Thermal Class of Thermally Upgraded Kraft Insulation in Synthetic and Natural Ester Liquids

Abstract

The use of ester liquids has continued to grow due to the high fire safety and environmentally friendly capabilities of the liquids, however the slower aging rate of cellulose in these liquids is often overlooked. There have been many aging tests completed to determine the thermal class of thermally upgraded Kraft (TUK) solid insulation in various insulating liquids using several test methods. However, limited information is published on the aging properties of TUK in ester liquids in accordance with the IEEE C57.100-2011 test standard. This paper provides comprehensive information on the thermal class evaluation of TUK in synthetic ester, canola natural ester, and soybean natural esters tested in the temperature range of 150 °C - 190 °C. The paper confirms the same thermal class for TUK in the various ester liquids and slower aging rate of TUK in ester liquids in comparison to mineral oil.