Sealed Aging Tests that Confirm Arrhenius Curve Parameters of TUK and Natural Ester Liquid

Abstract:
This paper reviews the natural ester aging data found in Annex C of IEC 60076-14 or the equivalent Annex B of IEEE C57.154. The work adds new aging data that extends the original aging times. It presents the results from almost 2 years of accelerated aging tests, consisting of thermally upgraded Kraft paper in soybean oil and high oleic sunflower oil using both glass and steel aging vessels. The sealed vessels were aged at 150deg C, 160deg C, 170deg C and 180deg C. Additional aging systems consisting of thermally upgraded Kraft paper in mineral oil were run as reference systems. The paper in mineral oil aged at rates consistent with the IEEE mineral oil unit life equation, providing the “confirmation” condition required by IEEE C57.100. The natural ester data were consistent between the soybean oil and high oleic sunflower oils as well as between the glass and steel aging vessels. The unit life coefficient is recalculated incorporating the new data, confirming integrally the previously adopted values of thermal classes.