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Introduction Introduction Document Transcript

  • 1. INTRODUCTION1.1GENERAL OVERVIEWFor the power generation with 2x110 MW, 3x210 MW, 2x195MW, K.S.T.P.S. authorities arerequired to have full control over all the auxiliaries which are basically operated on L.T. Systemi.e. 415 V 3-Ø power supply is made available to the system after providing the stationtransformer of 3x50 MVA capacity with different service transformers of capacity 1.0 MVA, 1.5MVA, 2.0 MVA, which are located near the load centre as the transformer having the voltage of6.6 KV /415 V. The 6.6 KV power is distributed through 6.6 KV interconnected Bus System forall the SEVEN units with a control through DC of 220 V. The 415 V power supply is done through a L.T. SWGR (Switchgear) which are locatednearby the distribution transformer as well as the load centers. The 6.6 KV power supply whichare either MOCB (Minimum Oil Circuit Breaker) or Air Circuit Breakers. The 6.6 KV power is supplied to various draining equipments is made through breakerswhich are either MOCB or air circuit breaker which are either of voltage makers as well as SF 6of NGEF make. The LT supply is also controlled through air break circuit breakers. The variousH.T. motors are switched on through Direct ON line (DOL) in order to increase the availabilityof equipment at full efficiency without time gap. Further, the 6.6 KV system which is normally in delta configuration and termed as anunearthed system. Earthing is detected by a protection system with alarm facility to takeremedial measures immediately and at the same time to maintain the generation level in the samecondition, prior to occurring the earth fault the single phase earth fault is detected in due coursetill the motor is not earthed to any phase. “PUBLIC ADDRESS SYSTEM” is available throughin area of each unit which helps in fast communication for prompt remedial measure. Soot Blowers are there in the boiler area on the furnace side or Zone which helps inblowing the soot / ash deposition regularly of the furnace wall / economizer tubes to keep heattransfer at the required parameter. 13
  • In April 1973, Central Electricity Authority prepared a Project Report for power stationcomprising of the two units of each of capacity 110 MW for RSEB. Subsequently in September1975 this was revised by the Consultant Thermal Design Organization, Central ElectricityAuthority for invention of 2x110 MW units being manufactured by BHEL, Hyderabad in 1 stStage. The planning commission cleared the project report in Sept, 1976 for installation of twounits each of 110 MW in first estimated cost of Rs. 143 Crores. *The total power generated in KSTPS is 1240 MW.1.1.1 Designed Stages STAGE I - 2x110 MW STAGE II - 2X210 MW STAGE III - 1X210 MW STAGE IV - 1X195 MW STAGE V - 1X195 MW1.1.2 LocationThe Kota Thermal Power Station is ideally on the left bank of Chambal River at Up Stream ofKota Barrage. The large expanse of water reached by the barrage provides an efficient directcirculation of cooling system for the power station. The 220 KV GSS is within ½ Kms. from thepower station.1.1.3 LandLand measuring approx. 250 hectares was required for the project in 1976. Ash tank isconstructed very near to the plant for the ease of disposal of ash and slurry.1.1.4 CoalCoal India limited owns and operates all the major coal fields in India through its coal producingsubsidiary companies viz. Eastern Coal Fields Limited, Western Coal Fields Limited. Coal Indialimited supplies coal from its coal mines of coal producing subsidiaries BCCL, SECL & ECL toKota Thermal Power Station through railway wagons. The average distances of SECL, ECL &BCCL are 800, 950 and 1350 Kms. respectively. 14
  • 1.1.5 WaterThe source of water for power station is reservoir formed by Kota Barrage on the ChambalRiver. In case of large capacity plants huge quantities of coal and water is required. The cost oftransporting coal and water is particularly high. Therefore, as far as possible, the plant must belocated near the pit rather than at load centre for load above 200 MW and 375 MW. Thetransportation of electrical energy is more economical as compared to the transportation of coal.1.1.6 Design FeaturesThe satisfactory design consists of the following steps. Estimation of cost. Selection of site. Capacity of Power Station. Selection of Boiler & Turbine. Selection of Condensing Unit. Selection of Electrical Generator. Selection of Cooling System. Design of Control and instrumentation system.The design of steam power station requires wide experience as the subsequent operation andmaintenance are greatly affected by its design. The most efficient design consists of properlysized component designed to operate safely and conveniently along with its auxiliaries andinstallation. 15 View slide
