transformer testing - weidmann-solutions.cn 2006 new mexico... · waukesha electric systems energy...

WAUKESHAELECTRICSYSTEMS

energy solutions… to power your future

Transformer TestingAt Factory and In Field

Transformer TestingAt Factory and In Field

H. Jin SimWaukesha Electric Systems

H. Jin SimWaukesha Electric Systems

Weidmann-ACTI Inc. Fifth Annual Technical Conference

New Diagnostic Concepts for Better Asset Management

November 13 - 15, 2006Hotel Albuquerque at Old Town Albuquerque, NM



Transformer TestingAgenda

General

Dielectric Tests

Performance Characteristics Tests

Temperature Rise Tests

Other Factory Tests

Field Testing Let’s make this interactive!

Please stop me and ask questions during the

presentation if you have them.



GeneralReasons for Testing

COMPLIANCE WITH CUSTOMER SPECIFICATIONS

ASSESSMENT OF QUALITY AND RELIABILITY

VERIFICATION OF DESIGN

COMPLIANCE WITH INDUSTRY STANDARDS

Test ClassificationRoutine

Design

Other

GeneralReasons for Testing

COMPLIANCE WITH CUSTOMER SPECIFICATIONS

ASSESSMENT OF QUALITY AND RELIABILITY

VERIFICATION OF DESIGN

COMPLIANCE WITH INDUSTRY STANDARDS

Test ClassificationRoutine

Design

Other

Factory TestFactory Test

TRANSFORMER TESTSTRANSFORMER TESTS

DIE ELECTRIC TESTS PERFORMANCECHARACTERISTICS

THERMAL TESTS OTHER TESTSDIE ELECTRIC TESTS PERFORMANCECHARACTERISTICS

THERMAL TESTS OTHER TESTS

TRANSIENTS 1) No-Load Loss 1) Winding Resistance *1) Insulation Capacitance1) Lightning Impulse 2) % Exc. Current 2) Heat Run Test and dissipation factori Full Wave 3) Load Loss iOil Rise 2) Sound Level Testsi Chopped Wave 4) % Impedance iWdg. Rise 3) 10 kV Exc. Currenti Steep Wave 5) Zero Sequence iHot spot rise 4) Megger

Impedances 3) Over Load Heat Run 5) Core Ground 6)Ratio Tests 4) Gas In Oil *6) Electrical Center

2) Switching Impulse 7) Winding Resistance 5) Thermal Scan *7) Recurrent Surge8) Dew Point9) Short-Circuit Test

*10) Control Circuit Test

*11) Test on Series Transformer

1) Applied Voltage *12) LTC Tests

2) 1∅ Induced *13) Preliminary Ratio Tests3) Induced Voltage *14) Test on Bushing CT 4) Partial Discharge *15) Oil Preservation System

*Quality Control Tests

1) No-Load Loss 1) Winding Resistance *1) Insulation Capacitance1) Lightning Impulse 2) % Exc. Current 2) Heat Run Test and dissipation factori Full Wave 3) Load Loss iOil Rise 2) Sound Level Testsi Chopped Wave 4) % Impedance iWdg. Rise 3) 10 kV Exc. Currenti Steep Wave 5) Zero Sequence iHot spot rise 4) Megger

Impedances 3) Over Load Heat Run 5) Core Ground 6)Ratio Tests 4) Gas In Oil *6) Electrical Center

2) Switching Impulse 7) Winding Resistance 5) Thermal Scan *7) Recurrent Surge8) Dew Point9) Short-Circuit Test

*10) Control Circuit Test

*11) Test on Series Transformer

1) Applied Voltage *12) LTC Tests

2) 1∅ Induced *13) Preliminary Ratio Tests3) Induced Voltage *14) Test on Bushing CT 4) Partial Discharge *15) Oil Preservation System

*Quality Control Tests

LOW (POWER) FREQUENCY




Dielectric Tests – BackgroundDielectric Tests – Background

DIELECTRIC ENVIRONMENTPower Frequency (Normal, Abnormal)

Natural (Lightning)

