ACKNOWLEDGEMENT

I WOULD LIKE TO THANK SENIOR MANAGER (HR - ED) SHRI B. R. PRASOON FOR HELPING ME IN COMPLETING THE VOCATIONAL TRAINING IN NTPC LIMITED KAHALGAON.

SECONDARY I WOULD LIKE TO THANK SHRI T.K. JHA DGM (EMD), SHRI S. K. ROHELA DGM (C & I), SHRI R. C. JHA DGM (OPN), SHRI R. SRIVASTAVA DGM (MM) FOR HELPING ME IN COMPLETING THE VOCATIONAL TRAINING IN NTPC LIMITED KAHALGAON.

I WOULD ALSO LIKE TO THANK MY PARENT AND THE ALMIGHTY FOR GIVING

ME MORAL STRENGTH. I AM HIGHLY OBLIGED TO SHRI R.K. GUPTA & ALL THE RESPECTED PERSONS WHO HAVE HELPED ME IN COMPLETING THE VOCATIONAL TRAINING SUCCESSFULLY.

PREFACE

TRAINING IS DEFINED AS ANY ATTEMPT TO IMPROVE EMPLOYEE PERFORMANCE ON A CURRENTLY HELD JOB OR ONE RELATED TO IT. THIS USUALLY MEANS CHANGES IN SPECIFIC KNOWLEDGE ,SKILLS, ATTITUDES, OR BEHAVIOUR ;TO BE EFFECTIVE TRAINING SHOULD INVOLVE A LEARNING EXPERIENCE, BE A PLANNED ORGANIZATIONAL ACTIVITY AND BE DESIGNED IN RESPONSE TO IDENTIFIED NEED. IDEALLY TRAINING ALSO SHOULD BE DESIGNED TO MEET THE GOAL OF THE ORGANIZATION WHILE SIMULTANEOUSLY MEETING THE GOAL OF THE INDIVIDUAL EMPLOYEES

KEY WORD PA PRIMARY AIR IA INDUCED AIR

ID FAN INDUCED FAN PF FAN PRIMARY FAN

FD FAN FORCED DRAFT FAN D/A DEAERATER

TG TURBINE SIDE SG BOILER SIDE

KSC 1KG/CM2

HPT HIGH PRESSURE TURBINE IPT INTERMEDIATE PRESSURE TURBINE

LPT LOW PRESSURE TURBINE BFP BOILER FEED PUMP

TDBFP TURBINE DRIVEN BOILER FEED PUMP MDBFP MOTER DRIVEN BOILER PUMP

ESP ELECTRO STATIC PRECIPITATER GT GENERATOR

ECN ECONOMISER RH REHEATER

SH SUPER HEATER SCAPH STEAM COIL AIR PREHEATER

UT UNIT TRANSFORMER UAT UNIT AUXILIARY TRANSFORMER

OAC OPEN APPROACH CHANNEL FST FEED STORAGE TANK

FRS FEED REGULATING STATION FW FEED WATER

DMW DEMINERALIZED WATER CFW CLARIFIED WATER

ECW EQUIPMENT COOLING WATER ACF ACTIVATED CARBON FILTER

GSF GRAVITY SAND FILTER OHT OVER HEAT TANK

INTRODUCTION

NTPC LIMITED, THE LARGEST THERMAL POWER GENERATING COMPANY IN INDIA, WAS INCEPTED IN YEAR 1975. IT IS A PUBLIC SECTOR COMPANY WHOLLY OWNED BY GOVERNMENT OF INDIA (GOI). IN A SPAN OF 30 YEARS, NTPC HAS EMERGED AS A MAJOR POWER COMPANY OF INTERNATIONAL REPUTE AND STANDARD. NTPC’S CORE BUSINESS INCLUDES ENGINEERING, CONSTRUCTION AND OPERATION OF POWER GENERATING STATIONS AND PROVIDING CONSULTANCY TO POWER UTILITIES AS WELL. PRESENTLY, THE TOTAL INSTALLED CAPACITY OF NTPC/JVS STANDS AT MORE THAN 27904 MW, WHICH INCLUDES 18 COAL AND 8 GAS/NAPHTHA BASED POWER STATIONS. NTPC IS EXECUTING KOL DAM HYDRO POWER PROJECT ( 800 ) MW IN HIMACHAL PRADESH AND TAPOBAN VISHUNGAD (520 MW) AND LOHARINAG PALA (600 MW) HYDRO PROJECTS IN UTTARAKHAND.

SALIENT FEATURES OF KHSTPP

● LOCATION- KAHALGAON,DISTRICT BHAGALPUR

● NEAREST RAILWAY STAION- KAHALGAON

● NEAREST MAJOR TOWN- BHAGALPUR

● NEAREST AIRPORT- PATNA,KOLKATA

● NEAREST HIGHWAY- NH-80

● TOTAL LAND- 3360 ACRES

● LAND FOR PLANT- 833 ACRES

● LAND FOR TOWNSHIP- 432 ACRES

● LAND FOR MGR- 522 ACRES

● LAND FOR ASH DYKE- 1395 ACRES

● MAKE-UP WATER- 28 ACRES

● SYSTEM APPROACH ROAD- 70 ACRES

● OTHERS- 30 ACRES

● INSTALLED CAPACITY- 840 MW

● CONFIGURATION- STAGE-I 4*210 MW

STAGE-II 2*500 MW(PHASE-I)

1*500 MW(PHASE-II)

● FUEL- COAL

● SOURCE- RAJMAHAL HURRA,CHUPERBITA OF ECIL

● NEAREST WATER SOURCE- RIVER GANGES

● COOLING WATER SYSTEM- CLOSED CYCLE INDUCED DRAFT SYSTEM

● BENEFICIARY STATES- THE STATES AND UT’S OF NR,WR,ER,SR

● APPROVED PROJECT COST- RS 1715 CRORE(STAGE-I)

RS 6330 CRORE(STAGE-II)

KAHALGAON SUPER THERMAL POWER PROJECT

BACKGROUND:

KAHALGAON SUPER THERMAL POWER PROJECT, STAGE II BEING SET UP BY NTPC IS LOCATED NEAR KAHALGAON TOWN IN BHAGALPUR DISTRICT OF BIHAR STATE. THE STAGE II, OF THE PROJECT SHALL COMPRISE OF THREE (3) UNITS OF 500 MW EACH. STAGE I OF THE PROJECT COMPRISING OF FOUR (4) UNITS OF 210 MW EACH IS PRESENTLY UNDER COMMERCIAL OPERATION. WITH THE ADDITION OF 3X500 MW UNITS UNDER STAGE II, THE ULTIMATE CAPACITY OF THE PROJECT WILL BE 2340 MW (STAGE I, 4X210 MW+ STAGE II, 3X500 MW).

LOCATION AND APPROACH:

THE PROPOSED EXPANSION STAGE II OF THE PROJECT IS LOCATED AT LATITUDE AND LONGITUDE 2515 N AND 8715 E RESPECTIVELY. THE NEAREST RAILHEAD COLGONG (KAHALGAON) RAILWAY STATION OF EASTERN RAILWAYS IS APPROXIMATELY 2.0 KM AWAY FROM THE PROJECT SITE. BHAGALPUR, THE NEAREST MAJOR TOWN, IS ABOUT 30 KM SOUTHWEST OF THE PROJECT SITE. THE NEAREST COMMERCIAL AIRPORT IS PATNA AND LOCATED AT A DISTANCE OF 250 KM APPROXIMATELY.

LAND REQUIREMENT:

A TOTAL AREA OF 3360 ACRES OF LAND HAS BEEN ACQUIRED FOR THE PROJECT IN STAGE I AND PROPOSED STAGE II OF THE PROJECT IS TO BE LOCATED WITHIN THE EXISTING AREA.

WATER REQUIREMENT:

THE PROJECT IS LOCATED NEAR RIVER GANGES. THE MAKE UP WATER REQUIREMENT FOR THE PLANT IS PROPOSED TO BE DRAWN FROM RIVER GANGES. THE WATER REQUIREMENT FOR STAGE II OF THE PROJECT SHALL BE OF THE ORDER OF 9000 CU.M/HR. THE BASIC REQUIREMENTS FOR RUNNING A THERMAL POWER PLANT MAKE UP WATER FOR COOLING TOWER SYSTEM AND OTHER PLANT REQUIREMENT AND A CONTINUOUS SUPPLY OF HIGH QUALITY COAL.

