Study on Micro-mechanism of Protective Effect of Metal Passivator Against Multiple Sulfides in Power Transformers

At present, there are few studies on the optimal additive concentration of passivator and the protective effectiveness of oil-paper insulation system containing multiple sulfides. Therefore, the passivator Methylbenzotriazole (TTA), which is widely used, and three typical sulfides, dibenzyl disulfide, hexadecanethiol and benzothiophene, are selected in this paper and simulated by reaction molecular dynamics. By measuring the van der Waals energy, molecular chain movement (MSD), elastic modulus and hydrogen bond number, the protective effect of TTA with different mass fractions on multiple sulfides was studied. The results show that TTA passivator can effectively protect the transformer oil-paper insulation system containing multiple sulfides. By reacting with oxygen to inhibit the lead substances required for the formation of corrosive sulfur and transferring from oil to insulating paper to form a protective film on the surface of copper windings, TTA passivator can hinder the reaction of sulfide and copper to a certain extent, and thus effectively delay the aging rate of oil-paper insulation. For insulating oil, before the mass fraction of passivator TTA was 150 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup>, the protective effect increased with the increase of passivator content. However, after 150 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup>, the aging of insulating oil was accelerated to a certain extent due to the solubility of TTA, but the aging rate was still lower than that of the blank control group. For insulating paper, the protective effect increases with the increase of passivator content, and TTA has no effect on the mechanical properties of insulating paper. From the perspective of comprehensive economy and protective effect, the best protective mass fraction of TTA is 50×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup>.