TESTING, TESTING, MAINTENANCE & MAINTENANCE & PROTECTION OF PROTECTION OF DISTRIBUTION DISTRIBUTION

TRANSFORMERSTRANSFORMERSPresented byPresented by

PRASHANT P. NANKARPRASHANT P. NANKARTRANS-DELTA TRANS-DELTA ELECTRICALSELECTRICALS

WHAT IS A WHAT IS A TRANSFORMER?TRANSFORMER?

TRANSFORMER IS A TRANSFORMER IS A STATIC DEVICE STATIC DEVICE WHICH WHICH TRANSFORMS A.C. TRANSFORMS A.C. ELECTRICAL POWER ELECTRICAL POWER FROM ONE VOLTAGE FROM ONE VOLTAGE TO ANOTHER TO ANOTHER VOLTAGE KEEPING VOLTAGE KEEPING THE FREQUENCY THE FREQUENCY SAME BY SAME BY ELECTROMAGNETIC ELECTROMAGNETIC INDUCTION.INDUCTION.

TYPES OF TRANSFORMER TYPES 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 12.HIGH VOLTAGE TESTING/SC TESTING TRF.12.HIGH VOLTAGE TESTING/SC TESTING TRF. 13.GROUNDING TRANSFORMERS13.GROUNDING TRANSFORMERS 14.CONVERTER TRANSFORMER14.CONVERTER TRANSFORMER

DISTRIBUTION DISTRIBUTION TRANSFORMERTRANSFORMER

TRANSFORMER WHICH IS USED FOR THE TRANSFORMER WHICH IS USED FOR THE PURPOSE OF DISTRIBUTION OF POWER.PURPOSE OF DISTRIBUTION OF POWER.

11KV/433V is the standard voltage rating.11KV/433V is the standard voltage rating. STANDARD KVA ratings areSTANDARD KVA ratings are

25,63,100,160,200,250,315,400,500,630,7525,63,100,160,200,250,315,400,500,630,750 , 1000 , 1250,1500,2000,2500 KVA.0 , 1000 , 1250,1500,2000,2500 KVA.

IS-2026 is the NATIONAL I S STANDARD.IS-2026 is the NATIONAL I S STANDARD.

MAIN FEATURESMAIN FEATURES OUTDOOR,OIL COOLED, 3 OUTDOOR,OIL COOLED, 3

PHASE,50HZPHASE,50HZ PRIMARY IS DELTA CONNECTED AND PRIMARY IS DELTA CONNECTED AND

SECONDARY IS STAR CONNECTED.SECONDARY IS STAR CONNECTED. NATURALY COOLED (ONAN TYPE).NATURALY COOLED (ONAN TYPE). AMONGST ALL THE TYPES OF AMONGST ALL THE TYPES OF

TRANSFORMERS THIS IS THE MOST TRANSFORMERS THIS IS THE MOST REQUIRED AND MOST USED TYPE.REQUIRED AND MOST USED TYPE.

PARTS OF PARTS OF TRANSFORMERTRANSFORMER

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

TESTING OF TESTING OF TRANSFORMERTRANSFORMER

TESTING IS CARRIED OUT AS PER IS-2026.TESTING IS CARRIED OUT AS PER IS-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 3.Seperate source voltage withstand test (High Voltage tests on

HV & LV)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 & 7.Measurement of LOAD LOSS & IMPEDENCE.(EFFICIENCY &

REGULATION)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)

TYPE TESTSTYPE TESTSTHESE TESTS ARE CARRIED OUT THESE TESTS ARE CARRIED OUT ONLY ON ONE TRANSFORMER ONLY ON ONE TRANSFORMER OF THE LOT.OF THE LOT.

