Abstract: The DL/T 285 method (the flat copper wrapped insulation paper method) was used to investigate the influence of the transformer base oils having different sulfur and aromatics content as well as common additives on potential corrosive sulfur measurement. The tests show that the detective results of potential corrosive sulfur for all base oils are non-corrosive, mainly no coloration changes of the copper wire and copper sulfide deposited on the insulating paper are found; however, the antioxidant addition has a certain effect on the test results, even if adding metal passivator; the phenolic antioxidant has an interference effect on the judgment for the results of corrosive sulfur by DL/T 285 method at higher temperature due to the reaction happens between additives and copper wire tested, leading to the appearance of blue and gray or purple and red stripes on the copper surface. When there is doubt about the analysis of the DL / T285 method, can use SEM-EDX elemental analysis to the flat copper wire used to determine if the corrosive element sulfur exists.

Key words: transformer oil, antioxidant additive, DL/T 285 method, corrosive sulphur