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In this paper, the electrical resistivity (determined with absorption/resorption currents) is used as a diagnostic factor in order to assess the mineral oil condition and to evaluate its elapsed and remaining lifetimes. Based on experimental results of thermal accelerated ageing, the lifetime values at constant temperature are calculated by the IEC and activation energy methods. The chosen end-of-life...
In this paper the results of an experimental study concerning the vegetable and mineral oil impregnated paper subjected to thermal ageing is presented. Using activation energy method, the paper lifetime is calculated. Samples of vegetable and mineral oil impregnated paper were aged at 155 °C. Dielectric properties, water content and degree of polymerization of aged samples were measured. Using the...
The power transformer's lifetime is strongly influenced by its insulation system degradation, especially by the paper degradation. As the vegetable oil should replace mineral oil, this paper presents a study concerning the dielectric properties variation of cellulosic paper impregnated with vegetable oil as a function of the ageing duration. In order to characterize the condition of the paper the...
The operational safety of transmission and distribution grids depends essentially on the power transformers' state. Lately, there is a tendency to replace mineral oils with vegetable oils because vegetable oils provide a higher explosion safety aspect for transformers due to their higher fire points. Further, vegetable oils are favorable for the environment due to their higher biodegradability. The...
The flow electrification of mineral oil produces local electric discharges which may facilitate the damage and worsen the physico-chemical properties of the electrical power transformer insulation systems. This paper presents a study concerning the influence of the mineral oil ageing condition on the flow electrification phenomenon. The flow electrification current has been measured with a spinning...
The static electrification phenomenon is a result of the mineral oil flow through the solid insulating components and cooling ducts. The contact of streaming high resistivity mineral oil with the solid surface of the paper insulation generates electrical charge accumulation, which can produce electrical discharge that affects the insulation system properties. Many experimental results indicate that...
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