is also known as Boost Charger. This is used at the time of
overhauling. It operates in two modes –
i. Constant current (CC)
ii. Constant Voltage (CV)
D. Capacity test of battery:
In order to maintain the condition of battery we do a capacity test. For 220V we first
discharge the battery at the rate of 140 A for 10 hrs. through a resistance boxes. We keep
on monitoring the –
Specific gravity of electrolyte
Temperature
Voltage
of each cell. If the voltage level goes below 1.85V, it indicates that the cell is defective
and needs replacement.
For recharging these batteries we charge them in constant current (CC) mode at
the rate of 6% for 1-2 days. During charging the battery gives a total of 270-280 V. In
order to maintain 220 V level we bypass some batteries till the supply is maintained.
Basic operation of charger:
In the charger there are two incomers and at a time only one switches in on. This supply
goes to the contactor which is tapped through the coils according to the voltage levels.
The diodes rectify ac to dc but since it is not ripple free so we apply the LC filter circuit
which lowers the ripple factor and gives us the DC same is the case with 24 V Charger.
From the charger one supply goes to the DCDB (Direct Coupled Digital Board)
and the other to the battery for charging.
36. 29
VII. SWITCHGEAR
Switchgear is an electrical functional switch used for starting any drive and provides
protection to the drive during on load condition. It is of two types:-
Low tension switchgear (below 1000 V)
High tension switchgear (above 1000 V)
A. L.T Switchgear
OPERATING VOLTAGE- 415VOLT
The main components are:
Relays
Contactors
Isolators
Fuses
Relays: the purpose of protective relaying system is to operate the circuit breaker so as to
disconnect only the faulty equipment from the system as quickly as possible thus
minimizing the trouble and damage caused by faults when they do occur. The general
relay used is BMR ( Bi-Metallic Relay). It trips due to thermal overloading when over
current passes through the bimetallic strips causes different expansions in different parts
as a result the BMR strip is bent.
Contactors: these are used on-load operations under normal conditions. Contactor is a
mechanical switching device capable of making carrying and breaking electric current
under normal circuit conditions including operating overload conditions
Isolators: These are disconnecting switches used for off-load operations. These are
operated manually. Before operation power is switched off. Isolators are kept in closed
position when the system components are in operation. During any maintenance work
isolators are kept open.
Fuses: It is a device used in circuit for protecting electrical equipments against overload
or short circuit. The fuse wire melts when an excessive current flows in the circuit and
thus isolates the faulty device from the supply circuit.
37. 30
B. H.T. Switchgear
OPERATIONG VOLTAGE - 6.6KV
For low voltage circuits fuses may be used to isolate the faulty circuit. For voltage higher
than 3.3 kV isolation is achieved by circuit breaker.
Requirement of circuit breaker:
After occurrence of fault the switchgears must isolate the faulty circuit as quickly
as possible i.e. keeping the delay to minimum.
It should not operate when an over current flows under healthy condition.
Basic principal of operation of circuit breaker:
Circuit breaker consists of a fix contact and sliding contact into which moves a moving
contact. The end of moving contact it attached to a handle that can be manually operated
or may operate automatically with the help of mechanism that has a trip coil energized
by secondary of CT. Under normal condition the secondary of CT is not energized
sufficiently to trip the coil but under false condition the coil is energized fully to operate
the trip coil and the circuit breaker is operated.
MOCB (Minimum oil circuit breaker)
SF6 (Sulphur hexafluoride circuit breaker)
Here oil and SF6 are used to quench the arc.
Bus ducts:
These serve as interconnection between transformer and switchgear and are non-
segregated phase type. These are natural air cooled.
Bus coupler:
It acts as interconnection between the two buses. If the supply of one bus fails then the
bus coupler connects the two buses and charges the bus from the other bus.
Different relays used:
Motor protection system
Earth fault relay
Over load relay
Lock out relay
Check synchronizing relay
39. 32
VIII. 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 530 deg 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 hydra step. Hydra
step is a phenomenon based on the difference in the conductivities of water and steam.
