A practical method for lifetime estimation of the used mineral oils

Mineral oil, with the main roles of insulating and cooling in power transformers, is very similar to the blood in human body. Because of the importance of power transformers in electrical networks, permanent care of the oil quality is indispensable. In this paper, a practical method for estimation of a used transformer oil´s lifetime is presented. Different kinds of tests, according to standards, were accomplished on oil specimens from 9 different power transformers of various ages. After ageing procedures on the oil specimens, the results were converted to Arrhenius plots. Using these diagrams, the remaining lifetime of the oil was estimated. It is shown that the Arrhenius plots, under special conditions, can be used to approximate the lifetime of insulating mineral oil.