BASICS OF TRANSFORMER

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NEED

WORKING PRINCIPLE

TYPES OF TRANSFORMERS

CONSTRUCTION FEATURES

TRANSFORMERS ACCESSORIES

MAJOR TRANSFORMERS IN POWER PLANTS

TRANSFORMER LOSSES

CONDITION MONITORING OF TRANSFORMERS

HISTORICALLY, THE FIRST ELECTRICAL POWERDISTRIBUTION SYSTEM DEVELOPED BY EDISONIN 1880s WAS TRANSMITTING DC (DIRECTCURRENT)

IT WAS DESIGNED FOR LOW VOLTAGES (SAFETYAND DIFFICULTIES IN VOLTAGE CONVERSION);THEREFORE, HIGH CURRENTS WERE NEEDED TOBE GENERATED AND TRANSMITTED TO DELIVERNECESSARY POWER

THIS SYSTEM SUFFERED SIGNIFICANT ENERGYLOSSES!

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THE SECOND GENERATION OF POWER DISTRIBUTIONSYSTEMS (WHAT WE ARE STILL USING) WAS PROPOSED BYTESLA FEW YEARS LATER.

HIS IDEA WAS TO GENERATE AC POWER OF ANYCONVENIENT VOLTAGE, STEP UP THE VOLTAGE FORTRANSMISSION (HIGHER VOLTAGE IMPLIES LOWERCURRENT AND, THUS, LOWER LOSSES),

TRANSMIT AC POWER WITH SMALL LOSSES, AND FINALLYSTEP DOWN ITS VOLTAGE FOR CONSUMPTION

POWER LOSS IS PROPORTIONAL TO THE SQUARE OF THECURRENT TRANSMITTED

THE STEP UP AND STEP DOWN VOLTAGE CONVERSION WASBASED ON THE USE OF TRANSFORMERS.

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O OPTIMISE COST OF BULK TRANSMISSION OFPOWER FROM GENERATORS TO CONSUMERS

REDUCTION IN TRANSMISSION LOSS

O REDUCE OR INCREASE VOLTAGE IN AC SYSTEM

NABLES SAFE SUPPLY VOLTAGE TO CONSUMERS

SOLATION OF TWO SYSTEMS FOR VOLTAGEREGULATION

A TRANSFORMER IS A DEVICEHAT CONVERTS ONE AC VOLTAGE TO ANOTHER AC VOLTAGET THE SAME FREQUENCY

CONSISTS OF ONE OR MORE COIL(S) OF WIRE WRAPPEDROUND A COMMON FERROMAGNETIC CORE

HESE COILS ARE USUALLY NOT CONNECTED ELECTRICALLYOGETHER

OWEVER, THEY ARE CONNECTED THROUGH THE COMMONAGNETIC FLUX CONFINED TO THE CORE

SSUMING THAT THE TRANSFORMER HAS AT LEAST TWOINDINGS, ONE OF THEM (PRIMARY) IS CONNECTED TO A

OURCE OF AC POWER; THE OTHER (SECONDARY) ISONNECTED TO THE LOADS.

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CORE TYPECIRCULAR SHAPED

WINDINGS

SHELL TYPE:RECTANGULAR SHAPED

WINDINGS

CORE

HE CORE WILL WORK AS A CAGE FOR THE MAGNETIC FLUX

OST OF THE FLUX WILL BE KEPT INSIDE THE CORE

HE CORE IS MADE WITH A VERY SPECIAL ELECTRICAL STEEL

HE STEEL IS MADE AS THIN INSULATED SHEETS WHICHUST BE MOUNTED ONE BY ONE

HE FINAL GOAL IS TO MINIMIZE THE SIZE OF THE COREND LOSSES.

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THE CORE: WHICH PROVIDES A PATH FOR THEMAGNETIC LINES OF FLUX

THE PRIMARY WINDING: WHICH RECEIVESENERGY FROM THE AC SOURCE

THE SECONDARY WINDING: WHICH RECEIVESENERGY FROM THE PRIMARY WINDING ANDDELIVERS IT TO THE LOAD

THE ENCLOSURE: WHICH PROTECTS THE ABOVECOMPONENTS FROM DIRT, MOISTURE, ANDMECHANICAL DAMAGE.

