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Les Recksiedler

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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  1. Three Winding ConverterTransformer Gassing and Failures Les Recksiedler

  2. 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

  3. 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

  4. Case A– Gassing Results • Duval’s Triangle – about 700 oC • No Furans one test only

  5. 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

  6. 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 ????

  7. 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

  8. 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

  9. 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?

  10. QUESTIONS & ANSWERS

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