MAKE UP WATER FOR COOLING WATER SYSTEM AND OTHER PLANT REQUIREMENTS IS BEING DRAWN FROM NTPC’S RAW WATER PUMP HOUSE LOCATED OVER AN INTAKE WELL IN RIVER GANGES. THE INTAKE IS LOCATED ON RIGHT BANK OF THE RIVER WHICH IS ABOUT 3KM FROM THE PROJECT / PLANT SITE. DURING COMMISSIONING OF STAGE – I (4 X 210 MW) OF THE PROJECT, DEEP CHANNEL OF THE RIVER WAS HUGGING THE RIGHT BANK OF THE RIVER AND THE INTAKE WAS LOCATED CLOSE TO THE DEEP CHANNEL OF THE RIVER.

SHOAL FORMATION HAS BEEN OBSERVED CLOSE TO THE INTAKE WELL LOCATION DURING LEAN PERIOD, WHICH MAY BE BECAUSE OF THE CHANGE IN RIVER COURSE. TO ENSURE CONTINUOUS SUPPLY OF MAKE UP WATER REQUIREMENTS FOR THE STATION AFTER COMMISSIONING OF STAGE – II OF THE PROJECT, A SURVEY WAS CONDUCTED TO ASCERTAIN THE ADVERSE EFFECTS OF SHOAL FORMATION AND HENCE, CARRY OUT SUCH REMEDIAL MEASURES WHICH WILL BRING BACK THE DEEP CHANNEL OF THE RIVER CLOSE TO THE INTAKE.

TOPOGRAPHIC AND HYDROGRAPHIC SURVEY OF THE SAME WAS CARRIED OUT AS A PART OF CONSULTANCY STUDIES DURING 6TH DECEMBER 2006 TO 10TH JANUARY 2007.

COAL REQUIREMENT:

COAL REQUIRED FOR RUNNING THE POWER PLANT IS PROCURED FROM LALMATIYA COALFIELD OF JHARKHAND. THE REQUIREMENT IS ALSO MET FROM CHUPERBITA, RAJMAHAL EXPANSION AND HURRA PROJECTS OF ECL.

KAHALGAON SUPER THERMAL POWER PROJECT

STAGE – II OF KAHALGAON SUPER THERMAL POWER PROJECT INCLUDES COMMISSIONING OF 3

UNITS EACH OF 500 MW CAPACITIES. UNIT 7 IS ONE SUCH UNIT OF 500 MW. IT SPANS FROM

1954 (S) TO 2260 (S) AND 3625 (E) TO 3797 (E) ENCOMPASSING AN AREA OF ABOUT 52000

SQ.M. THE MAIN AGENCY INVOLVED IN MAIN PLANT CIVIL WORKS IS M/S HSCL. THE WORK

STARTED ON 3RD FEB 2004 AND WAS EXPECTED TO TAKE ABOUT 39 MONTHS. BUT BECAUSE OF

FEW PRACTICAL DIFFICULTIES ENCOUNTERED DURING THIS TENURE, IT HAS CROSSED THE TIME LIMITS

AND IS STILL UNDER CONSTRUCTION.

THE ESTIMATED COST OF THE PROJECT IS 49.21 CRORE WHICH INCLUDES STRUCTURAL WORKS

AND CIVIL WORKS. ESTIMATE FOR STRUCTURAL WORKS IS 13 CRORE WHEREAS THE BALANCE

BUDGET IS FOR CIVIL WORKS WHICH INCLUDES PILING AND BALANCED CIVIL WORKS LIKE

FOUNDATION AND FINISHES. PILING ESTIMATE IS AROUND 13 CRORE AND THE REMAINING IS FOR

THE BALANCED CIVIL WORKS.

THE ENTIRE AREA IS SUPPORTED ON 2320 PILES OF WHICH THERE ARE 1976 PILES OF 760 MM

DIAMETER AND 344 PILES OF 600 MM DIAMETER. THE PILE GOES TO A DEPTH OF 30 M.

THE MAIN PLANT CIVIL PACKAGE OF # 7 INCLUDES TWO WIDE AREAS, WHICH ARE

TURBINE GENERATOR (T.G.) AREA THAT INCLUDES T.G. HALL, ALL FLOORS AT EACH

ELEVATION, AND TRANSFORMER YARD AREA.

STEAM GENERATOR (S.G.) AREA THAT INCLUDES BOILER, ELECTROSTATIC PRECIPITATOR

(ESP) AND ESP CONTROL ROOM BUILDING.

COAL BASED PLANT

COAL TO ELECTRICITYCOAL IS A FUEL THAT IS FOUND IN THE GROUND. IT IS MADE OF THE REMAINS OF PLANTS THAT DIED MILLIONS OF YEARS AGO. SOIL PILED UP ON TOP OF THE REMAINS AND THAT WEIGHT COMPACTED IT INTO A MORE DENSE MATERIAL, CALLED COAL. THE ENERGY IN THE COAL CAME FROM THE SUN AND WAS STORED IN THE PLANTS. WHEN THE COAL IS BURNED, IT GIVES UP THAT ENERGY AS HEAT. THE COAL'S HEAT ENERGY CAN THEN BE TURNED INTO ELECTRICAL ENERGY. THIS HAPPENS AT A POWER PLANT.

• FIRST THE COAL IS MINED AND TAKEN TO A POWER PLANT.

• THEN THE COAL IS BURNED IN A BOILER WHICH CAUSES THE WATER IN THE BOILER PIPES TO BECOME STEAM.

• THE STEAM TRAVELS THROUGH THE PIPES TO THE TURBINE.

• THE STEAM SPINS THE TURBINE BLADES.

• THE SPINNING BLADES TURN A SHAFT CONNECTED TO THE GENERATOR.

• IN THE GENERATOR, BIG MAGNETS SPIN CLOSE TO COILS OF WIRE.

• WHEN THIS HAPPENS, ELECTRICAL CURRENT IS PRODUCED IN THE WIRES.

• THEN THE ELECTRICITY GOES OUT THROUGH WIRES TO HOMES, SCHOOLS, AND BUSINESSES.

BOILER:

BOILER IS A DEVICE FOR GENERATING STEAM FOR POWER, PROCESSING OR HEATING PURPOSES.BOILER IS DESIGNED TO TRANSMIT HEAT FROM AN EXTERNAL COMBUSTION SOURCE (USUALLY FUEL COMBUSTION TO A FLUID ) CONTAINED WITHIN THE BOILER ITSELF.

THE HEAT GENERATING UNIT INCLUDES A FURNACE IN WHICH THE FUEL IS BURNED .WITH THE ADVANTAGE OF WATER –COOLED FURNACE WALLS, SUPERHEATERS,AIR HEATERS AND ECONOMISERS, THE TERM ‘STEAM GENERATOR’ WAS EVOLVED AS A BETTER DESCRIPTION OF THE APPARATUS.

BOILER MAY BE CLASSIFIED ON THE BASIS OF ANY OF THE FOLLOWING CHARACTERISTICS:

1. USE

2. PRESSURE3. MATERIALS4. SIZE5. TUBE CONTENT6. TUBE SHAPE AND POSITION7. FIRING8. HEAT SOURCE9. FUEL10. FLUID11. CIRCULATIONS12. FURNACE POSITION13. FURNACE TYPE14. GENERAL SHAPE15. TRADE NAME16. SPECIAL FEATURES

CATEGORIES OF BOILERS:

BOILERS ARE GENERALLY CATEGORISED AS FOLLOWS :

1) STEEL BOILERS2) FIRE TUBE TYPE3) WATER TUBE TYPE4) HORIZONTAL STRAIGHT TUBE5) BENT TUBE6) NATURAL CIRCULATION7) POSITIVE CIRCULATION8) SHELL TYPE9) CAST IRON BOILERS10) SPECIAL DESIGN BOILERS11) NUCLEAR REACTORS

ARRANGEMENT OF MAIN PARTS OF BOILER :

THESE ACCESSORIES INCLUDE –

1) ECONOMISER2) BOILER DRUM

3) DOWN COMERS4) WATER WALLS5) WATER WALL PLATEN(USED FOR PRESSURE BOILERS)6) PRIMARY SUPER HEATER7) PLATEN SUPER HEATER8) FINAL SUPER HEATER9) REHEATER10) BURNER11) IGNITORS

ARRANGEMENT OF BOILER:

#FURNACE

(A) TYPE : FUSION WELDED

(B) WIDTH : 14.46MTRS.

(C) BREADTH : 11.85MTRS.

(D) VOLUME : 7664 M3

(E) FURNACE EXPLOSION/ IMPLOSION PRESSURE : ± 660MMWCL.

(F) FURNACE SURFACE : 2712 M2

A BOILER FURNACE IS THAT SPACE UNDER OR ADJACENT TO A BOILER IN WHICHFUEL IS BURNED AND FROM WHICH THE COMBUSTION PRODUCTS PASS INTO THE BOILER PROPERLY. IT PROVIDES A CHAMBER IN WHICH THE COMBUSTION REACTION CAN BE ISOLATED AND CONFINED SO THAT THE REACTION REMAINS A CONTROLLED FORCE. IN ADDITION IT PROVIDES SUPPORT OR ENCLOSURE FOR THE FIRING EQUIPMENT.

