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PROTECTION OFPROTECTION OF
TRANSFORMERSTRANSFORMERS
Presented byPresented by
AMAR NAYYARAMAR NAYYAR
FINAL YEAR ELECTRICALSFINAL YEAR ELECTRICALS
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WHAT IS A TRANSFORMER?WHAT IS A TRANSFORMER?
TRANSFORMER IS ATRANSFORMER IS ASTATIC DEVICE WHICHSTATIC DEVICE WHICH
TRANSFORMS A.C.TRANSFORMS A.C.
ELECTRICAL POWERELECTRICAL POWERFROM ONE VOLTAGEFROM ONE VOLTAGE
TO ANOTHERTO ANOTHERVOLTAGE KEEPINGVOLTAGE KEEPINGTHE FREQUENCY SAMETHE FREQUENCY SAME
BY ELECTROMAGNETICBY ELECTROMAGNETICINDUCTION.INDUCTION.
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TYPES OF TRANSFORMERTYPES OF TRANSFORMER
BY APPLICATIONBY APPLICATION 1. DISTRIBUTION TRANSFORMER1. DISTRIBUTION TRANSFORMER 2.POWER TRANSFORMER2.POWER TRANSFORMER
3.CURRENT TRANSFORMER3.CURRENT TRANSFORMER 4.POTENTIAL TRANSFORMER4.POTENTIAL TRANSFORMER
5.FURNACE TRANSFORMER5.FURNACE TRANSFORMER
6.BOOSTER TRANSFORMER6.BOOSTER TRANSFORMER 7.RECTIFIER TRANSFORMER7.RECTIFIER TRANSFORMER 8.LOCOMOTIVE TRANSFORMER8.LOCOMOTIVE TRANSFORMER
9.MINING TRANSFORMER9.MINING TRANSFORMER 10.PHASE SHIFTING TRANSFORMER10.PHASE SHIFTING TRANSFORMER
11.WELDING TRANSFORMER11.WELDING TRANSFORMER 1
2.HIGH VOLTAGE TESTING/SC TESTING TRF.12.HIGH VOLTAGE TESTING/SC TESTING TRF.
13.GROUNDING TRANSFORMERS13.GROUNDING TRANSFORMERS 14.CONVERTER TRANSFORMER14.CONVERTER TRANSFORMER
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DISTRIBUTION TRANSFORMERDISTRIBUTION TRANSFORMER
TRANSFORMER WHICH IS USED FORTRANSFORMER WHICH IS USED FOR
THE PURPOSE OF DISTRIBUTION OFTHE PURPOSE OF DISTRIBUTION OF
POWER.POWER. 11KV/433V is the standard voltage rating.11KV/433V is the standard voltage rating.
STANDARD KVA ratings areSTANDARD KVA ratings are
25,63,100
,160,200
,250,315,4
00,500
,630,75
0,25,63,
100,160,200
,250,315,4
00,500
,630,75
0,
1000 , 1250,1500,2000,2500 KVA.1000 , 1250,1500,2000,2500 KVA.
ISIS--2026 is the NATIONAL I S STANDARD.2026 is the NATIONAL I S STANDARD.
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MAIN FEATURESMAIN FEATURES
OUTDOOR,OIL COOLED, 3 PHASE,50HZOUTDOOR,OIL COOLED, 3 PHASE,50HZ
PRIMARY IS DELTA CONNECTED ANDPRIMARY IS DELTA CONNECTED AND
SECONDARY IS STAR CONNECTED.SECONDARY IS STAR CONNECTED. NATURALY COOLED (ONAN TYPE).NATURALY COOLED (ONAN TYPE).
AMONGST ALL THE TYPES OFAMONGST ALL THE TYPES OF
TRANSFORMERS THIS IS THE MOSTTRANSFORMERS THIS IS THE MOSTREQUIRED AND MOST USED TYPE.REQUIRED AND MOST USED TYPE.
