Calcutta Elect ricity State Coopera tion Limited (CESC Ltd) Budge Budge Generating Station
SARTHAK MODAK
88, LENIN SARANI, KANCHRAPARA, NORTH 24 PARGANAS 743145
SAROJ MOHAN INSTIT UTE OF TECHNOLOGY, U
GUPTIPA RA, HOOGLY 712512
From 24thdec 2012 To 5thjan 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 cooperation 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. M aitra (DY. G ENERAL 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 (S R. MANAGER, PLG) Mr. Sub rata Mondal (DY. MANAGER, F &A) Mr. Santashri Ghosh (MANAGER, E&I) Mr. Kaushik Chaudhuri (MANAGER, OPS ) Mr. Samir Bandyopadhyay (MAN AGER, 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 (CO NS ULTANT HR) Mr. S. Roy (AS ST . 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:-
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DEPT: F&A
NAME:-
SIGNATURE:- ________________
DEPT: MMD
NAME:________________
SIGNATURE:-
DEPT:- E&I
NAME:________________
SIGNATURE:-
DEPT:-PLC
NAME:-
SIGNATURE:-
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MARKS OBTAINED IN WRITTEN TEST:____ ATTENDANCE:- _____
DEPT:-PTC NAME:-
SIGNATURE:- ______________
The Calcutta Ele ctric 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 theHowrah, 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 solar—will 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
COMMERCI AL GENERATION Unit # 1 07.10.97 Unit # 2
01.07.99
Unit # 2
28.01.10
Fuel source
ECL, BCCL , ICML & Im ported 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
Capacity
3
250 MW
Unit # 1 Trial Synchronization Commercial generation Full Load Generation
16.9.97 07.10.97 26.02.98
Unit # 2 Trial Synchronization Commercial generation Full Load Generation
06.03.99 01.07.99
09.08.99
Unit # 3 Trial Synchronization Commercial generation Full Load Generation
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, Tw o 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 w ith 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) 2) 3) 4) 5) 6)
Fuel & Ash Planning & department Environment department Mechanical Maintenance department Operations department Electrical & instrumental department 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 HAN DLING 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
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 Ma terial HandledMaterial
Semi Crushed Coal
Lump size
(-)100 mm
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) w agons 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.
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 bun kers. 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 dow n 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 un loader. 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. FO R ALL EXECUTIVES UPTO SR.DEPUTY MANAGER Logs
Performance
&reports Station reports Coal reports Ash reports
Department al logs Weighbridge data
Administratio Financ n
Performance monitoring Maintenance planning MTBF entry
Supervisor Dbl/Due off Workman OT
Survey defect management Mill performance Drawing& Documentatio n Energy monitoring
Attendance report Hol-call Entry
For you
e
Orders &bills OLMM reports Workmen SERC gatepass entry reports
Shift rota
EHS
Budget reports ERP reports Petty cash
Miscellaneou s
OH&S menu About you Emergency Leave plan reports NCR Transpor register t &medical Environme Puja nt advance Standard formats Notice board
Messages Infrastructur e Request Training
Chummery management Officers phone no. Blood group
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 b eing recorded by the following table.
FOR EXECUTI VES OF PLANNING ( UPTO SR. DEPUTY MANAGER ) O NLY 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 Target
Actual
YTD Target
actual
419.4 3 83.22
4664.9 5 95.28
4612.5 6 94.21
Yearl y target 5995
MTD actual
91.25
87.17
4553. 07 93.00
Generation (MU) PLF %
STN
11.20
STN
62.23
434.9 5 86.30
Auxiliary%
STN
9.24
8.15
8.53
8.19
8.27
8.20
8.14
8.26
PAF %
STN
99.87
97.97
99.07
99.20
96.00
95.95
97.11
Oil figure(ml/kwh ) Rate of unloading
STN
100.0 0 0.107
0.128
0.331
0.207
0.116
0.300
0.175
0.377
10
10.14
10
10.7
10
11.3
11.5
3
2.82
3
3.15
3
3.78
3.8
BOX 0 N BOBR 0.00
439.33
YTD actual
Parameters Unit trips(number) Tube leaks (no.) Reportable accidents SPM(mg/Nm3)
STN
Yearly target 8
Actual 4
STN STN
3 6
1 8
Unit1&2 40 Unit3 30 STN 2215
23 23 2230
Total gen loss(mu) Total R/M exp.