All routine testsAll routine tests Additionally following tests are Additionally following tests are

included in type testsincluded in type tests1.1. Lightening Impulse test.Lightening Impulse test.2.2. Temperature rise testTemperature rise test

SPECIAL TESTSSPECIAL TESTS Additional Impulse testAdditional Impulse test Short circuit testShort circuit test Measurement of zero Phase Measurement of zero Phase

sequence Impedance test.sequence Impedance test. Measurement of acoustic noise level.Measurement of acoustic noise level. Measurement of harmonics of the no Measurement of harmonics of the no

load current.load current. Magnetic balance test.Magnetic balance test.

ROUTINE TESTSROUTINE TESTS 1.Measurement of winding resistance1.Measurement of winding resistanceThis test measures the resistance of This test measures the resistance of

the HV & LV winding. The values of the HV & LV winding. The values of resistance should be balance for all resistance should be balance for all three phases and should match the three phases and should match the designed values.designed values.

Equipment used : Digital resistance Equipment used : Digital resistance meter.meter.

ROUTINE TESTSROUTINE TESTS 2.Measurement of insulation resistance2.Measurement of insulation resistance Measures the insulation resistance of Measures the insulation resistance of

HV & LV windings with respect to earth HV & LV windings with respect to earth (body) and between LV & HV winding.(body) and between LV & HV winding.

INSULATION TESTER OR MEGGER IS INSULATION TESTER OR MEGGER IS USED.USED.Recommended Values areRecommended Values are2000Mohms for HV & 500 Mohms for 2000Mohms for HV & 500 Mohms for LV.LV.

ROUTINE TESTSROUTINE TESTS 3.Seperate source voltage withstand test (High 3.Seperate source voltage withstand test (High

Voltage tests on HV & LV)- This test checks the Voltage tests on HV & LV)- This test checks the insulation property between Primary to earth, insulation property between Primary to earth, Secondary to earth and between Primary & Secondary to earth and between Primary & Secondary.Secondary.

HV high voltage test : LV winding connected together HV high voltage test : LV winding connected together and earthed. HV winding connected together and and earthed. HV winding connected together and given 28 KV ( for 11KV transformer) for 1 minute.given 28 KV ( for 11KV transformer) for 1 minute.

LV high Voltage test : HV winding connected together LV high Voltage test : HV winding connected together and earthed. LV winding connected together and and earthed. LV winding connected together and given 3 KV for 1 minute.given 3 KV for 1 minute.

Equipment used : High Voltage tester ( 100KV & 3KV)Equipment used : High Voltage tester ( 100KV & 3KV)

ROUTINE TESTSROUTINE TESTS 4.Induced Over voltage Withstand test (DVDF 4.Induced Over voltage Withstand test (DVDF

test)- This test checks the inter turn insulation.test)- This test checks the inter turn insulation.

For a 11KV/433V transformer,866 Volts are For a 11KV/433V transformer,866 Volts are applied at the 433V winding with the help of a applied at the 433V winding with the help of a Generator for 1 minute. This induces 22KV on Generator for 1 minute. This induces 22KV on 11KV side. The frequency of the 866V supply is 11KV side. The frequency of the 866V supply is also increased to 100HZ. also increased to 100HZ. Equipment used : MOTOR GENERATOR SETEquipment used : MOTOR GENERATOR SET

ROUTINE TESTSROUTINE TESTS 5.Measurement of voltage ratio5.Measurement of voltage ratio This test measures the voltage ratio as per This test measures the voltage ratio as per

the customer’s requirement.the customer’s requirement.V1/V2 = N1/N2V1/V2 = N1/N2The voltage ratio is equal to the turns ratio in The voltage ratio is equal to the turns ratio in

a transformer. Using this principle, the a transformer. Using this principle, the turns ratio is measured with the help of a turns ratio is measured with the help of a turns ratio meter. If it is correct , then the turns ratio meter. If it is correct , then the voltage ratio is assumed to be correct.voltage ratio is assumed to be correct.

Equipment used : Turns RatiometerEquipment used : Turns Ratiometer

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 The iron losses and no load current are measured in this test. The 433V winding is measured in this test. The 433V winding is charged at 433V supply & the 11KV winding is charged at 433V supply & the 11KV winding is left open .The power consumed by the left open .The power consumed by the transformer at no load is the no load loss in the transformer at no load is the no load loss in the transformer. transformer. Effect of actual frequency must be taken into Effect of actual frequency must be taken into account.account.