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PARTS OF TRANSFORMERPARTS OF TRANSFORMER
MAIN TANKMAIN TANK RADIATORSRADIATORS CONSERVATORCONSERVATOR EXPLOSION VENTEXPLOSION VENT
LIFTING LUGSLIFTING LUGS AIR RELEASE PLUGAIR RELEASE PLUG OIL LEVEL INDICATOROIL LEVEL INDICATOR TAP CHANGERTAP CHANGER WHEELSWHEELS HV/LV BUSHINGSHV/LV BUSHINGS
FILTER VALVESFILTER VALVES OIL FILLING PLUGOIL FILLING PLUG DRAIN PLUGDRAIN PLUG CABLE BOXCABLE BOX
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TESTING OF TRANSFORMERTESTING OF TRANSFORMER
TESTING IS CARRIED OUT AS PER ISTESTING IS CARRIED OUT AS PER IS--2026.2026. ROUTINE , TYPE TESTS & SPECIAL TESTSROUTINE , TYPE TESTS & SPECIAL TESTS
ROUTINE TESTS ( TO BE CARRIED OUT ON EACH JOB)ROUTINE TESTS ( TO BE CARRIED OUT ON EACH JOB)
1.Measurement of winding resistance1.Measurement of winding resistance 2.Measurement of insulation resistance2.Measurement of insulation resistance 3.Seperate source voltage withstand test (High Voltage tests on HV & LV)3.Seperate source voltage withstand test (High Voltage tests on HV & LV) 4.Induced Over voltage Withstand test (DVDF test)4.Induced Over voltage Withstand test (DVDF test)
5.Measurement of voltage ratio5.Measurement of voltage ratio 6.Measurement of NO LOAD LOSS & current.6.Measurement of NO LOAD LOSS & current.
7.Measurement of LOAD LOSS & IMPEDENCE.(EFFICIENCY & REGULATION)7.Measurement of LOAD LOSS & IMPEDENCE.(EFFICIENCY & REGULATION)
8.Vector Group Verification8.Vector Group Verification 9.Oil BDV test.9.Oil BDV test. 10.Tests on OLTC (if Attached)10.Tests on OLTC (if Attached)
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TYPE TESTSTYPE TESTS
THESE TESTS ARE CARRIED OUTTHESE TESTS ARE CARRIED OUT
ONLY ON ONE TRANSFORMER OFONLY ON ONE TRANSFORMER OFTHE LOT.THE LOT.
All routine testsAll routine tests
Additionally following tests are included inAdditionally following tests are included in
type teststype tests
1.1. Lightening Impulse test.Lightening Impulse test.
2.2. Temperature rise testTemperature rise test
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SPECIAL TESTSSPECIAL TESTS
Additional Impulse testAdditional Impulse test
Short circuit testShort circuit test
Measurement of zero Phase sequenceMeasurement of zero Phase sequenceImpedance test.Impedance test.
Measurement of acoustic noise level.Measurement of acoustic noise level.
Measurement of harmonics of the no loadMeasurement of harmonics of the no loadcurrent.current.
Magnetic balance test.Magnetic balance test.
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ROUTINE TESTSROUTINE TESTS
1.Measurement of winding resistance1.Measurement of winding resistance
This test measures the resistance of the HV & LVThis test measures the resistance of the HV & LV
winding. The values of resistance should bewinding. The values of resistance should bebalance for all three phases and should matchbalance for all three phases and should matchthe designed values.the designed values.
Equipment used : Digital resistance meter.Equipment used : Digital resistance meter.
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ROUTINE TESTSROUTINE TESTS
2.Measurement of insulation resistance2.Measurement of insulation resistance
Measures the insulation resistance of HV & LVMeasures the insulation resistance of HV & LV
windings with respect to earth (body) andwindings with respect to earth (body) andbetween LV & HV winding.between LV & HV winding.
INSULATION TESTER OR MEGGER ISINSULATION TESTER OR MEGGER IS
USED.USED.
Recommended Values areRecommended Values are
2000Mohms for HV & 500 Mohms for LV.2000Mohms for HV & 500 Mohms for LV.
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ROUTINE TESTSROUTINE TESTS
3.Seperate source voltage withstand test (High Voltage tests on3.Seperate source voltage withstand test (High Voltage tests onHV & LV)HV & LV)-- This test checks the insulation property betweenThis test checks the insulation property betweenPrimary to earth, Secondary to earth and between Primary &Primary to earth, Secondary to earth and between Primary &Secondary.Secondary.
