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Calcutta Electricity State Cooperation Limited
(CESC Ltd)
Budge Budge Generating Station
Name SARTHAK MODAK
Address 88, LENIN SARANI, KANCHRAPARA, NORTH
24 PARGANAS
Pin code - 743145
College SAROJ MOHAN INSTITUTE OF TECHNOLOGY,
U GUPTIPARA, HOOGLY
Pin code - 712512
Duration of Training From 24thdec 2012
To 5th
jan 2013
ACKNOWLEDGEMENT
This Acknowledgement is not a formality but a way to show my deep sense of gratitude to
all the people of BBGS for their inspiration & guidance during the training period whose co-
operation and suggestions helped me a lot to complete this project.
Firstly I would like to thank the following people for giving the opportunity to do the
training:
Mr. A. Saha (GENERAL MANAGER, BBGS)
Mr. S. Dutta (DY. GENERAL MANAGER, BBGS)
Mr. D. Maitra (DY. GENERAL MANAGER, HR)
Mr. S. Roy (DY.GENERAL MANAGER,BBGS)
I am also highly indebted to the following people under whose guidance I
successfully completed my training in various departments of BBGS:
Mr. Arijit Ghosh (SR. MANAGER, PLG)
Mr. Subrata Mondal (DY. MANAGER, F&A)
Mr. Santashri Ghosh (MANAGER, E&I)
Mr. Kaushik Chaudhuri (MANAGER, OPS)
Mr. Samir Bandyopadhyay (MANAGER, MMD)
I am also extremely thankful to the following people whose constant support,
encouragement & guidance helped me to do the training and understand the
essence of a power-generation plant:
Mr. S.P. Bhattacharya (CONSULTANT HR)
Mr. S. Roy (ASST. ENGINEER, HRD)
Last but not the least, I would like to sho my gratitude to all the labours, workers & various other employees of BBGS who have cordially helped me to understand
the various technical aspects of the power-plant at different instants throughout
the training period
SIGNATURES OF OFFICERS OF VARIOUS
DEPARTMENTS
DEPT: OPERATION
NAME:- SIGNATURE:-
_______________
DEPT: F&A
NAME:- SIGNATURE:- ________________
DEPT: MMD
NAME:- SIGNATURE:-
________________
DEPT:- E&I
NAME:- SIGNATURE:-
________________
DEPT:-PLC
NAME:- SIGNATURE:- _________________
MARKS OBTAINED IN WRITTEN TEST:-
____
ATTENDANCE:- _____
DEPT:-PTC
NAME:- SIGNATURE:- ______________
The Calcutta Electric Supply Corporation or CESC is an Indian electricity generating
company serving the area administered by the Kolkata municipal corporation, in
addition to the city of Kolkata, it also serves parts of the Howrah, Hooghly, 24 Parganas
(North) and 24 Parganas (South) districts of West Bengal.
On 7 January 1897 Kilburn & Co. secured the Calcutta (Now Kolkata) electric lighting
license as agents of The Indian Electric Company Limited. The company soon changed
its name to the Calcutta Electric Supply Corporation Limited. The first power
generating station was begun on April 17, 1899 near the Princep Ghat. The Calcutta
Tramways Company switched to electricity from horse drawn carriages in 1902. Three
new power generating stations were started by 1906. The company was shifted to
the Victoria House in Dharmatala in 1933, and still operates from this address.
Load-shedding (interruption of power supply due to shortage of electricity) was
common in Kolkata during 1970s and 1980s. In 1978 the company was christened as
The Calcutta Electric Supply Corporation (India) Limited. The RPG Group was associated
with The Calcutta Electric Supply Corporation (India) Limited from 1989, and the name
was changed from The Calcutta Electric Supply Corporation (India) Limited to CESC
Limited.
Recently the Calcutta power grid has seen progressively better performance and fewer
outages. In the power sector, CESC, currently having a generating capacity of 1225 MW,
has major plans to expand generating capacity to 7000 MW over the next five or six
years. The new power generating projects thermal, hydal and solarwill involve investments of more than ` 30,000 crore. Presently CESC Ltd is the flagship company
of RP-SANJIV GOENKA GROUP.
Generation and Distribution of Electricity since 1897
First Thermal Power Generation Company in India
Initial Licensed Area 14.44 sq. km
Brought Electricity to Kolkata 10 years after it came to London
Tunnel under Ganga for power transmission
In 1989, CESC became a part of RPG Group
In 2011, CESC became a part of RP-Sanjiv Goenka Group
Salient features:
No. of Consumers: 2.5 million
No. of Employees: 10000
Generation Capacity: 1225 MW
Substation Capacity: 7483 MVA
Transmission and Distribution Network: 18449 ckt. KM
Power Generation in the year 2010-11: 8756 MU
Power export in the year 2010-11: 146 MU
Power Import in the year 2010-11: 1523 MU
Total Revenue in the year 2010-11: 4092 crores
Profit after tax in the year 2010-11: 488 crores
Generating station features:
New Cossipore(NCGS):
Commissioned: 1949
Capacity: 100 MW (derated)
Feature of boiler: Stoker fired
Titagarh(TGS):
Commissioned: 1983
Capacity: 240 MW
Feature of boiler: P.F.
Southern(SGS):
Commissioned: 1991
Capacity: 135 MW
Feature of boiler: P.F.
Budge Budge(BBGS):
Commissioned: 1997
Capacity: 750 MW
Feature of boiler: P.F.
PROJECT PROFILE
Capacity 750 MW (3 x 250 MW)
Location PUJALI, BUDGE BUDGE, 24 PGS(S), WEST
BENGAL
COMMERCIAL GENERATION
Unit # 1 07.10.97
Unit # 2 01.07.99
Unit # 2 28.01.10
Fuel source ECL, BCCL, ICML & Imported Coals
Fuel requirement 2.45 million tons of coal per annum
Mode of transportation Rail
Water source River Hooghly
Land area 225 acres
Ash dumping area 91 acres
UNIQUE FEATURES
Largest coal fired thermal power station of CESC Ltd
Use of clarified water for condenser and other auxiliaries
Vertical Down-Shot fired boilers having Non Turbulent, Low NOx
Burners
Use of gas re-circulation in boiler
Use of Hydrogen Cooling and Stator Water Cooling for Generator (first in
CESC)
Use of Cooling Towers for Closed Circulating Water System (first in CESC)
Use of Zero Discharge System for Bottom Ash Disposal
Incorporation of Zero Effluent System
Installation and Operation of a High Concentration Slurry System (HCSS)
BUDGE BUDGE GENERATING STATION
No of units
3
Capacity
250 MW
Unit # 1
Trial Synchronization
16.9.97
Commercial generation
07.10.97
Full Load Generation
26.02.98
Unit # 2
Trial Synchronization
06.03.99
Commercial generation
01.07.99
Full Load Generation
09.08.99
Unit # 3
Trial Synchronization
12.07.09
Commercial generation
28.01.10
Full Load Generation
29.09.09
POWER GENERATION CYCLE
Heat for the power cycle of CESC, Budge Budge Generating Station Unit No. 1 & 2 is
derived from burning pulverized coal in a Natural Circulation, Balanced Draft, Two
Pass, Down-Shot Fired, Single Reheat Drum Type Boiler and Unit 3 is Natural
Circulation, Balanced Draft, Two Pass, Corner Fired, Single Reheat Drum Type Boiler.
