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Power Transformer Diagnostics: Novel Techniques and their Application Charles Sweetser Technical Service Manager

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  • 1. Power Transformer Diagnostics:Novel Techniques and their ApplicationCharles SweetserTechnical Service Manager
  • 2. Transformers
  • 3. Topics of Discussion Introduction to Power Transformers Life Expectancy Failure Modes Diagnostic Characteristics Diagnostic Characteristics Diagnostic Measurements Standard Measurements Advanced Measurements SFRA - Sweep Frequency Response Analysis DFR - Dielectric Frequency Response
  • 4. Transformer Considerations Transformer Types and Classifications Transformer Configurations Vector Groups Oil Preservation Systems Insulating Materials and Fluids Insulating Materials and Fluids Construction Forms Core Steel Ratings Cooling Schemes Tap Changers (OLTC, DETC) Bushings Surge Arresters
  • 5. Transformer Types and Classifications Distribution Power Rectifier Arc-Furnace Arc-Furnace Network Regulating (Voltage Regulators) Phase Shifting Reactors*
  • 6. Vector Groups
  • 7. Winding Types1. Disk Winding2. Pancake Winding3. Helical Winding4. Cylindrical or Layer Winding4. Cylindrical or Layer WindingCourtesy of Delta Star, San Carlos, CACourtesy of Delta Star, San Carlos, CA
  • 8. Construction FormsCore Form Concentric Less Iron More CUShell Form Interleaved More Iron Less CUCore Form Shell FormCore Form Shell Form
  • 9. Life Expectancy 180,000 hrs or 20.55 years 110 C Hottest Spot for 65 C Temp Rise insulation Degree of Polymerization (200 -1200 DP) 1200 DP - New Paper 1200 DP - New Paper 200 DP at 150,000 hrs (end of life) Heat Moisture Oxygen
  • 10. Failure Modes
  • 11. Failure Modes
  • 12. Core Failure Modes Over-Heating Bulk Movement Multiple Core Grounding Lamination Gaps Shorted Laminations Ungrounded Core
  • 13. Oil Analysis DGA and Oil Screen Hydrogen (H2) Methane (CH4) Ethane (C2H6) Ethylene (C2H4) Rate of Gas Generation Partial Discharge Arcing Electrical Heating Ethylene (C H ) Acetylene (C2H2) Carbon Monoxide (CO) Carbon Dioxide (CO2) Oxygen (O2) Nitrogen (N2) Electrical Heating Metal Heating Decomposition of Paper
  • 14. Oil Analysis DGA and Oil Screen Dielectric Breakdown IFT Color Acidity Power Factor Power Factor Moisture Specific Gravity Viscosity Degree of Polymerization DP (Paper) Furans (Oil)
  • 15. Transformer TestsDielectric Thermal MechanicalDGA DGA SFRAOil Screen Oil Screen Leakage ReactancePF/TD CAP IR PF/TD CAPExciting Ima DC Winding RES Exciting ImaTurns Ratio Tests DC Winding RESDFRInsulation Resistance
  • 16. Transformer Test Protocol1. Overall Power Factor and Capacitance (Tip-Up, Variable Freq)2. Bushings (C1, C2, Energized Collar) (Tip-Up, Variable Freq)3. Exciting Current4. Surge Arresters4. Surge Arresters5. Insulating Fluids6. Leakage Reactance (Frequency Response of Stray Losses)7. Turns Ratio Test8. DC Winding Resistance (Slope, Ripple)9. Insulation Resistance
  • 17. Overall PF and Capacitance
  • 18. Bushings Test Taps kV < 72 kV (C1 and C2) Potential Taps kV > 72 kV (C1 and C2) No Tap Use Energized Collar at 10 kV
  • 19. Bushings
  • 20. Surge Arresters Analyzed on the basis of Watts
  • 21. Advanced Diagnostics1. Advanced Power FactorTip-Up: Voids in InsulationVariable Frequency (15 Hz to 400 Hz): Moisture and Aging2. Advanced DC Winding Resistance2. Advanced DC Winding ResistanceRipple and Slope3. Advanced Leakage ReactanceFRSL (Frequency Response Stray Losses)4. SFRA - Sweep Frequency Response Analysis5. DFR - Dielectric Frequency Response
