1 TRAINING
REPORT
ON GAS TURBINE AND GENERATOR AT B.H.E.L.HYDERABAD FROM DATED 11/12/02 TO 18/12/02
BHEL collaborated with GE usa. In 1986 for for getting design supply and mfg. of hot gas path components as well services of gas turbine as per GE norms .and extend for further 10 years. GE has developed gas turbine frame series fr-1,2,3,5,6,9,with various models. Identification of gas turbine turbine are on ISO rating with with -application -application - series series - power in hp. - no. of shaft. shaft. As frame -5 some m/c having 2 shafts where the GT is used for variation of load (mechanical) .in this type compressor to HP turbine one shaft and L.P. L.P. turbine to load end II nd shaft . GT basically works on two thermal cycle.(1) On open cycle “Brayton Cycle” GT exhaust gas stack direct to atmosphere. (2) And in combined co mbined cycle, exhaust gas diverted to WHRB. And steam generate to run steam turbine on “Rankine cycle”.If 100% fuel is added to GT , only 29.5% converted to load +3.5% heat losses and 67% heat waste to exhaust which is diverted to WHRB and getting 80% (approx) efficiency of GT. Selection of GT for higher efficiency and higher specific out put / kg air flow. Firing temp. of fr5 -963*, fr.61104*, fr.9e-1124*, fr 6fa-1288*, fr9ec-1204*, fr9fa-1316*, fr9h-1418*c. As per P-V & T-O diagram press. difference P2 –P1 –P1 and heat addition addition at constant pressure pressure Effi =1x heat removal / heat added. So more heat addition efficiency will increase and more addition of heat firing firing st temp. rises. To accommodate higher temp. 1 stage bucket material is improved by coating and giving cooling holes inside bckt. So Bckt remain to normal temp. temp. and surface coating faces the higher temp. st Shock. in fr-9h GT as firing temp is to high 1 stage Bckt provided with spiral way holes with cooling media as steam to absorb more heat (lateen heat.) through max. surface area.. Major factor effecting the GT performance are:Ambient temperature –as ambient temp. rising high density of air comes to low and relatively • fuel consumption is low. Approx. if 10*c temp rise will down Effi. by 7%.even in below ‘o’*c turbine will work efficiently but load gear box capacity will restrict the Effi. Altitude(msl)same as above reason when altitude raise by 100mtrs.Effi. will down by 1%due to • low density . Relative humidity .as more humidity humidity in air density of air will be down. • Inlet pressure pressure drop 4” of H2O inlet drop produce 1.5% power out put loss,.5% heat rate • increase ,and 1.2*c of firing exhaust temp. rise. rise. 4”exhaust press. Drop .5% power out put less .5% heat rate increase and 1.2*c exhaust temp will • increase
2 Also in gas fuel more hydrogen available compare to any liquid fuel so at exhaust water particles also drop exhaust temp . NOX –as nitrogen is non acting but in higher temp, it reformed to NOX with oxygen composition .which is detected by flame temp. In gas NOX is available up to 118max.But in liquid fuel NOX availability is more than 225.For reducing NOX level water steam injected in firing zone to reduce the temp. Now another DLN system is offer for dry low NOX ,in this system fuel +air introduce in firing zone to bring the firing temp. Chiller plant or air cooler systems provide for air inlet temp. but o nly useful in dry and hot area.. Gas path description .. when turbine starting system actuated atomizing air is drown through air filter system to inlet plenum and compressed in 17th stages axial flow compressor, for pulsation protection 2 nos. of bleed valves are provided to extract excess air from system to exhaust on minimum firing mode after turbine speed reaches up to 95% bleed valves closed. IGV 34 to 57 % open up to FSNL mode and further on as per loading on turbine. Compressor air flows in to annular space surrounding 10 combustion chambers from which flow into space between outer combustion casing and liner and enter to combustion zone through metering holes in each liners. Fuel from a off base source is provided in ten equal flow line through ring header each terminating at fuel nozzle located on individual comb. Chamber .fuel is accurately d istributed / controlled to provide an equal flow in to 10 nozzle feed line at a rate required load ,speed of Gt through gas ratio valve . Nozzle introduce fuel in combustion chamber with air mixture for atomizing ,where 4 nos. spark plug ignited fuel .and flame is propagated through ‘crossfire tube ‘to all combustion chambers on pressure diff. flow phenomena . and established flame in each comb. Chamber . hot gases from comb. Chamber expand in to 10 separate transition piece attached to AFT of liners and flow from there enter into 3 stages turbine section of m/c. Each stage consist of a row of fixed nozzle followed by a rotatable turbine buckets.. In each following row of moving buckets a portion of kinetic energy .the jet is absorbed and useful work done on turbine rotor. After passing through the IIIrd stage bckt. the gases are directed to the exhaust hood and a diffuser which contain a series of turning vanes to take the gases from axial to radial direction ,there by minimize head loss these gases passes through exhau st plenum and introduce to atmosphere or to WHRB .resultant to shaft rotation is used to turn the generator for electricity or to any centrifugal power application . Turbine based support :The base upon which the gas turbine mounted is a structural steel fabrication(skid) it forms a single platform which support the basic G.T. unit and accessory equipments .In addition base support the gas turbine inlet and exhaust plenum .forward end of the base under the accessory compartment also function for lube oil storage tank. Oil drain ch annel is constructed along the web of the left longitudinal “I” beam. This channel extends from the oil tank to the end of the base, providing a passage for the lube oil header , lube oil feed and drain connection are made at the AFT drain channel . Finished pad on the bottom of the base facilitate it’s mounting on the site foundation .. Turbine supports – GT is mounted on it’s base by vertical support at three location Forward support is located at the lower half of the forward vertical flange of the compressor casing an d AFT two support are located on either side of the turbine shell. The AFT support one on each side of turbine shell are leg –type support with vertical support leg rest on m/c pad on the base and attached snugly of the turbine exhaust frame mounted support pad .Leg provided centre line support to supply casing alignment on the inner surface ,each support leg a water jacket is provided ,through which cooling water is circulated to minimize thermal expansion and to assist in maintaining alignment between the turbine and generator. Leg type support maintained axial and vertical position of turbine while ‘Jib key’ compel with turbine support leg to maintain it’s lateral position . Jib key is machined on the lower half of the turbine shell and it fits into guide block which is