However, during Light-up LDO is used for support & stabilization. For unit 1 & 2 each
unit has a 250 MW Rolls-Parsons turbo-generator, an Acc-Babcock make P.F boiler and
unit 3 has 250 MW BHEL make turbo-generator & P.F boiler with a maximum continuous
rating of 805T/hr of steam, and all auxiliary systems and equipment to make a
complete generating unit.
Each boiler has been provided with two forced draft fans (F.D), three induced draft fans
(I.D) for unit 1&2 & two induced draft fans (I.D) for unit 3, two primary air fans (P.A),
one primary tubular air heater, two secondary tubular air heaters for unit 1 & 2 and
two rotary air heater for unit 3, six Ball & Race type pulverizes, six Volumetric coal
feeders for unit 1 & 2 and five Bowl type pulverizes, five Gravimetric coal feeders for
unit 3, etc. Soot blowing is done by steam. Main and reheat steam temperature is
maintained from full load to 60% load. The boiler is capable of sustained stable
operation down to 2 Mills at 30% capacity without oil support for flame stabilization.
25% BMCR requirement can be achieved by burning LDO alone.
The main turbine is a Tandem Compounded, Three Cylinder, Single Reheat, Double
Flow LP cylinder, Condensing Type with uncontrolled Extraction.
In the power plant there are nine cycles which makes the whole power plant work.
They are:-
1) Coal Cycle
2) Steam Cycle
3) Reheat, Regenerative Cycle/ Turbine cycle
4) Electricity Cycle
5) Light diesel oil (LDO) Cycle
6) Ash cycle
7) Feed water Cycle
8) Air Cycle
9) Condenser Cooling Water Cycle
There are many departments in the Budge Budge Generating Station. They are:-
1) Fuel & Ash department
2) Planning & Environment department
3) Mechanical Maintenance department
4) Operations department
5) Electrical & instrumental department
6) Plant training center
FUEL AND ASH DEPARTMENT
The primary fuel for these units is bituminous coal supplied from coal mines. The coal
handling plant has been designed for 960 MTH coal of (-) 300 mm size which is
generally received at the site from the mines. Coal is unloaded in the yard either by
Roadside wagon tipplers or in the track hopper through bottom discharge wagons. The
coal is crushed in two stages before it is fed into the boiler bunkers. In the first stage it
is crushed to (-) 100 mm size by primary crushers and finally to (-) 20 mm by
secondary crushers. 2 x 100% parallel chains of conveyors are provided to convey coal
from the coal yard to boiler bunkers.
The FUEL AND ASH DEPARTMENT can be broadly divided into two plants:-
1) Coal handling plant
2) Ash handling plant
COAL HANDLING PLANT
Capacity:-
Design 960 T/Hr
Rated 800 T/Hr
No Of Wagon Tippler 2
No Of Track Hopper 1
Capacity 1500 MT
Primary Crusher
Quantity 2 Nos.
Type Rotary Breaker
Secondary Crusher
Quantity 2 Nos.
Type Ring Granulator
Each day he amount of coal required is about 10500T/day when the power plant is
working a 100% load for 24 hours. The coal comes from ECL, BCCL, ICML, & Imported
coal from Indonesia. Coal having ash contain less than 30% is used in power plant. The
coal coming from Indonesia has a ash contain less than 5%.
The coal comes via railway in BOBR & BOX(N) wagons. The BOBR wagons go into the
track hopper and the coal fall into 1A and 1B conveyer belt through a 300 sq mm net
while BOX(N) wagons unload into the wagon tripper which falls into the 1C & 1D
conveyer belt. Then they pass through two electromagnetic separators and fall into the
reversible belt feeder (RBF4A & RBF4B) and fall into the conveyer belt 2A & 2B. it leads
to the primary crusher house which granulates the coal to size lesser than 100 sq mm
it also separates the stone and coal. The stones go into the reject bin and the
granulated coal goes into a reversible belt feeder (RBF1A & RBF1B) which leads the coal
either to the coal stack yard or to the secondary crusher house.
The coal goes to the coal stack yard via the conveyer belt 8A & 8B then 10A & 10B then
to the Stacker-Cum-Reclaimer which stacks the coal in the coal yard. When it is needed
to reclaim the coal then the bucket wheel reclaimer reclaims the coal and sends it
through the conveyer belts 11A & 11B then to 12A & 12B then through flap gates to
conveyer belts 3A & 3B which goes into the secondary crusher house.
Stacker-Cum-Reclaimer
Type Slewing And Boom Stacker With Bucket Wheel
Reclaimer, Rail Mounted, Suitable For
Reversible Yard Conveyor.
Nos. 2
Total Travel (M) 308 M
Lump Size (-)100 Mm
Height Of Pile (M) 10.5
Type of Material
Handled-
Material Semi Crushed Coal
Lump size (-)100 mm
The secondary crusher house is a ring granular that granulates the coal to a size less
than 20 mm sq. From there the coal in conveyed through 4A & 4B to the bunkers. Unit 1
& unit 2 consists 6 bunkers each while unit 3 consists 5 bunkers. From there it goes
into the coal mill. There are six Ball & Race type pulverizes, six Volumetric coal feeders
for unit 1 & 2 and five Bowl type pulverizes, five Gravimetric coal feeders for unit 3.
The other part of this department is the ash handling plant.
ASH HANDLING SYSTEM
Fly Ash Handling System
Fly Ash Evacuation Rate 80 Mt/Hr
Capacities of Tank / Vessel
Air Heater 57 Litres
ESP 1 & 2 485 Litres
ESP 3 145 Litres
ESP 4 To 7 85 Litres
Bottom Ash System
Bottom Ash Cleaning Rate 60 MT/Hr
Effective Storage Capacity
Bottom Ash Hopper 150 MT (Approx)
De Watering Bin 432 MT (Approx)
Settling Tank 1240 CUM (Approx)
Surge Tank 1670 CUM (Approx)
Overflow Transfer Tank 21 CUM (Approx)
Decant Water Transfer Tank 35 CUM (Approx)
The complete ash handling system is divided as Bottom Ash Removal system and Fly
Ash Removal system. The Fly Ash Removal system is continuous, whereas Bottom Ash
Removal system is intermittent and carried out once per shift
Bottom Ash Removal system is a wet system. The bottom ash of each unit is crushed by
a convergent nozzle which is used to achieve high speed and hydraulically conveyed in
the form of slurry by divergent nozzle which is used to increase the pressure of the
water from bottom ash hopper to Dewatering bins/Ash tanks. Decanted water
separated from the bins is further re-circulated by sending the water and ash mixture
into the settling tank, where the ash settles down and clear water is taken out of it and
moved into the surge the surge tank and then again the water is taken to clear the
slurry. Collected bottom ash at the bins is removed by trucks. This method is called
Zero discharge system.