Since there is great pressure and temperature at the boiler great care should be
taken while going to the site and maintenance.
Since coal is burning in the furnace and then we have water tubes of the boiler
inside hence constant burning of coal produces ash which gets collected on the water
tubes and the start working as insulation, hence its necessary to blow this soot hence for
this purpose we use Soot Blowers.
Soot blowers are basically pipe like structures that go inside the furnace and the
boiler for efficient on load cleaning. Cleaning is done by the superheated steam which is
tapped from the super heater 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
40. 33
Before sending this steam to the turbine, the steam is again superheated and then its
temperature is around 580deg Celsius. 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 super heater and then finally to a high temperature
super heater. The steam which is now produced goes to the HP turbine.
Figure 11. Water tube Boiler Schematic Layout
41. 34
IX. ELECTROSTATIC PRECIPITATOR (ESP)
The ash content in the Indian coal is of the order of 30 to 40 %. When coal is fired in the
boiler, ashes are liberated and about 80% of ash is carried along with the flue gases. If
this ash is allowed to flow in the atmosphere, it will cause air pollution and lead to health
troubles. Therefore it is necessary to precipitate the dust from the flue gases and this
work is done by the electrostatic precipitator.
A. Working principle
The principle upon which an electrostatic precipitator works is that dust laden gases are
passed into a chamber where the individual particles of dust are given an electric charge
by absorption of free ions from a high voltage DC ionising field. Electric forces cause a
stream of ions to pass from the discharge electrodes (emitting) to the collecting
electrodes and the particles of ash in the gas are deflected out of the gas stream into the
collecting surfaces where they are retained by electrical attraction. They are removed by
an intermittent blow usually referred to as RAPPING. This causes the ash to drop into
hoppers situated below the electrodes. There are 4 steps that are involved:
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.
B. Description
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.
C. Parts of ESP
1. Basing-: the precipitator casing is robustly designed and has an all welded steel
construction.
2. Hoppers-: the hoppers are of pyramidical shape. The angle between hopper corner
and the horizontal is never less than 55 deg and often more to ensure easy dust flow.
42. 35
To ensure free flow dry ash into disposal system the lower portion of hopper are
provided with electrical heaters.
3. Collecting system-: the collecting system consists of electrodes which are based on
the concept of dimensional stability. They have a flat uniform surface for uniform
charge distribution. These electrodes have larger area and are grounded, hence have
zero potential.
4. Emitting system-: the emitting system consist of emitting or discharging electrodes
that are in the front of the helical wires for a non-uniform distribution to enhance the
rate of charging since a non-uniform field is created.
5. Rapping mechanism-: the Rapping mechanism is a process which is employed to
hammer out the ash particles which get precipitated on the respective plates. Hence
in order to hammer out those particles rapping motors are employed which hammer
at the rate of 2 to 3 cycles per minute. Various motors are employed and are called
collecting rapping motor and emitting rapping motor.
6. Insulators-: these are also employed for support since ESP is hung with the help of
these insulators.
7. Transformer Rectifier-: a transformer rectifier is employed which steps up the
voltage to 70KV and then it is rectified to -70 KV and is given to the emitting
electrode
Figure 12. Schematic Diagram of ESP
43. 36
D. Electrical scheme of ESP
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 the hoppers.
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%. The ESP is divided into 4
passes called A, B, C, D and has various fields per pass.
In stage-I we have 7 fields per pass and hence the total no. of fields is 28 whereas in
stage-II & III we have have 8 fields per pass and hence the total no. of fields is 32.
E. Variable frequency drive
From the electrostatic precipitator, the flue gases are sucked. It is a type of fan and is
called Induced draft fan. It sucks the flue gases from the ESP and then transfers them to
the chimney. In stage-I an IM is employed for this purpose but the speed control of that
motor is not possible. Sometimes the amount of flue gases coming out is small and other
times it is large but since no speed control is possible hence the flow of flue gases
become a tedious task. However in stage-II the speed control is possible since here we
have variable frequency drive. The motor which is employed here are synchronous
motor.
