Generator Edc

500 MW GENERATOR

Technical SpecificationMake: BHELType: THDF 115/59Cooling stator winding: Directly water cooledCooling stator core and rotor: Directly hydrogen cooled588 MVA, 500 MW, 21 kV, 16200 A, 0.85 pf (lag), 50 Hz, 3000 rpmHydrogen Pressure: 4.0 Kg/cm2Short circuit ratio: 0.48Class and type of insulation: MICALASTIC (similar to class F)No. of terminals brought out : 6

Types of Turbo generatorGenerator Modules: Air Cooled Turbo generator TARIHydrogen Cooled Turbo generator THRI Hydrogen/Water Cooled Turbo generator THDF (500 MW) and THW (210 MW)

Generator cooling System

Capability of Generator ModulesDESIGN VARIANT GENERATOR MODULE OUTPUT RANGETARI 93/38 75-92 MW AIR COOLED TARI 108/36 100-120 MWTARI 108/41120-140 MW TARI 108/46140-170 MW

THRI 93/38120-150 MW HYDROGEN COOLED THRI 108/44200-260 MWTHRI 108/44 B260-275 MW THRI 108/55350 MW THW-200-2UPTO 200 MW HYDROGEN/WATER THW-210-2200-219 MW COOLED THW-235-2220-237 MWTHDF 115/59500-585 MWTHDF 115/55500 MW(new)

COOLING SYSTEMSTATOR SLOT THDF THWW ROTOR SLOT

Rotor Slot Cooling

THDF: Ventilation SchemeGas flow path 1 enters rotor on Turbine end and cools rotor overhang and slotsGas flow path 2 cools stator coreGas flow 3 enters rotor on exciter end & cools rotor overhang & slots, as well as stator core end parts at both the endsHot gas from all paths returns through air gap to compressor, and to coolers

THDF: VENTILATION SCHEME

Main ComponentsStatorStator FrameStator CoreStator WindingGas CoolersEnd ShieldsRotorRotor ShaftRotor WindingRotor Retaining RingField Lead ConnectionFan

BearingShaft SealsTerminal BushingAuxiliary SystemSeal oil systemGas systemPrimary water systemExcitation systemMain Components

Main Parts of Turbo generatorStatorStator CoreEnd ShieldRotorWdg OverhangBearingShaft SealTerminal Bushing Oil CatcherCoolerRotor fanInsertCover

Stator BodyFabricated cylindrical gas tight steel structure with suitably welded circular ribs internally to provide rigidityRing shaped support for resilient core suspension arranged between circular ribsCan with stand explosion pressure of hydrogen air mixture without any residual deformationHydrogen gas coolers housed longitudinally inside stator bodyEnd shields which are gas tight and pressure resistant for closing casing and supporting fans and shaft sealsFirmly connected to foundation with anchor bolts through the feet

Stator Frame (Fabrication & Machining)

Stator Frame TARI 108/46

Main Parts of Turbo generatorCoolersTerminal bushingFoundation

It provides path for machines magnetic flux and has slots in which windings are assembledMade up of segmental, varnish insulated punching of steelVent segments at designed intervals for flow of cooling gasAxially compressed with pressure plate, clamping fingers and non magnetic through type clamping bolts which are insulated from the coreSupporting rings form part of inner frame cage which is suspended in outer frame by large no. of separate flat springsSprings are so arranged and tuned that forced vibration of core resulting from magnetic field will not be transmitted to frame and foundationStator Core

500MW TG: STATOR CORECAGEFLAT SPRINGCORE BAR

End ShieldCloses both ends of Stator FrameFabricated rigid box type structure in two partsSupports and houses bearingsProvision for mounting shaft seal body, hydrogen coolers, oil catchers, etcProvision for supply of Bearing Oil, Seal oil, Thrust oil and its drain

End Shield (Exciter side 500 MW)

End Shield (Turbine side 500 MW)

Generator voltage is induced in the stator windings and each conductor must be capable of carrying rated current without getting overheatedThree phase windings is double layer of individual bars Each stator slot accommodates two barsCoil groups connected to Connecting Bus bar and finally to Terminal BushingThe lengths of the overhang and the angle of overhang is optimized so as to give the minimum length of overhang Stator Winding

The upper layer of the winding bar is laid in the slot and separated from the lower bar by means of glass textolite packingBoth the bars are held in the slot by means of impact resistant plastic wedgesThe wedging is ensured to be very tight so that during the operation of the machine the same should not get loosenedFor protection against effects of magnetic forces due to load and to ensure permanent firm seating of bars in slots during operation, side ripple spring, and top ripple located beneath the slot wedge are insertedStator Winding

