Numerical Simulation of Thermal Condition in Mineral and Vegetable Oil for Power Transformers

A trend that has been observed in the past two decades is the replacement of the mineral oil from the insulation systems of power transformers (PT) with dielectric liquids whose impact on the environment is much lower. In this context, the vegetable oils specially designed for power transformers seems to be an effective alternative to mineral oil because they have certain properties that improve the safety of these equipment. The use of vegetable oils also targets the in-use transformers because it has been found that the replacement of mineral oil with vegetable oils extends the lifetime of PT. However, refilling the in-use transformers with vegetable oil requires investigating the new thermal conditions of PT. The aim of the present paper is to examine the thermal condition in mineral and vegetable oil based on a simplified model consisting of a cylindrical coil submersed in oil. Numerical simulation showed that, under the same conditions, the temperature obtained in the case of vegetable oil is higher by 0.5 °C than that obtained with the mineral oil.