Fly ash collected in ESP & Air heater hoppers is removed in dry form by dense phase
pneumatic conveying system in two stages. In the first stage, the flue gas enters the
ESP which consists of both negative & positive plates which are charged with 75Kv DC
supply. The dust from the flue gases get negatively charged and attaches with the
positively charged plates which are then removed by hammer, and collected in the
hopper. Fly ash collected in above hoppers is pneumatically conveyed with
compressed conveying air called Makeover system to Intermediate Surge Hoppers. In
the second stage, the dry fly ash is further conveyed from Intermediate Surge Hoppers
to Fly Ash Silos or river side Burge to export as to Bangladesh cement industry by P.D
pumps. Ash collected in Fly Ash Silos is removed by trucks through rotary unloader. A
High concentration slurry system (HCSS) has been incorporated at BBGS with
technology from Netherlands to handle the fly ash in the form of thick slurry which
has a viscosity thinner than toothpaste and thicker than glue is produced using special
pumps and transport the same to a distant location. This ash settles in the form of
mounds over which suitably identified plantation will take place to convert the entire
place into a environment friendly greenery zone. Provision has been made to unload
the ash from Intermediate Surge Hoppers to trucks through unloading system in case
of emergency.
A majority of the fly ash is at present exported to Bangladesh though barges for use in
their cement plants.
PLANNING & ENVIRONMENT DEPARTMENT
The planning department of BBGS CESC Ltd. Is the department which controls every
aspect of the progress of the company and supervises on the work of every department
.This kind of management is maintained by the data which is provided by the
respective departments .It not only monitors the progress of the company but also to
the details of every person of the company including employees and workers. Routine
maintenance , breakdown maintenance, and predictive maintenance are also being
supervised by this department.
Economics of this company is taken care by this dept. environment, emergency plan ,
health and safety as well as computer defect, training ,infrastructure request, ac
defect ,and phone numbers of officers are being supervised by this department.
A generating station is combination of huge mechanical devices. The criteria of
whether the machine is damaged or not is being set by this dept. for example to test
the bearing of a turbine the frequency of it must be within 8db if its freq. is more than
8 db then the bearing is in degrading condition .If it is above 12 db then the bearing
must be changed.
The whole of this management system is done by an oracle based software. The page
by which the whole system is managed is shown below.
FOR ALL EXECUTIVES UPTO SR.DEPUTY MANAGER
Logs
&reports
Performance Administratio
n
Financ
e
EHS For you Miscellaneou
s
Station
reports
Performance
monitoring
Supervisor
Dbl/Due off
Orders
&bills
OH&S menu About
you
Messages
Coal reports Maintenance
planning
Workman OT OLMM
reports
Emergency
plan
Leave
reports
Infrastructur
e Request
Ash reports MTBF entry Workmen
gatepass entry
SERC
reports
NCR
register
Transpor
t
&medical
Training
Department
al logs
Survey defect
management
Attendance
report
Budget
reports
Environme
nt
Puja
advance
Chummery
management
Weighbridge
data
Mill
performance
Hol-call Entry ERP
reports
Standard
formats
Officers
phone no.
Drawing&
Documentatio
n
Shift rota Petty
cash
Notice
board
Blood group
Energy
monitoring
Computer
defect
AC m/c
defect
The planning department of BBGS not only manages other departments and economy .it also
manages the details of the executives of its own dept. which includes officers transport,
strength, record, birthday, leave repots, leave summery ,BBGS gatepasses , Hol call allowance,
along with the computers in the wholw unit of BBGS. such details are being recorded by the
following table.
FOR EXECUTIVES OF PLANNING ( UPTO SR. DEPUTY MANAGER ) ONLY
Each and every department starting from coal unloading to generation of electricity has its own
monthly and yearly targets. This target is set by the planning department in BBGS and the end
of the respective month or year its is seen that the target is being achieved or not and the
required regulation is taken according to it. This determination is very valuable because it is
important to determine the position of the power plant among the others in India .
Apart from this planning department also makes a record of unit trips , leaks of tube , heat rate
, total generation loss , and environment related failures
Examples of such spreadsheets are respectively given:-
Parameters Daily
actual
MTD YTD Yearl
y
target
MTD
actual
YTD
actual Target Actual Target actual
Generation
(MU)
STN 11.20 434.9
5
419.4
3
4664.9
5
4612.5
6
5995 439.33 4553.
07
PLF % STN 62.23 86.30 83.22 95.28 94.21 91.25 87.17 93.00
Auxiliary% STN 9.24 8.15 8.53 8.19 8.27 8.20 8.14 8.26
PAF % STN 100.0
0
99.87 97.97 99.07 99.20 96.00 95.95 97.11
Oil
figure(ml/kwh
)
STN 0.107 0.128 0.331 0.207 0.116 0.300 0.175 0.377
Rate of
unloading
BOX
N
0 10 10.14 10 10.7 10 11.3 11.5
BOBR 0.00 3 2.82 3 3.15 3 3.78 3.8
One of the employees of any department can raise a issue regarding any machinery in the plant
planning department takes the issue into account and checks whether the issue is being solved
or not and take steps according to the progress of the work in desired time. Such a minutes of
the meeting is published below.
Parameters Yearly target Actual
Unit
trips(number)
STN 8 4
Tube leaks (no.) STN 3 1
Reportable
accidents
STN 6 8
SPM(mg/Nm3)
Unit1&2 40 23
Unit3 30 23
Heat
rate(Kcal/kwh)
STN 2215 2230
Total gen
loss(mu)
STN 39 3.06
Total R/M exp. STN 7195 3789
Env. Related
failures
STN 2 3
OPERATIONS DEPARTMENT
RANKINE CYCLE:
The Rankine cycle is a thermodynamic cycle which converts heat into work.The heat is
supplied externally to a closed loop, which usually uses water as the working fluid.This
cycle generates about 80% of all electric power used in America and throughout the
world including virtually all solar thermal, biomass, coal and nuclear power plants.It is
named after William John Macquorn Rankine, a Scottish polymath.
A Rankine cycle describes a model of the operation of steam heat engines most
commonly found in power generation plants. Common heat sources for power plants
using the Rankine cycle are coal, natural gas, oil, and nuclear.
The efficiency of a Rankine cycle is usually limited by the working fluid. Without the
pressure going super critical the temperature range the cycle can operate over is quite
small,turbine entry temperatures are typically 565C (the creep limit of stainless steel)
and condenser temperatures are around 30C. This gives a theoretical Carnot efficiency
of around63% compared with an actual efficiency of 42% for a modern coal-fired power
station. This low turbine entry temperature (compared with a gas turbine) is why the
Rankine cycle is often used as a bottoming cycle in combined cycle gas turbine power
stations
One of the principal advantages it holds over other cycles is that during the
compression stage relatively little work is required to drive the pump, due to the
working fluid being in its liquid phase at this point. By condensing the fluid to liquid,
the work required by the pump will only consume approximately 1% to 3% of the
turbine power and so give a much higher efficiency for a real cycle. The benefit of this
is lost somewhat due to the lower heat addition temperature. Gas turbines, for
instance, have turbine entry temperatures approaching 1500C.Nonetheless, the
efficiencies of steam cycles and gas turbines are fairly well matched.
There are four processes in the Rankine cycle. These states are identified by numbers
(in brown) in the above Ts diagram.
Process 1-2: The working fluid is pumped from low to high pressure. As the fluid is a
liquid at this stage the pump requires little input energy.
Process 2-3: The high pressure liquid enters a boiler where it is heated at constant
pressure by an external heat source to become a dry saturated vapor. The input energy
required can be easily calculated using mollier diagram or h-s chart or enthalpy-
entropy chart also known as steam tables.
