Experimental Studies on the Sulfur Corrosion Behavior of Copper Windings in Transformer After Different Processings

The sulfur corrosion of copper windings in the transformer can cause insulating performance degradation of insulating paper and oil, threatening the stable operation of the transformer. From the mechanism of sulfur corrosion, grain boundaries of copper windings are susceptible to corrosion of corrosive sulfur in insulating oil, when sulfur corrosion occurs in copper windings. Therefore, the experimental studies on intergranular corrosion (IGC) behavior of different grain boundaries were important. Here, optimized grain boundary character distribution (GBCD) of copper has been considered to be a new effective method of enhancing corrosion resistance of the copper windings by controlling the internal microstructure. GBCD-copper windings have been successfully prepared by optimized processing and heat treatment, which is the same processing of copper windings. After designed processings, GBCD-copper windings of different grain sizes (17.488 µm, 59.985 µm, 133.02 µm) were prepared successfully. According to IEC 62535 standard, these indicated copper windings were oil-sulfur experimented under 150°C in the insulating oil of 500mg/kg DBDS content for 3 days. Different copper windings, corresponding insulating papers and oils were observed and characterized. In addition, the insulating properties of insulating papers and oils were also measured, including the breakdown voltage, dielectric loss, volume resistivity of insulating oil, and thermal conductivity and polymerization of insulating papers. Finally, results show that with the increase of grain size, the corrosion deposits on copper windings gradually decrease, the content of copper and copper element in oil and paper decreases, and the electrical properties of insulating oil and paper improve significantly.