3 welded to the turbine base AFT cross beam. The key is securely in place in the guide block arrangement to prevent lateral or rotational movement of the turbine while permitting axial & radial movement resulting from thermal expansion . Compressor: compressor discharge casing consist of two cylinder on being a continuation of the compressor casing and other being the inner cylinder that surround the comp. rotor .Two cylinders are concentrically position by 10 radial struts. These trust extended from the inner cylinder outward to a vertical bulkhead has permitting air flow to enter the comb. System in 10 circular opening .A diffuser is formed by the tapered annulus between the outer cylinder and inner cylinder of discharge casing. The diffuser convert some of the compressor exit v elocity into added pressure. Compressor air mainly used for combustion ,cooling media and diluting flame temperature. compressor rotor and stator blades are made of same material ,compressor casing C.D.C are made from gray iron ductile casting. Compressor rotor and stator blades are air foil shaped & were design to compress air efficiently at high blade tip velocity , the blades are attached to wheel by dovetail arrangement . In stator for stage 1 to 4 are mounted similarly dovetail in to ring segment and they are inserted in to circumferential groove in the casing. instage 5 to 17 stator blades and exit guide vanes 1 &2 Have square base dove tail are directly inserted to circumferential groove of casing. Bearing Sealing air : sealing air for the bearing is provided from a connection on the compressor casing out of 5th stage orifice in the air line to the turbine bearings .Limit the flow of air and pressure to the proper value centrifugal separation in the piping remove any particles or dust to protect the bearings. In order to prevent compressor pulsation ,when the unit is accelerating during start up and decelerating during shut down in conjunction with the inlet guide vane operation , air is extracted from 11th stage and released to atmosphere through air operated “bleed valve” VA1-1,VA1-2..from compressor discharge air limit switch is provided 33CB1-2,on each valve to give an indication of valve position . Interval air cooling extracted from 16th stage ,it provide internal flow of cooling air through the centre of the turbine rotor and from there to1st stage buckets cooling holes. Air inlet system : for compressor air supply for suction is supplied through air inlet system which consist of an integrated self cleaning filter house and support structure on inlet ducting system. And inlet plenum leading to compressor section of turbine. Inlet air enters the inlet compartment and flow through ducting with built in acoustical silencer and trash screen to the inlet plenum before entering to the compressor. The elevated intake arrangement provides a compact system and minimize pick up to dust concentrated in air near the ground. All internal and external surface area of system is coated with corrosion preventive primer .Air flow qty. for fr-6 Gt 136kg/sec. or 26,000 CFM and for fr-9 GT 404kg/sec.Inlet duct prepare from 6mm.carbonsteel plate. Inlet duct consist of expansion joint ,extension duct, elbow, transition duct. Inlet silencer con tain silencing baffle constructed of low density insulating material which is encapsulated by perforated steel sheet. The vertical parallel baffle is specially design to eliminate fundamental compressor tone (noise) as well as alternating the noise at other frequency . Stationary trash screen within the transition duct provide for accessed cleaning and inspection through a removable access panel on the side of elbow, all surface wall painted with multiple coat zinc rich corrosion inhibiting paint. Exhaust system : The exhaust system is the portion of GT in which gases used to power the turbine wheel are redirected and released to atmosphere exhaust system direct the gases from the exha ust plenum laterally in to the exhaust ducting . Exh,. System provide exhaust plenum , exhaust .wrap around and exhaust joints. Exhaust temp. thermocouples are mounted in the AFT wall of exhaust plenum and sense exhaust temp. and input this value to control system . There are 18 nos of thermocouples in FR-6 Gt .. S.S plate 304/409 and 3mm in thickness cladding sheet and insulated with 250 mm thick ceramic wool between skin plates to maintained normal temp. Exhaust press. Is @ 200 to 250 mm of water column. and at 500 mm wcl value the tripping of GT set .If GT is meant for combined cycle the diverted damper stack arrangement is given to re direct exhaust flow towards the WHRB .TX (exhaust temp. ) main parameters to watch for the turbine running condition and firing temp. Cooling of turbine exhaust
4 casing and exhaust frame is accomplished by two motor driven centrifugal blower 88TK188TK2.discharge of each fan passes through the turbine shall and flow in to the exhaust frame via exhaust frame strut passages and to the atmosphere. Press. switch 63TK1 & 63 TK2. are provided ,if one fail alarm goes to control panel and on both failure turbine trip signal to control, These TK fan to protect Against de formation of turbine casing by high temp. Turbine combustion system : comb. system is reverse flow type includes 10 comb. chambers having main components are liner flow sleeve, transition pieces, cross fire tubes flame detectors fuel nozzles and essential piping .In reverse flow system high press. Air from air compressor discharge is directed around the T.P and in to annular space that surround each of the 10 comb. Chamber liners. Comp. discharge air which surround the liner flow radial in words through small holes on the liner wall and impinges against that are braced to the liner wall .This air than flow right towards the liner discharge end and form a film of air that shield the liner wall from the hot comb. Gases . Comb. chambers are numbered counter clock wise when viewed looking down stream . Disch. air enter the comb. chamber from cavity of the centre of the unit .This air flow upstream along the out side of the comb. liner towards the liner cap. This air enter the comb. Chamber reaction zone through the fuel nozzle swirl tip and through metering holes in caps and liners. The hot comb. gases through the reaction zone passes through a thermal soaking and than into a flame dilution zone where addition air is mixed with the comb. gases. Metering holes in dilution zone allow the correct amount of air flow to enter and cool the gases to the desire temp. Along the length of comb .liner and in the liner cap are opening whose unction is to provide a film of air for cooling the wall of the liner and cap . Transition pieces are fitted on the AFT end of liner with proper sealing for ensuring no leakage and T.P. further guided these hot gases from comb. Liner to 1st stage nozzle. T.P having AFT end shape in rectangular suitable for 1st stage nozzle where entering hot gases and totally sealing done by seals on mouth to get max. Effi. form hot gases by ensuring the flow in no zzles only. Both T.P. and comb. liner are having life of more than 