Challenges in oil test database analysis for ageing assessment of in-service transformers

Transformer ageing assessment is an essential step towards facilitating asset management decisions and it involves the interpretation of oil test results normally recorded in a huge database for a large population of in-service transformers. In addition to the need for analysing individual transformer data, this study aims to demonstrate and illustrate some typical challenges that asset managers could face in analysing oil test databases pertaining to large transformer populations. Through analysing multiple oil test databases of in-service transformers, potential challenges are found to be the change in measurement procedure, oil treatment practice, oil temperature and oil contamination. It is hoped that the recognition and the consideration of these challenges could serve as a foothold towards more confident and reliable ageing assessment of in-service transformers for justifying asset management decisions.