Research On The Generation Mechanism And Influential Factors Of Corrosive Sulfide And Corrosion Inhibition Techniques In Oil-impregnated Transformers

With the rapid enhancement of power capacity as well as the increasing voltage grade of electric equipment, the power grid will increasingly focus on the growing demand for transformer insulation. Mineral oils carry on several roles such as heat dissipation, insulation, arc extinction and fault information carriers in the power transformer, which plays a vital role in guaranteeing the operation for the transformers. Over the last decade, an increasing number of insulation failures have occurred as a result of corrosive sulfide in the transformer oil at home and abroad, threatening the stable operation of the transformer. Corrosive sulfide will corrode the copper wingdings to generate copper sulfide and then the oil-paper insulation system will be deteriorated easily, eventually leading to insulation breakdown. In the article the formation mechanism of copper sulfide in the mineral insulating oil and the inhibiting properties of oil additives on the corrosive sulfide were studied further to provide a reliable reference of copper sulfide generation and suppression.Firstly, for the further investigation of the mechanism of corrosive sulfur compounds, through a series of experiments the corrosive sulfide dibenzyl disulfide(DBDS) partially can be decomposed into benzyl mercaptan in the transformer oil at high temperature. And benzyl mercaptan is also a kind of corrosive sulfide which will corrode copper strips under aerobic conditions to generate copper sulfide. However, dibenzyl sulfide(DBS), the reaction by-product of dibenzyl disulfide and copper, cannot react on copper strips at 150°C effectively to generate copper sulfide. Whether DBS is corrosive at higher temperature, it remains furher research.Secondly, the effect of oxygen and acid on the copper sulfide generation is further analyzed. By comparing the experimental results, it can be concluded that oxygen can not only accelerate the deposition of copper sulfide on the insulating paper, but also accelerate the generation of copper sulfide. Meanwhile, acids will expedite the generation of copper sulfide at the same time in the transformer.Thirdly, the impact of the antioxidant di-tert-butyl-p-cresol(DBPC) on the generation and migration is systematically analyzed in the paper. The results indicate that DBPC cannot effectively consume DBDS to inhibit copper sulfide generation, but will accelerate the deposition of copper sulfide on the insulating paper. More than that, it will accelerate the aging of oil-paper insulation and further accelerate the formation of copper sulfide. At the same time, copper sulfide first starts to deposit on the first inter layer of the insulating paper in the forced oil-circulation transformers, and then spreads with the flow of the insulating oil to be deposited randomly on the windings in the transformer. The migration of copper sulfide is not diffused from layer to layer, and the deposition of copper sulfide doesn’t first start on the outermost layer of the insulating paper.Finally, the inhibitory effect of two common metal passivators benzoriazole(BTA) and N-aminomethylated benzoriazole(Irgamet 39) on copper sulfide is analyzed through a series of heating tests. The results show that BTA and Irgamet 39 can mitigate the corrosion phenomenon of the windings. When the BTA content is about 30 mg / kg and Irgamet 39 is about 100 mg / kg, it can achieve the ideal inhibiting effect. However, the metal deactivators cannot eliminate sulfur corrosion.