Man-made (Switching Impulse)



Factory TestFactory TestDielectric Tests – BackgroundTRANSFORMER INSULATION SYSTEMDielectric Tests – BackgroundTRANSFORMER INSULATION SYSTEM

Major InsulationMinor InsulationPhase to Phase Insulation



Factory TestFactory TestDielectric Tests•Impulse tests

–Lightning impulse•full wave, chopped wave, front of wave

–Switching impulse

•Low (power) frequency dielectric tests–Induced voltage test–Applied voltage test–Single phased induced test

•Additional dielectric tests–Partial discharge monitoring–1 hour test at 1.5 P.U. voltage



Factory TestFactory TestDielectric Tests – Impulse Tests



Factory TestFactory TestDielectric Tests – Impulse Tests•LIGHTNING IMPULSE

Front Time - 1.2 microseconds ± 30% Tolerance(1.67 Times the time between 30% and 90% voltage)

Tail Time - 50 microseconds ± 20%(Time to 50% peak voltage)

Chop Time ≥ 3 microseconds for ≥ 150 KV≥ 2 microseconds for < 150 KV

(Time to first zero on tail of the wave)

•TEST CIRCUIT:Test one terminal at a time, all other terminals are groundedCurrent is measured at other end of winding through a shunt



Factory TestFactory TestDielectric Tests – Impulse TestsDielectric Tests – Impulse Tests




Dielectric Tests – Impulse TestsDielectric Tests – Impulse Tests



Factory TestFactory TestDielectric Tests – Switching Impulse Tests

•SWITCHING IMPULSE TEST•Time to peak value > 100 microseconds •Time for 90 % of peak Value > 200 microseconds•Time to first zero on tail of the wave >1000 microseconds

• TEST CIRCUIT

•Test for each HV Line terminal•Ground Neutral terminal for all Wye connection, Ground other end of all Delta windings•All Line terminals to be kept open except test terminal




Dielectric Tests – Switching Impulse TestsDielectric Tests – Switching Impulse Tests



Factory TestFactory TestDielectric Tests – Applied Voltage Test•TEST CIRCUIT:

•All terminals of winding under test are shorted together and connected to the 60 Hz supply through a High voltage test transformer•All other winding terminals are shorted together and connected to ground•Tank is also connected to ground•Test voltage is raised slowly to the required voltage and held for 1 minute•The test is considered to be passed if there is no collapse of voltage or no audible internal sound




Dielectric Tests – Applied Voltage Test•TEST VOLTAGE

During this test as both ends of winding are connected,all parts of the winding and leads attain the same voltage level with respect to ground and all other windings

For Delta connected windings applied test voltage level is the voltage equivalent to BIL. For example – equivalent applied test voltage for 550 KV BIL is 230 KV

For Wye connected windings the applied test voltage is limited to the BIL of Neutral. For example if Line end BIL is 550 KV and neutral end BIL is 150 KV then equivalent applied test voltage is limited to 50 KV (equivalent for 150 BIL)



Factory TestFactory TestDielectric Tests – Induced Voltage Test•TEST CONNECTION

•Three phase voltage is applied to LV terminals at frequency ≥ 2 times rated frequency

•All other line terminals are left open

•Neutral and Tank is connected to ground



Factory TestFactory TestDielectric Tests – Induced Voltage Test•TEST VOLTAGE & DURATION

•For Class I Transformers (≤ 69 KV Class) –•Test voltage is equivalent to twice the volts/turn and line end is raised to achieve equivalent power frequency test voltage acrossphases

•Test duration is 7200 Hz, if test frequency is 200 Hz then testduration = 7200/200 = 36 seconds

•The test is considered to be passed if there is no collapse of voltage or no audible internal sound



Factory TestFactory TestDielectric Tests – Induced Voltage Test•TEST VOLTAGE & DURATION

•For Class II Transformers (> 69 KV Class) –

•Test voltage - 150% maximum tap voltage for 1 hour 173% maximum tap voltage for 7200 Hz

•Test voltage is raised slowly to 150% level and is held for few minutes and is raised to Enhancement level for 7200 Hz and then reduced to 150% (1 hour) level

