Modeling the parametrical reliability of power transformers

The paper is structured in three parts. The first part explains the parametrical reliability of the power transformers (PT) in oil in context with its global reliability, taking into account the parameters that defines the state of PT. Is presenting the proposed model to parametrical reliability evaluate of PT. There are given mathematical expressions of the parametrical reliability, in relation with the three parametrical categories, defined for the state of PT viewing the general state of the insulation, the traditional parameters of PT oil, the content of gases in the oil of transformer and its weight. There explains the parametrical risk failure of PT and its global parametrical reliability. In the second part are presented the studies results, effected to a number of 29 PT, the nominal power being between [10 h-25] MVA, located in electric stations of 110 kV/MV within the frame of analyzed power transmission and distribution system (PTDS), administrated by Electric Energy distribution and transmission Branch of Oradea -Romania Distribution Power and Supply (DSPO). There are determinate the paths successions stages by technical diagnosis of PT and there is exemplified the state parameters evolution in time. There gives the values of parametrical reliability function in relation with the three parametrical categories defined for the PT state. There is presented a assessment between the failure risk by derive of parameter and the unexpectedly failure risk by the analyzed PT. The conclusions as well as the recommendations to the analyzed PT exploitation activities are presented in the last part of the paper.