Study of chemical properties of insulation mixtures to be used in high-voltage equipment

Abstract

Reliable operation of high-voltage oil-filled equipment directly depends on the condition of the insulation. One of the main components of the insulation system is transformer oil, which has been used for more than 120 years. However, in the light of modern requirements for insulating materials, oil is significantly inferior to synthetic esters in terms of such properties as chemical stability, environmental safety and high fire resistance. At present, the mixing of synthetic ester and transformer oil can be considered as one of the ways to improve the properties of the latter. A change in the chemical properties of an insulating liquid during its aging, and, consequently, the formation of various impurities and a change in the structure of its component composition will also affect the electrical insulating characteristics of the liquid dielectric. And the more the liquid is oxidized, the more significantly the electrophysical parameters worsen, including the main parameter — electrical strength (or breakdown voltage).This paper presents the results of a study of the chemical properties of mixtures of oil and synthetic ester during prolonged exposure to elevated temperatures. The assessment of the quality of insulating mixtures was carried out by changing such indicators as optical turbidity, acid value, ester value, peroxide value, surface tension and corrosiveness. Fluid testing results in this study indicate that blending of synthetic ester with aromatic oil at 10% and 20% (v/v) results in mixtures that show signs of a colloidal system. This is evidenced by atypical trends in the diagrams indicating the change in peroxide value, acid value and optical turbidity during their aging at a temperature of 110ºС with free access of air to the surface of the mixture. Increasing the proportion of ester in the mixture to 30% and above leads to stabilization or slowdown of chemical reactions occurring due to thermal-oxidative effects. Under thermal exposure (without air access), the addition of synthetic ester to the aromatic oil in a volume of 30% or more significantly reduces the likelihood of sediment formation due to the destruction and polycondensation of aromatic hydrocarbons in mineral oil.