75,000 firing hrs .but during each inspection it is to be checked thoroughly and D.P .tested for any damages cracks and get repaired .from inside all combustion liners and transition pieces are having special “T.B.C.” coating to save parent material and give maximum life of desire firing hrs. Fuel nozzles: each comb. Chamber is equipped with a fuel nozzle that emits a metered amount of fuel in to comb .liner gaseous fuel admitted directly into each chamber through metering holes located at the outer edge of the swirl plate .when liquid fuel is used it is atomized in the nozzle swirl chamber by means of high press. Air. The atomized fuel air mixture is than sprayed in to combustion z one. Action of swirl tip impart a swirl to to combustion air with the result of more co mplete combustion & essentially smoke free operation of the unit. .during inspection fuel nozzle also checked and tested for any damages /leakages .There swirl holes and centre hole is likely to damage and de form the shape may leads to un even firing of fuel and resulted in improper combustion and firing temp. Flame zone in comb .liner is 6” to 9” and radiation zone is 2” from nozzle tip .Fuel nozzle fitted to cap and liner there is a gasket ensuring joint must be 1.0 to 1.5 mm thick other wise flame flow will not extended to desire length and causing damages of fuel nozzle tip by back flame heat . Cross fire tubes: To establish flame in each combustion chamber cross fire tubes arrangement provided & it varies in length as per GT design .In comb. chamber 2,3 & 7,8 spark plug provided for ignition of fuel After established flame in these chambers flame propagated in adjacent comb. Chamber through cross fire tubes which is work on press. Difference .And after ensuring flame in all comb. chambers flame detector give signal to IV monitor ,and firing press .is equal flame propagation is automatically stop. i.e. there is no flame in cross fire tubes after purpose is solves. Spark plug supplied110v> 10kv for sparking the fuel and combustion started and mark IV gets it flame available command and if not stabilize for 1 minute mark IV give trip command for turbine for improper combustion . Any erosion or change found on cross fire tubes is due to loose fitting only and found over burning marks .So ensure for proper fitting during assembly.
5 Turbine section : Three stage turbine section is the area which energy in the form of high energy produce by ignition of gas is converted into mech. Energy. Turbine section includes turbine rotor shell, exhaust diffuser ,nozzle, buckets and shrouds. The turbine rotor is of through bolted construction ,consisting of the distance piece and 1st stage wheel, 2nd and 3rd stage wheel ,3rd stage wheel and AFT wheel shaft .The wheels are held together with through bolts selective position of rotor member perform to minimize balance correction . The AFT wheel shaft connect 3rd stage turbine wheel to the load gear coupling, it includes no. 2 bearing journal. Buckets: Turbine buckets are increasing in size from 1st to 3rd stage because pressure reduction resulting from energy conversion in each stage , and increase annual area is required to accommodate the gas flow. Each 1st stage bucket contain a series of longitudinal air passage for bucket cooling Air is st introduce in each 1 stage bucket through a cavity between the wheel and the base of the bucket dove tail . The air flow Through a series of cooling holes spanning the bucket length wise and exit from these holes at each recessed bucket tip , the holes are spaced and sized to obtained optimum cooling of the air foil with with a minimum of compressor extraction air . Bucket material is IN738 earlier and modified to GTD 111 cobalt based . And nozzle material FSX 414 earlier modified to GTD 222 , and now used in II nd and III rd stage nozzle also. Material composition is CrTiwMo nickel based . Cooling system of turbine and it’s components : Turbine rotor must be cool to maintained reasonable operating tepm. And there fore assure a longer service life cooling is accomplished by means of a positive flow of cooling air radically out ward through a space between the wheel and the buckets and the stator in to main gas stream . This area is called wheel space . 1st stage forward wheel space is cooled by compressor discharge air at the AFT end of the compressor rotor is a high pressure packing between rotor and the inner barrel of compressor discharge casing. Part of the leakage through this labyrinth furnish the air flow through the 1st stage forward wheel space and discharge in to main gas stream AFT the 1st stage nozzle. 1st stage AFT wheel space is cooled by 2nd stage nozzle cooling air . 2 nd stage forward wheel space is cooled by leakage of air from 1st stage AFT wheel space through inter stage labyrinth .This air is returned to the gas path at the 2nd stage bucket . The 2nd stage after wheel space is cooled by air from internal extraction system , this air enters the wheel space and return to the gas path at the 3 rd stage nozzle entrance . 3rd stage wheel space is cooled by leakage from the 2nd stage AFT wheel space through the inter stage labyrinth ,this gas re enters the gas path at the 3rd stage bucket entrance . 3Rd stage AFT wheel space is cooled by the fifth stage extraction air from compressor . this cooling air is piped to the turbine shall , the air flow through holes in shell and enter the exhaust from struts and than the majority is finally dispatched to the 3rd stage AFT wheel space cavity .Remaining air is than piped out of the AFT end of the diffuser to a purchaser connection . stator : Turbine shell and exhaust frame is complete the major portion of the gas turbine structure ,The turbine nozzle ,shrouds , bearing no 2 and turbine exhaust diffuser are internally supported from these components. shell : turbine shell controls the axial and radial position of shrouds and nozzles. Resultantly it controls turbine clearance and relative position of the nozzles to the turbine buckets. This position is critical to gas turbine performance . The hot gases contained by the turbine shell are a source of heat flow in to the shell , to control diameter it’s important to reduce heat flow in to shell by design and to cool it to it’s limit it’s temp. Heat flow limitation incorporate insulation ,cooling and multi layer structure , cylinder portion of the shell id cooled by fifth stage air flowing axially through the shell and out through holes in AFT vertical flanges in exhaust frame .The air is than used further cooling of the exhaust frame and 3rd stage AFT wheel space . NOZZLES. In the turbine section there are three stages of stationary nozzles which direct the high velocity hot gases expanded against the turbine buckets and turbine rotor to rotate because high pressure drop across these nozzles , there are seals at the both inside diameter and the out side diameter
6 to prevent losses of system energy by leakage. As nozzles operate in the hot combustion gas flow they are subjected to thermal stresses in addition to gas pressure loading.
