Comparative Study of Accelerated Thermal Aging of Papers in Mineral Oil, Natural Ester, and Gas-to-Liquid

Mineral oil has long been used as an insulating liquid in transformers. Natural ester-based oil is an alternative due to its non-toxic and biodegradable characteristics. Then this study compared the rate of degradation of accelerated thermal aging paper impregnated in natural ester oil (NE) with mineral oil (MO) and Gas-to-Liquid (GTL). Sealed glass bottles containing thermally upgraded kraft paper (TUK), kraft paper (KP), pressboard (PB), and oil in an atmospheric environment were aged in an oven at 150 °C within 1344 hours. Observations were made at intervals of 336 hours during the aging. The rate of degradation of the paper was observed through the Degree of Polymerization (DP) test of kraft paper, while the chemical structure of the paper was observed through the Fourier Transform Infrared (FTIR) test of the paper. In addition, acid and moisture tests were also carried out to observe the oil-paper interaction during aging. The depolymerization rate of paper in natural ester oil is smaller compared to other oils. This indicates that NE has better thermal stability and can extend life of the transformer paper. The paper aging rate in MO is similar to GTL Oil because they both are hydrocarbons-based.