WAUKESHA ELECTRIC SYSTEMS energy solutions … to power your future Transformer Testing At Factory and In Field Transformer Testing At Factory and In Field H. Jin Sim Waukesha Electric Systems H. Jin Sim Waukesha Electric Systems Weidmann-ACTI Inc. Fifth Annual Technical Conference New Diagnostic Concepts for Better Asset Management November 13 - 15, 2006 Hotel Albuquerque at Old Town Albuquerque, NM
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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
WAUKESHAELECTRICSYSTEMS
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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.
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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
•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
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
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Factory TestFactory Test
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)
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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
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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
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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
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Factory TestFactory TestDielectric Tests – Induced Voltage TestDielectric Tests – Induced Voltage Test
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Factory TestFactory 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
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Factory TestFactory Test
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.
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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
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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
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Factory TestFactory Test
Temperature Rise Tests•Measurements of Winding Resistance
•Temperature Rise Test
•Over Load Heat Run
•Gas In Oil Analysis
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Factory TestFactory Test
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
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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
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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
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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
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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
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Factory TestFactory Test
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
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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
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Factory TestFactory Test
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
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Questions?Questions?
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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• 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)
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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
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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
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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)
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
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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
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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.
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Field Diagnostic TestingField Diagnostic Testing• Electrical Testing – Others
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
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Start-up ConsiderationsStart-up Considerations
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