Ageing assessment of transformer paper insulation through detection of methanol in oil

Ageing assessment of transformer paper insulation is important due to its irreversible ageing nature. Due to the poor accessibility of the paper samples in field transformers, large efforts were made to seek for chemical parameters in oil to indicate paper ageing, e.g. furanic compounds and dissolved carbon oxides. In recent years, alternative parameters including methanol and ethanol in oil were proposed to be related with paper ageing. In this study, a laboratory ageing experiment was conducted at 120 °C with an inhibited mineral oil and an ordinary kraft paper. Methanol and ethanol in oil were measured through an in-house developed method based on a headspace gas chromatography mass spectrometry (HS-GC-MS) setup. Result showed that methanol in oil increases linearly with the chain scission in paper which suggests its suitability to indicate early paper ageing.