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2 ADJACENT COILS

COILS NOT PHYSICALLY CONNECTED TO EACH OTHER

HE PRIMARY WINDING IS CONNECTED TO A 50 HERTZ ACOLTAGE SOURCE

HE MAGNETIC FIELD (FLUX) BUILDS UP (EXPANDS) ANDOLLAPSES (CONTRACTS) ABOUT THE PRIMARY WINDING

HE EXPANDING AND CONTRACTING MAGNETIC FIELDROUND THE PRIMARY WINDING CUTS THE SECONDARYINDING AND INDUCES AN ALTERNATING VOLTAGE INTO

HE WINDING

HIS VOLTAGE CAUSES ALTERNATING CURRENT TO FLOWHROUGH THE LOAD

HE VOLTAGE MAY BE STEPPED UP OR DOWN DEPENDING ONHE DESIGN OF THE PRIMARY AND SECONDARY WINDINGS.

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HEN A LOAD DEVICE IS CONNECTED ACROSS THE SECONDARYINDING OF A TRANSFORMER, CURRENT FLOWS THROUGH THECONDARY AND THE LOAD

E MAGNETIC FIELD PRODUCED BY THE CURRENT IN THECONDARY INTERACTS WITH THE MAGNETIC FIELD PRODUCED BYE CURRENT IN THE PRIMARY

IS INTERACTION RESULTS FROM THE MUTUAL INDUCTANCETWEEN THE PRIMARY AND SECONDARY WINDINGS.

SIMPLE TRANSFORMER INDICATING PRIMARY- AND SECONDARY-WINDING FLUX RELATIONSHIP

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THE VOLTAGES IN THE PRIMARY & SECONDARYCOILS DEPEND ON NUMBER OF TURNS IN COILS

Vp = PRIMARY VOLTAGEVs = SECONDARY VOLTAGENp = NUMBER OF TURNS OF PRIMARY COILNs = NUMBER OF TURNS OF SECONDARY COIL

THERE ARE 2 TYPES OF TRANSFORMERS

STEP-UP TRANSFORMER

Vs VpNs Np

STEP-DOWN TRANSFORMER

Vs < Vp Ns < Np

CIRCUIT SYMBOL

CIRCUIT SYMBOL

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IF NO POWER IS LOST IN A TRANSFORMER

(NO POWER LOSS)

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F THE SECONDARY OF A TRANSFORMER HAS TWO TIMES ASANY TURNS AS THE PRIMARY, THE VOLTAGE INDUCED INTOHE SECONDARY WILL BE TWO TIMES THE VOLTAGE ACROSSHE PRIMARY

F THE SECONDARY HAS ONE-HALF AS MANY TURNS AS THERIMARY, THE VOLTAGE ACROSS THE SECONDARY WILL BENE-HALF THE VOLTAGE ACROSS THE PRIMARY.

OWEVER, THE TURNS RATIO AND THE CURRENT RATIO OF ARANSFORMER HAVE AN INVERSE RELATIONSHIP.

HUS, A 1:2 STEP-UP TRANSFORMER WILL HAVE ONE-HALFHE CURRENT IN THE SECONDARY AS IN THE PRIMARY.

2:1 STEP-DOWN TRANSFORMER WILL HAVE TWICE THEURRENT IN THE SECONDARY AS IN THE PRIMARY.