•During this 1 hour test RIV (Partial Discharge) is recorded every 5 minutes. As per ANSI standards guaranteed level is ≤ 100 micro-volts

•The test is considered to be passed if during 1 hour duration of test RIV level is ≤ 100 micro-volts and if increase in RIV readings during 1 hour period is ≤30 micro-volts



Factory TestFactory TestDielectric Tests – Induced Voltage TestDielectric Tests – Induced Voltage Test




Perf. Char. – No-Load Loss and Exciting CurrentPerf. Char. – No-Load Loss and Exciting Current

•Losses of unloaded transformer excited at rated voltage and frequency•Include Core loss, Dielectric Loss, and I2R Loss•Core Loss – Hysteresis loss & Eddy Current loss•Hysteresis Loss – Flux Density & Grade of Steel•Eddy Current Loss – Frequency & Temperature•Average Voltage Voltmeter Method to measure the voltage•Compared to the RMS voltage to make correction to sine wave basis




Perf. Char. – No-Load Loss and Exciting CurrentPerf. Char. – No-Load Loss and Exciting Current

Test Circuit –Transformer is excited from either TV/LV or HV side at 60 Hz. with a variable voltage sinusoidal source. All other terminals are left open. Applied voltage is slowly increased to test voltage 90%, 100%, 110% or any other % of the Rated voltage as required.



Factory TestFactory TestPerformance Characteristics – Load Loss and % Impedance

•Load loss is the Losses of Transformer caused by Load Current

•Load Loss = I2R loss + Eddy loss + Stray loss

•Eddy losses depend on;

conductor thickness and width

leakage flux distribution

•Stray loss depends on;

% impedance

Winding dimensions, and clearance to tank and clamps



Factory TestFactory TestPerf. Char. – Load Loss and % ImpedanceTest Circuit

Transformer is excited from one side at rated frequency with a variable voltage source

The other side is shortedApplied voltage is raised to produce rated test currents in windings




Temperature Rise Tests•Measurements of Winding Resistance

•Temperature Rise Test

•Over Load Heat Run

•Gas In Oil Analysis




Temperature Rise Tests•Factors Affecting Winding Resistance Measurement

•Transformer Saturation Time

•Transformer Connection

•Characteristics of D.C. Source

•Average Winding Temperature at Cold Resistance Measurement



Factory TestFactory TestTemperature Rise Tests

•Performed at Base ONAN and Maximum ONAF RatingIf maximum current/loss can not be fed due to test limitations, then

transformer can be loaded to 80% loss levels @ 90% current as per C57.12.90

•Performed by shorting all 3 LV terminals and applying voltage from HV winding to circulate sufficient current to produce maximum total loss•After reaching steady state oil temp. rise, current is reduced to rated value and circulated for 1 hour. Hot winding resistance is measured and curve plotted to arrive value at time of shutdown (Time zero)•Temperature correction is applied to steady state Top-oil Rise, Mean oil Rise for total /test losses if applicable as per clause11.5.2.2.1/C57.12.90•Temperature correction is applied to winding gradient to correctto rated current if applicable as per clause 11.5.2.1/C57.12.90



Factory TestFactory TestTemperature Rise Tests

•Measurements during Temperature Rise Test –Top oil Temperature, 3 Ambient Temperatures, Top and Bottom Radiator Temperature, & Hot winding resistance at shut down

•Top Oil Rise = Top oil temperature – Average ambient•Average oil rise = average of top & bottom header temperature•Average winding rise = (Hot Resistance / Cold Resistance)*(234.5+ambient temp) – ambient•Gradient = Average winding rise – Average oil rise•Hot spot Rise = Top oil rise + Hot spot gradient•Hot spot gradient = Gradient (1 + k)•k = hot-spot factor calculated based on maximum eddies due to actual radial and axial field



Factory TestFactory TestTemperature Rise TestsFor 65 °C Rise Transformers, the guaranteed temperature limits for normal loss of life as per clause 5.11.1 of Std. C57.12.00 are;