STN STN
39 7195
3.06 3789
Env. Related failures
STN
2
3
Heat rate(Kcal/kwh)
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.
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 565°C (the creep limit of stainless steel) and condenser temperatures are around 30°C. 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 1500°C.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 enthalpyentropy chart also know n 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 w et vapor then enters a condenser where it is condensed at a constant temperature to become a saturated liquid. In an ideal Rankine cycle the p ump 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 w ay 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 superheater.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 w ater concentration is done from the drum.
RISER AND DOWN COMERS Boiler is a closed vessel in w hich 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 w ater to the furnace and some of other know n 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 w all tubes. It is composed of 119 assemblies at 1114mm centers across the furnace width. The horizontal section of the superheater is locatedspaced in the rear vertical gas pass above the economizer. It is composed of 134 assemblies at 102 mm centers across furnace width. The steam cooled w all section from the side front and rear w alls 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 the boiler water could stagnate and indrum the economizer. Towater avoidgoes this, inside economizer re circulation is provided fromover the heat boiler 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 c an 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 ofpressure safety valves (PSV) or pressure relief valves (PRV), w hich 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 mech anical 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 tow ards 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 HP
Unit 1
Unit 2 & Unit 3
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, 3Ø 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-dow n and loading of the turbine can be achieved automatically. The turbine throttle pressure is 146 Kg/Cm2 (abs.), the main steam temperature is 537°C and the reheat steam temperature is 535°C. 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 pow erplants 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 w hen 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 feedw ater 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 dru m. 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, w hile 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 circulatingcooling 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, the booster pump the main pump. enters the booster pump at 7kg/first and it increases thethen pr essure to about 20 The kg/ water . 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 w ater 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 (daily and routine) of and the equipment and includes activities likemaintenance regularly monitoring the temperature 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 F uel 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 w orking 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.
1.
2. 3. 4.
Description
Check Nitrogen Pressure of all Accumulators Change all filters on P1 line Check all wear outs, cuts and abrasion of all hoses Check for oil leaks from Actuator seals, Servo valves, Blocking units, Fast closing and opening devices
OK/N ot OK
Values & Condition Charging Pressure for 10L and 32L Accumulators=80 Bar, and for 50L=120 Bar Every 6 months
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 Measure gap of both sides of
7.
T-end ofCoupling antirotation device on HPBP
Torque tightness oh HP coupling bolts: Torque tightness of HP indicator bolts: Torque tightness of antirotation device bolts: Mention previous readings: (north): (south):
Check filtering of HSU filter pump in oil taking out mode Check cut-in and cut-out pressure of Pp. and time of cut-in and cut-out
8. 9.
Monthly check list for Cooling Tower F an Description 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 ⁰
⁰
Job Done
Remark
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 Rated Terminated Voltage
0.85 16500V
0.85 16500V
Rated Current
10291A
10291A
50 Hz
50 Hz
Frequency
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 w indings 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 BusBars. 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
To SB-1B Incomer
LV 2
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: st
UB#1A(1 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 w hich 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 TRANSF ORMER FDR: 1600 KVA CT TRANSFRMR:
2000 KVA
TRNSFRMR FOR IA PA COMP:
1600 KVA
INTAKE WTR TRNSF RMR:
1600 KVA
STN. AUXILIARY TRNS:
2000 KVA
TR. FO R ADMIN BUILDING:
500 KVA
TR. FO R SECURITY BUILDING:
500 KVA
BUSDUCT TRNS. :
415 V, 250 A
ASH HANDLIN G SWGR:
45 KW, 4A
TIE TO AS H HANDLING SWGR: CONVEYOR:
6.6 KV
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 w e 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 w hich 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 doesn’t 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 w as 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 w orking 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 w hat has been learnt in the class. Also, the training was an opportunity for me to increase my human relation both socially and professionally.
