Les Recksiedler Three Winding ConverterTransformer Gassing and Failures 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
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Presentation Transcript
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Les Recksiedler Three Winding ConverterTransformer Gassing and Failures<br>
02
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 Background – Transformers with a Wye and Delta secondary winding<br>
03
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 Case A– Three Phase Transformers with a Wye and Delta secondary winding<br>
04
Duval’s Triangle – about 700 oC
No Furans one test only Case A– Gassing Results<br>
05
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<br>
06
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 ????<br>
07
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<br>
08
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<br>
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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?<br>
