Abstract
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.
Highlights
IntroductionMultiple factors, such as electrical, mechanical and thermal stresses, influence the lifespan of transformers
Multiple factors, such as electrical, mechanical and thermal stresses, influence the lifespan of transformers. These factors interact with the components of the transformer insulation system, which is typically composed of cellulosic insulation materials in the form of paper, pressboard and transformer boards, as well as mineral oil
The combined action of temperature, oxygen and moisture over the transformer’s lifetime causes the oil and solid insulation material to degrade and to generate gaseous decomposition products dissolved in the mineral oil
Summary
Multiple factors, such as electrical, mechanical and thermal stresses, influence the lifespan of transformers. 1980s, consists of the measurement of carbon oxides and carbon dioxide present in the transformer oil They can be generated from paper degradation but from long-term oxidation of the oil in open-breathing units during normal operation or in nitrogen-conservator units facing air entry. The second generation, introduced in the 1990s, involves the measurement of a family of furanic compounds such as 5-hydroxymethyl-2-furaldehyde, furfuryl alcohol, 2-furaldehyde known as 2-furfural, 2-acetyl furan, and 5-methyl-2-furaldehyde present in oil From this family, the determination of 2-furaldehyde (2-FAL) is a routine test in transformer monitoring. This review outlines the progress in the use of methanol as a chemical marker in transformer oil insulation It presents an overview of accelerated ageing studies and kinetic studies of methanol formation. The analysis of this molecule dissolved in oil is about to be normalized by international organizations [16,17]
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