Abstract
The data from physico-chemical analyses of transformer oil for a transformer fleet comprising more than 300 equipment units that were gathered for five years at the diagnostic laboratory of the Tatneft' Joint Stock Company's enterprise were subjected to statistical analysis. The transformer oil characteristics were measured in accordance with the RD (Guiding Document) 34.43.105-89 "Guidelines for Using Transformer Oils" and Chapter 1.8 of the 7thed. of PUE (Russian Electrical Code) "Regulations for Carrying out Acceptance Tests."The following indicators were used for carrying out the analysis: purity class, moisture content, specific gravity, flash point in a closed crucible, acidity value, dielectric loss tangent, and breakdown voltage. To identify the main factors related to breakdown voltage, a matrix of pair correlations was constructed, based on which a negative correlation between the moisture content and breakdown voltage was revealed. In addition, the effect of seasonal variations on the transformer oil characteristics was studied. Statistical processing of data for the cold and warm seasons showed that the moisture content in the warm period is by 26 % higher than it is in the cold period of the year, and that the opposite is the case for the breakdown voltage. Based on the analysis performed for the entire fleet of transformers operated by JSC Tatneft, a conclusion was drawn that moistening of oil is a direct factor decreasing the breakdown voltage. The other factors, including the presence of mechanical impurities; degradation of paints, varnishes and solid insulation; and oil oxidation are characterized by a more intricate mechanism of affecting the breakdown voltage.
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