Top oil Rise - 65 °C

Average Winding Rise - 65 °C

Hot Spot winding Rise - 80 °C



Factory TestFactory TestTemperature Rise TestsOverload Testing Of Transformers

•As per the user requirements, overload test is performed at 125% , 130% , 140% load or 150% load for specified duration or until steady state condition•If overload test is not specified, then expected temperature rise/design values for required overload with calculated “m” and “n” exponents are provided•When specified, Heat Run Test is conducted at 3 different load levels to calculate “m” and “n” exponents which are used to calculate winding gradients and top oil rise at specified overload rating•Top oil Rise from 3 heat-run tests is plotted for different loads to calculate Top oil exponent “n” as per clause 9.8.4 of IEEE Std. C57.119-2001•Winding gradient from 3 heat-run tests is plotted for different currents to calculate winding exponent “m” as per clause 9.8.5 of IEEE Std. C57.119-2001




Temperature Rise TestsDissolved gas in oil Analysis

•Oil sample is taken from the tank Before and After test•Oil sampled are tested for various dissolved gasses

H2, CH4, C2H6, C2H4, C2H2, CO, CO2

•The change in gas levels must be within permissible limits set by customer or manufacturer’s standards•This test is also used as a diagnostic test to monitor condition of transformer in service as per IEEE Guide C57.104-1991•PC57.130 IEEE Trial-Use Guide for the Use of DGA during Factory Temperature Rise Tests…. Will be used when it is approved and published



Factory TestFactory TestOther Factory Tests•Front of Wave Impulse Tests

•Sound Level Tests

•Zero Sequence Impedance Measurements

•Infrared Scan during Temperature Rise Tests

•Any other Special Tests




Witnessing

Majority of users do NOT witness factory tests

Many users will witness at least Dielectric tests for:New supplier

New, special application design

Many users use independent consultants for this



Questions?Questions?



Field TestingField Testing

Field Acceptance Tests• Depends on Product and Manufacturer

• Typical Manufacturer’s Instruction Manual will have….To assure full warranty protection, the following testsmust be performed before the transformer is energized:1. Ratio Test2. Oil Dielectric Strength*3. Oil Power Factor4. Water in Oil Content*5. Insulation Power Factor6. Dew Point - as received or when removed from storage

*On oil samples taken from the bottom of the unit after final vacuum oil fill and standtime

Field Acceptance Tests• Depends on Product and Manufacturer

• Typical Manufacturer’s Instruction Manual will have….To assure full warranty protection, the following testsmust be performed before the transformer is energized:1. Ratio Test2. Oil Dielectric Strength*3. Oil Power Factor4. Water in Oil Content*5. Insulation Power Factor6. Dew Point - as received or when removed from storage

*On oil samples taken from the bottom of the unit after final vacuum oil fill and standtime



Field Diagnostic TestingField Diagnostic Testing

WindingsResistanceRatio/Polarity/Phase RelationshipExcitation CurrentShort Circuit ImpedanceInsulation ResistanceCapacitancePower Factor/Dissipation FactorInduced Voltage/Partial Discharge/RIV

WindingsResistanceRatio/Polarity/Phase RelationshipExcitation CurrentShort Circuit ImpedanceInsulation ResistanceCapacitancePower Factor/Dissipation FactorInduced Voltage/Partial Discharge/RIV




BushingsCapacitanceDielectric LossPower Factor/Dissipation FactorPartial DischargeTemperature (Infrared)Oil LevelVisual Inspection

BushingsCapacitanceDielectric LossPower Factor/Dissipation FactorPartial DischargeTemperature (Infrared)Oil LevelVisual Inspection



Field Diagnostic TestingField Diagnostic TestingInsulating Oil

Water ContentDissolved GasDielectric StrengthParticle CountDielectric LossPower Factor/Dissipation FactorInterfacial TensionAcidityVisualColorOxidation StabilityNow…. Corrosive Sulfur per MODIFIED ASTM D 1275