Process 3-4: The dry saturated vapor expands through a turbine, generating power.
This decreases the temperature and pressure of the vapor, and some condensation may
occur. The output in this process can be easily calculated using the Enthalpy-entropy
chart or the steam tables.
Process 4-1: The wet vapor then enters a condenser where it is condensed at a constant
temperature to become a saturated liquid.
In an ideal Rankine cycle the pump and turbine would be isentropic, i.e., the pump and
turbine would generate no entropy and hence maximize the net work output. Processes
1-2 and 3-4 would be represented by vertical lines on the T-S diagram and more closely
resemble that of the Carnot cycle. The Rankine cycle shown here prevents the vapor
ending up in the superheat region after the expansion in the turbine, [1]
which reduces
the energy removed by the condensers
REGENERATIVE RANKINE CYCLE:
The regenerative Rankine cycle is so named because
after emerging from the condenser(possibly as a sub-cooled liquid) the working fluid is
heated by steam tapped from the hot portion of the cycle. On the diagram shown, the
fluid at 2 is mixed with the fluid at 4 (both at the same pressure) to end up with the
saturated liquid at 7. The Regenerative Rankine cycle(with minor variants) is commonly
used in real power stations.
Another variation is where 'bleed steam' from between turbine stages is sent to
feedwater heaters to preheat the water on its way from the condenser to the boiler .
BOILER
Boiler is a steam raising unit of single radiant furnace type with auxiliaries,
designated to generate steam 272 kg/hr. at 91.4 kg/cm
2 V pressure. The unit burns pulverized low grade bituminous coal and is equipped
with oil burners. This plant is designed to operate at a 475m.above sea level the
ambient temperature is 40degree C with a humidity of 70%.Furnace consists of walls,
tangent bare water tubes. Rear water tubes from a cavity for the pendant super-
heater.There are many advantages of using water tube boiler: Water tube boilers are
small in size,the volume of the boiler is comparatively small in comparison to the same
size fire tubeboiler, better circulation of water in the boiler is possible.
MANUFACTURER :
Unit 1 & Unit 2: M/S ABB ABL Limited,Durgapur
Unit 3: M/S BHEL
TYPE:
Horizontal single drum,natural circulation,water wall tube
Each boiler has been provided with two forced draft fans (F.D), three induced draft fans
(I.D) for unit 1&2 & two induced draft fans (I.D) for unit 3, two primary air fans (P.A),
one primary tubular air heater, two secondary tubular air heaters for unit 1 & 2 and
two rotary air heater for unit 3, six Ball & Race type pulverizers, six Volumetric coal
feeders for unit 1 & 2 and five Bowl type pulverizers, five Gravimetric coal feeders for
unit 3, etc. Soot blowing is done by steam. Main and reheat steam temperature is
maintained from full load to 60% load. The boiler is capable of sustained stable
operation down to 2 Mills at 30% capacity without oil support for flame stabilisation.
25% BMCR requirement can be achieved by burning LDO alone .
BOILER
BOILER DRUM
The steam drum is made up of high carbon as its thermal stress is very high. There is a
safety valve in the drum, which may explode if the temperature and the pressure of the
steam are beyond a set value. A safety is a valve mechanism for the automatic release
of a gas from a boiler, pressure vessel or other system when the pressure or
temperature exceeds preset limits.
It is a part of a bigger set named Pressure Safety Valve (PSV) or Pressure Relief Valve
(PRV). The other parts of the set are named relief valves.
The boiler drum has the following purpose:
1.It stores and supplies water to the furnace wall headers and the generating tubes.
2.It acts as the collecting space for the steam produced.
3.The separation of water and steam tube place here
4.Any necessary blow down for reduction of boiler water concentration is done from
the drum.
RISER AND DOWN COMERS
Boiler is a closed vessel in which water is converted into the steam by the application
of the thermal energy. Several tubes coming out from the boiler drum surrounding the
furnace.Outside the water wall there is a thermal insulation such that the heat is not
lost in the surroundings. Some of the tubes of the water wall known as the down
comer, which carries the cold water to the furnace and some of other known as the
riser comer, which take the steam in the upward direction. At the different load riser
and the down comers may change their property. There is a natural circulation of water
in the riser and the down comers due to different densities of the water and the steam
water mixture. As the heat is supplied, the steam is generated in the risers. Lower
density of the steam water mixture in the riser than water in the down comer causes
natural circulation of water. Down comer connected to the mud drum, which
accumulates the mud and the water.
SUPER HEATER
The super heater rises the temperature of the steam above its saturation point and
there are two reasons for doing this: FIRST- There is a thermodynamic gain in the
efficiency. SECOND- The super-heated steam has fewer tendencies to condense in the
last stages of the turbine.
It is composed of four sections, a platen section, pendant section, rear horizontal
section and steam cooled wall and roof radiant section. The platen section is located
directly above the furnace in front of the furnace arch. It is composed of 29 assemblies
spaced at 457.2mmcenters from across the width of the furnace. The pendant section
is located in the back of the screen wall tubes.
It is composed of 119 assemblies at 1114mm centers across the furnace width. The
horizontal section of the superheater is located in the rear vertical gas pass above the
economizer. It is composed of 134 assemblies spaced at 102 mm centers across
furnace width. The steam cooled wall section from the side front and rear walls and the
roof of the vertical gas pass.no reheater is used.
SPRAY ATTEMPERATOR
In order to deliver a constant steam temperature over a range of load, a steam
generating unit(Boiler) may incorporate a spray attemperator. It reduces the steam
temperature by spraying controlled amount of water into the super-heated steam. The
steam is cooled by evaporating and super heating the spray water. The spray nozzle is
situated at the entrance to a restricted venture sections and introduces water into the
steam. A thermal sleeve linear protects the steam line from sudden temperature shock
due to impingement of the spray droplets on the pipe walls. The spray attemperator is
located in between the primary super heater outlet and the secondary super heater
inlet. Except on recommendation of the boiler manufacturer the spray water flow rate
must never exceed the flow specified for maximum designed boiler rating. Excessive
attemperation may cause over heating of the super heater tubes preceding the
attemperator, since the steam generated by evaporation of spray water and it does not
pass through the tubes. Care must also be taken not to introduce so much that the
unevaporated water enters the secondary stage of the super heaters.
AIR PRE-HEATER
The air heater is placed after the economizer in the path of the boiler flue gases and
preheats the air for combustion and further economy. There are 3 types of air pre
heaters: Tubular type, rotary type and plate type. Tubular type of air heater is used in
TGS. Hot air makes the combustion process more efficient making it more stable and
reducing the energy loss due to incomplete combustion and unburnt carbon. The air is
sent by FD fan heated by the flue gas leaving the economizer. The preheated air is sent
to coal mill as primary air where coal is pulverized. The air sucked is heated to a
temperature of 240-280oC. The primary air transports the pulverized coal through
three burners at TGS after drying in the mill.
ECONOMIZER
The heat of the flue gas is utilized to heat the boiler feed water. During the start up
when no feed water goes inside the boiler water could stagnate and over heat in the
economizer. To avoid this, economizer re circulation is provided from the boiler drum
to the economizer inlet. The feed water coming out from deaerator passes through to
special shape of pipes inside the economizer. The special shapes of tubes provide
increase the contact surface area between the flue gas and the feed water, so that
maximum heat exchanging can take place.
