The article analyzes the factors that accelerate the aging process of the oil-paper insulation of the condenser type and shorten its service life. Attention is drawn to the fact that the breakdown of flat insulation made of condenser paper occurs at the location of the inclusion, which approximately corresponds to the field of uniform field. An example of damage to the insulation of a current transformer due to its aging and moisture is given. This work was analysed the influence of thickness and density of paper, grade of mineral oil on short-term electrical strength. The characteristics of the insulating papers of the permeable composition largely determine the electrical strength of the paper-oil insulation.Since paper-oil insulation consists of a series of successive layers of paper and oil, it is advisable to present such insulation by the equivalent scheme shown in fig. 1, in which the thickness of the paper-oil dielectric is divided into two layers: paper (fiber) and mineral oil, connected in series. a) b) FIGURE 1.Equivalentpaper-oilinsulationscheme: a -tocalculatethevoltageontheoillayer;btocalculatethedielectriclossininsulation.The increase in the dielectric constant of the paper is accompanied by an increase in the tension in the oil layers of paper and oil insulation, which promotes the development of discharges in these layers and facilitates the breakdown of the insulation. As a result, the effect of paper density has a different effect on the short-term and long-term strength of the insulation. In determining the short-term strength, the influence of the first factor prevails, which contributes to its increase with increasing paper density. For example, by increasing the density of paper from 0.7 to 1.3 g/cm 3 , the electrical strength of sheet insulation (flat samples) increases by 60%.However, in determining the long-lasting strength, partial breakdowns in the oil layers lead to considerable destruction of the insulation. In this case, as the paper density increases, the breakdown strength is reduced and the insulation life is shortened.

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The article analyzes the damage of the main elements of current measuring transformers (CMT) and proposes a mathematical model of the residual life of CMT obtained by fuzzy modeling using Matlab software.