TB 406 2010 JWG A2/B4.28 HVDC Converter Transformers - Design review, test procedures, ageing evaluation and reliability in service

JWG A2/B4.28 monitored the reliability in service of HVDC Converter Transformers and the TB reports, over a period 1971-2009, an encouraging decrease in the failure rate. It also reviewed existing standard test specifications, with a view of representing the real service conditions. The importance of the Polarity Reversal (PR) test and the effect of the oil conductivity and the polarization time are stressed. The conclusion is that at this stage the existing test should not be modified.

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1 Introduction
2 Failure Survey and Analysis
      2.1 Failure Description
      2.2 Failure Survey Discussion
3 Guidelines for Conducting Design Reviews for HVDC Converter Transformers
      3.1 System Data
      3.2 Insulation Design
4 Review of Test Requirements
      4.1 Polarity Reversal
            4.1.1. Influence of Oil Conductivity and Polarization Time on PR
            4.1.2. Polarity Reversal During DC Line Faults
            4.1.3. Investigation of Possible Improvements of the PR Test
            4.1.4. Present Knowledge About Oil Electrical Conductivity
            4.1.5. Recommendations Regarding the PR Test
5 Conclusion
6 Bibliography