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POWER TRANSFORMERS : USED INTRANSMISSION NETWORK OF HIGHER VOLTAGES,DEPLOYED FOR STEP-UP AND STEP DOWNTRANSFORMER APPLICATION (765 kV, 400 kV,220 kV, 110 kV, 66 kV, 33kV,22kV)

DISTRIBUTION TRANSFORMERS: USED FORLOWER VOLTAGE DISTRIBUTION NETWORKS AS AMEANS TO END USER CONNECTIVITY. (11kV, 6.6kV, 3.3 kV, 440V, 230V)

TRANSFORMER CONNECTIONS

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DELTA/STAR: USED IN GENERATING STATIONSFOR STEP-UP

STAR/DELTA: USED IN RECEIVING STATIONSFOR STEP-DOWN

ALL GTs ARE DELTA/STAR CONNECTED

ALL TIE IN TRANSFORMERS ARE STAR/STARCONNECTED.

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TRANSFORMER CONNECTIONSSTAR / STAR CONNECTION

STAR / DELTA CONNECTION

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O-LOAD LOSSES TAKE PLACE MAINLY IN THE CORE SHEETS. ITORRESPONDS TO ABOUT 25% OF THE TRANSFORMER LOSSES

HE DC LOSSES TAKE PLACE EXCLUSIVELY IN WINDINGS

HE EDDY/STRAY LOSSES TAKE PLACE IN ALL PIECES OF METALNSIDE THE TRANSFORMER (FRAMES, CORE, WINDING, TANKSTC), A LARGE PART OF IT ARE GENERATED IN THE WINDINGS

SPECIALLY DANGEROUS LOSSES ARE THE ONES CONCENTRATED INSMALL VOLUME SINCE THEY MAY CAUSE A HOT-SPOT.

TO MODEL A REAL TRANSFORMER ACCURATELY, WENEED TO ACCOUNT FOR THE FOLLOWING LOSSES:

COPPER LOSSES:RESISTIVE HEATING IN THE WINDINGS I2R

EDDY CURRENT LOSSES : RESISTIVE HEATING IN THECORE, PROPORTIONAL TO THE SQUARE OF VOLTAGE APPLIED TOTHE TRANSFORMER

HYSTERESIS LOSSES : ENERGY NEEDED TO REARRANGEMAGNETIC DOMAINS IN THE CORE

LEAKAGE FLUX : FLUX THAT ESCAPES FROM THE CORE ANDFLUX THAT PASSES THROUGH ONE WINDING ONLY.

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NOT ALL THE MAGNETIC FIELD PRODUCED BYTHE PRIMARY IS INTERCEPTED BY THESECONDARY.

A PORTION OF THE LEAKAGE FLUX MAY INDUCEEDDY CURRENTS WITHIN NEARBY CONDUCTIVEOBJECTS, SUCH AS THE TRANSFORMER'SSUPPORT STRUCTURE, AND BE CONVERTED TOHEAT.

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SSES IN THE TRANSFORMER ARE OF THE ORDER OF 1% OF ITSLL LOAD KW RATING

ESE LOSSES GET CONVERTED IN THE HEAT THEREBY THEMPERATURE OF THE WINDINGS, CORE, OIL AND THE TANK RISES

E HEAT IS DISSIPATED FROM THE TRANSFORMER TANK AND THEADIATOR IN TO THE ATMOSPHERE

RANSFORMER COOLING HELPS IN MAINTAINING THEMPERATURE RISE OF VARIOUS PARTS WITHIN PERMISSIBLEMITS

CASE OF TRANSFORMER, COOLING IS PROVIDED BY THERCULATION OF THE OIL

RANSFORMER OIL ACTS AS BOTH INSULATING MATERIAL AND ALSOOOLING MEDIUM IN THE TRANSFORMER

R SMALL RATING TRANSFORMERS HEAT IS REMOVED FROM THERANSFORMER BY NATURAL THERMAL CONVECTION

R LARGE RATING TRANSFORMERS THIS TYPE OF COOLING IS NOTFFICIENT, FOR SUCH APPLICATIONS FORCED COOLING IS USED.

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DIFFERENT TRANSFORMER COOLING METHODSARE:AIR COOLING FOR DRY TYPE TRANSFORMERS:

AIR NATURAL TYPE (A.N.)

AIR FORCED TYPE (A.F.)