ELECTROSTATIC PRECIPITATOR
It is a device that separates fly ash from outgoing flue gas before it discharged to the
stack.There are four steps in precipitation:-
1.Ionization of gases and charging of dust particles.
2.Migration of particle to the collector.
3.Deposition of charged particles on collecting surface.
4.Dislodging of particles from the collecting surface.By the electrostatic discharge the
ash particles are charged due to high voltage (56KV)between two electrodes.
Generally maximum amount of ash particles are collected in the form of dry ash,
stored inside the SILO.
Rest amount of ash (minimum) are collected in the form of bottom ash and stored
under the water inside HYDROBIN.
SAFETY VALVE
A safety valve is a valve mechanism which automatically releases a substance from a
boiler, pressure vessel, or other system, when the pressure or temperature exceeds
preset limits. It is one of a set of pressure safety valves (PSV) or pressure relief valves
(PRV), which also includes relief valves, safety relief valves, pilot-operated relief
valves, low pressure safety valves, and vacuum pressure safety valves.
Vacuum safety valves (or combined pressure/vacuum safety valves) are used to
prevent a tank from collapsing while it is being emptied, or when cold rinse water is
used after hot CIP (clean-in-place) or SIP (sterilization-in-place) procedures. When
sizing a vacuum safety valve, the calculation method is not defined in any norm,
particularly in the hot CIP / cold water scenario, but some manufacturers have
developed sizing simulations
No of Safety valves Unit#1&2 Unit#3
At Drum 2 3
At Superheater 2 2
At CRH 4 1
At HRH 2 4
No of Air heater 3 2
No of F.D Fan 2 2
No of I.D Fan 3 2
No of P.A Fan 2 2
No of Coal Mills
6
5
TURBINE
Turbine is a rotating device which converts heat energy of steam into mechanical
energy. It is a two cylinder machine of impulse reaction type comprising a single flow
high pressure turbine and a double flow low pressure turbine.The H.P. turbine shaft
and the generator are all rigidly coupled together, the assembly being located axially
by a thrust bearing at the inlet end of H.P. turbine. The turbine receives high pressure
steam from the boiler via two steam chests. The H.P.turbine cylinder has its steam
inlets at the end adjacent to the no. one bearing block, the steam flow towards the
generator. Exhaust steam passes through twin over-head pipes to the L.P.turbine inlet
belt where the steam flows in both directions through the L.P. turbine where it
exhausts into under slung condenser.Steam is extracted from both the H.P. & L.P.
turbine at various expansion stages & fed into four feedwater heaters. Here spherically
seated Journal Bearing is used.
The main turbine is a Tandem Compounded, Three Cylinder, Single Reheat, Double
Flow LP cylinder, Condensing Type with uncontrolled Extraction .
No. of cylinders HP-1 Single Flow
IP-1 Single Flow
LP-1 Double Flow
SV Pressure & Temp 146 kg/cm^2 Abs & 537deg C
Reheat Pressure & Temp
35.7 kg/cm^2 Abs & 535deg C
Speed
3000 Rev/Min
No. of blading stages
Unit 1
Unit 2 & Unit 3
HP 1-Impulse
25-Reaction
18-50% Reaction
IP 16-50% Reaction
17-Reaction
LP 4-50% Reaction per
flow,3-variable reaction
8-Reaction per flow
The steam turbine drives a 250 MW, 3 Alternator with Hydrogen cooled Rotor and
Stator Core and DM water cooled Stator Windings(Unit 1&2) at a speed of 3,000 rpm.
The turbine shafts & generator rotor are rigidly coupled together. The generator field is
excited from a static excitation system. Power is generated at 16.5 kV and is stepped
up to a voltage of 132 kV (unit 1&2) and 220 kV (unit 3) in a generator transformer for
onward transmission to the system and there is an inter connection between 132 kV
switchyard and 220 kV switchyard thru ICT(Inter connecting transformer). The turbine
utilizes an electro-hydraulic governing system. The start-up, shut-down and loading of
the turbine can be achieved automatically. The turbine throttle pressure is 146 Kg/Cm2
(abs.), the main steam temperature is 537C and the reheat steam temperature is 535C.
The turbine cycle includes two stages of feed-water pumping (boiler feed pumps and
condensate extraction pumps), consisting seven stages of regenerative feed-water
heating by turbine bled steam, viz, two high pressure regenerative closed feed-water
heaters at the boiler feed pump discharge, four low pressure closed feed-wafer heaters
at the condensate extraction pump discharge and one direct contact heater (deaerator)
for unit 1&2 and two high pressure regenerative closed feed-water heaters at the boiler
feed pump discharge, three low pressure closed feed-wafer heaters at the condensate
extraction pump discharge and one direct contact heater (deaerator) for unit 3. All the
feed-water heaters are of horizontal type. The two (2) lowest pressure heaters LPH-1 &
2 (unit 1&2) and LPH-1 (unit 3) are located inside the neck of the condenser and LPH-1
is provided with an external drain cooler.
Turbine Generator
CONDENSER
Condenser is a device used for converting a gas or vapour to liquid. Condensers are
employed in power plants to condense exhaust steam from turbines. In doing so, the
latent heat is given up by the substance and it will be transferred to the condenser
coolant.
A surface condenser is a shell and tube heat exchanger installed at the outlet of every
steam turbine in thermal power stations.
The cooling water flows through the tube side and the steam enters the shell side
where the condensation occurs on the outside of the heat transfer tubes. The
condensate drips down and collects at the bottom, in a pan called hot well. Initial air
extraction from the condenser and steady vacuum inside the condenser is achieved by
two nos. motor driven, water sealed, air extraction pumps commonly called NASH
pump. During normal operation of the plant, vacuum is maintained by the circulating
water flowing inside the condenser and the non-condensable gases are extracted by
one of the NASH pumps. 2 nos. separate condensate storage tanks, interconnected to
each other, are provided for the three units. Condensate storage tanks receive
demineralised water from DM Plant.
FEEDWATER HEATER
Feedwater heaters are used in powerplants to preheat water delivered hot steam to the
generating boiler. Preheating the feedwater reduces the irreversibilities insteam
generation and hence improves the efficiency of the system. This method is
economical and reduces thermal shock when the feed water is introduced back in the
cycle. In steam power plants, there are two kinds of low pressure & high pressure
heater. These heaters help to bring the feedwater to satuiration temperature very
gradually. Feed water is taken from the De-aerator, a feed water storage tank, by motor
driven feed water pumps, and discharged through two stages of high pressure
regenerative feed water heaters and flue gas heated economizer into the boiler drum.
Provision is kept for condensate bypassing of LP Heaters in two groups in the event of
heater flooding so that the turbine is protected from water ingress viz. LP Heaters-2 &
1 and drain cooler as one group, and LP Heaters-3 & 4 as the other of unit 1&2 and LP
Heaters-1 and drain cooler as one group, and LP Heaters-2 & 3 as the individual of unit
3. LP Heater-2 drain is cascaded to LP Heater-l via a flash box, while LP Heater-l drain is
cascaded to the condenser-drains flash box via the drain cooler. LP Heater-4 drain is
similarly cascaded to LP Heater-3, while LP Heater-3 normal drain is pumped forward
by a 1 x 100% drain pump via control valves to LP Heater-3 main condensate outlet of
unit 1&2. LP Heater-2 drain is cascaded to LP Heater-l and alternate drain to LP Heater
flash box, while LP Heater-l drain is cascaded to the condenser-drains flash box via the
drain cooler. LP Heater-3 drain is similarly cascaded to LP Heater-2 and alternate drain
to LP Heater flash box.