THE FURNACE MUST PROVIDE THE FOLLOWING –

>> PROPER INSTALLATION,OPERATION AND MAINTENANCE OF FUEL BURNING

EQUIPMENT.

>> SUFFICIENT VOLUME FOR COMBUSTION REQUIREMENTS .

>> ADEQUATE REFRACTORIES AND INSULATION .

#BOILER DRUM :

THE FUNCTION OF STEAM DRUM IS TO SEPARATE THE WATER FROM THE STEAM GENERATED IN THE FURNACE WALLS AND TO REDUCE THE DISSOLVED SOLID CONTENTS OF THE STEAM TO BELOW THE PRESCRIBED LIMIT OF 1PPM. THE DRUM IS LOCATED ON THE UPPER FRONT OF BOILER.

#ECONOMISER :

THE PURPOSE OF ECONOMISER IS TO PREHEAT THE BOILER FEED WATER BEFORE IT IS INTRODUCED INTO THE STEAM DRUM BY RECOVERING HEAT FROM THE FLUE GASES LEAVING THE BOILER. THE ECONOMISER IS LOCATED

IN THE BOILER REAR GAS PASS BELOW THE REAR HORIZONTAL SUPERHEATER.THE ECONOMISER IS CONTINUOUS UNFINNED LOOP TYPE AND WATER FLOWS IN UPWARD DIRECTION AND GAS IN THE DOWNWARD DIRECTION.

#SUPERHEATER :

THERE ARE THREE STAGES OF SUPERHEATER BESIDES THE SIDE WALLS AND EXTENDED SIDEWALLS .THE FIRST STAGE CONSISTS OF HORIZONTAL SUPERHEATER OF CONVECTION MIXED FLOW TYPE WITH UPPER AND LOWER BANKS LOCATED ABOVE ECONOMISER ASSEMBLY IN THE REAR PASS.THE UPPER BANK TERMINATES INTO HANGER TUBES,WHICH ARE CONNECTED TO OUTLET HEADER OF THE FIRST STAGE SUPERHEATER.THE SECOND STAGE SUPERHEATER CONSISTS OF PENDANT PLATEN WHICH IS OF RADIANT PARALLEL FLOW TYPE.THE THIRD STAGE SUPERHEATER CONSISTS OF PENDANT PLATEN WHICH IS OF RADIANT PARALLEL FLOW TYPE.THE THIRD STAGE SUPERHEATER PENDANT SPACED IS OF CONVECTION PARALLEL FLOW TYPE.

THE OUTLET TEMPERATURE AND PRESSURE OF THE STEAM COMING OUT FROM THE SUPERHEATER IS 540 DEGREE CELSIUS AND 157KG/CM^2 RESPECTIVELY FOR H.P. UNITS

#REHEATER :

THE FUNCTION OF REHEATER IS TO REHEAT THE STEAM COMING OUT FROM THE HIGH PRESSURE TURBINE TO A TEMPERATURE OF 540 DEGREE CELSIUS.

THE REHEATER IS COMPOSED OF TWO SECTIONS. THE FRONT PENDANT SECTION AND REAR PENDANT SECTION.

THE REAR PENDANT SECTION IS LOCATED ABOVE THE FURNACE ARC AND THE REAR WATER WALL AND FRONT PENDANT SECTION IS LOCATED BETWEEN THE REAR WATER HANGER TUBES AND THE SUPERHEATER PLATEN SECTION

#BURNERS :

THERE ARE TOTAL TWENTY FOUR PULVERISED COAL BURNERS FOR CORNER FIRED C.E. TYPE BOILERS AND TWELVE OIL BURNERS PROVIDED EACH IN BETWEEN TWO PULVERISED FUEL BURNER.THE PULVERISED COAL BURNERS ARE ARRANGED IN SUCH A WAY THAT SIX MILLS SUPPLY THE COAL THE BURNERS AT 4 CORNERS,OF THE FURNACE.ALL THE NOZZLES OF THE BURNERS ARE INTER LINKED AND CAN BE TILTED AS A SINGLE UNIT FROM +30 TO -30 DEGREE.

THE OIL BURNER ARE FED WITH HEAVY FUEL OIL TILL LOAD REACHES TO ABOUT 25%.

#IGNITERS :THERE ARE TWELVE SIDE EDDY PLATE OIL/H.E.A. IGNITERS PER BOILER. THE ATOMISING AIR FOR IGNITORS ARE TAKEN FROM PLANT AIR COMPRESSERS AT 7KG/CM^2(GAUGE).

THE BURNER ARE LOCATED AT THE THREE ELEVATIONS. EACH ELEVATION HAS FOUR OPIL BURNERS AND IGNITORS.THESE ELEVATIONS ARE NORMALLY KNOWN AS AB ELEVATION,CD ELEVATION AND EF ELEVATION.MAINLY TWO TYPES OF IGNITORS ARE USED :

>> EDDY PLATE IGNITOR

>> HIGH ENERGY ARC TYPE IGNITORS

BOILER DESIGN & FIELD DATA :

RATING : MS 690 T/HR, 140 KG/CM2, 540 0C,

RH 569 T/HR, 27.6 KG/CM2, , 328 0C/540 0C.

FEED WATER TEMPERATURE : 248°C

BOILER DRUM PRESSURE : 161KGF/CM2

OVERALL DIMENSION : WIDTH (ALONG COLUMN AXIS) 29.46 M,

: DEPTH (ALONG COLUMN AXIS) 42.01 M,

: HEIGHT (ELEVATION OF CENTER LINE) 68.9 M.

MASS OF PR. PARTS : 1954 TONS.

MASS OF BOILER METAL : 7250 TONS.

GUARANTEED BOILER EFFICIENCY AT AIR TEMP 30 0C

= 89 %.(AT NET COMBUSTIBLE BASIS)

= 87.15 %.(AT GROSS CALORIFIC VALUE BASIS)

DESIGN EFFICIENCY OF BOILER (APPROX.) : 91.64 %

LOSSES : IN FLUE GAS 5.97 %,

:NON COMBUSTIBLE 2 % (CHEMICALS 0.15%, MECH.BALANCE),

: INTO AMBIENT 0.3%,

: INTO ASHES 0.09 %.

EXIT FLUE GAS TEMP.: 137 0C, (WITH WORST COAL 142 0C).

FLUE GAS TEMP AT FURNACE OUTLET : APPROX. 1120 0C,

TEMP. OF HOT AIR : 388 0C, (WITH WORST COAL 391 0C)

LOAD WITHOUT FURNACE OIL : WITH GUARANTEED FUEL : 70 TO 100%,

: WITH LOW GRADE FUEL : 85 TO 100%,

: WITH HIGH GRADE FUEL : 55 TO 100%.

BOILER LOAD WITH ALL 12 OIL BURNERS (APPROX.) : 30 % OF NOMINAL LOAD

TOTAL COAL FIRING RATE : 126.4 TO191T/ HR

GENERATOR

TURBO GENERATOR HAS 3 CIRCUITS, A) MAGNETIC CIRCUIT, B) ELECTRIC CIRCUIT AND C) MECHANICAL SUPPORTS AND AUXILIARIES.

TURBO GENERATORS: STEAM TURBINES RUN EFFICIENTLY ONLY AT HIGH SPEEDS, SO THAT 2-POLE GENERATOR IS COMMON EVEN AT HIGH RATINGS. THE ELECTRIC AND MAGNETIC LOADING IS EXCEPTIONALLY HIGH. THE ROTOR DIAMETER IS LIMITED TO 1.2M. THE ACTIVE CORE LENGTH MUST BE OF THE ORDER OF 10MM PER MVA. THUS THE LENGTH OF A 500MW GENERATOR MAY BE 5M AND SHAFT LENGTH MAY BE 12M. STATOR CORE DIAMETER 3M AND CASING 4M. THE STATOR WINDINGS ARE DOUBLE LAYER FORM SO THAT HARMONICS CAN BE

REDUCED BY CHORDING. FOR LARGE GENERATORS THE STATOR MMF MAY REACH UP TO 300KA-T PER POLE AND TO AVOID EXCESSIVE DEMAGNETISATION EFFECT THE ROTOR MMF MUST BE OF COMPARABLE MAGNITUDE AS DEFINED BY THE SHORT CIRCUIT RATIO. AS IT IS UNDESIRABLE TO HAVE HIGH TOOTH SATURATION, LONG AIR GAP IS NECESSARY- 5MM FOR 1MVA MACHINE TO 100MM FOR 500MVA MACHINE.

