Analysis of AC Transformer Reliability

The reliability of the global power transformer fleet was reviewed again, continuing CIGRE’s long legacy of surveying started forty years ago. As technology and working practices are updated it is important to periodically review reliability and how it is changing. More than 425,000 transformer years of operation collected, there were 1,204 major failures and 1,916 retirements from 66 utilities in 27 different countries. In addition to retirements and major failures, the age distribution was also analysed. As a result of increased emphasis on improving reliability over the life cycle, the failure rate has now fallen by more than half since the last Working Group. For all major failures, the hazard curve was fairly random with a slow increase with age. Failures resulting in the transformer being scrapped showed a clear age-dependency. The hazard rate for scrapped units accelerated after twenty years of age.
Data was sought from new applications of transformers, such as solar and wind farms. However, as they are relatively new there has not been enough operational service-years and failures to make statistically significant conclusions. A recommendation is to continue these surveys to continue to build experience. A thorough discussion has been given on how the industry has improved the reliability of power transformers, with advice how an owner can request a quality design and maintain longevity over the long operating life of this asset class.