Insulating OilWater ContentDissolved GasDielectric StrengthParticle CountDielectric LossPower Factor/Dissipation FactorInterfacial TensionAcidityVisualColorOxidation StabilityNow…. Corrosive Sulfur per MODIFIED ASTM D 1275




Tap ChangersLTC

Contact ContinuityTemperature (Infrared)RatioTimingMotor CurrentLimit Switch

DETCContact PressureCenteringRatioVisual Inspection

Tap ChangersLTC

Contact ContinuityTemperature (Infrared)RatioTimingMotor CurrentLimit Switch

DETCContact PressureCenteringRatioVisual Inspection




CoreInsulation ResistanceGround Test

CoreInsulation ResistanceGround Test




Tanks and Associated DevicesConservatorInert Air SystemGaugesRelaysCooling SystemPressureTemperature (Infrared)Visual Inspection

Tanks and Associated DevicesConservatorInert Air SystemGaugesRelaysCooling SystemPressureTemperature (Infrared)Visual Inspection



Field Diagnostic TestingField Diagnostic Testing• Electrical Testing – Insulation Power Factor

Typical Values ofV ≅ 0.1 – 12.0 kV

Good insulationPF ≅ DF ≤ 0.5%

Temperature Sensitive

Testing “Major” Insulation



Field Diagnostic TestingField Diagnostic Testing• Electrical Testing – Turns Ratio

Can detect problems in:•Turn to Turn•Section to Section•DETC Alignment•Loose Connection•Grounded Conductor

Easy to perform in Field



Field Diagnostic TestingField Diagnostic Testing• Electrical Testing – Insulation Resistance

• Use megger for test• All windings immersed in insulating

liquid• All windings short-circuited• All bushings in place• Measure between windings and to

ground




Minimum values for Transformers




Polarization Index = R10 / R1

R10 = 10th minute readingR1 = 1st minute reading

GoodAbove 2.0

Fair1.25 – 2.0

Questionable1.1 – 1.25

Poor1.0 –1.1

DangerousLess than 1

CommentPI




• Electrical Testing – Winding Resistance

Can detect defects such as;•Poor bolted joints•Corrosion•Fractures of conductors

“Drop of Potential” method

Highly accurate Kelvin Bridge or Micro-ohmmeter can also be used successfully in field.



Field Diagnostic TestingField Diagnostic Testing• Electrical Testing – Winding Resistance

Transformer Test reports show all winding resistances as they are all in “Series” connection

Compare the results for each phase to the other phases and to the earlier readings. More than 2% variance from expected should beinvestigated.



Field Diagnostic TestingField Diagnostic Testing• Electrical Testing – Calibration and testing of

Protective Relays

Visual ChecksElectrical TestingRelay Testing / Setting Operational Testing Relay ReplacementThermo-graphic Survey / InspectionBattery Testing and Maintenance

A stitch in time saves nine……(Benjamin Franklin)



Field Diagnostic TestingField Diagnostic Testing• Electrical Testing – “Hi-Pot” and DC Leakage

Terminals are shorted togetherTests between windings (H to L)Tests between windings and groundVoltage applied can be either DC or ACLeakage current can be measured and used to determine the integrity of insulation system

It is a Pass/Fail test that can be destructive(If fails, it must be repaired before returning to service)



Field Diagnostic TestingField Diagnostic TestingElectrical Testing - Frequency Response Analysis (FRA)

FRA is a diagnostic tool for modeling the transfer function of a test specimen

Sweep Frequency Response Analysis (SFRA)and Impulse method being used today



Field Diagnostic TestingField Diagnostic Testing• Electrical Testing –

Frequency Response Analysis

104

105

106

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

Frequency - Hz

dB

Measures the “transfer function” of RLC network

Initial set of measurements are called “Finger Prints”Later measurements are compared to the finger prints to see if anything changed

Comparisons can also be made between “Similar” units or different phases of the same unit



Field Diagnostic TestingField Diagnostic Testing• Electrical Testing –

Frequency Response Analysis

List of FRA application:Determine loose windings to perform re-tighteningDetermine core/coil deformations and movementsOther internal faults after shipments or through-fault events