Using variable frequency drive voltage is compensated at low frequencies, the
torque at low speeds is improved. To obtain the voltage boost, we require a controlled
converter as well as a controlled inverter.
The panel in Figure 11 is a variable frequency drive panel. First the three phase
supply from transformer is fed to the controlled rectifier which the ac to dc. The
advantage of using a controlled rectifier is that the average value of the output can be
44. 37
controlled by varying the firing angle. Then its output is fed to the inverter which is a
type of load commutated inverter. Before passing it to the inverter a reactor is also
employed in between this reduces the ripples. The inverter then converts dc to ac and the
ac is fed to the synchronous motor. The speed of synchronous motor is fixed and is given
by 120 f / p. since the only thing variable in the expression is the frequency which is
directly proportional to the speed. Hence the inverter varies the frequency and hence
controls the speed of the motor. The controlled rectifier in the circuit is used for voltage
control while the load commutated inverter is used for frequency variation
Figure 13. Electrical scheme of VFD
Two channel arrangement for synchronous motor
The stator of the synchronous motor is given supply using two channels. Normally the
motor works on both channels but under some faulty conditions on any one of the
channels the other channel can continue working since the motor is required for
continuous operation
Figure 14. Two channel arrangement of synchronous motor
45. 38
Hence the frequency is varied from 0.5 Hz to 47.5Hz. When both channels
operate the motor moves at 575rpm and when one channel is in operation the maximum
speed is 475rpm. The power and current ratings in case of both the channels is 1414KW
& 420Amp. In case only one channel is working then the power is 635KW and current is
380Amp.
TABLE VIII
Specification of Synchronous Motor
KW
rating
KVA
rating
P.F. Speed
(rpm)
Stator
voltage
Excitation
voltage
Insulation
class
Wt.
(Kg)
1414KW 1646 0.9
(lead)
575 2X1200
V
170 V dc F 19,000
Advantages of Variable Frequency Drive
1. Speed control is fine as the frequency is varied from 0.5Hz to 47.5 Hz.
2. Very low starting current as motor starts on reduced voltage.
3. Power consumption is low.
4. Motor life is improved
46. 39
X. COAL HANDLING PLANT
A. Introduction
NTPC Unchahar gets its coal supply mainly from Bihar. Now coal is also coming from
Australia, as coal produced in India is of low grade and ash content is more. The coal
being filled in the wagons of the rail reaches plant. The purpose of this plant is to convey
the coal to the bunker in the size not larger than 20mm.It handles and transports the coal
to the bunker from the wagons by passing through various conveyors, transfer points,
crusher houses, etc.
BCCL costs Rs.4/kg
CCI cost Rs.6/kg
B. Properties of Coal
1. Calorific value: the heat evolved when unit amount of coal is burned.
2. Gross calorific value: the heat evolved when all the products of combustion are
cooled to the atmospheric temperature.
3. Net calorific value: it is the value obtained when GCV is subtracted by sensible
and latent heat of water in the products of combustion.
4. Grindablity: it is the ease with which the coal can be ground to fine sizes. It is
measured on the hard grove scale. Coal used here has a Grindablity index of 55.
C. Coal analysis
It is done in two ways:
1. Proximate analysis: it gives the behaviour of coal when heated.
2. Ultimate analysis: it tells the elementary composition of coal. It is useful in
determining the air required for combustion and in finding the weight of
combustion products.
D. Different methods of unloading the coal
1. Manual Unloading: - Previously, manpower was used for unloading the wagons.
But it was very time consuming and more workers were required for the job to be
done.
47. 40
2. Box in (using wagon tippler for unloading): - This method is still used in stage-1
of NTPC Unchahar. For this method, Indian Railway grants 10 hours for
unloading the 58 wagons. In this method, Wagons are separated and tippled by using
wagon tippler. The Beetle Feeder is used to move the wagon on wagon tippler. The
coal from the wagons gets accumulated in The Track Hopper. At this time; the size
of the coal is approximately 300mm.
