Evaluation of the Effect of Essential Oil Blends on the Condition of Paper Insulation

Almost from the moment the first power transformer was manufactured and up to the present time, the insulation system for the most of transformers, includes two main components - solid (cellulose) and liquid insulation. Such a hybrid system ensures highly reliable operation of the power transformer for several decades. However, the ever-increasing demand for electricity requires generation, transmission and distribution networks to increase its production and transmission. Consequently, the thermal load on the insulation system of transformers increases, which leads to an increase of the insulation aging rate and a reduction in its service life. Therefore, first of all, there is a need to enhance the properties of insulating materials. Improving the insulating properties in practice can be achieved by modifying the structure of the cellulose insulation and/or liquid dielectric. Another way to improve the performance properties of cellulose materials can be impregnation with dielectric liquids, which have the highest chemical stability. Therefore, the purpose of this work is to physical simulate the aging process of paper insulation samples impregnated with mixtures of transformer oil with ester dielectric liquid containing the latter 10, 20, 30% and evaluate their effect on the state of the paper. The objects of study were transformer oil with a high content of aromatic hydrocarbons, ester biodegradable dielectric liquid Midel 7131, mixtures of oil and ester, as well as creped electrical insulating paper. The aging of paper impregnated with insulating mixtures was carried out at temperatures of 90, 110 and 130°C for 2000 hours. At certain intervals, such an indicator as the degree of polymerization of paper insulation was measured. As a result of the research, it was found that the depolymerization of cellulose in the studied temperature range from 90 to 130°C proceeds to the greatest extent in the mineral oil itself. The addition of synthetic ester to mineral oil in an amount of 10 to 30% by volume improves the thermal stability of not only the oil itself, but also the paper immersed in these mixtures (at a temperature of 110°C - by 4-10%; at a temperature of 130 °C - by 16-36% relative to the value of the degree of polymerization of paper aged in oil). The positive effect of essential oil mixtures on the intensity of aging of cellulose insulation is also fixed visually.