Biocorrosion in transformer oils

The acid value, surface tension, pH value of aqueous extract and oil colour were measured in non-inhibited transformer oils aged by microbiol and thermooxidation effects. It is found that considerable microbial degradation of transformer oil occurs when free water is present in the oil. Degradation is accelerated by the biological decomposition of moistened crepe-paper and cotton-tape wrappings which are immersed in the transformer oil.