  • 2.GENERAL LAYOUT AND BASIC IDEAA control system of station basically works on Rankin Cycle. Steam is produced in Boiler isexported in prime mover and is condensed in condenser to be fed into the boiler again. FIG.1The Kota Thermal Power Station is divided in four main circuits: Fuel and Ash Circuit. Air and Gas Circuit. Feed water and Steam Circuit. Cooling Water Circuit. 16 View slide
  • 2.1 FUEL & ASH CIRCUITFuel from the storage is fed to the boiler through fuel handling device. The fuel used in KSTPSis coal, which on combustion in the boiler produces the ash. The quantity of ash produced isapproximately 35-40% of coal used. This ash is collected at the back of the boiler and removedto ash storage tank through ash disposal equipment.2.2 AIR AND GAS CIRCUITAir from the atmosphere is supplied to the combustion chamber of Boiler through the action offorced draft fan and induced draft fan. The flue gases first pass around the boiler tubes andsuperheated tubes in the furnace, next through dust collector (ESP) & then economizer. Finally,they are exhausted to the atmosphere through fans.2.3 FEED WATER AND STEAM CIRCUITThe condensate leaving the condenser is first heated in LP heaters through extracted steam fromthe lower pressure extraction of the turbine. Then it goes to de-aerator where extra air and non-condensable gases are removed from the hot water to avoid pitting/oxidation. From de-aerator itgoes to BFP (boiler feed pump) which increases the pressure of the water, then passes throughthe HP heater and enters into the boiler drum through economizer. This wet steam passes throughsuperheater. From superheater it goes into the HP turbine then to IP turbine and finally to the LPturbine and then exhausted through the condenser into hot well.2.4COOLING WATER CIRCUITA large quantity of cooling water is required to condense the steam in condenser and marinatinglow pressure in it. The water is drawn from reservoir and after use it is drained back into theriver. 17
  • 3.PROCESSING OVERVIEW3.1COAL HANDLING PLANTIt can be called the heart of thermal power plant because it provides the fuel for combustion inboiler. The coal is brought to the KSTPS through rails via 16 railway tracks. The main coalsources for KSTPS are SECL (South Eastern Coalfields Limited), ECL (Eastern CoalfieldLimited) and BCCL (Bharat Coking Coal Limited). Everyday 6 to 7 trains of coal are unloadedat KSTPS. Each train consists of 58 wagons and each wagon consists of 60 tonnes tonnes ofcoal. The approximate consumption at KSTPS is about 20,000 per day. It costs approximate 2crores of rupees per day including transportation expenses. The coal is firstly unloaded from wagon by wagon tipplers, then crushed by crushers andmagnetic pulley and pulverized to be transformed to the boiler. The whole transportation of coalis through conveyor belt operated by 3-Ø Induction motor. The coal handling plant can broadly be divided into three sections:1) Wagon Unloading System2) Crushing System3) Conveying System3.1.1 WAGON UNLOADING SYSTEMWagon Tippler unloads the coal from wagon to hopper which is made of Iron, in the form of netso that coal pieces of only equal to and less than 200 mm size pass through it. The bigger onesare broken by the workers with the help of hammers. From the hopper coal pieces fall on thevibrator. It is a mechanical system having two rollers each at its ends. The rollers roll with thehelp of a rope moving on pulley operated by a slip ring induction motor. 18
