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Three Winding ConverterTransformer Gassing and Failures. Les Recksiedler. Background – Transformers with a Wye and Delta secondary winding . Similar transformers not gassing or failing Increased harmonic currents No gassing during factory load run

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Les Recksiedler


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slide2

Background – Transformers with a Wye and Delta secondary winding

  • Similar transformers not gassing or failing
  • Increased harmonic currents
  • No gassing during factory load run
  • No increase in gassing during 2 day Field test load run
  • One supplier known for “cookie cutter” approach
  • Failure of three winding transformers in USA analyzed to be due to harmonics.
  • All transformer in each HVDC system either gassing or not.
  • Data is sparse
slide3

Case A– Three Phase Transformers with a Wye and Delta secondary winding

  • HVDC System one year earlier all transformers not gassing
  • All Transformer one year later gassing badly
  • One transformer failed after 5 years
  • 3 transformer failures so far in 26 years
  • Reports not available for transformer repairs
  • No gassing during factory load run assumed to be 12 hours
  • No appreciable gas increase during 2 day Field load run.
  • Appreciable gassing within two months of in-service
slide4

Case A– Gassing Results

  • Duval’s Triangle – about 700 oC
  • No Furans one test only
case a field load run tests two days
Case A – Field Load Run Tests – Two Days
  • Hydrogen 117 ---- 133
  • Methane 273-----259
  • Ethane 95------99
  • Ethylene 305----311
  • Acetylene 3--------3
  • CO 438---- 419
  • CO2 1671----1689
  • TDCG 1231----1224
case b single phase transformers with a wye and delta secondary winding
Case B – Single Phase Transformers with a Wye and Delta Secondary winding
  • All transformers in one HVDC system gassing
  • One unit has acetylene and is being repaired
  • Similar HVDC scheme all transformers not gassing
  • Same supplier for both.
  • Non gassing transformers produced 11 years earlier
  • Remaining units are acceptable ????
case b gassing results two worst units excluding unit with acetylene
Case B – Gassing Results – Two worst units excluding unit with Acetylene
  • Unit 1 Unit 2 Condition/Risk
  • Methane 800 500 Medium
  • Ethylene 780 650 High
  • Acetylene < 5 < 5 Normal
  • Extreme gassing above 70% loading
  • Gassing 100 to 1000 times the daily gas volume in IEC 60599 table A3 at high loading
case c gassing and failures linked to harmonics
Case C – Gassing and Failures linked to Harmonics
  • IEEE transactions Volume 19, No 1, pp208-213 dated January 2004, “Thermal problems caused by Harmonic Frequency Leakage Fluxes in 3 Phase 3 winding Converter Transformers”
  • Magnetic fluxes must be managed
  • Use CTC cable
  • Leads arranged to cancel fluxes
  • Increased distances
  • Non-magnetic structural framework
conclusions
Conclusions
  • Factory Testing cannot ensure a reliable converter transformer?
  • Design Review a possible solution?
  • What are critical factors to consider? Winding configuration, lead routing, flux cancellation?
  • Should warranty consider gassing results? If so at what level?