Sealed Vessel Tests of Plain Kraft to Determine Arrhenius Curve Parameters

摘要

This paper reports new aging data for plain (not thermally upgraded) Kraft insulating paper, allowing the recalculation of the Arrhenius unit life curve “A” parameter and the resulting adjustment of the unit life temperature. The objective of the study was to obtain additional end of life data. Previous tests did not always achieve end of life when the samples were removed from ovens, as the reduced aging rate of the natural ester/Kraft insulating system extended the time to end of life. To help assure end of life points would be achieved, higher temperatures and longer time durations were used for the aging process. The new data confirms that the previous Arrhenius curve parameters presented in IEEE C57.154 and IEC 60076-14, while valid, were too conservative. The natural ester/Kraft system aging was carried out in sealed steel aging vessels at 150 °C, 165 °C and 180 °C. Additional sealed steel aging vessels containing plain Kraft paper in mineral oil were run as reference systems. The mineral oil/Kraft system degraded at rates consistent with the IEEE mineral oil/Kraft unit life equation and end-of-life points, confirming that the experimental procedure is valid. The natural ester soybean oil aged plain paper data follow previously known aging characteristics. However, the extended aging times provide additional and more accurate end point data. A new unit life “A” coefficient of 3.19×10^{-17 is calculated, and gives a unit life of “1” at 122 °C, rendering the previously adopted thermal class values conservative.}