1st stage nozzle : 1st stage nozzle received hot combustion gas from the combustion system via T.P. T.P. are sealed to both the outer and inner side wall on entrance side of nozzle segment ,each with two partition on air foil are contained by horizontally split retaining ring which is centre line to the turbine shell on legs at the side and guided by pin at the top and bottom vertical center line . This permit radial growth of retainer ring from changes in tepm .while ring remain in centered in the shell . The AFT outer diameter of the retaining ring is located against forward face of the 1st stage turbine shrouds and act as to prevent air leakages of compressor discharge air between nozzle and shell .On inner side wall nozzle is sealed by “U” shaped sealed segment installed between nozzle and 1st stage support ring bolted to CDC. Nozzle is prevented to moving forward by four lug welded to the AFT out side diameter of the retaining ring . at 45* from vertical and horizontal centre line These lug fit in a groove m/c in turbine shell just forward of 1st stage shroud “T” hook by removing the horizontal joint support block and bottom centre line guide pin . nd 2 stage nozzle : combustion air exiting from 1st stage bucket is again expanded and re directed against 2nd stage bucket by 2nd stage nozzle is made of 16 cast segments each with three partition or air foil .The nozzle segments are held in a circumferential position by radial pin from the shell in to axial slots in the nozzle outer side wall .Close fitting tongue and groove fits between nozzle and shroud act as a out side diameter air seal is cooled with compressor discharge air . rd 3 stage nozzle: received the hot gas from 2cd stage bucket as it increase in velocity by pressure drop and direct this gas flow to 3rd stage bucket .Nozzles consist of 16 cast segment each with four partition or air foil fitted at the out side wall forward and after side in grooves in the turbine shroud in a manner identical to that used on 2nd stage nozzle . 3rd stage nozzle is circumferentially positioned by radial pin form the shell . Diaphragms.: this diaphragm prevent air leakage past the inner side wall of the nozzle and the turbine rotor .The high / low labyrinth type seal teeth are machined in to inside diameter of diaphragm .Minimum radial clearance between stationary part and the moving part are essential for maintaining low inter stage leakages results higher turbine efficiency . SHROUDS : Unlike the compressor blades ,turbine bucket tip do not run directly against an integral machined surface of the casing but against annular curved segments called turbine shroud. Primary function is to provide a cylindrical surface for minimize bucket tip clearance leakage and another function is to provide a high thermal resistance between hot gases and comparatively co ol shell .By accomplishing this function the shell cooling load is hectically reduce and shell diameter is controlled ,shell roundness is maintained and important is turbine clearance are assured . fitting in circumferential position a shell by radial pin and joints between shroudsegments are sealed by inter connecting tongue groove .” modified version of shrouds are “HONEY COMB” shroudsand tooth cutter tip bucket reduce bucket tip clearance and increase efficiency . EXHAUST FRAME: Exhaust frame is bolted to the AFT flange of turbine shell ,structurally the frame consist of inner cylinder inter connected by radial strut . Exhaust diffuser is located between inner and outer cylinder .Gases exhaust from the 3rd turbine stage enter the diffuser where velocity is reduce by diffusion and pressure re cover .At the exit of diffuser turbine vanes assist in directing the gases to exhaust plenum .The struts must be maintained at a uniform temp. in order to control centre and central position of the rotor in relation to the stator. This temp. stabilizing is accomplished by protecting the struts from exhaust gases with metal wrapper fabricated in to the diffuser .This wrapper also provide a circuit of cooling air (i.e. TK fan air).In Turbine shell cooling air flows through space between struts and wrapper to meet uniform temp. of struts.
7 TURBINE BEARINGS : Gt contain two main journal bearing used to support gas turbine rotor .The unit also includes thrust bearing to maintain rotor to stator axial position .These bearings and seals are in corporated in two bearings. one at inlet end and other in exhaust frame. These bearings are pressure lubricated by fluid supplied through main lube o il system .
1.