3. BOBR: - This method is used in used in stage -2 and stage-3 of NTPC
Unchahar. Indian Railway grants only 2.5 hours for Unloading 58 BOBR wagons.
This is an advanced technology in which we use the compressor system. In Bottom
Open Bottom Release (BOBR) technology the wagons are opened from side.
Pressure is applied by the compressor to open the bottom gates of the wagon so that
the coal gets released over the track hopper and wagon get unloaded quickly.
E. Various equipment used in CHP
i. Marshalling Yard: it consist of railway tracks provided to receive the
loaded trains, to unload them and to put them back in formation without
interference between loaded and empty racks.
ii. Wagon Tripler: The wagon Tripler is a most important device in thermal power
project. The Wagon Tripler turns back the wagon at 135-degree angle and the
structure of the wagon tippler is to be very heavy. Upper side of the wagon is
fixed with the many angles for supporting the wagon. When the wagon is fixed
on the Platform then whole platform is turned back and the coal fall down in the
wagon tippler hopper. The unloading time of the Rack is 6hours. Here the type of
the rack is Box C / Box N type.
Wagon Tripler Hopper: - The Wagon Tripler Hopper is a part of the wagon
tippler where the coal is stored from the wagon triple. The size of the coal
here is less than 300mm.
Vibrating Feeder: - The vibrating feeder is used for falling the coal on the
conveyer through Wagon tippler Hoper. Before Wagon tippler Hoper and
Vibrating Feeder the gate is providing to control the flow of the coal.
48. 41
Beetle Charger: - The Beetle charger is a traveling device that is used to
carry the wagon on the wagon tippler platform.
Dust Suppuration: - Dust Suppuration is a useful device. When the wagon
are tippling then the dust is mixed in the air and that area becomes very dusty
then Dust Suppuration operates and water flows through its points and the
dust settles down. It is an automatic device.
iii. Paddle Feeder: - They have been installed on conveyors below the manual
unloading track hopper. There are 6 nos. of paddle feeders, 3 on each conveyer. 3
Paddle Feeders of each conveyer move to and fro within a limiting range. The
rotating part of the paddle feeder is called as plough wheel. Plough wheel has 6
blades. By the rotation of the plough wheel, the coal of the track hopper gets
accumulated between the blades and is discharged on the conveyor below it. The
main components of paddle feeder are:
Plough wheel - It is the rotating part consists of 6 blades. It is attached with
the rotor of 3-phase slip ring induction motor.
Reduction gear box - It is installed to control the speed of plough wheel.
End limit switch (left or right) - It provides the limiting motion of the
paddle feeders.
Anti-collision switch - It provides the prevention from collision between two
paddle feeders.
Interlock system - It is provided for safety purpose. By this, the conveyor
belt moves first then paddle feeder starts.
iv. Vibrating Feeder: - They have been installed below the track hoppers of wagon
tippler. The coal is accumulated over the vibrating feeder so by giving vibrations
to the vibrating feeder we discharge the coal from track hopper to the conveyors.
Their main purpose is to provide uniform feeding on the conveyors. The vibrating
feeders consist of a tray to which vibrator body is fixed on the rear end.
v. Transfer Points: - Transfer Point is provided with flap gate and Conveyer. In
transfer Point the coal is transferred from one conveyer to other conveyer.
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vi. Flap Gate: - The flap Gate is a two-way device. It consists of two gates. Both
gates cannot operate together. By help of the flap Gate, we change the way of
coal that fall down on the conveyer.
vii. Conveyers: - The Conveyer Belt is a moving device. It travels on its platforms.
The shape of the conveyer belt is to be flat but on the platforms it is to be in curve
shape. The coal falls down the conveyer and goes to the primary Crusher House
Platforms. The capacity of conveyer in Stage – I is 800MT/ hr. & in Stage –II is
1200MT / hr.
