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.