  • 22. Variable Frequency Losses1.50E-032.00E-032.50E-03SerialParallelSum0.00E+005.00E-041.00E-031.50E-030 50 100 150 200 250 300 350 400
  • 23. Normal Power Factor
  • 24. Power Factor Influenced by Moisture
  • 25. Slope and RippleRippleSlope DRipple
  • 26. Advanced DC Resistance - SlopeSlope-0.2A/s-0.1A/s0.0A/sA UPA DOWN-0.6A/s-0.5A/s-0.4A/s-0.3A/s-0.2A/s000 005 010 015 020 025 030 TapsA DOWNB UPB DOWNC UPC DOWN
  • 27. Advanced DC Resistance - SlopeSlope-0.2A/s0.0A/s0 2 4 6 8 10 12A UP-1.2A/s-1.0A/s-0.8A/s-0.6A/s-0.4A/sTapsA UPA DOWNB UPB DOWNC UPC DOWN
  • 28. Advanced DC Resistance - RippleRipple35.0%40.0%45.0%50.0%A UPA DOWN0.0%5.0%10.0%15.0%20.0%25.0%30.0%35.0%0 2 4 6 8 10 12TapsA DOWNB UPB DOWNC UPC DOWN
  • 29. FRSL - GoodR(f)3.0 Ohm3.5 Ohm4.0 Ohm4.5 Ohm0.0 Ohm0.5 Ohm1.0 Ohm1.5 Ohm2.0 Ohm2.5 Ohm3.0 Ohm0 100 200 300 400 500Frequency (Hz)ABC
  • 30. FRSL Poor ResultShort-Circuit Between Parallel StrandsR(f)250300501001502000 50 100 150 200 250 300 350 400Frequency [Hz]ABC
  • 31. Dielectric Frequency Response (DFR)HV-windingVoltage source~Current meter110PowerFactorPower Factor in Frequency Domain?TankGuardLV-windingMain insulation 0,0010,010,10,0001 0,001 0,01 0,1 1 10 100 1000Frequency (Hz)Power?
  • 32. Moisture in Transformers1. Reduces Dielectric Strength2. Promotes the Formation of Bubble2. Promotes the Formation of Bubble3. Ages Insulation with Heat and Oxygen
  • 33. Moisture Terminology Paper, Pressboard, and Oil1. Water Content Pressboard & Paper (percentage of total mass) Oil (PPM)2. Moisture Saturation P,P,O (Relative, Humidity)
  • 34. Moisture Fact in Transformers1. If mass of oil equals paper-pressboard,then at equilibrium the water content is(2000:1)2. In transformers there is 10X more oilmass than paper and pressboard, sothe water content is (200:1)
  • 35. Oil Ratio to Paper : PressboardMass of the oil:100,000 kg = 220,000 LbsWater content at 60 C:40 ppmMass of the solid insulation:13,000 kg = 20,000 LbsWater content at 60 C:4 %Mass of the water, dissolved in the oil:4 kg = 8.8 LbsMass of the water contained in thepaper:520 kg = 1200 Lbs
  • 36. .DUO )LVFKHU 7LWUDWLRQ DQG (TXLOLEULXP &XUYHV9[%]1120 C 30 C 40 C50 C Curves are only validfor new oil and newpaper, for agedoil/paper differentcurves are necessary Balance between water0123456780 10 20 30 40 50 60 70 [ppm] 90WaterContentinthePaperWater Content in the Oil60 C80 C100CTemperaturelowhigh Balance between watercontent in the paperand in oil needsconstant temperaturesover a long period Only averagemeasurement
  • 37. Water Content RecommendationsCategory Moisture content in % Dry below 2.2 Moderately wet 2.2-3.7 Moderately wet 2.2-3.7 Wet 3.7-4.8 Extremely wet above 4.8
  • 38. Measurement Characteristics Current in wide frequencyrange,e.g. 1 mHz 1 kHz Display as dissipationfactor or complexcapacitance or complexpermittivity)()()()()(000 UjCjI++=)()()()()()()()(tan 00++===CCDissipationfactorpermittivityInterpretation Slope - oil conductivity Hump - insulation geometry Low frequencies- moisture and aging- long test duration0.0010.010.11100.0001 0.001 0.01 0.1 1 10 100 1000Frequency (Hz)Dissipationfactorhighlowhighhighlowlowmoistureofcelluloseandaginginsulationgeometryoilconductivitymoisture ofcellulose,aging
  • 39. Measurement Examples0.050.10.20.51.02.05.0New Moderate Aged0.1260HzFreq/Hz0.0001 0.010 0.10 1.0 10.00.0050.010.020.0510000.0010.00240.0036New, dry, cold: 1kHz - 0.1 mHzModerate: 1kHz - 1 mHzVery aged: 1kHz - 10 mHz
  • 40. 3.1 % at 9 qC Oil Sample Yielded 5.0%