Bearing -1 class journal and thrust type elliptical load equalizing and unload equalizing. Bearing -2 is type of journal elliptical . Bearing -1 sub assembly is located in the centre of the casing and contain three brgs. 1) active loaded thrust brg . 2)inactive unloaded thrust brg. 3) journal brg.. Additionally it contain one “running type “ring seal two labyrinth seal and housing in which components are installed .The components are keyed to prevent rotation .Bottom part of the housing is a part of inlet casing , the top of the housing is a separate casting flanged and bolted to the bottom half. The labyrinth seal at each end of the bearings are pressurized with air extracted from compressor 5th stage .Running type seal at the forward end of the thrust brg. Cavity contain the lubricant and limit entrance of air in to cavity . BRG-2 sub assembly is centralized supported and located inside the exhaust frame inner tunnel. This support includes ears at the horizontal and a jib key at the bottom center line. This permit relative growth result from temp .difference while the BRG remain centered in the exhaust frame. Assembly includes an elliptical liner labyrinth seal and bearing housing with separate brg. Liner retaining strap bolted to the lower half of the housing .These components are keyed to prevent rotation , labyrinth seal at each end of housing pressurized with air from comp. 5th stg air. COUPLING : Coupling are used to transmit starting torque from accessory gear to Gas turbine compressor and to transmit shaft H.P. from turbine to driven reduction gear or load . Accessory gear coupling – a splined oil filled flexible coupling is to connect Acc. Drive to GT shaft at the compressor end. This coupling employ a hub male teeth at each end that mashed with a sleeve of female teeth to transmit torque. The teeth of the male hub are crowned and side force and AFT within the female spline which allow three type of misalignment , angular parallel and combination of both .The oil lubricant for yhe coupling is sealed in to each coupling end by a plug with ‘o’ ring. Load coupling a rigid hollow coupling connect to turbine rotor shaft to the reduction gear each end of the coupling is bolted at positive flange connection . GT SUPPORT SYSTEM : GT support system includes lube oil system for furnishing normal lubricant and absorbing the heat rejection of the gas turbine. 2. hydraulic supply system which provides the necessary hydraulic flow and pressure for control device on the turbine . 3. trip oil system which operate device or the control ,hydraulic trip sub system . 4. Cooling water system which cooled the lube oil ,generator air cooler. 5. Starting system includes starting device and required logic sequence for starting GT and bringing it to operating speed ( electric motor , diesel engine require torque converter, steam turbine ,gas expander not require TC. ) 6. Cooling and sealing air system which provides necessary air flow from turbine compressor to other parts of the turbine ,rotor ,stator to prevent excessive temp. built up and to prevent oil leakage from the bearings. 7. Fuel system supplies control the flow and direct the fuel to the fuel nozzle in the gas turbine combustor. The fuel system include gas ,liquid and dual fuel system . 8. Atomizing air system provide sufficient pressure in the air atomizing chamber of the fuel nozzle to break the fuel jet up to a fine mist permitting ignition and combustion with increased efficiency. 9. Ventilation and heating system provides the ventilation of hot air from compartments work in the allowable compartment temp.(BT fan VG fan ) 10. Fire protection system provide extinguish fire in the compartment in case any fire take place .Co2 battery system provision is there.
8 11. Inlet exhaust system provide atmosphere air to be brought in to the compressor through inlet ducting and let exhaust gases to atmosphere or to HRSG.
GAS FUEL SYSTEM : is designed to deliver gas fuel to turbine combustion chamber at the proper pressure and flow rates to meet all to starting ,accelerating and loading requirement of GT operation . Major components of gas fuel system is the gas stop /ratio control valve assembly located in gas fuel module .associate with necessary piping strainer fuel vent valve, control servo valve press. gauges .and distribution piping to combustion fuel nozzle. Major components are gas fuel strainer ,gas stop ratio valve and control valve(VSR-1.VGC-1)fuel gas pressure low alarm switch(63FG-3) pressure gauges, gas fuel vent valve (20VG-1), gas fuel trip vale (VHS-1),stop ratio and control servo valve (65GC-1)gas control valve (LVDT, 96GC-1,2)pressure transducer (96FG2A,2B, 2c) , stop ratio valve LVTD(96SR1,2)gas fuel servo hyd. supply filter9 FHT-1)gas fuel manifold and nozzle (MG-1-1). TURBINE PROTECTION SYSTEM B: turbine protection system are set up to detect and alarm such a failure ,if the condition is serious enough to disable the protection completely ,the turbine will be trip .protection system respond simple signals such as pressure switch as used for low lube oil press. And they also respond to more complex parameters such as over speed ,over temp. vibration ,combustion monitor and loss of flame. some of protection system are ope rate through MASTER CONTROL and protection circuit in speedtronic while totally mechanical system operate directly on the components of the turbine. 1. Trip oil system : Hydraulic trip system called trip oil system is the primary protection interface between turbine control and protection system and the components on the turbine which admits or shut off fuel. 2. Over speed protection .speedtronic over peed system is designed to protect GT against possible damage caused by over speeding of turbine shaft. Primary over speed protection system is electronic over speed system consist of a magnetic pick up to sense turbine speed ,speed detection soft ware and associate logic circuit. turbine speed signal (TNH) deliver from magnetic pick up 77NH1-2-3.and compare to over speed (TNKOS1) TNH exceed the set point over speed trip signal L12H is transmitted to master protection .Mechanical over speed bolt in accessory gear spring loaded eccentrically located bolt in cartridge and spring force hold the bolt, when turbine speed increase centrifugal force acting on the bolt and bolt moves outward contact with over speed mechanism and over speed limit switch 12HA to operate protection .Over speed tripping setting normally higher than electrical over speed trip setting. Electrical setting is at 11 0% and mechanical over speed sets at 112.5% of normal speed of turbine . Loss of speed signal is also trip command given to turbine. 3. Over temp. protection . system protect the turbine against possible damages caused by over firing .over temp. alarm (L30TXA) represent the value of exhaust temp. thermo couple. Compared with alarm and trip set as per design limiting of firing temp. range. 4. Flame detection protection system : To avoid possible accumulation of explosive fuel mixture in turbine during loss of flame detector signal is start up of turbine ,if one failed alarm given to speed tronic and if both detector failed trip signal g iven to master control .also during ignition on start up of turbine flame scanner not sense the flame for more than 1 minute period flame failure trip command gives to turbine. 5. Vibration protection :in turbine both bearing and including lg box and generator side bearings are provided with vibration pick up to measure velocity in mm. and having double protection system to avoid any false trip signal .normally setting for alarm is set to 12mm/secand 25mm/sec trip signal to master control . 6. damages in combustion zone bearing uneven heating / fuel is done by examining exhaust thermocouples temp. and compressor discharge temp. thermocouples .from changes may occur in pattern of thermocouples reading warning and protection signal are generated .Depending on turbine model –series and type of thermocouples SA “allowable spread “ based on average exhaust
