A failure probability model of the moistened oil-paper insulation of transformers based on strength-stress model

It's easier for the oil-immersed power transformer to fail when moistened. As is known to us all, moisture may cause the great decrease of the breakdown voltage of the oil-paper insulation system. So, the failure probability model of transformer was established in this paper by using the theory of strength-stress model which is successfully used in the mechanical reliability field. The model could be used to quantitatively calculate the failure probabilities of a single transformer or transformers in a certain region. The appropriate descriptions of stress and strength were introduced to fit the strength-stress model for the two kinds of failures respectively. The random amplitude and times of lightning in a certain period are described by double integral of their probability density functions. The moisture content of one transformer influences the failure probability by changing the strength of the oil gap.