COOLING FOR OIL IMMERSED TRANSFORMERS:OIL NATURAL AIR NATURAL TYPE (O.N.A.N.)

OIL NATURAL AIR FORCED TYPE (O.N.A.F.)

OIL FORCED AIR NATURAL TYPE (O.F.A.N.)

OIL FORCED AIR FORCED TYPE (O.F.A.F.)

OIL IMMERSED WATER COOLING:OIL NATURAL WATER FORCED (O.N.W.F.)

OIL FORCED WATER FORCED (O.F.W.F.)

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RANSFORMERS ABOVE 60 MVA EMPLOY A COMBINATION OF FORCED OILND FORCED AIR COOLING

IL NATURAL AIR FORCED TYPE OF COOLING IS NOT ADEQUATE TO REMOVEHE HEAT CAUSED BY THE LOSSES WHICH IS APPROXIMATELY EQUAL TO% OF THE TRANSFORMER RATING (0.6MW)

N CASE OF FORCED OIL AND FORCED AIR COOLING SYSTEM A SEPARATEOOLER IS MOUNTED AWAY FROM THE TRANSFORMER TANK

HIS COOLER IS CONNECTED TO THE TRANSFORMER WITH PIPES AT THEOTTOM AND THE TOP

HE OIL IS CIRCULATED FROM THE TRANSFORMER TO THE COOLERHROUGH THE PUMP

HE COOLER IS PROVIDED WITH THE FANS WHICH BLAST AIR ON THEOOLING TUBES

HIS TYPE OF COOLING IS PROVIDED FOR THE HIGHER RATINGRANSFORMERS AVAILABLE AT THE SUBSTATIONS AND POWER STATIONS.

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IS TYPE OF COOLING SYSTEM NEEDS A HEAT EXCHANGER INHICH THE HEAT OF THE TRANSFORMER OIL IS GIVEN TO THE

OOLING WATER

E COOLING WATER IS TAKEN AWAY AND COOLED IN SEPARATEOOLERS

E OIL IS FORCED THROUGH THE HEAT EXCHANGER

E OIL PUMP PUMPS THE OIL FROM TRANSFORMER TO THE HEATCHANGER THOUGH THE TOP PIPES

L FROM THE HEAT EXCHANGER IS PUMPED BACK TO THERANSFORMER THROUGH THE BOTTOM PIPE

IS TYPE OF COOLING IS PROVIDED FOR VERY LARGERANSFORMERS WHICH HAVE RATINGS OF SOME HUNDREDS OF MVAENERATING TRANSFORMER WILL HAVE VERY HIGH RATING AND

ATING EQUAL TO THE RATING OF THE GENERATOR)

IS TYPE OF TRANSFORMERS IS USED IN LARGE SUBSTATIONS ANDOWER PLANTS

GENERATOR TRANSFORMER (GT)

STATION TRANSFORMER (ST)

UNIT AUXILIARY TRANSFORMER (UAT)

EXCITATION TRANSFORMER

NEUTRAL GROUNDING TRANSFORMER

AUXILIARY TRANSFORMERS

AUTO TRANSFORMER

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GENERATOR TRANSFORMER: THE GENERATORS CONNECTED TO THIS TRANSFORMER BY MEANS OFSOLATED BUS DUCTS.

THIS TRANSFORMER IS USED TO STEP UP THEGENERATING VOLTAGE OF AROUND 15KV TO GRIDVOLTAGE.

THIS TRANSFORMER IS GENERALLY PROVIDED WITHOFAF COOLING.

T IS ALSO PROVIDED WITH OFF CIRCUIT/ON LOADTAPS ON THE HIGH VOLTAGE SIDE.

THIS TRANSFORMER HAS ELABORATE COOLINGSYSTEM CONSISTING OF NUMBER OF OIL PUMPS ANDCOOLING FANS APART FROM VARIOUS ACCESSORIES.

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HE UAT DRAWS ITS INPUT FROM THE MAIN BUS-DUCT CONNECTING GENERATOR TO THE GENERATOR

RANSFORMER.

