How often should transformer oil be changed?

How often should transformer oil be changed? The frequency of transformer oil changes depends on several factors, including the type of transformer, operational conditions, and the quality of the oil. Generally, transformer oil should be tested regularly, typically every 1-3 years, for properties like moisture content, acidity, and furan analysis. If the tests indicate significant degradation of the oil or if there are signs of contamination, a change may be necessary. Regular maintenance and monitoring can extend the life of the oil, often allowing for changes every 5-10 years, provided the oil remains within acceptable limits.