HV high voltage test : LV winding connected together and earthed.HV high voltage test : LV winding connected together and earthed.HV winding connected together and given 28 KV ( for 11KVHV winding connected together and given 28 KV ( for 11KVtransformer) for 1 minute.transformer) for 1 minute.
LV high Voltage test : HV winding connected together and earthed.LV high Voltage test : HV winding connected together and earthed.LV winding connected together and given 3 KV for 1 minute.LV winding connected together and given 3 KV for 1 minute.
Equipment used : High Voltage tester (100KV & 3KV)Equipment used : High Voltage tester (100KV & 3KV)
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ROUTINE TESTSROUTINE TESTS
4.Induced Over voltage Withstand test (DVDF test)4.Induced Over voltage Withstand test (DVDF test)--This test checks the inter turn insulation.This test checks the inter turn insulation.
For a 11KV/433V transformer,866 Volts are applied atFor a 11KV/433V transformer,866 Volts are applied atthe 433V winding with the help of a Generator for 1the 433V winding with the help of a Generator for 1minute. This induces 22KV on 11KV side. Theminute. This induces 22KV on 11KV side. Thefrequency of the 866V supply is also increased tofrequency of the 866V supply is also increased to100HZ.100HZ.
Equipment used : MOTOR GENERATOR SETEquipment used : MOTOR GENERATOR SET
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ROUTINE TESTSROUTINE TESTS
5.Measurement of voltage ratio5.Measurement of voltage ratio
This test measures the voltage ratio as per the customersThis test measures the voltage ratio as per the customersrequirement.requirement.
V1/V2 = N1/N2V1/V2 = N1/N2
The voltage ratio is equal to the turns ratio in aThe voltage ratio is equal to the turns ratio in atransformer. Using this principle, the turns ratio istransformer. Using this principle, the turns ratio is
measured with the help of a turns ratio meter. If it ismeasured with the help of a turns ratio meter. If it iscorrect , then the voltage ratio is assumed to be correct.correct , then the voltage ratio is assumed to be correct.
Equipment used : Turns RatiometerEquipment used : Turns Ratiometer
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ROUTINE TESTSROUTINE TESTS
6.Measurement of NO LOAD LOSS & current.6.Measurement of NO LOAD LOSS & current.
The iron losses and no load current are measured inThe iron losses and no load current are measured inthis test. The 433V winding is charged at 433V supplythis test. The 433V winding is charged at 433V supply
& the 11KV winding is left open .The power consumed& the 11KV winding is left open .The power consumedby the transformer at no load is the no load loss in theby the transformer at no load is the no load loss in thetransformer.transformer.
Effect of actual frequency must be taken into account.Effect of actual frequency must be taken into account.
Equipment used : Wattmeters or power analyser.Equipment used : Wattmeters or power analyser.
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ROUTINE TESTSROUTINE TESTS
7.Measurement of LOAD LOSS &7.Measurement of LOAD LOSS &
IMPEDENCE.(EFFICIENCY &IMPEDENCE.(EFFICIENCY ®ULATION)REGULATION)
This test measures the power consumed by theThis test measures the power consumed by thetransformer when the 433V winding is shorttransformer when the 433V winding is short
circuited and The rated current is passedcircuited and The rated current is passed
through the 11KV winding.through the 11KV winding.
Equipment used : Wattmeters or power analyser.Equipment used : Wattmeters or power analyser.
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ROUTINE TESTSROUTINE TESTS
8.Vector Group Verification test8.Vector Group Verification test
This test verifies the DynThis test verifies the Dyn--11 vector group of a11 vector group of a
distribution transformer.distribution transformer.
Equipment used : voltmeter.Equipment used : voltmeter.
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ROUTINE TESTSROUTINE TESTS
Oil BDV TEST.Oil BDV TEST.
Oil breakdown voltage is checked as per ISOil breakdown voltage is checked as per IS--335.335.
100 mm L X 70 mm B X 80 mm Ht. glass pot.100 mm L X 70 mm B X 80 mm Ht. glass pot.500ml Oil sample.500ml Oil sample.
