Behavior of transformer mineral oil mixtures submitted to isothermal charging currents

This work aims at the characterization of power transformer oil mixtures by using dc charging currents measurements for long field application times. The principle of this approach is inspired from the technique of measurements carried out on solid dielectrics used in high voltage insulation. It will be applied to characterize mixtures between two compatible oils of different provenances and ages. The obtained results are conclusive and reinforce those obtained by classical physicochemical methods of characterization. For the purpose, we intent to link between the space charge behavior in the insulation and its several characteristics. Moreover, in addition to the fact that the obtained results are in good agreement with the physicochemical characteristics, the charging currents reported at room temperature enabled us to determine the mixture resistivity and charge carriers´ mobility.