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Electrical Measurement Methods I

New Experience in the Transformer Diagnosis Michael Krüger, OMICRON Austria . Electrical Measurement Methods I. Electrical Measurement Methods II. Content. Winding Resistance Measurement

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Electrical Measurement Methods I

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  1. New Experience in the Transformer Diagnosis Michael Krüger, OMICRON Austria

  2. Electrical Measurement Methods I

  3. Electrical Measurement Methods II

  4. Content • Winding Resistance Measurement • Fault Finding on Transformer Windings with FRA • Moisture Measurement on Transformers • Partial Discharge Measurement on Transformers

  5. Winding Resistance Measurement

  6. Diverter Switch Contact of Phase V

  7. Winding Resistance after Repair

  8. Content • Winding Resistance Measurement • Fault Finding on Transformer Windings with FRA • Moisture Measurement on Transformers • Partial Discharge Measurement on Transformers

  9. Fault on a 115kV / 34.5kV Transformer • There was a breakdown in phase B of the 34.5 kV busbar in the substation • The differential protection relay of the faulty transformer tripped

  10. DGA Phase 1: Trip out of Service, Differential Phase 2: DGA second DGA showed 19ppm C2H2

  11. Transformer Model for FRA

  12. Swept Frequency Response Analysis (SFRA) Phase Magnitude

  13. FRA LV Winding – Comparison of the 3 Phases B Phase

  14. Radial Forces Buckling with inner supports Higher order or forced Buckling The conductors can bend between the supports all along the circumference Buckling without inner supports Free mode or free Buckling Source: Brochure CIGRE WG 12.19 : The Short Circuit Performance of Power Transformers

  15. Radial Failure (Buckling)

  16. Failure Modes due to Radial Forces B phase with buckling C phase without buckling Source: Cigre Brochure 342 “ MECHANICAL-CONDITION ASSESSMENT OF TRANSFORMER WINDINGS USING FREQUENCY RESPONSE ANALYSIS (FRA)”

  17. Comparison FRA LV Winding with Cigre Case Study of Buckling Systematic shift of several resonances www.e-cigre.org B Phase

  18. B Phase Take a closer look

  19. B Phase

  20. Content • Winding Resistance Measurement • Fault Finding on Transformer Windings with FRA • Moisture Measurement on Transformers • Partial Discharge Measurement on Transformers

  21. Water in the Transformer Most of the water is contained in the paper! Mass of the solid insulation: 13,000 kg = 20,000 Lbs Water content at 60 °C: 4 % Mass of the water contained in the paper: 520 kg = 1200 Lbs Mass of the oil: 100,000 kg = 220,000 Lbs Water content at 60 °C: 40 ppm Mass of the water, dissolved in the oil: 4 kg = 8.8 Lbs

  22. Determination of the Water Content in Paper [Karl Fischer Titration and Equilibrium Curves] • Curves are only valid for new oil and new paper, for aged oil/paper different curves are necessary • Oil sampling is critical (round robin tests) • Balance between water content in the paper and in oil needs constant temperatures over a long period • Only average measurement

  23. History of Dielectric Diagnostic Methods • 1960+ • Dissipation factor at power frequency • Polarization index • At that time: No reliable method for onsite moisture diagnostics • 1991 RVM for water determination • Soon questioned by users (Kachler 1996) • 1999+ Polarization Depolarization Currents • Technical University Zurich Switzerland • 1999+ Frequency Domain Spectroscopy • KTH Stockholm with ABB • 2007 Combination of PDC and FDS

  24. Dielektric Response in the Time DomainPolarisation Depolarisation Current (PDC) Current = f(t)

  25. Dielektric Response in the Frequency DomainFrequency Domain Spectroscopy (FDS) or Dielectric Frequency Response (DFR)

  26. 1 100 Power factor Current [nA] 0.001 0.1 1000 1 Frequency [Hz] 1 1000 Time [s] 1000 14 1 100 12 Trans- formation 10 10 Power factor Duration / h 1 8 Frequency range / Hz 0,1 6 0,01 4 0.001 0.001 1000 0,001 Frequency [Hz] 2 0,0001 0 FDS PDC DIRANA Dielectric Response Measurement with Frequency Domain Spectroscopy (FDS) and Polarisation & Depolarisation Current (PDC) PDC FDS Combination of PDC und FDS reduces measurement time

  27. Interpretation and Analysis Öl 1pS/m Overall Response1%, 1pS/m, X30, Y15 1,0 2,0 0,5 Pressboard Transition from Capacitive to Resistive Voltage Distribution Pressboard: Water, lmw Acids Oil: Carbon, Sludge, hmw Acids 10 Pressboard Dissipation factor 1 0.1 0.01 0.001 0.0001 0.001 0.01 0.1 1.0 10 100 1000 0.0001 f/Hz

  28. Analysis of the Water Content by Comparison to Model Results XY-Model Oil Y Spacers Comparison Fitting Oil Barriers Water Content Oil Conductivity Measurement Laboratory Results Temperature X Source: Weidmann

  29. FDS / PDC Measurement on a 130 MVA Transformer – Situation 2006 • 130 MVA • 230 / 115 / 48 kV • Year of manf. 1967 • Rubber membrane in the expansion vessel

  30. FDS / PDC Measurement on a 130 MVA Transformer – Water Content Distribution Average Oilsample FDS HV-LV Oilsample RH % Karl Fischer mg/kg (Oommen equilibrium) FDS/PDC 1mHz-1kHz 5 4 3 Moisture in paper [%] Tertiary not in use 2 1 0 FDS LV- Tertiary FDSTertiary-Tank

  31. 130 MVA Transformer On-Line Drying

  32. History 2006 – 2008 - 2010

  33. Content • Winding Resistance Measurement • Fault Finding on Transformer Windings with FRA • Moisture Measurement on Transformers • Partial Discharge Measurement on Transformers

  34. Diagnostic Measurement on a Cast Resin Type Transformer

  35. Cracks in the Epoxy

  36. PD Measurement Circuit

  37. Test Arangement CPC100 CP CU1 Compensating Capacitors

  38. Test Arangement Coupling Capacitor and MPD600

  39. 500kHz 2 MHz 8 MHz Separation of PD Sources in 3CFRD 3CFRD 500kHz 8MHz 2MHz timeframe 1 µs 500 kHz 2 MHz 8 MHz 3CFRD = 3 Center Frequency Relation Diagram

  40. PD Measurement without 3CFRD Filtering

  41. 3CFRD Filtering

  42. PD Measurement with 3CFRD Filtering

  43. PD Measurement without 3CFRD Filtering

  44. On-Line PD Measurement on a Transformer

  45. On-Line PD Measurement on a Transformer GIS - Cable Connection (GIS Side) 1 2 3

  46. Online PD Measurement at the GIS Side red phase GIS yellow phase GIS blue phase GIS

  47. Sensors 1, 2 and 3 at the GIS Side and Sensor 4 at the Transformer Side 4 100m

  48. PD Measurement at the GIS and the Transformer Side blue phase GIS blue phase Tr

  49. PD Measurement at GIS and TR Side Trigger = TR Side - Delay on GIS Side trigger = blue phase Tr delayed signal blue phase GIS

  50. Jumper between Oil/Oil Bushing and Cable Termination

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