9 temp. and compressor discharge temp. S1- difference between higher and lowest thermocouples reading. S2- difference between highest and 2 nd lowest thermocouples reading. S3- difference between highest and 3 rd lowest thermocouples reading. Allowable spread must be between the limit TTXSPL 7 and TTXSPL6 in degree Fahrenheit. Operation : smoothly start of GT -> accelerating of GT -> bring up to FSNL mode. Check prior to operation of GT (protection system ), generator lock out relay is reset . turbine speed is’o’for clutch engagement = > 60 % torque transmitted through ratchet system . • Bleed valves are open -> for compressor pulsation protection . • Flame is not detectable in all scanner (i.e. no flame in turbine) • Over speed bolt is in reset position . • Inlet guide vane closed position. • Off position is not selected . • Master protection L4 logic reset .,, and master control are agree. • E.O. Pump D.C voltage is normal . • Diesel test ins not in progress. • Procedure: select unit control display “auto” operation in case a ll start up permissive are met ,it will display “READY TO START “ , select start along with “execute ” switch to start the turbine .The unit auxiliaries are started on auto AOP to establish lube o il pressure starting clutch engagement by means of ratchet operation .With clutch engaged and lube oil pressure and other permissive satisfied master protection L 4 will be satisfied -> display change to STARTING. - starting device (diesel engine) will start and run at idle speed for2 minutes for warm up At the end of diesel warm up period ratchet will operate continuously and diesel will accelerated . - The turbine shaft will begin to rotate and accelerate ,when the unit reaches 10 RPM the hydraulic ratchet will be turn off. CRT will change display -> from starting to cranking. - When the unit reaches up to 20 % speed the minimum speed signal “14HM ” will be on CRT. during this period purging of turbine completed. purging time 1 to 3 minutes depend upon turbine frame. - FSR will be set to firing value(fsr electrical signal determine amount of fuel delivery to turbine) ignition sequence is initiated CRT display will change from “CRANKING” to “FIRING” . - When the flame established CRT display indicate flame in combustion chambers # 2, # 3. # 7,# 8. - FSR is set back to warm up value and CRT display WARMING UP .IF flame goes out during 60 sec. firing period FSR will reset to firing value and are again start for cranking mode but still not establish flame unit will be trip . - The end of the warm up period with flame established FSR will begin increasing and CRT will display ACCELERATING .and turbine will increase it’s speed . - Turbine will continue to accelerate and when it reaches @ 50 to 60 %speed starting device will disengage and shut down after taking cool down before totally shut down. - When turbine will reaches to operating speed CRT will display “14HS” the auxi. Oil pump cut off and oil supply take over by shaft driven pump. Similarly AUXI. hydraulic. oil pump cut off and shaft driven pump MHOP take over .IGV are open to 57 o and compressor bleed valves are closed . Field flashing is terminated .and CRT will display “FSNL”. - Then synchronize the turbine with grid system on auto or manually .on auto CRT will read synchronizing in lieu of FSNL. And turbine speed match to the system (to less than 1/3 HZ. Difference)and proper phase relation achieved generator breaker will be closed . The machine will be load to spinning reverse unless a load point BASE,PEAK or PRE SELECT load has to selected .normal loading rate is 3.3 % of full load /sec. SHUT DOWN and COOLING OF GT : manual shut down is initiated by selection “stop” on control selector, shut down procedure will follow automatically .Through gene rator unloading turbine reduction fuel shut off at part speed and initiation of cool down sequence the unit comes to rest .
10 Emergency shut down initiated by depressing “EMERGENCY STOP” push button . emergency shut down can also be initiated by pushing the manually emergency trip valve on the over speed trip mechanism mounted on the side of Acc. Gear box. Cooling down : immediately following shut down turbine has been on fire mode the rotor is turned to provide uniform cooling to prevent rotor bowing and resultant rubbing and imbalance and relied damages. The turbine can be started and loaded at any time during cool down cycle. Normally 12 to 13 minutes costing down period should be noted to stand still turbine rotor .Cool down time should be on hydraulic ratchet for at least 24 hrs. to ensure minimum protection against rub and un balance. BHEL recommended minimum 48 hrs. on hydraulic ratchet to ensure uniform cooling of rotor. Absolute maximum temp. value permissible during operation of wheel space stage wise 770/900/950o FERN. For 1st stage 950 0fer. For 2nd stage, 900/800 0 fern. For 3rd stage . High wheel space temp. may be caused by any following faults. - Restriction of cooling air. - Wear of turbine seals. - Excessive distraction of turbine stator. - Improper position of thermocouples . - Mal function in combustion system . - Leakage in external piping . - Excessive distortion of exhaust inner diffuser . Oil pressure limit in lube oil header is 25 PSI. turbine will be trip on low lube oil pressure at 8PSI. EOP can run with GT up to 14HA speed level during startup. VIBRATION LIMIT : over all vibration velocity of GT should never exceed 1.0 inch(25mm) / sec. either vertical or horizontal.If vibration limit exceed more than ½ inch(12mm)/sec. alarm display on CRT . LOAD LIMIT: maximum load capacity of GT is given in control specification in upper limit of generator capability ref. to reactive capability curve of the generator . COMBUSTION INSPECIPON : A brief shut down is required to change out / inspecting for GT combustion components , inspection (CI) normally done after 8000firing hrs.and in this CI combustion zone and it’s components are to be checked for any damages or D.P. tested for any cracks. i.e. combustion can ,caps and liners nozzles transition pieces. cross fire tubes etc. to be checked .A visual inspection of a leading edge of 1st stage turbine nozzle partition and buckets should be made during CI to note any wear and deterioration of these parts will help to establish theschedule for next HGPI. HOT GAS PATH INSPECTION (HGPI) normally carried out after 24000 firing hrs. of GT run includes combustion inspection just describe and in addition detail inspection nof turbine nozzle and turbine buckets. To perform this inspection half of the turbine shall and 1st stage nozzle to be removed .and 2nd ,3rd stage nozzles and buckets inspected visually. A complete set of clearance of turbine should be taken during HGPI. MAJOR INSPECTION (MI): normally MI is done after 48,000 firing hrs of GT , and it involves flange to flange components of Gt This inspection includes elements of CI and HGPI ,in addition casing are inspected for cracks and erosion compressor rotor and stator blades are to be checked for tip clearance rub bowing ,cracking, and warp ages shrouds are checked for clearance erosion ,rubbing and build up, seals and hook fit nozzles and diaphragm are inspected for rub erosion fretting or thermal deterioration .Bearings and seals are inspected for clearance and wear .all clearance are checked against their original value . PROTECTION SYSTEM: protection system are set up to detect and alarm the failure,if failure is a serious nature protection system will trip the turbine.
