Influential Factors and Correction Method of Furfural Content in Transformer Oil

Furfural content in transformer oil is considered a credible method to evaluate the aging extent of insulation paper and is extensively applied to the aging assessment of insulation system in transformers. Clearly, the accuracy of furfural analysis is directly related to the stability of furfural in oil, which, nevertheless, may be affected by various factors. In this research, furfural was added to insulation oil directly to analyze its stability in oil firstly. Furfural contents in different conditions, such as different temperatures, copper, and oxygen atmosphere, are measured regularly. The results corroborate that the furfural content in the oil keeps constant when the oil temperature is less than 130°C without copper or oxygen; copper cannot make furfural in oil degrade without oxygen when the temperature is below 90°C. These results indicate that the furfural is stable at the common operating temperature of transformer oil (40°C ~ 70°C) as long as no oxygen is in oil. Oxygen is the main degradation cause of furfural in oil, and high temperature and copper accelerate this progress. The oxidation product of furfural in oil has been explored, which shows that the furoic acid is the main degradation product of furfural when the temperature is less than 90°C. Thus, the furoic acid content in oil can be measured as a reference to increase the accuracy of the furfural analysis.