STATOR SLOT

Ripple spring of generator

Stator bars, phase connectors and bushings are direct water cooledTo minimize stray losses, bars are composed of separately insulated strands Roebel transposed by 540O in slot portion and bonded together with epoxy resins in heated moldsBars consist of hollow and solid strands distributed over entire bar cross-section for good heat dissipationThe use of combination of several groups each consisting of two solid and one hollow conductor effectively reduces the depth of the slot which affect the losses in the winding, and better utilization of slotsAt bar ends, all solid strands are jointly brazed into a connecting sleeve and hollow strands into a water boxStainless steel ring headers and black Teflon tubes used for primary waterAnnular water manifolds insulated from stator frameMICALASTIC insulation is usedStator Winding

STATOR WINDING BARS Due to variable magnetic flux distribution along stator slot height, inductance of strips in a bar are differentIn a bar with straight strips therefore,current distribution shall be non-uniformThis is compensated by twisting these strips in a bar in its slot part, known as transposition. Such bars are also called Roebel transposed bars

ROEBEL BARS Such transposition of strips equalizes their inductances, so that there can be no circulating currents internally amongst them even if the bar ends at nose joints are shortedTransposition is either 360- KWU practice or 540 Russian practiceBoth closely compensate for slot part. However, there are overhang parts360540SLOT PART

Adequate protection provided to avoid corona and surface dischargeTo minimize corona discharges between the insulation and the slot wall, a final coat of semi-conducting varnish is applied to the surfaces of all bars within the slot rangeHigh-quality mica, selected epoxy resins and a matching vacuum impregnation process (VPI) are the characteristic features of the Micalastic insulation for large turbo generatorsRTDs are Provided to record tempStator Winding

Stator End Winding Assembly

High mechanical stresses resulting from centrifugal forces and short circuit torques calls for high quality treated steelA high strength low alloy steel single forging prepared by vacuum cast steel ingotSlots for housing field windings longitudinally and are distributed over the circumference so that two solid poles are obtainedSupported on two journal BearingsTwo axial fans are mounted on both sides of the rotorSpecial ducts (fins) are provided in the rotor body, through which the cooling gas flows to the rotor end windingsRotor Shaft

Due to non uniform slot distribution on circumference, different moment of inertia are obtained in the main axis of rotor and causing oscillating shaft deflection at twice the system frequencyVibrations are compensated by transverse slotting of pole (cross pole slots)After completion, the rotor is balanced in various planes at different speeds and then subjected to an over speed test at 120% of rated speed for two minutesRotor Shaft

Rotor Body with cross Pole SlotRotor WedgeCrossPoleSlot

Made from hard drawn silver bearing de-oxidized copper hollow conductors having trapezoidal cross-section with two lateral cooling ductsInter turn insulation is class F laminated glass-epoxySlot insulations are L-shaped cells of glass-Nomex-epoxy resinRotor windings held in position against centrifugal forces by wedges in slot portion and by non-magnetic steel retaining rings in overhang portionSlot wedges are made from copper-nickel-silicon alloy and silver plated featuring high strength and good electrical conductivity of eddy currents flowing on rotor surface in case of unbalance or asynchronous machine operation and used as damper winding barsRotor Winding

Rotor End Winding

The non-magnetic (to reduce stray losses) retaining ring contain the centrifugal forces due to end windings (overhang part of the winding)One end of each ring is shrunk on rotor body, while other end overhangs the end windings without contacting the shaft to ensure an unobstructed shaft deflection at the end windingsSnap ring is provided for additional protection against axial displacement of retaining ringClass F layers electrically insulate the ring from the copper underneathSeating surfaces of rings and the shaft are silver coatedRetaining ring shrink-fit areas act as short circuit rings to induce currents in damper systemRotor Retaining Ring

Rotor field current leads are connected to the brushless exciter leads at the exciter coupling with silver plated Multikontakt plug-in contacts which allow for unobstructed thermal expansion of the field current leadsCurrent from field leads is transferred to rotor coils by means of thread less special current carrying bolts which are adequately sealed by rubber rings to avoid any hydrogen escapeThe radial terminal bolts and two semicircular conductors located in the hollow bores of the exciter and rotor shaftsField Connections

Water cooled terminal bushings housed in lower part of stator on exciter end sideTerminal bushings are housed in a chamber of non-magnetic steel plates and effecting sealing provided between bushings and stator bodyThree phase and three neutral terminals brought outTerminal Bushing

