Comparative Studies on Furans as Aging Markers for Power Transformers

The investigation on the aging marker for palm fatty acid ester (PFAE)-filled transformer was performed. Sealed aging stainless steel tanks containing transformer components in the same ratio as a 27-MVA power transformer, were aged at 151 °C–168.5 °C for 48–2880 h in a strictly controlled oxygen-free and low initial moisture environment. The generation of 2-furaldehyde (2FAL) and other four kinds of furans including 5-hydroxymethylfurfural (5HMF), 2-furfuryl alcohol (2FOL), 2-acetylfuran (2ACF), and 5-methyl furfural (5MEF) from cellulosic insulating components impregnated in mineral oil (MO) and PFAE after thermally aging tests are determined and compared. The results indicate that the concentration of 2FAL, 2ACF, and 5MEF maintains an increasing trend with the aging time and temperature for both fluids. The correlations between 2FAL and the degree of polymerization (DP) of high-density pressboard (HPB) in both fluids are established. The results demonstrate that 2ACF and 5MEF can also be used as aging markers for transformer in spite of their much lower concentrations in the aged fluids.