Figure 15. Forward Conveyor Figure 16. Return Conveyor
viii. Protecting devices provided to the Conveyer
Zero Speed Switch: - The Zero Speed Switch prevents the Conveyer from
over load run. When the conveyer is over loaded, the speed of the conveyer is
reduced and Zero Speed Switch is operated and stops the conveyer. This
device is provided at Head End of the Conveyer. The Zero Speed Switch is a
Centrifugal Switch.
Pull cord Switch: - This is a manual protecting device. When the Worker
sees any mistake like big stone or any dangerous fault, pulls this cord. The
Pull Cord Switch is to be operated, and the Conveyer stops.
Belt Sway Switch: - The Belt Sway Switch also protects the conveyer. This
device is provided on both side of the conveyer. When the conveyer leaves its
way the switch is operated and the conveyer stops. This is also an automatic
protecting device.
Linear heat sensing cable: - This protection is for any type of heat related
procedures. If by any means the temperature of the conveyor belt increases
beyond a certain limit then this protection comes into action. In this
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protection a special temperature sensing type wire runs through the periphery
of the conveyor structure.
ix. Primary crusher (rotary breaker): - In Primary Crusher House, the coal breaks
in Rotary Breaker. Here the coal comes from the Transfer point; breaks here and
the stone fall down to a separate place. Coal is converted from 300mm to 150mm
size.
Parts of the Primary Crusher House –
Rotary Breaker: - The Rotary Breaker has a rotating mechanism. It is
rotated on the shaft. The coal come from the conveyer through the Flap Gate
falls down into the rotary breaker. The rotary breaker is to be rotated and coal
moves up and down and collides and hence breaks. The Rotary Breaker is
H.T. 170KW 6.6KV Motor.
Belt Feeder: - The Belt Feeder is a small size of the conveyer. It is used
for feeding the coal to the conveyer through Flap Gate.
x. Secondary Crusher (Ring Granulator): - In Secondary crusher House first the
magnetic part separate from the coal and then feed to the Secondary Crusher.
This Crusher breaks the coal in 20mm size and coal is sent to the Flap Gate and
then feeded to the conveyer. The Secondary crusher is hammer type. H.T. motor
are used for breaking of the coal. Specifications are 700KW 6.6KVMotor.
xi. Cross Belt Magnetic Separators: - They will remove the ferrous particles, which
passes along with the coal. It consists of electromagnet around which a belt is
moving. It is suspended from top, perpendicular to the conveyor belt at certain
height. Whenever any iron particle passes below the CBMS, it is attracted by the
magnet and stick to the cross belt below it. The CBMS capacity is of 50kg.
xii.Metal Detector: - The purpose of installation is to detect any metallic piece
passing through the conveyor. Whenever the pieces pass below the search coil of
the metal detector, it gives the trip command to the conveyor. Simultaneously,
sand bag marker will fall on the conveyor belt so that the metal can be searched
easily and removed.
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xiii. Stacker/Reclaimer: - It is a very important device. The whole Structure of
it is called Super Structure. It stacks the excessive coal and reclaims the coal on
its requirement. It is a two-way device. It consists of following main parts:
Stacker: - The Stack is a position (1). When the rack comes, the
excessive coal is send to the stacker through the conveyer from Secondary
Crusher house. The coals are stacked at the Secondary Crusher Coal Heap. The
coal falls down from the stacker through Boom Conveyer.
Reclaimer: - The Reclaimer is position (2). When the rack is not coming
and there is a shortage of coal, then reclaiming is to be started and the coal is
lifted from the Secondary Crush Coal Heap and fed to the bunker.
Boom Conveyer: - The Boom conveyer is a Bi-directional conveyer. It
moves clockwise & anticlockwise direction. In stacking position, it is moving in
clockwise direction and in the reclaiming position it’s moving in anticlockwise
direction. They are provided with Center Chute and End Chute on the both end.