ROTOR: THE I2R LOSS PER UNIT MASS OF CONDUCTOR MATERIAL IS OF THE ORDER OF 150W/KG IN STATOR AND 500W/KG IN THE ROTOR. THEREFORE THE ROTOR IS THE LIMITING MEMBER. THE DIAMETER IS LIMITED BY THE CONSIDERATIONS OF CENTRIFUGAL FORCE, DEFLECTION AND CRITICAL SPEED. AN EXCITATION HAS TO BE PROVIDED IN ACCORDANCE WITH THE STATOR ELECTRIC LOADING AND SHORT CIRCUIT RATIO. THE EXCITATION WINDING MUST BE CONTAINED IN THE SLOTS OF SUCH WIDTH SO AS TO LEAVE TEETH ADEQUATE TENSILE STRENGTH AND BENDING STRENGTH AND TO CARRY MAGNETIC FLUX WITHOUT EXCESSIVE SATURATION.

ROTOR: CYLINDRICAL TYPE, SHAFT AND BODY FORGED IN ONE PIECE FROM NICKEL-CHROMIUM- VANADIUM-MOLYBDENUM STEEL HAVING ULTIMATE STRENGTH UP TO 800N/ M2. SLOTS ARE MILLED OUT AXIALLY. DYNAMICALLY BALANCED WITH HIGH DEGREE OF ACCURACY UP TO 20% OVER SPEED FOR 2 MINUTES. CRITICAL SPEED IS AT 1200RPM (1370RPM) AND 2.7 AND 3.0 TIMES THIS SPEED.

WINDING: HARD DRAWN SILVER BEARING COPPER, INSULATION: EPOXY GLASS, NONMAGNETIC STEEL RETAINING RING FOR OVERHANG.

FANS: PROPELLER TYPE, SHAFT MOUNTED ON EITHER SIDES

SLIP RINGS: FILED LEAD: SLIP RINGS TO WINDINGS VIA SEMI FLEXIBLE COPPER LEADS.

STATOR: COLD ROLLED GRAIN ORIENTED SILICON STEEL, MECHANICALLY STRONG TO WITHSTAND INTERNAL PRESSURE OF EXPLOSION OF HYDROGEN AND AIR MIXTURE. MECHANICAL PROBLEMS ARISE BECAUSE OF THE DOUBLE FREQUENCY VIBRATIONS SET UP BY THE ROTATION OF THE AXIS OF THE MAGNETIC FIELD AND FROM INTERNAL PRESSURE OF THE HYDROGEN COOLANT. CORE VIBRATION IS PREVENTED FROM BEING TRANSMITTED TO THE CASING BY A FORM OF FLEXIBLE MOUNTING.

WINDING: 3 PHASE, DOUBLE LAYER, SHORT CHORDED, SINGLE TURN, TWO PARALLEL WINDING (DOUBLE STAR). EACH CONDUCTOR IS ELABORATELY SUBDIVIDED TO LIMIT EDDY CURRENT LOSS. THE INSULATION MAY BE MICA PAPER AND ASBESTOS OR GLASS FIBRE TAPE WITH POLYESTER OR EPOXY BONDING TO GIVE MECHANICAL STRENGTH. THE END WINDINGS MUST BE VERY SECURELY BRACED AGAINST MOVEMENT UNDER THE IMPACT OF SHORT CIRCUIT ELECTROMAGNETIC FORCES, HARD WOOD BLOCKS WITH GLASS FIBRE CORD OR TAPE MAY BE USED, WITH METALLIC (NON-MAGNETIC) BRACKETS AS ANCHORAGE.

EDDY CURRENTS: THE PARASITIC EDDY CURRENTS IN AN ISOLATED CONDUCTOR DUE TO ITS OWN FIELD ARE CALLED THE SKIN EFFECT. THEY ARISE ON ACCOUNT OF THE INDUCTANCE OF THE CENTRAL PART OF THE CONDUCTOR EXCEEDS THAT OF THE OUTER PARTS. THEREFORE THE CURRENTS ARE CONFINED TO THE PERIPHERY.

THE GREATER INDUCED EMF OF SELF INDUCTION IN THE MIDDLE PARTS OF THE CONDUCTOR CAUSES CIRCULATING CURRENTS WHICH, SUPERIMPOSED ON THE MAIN CURRENT INCREASES THE I2R LOSS. THE EFFECTS OF ALTERNATING LEAKAGE FIELDS ARE INTENSIFIED BY THE PROXIMITY OF FERROMAGNETIC MATERIAL.

SLOT CONDUCTORS: THE FIRST ORDER EDDY CURRENT DISTURB THE ORIGINALLY UNIFORM CURRENT DENSITY, SUPERIMPOSING A SECOND ORDER MMF, FLUX, EMF AND EDDY CURRENTS WHICH IN TURN DEVELOP THIRD ORDER COMPONENT AND SO ON. NOT ONLY DOES EDDY CURRENT THE I2R LOSS, BUT ALSO DISTURB THE FIELD DISTRIBUTION.

THE LARGE CURRENTS IN STATOR PRODUCE HIGH PULSATIONAL FORCES BETWEEN CONDUCTORS, REACHING UP TO 80KN/M IN 500MW MACHINES.

DISTILLATE HEADER: RING TYPE WATER HEADER OF COPPER INLET AND OUT LET HEADERS –TURBINE SIDE.

TERMINAL BUSHINGS: WATER-COOLED; THEY ARE HOUSED IN A CHAMBER MADE OF NONMAGNETIC STEEL PLATES.

AIR GAP: TURBO GENERATORS HAVE LARGE RADIAL GAPS FOR REASONS OF OPERATIONAL STABILITY. IN CONVENTIONAL TOOTHED STATOR, THE SLOTTING CONCENTRATES THE FLUX INTO THE TEETH, SATURATION AND CORE LOSS LEVELS ARE HIGH AND POLE FACE LOSSES OCCUR. THE DEEP SLOTS MAKE CONDUCTOR TRANSPOSITION ESSENTIAL AND INTRODUCE SOME DIFFICULTIES IN DIRECT WATER-COOLING. THE HIGH VOLTAGE INSULATION IN WINDINGS RESULTS IN LOW SPACE FACTOR AND END WINDINGS BULKY AND NEEDS ELABORATE SUPPORT.

LARGE TURBO GENERATORS:

THE SPEED IS FIXED BY THE FREQUENCY. THE DIMENSIONS ARE FIXED BY THE ROTOR DIAMETER (D) AND THE ACTIVE CORE LENGTH (L). THE LIMIT OF D IS SET BY THE CENTRIFUGAL FORCES WHILE THOSE OF L CONCERNS THE RIGIDITY OF THE ROTOR. THE PRESENT LIMIT OF D FOR 50HZ IS 1.2M, AND LENGTHENING OF ROTOR BEYOND L=5D, GIVES NO IMPROVEMENT. BUT A SMALL IMPROVEMENT OF D WILL GIVES SUBSTANTIAL RISE IN CAPABILITY. FOR ROTATIONAL SPEED N, THE ROTATIONAL STRESS IS PROPORTIONAL TO D2N2.

THE DL PRODUCT AFFECTS THE CRITICAL SPEED. FOR LARGE MACHINES COMPLEX CALCULATIONS ARE REQUIRED, TAKING INTO ACCOUNT DIFFERING RIGIDITIES OF THE DIRECT AND QUADRATURE AXES OF ROTOR, EFFECTS OF BEARING DEFORMATION AND CHARACTERISTICS OF THE GENERATOR-TURBINE COUPLING. VIBRATION PROBLEMS CAN BE COMPLEX. A 2-POLE STATOR IS DEFORMED INTO AN ELLIPSE BY INTENSE MAGNETIC ATTRACTION; WITH MINOR AXIS DIRECTED ALONG THE AXIS OF THE AIR GAP FLUX, AS THE ROTOR

ROTATES SO DOES THE DEFORMATION. THIS INITIATES A STRONG VIBRATION AT TWICE THE ROTATIONAL SPEED. VIBRATION AFFECTS THE WINDING BOTH IN THE SLOTS AND IN THE OVERHANG.

THE HEAT TRANSFER CAPACITY OF WATER IS 50 TIMES THAT OF AIR, BUT ITS DENSITY IS 1000 TIMES GREATER.

GAS COOLERS: MADE OF ADMIRALITY BRASS TUBES. END COVER OF WATER CHAMBERS CAN BE REMOVED WITHOUT PURGING HYDROGEN FROM GENERATOR.

BRUSH GEAR: BRUSHES IN THE UPPER 2/3RD PERIPHERY, BRUSHES CAN BE CHANGED DURING NORMAL RUNNING.

SHAFT SEALS: TO PREVENT ESCAPE OF HYDROGEN.

EXCITATION SYSTEM: WHY NOT DC EXCITERS?