HE TOTAL KVA CAPACITY OF UNIT AUXILIARYRANSFORMER REQUIRED CAN BE DETERMINED BY

ASSUMING 0.85 POWER FACTOR AND 0.9 EFFICIENCY FOROTAL AUXILIARY MOTOR LOAD.

T IS SAFE AND DESIRABLE TO PROVIDE ABOUT 20% EXCESSCAPACITY THAN CIRCULATE SO AS TO PROVIDE FORMISCELLANEOUS AUXILIARIES AND POSSIBLE INCREASE INAUXILIARY LOAD.

WITH HIGHER UNIT RATINGS AND HIGHER STEAMCONDITIONS, THE AUXILIARY POWER REQUIRED ALSONCREASES AND LIMITATIONS IMPOSED BY THEWITCHGEAR VOLTAGES AVAILABLE, INDICATE THE

MAXIMUM SIZE OF UNIT AUXILIARY TRANSFORMER WHICHCAN BE USED 36

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THE STATION TRANSFORMER IS REQUIRED TO FEEDPOWER TO THE AUXILIARIES DURING START UPS.

THIS TRANSFORMER IS NORMALLY RATED FOR THENITIAL AUXILIARY LOAD REQUIREMENTS OF UNIT.

N TYPICAL CASES, THIS LOAD IS OF THE ORDER OF60% OF THE LOAD AT FULL GENERATING CAPACITY.

BUT IN LARGE STATIONS WHERE MORE THAN ONEUNITS ARE OPERATING, THE STATION TRANSFORMERSSHOULD HAVE SUFFICIENT CAPACITY TO START TWOUNITS AT A TIME IN ADDITION TO FEEDING THECOMMON AUXILIARIES.

T IS ALSO PROVIDED WITH ON LOAD TAP CHANGER TOCATER TO THE FLUCTUATING VOLTAGE OF THE GRID.

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HESE TRANSFORMERS ARE EMPLOYED IN THE POWER PLANTS FORELIVERING POWER TO LOW VOLTAGE LOADS (VOLTAGE BELOWKV).

HESE TRANSFORMERS CONNECTS BETWEEN HV DISTRIBUTIONUSES AND LV DISTRIBUTION BUSES OF THE PLANT.

HEIR RATING WILL BE AROUND 1 TO 5MVA, NATURAL OILOOLING OR AIR COOLED TRANSFORMERS ARE USED.

OME OF THE POINTS RELATED TO STATION AUXILIARYRANSFORMERS ARE LISTED BELOW:

HESE TRANSFORMERS ARE LOCATED IN POWER PLANT TO STEPOWN VOLTAGE FROM 6.6KV TO 415V.

HE RATING FOR THIS TRANSFORMER CORRESPONDS TO THEATING OF THE AUXILIARY LOAD IT SHOULD BE BEARING.

HESE TRANSFORMERS ARE INDOOR TYPE AND USUALLY DRY TYPERANSFORMERS ARE USED.

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THE CONSERVATOR (RESERVOIR)AT TOP PROVIDES OIL TOATMOSPHERE ISOLATION ASCOOLANT LEVEL ANDTEMPERATURE CHANGES.

THE WALLS AND FINS PROVIDEREQUIRED HEAT DISSIPATIONBALANCE

CUTAWAY VIEW OF OIL MMERSED CONSTRUCTION

TRANSFORMER

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SINGLE-PHASE TAPPED AUTOTRANSFORMER WITH OUTPUT VOLTAGE RANGE OF 40% –115% OF INPUT

AUTOTRANSFORMER IS AN ELECTRICAL TRANSFORMER WITH ONLY ONENDING. THE "AUTO“ PREFIX REFERS TO THE SINGLE COIL ACTING ON

SELF AND NOT TO ANY KIND OF AUTOMATIC MECHANISM.

AN AUTOTRANSFORMER, PORTIONS OF THE SAME WINDING ACT AS BOTHE PRIMARY AND SECONDARY SIDES OF THE TRANSFORMER. THE WINDINGS AT LEAST THREE TAPS WHERE ELECTRICAL CONNECTIONS ARE MADE.

