CESC Budge Budge VT Report

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


Budge Budge(BBGS):

Commissioned: 1997

Capacity: 750 MW


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


06.03.99


01.07.99


09.08.99

Unit # 3


12.07.09


28.01.10


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.

Documents

CESC Budge Budge VT Report