LARGE NUMBERS OF BRUSHES, EXTENSIVE COMMUTERS AND BRUSH GEAR MAINTENANCE. DURING CHANGE OF LOAD CHANCES OF FLASH OVER. FOR RELIABILITY EXCITERS ARE DIRECTLY COUPLED, THIS MEANS REDUCTION IN GEARS THAT ARE

NECESSARY. AT HIGHER SPEEDS INVARIABLY COMMUTATION PROBLEMS.

AVR: STATIC EXCITATION SYSTEM, AUTOMATIC AND SEPARATE VOLTAGE REGULATORS

MAXIMUM AND MINIMUM EXCITATION LIMITERS

CHANGE OVER TO MANUAL CONTROL IN CASE OF FAULT IN AUTO MODE.

GENERATOR OPERATIONAL LIMITS:

TERMINAL VOLTAGE - ± 5% (AT RATED POWER AND PF) STATOR CURRENT - ± 5% (AT RATED POWER AND PF) VOLTAGE - ± 10% CURRENT - +105% FREQUENCY - ± 5 ( DUE TO TURBINE LIMITATIONS, +2% AND –3%)

ADVANTAGES OF HYDROGEN AS COOLANT:

1) LESSER DENSITY, LESSER WINDAGE LOSS

1/14TH THE AIR DENSITY

ADVANTAGE IS LIMITED TO 1/10TH

USE OF HYDROGEN INCREASES THE EFFICIENCY BY ½ TO 1%2) REDUCTION IN SIZE OF THE MACHINE

THERMAL CONDUCTIVITY IS 7 TIMES THAT OF AIR. HEAT TRANSFER IS 1.5 TIMES. AT 0.5 PSI –RATING IS INCREASED BY 20-25% AT 30 PSI – RATING IS INCREASED BY 35%

3) INCREASED LIFE OF THE MACHINE

ENCLOSED CONSTRUCTION KEEP THE DIRT AND MOISTURE OUT. NO DETERIORATION OF ARMATURE INSULATION. THAT IS DURING CORONA, OZONE, NITRIC ACID

ARE FORMED WHICH ATTACKS THE INSULATION. 4) INCREASE IN OUT PUT FROM THE SAME MACHINE

EVERY 0.07 AT. PRESSURE INCREASE UP TO 1 AT. INCREASE THE MACHINE OUT PUT BY 1%. EVERY 0.07 AT. PRESSURE INCREASE FROM 1AT. TO 2 AT. INCREASE THE MACHINE OUT PUT BY

0.5%. INCREASE IN HYDROGEN PRESSURE ENHANCES THE WIND AGE LOSSES.

DISADVANTAGES: FORMS EXPLOSIVE MIXTURE WITH AIR BETWEEN 5 / 95% TO 75 / 25%.

COMPLICATED CONTROL AND GAS TIGHT SEAL SYSTEM. EXPLOSION PROOF CONSTRUCTION – INCREASED COST. PURGING OUT FACILITY WITH CO2.

AS DIAMETER OF MACHINE CANNOT BE INCREASED, FOR CAPACITY, CONDUCTOR LENGTH HAS TO BE INCREASED. – COOLING WITH GAS WITH GAS BECOMES DIFFICULT.

TECHNICAL DATA OF GENERATOR OF KAHALGAONTYPE TBB-220-2ET3

POWER 247.059MVA, 210MW

RATED VOLTAGE 15.75KV

RATED CURRENT 9056A,

POWER FACTOR 0.85PF,

EFFICIENCY 98.55%

SPEED 3000RPM, 50HZ

CONNECTION DOUBLE STAR

INSULATION CLASS CLASS F

CONDUCTOR / SLOT 2

TURNS / PHASE 10

TERMINALS / PHASE 3

NO. OF SLOTS 60

NO. OF TERMINALS 9

EFFECTIVE CORE LENGTH (L) 4.06M

TOTAL LENGTH OF STATOR

LENGTH OF TURN 13.95M

FLY WHEEL EFFECT 5.6 T.M2

CRITICAL SPEED 1370, 3400

MAX. TORQUE AT SC IN STATOR 8 FOLD

GAS VOLUME 56M3 (WITH ROTOR), 60M3 (WITHOUT ROTOR)

CAPACITANCE STATOR –0.69 MICRO F,

MAX. TEMP. STATOR WINDING –75C, STATOR CORE –105C

DC RESISTANCE 1.6 MILLI

REACTANCE XD X’D X’’D X2 X0

206% 26% 17.5% 21.3% 10.3%

TESTED HI VOLTAGE 49KV PEAK-TO-PEAK, 34.5KV RMS.

O/L CAPACITY OF STATOR 1.1 1.15 1.2 1.3 PU

30 15 3 1 MIN.

NEG. SEQ. O/L CAPACITY 0.25 0.50 1.0 2.0 PU

128 32 8 2.0 SEC.

MOTORING MODE STEAM LESS CONDITION IS OF NO DIRECT HAZARD TO GENERATOR. BECAUSE CONDITIONS OF TURBINE IT IS NOT OPERATED FOR MORE THAN 3 MIN. IN STEAM LESS CONDITION

MANOEUVRING 330 STARTS AND STOPS PER YEAR.

RATE OF LOAD PICK UP 6 % PER MIN.

RATE OF REACTIVE LOAD PICK UP 6% PER MIN.

ROTOR 2330A, 303V, CLASS F

NO. OF TURNS 9

DAMPER WINDING (4 INNER + 4 OUTER) DAMPER SEGMENTS

TESTED HI VOLTAGE 3.33KV FOR 1 MIN.

CAPACITANCE 0.29 MICRO F,

MAX. TEMP. ROTOR WINDING -115C

IMPEDANCE 4.54 AT 230V, AT 50HZ

OVER SPEED TEST 3600 RPM FOR 2 MIN.

TOTAL LOSSES 2892 KW

EXCITATION LOSS 818 KW

COPPER LOSS 964 KW

MECHANICAL LOSS 730 KW

NO LOAD LOSS 380 KW

LOSS OF FIELD GEN. CAN RUN WITH OUT FIELD FOR A MAX. 15 MIN. AT 40% THE RATED LOAD.

IN CASE OF LOSS FIELD, REDUCE THE LOAD TO 60% WITHIN 30 SEC. AND TO 40% LOAD IN 1.5 MIN.

ROTOR EARTH FAULT -FIRST 5 K

O/L CAPACITY OF ROTOR 1.1 1.2 1.5 2.0 PU

3600 240 60 20 SE

C.

GENERATOR SCC

IF, A 193 570 985 1390 1760

STATOR, A 975 2980 5080 7160 9020

GENERATOR OCC

STATOR VOLTAGE, KV 5.12 5.8 7.87 10.0 11.8 15.75 17.1

IF, A 237 267 362 464 560 800 920

GENERATOR OPERATING CONDITIONS

MAX. CONTINUOUS LOAD 214.5 MW, AT 0.85PF, AND COOLING WATER TEMPERATURE OF 36C AT GAS COOLER OUT LET

PERMITTED VOLTAGE VARIATION FOR WHICH THE MAXIMUM CONTINUOUS POWER IS RETAINED

±5% OF THE RATED, I.E. 14.96KV TO 16.53KV

MAX. VOLTAGE PERMITTED 110% OF RATED, I.E. 17.32 KV

VOLTAGE, % OF RATED VALUE

110 109 108 107 106 105 100 95 90

POWER, % OF RATED VALUE

88 91 93.5 96.5 98 100 100 100 94.5

STATOR CURRENT, % OF RATED

80 83.5 86.5 90 92.5 95 100 105 105

VARIATION OF GENERATOR POWER WITH RESPECT TO VARIATION OF VOLTAGE

VOLTAGE IN KV 17.32 17.16 17.01 16.85 16.69 16.53 15.75 14.96 14.17

POWER IN MW 188.7 195.2 200.5 207.0 210.2 214.5 214.5 214.5 202.7

STATOR CURRENT IN KA

7248 7565 7836 8154 8380 8607 9060 9513 9513

BRIEF DESCRIPTION OF 6.6KV HT.SW.GR OF MAINPLANT SCHEME

6.6KV SWITCHER OF KAHALGAON IS DESIGNED AND SUPPLIED BY RUSSIA. EACH UNIT CONSISTS OF TWO 6.6KV BUSHES, NAMED AS BA & BB. EVERY BUS IS CHARGED BY TWO SOURCES, NAMELY STATION OR RESERVE INCOMER AND UAT OR WORKING INCOMER. THESE INCOMER ARE CHARGED BY TWO TRANSFORMERS, I.E. 63 MVA STATION TRANSFORMER (ST) & 40 MVA UNIT AUXILIARY TRANSFORMER (UAT). THE ST IS CHARGED FROM SWITCH YARD 132 KV BUS AND UAT IS CHARGED FROM ITS UNIT GENERATOR AT 15.75KV. THESE TRANSFORMERS ARE HAVING DOUBLE SECONDARY WINDINGS OF 6.6KV.

