Abstract: Influences of temperature, time and base oil types on corrosion sulfur determined for transformer oil were tested according to ASTM D1275B standard test method for corrosive sulfur in electrical insulating oils and the corrosion mechanism of sulfide was studied. It is found that the irregular operations are reasons for differences of corrosive sulfur test results between different analyzers. It was suggested for user to use lower sulfur transformer oil, to avoid local overheating as a result of transformer overloaded, and to keep the base oil unchanged when selecting sulfur-containing additives.

Key words: transformer oil, electrical insulating oil, corrosive sulfur, sealability