Methanol detection in transformer oils using gas chromatography and ion trap mass spectrometer

Paper ageing is an irreversible process, which has made paper insulation a lifetime determining factor for transformers. Chemical indicators in oil such as carbon oxide gases and 2-FAL, are used to indicate the ageing state of paper as it is difficult to obtain paper samples to measure DP or tensile strength. Methanol amount in oil was recently found to be an early-ageing indicator for paper. In this study, a headspace gas chromatography mass spectrometry setup was developed to measure methanol in transformer oil. This setup consists of an auto sampler with a gas tight syringe, a gas chromatography unit with 60 m VF-624ms column and a quadrupole ion trap type mass spectrometer unit. Measurement of several laboratory-aged and service-aged oil samples were conducted with both external standard and internal standard calibration methods. Higher methanol values obtained from internal standard method confirmed that it is more suitable than external standard method.