DEAREATOR
Deaerator is a device widely used for the removal of oxygen and other dissolved gasses
from thefeedwater. It mostly uses low pressure steam obtained from an extraction
point in their steam turbine system. They use steam to heat the water to the full
saturation temperature corresponding to the steam pressure in the deaerator and to
scrub out and carry away dissolved gases. Steam flow may be parallel, cross, or
counter to the water flow. The deaerator consists ofa deaeration section, a storage
tank, and a vent. In the deaeration section, steam bubbles through the water, both
heating and agitating it. Steam is cooled by incoming water and condensed at the vent
condenser. Noncondensable gases and some steam are released through the vent.
Steam provided to the deaerator provides physical stripping action and heats the
mixture of returned condensate and boiler feedwater makeup to saturation
temperature. Most of the steam will condense, but a small fraction must be vented to
accommodate the stripping requirements. Normal design practice is to calculate the
steam required for heating and then make sure that the flow is sufficient for stripping
as well.
COOLING TOWER
Cooling towers are heat removal devices used to transfer process waste heat to the
atmosphere. Cooling towers may either use the evaporation of water to remove process
heat and cool the working fluid or, in the case of closed circuit dry cooling towers, rely
solely on air to cool the working fluid. The primary use of large, industrial cooling
towers is to remove the heat absorbed in the circulating cooling water systems used in
power plants. The circulation rate of cooling water in a typical 700 MW coal-fired
power plant with a cooling tower amounts to about 71,600 cubic metres an hourand
the circulating water requires a supply water make up rate of perhaps 5 percent.
Facilities such as power plants,steel processing plants use field erected type cooling
towers due to their greater capacity to reject heat.
With respect to the heat transfer mechanism employed, the main types are:
Dry cooling towers operate by heat transfer through a surface that separates the
working fluid from ambient air, such as in a tube to air heat exchanger, utilizing
convective heat transfer. They do not use evaporation.
Wet cooling towers or open circuit cooling towers operate on the principle of
evaporative cooling. The working fluid and the evaporated fluid (usually water)
are one and the same.
Fluid coolers or closed circuit cooling towers are hybrids that pass the working fluid
through a tube bundle, upon which clean water is sprayed and a fan-induced draft
applied. The resulting heat transfer performance is much closer to that of a wet cooling
tower, with the advantage provided by a dry cooler of protecting the working fluid
from environmental exposure and contamination
CONDENSATE EXTRACTION PUMP (CEP)
The pumps are vertical multi-stage bowl diffuser type, arranged inside a suction
barrel. The condensate pump is normally located adjacent to the main condenser
hotwell often directly below it. The condensate water is drawn from the condenser by
the extraction pumps and sent to the low pressure feed heaters.
BOILER FEED PUMP (BFP)
A boiler feedwater pump is a specific type of pump used to pump feedwater into a
steam boiler. The water may be freshly supplied or returning condensate produced as
a result of the condensation of the steam produced by the boiler. It consists of two
parts, first the booster pump then the main pump. The water enters the booster pump
at 7kg/ and it increases the pressure to about 20 kg/ . Then it enters the main
pump and by fluid coupling mechanism it increases the pressure to 150 kg/ . It is
achieved by increasing the speed to about 5700 r.p.m. If the amount of oil is
decreased in between the fluid coupling then the speed will decrease. Thus a gear box
is not required, instead a device called scoop is required that removes the oil and
control the speed of rotation. It consumes the highest amount of power about 8.8 MW.
DEMINERLISING PLANT
Raw water is passed via two small polystyrene bead filled (ion exchange resins)
beds. While The cations get exchanged with hydrogen ions in first bed,the anions are
exchanged with hydroxyl ions, in the second one. Demineralized water also known as
deionized water, water that has had its mineral ions removed. Deionization is a
physical process which uses specially manufactured ion exchange resins which
provides ion exchange site for the replacement of the mineral salts inwater with water
forming H+ and OH- ions. Because the majority of water impurities are dissolved
salts,deionization produces a high purity water that is generally similar to distilled
water, and this process is quick and without scale buildup. De-mineralization
technology is the proven process for treatment of water. A DM Water System produces
mineral free water by operating on the principles of ion exchange, degasification, and
polishing. Demineralised Water System finds wide application in the field of steam,
power, process, and cooling.
AIR & FLUE PATH
Drives & Equipments :
FD fans - 2 nos.
PA fans 2 nos.
Scanner air fans 2 nos. (Fan A-AC ; Fan B-DC).
Regenerative air preheater 2 nos.
Seal air fans 2 nos.
ID Fans - 2 nos.
Air & Flue path dampers & gates.
Fans in air & flue path:
FD fans : Air suction from atmosphere.
Motor rated continuous output : 750 KW
Full load /No load amps : 81 / 24
Rated rpm : 1486
PA fans : Air suction from atmosphere.
Scanner air fans : Suction from FD fan discharge cross over duct.
Seal air fans : Suction from cold PA header.
ID fans: Motor rated continuous output : 1800 KW
Full load /No load amps : 199 / 74
Rated rpm : 746.
MECHANICAL MAINTENANCE DEPARTMENT
Maintenance is a set of organised activities that are carried out in order to keep
equipment in its best operational condition with minimum cost acquired. It includes
performing routine actions which keep the device in working order or prevent trouble
from arising.
MAINTENANCE TYPES
Broadly speaking, there are three types of maintenance in use:
Preventive Maintenance: Preventive maintenance is the maintenance performed
in an attempt to avoid failures, unnecessary production loss and safety
violations. It includes scheduled maintenance (daily and routine) of the
equipment and includes activities like regularly monitoring the temperature and
pressure of the bearing, grease, windings, oil, air and gases, the flow of air,
water and oil, the rotation of bearing lubricating rings, moisture content in the
gases, etc. It is the maintenance before the breakdown occurs.
Corrective Maintenance: It is the maintenance where equipment is maintained
after break down. This maintenance is often most expensive because worn
equipment can damage other parts and cause multiple damage. The corrective
maintenance is carried out to bring it back the equipment in the working order.
Predictive Maintenance: This kind of maintenance includes activities to foresee
events in the future that could lead to damage of the equipment or cause a
failure in the system. It implies vibration monitoring, Ultrasound tests, Breaker
timing test, Thermograph etc.
The major divisions in this department include:
Maintenance of Boiler & its auxiliaries: Boiler
ID Fan
FD Fan
PA Fan
Coal Mill
Various Pumps, etc.
Maintenance of Turbine & its auxiliaries:
Turbine
CEP
BFP
NASH Pump
HP_LP Bypass System
Condensate Transfer Pump
Circulating Cooling Water (CW) Pumps
Service Cooling Water Pumps, etc.
Maintenance of Fuel and Ash: Conveyor System
Rotary Breakers
Crusher
Wagon Tipplers
Track Hoppers
Bottom & Fly Ash
While performing maintenance activities, it is important we maintain a schedule for the
same, take in to safety considerations, keep all necessary tools and equipment in the
vicinity of the equipment, ensuring only skilled man power to handle the machine.
