Electrical and Physicochemical Properties and Transient Charging Currents in Mineral and Vegetable Oils Mixtures

The present work aims at investigating the possibility of mixtures between naphthenic transformer mineral oil (MO) and natural ester olive oil (VO). Ten mixture ratios between the two non-inhibited oils have been constituted. The variations of the electrical and physicochemical checking parameters (density, color number, water content, acidity, breakdown voltage and dissipation factor) are first analyzed and discussed in comparison with their initial values and those recommended by standards. Then, DC fields are applied during 3000 s and isothermal charging current measurements are made. The two original oils are both uninhibited, new and contain water contents in the limits of their saturation levels. The study reveals a favor for the vegetable oil and mixtures up to 15 % of mineral oil, especially with regard to breakdown voltage and charging current behavior. On the other hand, the addition of VO amounts until 15% improves significantly all the properties of the MO in spite of the high water amounts contained in the base VO.