Spherical electrodes with gap of 2.5 mmSpherical electrodes with gap of 2.5 mm
Recommended value : 60KVRecommended value : 60KVEquipment used : OIL BDV TEST SET.Equipment used : OIL BDV TEST SET.
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TYPE TESTSTYPE TESTS
LIGHTENING IMPULSE TESTLIGHTENING IMPULSE TESTAll the dielectric tests check the insulation level of the job.All the dielectric tests check the insulation level of the job.Impulse generator is used to produce the specified voltage impulseImpulse generator is used to produce the specified voltage impulse
wave of1.2/50 micro seconds wavewave of1.2/50 micro seconds wave
One impulse of a reduced voltage between 50 to 75% of the fullOne impulse of a reduced voltage between 50 to 75% of the fulltest voltage and subsequent three impulses at full voltage.test voltage and subsequent three impulses at full voltage.
For a three phase transformer, impulse is carried out on all threeFor a three phase transformer, impulse is carried out on all threephases in succession.phases in succession.
The voltage is applied on each of the line terminal in succession,The voltage is applied on each of the line terminal in succession,
keeping the other terminals earthed.keeping the other terminals earthed.The current and voltage wave shapes are recorded on theThe current and voltage wave shapes are recorded on the
oscilloscope and any distortion in the wave shape is the criteriaoscilloscope and any distortion in the wave shape is the criteriafor failure.for failure.
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SPECIAL TESTSPECIAL TEST
Short circuit withstand ability test.Short circuit withstand ability test.This tests measures the ability of the transformer to withstand the mechanicalThis tests measures the ability of the transformer to withstand the mechanical
and thermal stresses caused by the external short circuit.and thermal stresses caused by the external short circuit.HV terminals are connected to the supply bus of the testing plant. The LV isHV terminals are connected to the supply bus of the testing plant. The LV is
short circuited. The testing plant parameters are such adjusted to give theshort circuited. The testing plant parameters are such adjusted to give the
rated short circuit current.rated short circuit current.Supply is made on and closed after specified duration of short circuit. The recordSupply is made on and closed after specified duration of short circuit. The record
of current wave form is noted.of current wave form is noted.There should not be any mechanical distortion, fire to the transformer during thisThere should not be any mechanical distortion, fire to the transformer during this
test. Similarly no wave form distortion. The transformer should alsotest. Similarly no wave form distortion. The transformer should alsowithstand the routine tests after the short circuit test.withstand the routine tests after the short circuit test.
The reactance of the winding measured before and after the S.C. test should notThe reactance of the winding measured before and after the S.C. test should notvary beyond the limits stated in the IS2026.vary beyond the limits stated in the IS2026.
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MAINTENANCE OFMAINTENANCE OF
TRANSFORMERTRANSFORMER
Transformer is the heart of any power system.Transformer is the heart of any power system.
Hence preventive maintenance is always costHence preventive maintenance is always costeffective and time saving. Any failure to theeffective and time saving. Any failure to the
transformer can extremely affect the wholetransformer can extremely affect the wholefunctioning of the organization.functioning of the organization.
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MAINTENANCE PROCEDUREMAINTENANCE PROCEDURE
OIL :OIL :
1.1. Oil level checking. Leakages to be attended.Oil level checking. Leakages to be attended.
2.2. Oil BDV & acidity checking at regularOil BDV & acidity checking at regularintervals. If acidity is between 0.5 to 1mgintervals. If acidity is between 0.5 to 1mg
KOH, oil should be kept under observation.KOH, oil should be kept under observation.
3.3.
BDV, Color and smell of oil are indicative.BDV, Color and smell of oil are indicative.
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MAINTENANCE PROCEDUREMAINTENANCE PROCEDURE
1.1. Sludge, dust, dirt ,moisture can be removed bySludge, dust, dirt ,moisture can be removed byfiltration.filtration.
2.2. Oil when topped up shall be of the same make. ItOil when topped up shall be of the same make. It
may lead to sludge formation and acidic contents.may lead to sludge formation and acidic contents. Insulation resistance of the transformer should beInsulation resistance of the transformer should be
checked once in 6 months.checked once in 6 months.