TOTRANSFORMERS HAVE THE ADVANTAGES OF OFTEN BEING SMALLER,GHTER, AND CHEAPER THAN TYPICAL DUAL-WINDING TRANSFORMERS, BUTTOTRANSFORMERS HAVE THE DISADVANTAGE OF NOT PROVIDINGECTRICAL ISOLATION.

STEP DOWN VALUES TO SAFE LEVELS FORMEASUREMENT

OTENTIAL TRANSFORMERSALSO CALLED VOLTAGE TRANSFORMERS

STANDARD OUTPUT 120V

URRENT TRANSFORMERSSTANDARD OUTPUT OF 1 OR 5 AMPS

METERING AND RELAYING STANDARDS

CAN PRODUCE HIGH VOLTAGES IF OPEN CIRCUITED

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TANK

RADIATOR/ FAN/PUMP

BUSHINGS

TAP CHANGER

CONSERVATOR

BREATHER

TEMPERATURE INDICATORS

BUCHHOLZ RELAY/OIL SURGE RELAY

OIL LEVEL GAUGE

PRESSURE RELIEF DEVICE (PRD)

VALVES

ROLLER

COOLER CONTROL CUBICLE (MARSHALLING BOX)

REMOTE TAP CHANGER CONTROL CUBICLE (RTCC)44

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RADIATORS ARE USED TOINCREASE THE COOLINGAREA

DUE TO TRANSFORMER OILGETS HEATED UP, HOT OILRISES TO TOP & FLOW TORADIATOR

IN RADIATOR WHILEFLOWING DOWN, OILDISSIPATES HEAT TOCOOLING MEDIUM

COLD OIL AGAIN ENTERSTRANSFORMER AT BOTTOMOF RADIATOR

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ITH THE VARIATION OF TEMPERATURE THERE ISORRESPONDING VARIATION IN THE OIL VOLUME

O ACCOUNT FOR THIS, AN EXPANSION VESSEL CALLEDONSERVATOR IS ADDED TO THE TRANSFORMER WITH AONNECTING PIPE TO THE MAIN TANK

SMALLER TRANSFORMERS THIS VESSEL IS OPENO ATMOSPHERE THROUGH DEHYDRATING BREATHERSO KEEP THE AIR DRY)

LARGER TRANSFORMERS, AN AIR BAG IS MOUNTEDSIDE THE CONSERVATOR WITH THE INSIDE OF BAG OPEN

O ATMOSPHERE THROUGH THE BREATHERS AND THEUTSIDE SURFACE OF THE BAG IN CONTACT WITH THE OILURFACE.

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ICA GEL BREATHER

OTH TRANSFORMER OIL AND CELLULOSIC PAPER AREIGHLY HYGROSCOPIC

APER BEING MORE HYGROSCOPIC THAN THE MINERAL OILO THE MOISTURE, IF NOT EXCLUDED FROM THE OILURFACE IN CONSERVATOR, THIS WILL FIND ITS WAYINALLY INTO THE PAPER INSULATION AND CAUSESEDUCTION INSULATION STRENGTH OF TRANSFORMER.

O MINIMISE THIS THE CONSERVATOR IS ALLOWED TOREATHE ONLY THROUGH THE SILICAGEL COLUMN, WHICHBSORBS THE MOISTURE IN AIR BEFORE IT ENTERS THE-ONSERVATOR AIR SURFACE.

