Early stage detection of insulating oil decaying

It is an established fact that regular oil analysis is extremely useful in monitoring the condition of power transformers. To ensure long-term reliability of oil filled power transformers, it is important to identify the degradation characteristics of insulating oil in long-term operations, which are the dominant factors of the transformer dielectric strength. In this contribution, oil decaying was monitored with various ASTM test methods. Oil samples were submitted to thermal aging with oxygen inlet in laboratory conditions. Many key parameters providing a “picture” of the fluid have been determined. From the obtained results, some correlations were found between some of them. Dissolved decay products, which change with a higher rate than interfacial tension and total acid values, can be possibly used as an effective index for insulating oil degradation.