Boom hoist: - The Boom hoist is a link of the Super Structure. The hoist
is moved up and down. For controlling the up & down position, limit switch is
provided.
Slew drive: - The Slew Drive moves at 180-degree. When the coal is
stored on both the side of the track of travel, then the Slew Drive moves and lifts
or fall the coal from Boom Conveyer. For control the rotation of Slew Drive, the
limit switch is provided.
Bucket wheel: - The Bucket Wheel is used when there is a requirement of
the coal. It is a rotary device. It is always rotated in anticlockwise. In the
Reclaiming position, the Center Chute is to be up and End Chute of the Boom
Conveyer is fixed on the conveyer. The Bucket Wheel rotates; when the Bucket
of the wheel is full with coal and the wheel is rotated the coal fall down on the
Boom conveyer and the coal is send to the Super Structure.
Travel: - It is a slip ring induction motor driven system. The Super
Structure moves on it. The normal speed of the Travel is 10 meter / minute. It
moves on its track from one end to other end.
The stacker reclaimer does the following three functions:
1. travelling (movement in forward and reverse direction)#
2. luffing (up and down movement)
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3. slewing (left and right movement)
The stacker reclaimer also has two cable reeling drums in which the reeling action is
done by electrical medium and the unreeling is done mechanically. Great care has to be
taken during this operation since any loop hole can lead to accidental results. During the
stocking operation the coal from the crusher house is diverted towards the stockyard
conveyor at a transfer point. The above conveyor discharges coal to the boom conveyor
through a discharge chute. The boom conveyor running in the forward direction creates
coal stacks.
During reclaiming, coal from the stockyard falls on the boom conveyor with the help
of bucket wheel and the boom conveyor during this period rotates in the reverse
direction. The coal from the central chute falls on the conveyor belts used for transferring
the coal from the stockyard.
Advantages:
1. It can operate at full load capacity in bad weather.
2. It is productive at all times as no return journey is to be performed.
The only drawback is that it is expensive.
xiv.Transfer Tower: - Here the coal is send to the Tipper. Transfer Tower is
provided with a coal sampler.
xv. Tipper: - The Tipper is a three-way device to feed the coal in Bunker. It is
moveable device. It is move on its track.
xvi.Bunker: - Here the coal is collected from the tipper and stored. The capacity of
the bunker for Stage-I is 4800MT & Stage-II is 8700MT.
F. Some Special Motors Of CHP
1. Secondary Crusher house motor :-
450 kW P.F. = 0.77
Supply 6.6 kV 746 rpm
2. Primary Crusher house motor:-
700 kW P.F. = 0.78
Supply 6.6 kV 742 rpm
3. Stacker Reclaimer:-
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5.5 kW P.F. = 0.70
Supply 6.6 kV 965 rpm
4. Wagon Trippler motor:-
175 kW
Supply 415 V
5. Rotary Breaker motor:-
175 kW P.F. = 0.8
Supply 6.6 kV 1485 rpm
6. Vibrating Feeder motor:-
40 kW 1470 rpm
Supply 415 V efficiency = 93 %
G. Power and Distribution Diagrams
Stage-I
Figure 17. Power distribution diagram of CHP in stage I
Stage-II
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Figure 18. Power distribution diagram of CHP in stage II
XI. CONCLUSION
On completion of my vocational training at NTPC Feroze Gandhi Unchahar Thermal
Power Project, I have come to know about how the very necessity of our lives nowadays
i.e how electricity is generated. What all processes are needed to generate and run the
plant on a 24x7 basis?
NTPC Unchahar is one the plants in India to be under highest load factor for the
maximum duration of time and that to operating at highest plant efficiencies. This plant
is an example in terms of working efficiency and management of resources to all other
thermal plants in our country. The operating plf of the NTPC as compared to the rest of
country is the highest with 87.54% the highest since its inception.
The training gave me an opportunity to clear my concepts from practical point of
view with the availability of machinery of diverse ratings.