Also the various maintenance activities should be practiced in a sequential manner and
proper note be taken. Given below are checklists for HP-LP Bypass Maintenance and for
Cooling Tower Fan Maintenance.
LUBRICATION SYSTEM
Lubrication is an essential activity for the healthy working of equipment. It is the
process or technique employed to reduce wear off one or both surfaces in close
proximity and moving relative to each other, by interposing a lubricant by interposing
a lubricant between the surfaces to carry or to help carry the load between the
opposing surfaces. Lubrication purposes to:
Lubricate: Reduces Friction by creating a thin film(Clearance) between moving
parts (Bearings and journals)
Cool: Picks up heat when moving through the engine and then drops into the
cooler oil pan, giving up some of this heat.
Seal: The oil helps form a gastight seal between piston rings and cylinder walls
Clean: As it circulates through the engine, the oil picks up metal particles and
carbon, and brings them back down to the pan
Absorb Shock: When heavy loads are imposed on the bearings, the oil helps to
cushion the load.
Absorb Contaminants: The additives in oil helps in absorbing the contaminants that
enter the lubrication system.
The checklist for maintenance of HP-LP Bypass System
S.
No.
Description OK/Not OK Values & Condition
1. Check Nitrogen Pressure of
all Accumulators
Charging Pressure
for 10L and 32L
Accumulators=80
Bar, and for 50L=120
Bar
2. Change all filters on P1 line Every 6 months
3. Check all wear outs, cuts and
abrasion of all hoses
4.
Check for oil leaks from
Actuator seals, Servo valves,
Blocking units, Fast closing
and opening devices
5.
Check for any steam and
water leaks from any steam
and water valves
6.
Check tightness of coupling
bolts, bolts of locking
arrangement & bolts of
antirotation device on HPBP
valve
Torque tightness oh
HP coupling bolts:
Torque tightness of
HP indicator bolts:
Torque tightness of
antirotation device
bolts:
7.
Measure gap of both sides of
T-end of antirotation device
on HPBP Coupling
Mention previous
readings:
(north):
(south):
8. Check filtering of HSU filter
pump in oil taking out mode
9.
Check cut-in and cut-out
pressure of Pp. and time of
cut-in and cut-out
Monthly check list for Cooling Tower Fan
Description Job Done Remark
1.Check tightness of coupling bolts between
gear and motor
2. Check condition of above coupling bushes.
3. Check tightness of base bolts of gear box,
motor and base frame
4. Check tightness of fan blades& U bolts
5. Check gear teeth condition
6. Check the end play
7. Measure the blade (pitch) angle~ should be
6.5 or 15
8. Check the track variation
9. Check condition of leading & trailing edge of
blade
10. Clear the drain hole at tip of the blade
11. Record tip clearance of all blades
12. Check match mark on blades, U bolts,
clamp, hub plate
13. Check condition of blade
14. Check oil leakage, level & oil condition
15. Check oil quality
16. Check condition of cap on oil filling pipes
17. Check play in the output shaft by hand
feeling
18. Clean Breather of the gear box
ELECTRICAL & INSTRUMENT DEPARTMENT
B.B.G.S. Generator
Unit 1&2 Unit 3
Maximum Continuous Rating 250 MW 250 MW
Maximum Continuous Rating 294 MVA 294 MVA
Rated Power Factor 0.85 0.85
Rated Terminated Voltage 16500V 16500V
Rated Current 10291A 10291A
Frequency 50 Hz 50 Hz
Number of phases 3 3
The generators at BBGS are hydrogen and DM water cooled type. The outer part of the
cylinder has hydrogen operated coolers white the inner part has the core and the
windings. DM water is circulated all along the cylinder by two AC pumps. The stator
core and the rotors are cooled by hydrogen circulated by centrifugal pumps mounted
on each side of the generator.
The rotor is made with alloy forgings with steel at the exciter end. The rotor windings
are formed from copper strips. Each end of rotor shaft is supported by journal
bearings, lubricated from Turbine Lube Oil system. Exciter end bearing pedestal is fully
insulated to prevent eddy current circulation through bearing and oil films.
The generator field current is supplied by a static excitation system. The current is
supplied by an excitation transformer and a thyristor controlled rectifier.
The turning gear drive is coupled to the generator rotor and when meshed, allows
turbine and generator shafts to be rotated slowly before run up and after shut down to
prevent rotor distortion due to uneven heating.
There are 3 types of transformers in the plant namely GT(Generator
Transformer),ST(Station Transformer),UT(Unit Transformer).The GT is used to step up
the voltage generated(16.5KV) to 132KV in case of unit#1 &2,16.5KV to 220KV as the
voltage generated(16.5KV) to 132KV in case of unit#1 &2,16.5KV to 220KV as
mentioned earlier. The ST & UT are used for in-plant power of BBGS for meeting the
power requirements of the auxiliaries such as FD Fan, PA Fan, ID Fan, coal mills,
conveyors, centrifugal pumps, CW Pump etc as well as the lighting loads of the various
buildings of the plant. The start up power of the plant is provided by the UT which
steps down the voltage from 16.5KV to 6.6K whereas the ST taps voltage from the Bus-
Bars.
The specifications of the various generators of unit#1 &2 are as follows :
GT#1,GT#2(Generator Transformer) :
315 MVA,138/16.5 KV
X=12-15% Yd 11
The GT is having vector notation Yd 11(30deg lag between prim. & sec.
side) which is used generally as a convention
The alternators(3-phase)of the Turbine-Generator set is Wye-connected so
that during earth fault the fault current(the sum of the currents in the 3 phases is not
equal to zero during earth fault) flows into the ground through the neutral wire
without hampering the generator.
The LV side (16.5KV) of the GT is delta connected. This is because if there
is an earth fault on the LV side of the GT then using Wye connection will cause the fault
current to flow through the neutral wire. This fault current may enter into the
generator circuit through the neutral wire of the Wye connected generator & hamper
the generator. To avoid such a situation LV side(16.5KV) of the GT is delta connected.
The HV side of the GT which is connected to the transmission line is Wye
connected.
The neutral wire for bypassing the fault current is connected to
NGT(Neutral Grounding Transformer) which steps down the current to a smaller value
so that the fault current does not hamper any devices.
Unit Transformer : (UT#1)
HV/LV1/LV2
40/25/15MVA
16.5/6.5/6.5 KV
ON LOAD TAP + 8*1.25%
X= [ HV-LV1= 15%,HV-LV2=11.5%,LV1-LV2=22.5%(MIN)]
(ALL IMPEDANCE ON 40MVA BASE)
HV
UT-1
LV 1 LV 2
To UB-1B Incomer To UB-1A Incomer
Station Transformer: (ST#1)
HV/LV1/LV2
60/30/30MVA
132/6.9/6.9KV
ON LOAD TAP +6-1.0 * 1.0 %
X= [HV-LV1=32.7%, HV-LV2=19.6%,LV1 -LV2=48.8%(MIN)] (ALL IMPEDANCE ON 60MVA BASE)
HV
ST-1
LV 1 LV 2
To SB-1B Incomer To SB-1A Incomer
The UT has two LV sides namely LV1 & LV2 having voltage rating of 6.5KV
each.These two LV sides are used to charge the UB-1A & UB-1B(Unit Board) through the
incomers which are connected to UT-1.The UT is used to charge the UB-1A & UB-1B.