GENERALLY, THE BUSES ARE LOADED ON UAT, WHEN THE UNITS ARE IN RUNNING CONDITION. WHEN UNIT TRIPS, STATION COMES INTO SERVICE BY AUTO-CHANGE OVER SCHEME (ACO). THE ACO SCHEME OPERATES FOLLOWING CONDITION:

1. WHEN GROUP - I PROTECTION OF UNIT OPERATES,2. WHEN GROUP - II PROTECTION OF UNIT OPERATES,3. UNDER VOLTAGE IN THE BUS, & 4. MECHANICAL PROBLEM IN UAT BREAKER.

APART FROM ABOVE, CHANGEOVER CAN ALSO BE DONE MANUALLY FROM UCB. THE ABOVE ACO IS ONLY FOR CHANGE OVER FROM UAT INCOMER TO STATION INCOMER.

SWITCH-GEAR

SWITCH GEAR IS A CONTROL SWITCH THAT CONTROL THE OPERATION OF A POWER CIRCUIT. THE TWO FUNCTION OF A SWITCH IN POWER SYSTEMS ARE –

I). TO PERMIT THE TRANSMISSION LINES TO BE CONVENIENT PUT INTO AND TAKEN OUT FROM SERVICE.

II). TO DISABLE THE SOME PLANT AND LINES WHEN THESE BECOME FAULTY, TO BE RAPIDLY AND SAFELY ISOLATED BY AUTOMATIC MEANS.S

BREAKER:

THE BREAKER USE AT OUR MAIN PLANT AT KAHALGAON STPP, ARE OF RUSSIAN MAKE. AIR CIRCUIT BREAKER. ITS RATINGS ARE AS FOLLOW:

RATED VOLTAGE : 6.6KV

MAXIMUM OPERATING VOLTAGE : 7.2KV

RATED CURRENT : 1600:2500:3200 AMPS.

SHORT CIRCUIT CURRENT : 40KA

CLOSING TIME / TRIPPING TIME : <75 MSEC

1600 AMP BREAKERS ARE USED IN ALL FEEDERS, WHEREAS, 2500 AMP BREAKERS ARE USED FOR STATION & UAT INCOMERS. THE 3200 AMP RATED BREAKERS ARE USED IN BV01, BW01, BL12, BM12, BV02 & BW02. THESE BREAKERS CONSIST OF A 900 WATT. UNIVERSAL. SPRING CHARGING MOTOR FOR CHARGING THE ACTUATING SPRINGS.

A BLOW OUT DEVICE IS ALSO FITTED IN THE BREAKER TO QUENCH THE ARE GENERATED DURING OPERATION OF THE SAME. THIS BLOW OUT DEVICE PUSHES THE ARC IN TO THE ARC CHUTE AND EXPANDS THE SAME TO EXTINGUISH IN MINIMUM POSSIBLE TIME.

THE BREAKERS ARE KEPT IN SPECIAL TYPE OF CABINET, WHERE DROPPERS OF BUS AND OUTGOING CABLES ARE TERMINATED. THESE BREAKERS OPERATES ON DUAL OPERATING SYSTEM - ELECTRICAL & MANUAL. MANUAL OPERATION SHOULD BE DONE ONLY IN EMERGENCY. THE BREAKER OPERATES THROUGH CLOSING & TRIPPING MECHANISM, WHEN A COMMAND IS GIVEN ELECTRICALLY.

IN THE CABINET, HIGH CLASS CURRENT TRANSFORMERS (CT) ARE MOUNTED ON THE OUTGOING CABLE FOR THE PROTECTION AND METERING CIRCUIT. ONE NUMBER CORE BALANCE CURRENT TRANSFORMER (CBCT) IS ALSO FIXED ON THE OUTGOING CABLE TO DETECT EARTH FAULT IN THE EQUIPMENT OR CABLE.

6.6 KV CIRCUIT BREAKER

A CIRCUIT BREAKER IS A DEVICE WHICH:-

MAKES OR BREAKS A CIRCUIT EITHER MANUALLY OR BY REMOTE CONTROL UNDER NORMAL CONDITIONS. BREAKS A CIRCUIT AUTOMATICALLY UNDER FAULT CONDITIONS. THUS A CIRCUIT BREAKER IS JUST A SWITCH WHICH CAN BE OPERATED UNDER NORMAL & ABNORMAL

CONDITIONS BOTH AUTOMATIC OR MANUALLY. TO PERFORM THIS OPERATION, A CIRCUIT BREAKER IS ESSENTIAL CONSISTING OF FIXED AND MOVING CONTACTS CALLED ELECTRODES. WHEN A FAULT OCCURS ON POWER SYSTEM, THE TRIP COIL OF CIRCUIT BREAKERS ENERGIZED WHICH PULLS APART MOVING CONTACTS, THUS OPEN THE CIRCUIT DC SUPPLY IS USED FOR THE OPERATION OF CIRCUIT BREAKER. ON THE BASIS OF MEDIUM USED FOR EXTINCTION THE CIRCUIT BREAKER ARE CLASSIFIED AS:

1. OIL CIRCUIT BREAKERS 2. AIR BLAST CIRCUIT BREAKER 3. SULPHER HEXAFLURID CIRCUIT BREAKER.

OIL CIRCUIT BREAKER

IT IS WELL KNOWN THAT WHEN A CIRCUIT CARRYING A LARGE CURRENT IS BROKEN, AN ARC OCCURS AT THAT POINT WHERE THE CONTACTS ARE SEPARATE; THE ARCHING IS SPECIALLY SEVERE WHEN HIGH VOLTAGES ARE INVOLVED AND IF A SHORT CIRCUIT OCCURS ON A HIGH VOLTAGE CABLE WHICH IS SUPPLIED FROM LARGE POWER STATION. THE ARC WOULD BE POWERFUL TO BRIDGE THE CONTACTS OF THE SWITCH AND DESTROY IT BY BURNING. THE DEVICE IS EMPLOYED AS AN OIL BREAKER. AN OIL BREAKER POSSES THE PROPERTY OF ALWAYS BREAKING AN ALTERNATIVE CURRENT AT ITS ZERO VALUE.

THESE SWITCHES ARE SUITABLE FOR A MAXIMUM VOLTAGE OF 6.6 KV. THE CONTACTS OF THESE SWITCHES, WHICH BREAK HIGH TENSION CIRCUIT, ARE IMMERSED IN OIL TO ENSURE RAPID & EFFECTIVE RAPTURE OF THE CIRCUIT. WHEN THE ARC OCCURS, THE OIL IN ITS PATH IS VAPORIZED AND THE GAS THEREBY GENERATED EXTRACT A PRESSURE ON THE SURROUNDING OIL. THIS PRESSURE IS UTILIZED IN ARC CONTROLLED DEVICES TO CAUSE A MOVEMENT OF FRESH COOL OIL ACROSS THE PATH OF THE ARC, THEREBY EFFICIENTLY ASSISTING ITS INTERRUPTION.

2. AIR BLAST CIRCUIT BREAKER

ALL AIR BLAST CIRCUIT BREAKER REQUIRES AN AUXILIARY COMPRESSED AIR SYSTEM WHICH SUPPLIES AIR TO THE BREAKER AIR RECEIVER. WHEN OPENING IS REQUIRED, COMPRESSED AIR IS ADMITTED TO THE ARC EXTINCTION CHAMBER. IT PUSHES AWAY THE MOVING CONTACTS. IN DOING SO THE CONTACTS ARE SEPARATED AND THE AIR BLAST TAKES AWAY THE IONIZED GASES ALONG WITH IT AND ASSISTS ARC EXTINCTION. AIR BLAST CIRCUIT BREAKER EXTINGUISHES THE ARC. WITHIN ONE OR TWO CYCLE AND ARC CHAMBER IS FILLED WITH A HIGH PRESSURE AIR, WHICH PREVENTS RESTRIKE.

3. SULPHER HEXAFLURID CIRCUIT BREAKER

IN SF6 CIRCUIT BREAKER SF6 GAS IS BLOWN AXIALLY ALONG THE ARC. THE HEAT IS REMOVED FROM THE ARC BY AXIAL CONVECTION AND RADIAL DISSIPATION. CONSEQUENTLY, THE ARC DIAMETER REDUCES DURING THE DECREASING NODE OF THE CURRENT WAVE. THE DIAMETER BECOMES SMALL DURING CURRENT ZERO. TURBULENT FLOW IS INTRODUCED AROUND

.

CURRENT ZERO FOR EXTINGUISH THE ARC. THE ABOVE DIAGRAM SHOW THE LAYOUT DIAG OF SF6 CIRCUIT BREAKER.

