English title

Transformer is one of the most important components of power system, which determining its reliability is very important. To evaluate transformer overall reliability, in addition to probability of failures occur due to chance events, the probability of failures owing to aging should be taken into account. To determine transformer reliability in aging area, estimating its remaining life is of great importance. One of the parameters that affects on transformer mean lifetime is its hot spot temperature, that is a function of transformer loading. Effects of loading on transformer reliability is modeled in this paper. At first transformer reliability in useful lifetime interval is discussed to be used in transformer overall reliability formulation. Using thermal modeling and aging acceleration factor, impacts of transformer loading on variation of transformer mean lifetime is formulated. Then using calculated mean lifetime and by using normal distribution function, transformer reliability in aging area is modeled. Electric and thermal characteristics data and also hourly load data of a real transformer in one year are applied to the model. Using them, impacts of various loading strategy and age increasing on transformer reliability in wearout area as well as transformer overall reliability are simulated and analyzed. The results show the significant impact of loading on transformer reliability and can be used for on-line monitoring of transformers.