Furfural analysis of transformer oil
Furan derivatives are a measure of the degradation of cellulose paper. When the paper ages, its degree of polymerization reduces, so its mechanical strength decreases. The degree of polymerization of the paper can be directly related to the concentration of furan derivatives in transformer oil and other mineral insulating oils. Therefore, it is important to get to know the types and concentrations of furan derivatives in oil to monitor and control the transformer and other electrical equipment.
Although by dissolved gas analysis one can predict the condition of the paper insulation primarily, but it is not very sensitive method. There is a guide line in IEC-599, where it is told that if the ratio of CO2 and CO in DGA results is more than 11, it is predicted that the condition of paper insulation inside the transformer is not good. A healthy cellulose insulation gives that ratio in a range of 4 to 11. But still it is not a very sensitive way of monitoring the condition of paper insulation. Because CO2 and CO gases also produced during oil breakdown and sometimes the ratio may misleads the prediction.
When oil is soaked into paper, it is damaged by heat and some unique oil soluble compounds are realized and dissolved in the oil along with CO2 and CO. These compounds belong to the Furfuraldehyde group. These are some times called Furfural in short. Among all Furfurals compounds 2- Furfural is the most predominant. These Furfural family compound can only be released from destructive heating of cellulose or paper. Furfuraldehyde analysis is very sensitive as because damage of few grams of paper is noticeable in the oil even of a very large size transformer. It is a very significant diagnostic test. It is best test for assessing life of transformer. The rate of rise of percentage of Furfurals products in oil, with respect to time, is used for assessing the condition and remaining life of paper insulation in power transformer.