  • FIG 2. The four rollers place themselves respectively behind the first and the last pair of wheels ofthe wagon. When the motor operates the rollers roll in forward direction moving the wagontowards the “Wagon Table”. On the Wagon table a limit is specified in which wagon has to bekept otherwise the triple would not be achieved.3.1.2 CRUSHING SYSTEMIt consists of crushers which are used to crush the coal to 20 mm size. There are mainly twotypes of crushers working in KSTPS:-Primary Crushers i.e. 1) Rail crushers or 2) Rotary breaker.Secondary Crushers i.e. Ring granulators. Primary Crushers:- These are provided in only CHP stage 3. These are:1) Rail crushers, 2) Rotary breaker 19
  • Secondary Crusher:- In this, there are following ways to reduce material size:1) Impact attrition, 2) Shearing, 3) Compression.Most of the crushers employ a combination of three crushing methods.3.1.3 CONVEYING SYSTEMThe stacker/re-claimer unit stacks the material on to the pipe and feeds on to the main lineconveyor. Simultaneously vibrating feeder on the intermediate conveyor feeds the boomconveyor of the stacker/reclaimer. Feeder is erected to serve the purpose of storage.Underground machines known as plow feeder collect the coal from conveyor and drop it to otherside from other conveyor, with the help of jaws and this coal is taken to huge erected structurefrom where the coal falls to the ground. Figure 3.2 20
  • 3.2.ASH HANDLING PLANTThis plant can be divided into 3 sub plants as follows:-1) Fuel and Ash Plant2) Air and Gas Plant3) Ash Disposal & Dust Collection Plant3.2.1 FUEL AND ASH PLANTCoal is used as combustion material in KSTPS. The Pulverization also increases the overallefficiency and flexibility of boilers. However, for light up and withstand static load, oil burnersare also used. Ash produced as the result of combustion of coal is connected and removed by ashhandling plant which consists of specially designed bottom ash and fly ash in electro staticprecipitator economizer.3.2.2 AIR & GAS PLANTAir from atmosphere is supplied to combustion chamber of boiler through the action of forceddraft fan. In KTPS there are 2 FD fans and 3 ID fans available for draft system per unit.Additional amount of air used called secondary air is supplied by Forced Draft (FD) Fan. The air,before being supplied to the boiler, passes through pre-heater where the flue gases formed due tocombustion of coal heat it. In economizer the heat of flue gases raises the temperature of feedwater. Finally the flue gases after passing through the Electro-Static Precipitator is exhaustedthrough chimney.3.2.3 ASH DISPOSAL & DUST COLLECTION PLANTKSTPS has dry bottom furnace. Bottom ash hopper receives the bottom ash from the furnacefrom where it is stored and discharged through the clinker grinder. Two slurry pumps areprovided which are common to both units & used to make slurry and further transportation to ashdyke thro independent fly ash system. The ash removed from fly ash hoppers is in dry state &carried to the collecting equipment where it is mixed with water and resulting slurry sump isdischarged. 21
  • ugh pipe line. Dry free fly ash is collected in 31 fly ash hoppers, handled by two independent flyash system. The ash removed from fly ash hoppers is in dry state & carried to the collectingequipment where it is mixed with water and resulting slurry sump is discharged.3.3 ELECTRO-STATIC PRECIPITATOR3.3.1 SCOPE & PRINCIPLE OF OPERATIONAs far as air pollution is concerned, various flue gases filter are available. The choice dependson the size of suspended particle matter. These filters are E.S.P. Fabric filter, High efficiencycyclone separators etc. For fly ash, the particle sizes vary from 0.75 microns to 100 micron. In anESP the dust lidded gas is passed through an intense electric field, which causes ionization of thegases & they changed into ion. While travelling towards opposite charged electrode, ions getdeposited as particles and thus dust is electrically deposited an electrode. Figure 3.3 22
  • 3.3.2 E.S.P. FIELD WORKINGThe field consists of emitting and collecting electrodes structure which are totally isolated fromeach other and hanging with the top roof of field. The emitting electrodes are also isolated fromthe roof through the support insulators which also feed the supply to these electrodes. Thecollecting electrodes are of the shape of flat plates. Emitting electrodes are of the shape ofspring..4.BOILERA boiler (or steam generator), one of the major components of the thermal plant is a closedvessel in which water, under pressure is converted into steam. It is always designed to absorbmaximum amount of heat released in process of combustion, which is transferred to the boiler byall the three modes of heat transfer i.e. conduction, convection and radiation.4.1CLASSIFICATION OF BOILERS4.1.1FIRE TUBE BOILERIn this type the products of combustion pass through the tubes which are surrounded by water.These are economical for low pressure only.4.1.2WATER TUBE BOILERIn this type of boiler water flows inside the tubes and hot gases flow outside the tubes. Thesetubes are interconnected to common water channels and to steam outlet. 23