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OST OF THE TRANSFORMER (SMALL TRANSFORMERSAVE ONLY OTI) ARE PROVIDED WITH INDICATORSHAT DISPLACE OIL TEMPERATURE AND WINDINGEMPERATURE

HERE ARE THERMOMETERS POCKETS PROVIDED IN THEANK TOP COVER WHICH HOLD THE SENSING BULLS INHEM

IL TEMPERATURE MEASURED IS THAT OF THE TOP OIL,WHERE AS THE WINDING TEMPERATURE MEASUREMENT ISNDIRECT, THIS IS DONE BY ADDING THEEMPERATURE RISE

OR PROPER FUNCTIONING OR OTI & WTI IT IS ESSENTIALO KEEP THE THERMOMETERS POCKET CLEAN AND FILLED

WITH OIL.53

RANSFORMERS TANK IS A PRESSURE VESSEL AS THE INSIDERESSURE CAN GROUP STEEPLY WHENEVER THERE IS AAULT IN THE WINDINGS AND THE SURROUNDING OIL ISUDDENLY VAPORIZED

ANKS ARE TESTED FOR A PRESSURE WITHSTAND CAPACITYF 0.35 kg/ cm2 TO PREVENT BURSTING OF THE TANK, THESEANKS ARE IN ADDITION PROVIDED WITH EXPANSION VENTSITH A THIN DIAPHRAGM MADE OF

AKELITE/COPPER/GLASS AT THE END

N PRESENT DAY TRANSFORMERS, PRESSURE RELIEFEVICES ARE REPLACING THE EXPANSION VENTS, THESE AREMILAR TO SAFETY VALVES ON BOILERS (SPRING LOADED).

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WORKS AS A PRESSURE RELEASING VALVE

EQUIPPED WITH ALARM/TRIP CONTACT

OPERATING PRESSURE:8 kg/ cm2

WINDING AND TERMINAL FAULTS

CORE FAULTS

TANK AND TRANSFORMER ACCESSORY FAULTS

ON–LOAD TAP CHANGER FAULTS

ABNORMAL OPERATING CONDITIONS

SUSTAINED OR UNCLEARED EXTERNAL FAULTS

THE APPROXIMATE PROPORTION OF FAULTS DUE TO EACH OF THE CAUSES LISTED ABOVE IS SHOWN IN FIGURE

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FAILURES IN TRANSFORMERS CAN BE CLASSIFIEDNTOINDING FAILURES DUE TO SHORT CIRCUITS (TURN-TURN

AULTS, PHASE-PHASE FAULTS, PHASE-GROUND, OPENINDING)

ORE FAULTS (CORE INSULATION FAILURE, SHORTEDAMINATIONS)

RMINAL FAILURES (OPEN LEADS, LOOSE CONNECTIONS,HORT CIRCUITS)

N-LOAD TAP CHANGER FAILURES (MECHANICAL,ECTRICAL, SHORT CIRCUIT, OVERHEATING)

BNORMAL OPERATING CONDITIONS (OVERFLUXING,VERLOADING, OVERVOLTAGE)

XTERNAL FAULTS 57

SOURCES OF ABNORMAL STRESS IN ATRANSFORMER ARE:

OVERLOAD

SYSTEM FAULTS

OVERVOLTAGE

REDUCED SYSTEM FREQUENCY

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VERLOAD CAUSES INCREASED 'COPPER LOSS' AND AONSEQUENT TEMPERATURE RISE, OVERLOADS CAN BEARRIED FOR LIMITED PERIODS

YSTEM SHORT CIRCUITS PRODUCE A RELATIVELY INTENSEATE OF HEATING OF THE FEEDING TRANSFORMERS, THEOPPER LOSS INCREASING IN PROPORTION TO THE SQUAREF THE PER UNIT FAULT CURRENT

RANSIENT OVERVOLTAGES ARISE FROM FAULTS,WITCHING, AND LIGHTNING DISTURBANCES AND AREIABLE TO CAUSE INTERTURN FAULTS

EDUCTION OF SYSTEM FREQUENCY HAS AN EFFECT WITHEGARD TO FLUX DENSITY, SIMILAR TO THAT OFVERVOLTAGE.

