Methanol and furan detections in a gas to liquid hydrocarbon oil for indicating cellulose insulation ageing

Ageing assessment of cellulose insulation in a transformer is normally conducted through indirect measurements of chemical markers in oil. In addition to the conventional paper ageing indicator 2-FAL, methanol in oil was proposed as an additional indicator to provide early ageing information. Relationships between the paper ageing and the concentration of the indicators in oil could be affected by the type of oil due to stability and partitioning issues. Therefore it is important to investigate the suitability of the paper ageing indicators for alternative insulating oils. This paper shows the results of a laboratory ageing experiment conducted to investigate the relationships between the paper ageing and the ageing indicators of 2-FAL and methanol in a Gas to Liquid (GTL) hydrocarbon oil. The ageing experiment was conducted at 100 °C for up to 126 days. A conventional mineral oil was also tested as benchmark. Variations of both methanol and 2-FAL against DP of paper aged in the GTL oil were found to be similar to those in the mineral oil.