  • 4.2 FEATURES High evaporation capacity due to availability of large heating surface. Better heat transfer to the mass of water. Better efficiency of plant owing to rapid and uniform circulation of water in tubes. Better overall control. Easy removal of scale from inside the tubes.In KSTPS, Natural circulation, tangentially fired, over hanged type, Water tube boilers are used.Oil burners are provided between coal burners for initial start up and flame stabilization. Firstly,light oil (diesel oil) is sprayed for initialization then heavy oil (high speed diesel oil) is used forstabilization of flame. Pulverized coal is directly fed from the coal mills to the burners at thefour corners of the furnace through coal pipes with the help of heated air coming from PA fan.The pressure inside boiler is negative so as to minimize the pollution and losses & to prevent theaccidents outside the boiler. This equipment systematically feed fuel to furnace as per load requirement. The UVflame scanners installed in each of the four corners of the furnace, scan the flame conditions andin case of unsafe working conditions, trip the boiler and consequently the turbine.4.3FURNACEFurnace is primary part of the boiler where thechemical energy available in the fuel is convertedinto thermal energy by combustion. Major factorsthat assist for efficient combustion are thetemperature inside the furnace and turbulence,which causes rapid mixing of fuel and air. Inmodern boilers, water-cooled furnaces are used. Figure 5 24
  • 4.4PULVERISED FUEL SYSTEMThe boiler fuel firing system is tangentially firing system in which the fuel is introduced fromwind nozzle located in the four corners inside the boiler. The crushed coal from the coal crusher is transferredinto the unit coalbunkers where the coal is stored for feedinginto pulverizing mill through rotary feeder. Then coal burnersare employed to fire the pulverized coal along with primary airinto furnace. These burners are placed in the corners of thefurnace and they send horizontal streams of air and fuel tangentto an imaginary circle in the center of the furnace. 4.4.1 FUEL OIL SYSTEM Figure 6The functional requirement of the fuel burning system is to supply a controllable anduninterrupted flammable furnace input of fuel and air and to continuously ignite and burn thefuel as rapidly as it is introduced into the furnace. This system provides efficient conversion ofchemical energy of fuel into heat energy. The fuel burning system should function such that fueland air input is ignited continuously and immediately upon its entry into furnace. Ignition takes place when the flammable furnace input is heated above the ignitiontemperature. Ignition energy is usually supplied in the form of heat, provided by oil guns and byigniters.4.5 BOILER DRUMThe drum is a pressure vessel. Its function is to separate water and steam from the mixture(steam & water) generated in the furnace walls. It provides water storage for preventing thesaturation of tubes. It also houses the equipment needed for purification of steam. The drum 25
  • internals reduce the dissolved solids content of the steam to below the acceptable limit. Drum ismade up of two halves of carbon steel plates having thickness of 133 mm. Figure 7Boiler drum is located at a height of 53m from ground. The drum form the part of boilercirculating system i.e. movement of fluid from the drum to the combustion zone and back toboiler drum. Feed water is supplied to the drum from the economizer through feed nozzles.Water from the drum goes to water walls through six down comers.Main parts of boiler drum are:- Feed pipe Riser tube Down comer Baffle plate Chemical dosing pipe Turbo separation Screen dryer Drum level gauge 26
