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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. [ABSTRACT FROM AUTHOR]

The film-impregnated dielectric under operating conditions is subject to prolonged exposure to electric and thermal fields, as well as mechanical loading. In addition to critical partial discharges, the most serious drawback that impairs the film and condenser reliability in general is the deterioration of the electro-physical characteristics of the polypropylene film and liquid dielectric due to the gradual dissolution of the polymer in the liquid dielectric, which is determined by their chemical composition. This interaction of components, which was investigated in detail, has a thermo activation nature, which relates to the processes of rearrangement of atoms or molecules with the overcoming of potential barriers, and is manifested in the swelling of the polypropylene film with subsequent dissolution of the amorphous component in the polymeric component. As a consequence, irreversible structural changes of the film occur, which lead to a decrease in its electrical and mechanical strength, as well as to an increase in the dielectric loss of the liquid dielectric. Capacitor (Fig. 1 (a)) is designed to provide high-frequency communication at frequencies from 24 to 1500 kHz in power lines with a nominal voltage of 35, 110, 150, 220, 330, 500 kV AC 50 and 60 Hz. Coupling capacitor impregnated with environmentally friendly liquid - condenser oil. The short-circuits consist of capacitor sections (Fig. 1 (b)): a thin layer of dielectric is laid between two thin wide metal strips, and the dielectric film is placed on top and below the metal strips - capacitor covers. This paper gives the detail analysis of dielectric properties of capacitor paper. [ABSTRACT FROM AUTHOR]