Impact of various stresses on the streaming electrification of transformer oil

•The streaming electrification of fresh and aged oils were investigated in a spinning disk system.•Several ASTM test methods were used to monitor the physicochemical properties of oil.•The Electrostatic Charging Tendency (ECT) is affected by the relative quantity of free radicals.•The ECT is influenced by the type of paper.•The streaming current increases as oil degrades under the impact of various stresses.

In this contribution the influence of various stresses and their combined impact on the electrostatic charging tendency of oil is studied. Various physicochemical properties were measured according to ASTM Standards to detect changes in oil quality. A free radical reagent, 2.2 diphenyl-1-picrylhydrazyl (DPPH), was added to oil before and after the application of stresses to determine free radical concentration. The results obtained show that the application of stresses contributes to an increase in the electrification current. These results also demonstrate that electrification current is affected by the quantity of the free radicals.