NSUFFICIENT OIL LEVEL

EEPAGE OF WATER IN OIL

ROLONGED OVER LOADING

NGLE PHASE LOADING

NBALANCED LOADING

AULTY TERMINATION (IMPROPER SIZED LUGS ETC)

OWER THEFT

ROLONGED SHORT CIRCUIT

AULTY OPERATION OF TAP CHANGER SWITCH

ACK OF INSTALLATION CHECKS60

OURLY THE FOLLOWING PARAMETERS ARE TO BE CHECKED EVERYHOUR AND RECORDED, IF THE OBSERVED VALUE EXCEEDSTHE VALUE GIVEN BY THE SUPPLIER, IMMEDIATE REMEDIALACTION SHOULD BE TAKEN.

1. WINDING TEMPERATURE

2. OIL TEMPERATURE

3. LOAD CURRENT

4. TERMINAL VOLTAGE

NORMALLY, MAXIMUM ALLOWED WINDING TEMPERATUREIS 55ºC ABOVE AMBIENT AND OIL TEMPERATURE IS 45ºCABOVE AMBIENT (ACTUAL ALLOWED VALUE MAY VARYFROM SUPPLIER TO SUPPLIER).

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AILY. OIL LEVEL IN MAIN CONSERVATOR

. OIL LEVEL IN OLTC

. OIL LEVEL IN BUSHING

4. LEAKAGE OF WATER INTO COOLER (OFWF)

. WATER TEMPERATURE (OFWF)

. WATER FLOW (OFWF)

. COLOUR OF SILICA GEL

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UARTERLY CHECKING/ REPLACEMENT

RECONDITIONING OF SILICA GEL BREATHER

CHECKING OF WATER COOLER FUNCTIONING

CHECKING OF COOLING FANS FUNCTIONING

GEAR OIL FOR TAP CHANGER MECHANISM

CHECKING OF COOLING PUMPS AND MOTOR FUNCTIONING

ALF YEARLY

INSPECTION OF ALL GASKETS AND JOINTS

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NNUALLY

1. PROTECTIVE RELAYS, ALARMS, METERS AND CIRCUITSTO BE CHECKED AND CALIBRATED

2. IR (INSULATION RESISTANCE) VALUE AND POLARISATION INDEX

3. TAN DELTA AND CAPACITANCE OF BUSHINGS

4. BDV (BREAK DOWN VOLTAGE) OF TRANSFORMER OIL

5. OIL RESISTIVITY

6. POWER FACTOR OF OIL

7. INTERFACIAL TENSION OF OIL

8. ACIDITY AND SLUDGE OF OIL

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ANNUALLY

9. FLASH POINT OF OIL

10. WATER CONTENT OF OIL

11. DISSOLVED GAS ANALYSIS

12. REPLACING OF OLTC OIL

13. THERMO VISION SCANNING

14. EARTHING MEASUREMENTS

15. TAN DELTA AND CAPACITANCE OF WINDING

NCE IN FIVE YEARS 1. FURAN ANALYSIS (ONCE IN A YEAR AFTER THE

FIRST 5 YEARS)

. OVERHAULING OF OLTC DIVERTER SWITCH (ONCEIN 5 YEARS OR AFTER COMPLETION OF 50,000OPERATIONS WHICHEVER IS EARLIER).

NCE IN TEN YEARS

OVERHAUL, INSPECTION INCLUDING LIFTING OF CORE AND WINDING.

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URAN ANALYSIS ON TRANSFORMER OIL INDICATES THEEGREE OF DEGRADATION OF THE TRANSFORMER PAPERNSULATION.

HIS IS USUALLY DONE IN TRANSFORMERS AGING ABOVE 15EARS.

URAN INDICATES THE COMPOUNDS OF CARBON ANDYDROGEN.

WHEN THE FURAN COUNT IS ABOVE 2500PPB, IT MEANS THERANSFORMER IS ABOUT TO FAIL.

URAN ANALYSIS IS IMPORTANT IN DECIDING WHEN TOISCARD A TRANSFORMER UNIT OR RETAIN.

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RK JAISWAL

• +91 9650993009• jaiswalrk1950@gmail.com

NK TUTEJA

• +91 9810174125• narindertuteja@gmail.com

THANK YOU!