Equipment used : Wattmeters or power analyser.Equipment used : Wattmeters or power analyser.

ROUTINE TESTSROUTINE TESTS 7.Measurement of LOAD LOSS & 7.Measurement of LOAD LOSS &

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

This test measures the power consumed by This test measures the power consumed by the transformer when the 433V winding the transformer when the 433V winding is short circuited and The rated current is short circuited and The rated current is passed through the 11KV winding.is passed through the 11KV winding.

Equipment used : Wattmeters or power Equipment used : Wattmeters or power analyser.analyser.

ROUTINE TESTSROUTINE TESTS 8.Vector Group Verification test8.Vector Group Verification testThis test verifies the Dyn-11 vector This test verifies the Dyn-11 vector

group of a distribution transformer.group of a distribution transformer.

Equipment used : voltmeter.Equipment used : voltmeter.

ROUTINE TESTSROUTINE TESTS Oil BDV TEST.Oil BDV TEST.Oil breakdown voltage is checked as per IS-Oil breakdown voltage is checked as per IS-

335.335.100 mm L X 70 mm B X 80 mm Ht. glass 100 mm L X 70 mm B X 80 mm Ht. glass

pot.pot.500ml Oil sample.500ml Oil sample.Spherical electrodes with gap of 2.5 mmSpherical electrodes with gap of 2.5 mmRecommended value : 60KV Recommended value : 60KV Equipment used : OIL BDV TEST SET.Equipment used : OIL BDV TEST SET.

TYPE TESTSTYPE TESTS LIGHTENING IMPULSE TESTLIGHTENING IMPULSE TESTAll the dielectric tests check the insulation level of the All the dielectric tests check the insulation level of the

job.job.Impulse generator is used to produce the specified Impulse generator is used to produce the specified

voltage impulse wave of 1.2/50 micro seconds wavevoltage impulse wave of 1.2/50 micro seconds waveOne impulse of a reduced voltage between 50 to 75% of One impulse of a reduced voltage between 50 to 75% of

the full test voltage and subsequent three impulses at the full test voltage and subsequent three impulses at full voltage.full voltage.

For a three phase transformer, impulse is carried out on For a three phase transformer, impulse is carried out on all three phases in succession.all three phases in succession.

The voltage is applied on each of the line terminal in The voltage is applied on each of the line terminal in succession, keeping the other terminals earthed.succession, keeping the other terminals earthed.

The current and voltage wave shapes are recorded on The current and voltage wave shapes are recorded on the oscilloscope and any distortion in the wave shape the oscilloscope and any distortion in the wave shape is the criteria for failure.is the criteria for failure.

SPECIAL TESTSPECIAL TEST Short circuit withstand ability test.Short circuit withstand ability test.This tests measures the ability of the transformer to withstand This tests measures the ability of the transformer to withstand

the mechanical and thermal stresses caused by the external the mechanical and thermal stresses caused by the external short circuit.short circuit.

HV terminals are connected to the supply bus of the testing HV terminals are connected to the supply bus of the testing plant. The LV is short circuited. The testing plant plant. The LV is short circuited. The testing plant parameters are such adjusted to give the rated short circuit parameters are such adjusted to give the rated short circuit current.current.

Supply is made on and closed after specified duration of short Supply is made on and closed after specified duration of short circuit. The record of current wave form is noted.circuit. The record of current wave form is noted.

There should not be any mechanical distortion, fire to the There should not be any mechanical distortion, fire to the transformer during this test. Similarly no wave form transformer during this test. Similarly no wave form distortion. The transformer should also withstand the distortion. The transformer should also withstand the routine tests after the short circuit test.routine tests after the short circuit test.

The reactance of the winding measured before and after the The reactance of the winding measured before and after the S.C. test should not vary beyond the limits stated in the S.C. test should not vary beyond the limits stated in the IS2026.IS2026.