11 Protection system respond to –simple trip signal i.e . low lube oil pressure, high gas compressor discharge press. Etc.few operate during strictly emergency and abnormal operating condition . GENERATOR : Generator mechanical aspects: Rotor, stator ,and for EMF. Magnetic flux , conductor and motion is essential to drive electric motive force . Labeling of generator as “TARI-800-24P-0” where “T” for turbine generator,”A” for air cooled , “R” for radial cooling in rotor, “I” for insulation class,800 indicate diameter of rotor active ,24 for length of stator actual , “p” for terminal voltage (P-11kv, Q- 13.6kv)and “o’ is speed of rotor . In generator stator losses called corona losses and in rotor iron losses, copper losses , mechanical losses are bearing and air friction losses. Generator over all Efficiency is @ 98.3 % and 1.7 % countable losses. If 100 MW generator having 1700kw losses which generated so huge amount of heat in shell, so dissipate this heat cooling system used in generator are air co oled, H2O water cooled and H2 (hydrogen ) cooled .Now up to 240 MW generator air cooled facility provided. Previously in H2 cooling generator, H2 purity is most important factor to maintain purity up to 99.7 %. so preferable for air cooler generator for safety in gas turbine. GT generator are design 20 % higher capacity of gas turbine capacity because GT will run on ambient temp. and in cool and dry place it will run on it’s full capacity also.Generator selection based on 1)system voltage ,2)generator efficiency , 3)power factor -0.8 is standard ,4) insulation class, 5) SCR- start current ratio .> 0.43 and < 0.5 . Generator rotor :- rotor shaft is forged from a vacuum cast steel ingot.High mechanical stresses resulting from centrifugal force and short circuit torque call for a high quality heat treated steel ensuring specified mechanical and magnetic as well homogenous forging. Approx. 60 % of rotor body circumference has longitudinal slots which holds winding. Slot pitch is selected so that 2 solid poles are displaced by 180 0, rotor wedges act as damper winding within the range of winding slot. Rotor teeth at the end of the rotor body are provided axial and radial holes ,enabling the cooling gas to be discharge in to air gape after intensive cooling of the end winding .The cooling air from the slot portion is admitted in to the slot bottom du ct below the rotor winding and hot gases at the end of rotor body is than discharge in to the air gape between rotor body and stator core. Through radial opening in the rotor and in the conductor. Rotor winding – solid conductors have a rectangular cross section and are provided with axial slot for the discharge of the cooling air. Individual conductors to obtain half turn after insertion in to the rotor slot these turns are combined to form of a full turns of series connected turns of one slot constituting a coil . Individual coil of a rotor winding are electrically series connected so that one NORTH and one SOUTH magnetic pole are obtained . conductor are made of copper with silver content @ 0.1 % as compared to electrolyte copper silver alloyed copper has high strength properties at higher temp. so that coil deformation due to thermal stress are eliminated . Insulation : insulation between individual turns is made of layer of glass fiber laminate. The coils are insulated from the rotor body with “L” shaped strips of glass fiber laminate with nomex inter liner . The centrifugal force of the rotor and winding are contained by retaining ring . Retaining rings are made of non-magnetic high strength steel in order to reduce stray losses . Each retaining ring with it’s shrink fitted hub is shrunk on the rotor body in an over hang position .The retaining ring is secured in the axial position by a snapping . STATOR: approx. weight of stator is 37 to 50 tones . the stator frame is of welded construction and support the laminated core and the winding .Both the air ducts pipes and welded radial ribs provide for rigidity of the stator frame. Footing are provided to the stator frame to support the stator on the skid. Stator is firmly fitted to the skid with bolts through the feet . Stator core is stacked from insulated electrical sheet steel lamination with a law loss index and supported in the stator frame from insulated dovetailed gu ided bars. Axial compression of the stator core is obtained by clamping fingers ,clamping plate and non- magnetic through type bolts which are
12 insulated from the core. The clamping fingers ensure a uniform clamping pressure, especially within the range of the teeth and provide a uniform intensive cooling of stator core end. Stator winding is short pitch two layers consist of individual bars .The bars are located in slot of rectangular cross section which are uniformly distributed on the circumference of the stator corein order to minimize the losses. The bars are composed of separately insulated strands which are transposed to 360 0. INSULATION: High voltage insulation is provided according to process “resin rich mica base thermo setting epoxy “ several half over lapped continuous layer of resin rich mica tapes are applied to the bars and insulation is cured under temp. and pressure. in a precisely mfg. moulds. High voltage insulation obtained is void free and in characterize by it’s excellent electrical ,mechanical and thermal properties .It’s moisture absorption is extremely low and oil resistance .To minimize corona discharge between insulation and the slot wall a final coat of semi conducting varnish is applied to the surface of all bars .within the slot range .In addition all bars are provided with an end corona protection to control the electric field at transition from the slot to the end wiring . and to prevent the formation of creep age spark concentration . The stator winding is connected in the generator interior .The stator winding connection are brought out act put leads located at the exciter end. BEARINGS: generator rotor is supported on two sleeve bearings ,to eliminate shaft current the exciter end bearing is insulated from skid and oil piping .Temp. of each bearing monitor with two RTD. Embedded in the lower bearing