IEEE Transformers Committee FRA Working GroupWhat to measure, How to measure, & Acceptance Criteria (PC 57.149)



Field Diagnostic TestingField Diagnostic Testing• Electrical Testing – Partial Discharge Detection

During the normal operation or induced potential tests, PD can be detected using RIV, Electrical PD measurements, or Acoustic PD measurements

RIV PD



Field Diagnostic TestingField Diagnostic Testing• Electrical Testing – Partial Discharge Detection

PD activity inside the unit could mean the beginning of an eventual flash-over and arcing

PD activity inside can also be indirectly detected with DGA

Depending on how severe the PD activity, prepare for major repair or replacement



Field Diagnostic TestingField Diagnostic Testing• Other Testing – Degree of Polymerization (DP)

Degree of polymerization = measurement of ‘n’

New material DP ≅ 1000 – 1400Near the end of life DP ≅ 150 – 200

Requires very little quantity to testCorrelates well with mechanical strength of cellulose



Field Diagnostic TestingField Diagnostic Testing• Electrical Testing – Excitation Test

Testing is done with single phase AC

Results are compared to previous readings and between phases (For three phase three legged unit, the middle phase reads lower current than outer legs. Currents on the outer legs should be within 15% of each other.)

Can detect defects in windings and the core structure, turn to turn insulation, tap changing devices, etc.



Field Diagnostic TestingField Diagnostic Testing• Electrical Testing – Others

•Impedance measurements

•Core Megger

•Series of Bushing tests (Capacitance, Dielectric Loss, PF/DF, PD, Visual Inspection)

•Cooling System (Fans, Pumps, Cooling Control Circuits)



Field Diagnostic TestingField Diagnostic Testing• Others – Infrared



Start-up ConsiderationsStart-up Considerations

Testing AFTER all preparations BEFORE energization

• Insulation resistance (winding to ground and between windings)

• Insulation power factor or dissipation factor test on each winding to ground and between windings

• Core insulation

• PF/DF on Bushings

• Winding Ratio on all taps

• Winding resistance of all windings


• Insulation resistance (winding to ground and between windings)

• Insulation power factor or dissipation factor test on each winding to ground and between windings

• Core insulation

• PF/DF on Bushings

• Winding Ratio on all taps

• Winding resistance of all windings





• Dielectric liquid (Screen tests and DGA)

• Exciting Current

• Check operation of auxiliary equipment• LTCs, liquid-circulating pumps, fans, or liquid or water flow meters in

accordance with manufacturer's instructions

• Frequency Response measurement compared to factory resultsAll these tests should be within acceptable limits prior to energization


• Dielectric liquid (Screen tests and DGA)

• Exciting Current

• Check operation of auxiliary equipment• LTCs, liquid-circulating pumps, fans, or liquid or water flow meters in

accordance with manufacturer's instructions

• Frequency Response measurement compared to factory resultsAll these tests should be within acceptable limits prior to energization



Start-up ConsiderationsStart-up ConsiderationsEnergization

Set cooling controls to automaticEnergize the transformerHold at rated voltage and no-load for at least 8 h or at the manufacturers recommended timeTest gas blanket for oxygen and combustible gasCheck operation of LTC mechanism and auxiliary equipment during this timeNote excessive audible noise and vibrationObserve the transformer carefully for the first few hours after load is applied

EnergizationSet cooling controls to automaticEnergize the transformerHold at rated voltage and no-load for at least 8 h or at the manufacturers recommended timeTest gas blanket for oxygen and combustible gasCheck operation of LTC mechanism and auxiliary equipment during this timeNote excessive audible noise and vibrationObserve the transformer carefully for the first few hours after load is applied




Critical Transformers:

Always follow the Manufacturer’s recommendations

It is a good idea to have qualified engineers/technicians from the manufacturer to perform the installation, testing, and commissioning work or as a minimum, have them on-site for consultation/supervision



Questions?

Thank You

Questions?

Thank You

transformer testing - weidmann-solutions.cn 2006 new mexico... · waukesha electric systems energy...

Documents