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This manuscript presents a comprehensive literature review with the aim to provide readers a reference document with up-to-date information on the field of methanol use as a chemical marker. It has been a little more than a decade since methanol was first introduced as a marker for assessing solid insulation condition in power transformers. It all started when methanol was identified in the laboratory during thermal ageing tests carried out with oil-immersed insulating papers and was subsequently also identified in transformer field samples. The first publication on the subject was released in 2007 by our research group. This review covers the methanol fundamentals such as the analytical methods for its determination in transformer oil, which is generally performed by headspace gas chromatography with mass spectrometry or flame ionization as a detector. Current standardization efforts for its determination include ASTM working group 30948 and IEC TC10. Kinetic studies have confirmed the relationship between methanol generation, the number of broken 1,4-β-glycosidic bonds of cellulose and changes in mechanical properties. Laboratory tests have confirmed its stability at different accelerated ageing temperatures. Several utilities have identified methanol during field measurements, case studies on power and some distribution transformers are presented, as well as transformer postmortem investigations. These field-testing results demonstrate its utility in monitoring cellulosic insulation degradation. Recently, a model of methanol interpretation has become available that allows for evaluation of the average degree of polymerization of core type transformer cellulose winding. Methanol has a role as an indicator of cellulosic solid insulation ageing in transformer mineral oil, and it is expected that in the future it will be in routine use by utilities. [ABSTRACT FROM AUTHOR]

Abstract: Methanol and ethanol have been identified as oil-soluble by-products generated by the aging of oil-impregnated cellulosic insulation materials of power transformers. Their presence provides useful information for diagnostics and end-of-life transformer estimation. Despite their value as cellulose degradation indicators, their sensitive and accurate determination is challenged by the complex oil matrix. To overcome this constraint, we present a simple, fast and direct procedure for their simultaneous determination in mineral insulating oil samples. The procedure uses a static headspace sampler coupled with a gas chromatograph equipped with a mass spectrometer. The selected method parameters permitted adequate separation of these two compounds from the complex oil matrix and quantification at ngg−1 concentrations. An original internal standard procedure was developed, in which ethanol-d6 was added to all studied samples and blanks, with adequate resolution between the internal standard and its isotopomer ethanol. The method was validated in terms of accuracy and reproducibility for both analytes. The method detection limit, 4ngg−1 for methanol and ethanol, is well below the value (μgg−1) achieved by a standardized method for methanol determination in crude oil. During method validation studies, a relative error of approximately 6% was obtained for both methanol and ethanol with excellent reproducibility, average %RSD, below 2%. An experiment control chart, constructed to evaluate long-term reproducibility, indicate an overall good reproducibility (%RSD<3%) for 1000ngg−1 control solutions. The applicability of the method to the direct analysis of trace methanol and ethanol in oil from field transformer samples was successfully demonstrated. This analytical method is of high relevance to the electrical utilities as it allows indirectly assessment of the level of deterioration of the critical cellulose, an inaccessible part of a power transformer. [Copyright &y& Elsevier]