  • 4.6DRAFT SYSTEMThe combustion process in a furnace can take place only when it receives a steady flow of airand has the combustion gases continuously removed. Theoretically balanced draft means keepingfurnace pressure equal to atmospheric pressure, but in practice the furnace is kept slightly belowatmospheric pressure.4.6.1DRAUGHT FANSA fan can be defined as volumetric machine which moves quantities of air or gas from one placeto another. In doing this, it overcomes resistance to flow by supplying the fluid with the energynecessary for contained motion. The following fans are used in boiler house: Primary air fan (P.A. fan) or Exhauster fanPulverized coal is directly fed from coal mills to the burners at the four corners of the furnacethrough coal pipes with the help of heated air coming from PA fan. Secondly, this fan also driesthe coal. Forced draught fan (F.D. fan)The combustion process in the furnace can take place only when it receives a steady flow of air.This air is supplied by FD fan. Thus FD fan takes air from atmosphere at ambient temperature &so provides additional draught. Its speed is 1500 RPM4.6.1.3 Induced draught fan (I.D. fan) Figure 8 27
  • The flue gases coming out of the boiler are passed to the ESP & then dust free gases aredischarged up by the chimney to the atmosphere through the ID fan. Its speed is 745 RPM.4.6.2 IGNITER AIR FANIt is used to provide necessary combustion air to igniter. Two fans are usually provided. One willrun and 2nd will remain as stand by. A control damper is provided on the discharge whichmodules to maintain a constant differential pressure across igniter when any igniter is in service.Typical speed is 1460 RPM.4.6.3 SCANNER AIR FANUsed to provide necessary cooling air to the flame scanners. Two air fans are usually provided.One will run and other will remain as stand by. When F.D. fans trip, the scanner air fan will drawair from atmosphere through emergency damper. Typical speed 3000 RPM.4.7ECONOMIZER . FIG.9 28
  • The flue gases coming out of the boiler carry lot of heat. An economizer extracts a part of thisheat from the flue gases and uses it for heating the feed water before it enters into the steamdrum. The use of economizer results in saving fuel consumption and higher boiler efficiency butneeds extra investment. In an economizer, a large number of small diameter thin walled tubes areplaced between two headers. Feed water enters the tubes through the other. The flue gases flowoutside the tubes.4.8. HEATERS4.8.1 AIR PRE-HEATERS Figure 10Air pre-heaters are employed to recover the heat from the flue gases leaving the economizer andare used to heat the incoming air for combustion. This raises the temperature of the furnacegases, improves combustion rates and efficiency and lowers the stack (chimney) temperature,thus improving the overall efficiency of the boiler. Cooling of flue gases by 20% raises the plantefficiency by 1%.4.8.2 SUPER-HEATER 29
  • Superheated steam is that steam, which contains more heat than the saturated steam at the samepressure. This additional heat provides more energy to the turbine and thus the electrical poweroutput is more. A super-heater is a device which removes the last traces of moisture from the saturatedsteam leaving the boiler tubes and also increases its temperature above the saturation temperature.4.8.3 RE-HEATERRe-heaters are provided to raise the temperature of the steam from which part of energy hasalready been extracted by HP turbine. This is done so that the steam remains dry as far aspossible through the last stage of the turbine. A re-heater can also be convection, radiation orcombination of both.4.9. CIRCULATION SYSTEMIn natural circulation system, water delivered to steam generator from header, which are at atemperature well below the saturation value corresponding to that pressure. After header, it isdelivered to economizer, which heats it to above the saturation temperature. From economizerthe water enters the drum and thus joins the circulation system through down covering waterwall tubes. In water wall tubes a part of the water is converted to steam due to boiler and themixture flows back to the drum. In the drum, the steam is separated out through the steamseparators and passed to the super heater. After the super heater when the steam temperaturebecomes high and pressure up to 150 Kg/cm3 steam is allowed to enter the turbine to convertpotential energy to kinetic energy.4.10. SOOT BLOWER 30
