AMAR NAYYAR

8/3/2019 AMAR NAYYAR

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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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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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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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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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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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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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7.Measurement of LOAD LOSS &7.Measurement of LOAD LOSS &

IMPEDENCE.(EFFICIENCY &IMPEDENCE.(EFFICIENCY &REGULATION)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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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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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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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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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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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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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.

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