Megger values along with oil values indicate theMegger values along with oil values indicate thecondition of transformer.condition of transformer.
Periodic Dissolved Gas Analysis can be carried out.Periodic Dissolved Gas Analysis can be carried out.
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MAINTENANCEMAINTENANCE
BUSHINGSBUSHINGS
Bushings should be cleaned and inspected for anyBushings should be cleaned and inspected for any
cracks.cracks.Dust & dirt deposition, Salt or chemicalDust & dirt deposition, Salt or chemical
deposition, cement or acid fumes depositionsdeposition, cement or acid fumes depositions
should be carefully noted and rectified.should be carefully noted and rectified.
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MAINTENANCEMAINTENANCE
Periodic checking of any loose connections of thePeriodic checking of any loose connections of theterminations of HV & LV side.terminations of HV & LV side.
Breather examination. Dehydration of Silica gel ifBreather examination. Dehydration of Silica gel ifnecessary.necessary.
Explosion vent diaphragm examination.Explosion vent diaphragm examination. Conservator to be cleaned from inside after every threeConservator to be cleaned from inside after every three
years.years. Regular inspection of OIL & WINDINGRegular inspection of OIL & WINDING
TEMPERATURE METER readings.TEMPERATURE METER readings. Cleanliness in the Substation yard with all nets, vines,Cleanliness in the Substation yard with all nets, vines,
shrubs removed.shrubs removed.
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PROTECTION OFPROTECTION OF
TRANSFORMERSTRANSFORMERS
The best way of protecting a transformer is toThe best way of protecting a transformer is to
have good preventive maintenance schedule.have good preventive maintenance schedule.
Oil Temperature Indicators.Oil Temperature Indicators.Winding Temperature indicators.Winding Temperature indicators.
Buchholz Relay.Buchholz Relay.
Magnetic Oil level Gauge.Magnetic Oil level Gauge. Explosion Vent.Explosion Vent.
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PROTECTION OFPROTECTION OF
TRANSFORMERSTRANSFORMERS
HT fuse & D.O. fuse.HT fuse & D.O. fuse.
LT circuit breaker.LT circuit breaker.
HT Circuit breaker with Over load, Earth FaultHT Circuit breaker with Over load, Earth Faultrelay tripping.relay tripping.
Oil Surge Relay for OLTC.Oil Surge Relay for OLTC.
PRV for OLTC.PRV for OLTC.
HORN GAPS & Lightening Arrestor.HORN GAPS & Lightening Arrestor. Breather.Breather.
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FAILURES & CAUSESFAILURES & CAUSES
Insufficient Oil level.Insufficient Oil level. Seepage of water in oil.Seepage of water in oil. Prolonged Over loading.Prolonged Over loading.
Single Phase loading.Single Phase loading. Unbalanced loading.Unbalanced loading. Faulty Termination (Improper sized lugs etc)Faulty Termination (Improper sized lugs etc) Power Theft.Power Theft.
Prolonged Short Circuit.Prolonged Short Circuit. Faulty operation of tap changer switch.Faulty operation of tap changer switch. Lack of installation checks.Lack of installation checks.
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FAILURES & CAUSESFAILURES & CAUSES
Faulty designFaulty design
Poor WorkmanshipPoor Workmanship
Improper formation of core.Improper formation of core.Improper core bolt insulation.Improper core bolt insulation.Burr to the lamination bladesBurr to the lamination bladesImproper brazing of joints.Improper brazing of joints.
Burr /sharp edges to the winding conductor.Burr /sharp edges to the winding conductor.Incomplete drying.Incomplete drying.Bad insulation covering.Bad insulation covering.Insufficient cooling ducts in the winding.Insufficient cooling ducts in the winding.
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FAILURES & CAUSESFAILURES & CAUSES
Bad Quality of raw material.Bad Quality of raw material. Transit damaged transformers.Transit damaged transformers.
After failure , transformer is removed andAfter failure , transformer is removed and
replaced with new/repaired one withoutreplaced with new/repaired one withoutremoving the cause of failure which results inremoving the cause of failure which results inimmediate or short time failure.immediate or short time failure.