  • 41. What is SFRA? Powerful and sensitive tool to assess themechanical and electrical integrity ofpower transformers active part Measurement of the transfer functionover a wide frequency range
  • 42. Diagnostic Category Dielectric Thermal Mechanical Mechanical Use SFRA:1. Transportation2. Post Fault
  • 43. Life CycleDelivery PortManufacturer WorkshopQuality AssuringAfter Short Circuit TestTransport CheckingTruck Transport 1Reception PortAfter Short Circuit TestFailure InvestigationTransport CheckingRoutine MeasurementAfter Transients/OvercurrentsFailure Investigation (DGA)Truck Transport 2Ship Transport
  • 44. > 17/03/2010The SFRA Measurement PrincipleTransformatorErregungssignal(variable Frequenz)Antwortsignal-3-2-101230 50 100Zeit t in sSpannungU1/U1inV/V123SpannungU/U1inV/VU2^U1^1-|TF(f1)|-3-2-101230 50 100Zeit t in sSpannungU2/U1inV/VInput signal(sine wave ofvariable frequency)Output signal0.00.20.40.60.81.00.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4f in MHz|TFU2/U1(f)|inV/V|-200.0-150.0-100.0-50.00.050.0100.0150.0200.00.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4f in MHzarc(TFU2/U1(f))indegBetragsfunktion|TFU2/U1(f)|Phasenfunktionarc(TFU2/U1(f))-3-2-100 50 100Zeit t in sSpannungU/U1inV/VU2^U1^|TF(f1)| =M(f1)/2farc(TF(f1)) =M(f1)N Vf/Hz1.000e+002 1.000e+003 1.000e+004 1.000e+005dB-90-80-70-60-50-40-30-20-10NVf/Hz1.000e+002 1.000e+003 1.000e+004 1.000e+005-150-100-50050100150PhaseMagnitude
  • 45. Theoretical BackgroundMeasurementcableMeasurementcableCMCCMCCMCCMCRMC12 RMC34Complex RLC NetworkCables Grounding)sin()( += tYtytXtx sin)( =)/(log20 1210 UUk =specimenmmZRRsUsUTF+==)()(12Complex RLC NetworkU1 50 U2 5050)/(log20 1210 UUk =)/(tan 121UU = H1 H2 H2 H3 H3 H1f/Hz1.000e+002 1.000e+003 1.000e+004 1.000e+005 1.000e+006dB-120-110-100-90-80-70-60-50-40-30-20-10010H1H2 H2H3 H3H1f/Hz1.000e+002 1.000e+003 1.000e+004 1.000e+005 1.000e+006-200-150-100-50050100150Magnitude (k) Phase
  • 46. Passive Components
  • 47. RLC Characteristics101102103104105106107-150-100-500Frequency (Hz)Amplitude[dB]101102103104105106107-100-500Frequency (Hz)Phase[]L=200 mHL=2 mHL=20 HL=200 mHL=2 mHL=20 H101102103104105106107-200-150-100-500Frequency (Hz)Amplitude[dB]C=1uFC=20nFC=1pF101102103104105106107050100Frequency (Hz)Phase[]C=1uFC=20nFC=1pF
  • 48. Typical Resultsf/Hz5.000e+001 1.000e+002 5.000e+002 1.000e+003 5.000e+003 1.000e+004 5.000e+004 1.000e+005 5.000e+005 1.000e+006-40-30-20dB-70-60-50N W sec N V sec N Uf/Hz5.000e+001 1.000e+002 5.000e+002 1.000e+003 5.000e+003 1.000e+004 5.000e+004 1.000e+005 5.000e+005 1.000e+006-100-50100150
  • 49. Failure Modes Radial Hoop Buckling Deformation Axial Winding Elongation Telescoping Overall- Bulk & Localized Movement Winding Turn-to-Turn Short Circuit Open Circuited Winding
  • 50. Radial Failure
  • 51. Axial FailurePag
  • 52. Conductor Tilting
  • 53. Core FaultsPag
  • 54. Measurements Types Open Circuit - Exciting Ima Short Circuit - Leakage Reac Interwinding - CAP Interwinding - CAP Transfer Voltage - TTR
  • 55. HV and LV Open Circuit
  • 56. Open Circuit Tests
  • 57. Open Circuit vs. Short Circuit
  • 58. Short Circuit Tests
  • 59. Analysis Strategies Baseline Similar Unit Similar Unit Phase Comparison
  • 60. FRA Industry Groups CIGRE WG A2.26 (Guide) DL 911/2004 (Standard) IEC 60076-18 (Draft) IEC 60076-18 (Draft) IEEE WG PC57.149 (Guide) D8
  • 61. Standardization in the WorldCHINADL 911/2004DL 911/2004PC57.149/D8PC57.149/D8WG A2.26WG A2.26IEC 60076IEC 60076--1818
  • 62. Available DocumentsCigr Brochure 342 DL 911/2004
  • 63. Available DocumentsIEC 60076-18 IEEE PC57.149
  • 64. Thank You for Your Attention