SAFETY:

THOUGH THE DESIGN OF THE BREAKER CABINET AT KAHALGAON IS VERY SAFE, BUT SAFETY ASPECT FOR OPERATION SHOULD NEVER BE OVER LOOKED. BY KEEPING A FEW THINGS IN THE MIND AND IN DAILY ROUTINE, MANY ACCIDENTS CAN BE AVOIDED. HERE ARE A FEW TIPS, WHICH AN OPERATION MAN MUST CHECK WHILE OPERATING THE BREAKERS:

1. ALWAYS SEE THE EARTH SWITCH POSITION, WHILE RACKING - IN THE BREAKER. THE EARTH SWITCH POSITION MUST BE IN 'OFF' POSITION, WHEN THE BREAKER IS PUSHED IN SERVICE POSITION.

2. NEVER OPERATE EARTH SWITCH OF UAT, STATION INCOMER, BV01, BW01, BL12, BM12, BV02 OR BW02 WITHOUT CONFIRMING THE PROPER ISOLATION.

3. BEFORE OPERATING EARTH SWITCH IN A TRANSFORMER FEEDER. LT INCOMER ISOLATION MUST BE CONFIRMED.

4. ALL FLAGS SHOULD BE RESET BEFORE SWITCHING ON THE CONTROL SUPPLY.5. NEVER USE EXCESSIVE FORCE TO INSERT THE BREAKER IN TO SERVICE POSITION. CHECK THE FINGER CONTACT

OF THE BREAKER AND SHUTTER MECHANISM OF THE CABINET, IF THE SAME IS NOT GOING IN THE SERVICE POSITION.

6. FREENESS OF THE PAD LOCK SHOULD BE ENSURED AFTER PUTTING THE BREAKER IN SERVICE OR TEST POSITION.

7. THE MULTI-PIN OF THE BREAKER SHOULD BE TIGHTENED AFTER KEEPING THE CONTROL SUPPLY OFF. 8. THE DOOR OF THE BREAKER CABINET MUST BE CLOSED BEFORE MAKING THE CONTROL SUPPLY 'ON'.

EMERGENCY :

AN OPERATION STAFF SHOULD KNOW TO COPE WITH EMERGENCY SITUATIONS. THE MAY ARISE IN CASE OF DC (CONTROL SUPPLY) FAILURE, BLACK OUT, FIRE, ETC. IN CASE OF DC FAILURE, ALTERNATIVE SOURCE MAY BE SWITCHED 'ON' WHOSE SWITCHES ARE IN SINGLE CONTROL CABINET, LOCATED AT THE BOTH END OF SWITCHGEAR.

IF THE DC SUPPLY DOES NOT RESTORE BY ALTERNATIVE SOURCE ALSO, ALL THE BREAKERS OF THE PARTICULAR BUS SHOULD BE MANUALLY TRIPPED IN CONSULTATION WITH SHIFT - IN - CHARGE, AS ALL THE CONTROL & PROTECTION SYSTEM WILL BE OUT. THE SAME THING SHOULD ALSO BE DONE IN BLACK OUT CONDITION.

IN CASE OF FIRE, THE SUPPLY OF THE PARTICULAR FEEDER SHOULD BE MADE OFF, IF POSSIBLE AND THE FIRE SERVICES MAY BE CALLED IN IMMEDIATELY. FIRE EXTINGUISHERS MAY BE USED FOR PUTTING OFF THE FIRE. ALL DOORS SHOULD BE OPEN AND VENTILATION FANS MAY BE SWITCHED ON.

BASICS OF PROTECTIVE RELAYING

INTRODUCTION: THE PURPOSE OF AN ELECTRICAL POWER SYSTEM IS TO GENERATE AND SUPPLY ELECTRICAL ENERGY TO THE CONSUMER SAFELY & RELIABLY. THE PURPOSE OF A PROTECTIVE SYSTEM IS TO ISOLATE THE FAULTY SECTION OF THE POWER SYSTEM AS QUICKLY AS POSSIBLE FROM THE HEALTHY SYSTEM:

(A) TO AVOID DAMAGE TO THE HEALTHY PARTS OF THE SYSTEM.(B) TO AVOID DAMAGE TO THE AFFECTED PARTS.(C) TO AVOID LOSS OF SYNCHRONISM OF THE HEALTHY GENERATOR OF THE PLANT.

IN ASSOCIATION WITH C.T./P.T AND (C.B) CIRCUIT BREAKERS , THE PROTECTIVE RELAY AVERTS THE ABOVE EFFECTS.

AC.T / P.T. / OR C.V.T/ PROVIDED INFORMATION TO THE RELAY REGARDING THE ELECTRICAL STATE OF THE SYSTEM;

WHENEVER THE ELECTRICAL STATE OF THE SYSTEM GOES BEYOND A PREDETERMINED VALUE, THE RELAY GIVES A TRIPPING SIGNAL TO THE CIRCUIT BREAKER; THE CIRCUIT BREAKER THUS TRIPS AND DISCONNECTS THE FAULTY ELEMENTS OF THE POWER SYSTEM. C.B. LOCATION IS SO CHOSEN THAT EACH GEN. TRANSFORMER, BUS, TRANSMISSION LINE ETC. CAN BE COMPLETELY DISCONNECTED FROM REST OF SYSTEM.

PROTECTIVE RELAYS: -

THE RELAY IS USED TO DETECT THE ABNORMAL CONDITIONS SUCH AS SHORT CIRCUITS, EARTHING OF LIVE EQUIPMENT / PARTS, OVERLOADS, OVER VOLTAGES, UNDER VOLTAGES, UNBALANCED LOAD, UNDER FREQUENCY, ABNORMAL GAS PRESSURE IN THE TRANSFORMER ETC. THE BASIC FUNCTION OF RELAY IS TO DISCONNECT THE FAULTY OR ABNORMAL SYSTEM EQUIPMENT THROUGH CIRCUIT BREAKER TO AVOID DAMAGE TO THE EQUIPMENT OR INSTABILITY OF THE SYSTEM IN THE SHORTEST POSSIBLE TIME.

PRIMARILY THE RELAY SOUNDS AN ALARM TO INDICATE EXISTENCE OF AN ABNORMALITY. NORMAL AND ABNORMAL CONDITIONS ARE DISTINGUISHED BY RELAY SENSING ELEMENTS WHICH REPPOND TO SET ACTUATING PARAMETERS LIKE CURRENT, VOLTAGE, PHASE ANGLE, FREQUENCY, WAVW SHAPE ETC.

THE OPERATING PARAMETERS ARE:

– MAGNITUDE

– PHASE ANGLE

– FREQUENCY

– DURATION (TIME)– RATE OF CHARGE

– DIRECTION

– WAVE SHAPE

ELECTROMAGNETIC RELAYS:

OPERATING PRINCIPLES:

- ELECTROMAGNETIC ATTRACTION

- ELECTROMAGNETIC INDUCTION

- THERMAL EFFECT (HEAT PRODUCED I2 RT.)ACTUATING STRUCTURES:

- SHADED POLE STRUCTURE

- WATT HOUR METER STRUCTURE

- INDUCTION CUP (SIGNAL LOOP AND DOUBLE LOOP STRUCTURE)

STATIC RELAYS:

THE DEVELOPMENT OF STATIC RELAYS HAS BEEN VERY FAST AS THESE HAVE MANY ADVANTAGE AS COMPARED TO ELECTROMAGNETIC RELAYS: -

- ABSENCE OF MOVING PARTS

- LOW BURDEN ON CTS & VTS

- FAST OPERATION ( 1-2 MS)- HIGH RESISTANCE TO SHOCKS AND VIBRATION

- LOW MAINTENANCE

- MINIATURIZATION

BASIC OPERATION OF THE STATIC RELAYS REVOLVES AROUND THE LINARY SIGNAL CONVERSION WITH MEASURING FUNCTIONS. THE TRANSDUCER ELEMENT SUCH AS CURRENT, VOLTAGE, PHASE ANGLE OR FREQUENCY AND DERIVED VALUES OBTAINED BY DIFFERENTIATION, INTEGRATION OR OTHER OPERATIONS IN THE CONVERTER SECTION APPEAR AS ANALOGUE INPUT TO MEASURING CIRCUITS. THE OUTPUT IS BINARY SIGNAL THE ACTUATING CIRCUIT.

REQUIREMENT OF PROTECTIVE RELAYS :

WHENEVER THERE IS ANY FAULT OR ABNORMALITY OCCURRING IN THE SYSTEM IT IS VERY MUCH IMPORTANT TO DE-ENERGIZE THE FAULTY SYSTEM QUICKLY AND SELECTIVELY TO MINIMIZE THE SPREAD OF DAMAGE IN THE FAULTY EQUIPMENT AND TO PERMIT CONTINUITY OF SUPPLY TO THE HEALTHY SECTION OF THE SYSTEM.