The UB-1A consists of two portions:
UB#1A(1st portion):
The auxiliaries connected to this portion are as follows:
ID FAN# 1A 1*1580 KW
PD FAN# 1A 1*1182 KW
PA FAN# 1A 1*940 KW
COAL MILL# 1A/B/C 3*409 KW
CEP# 1A 1*760 KW
A.C.W PP# 1A 1*290 KW
SPARE FDR 1*1580 KW
CW PP #1A 1*1420 KW
UB#1A(2nd portion) :
ID FAN# 1B/1C 2*1580 KW
FD FAN# 1B 1* 1182 KW
PA FAN# 1B 1*940 KW
COAL MILL# 1D/E/F
CW# 1B 1*1440 KW
UB #1B:
BFP# 1A 1*8800 KW
The UB#1A & UB#1B are charged by UT- 1.The SB# 1A & SB#1B are charged
by the ST-1.Similar is the case for unit# 2.The UB caters to the independent drives (coal
mills, CW PP, FD FAN, ID FAN etc) which are different for each unit whereas the SB
caters to the dependent drives (Intake PP, coal plant etc) which are the same for all the
units.
We observe that UB#1A caters to a number of auxiliaries such as PD FAN, ID
FAN, COAL MILL, CW PP, ACW PP etc whereas the UB#1B caters to BFP only. This is
because the BFP is rated with high wattage consumption whereas the other auxiliaries
are of considerably lower power consumption. Thus is BFP & the other auxiliaries are
present on the same UB then the total power available on the UB will the consumed by
the auxiliaries itself leaving the BFP un-operated. Thus the BFP is present in a separate
UB.
Now if due to shutdown or failure of the UT#1,the LV sides of the UT are
unable to charge the UB#1A & UB#1B,then the SB#1A(Station Board 1A) & the
SB#1B(Station Board 1B) are used to charge the UB#1A & UB#1B respectively with the
help of a tie between the SB & UB.
A large number of circuit breakers are used in the total electrical system
like SF6 gas circuit breaker(6.6 KV),Air circuit breaker(415 V) as well as a number of
isolators, insulators, earth switches, CT(Current Transformer),PT(Potential
Transformer) ,overload protection, Bus Coupler Breakers are used.
The 3.5m level consists of all the boards which consists of a large number
of relays, circuit breakers etc which delivers power to the various auxiliaries. Some of
the specifications are given as follows:
INCOMER FROM ST1-LV1 :
The relays are Combiflex Relays, Trip Circuit Relay, Tripping Relay, O|C & EF Prot.
Indicators such as Autotrip circuit unhealthy, Gas pressure low, Breaker on, Breaker off, spring charged.
Number of switches are there such as Breaker open & Breaker close, Ammeter Switch(K, Y, B, Off),Emergency Trip,(Remote, Local, SWGR)
DM WTR SYS TR# DMT-1: 1600 KVA
SPARE TRANSFORMER FDR: 1600 KVA
CT TRANSFRMR: 2000 KVA
TRNSFRMR FOR IA PA COMP: 1600 KVA
INTAKE WTR TRNSFRMR: 1600 KVA
STN. AUXILIARY TRNS: 2000 KVA
TR. FOR ADMIN BUILDING: 500 KVA
TR. FOR SECURITY BUILDING: 500 KVA
BUSDUCT TRNS. : 415 V, 250 A
ASH HANDLING SWGR: 45 KW, 4A
TIE TO ASH HANDLING SWGR: 6.6 KV
CONVEYOR: 250 KW
Dry Type Transformer :
1600KVA
Type of cooling- AN
Temp- 90 deg C
Insulation Class- F
Insulation level HV 60 KVP|20 KVP rms
Rated Current HV (amps) 139.96
Rated current LV (amps) 2133.4
Impedance volts % - 8 + IS Tol
Model- Cast resin dry type
Vector Group- Dyn 11
Freq-50 Hz
The stepped up voltage of 132 KV by GT#1 & 2,& 220 KV by GT# 3 are fed
through CT to the Moose conductors(ACSR).For unit#1 & unit#2,there is one GT for
each phase(R,P,Y) whereas there is only one GT for unit#3 supplying the R,Y,B phase.
On the back of these transformers, NGTs are situated. The moose conductors from the GT enter the switchyard.
SWITCHYARD
Switchyard is a very important part of the electrical circuit. It generally consists of
three buses, which are the two main bus & one transfer bus. A portion of the transfer
bus is connected with the generating transformers which are at 132KV for unit 1&2 and
220KV for unit 3. Due to the inequality between the two voltages, they are connected
with the interconnected transformer (ICT) to form a common bridge between the two
transformers. The transfer bus is connected in series with the main bus 1 or main bus
2 or neither of them. The line first comes from the generating transformer and then
through a series of isolators and circuit breakers main bus 1 or the main bus 2 is
connected. Two main bus are used as one is kept in standby mode if a fault occurs in
anyone of them then the other one can be used. The 132KV & 220KV line are also
connected to the transmission line. When in one main bus bar a fault occurs and we
need to transfer the bus, let in main bus 1 a fault occurs & we need to transfer it to
main bus 2 then we first connect the transfer bus thus for a brief moment the feeder
gets the voltage from both main bus 1 & transfer bus, then we open the main bus 1
thus for that brief moment the feeder gets the voltage from the transfer bus only. Then
we connect the main bus 2 also, thus for a brief moment the feeder gets the voltage
from both main bus 2 & transfer bus, then we open the open the transfer bus and the
feeder gets power from main bus 2 only. The main buses are connected with the
station transformer, it steps down the voltage to about 6.9KV which is used to drive
the plant during any plant failure. There are 3 station transformers one for each unit.
When the plant will fail to generate, then the station transformer with the help of the
switchyard gets the power from other unit and keeps the necessary machineries
working at that time.
The isolators in the switchyard have two functions, which are basically isolation of the
feeders and also used to ground the system. Generally two motors are used one for
isolating and another for grounding the isolator. The circuit breakers generally denoted
by 52 are SF6 circuit breakers. These circuit breakers are used are SF6 is a very stable
gas and arching doesnt occur that easily. When the main line carrying 132KV & 220KV
enters or exits the switchyard it goes through current transformer which is in series
with the line & capacitance coupled voltage transformer as potential transformer in
parallel with the circuit, one end of the capacitance coupled voltage transformer is
connected to the ground. The interconnecting transformer is a core type transformer,
which is used as it is more economical & also because the ratio of voltages between low
voltage & high voltage side is not more then 1:3.
CONCLUSION
Working with Calcutta Electricity State Cooperation Limited (CESC Ltd) as a vacational
training was a very nice experience. I learnt a lot about designing basic systems in
electrical and how the importance of electrical power generation, maintenance and
operation, in any project. I also practiced what I learnt in the college and applied it on
field. Working with Electrical department enhanced my major understanding .In
addition, I gained a good experience in term of self confidence, real life working
situation, interactions among people in the same field and working with others with
different professional background. I had an interest in understanding basic
engineering work and practicing what has been learnt in the class. Also, the training
was an opportunity for me to increase my human relation both socially and
professionally.