  • The boiler tubes are cleaned with the help of steam by the process called soot blowing. We arewell known that a greater no. of tubes are presented inside the boiler. Slowly and slowly the fineash particles are collected on the tube surface and from a layer this is called soot. Soot is athermal insulating material. There are mainly three types of soot blower are used in KSTPS: - Water wall soot blower Super heater soot blower Air pre heater soot blower4.11. FUEL SPECIFICATIONSa) COALType : Slack CoalQuantity consumed : 20000 tonnes per dayType of handling : ConveyorAsh disposal : Wet systemb) OILType : HSD and fuel oilNo. of chimney : 4Height of Chimney : 180 MetersVolume of flue Gas : 198 M3/ Sec Air emittedTemp. of flue gases : 140oCESP : One for each unit 31
  • 4.12. GENERAL DESCRIPTIONBoilers are tangentially fired; balance draft, natural circulation, radiant type and dry bottom withdirect fired pulverized coal from bowl/ball mills. They are designed for burning low grade coalwith high ash content. Oil burners are located between coal burners for flame stabilization.Pulverized coal is directly fed from the coal mills to the burners at the four corners of the furnacethrough coal pipes. The pulverized fuel pipes from the mills to the bunkers are provided withbasalt lined bends to reduce erosion and to improve the life of these pipes owing to poor grade ofcoal, there is a high percentage of mill rejects. The mill rejects are conveyed in a sluice way toan under-ground tank. From this tank the mixture is taken to an overhead hydro-bin where wateris decanted and the mill reject are disposed off by trucking. The air required for combustion is supplied by two FD fans.Three ID fans each of 60% capacity have been provided one ID fan to serve as standby. Facilities have been provided to simultaneously unload and transfer 10 light oil and 40 heavyoil tankers to the designated tanks. Oil preheating arrangement is provided on the tanks floorsfor the heavy oil tanks. 32
  • 5.STEAM TURBINE & GENERATION5.1INTRODUCTIONTurbine is a machine in which a shaft is rotated steadily by impact or reaction of current orstream of working substance (steam, air, water, gases etc.) upon blades of a wheel. It convertsthe potential or kinetic energy of the working substance into mechanical power by virtue ofdynamic action of working substance. When the working substance is steam it is called thesteam turbine. FIG. 5.2WORKING PRINCIPLEWorking of the steam turbine depends wholly upon the dynamic action of Steam. The steam iscaused to fall in pressure in a passage of nozzle, due to this fall in pressure a certain amount ofheat energy is converted into mechanical kinetic energy and the steam is set to move with a 33
  • greater velocity. The rapidly moving particles of steam enter the moving part of the turbine andhere suffer a change in direction of motion. It gives rise to change of momentum and thereforeconstitutes the driving force of the machine. The procedure of expansion and direction changingmay occur once or a number of times in succession. The majority of the steam turbine have, therefore two important elements. These are-1. The nozzle in which the system expands from high pressure end is comparatively in rapidmotion to that of lower pressure end.2. The blades attached to the rotating elements, in which the steam particles changes itsdirections and hence its momentum, are attached to the stationary part of the turbine i.e. stator,casing or cylinder. Although the fundamental principles of all steam turbine are same, yet the methods vary andthus certain types of turbines have come into existence. 5.3DESCRIPTION 5.3.1 STEAM FLOW210 MW steam turbine is a compound machine with HP, IP & LP parts. The HP part is singleflow cylinder and IP & LP parts are double flow cylinders. The individual turbine rotors andgenerator rotor are rigidly coupled. The HP cylinder has a throttle control. Main steam isadmitted before blending by two combined main stop and control valves. The IP turbine exhaustsdirectly goes to LP turbine by cross ground pipes. 5. 3.2 HP TURBINEThe HP casing is a barrel type casing without axial joint. Because of its rotation symmetry thebarrel type casing remain constant in shape and leak proof during quick change in temperature.The inner casing too is cylinder in shape. This is suitable for quick start up and loading. The HPturbine consists of 25 reaction stages. The moving and stationary blades are inserted intoappropriately shaped inner casing and the shaft to reduce leakage losses at blade tips. 34