MAINTENANCE OF MAINTENANCE OF TRANSFORMERTRANSFORMER

Transformer is the heart of any Transformer is the heart of any power system. Hence preventive power system. Hence preventive maintenance is always cost maintenance is always cost effective and time saving. Any effective and time saving. Any failure to the transformer can failure to the transformer can extremely affect the whole extremely affect the whole functioning of the organization. functioning of the organization.

MAINTENANCE MAINTENANCE PROCEDUREPROCEDURE

OIL : OIL : 1.1. Oil level checking. Leakages to be Oil level checking. Leakages to be

attended.attended.2.2. Oil BDV & acidity checking at regular Oil BDV & acidity checking at regular

intervals. If acidity is between 0.5 to intervals. If acidity is between 0.5 to 1mg KOH, oil should be kept under 1mg KOH, oil should be kept under observation.observation.

3.3. BDV, Color and smell of oil are BDV, Color and smell of oil are indicative.indicative.

MAINTENANCE MAINTENANCE PROCEDUREPROCEDURE

1.1. Sludge, dust, dirt ,moisture can be removed by Sludge, dust, dirt ,moisture can be removed by filtration.filtration.

2.2. Oil when topped up shall be of the same make. Oil when topped up shall be of the same make. It may lead to sludge formation and acidic It may lead to sludge formation and acidic contents. contents.

Insulation resistance of the transformer should Insulation resistance of the transformer should be checked once in 6 months.be checked once in 6 months.

Megger values along with oil values indicate Megger values along with oil values indicate the condition of transformer.the condition of transformer.

Periodic Dissolved Gas Analysis can be carried Periodic Dissolved Gas Analysis can be carried out.out.

MAINTENANCEMAINTENANCE BUSHINGSBUSHINGSBushings should be cleaned and Bushings should be cleaned and

inspected for any cracks.inspected for any cracks.Dust & dirt deposition, Salt or Dust & dirt deposition, Salt or

chemical deposition, cement or acid chemical deposition, cement or acid fumes depositions should be fumes depositions should be carefully noted and rectified.carefully noted and rectified.

MAINTENANCEMAINTENANCE Periodic checking of any loose connections Periodic checking of any loose connections

of the terminations of HV & LV side.of the terminations of HV & LV side. Breather examination. Dehydration of Breather examination. Dehydration of

Silica gel if necessary.Silica gel if necessary. Explosion vent diaphragm examination. Explosion vent diaphragm examination. Conservator to be cleaned from inside after Conservator to be cleaned from inside after

every three years.every three years. Regular inspection of OIL & WINDING Regular inspection of OIL & WINDING

TEMPERATURE METER readings.TEMPERATURE METER readings. Cleanliness in the Substation yard with all Cleanliness in the Substation yard with all

nets, vines, shrubs removed.nets, vines, shrubs removed.

PROTECTION OF PROTECTION OF TRANSFORMERSTRANSFORMERS

The best way of protecting a The best way of protecting a transformer is to have good transformer is to have good preventive maintenance schedule.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.

PROTECTION OF PROTECTION OF TRANSFORMERSTRANSFORMERS

HT fuse & D.O. fuse.HT fuse & D.O. fuse. LT circuit breaker.LT circuit breaker. HT Circuit breaker with Over load, HT Circuit breaker with Over load,

Earth Fault relay tripping.Earth Fault 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.

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 Faulty Termination (Improper sized lugs

etc)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.

FAILURES & CAUSESFAILURES & CAUSES

Faulty designFaulty design

Poor WorkmanshipPoor WorkmanshipImproper 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.

FAILURES & CAUSESFAILURES & CAUSES

Bad Quality of raw material.Bad Quality of raw material. Transit damaged transformers.Transit damaged transformers. After failure , transformer is removed After failure , transformer is removed

and replaced with new/repaired one and replaced with new/repaired one without removing the cause of failure without removing the cause of failure which results in immediate or short time which results in immediate or short time failure.failure.