An aging assessment of transformers in 1E power systems

This paper presents the findings of the Idaho National Engineering Laboratory (INEL) Phase 1 study of the effects of age on nuclear power plant Class 1E power transformers, the significance of transformer aging on plant safety, and the capabilities to mitigate the effects of transformer aging to prevent risk significant failures. The following areas were included in the INEL study: The characteristics of Class 1E power transformers used in nuclear power plants were determined. All known transformer stressors were identified, their effect on transformer materials determined, and the effects of these stressors with time assessed. On- and off-line techniques to detect the degradation of all types of transformers were identified and their effectiveness examined. The information provided in reactor operation data bases was evaluated. The capability of various recommendations to mitigate the effects of transformer aging and prevent unexpected transformer failures was evaluated. The risk significance of transformer aging was determined. Conclusions have been made on the effects of aging on transformer performance, the capability to prevent/detect/mitigate aging effects prior to transformer failure, and the effectiveness of current maintenance and monitoring methods