Main Parts of Turbo generatorCoolersTerminal bushingFoundation

Terminal Bushing Box 500 MW

Excitation SystemStatic Excitation Rotor Field Winding is connected to Slipping mounted on rotor Excitation is provided by current transfer by contact through Carbon Brushes, Slip ring and field lead

Brush Gear

AVRAUTOMANFDRFF415 v ACSTATIC EXCITATION SYSTEM ( 210 MW)F B15.75 kV575 v

Static Excitation System

Brush Gear AsslyBrush Holder

Brushless Excitation SystemBrushless ExciterEliminates Slip Rings, Brushgear and Field Breaker

Eliminates all problems associated with transfer of current via sliding contacts

Simple, Reliable and ideally suited for large sets

Minimum operating and maintenance cost

Self generating excitation unaffected by system fault/disturbances because of shaft mounted pilot exciter

Increasingly popular system the world over

Brushless excitationPILOT EXCITERMAIN EXCITERGENERATORFIELD BREAKERFIELD (PM)ARMATUREROTATING DIODESRYB

AVRBRUSHLESS EXCITATION - BASIC EXCITATION SYSTEM SCHEMEBRUSH FOR E/F DETECTION PILOT EXCITER QUADRAT. AXIS COIL EXCITER R - C BLOCK

TG ROTOR TG STATOR +

PMG Rotor & Fan

Rectifier Wheel

Comparison

S.NODescriptionBrushless Excitation Static Excitation 1Type of system.Brushless system gets activated with pilot exciter, main exciter and rotating diodes.Static excitation system uses thyristors & taking supply from output of the generator 2Dependency on external supply.No external source requirement since pilot exciter has permanent magnet field.Field flashing supply required for excitation build up. 3Response of the excitation system.Slower than static type since control is indirect (on the field of main exciter) and magnetic components involved.Very fast response in the order of 40 ms. due to the direct control and solid state devices employed. 4Requirement of additional bearing and increase of turbo generator shaft length.One additional bearing and an increase in the shaft length are required.No additional bearing and increase in shaft length are required. 5Maintenance.Less since sliprings and brushes are avoided.More since slip rings and brushes are required. Also over hang vibrations are very high resulting in faster wear and tear.

Auxiliary System1.Gas Flow System

2. Seal Oil System

3. Primary Water System

HYDROGENCO2H2 DRIER HYDROGEN GAS SYSTEMCO2 H2 DISTRIBUTOR+ WASTE DETECTOROUT 65 barAIRGAS ANALYZER

Coolant Temperature Control Load changes lead to mechanical stresses as there is unequal expansion of winding copper, insulation and core iron due to their unequal thermal expansion coefficientsCW flow to Hydrogen gas coolers is varied with load automatically, so as to achieve uniform temperatures at different loadsCold gas temperature is changed with load by sensing stator current

1. PRIMARY WATER TANK2. PRESSURE REGULATOR3. WASTE GAS TO ATM.4. PUMP5. COOLER6. FILTER7. BYPASS LINE8. CW FOR STATOR WDG.9. ION EXCHANGER10. CW FOR BUSHINGS11. TEFLON HOSE12. C W MANIFOLD13. ALKALISER UNIT

Primary Water SystemLosses in wdg, bushings, bus bar are dissipated

STATOR WINDING PRIMARY WATER }{M MMFFF}{}{}{ N2 GASWASTE GASPW TANKPUMPSNaOH FLOWMETERSF

Primary Water Treatment SystemPW pumps have effective gland sealing to prevent air suction (if air is sucked, O2 increase and conductivity value shall go up and also Cu corrosion rate goes up)Mixed bed ion exchanger removes Cl- and HCO3 ions to prevent loss of alkalinity (keep conductivity low)Na+ are also removed, but later added by dilute NaOH injection5 micron filter to arrests resin particlesIntegrating flow meter and conductivity meter provided

Conductivity vs pH6 7 8 9101.0 0.10.01pH AT 18 C MICROMHOS/CM NaOHHCl0.0510 PERMISSIBLE ZONE

HOLLOW COPPER CORROSION - 3 10 000 HRS. SIMULTAED TESTS1357COROSIONRATE P.U.O2 CONCENTRATION ppbpH = 7pH= 8pH= 8.51010025010005000PERMISSIBLE ZONE

Seal Oil SystemPrevents H2 losses at the shaft entry into stator

GENERATORBRG.5BRG.-6MOTL.O.L.O.H2 SIDE SEAL OILAIR SIDE SEAL OILH212DCH2HIGH LEVELBVEFSYPHONPRE-CHAMBER

Thank You

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