Methanol Marker for the Detection of Insulating Paper Degradation in Transformer Insulating Oil

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.

Investigation on Formation Mechanisms of Methanol During Cellulose Insulation Aging Based on Molecular Dynamics Simulation

“…The simulation results of the catalytic mechanism are consistent with several significant experimental studies [44]- [46]. It has been reported that the main degradation mechanism of cellulose is acid hydrolysis, especially for the amorphous region [15], [44], [47], [48]. With the aging of cellulose insulation, a large amount of low-molecular-weight acids (e.g.…”

A review on a novel method for aging evaluation of transformer insulating paper based on methanol

“…In order to study the correlation between methanol content in oil and insulation state of transformer paper, it is necessary to realize high-precision quantitative measurement of methanol in oil produced by aging of transformer insulating paper. The methanol concentration in the oil produced by the aging of transformer paper is the lowest at the ppb level, and the ordinary gas chromatograph cannot achieve that detection accuracy [71,72]. On the other hand, the composition of the aged insulating oil is very complex.…”

A Novel Methanol-Based DP Estimation Method With a New Methanol Peak Detector Index for Aging Assessment of Power Transformer Insulation Paper

“…As a result, some DP estimation models based on 2-FAL have been proposed [15]. It must be noted that when TUK paper is used in the transformer, the presence of 2-FAL is low compared to standard Kraft paper transformers for an equivalent DP value [16]. According to [16], a new aging indicator is needed with the increasing use of TUK paper in modern transformers that produce a small amount of 2-FAL compared to standard Kraft.…”