Mineral oil lifetime estimation using activation energy

Abstract

Lifetime estimation of mineral oil is based on IEC 60216-1/2001, using accelerated thermal ageing at three temperatures), method which requires a long experimental time. In order to reduce the experimental times, this paper proposes a simpler method to draw the lifetime curve by determining an experimental point (carrying out only a thermal ageing at the highest temperature - which requires the least time) and curve slope (based on the activation energy of oxidation reaction). Assuming the volume resistivity and the loss factor as diagnostic factors, their variation curves with ageing time were drawn, and the lifetime values were calculated. Using differential calorimetry measurements (DSC curves) for four heating rates, the activation energy value Wa of oxidation reactions was obtained. Knowing the Wa value and the ageing time τ to achieve the end of life criterion for thermal ageing at the highest temperature (155 °C), the D3 lifetime value was determined and compared with D1 and D2 values obtained by accelerated thermal method at three temperatures. Finally is showed that, the differences between D3 and D1,2 values are relatively reduced and the method based on activation energy obtained by DSC, can be used to assess the lifetime of mineral oil.