  • 5.3.3 IP TURBINEThe IP turbine is of double flow construction (double shell construction). The double flow innercasing is supported kinematically in the outer casing. The steam from HP turbine after reheatingenters the inner casing from above and below through two inlet nozzles. The arrangements ofinner casing confines high steam inlet condition, while the joints of outer casing is subjected onlyto lower pressure and temperature at the exhaust of inner casing. The pressure in outer casingrelieves the joint of inner casing so that this joint is to be sealed only against resulting differentialpressure. The IP turbine consists of 20 reaction stages per flow. The moving and stationaryblades are inserted in appropriately shaped grooves in shaft and inner casing.5.3.4 LP TURBINEThe casing of double flow type LP turbine is of three shell design. The shells have rigidly weldedconstruction. The outer casing is supported by the ends of longitudinal beams on the base platesof foundation. The double flow inner casing consists of outer shell and inner shell. The innershell is attached to outer shell with provision of free thermal movement. Steam admitted to LPturbine from IP turbine flows into the inner casing from both sides through steam inlet nozzles. 5.4.ELECTRICITY GENERATIONThermal power station burns the fuel and use the resultant heat to raise the steam temperaturewhich drives the turbo-generator. The fuel may be “Fossil” (Coal, Oil and Natural Gas) but theobject is same to convert the heat into mechanical energy and further to electrical energy byrotating a magnet inside the set of winding. In a coal fired thermal power station other rawmaterials are air and water. Meanwhile the heat reloaded from the coal has been absorbed by a long tube which liesin boiler walls. Inside the tubes “Boiler Feed Water” is transferred into turbine blades and makesthem rotate. To the end of the turbine rotor of generator is coupled, so that when turbine rotates 35
  • the rotor turns with it. The rotor is housed inside the stator having coil of copper bars in whichelectricity is produced through the movement of magnetic field created by rotor. The electricitypasses from the stator winding to the transformer which steps up the voltage so that it can betransmitted effectively over the power line of grid. The steam which has given up its heat energy in changed back into a condensate so that itis ready for reuse. The cold water is continuously pumped in condenser. The steam passingaround the tubes loose heat and rapidly change into water. The cooling water is drawn from theriver but the Boiler Feed Water must be pure than potable water (DM Water).*The rated speed of turbine is 3000rpm. 36
  • 6.WATER TREATMENT PLANTThe principle problem in high pressure boiler is to control corrosion and steam quality. Internalcorrosion costs crores of rupees in repair. Without strict control, impurities in steam also formdeposit over turbine blades and nozzles. The impurities present in water are as follows:-  Un-dissolved and suspended solid materials.  Dissolved slats and minerals.  Dissolved gases.  Other minerals (oil, acid etc.).  Turbidity & Sediment.  Silica.  Micro Biological.  Sodium & Potassium Salt.  Dissolved Sales Minerals.  O2gas.  CO2 gas.Thus to make water pure for feeding in B.F.P. and to have protection against corrosion and otherabove mentioned problems de-mineralisation is needed. The procedure is explained as-6.1 D.M. PLANTIn this plant process, impure water is fed. This plant consists of two streams, each stream passesthrough activated carbon filter, weak acid, cation exchanger and mixed bed exchanger. Theimpure water is fed to DM plant through 250 dia. header from it is taken to softening plant. Twofiltered water booster pumps are provided on filtered water line for meeting the pressurerequirement in DM Plant. Sodium Sulphate solution of required strength is dosed into different filtered water streamsby means of dosing pump to neutralize chlorine prior to activated carbon filter. Water passes 37
