Application of chromato-mass spectrometry to determine the acid composition of transformer oil

Abstract

This article presents the results of a study of the acid
composition of transformer oil from high-voltage
transformers that have been in operation for more than
30 years. The acid composition of oils is studied using
a new technique based on a highly sensitive and highly
selective analysis method — chromato-mass spectrometry.
The technique makes it possible to determine the acid
composition of the insulating oil in the context of low
molecular weight acids (LMA), high molecular weight
acids (HMA) and phenolic compounds (PC). The structure
of some compounds identified in oil is given. It has
been established that during oil aging, among the acid
compounds, the following are predominantly formed:
HMA (60–95 %) > PC (3–16 %) > LMA (1–6 %). As
part of the research, it is found that the share of the most
dangerous low molecular weight acids in the total amount
of acidic compounds is no more than 12 %. The rest of the
acidity of the oil is due to the presence of macromolecular
and phenolic compounds, which do not adversely
affect the insulating properties of oil and paper in the
detected concentrations, and some of them (compounds
of a phenolic nature), on the contrary, even improve the
stability against oxidation. These extended tests of oil
samples from operating high-voltage equipment are of
practical value in preventive diagnostics of the condition
of its insulation.