sleeve so that the measuring point is directly located below the Babbitt. All bearings have provision for fitting vibration pick up to monitor bearing vibration , oil supply for the bearings is obtained from turbine oil system . For small capacity of generator cylindrical bearings are used . and in high capacity generator elliptical self alignment fitting brg. Fitted in bearing housing bearings are used .Bearing pedestal is provided with spherical seating surface and bearing shell rest in it with it’s outer spherical surface .The spherical surface provide self alignment property to the bearing . step is provided on top half of bearing shell to prevent from rotation . STATOR FRAME AND STATOR END COVERS: The stator frame with core and stator winding is the heaviest component of the entire generator. A rigid frame is required due to the forces and torque arising during operation .In order to minimize hysteretic and eddy current losses of the rotating magnetic flux which interact with the core. Entire core is build up of thin lamination layer of numbers of individual segments .segments are made of electric sheet steel ,lamination having a high silicon content and than care fully de bured . The segments are staggered from layer to layer so that a core of high mechanical strength and uniform permeability to magnetic flux is obtained .segments are stacked on insulated trapezoidal guided bar which holds them in position . One guided bar is not insulated to provide for grounding of laminated core. To remove the heat from stator core ,spacer segments placed at intervals along the core length divided the core in to section to provide radial passage wide enough for the cooling air to flow.
Rotor fan: generator cooling air is circulated by two axial flow fan located on the rotor shaft one at either end, to augment the cooling of the rotor winding ,the pressure established by the fan work in conjunction with the air expelled from the discharge parts along the rotor .The blades of the fan have threaded root from being screwed in to the rotor shaft .The blades are drop forged from an aluminum alloy . Threaded root fastening permits the blades angle to be changed . Each blade secured at it’s root with a threaded pin . AIR COOLER : close circuit cooler is design on the principle of cross counter flow with using cooling media is water .Elements of the cooler are copper finned brass tube ,steel tube plates side plates and water chamber. Finned tubes ends are expanded in tube plates in order to water tight joints. Air cooler unit is fabricated from steel plates and angles. Individual cooler elements are inserted
13 horizontally to the cooler unit .sealing rubber gasket is provided between cooler element and air cooler unit wall at both end. The air is cooled to the require temp. with + 15 0 c tolerance and maximum pressure allowed for cooling water is 6 kg / cm 2 . ROTOR GROUNDING SYSTEM: Grounding brackets are fitted to the turbine end bearing cover towards the Generator to remove static charge of the shaft. Brush holder are arranged with 900 displacement which ensure that at least one brush will make contact with the rotating shaft journal . EXCITER:There are three type of excitation system 1) conventional type slip ring 2) brushless exciter3)static exciter. previously old design slip ring design excitation system is available, but n ow brush less exciter is commonly used. Advantages o f brush less exciter over slip ring type exciter are as under -No commutator required for conversion AC to DC.. -No carbon brushes used ,so there is no dusting or replacing carbon brushes . -There is no sparking and erosion -No slip rings on generator rotor . -Cable connecter eliminate as mechanical coupling in B.L. exciter. -Ensure electrical contact. - No carbon brush hence no carbon deposition for low I.R. problem . - No inventory of carbon brush .and no periodical replacement of brushes . - No maintenance is required . This brush less exciter is design by SIMENS .and electrical components are imported and guaranteed for 25 years. i.e. fuse, diode, etc. Brush less exciter mainly consist of rectifier wheel ,three phase main e xciter, three phase pilot exciter, Three phase pilot exciter has a revolving field with PMG poles,The three phase AC is feed to the field to the revolving armature main exciter via a stationary regulator and rectifier unit.The three phase AC induced in the rotor of the main exciter is rectified by the rotating rectifier bridge and fed to the field winding of the generator rotor through the DC lead in the shaft .Dc supply pin are ofcopper cadium material . The fuse in the rectifier wheel may be checked during operation with the stroboscope provision given on exciter body . There are 18 nos of diode and having separate fuse . For earth fault should remain ,< 500 k ohms and at 800 k ohms m/c will trip. For rotor magnetism exciter gap between stator and rotor (air gape) 2.5 mm max. checked always. Generator voltage should not be more than design voltage i.e. 11kv. Salient features of AVR - Auto regulation work un der excitation limit –manual regulation work field forcing limit-follow up circuit V / Hz limiter .-stator current limiter . Null voltage should be zero when change over from auto to manual or reverse . In GT if class ”A ”trip means generator side /electrical fault occur and in class ”B” trip turbine side protection system operate . GENERATOR OPERATION: Checking transmitters ; metering ,signaling, alarm system temp. measuring local – remote, cooling water supply for cooler of generator air system to be put in service , oil system for bearings put in service. and ensure the adequate oil flow oil inlet temp. as per recommended ,during run up critical speed should be passed through quickly and at a uniform rate. During start up check bearing oil pressure, oil inlet temp. measuring and supervisory device air coolers AVR etc. Run up generator check bearing vibration and brg. Metal temp. speed ,field circuit breaker set point of rated voltage ,speed and after found normal synchronizing th turbine generator with grid system and manually loading increase.
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