  • through an activated carbon filter to remove residual chlorine from water. Water then goes toweak base anion exchanger unit & enters de-gasified unit where free CO2 is scrubbed out ofwater by upward counter flow of low pressure air flow. This de-gasified water is pumped tostrong base exchanger (anion exchanger).6.2C.W. PLANTCirculating water pump house has pumps for condensing the steam for condenser. Aftercondensing the water is discharged back into the river. Each of the 5 pumps for 1st and 2nd unithas capacity of 8275 M3/Hr, and develop pressure about 1.94 kg. /Cm2. 3 seal water pumps areused for sealing circulating water pump shaft at pr. 4.5 kg. /cm2. One pump is taken standby at atime. From main line water passes through filter bed to filter the water. Chlorified water ispumped to 42 m elevation where water is stored in tank and used for cooling the oil coolers andreturns back to river. 6.3B.C.W. PUMP HOUSEFiltered water after demineralization is used for Bearing Cooling from BCW pump house. Waterenters at 30-32oC and leave exchanger at 38oC. The raw water used in ash handling plant andremaining quantity is stored in BCW Pump House. From here the water is pumped to CWpumps. BCW here stand for water used for cooling oil used for cooling the bearing. In CWpump house water is discharged from nozzle and impinged for travelling water screens forcleaning it. 38
  • 7.SWITCH YARD7.1 220 KV SYSTEMTwo 220 KV bus bars have been provided in switch yard and are inter-connected through a buscoupler. Each of the generators is connected to this system through a step up of 125 MVA 240 /11 KV yard generator transformers. There are two step down transformer each feeding 6.6 KV.Each station transformer has two windings one secondary side and one primary side. Fourfeeders take off from 220 switch yard, 2 to SKATPURA GSS and other 2 to HEERAPURA,Jaipur GSS. Each of the four feeders is provided with bypass isolators which are connectedacross line breaker and breaker isolator. A brief description of equipments of 220 KV system isas follows-7.1.1 CIRCUIT BREAKERSEach of generator transformer, station transformer, line feeder and bus coupler is provided withminimum oil circuit breaker of BHEL make. It is used to break the circuit either in loadcondition or in no load condition.7.1.2 ISOLATORSAll the isolators are provided in 220KV switchyard and are motor operated. Triple pole doublebreaker type and power switch yard L&T make these and are rates for 245 KV and 1250 A. Thefour isolators are provided with earth switch.7.1.3 CIRCUIT TRANSFORMERAll the 220 KV current transformers are provided for measuring and protection. They are BHELmake, single phase, oil filled nitrogen sealed outdoor type. 39
  • 7.1.4 POTENTIAL TRANSFORMEREach of 220 KV buses is provided with three P.T.’S for each phase of BHEL make. There aresingle phase, oil filled outdoor. N2 sealed magnetic type. Potential Transformer has twosecondary windings on secondary side.7.1.5 LIGHTENING ARRESTORFor protection against lightening, each of line feeders, generator transformer and stationtransformer has been provided with three L.A. (one for each phase). All the L.A. are 2 Øoutdoor types and are rated for 198 KV. The L.A. of generator transformer and stationtransformer are located nearby. If we have to do some work on line, firstly line through earthingisolator is earthed for discharging the line capacitance and then work is proceeded. 40
  • 8.PROTECTION AND MISCELLANEOUS 8.1GENERAL PROTECTIONGenerator is the most important electrical equipment of many generating station. Tripping ofeven a generating unit may cause overloading of associated machines and even to system un-stability. The basic function of protection applied to generator is to reduce voltage to minimumby rapid discrimination clearance of faults. Unlike other apparatus the opening of C.B. to isolatefaulty generator is not sufficient to prevent future damage. 8.1.1SPECIFIC PROTECTIONFollowing are the protection purposes for the plant-1. Field Protection.2. Pole Slipping.3. Plane Overload Protection.4. Inter-turn Fault.5. Negative Phase Sequence Protection.6. Reverse Power Protection.7. Forward Power Protection.8. Under Frequency & Over Frequency Protection.9. Generator Voltage Protection.10. Rotor Earth Fault Protection. 41
  • 42