TO FULFILL THE PURPOSE FOR WHICH A PROTECTIVE SYSTEM HAS BEEN PROVIDED THE FOLLOWING IMPORTANT REQUIREMENTS ARE TO BE CONSIDERED:

- SENSITIVITY

- SELECTIVITY OR DISCRIMINATION

- SPEED - RELIABILITY

TRANSMISSION LINE PROTECTION

MAJORITY OF LINE FAULTS HAVE BEEN FOUND TO BE SINGLE PHASE TO GROUND FAULTS. THE PROTECTION SCHEMES FOR TRANSMISSION LINES ARE QUITE STANDARDIZED AND LOTS OF IMPROVEMENTS HAVE RECENTLY BEEN INCORPORATED. THE BASIS PROTECTIVE SCHEMES ARE: - DISTANCE PROTECTION FOR PHASE FAULTS AND EARTH FAULTS. - OVER VOLTAGE PROTECTION.- DISTANCE PROTECTION.

TIME AND GRADED CURRENT PROTECTION IS USED WHERE A TIME LAG CAN BE PERMITTED AND INSTANTANEOUS OPERATION IS NOT NECESSARY FROM STABILITY POINT OF VIEW. THESE ARE USED AS BACK-UP PROTECTION TO THE MAIN PROTECTION PROVIDED BY DISTANCE RELAYING SCHEME.

DISTANCE RELAYING:THERE ARE THREE MAIN TYPES OF MEASURING UNITS: -- IMPEDANCE TYPE

- REACTANCE TYPE

- MHO TYPE

FOR VERY SHORT LINES REACTANCE TYPE RELAYS ARE USED BECAUSE IT IS PRACTICALLY UNAFFECTED BY ARC RESISTANCE. FOR SHORT LINES ARC RESISTANCE IS LARGE. FOR MEDIUM LENGTH LINES IMPEDANCE TYPE RELAY IS SUITABLE. FOR LONG TRANSMISSION LINES MHO TYPE RELAYS ARE USED FOR PROTECTION FROM PHASE FAULTS. WHERE LENGTH OF TRANSMISSION IS LONG CARRIER CURRENT PROTECTION IS PROVIDED FOR SIMULTANEOUS OPENING OF CIRCUIT BREAKERS AT BOTH ENDS OF THE LINE. WITH STEPPED TIME – DISTANCE CHARACTERISTIC OF

DISTANCE RELAYS, THE FIRST DISTANCE STEP IS GENERALLY TO COVER ABOUT 80% OF FIRST LINE SECTION. THE RELAY AT REMOTE AND IS ARRANGED IN A SIMILAR WAY BUT IN OPPOSITE DIRECTION.

WHEN THE FAULT OCCURS IN ZONE I, A SIGNAL RECEIVED FROM A RELAY AT OPPOSITE AND IS USED TO EXTEND THE FIRST ZONE FROM 80% TO ALMOST 100% OF THE LINE BY SHUNTING THE TIME ELEMENT OF ZONE – 2 RELAY ARE SHUNTED BY NORMALLY OPEN CARRIER RECEIVER RELAY CONTACTS. THUS ALL FAULTS WITH IN THE PROTECTED SECTION CAN BE CLEARED APPROXIMATELY AT THE SAME TIME.

PROTECTION OF GENERATORS:

1. THERMAL OVER LOADING:- CONTINUOUS OVER LOADING

- FAILURE OF COOLING SYSTEM

- RTD, STATOR OVERLOAD PROTECTION WITH

- E/C RELAYS

-2. EXTERNAL FAULT FED BY THE GENERATOR:

- OVERLOAD PROTECTION FOR SMALL GENERATORS

- NEGATIVE PHASE SEQUENCE RELAY -

3. STATOR FAULTS:PHASE-TO-PHASE, PHASE TO EARTH AND INTER TURN FAULTS. BIASED DIFFERENTIAL PROTECTION EARTH FAULT PROTECTION.

4. ROTOR EARTH FAULTS: SINGLE FAULT DOES NOT HARM

SECOND FAULT CAUSES UNBALANCED

MAGNETIC FORCES CAUSING DAMAGE TO SHAFT BEARING ROTOR EARTH FAULT PROTECTION RELAYS.

5. LOSS OF FIELD: TRIPPING OF FIELD CIRCUIT BREAKER GENERATOR RUNS AS INDICATION GENERATOR DERIVING EXCITATION CURRENTS FROM BUS-BARS, SPEED INCREASES SLIGHTLY.

6. MOTORING OF GENERATOR: WHEN INPUT TO PRIME MOVER STOPS THE GENERATOR DRAWS POWER FROM BUS BARS AND RUNS AS SYNCHRONOUS MOTOR IN THE SAME DIRECTION.- REVERSE POWER PROTECTION RELAY.

7. SINGLE PHASING:- USUAL THERMAL OVERLOAD RELAYS.- SPECIAL SINGLE PHASE PREVENTING RELAY

8. STALLING:- THERMAL RELAYS

- INSTANTANEOUS O/C RELAYS 9. ROTOR FAULTS:

- INSTANTANEOUS O/C RELAYS

10. SWITCHING SURGES:- RC SURGE MODIFIERS (100 R, 0.1 UF CONNECTED BETWEEN PHASE AND GROUND)

PROTECTION OF LARGE MOTORS:

1. OVERLOAD PROTECTION

- THERMAL OVER LOAD RELAYS - OVER LOAD RELEASE

- INVERSE OVER CURRENT RELAYS

- MINITIATURE C/B WITH BUILT UP TRIP COILS

2. PHASE FAULTS AND EARTH FAULTS: - HIGH SET INSTANTANEOUS O/C RELAYS.- DIFFERENTIAL PROTECTION

- HRC FUSES ( OLD INSTALLATIONS ) 3. UNDER VOLTAGE:

- UNDER VOLTAGE RELEASE

- UNDER VOLTAGE

4. UNBALANCED VOLTAGE:- NEGATIVE PHASE SEQUENCE RELAYS

5. REVERSE PHASE SEQUENCE: - PHASE REVERSAL PROTECTION

TRANSFORMERS

THE TRANSFORMER IS THE MOST CONVENIENT & ECONOMICAL DEVICE FOR TRANSFER OF POWER FROM ONE VOLTAGE TO ANOTHER VOLTAGE AT THE SAME FREQUENCY. IT WORKS ON THE PRINCIPLE OF ELECTROMAGNETIC INDUCTION. THERE IS HARDLY ANY INSTALLATION WITHOUT A TRANSFORMER. DUE TO THIS EQUIPMENT, IT HAS BEEN POSSIBLE TO TRANSMIT BULK POWER TO LOAD CENTERS FROM FAR OFF POWER HOUSES AND TO VARIOUS MACHINERIES AND SWITCHGEARS OF THE POWER PLANT. TRANSFORMERS ARE OF TWO TYPES:-

#STEP-UP TRANSFORMER - WHICH STEP-UP THE VOLTAGE AT SECONDARY SIDE CALLED STEP-UP TRANSFORMER.

#STEP-DOWN TRNSFORMER- WHICH STEP-DOWN THE VOLTAGE AT SECONDARY SIDE ARE CALLED STEP-DOWN TRANSFORMER.

IMPORTANT TRANSFORMERS IN THE PLANT

1. GENERATOR TRANSFORMER ( 240 MVA, 15.75 KV/220KV) –

IT CONVERTS 15.75 KV WHICH IS SUPPLIED FROM GENERATOR TO 220KV AND SUPPLIED IT TO THE BUS BAR/ GRID.

2.STATION SERVICE TRANSFORMER (40MVA, 220KV/7KV) –

IT CONVERTS 220KV WHICH IS COMING TO STATION FROM BBMB TO 7KV AND FED TO STATION AUXILIARY.

3. UNIT AUXILIARY TRANSFORMER (15MVA, 15.75KV/7KV) –

IT CONVERTS 15.75KV WHICH IS SUPPLIED FROM GENERATOR AND STEP DOWN TO 7KV TO FED UNIT AUXILIARY. THE UNIT AUXILIARY TRANSFORMERS ARE OF TWO IN NO.

THE ABOVE THREE TRANSFORMERS ARE MAIN TRANSFORMERS USE IN THE PLANT. AND SPECIAL CARE IS TAKEN FOR THE SAFETY OF THE TRANSFORMER. TIME TO TIME VARIOUS TESTS IS DONE FOR THE SAFETY OF TRANSFORMER.

REFERENCES

POWER PLANT FAMILIARIZATION

KAHALGAON -TECHNICAL DIARY

WWW.POWERMIN.NIC.IN HTTPS://WWW.NTPC.CO.IN/