Analysis methods of sulfide and sulfoxide compounds in mineral insulating oil for diagnosis on electrostatic charging of power transformers

Analysis methods of sulfide and sulfoxide compounds in mineral insulating oil are developed to diagnose an electrostatic charging of a power transformer due to oil circulation. When sulfonium ions are generated from sulfide compounds via sulfoxide compounds, they tend to increase an electrostatic charging tendency (ECT) in the oil, which causes the electrostatic charging of a power transformer. Selective analysis methods for sulfide and sulfoxide compounds are developed by combining solid extractions with a gas chromatography because it is difficult to detect sulfonium ions directly. Sulfide compounds are selectively extracted from oils by palladium chloride-impregnated silica gel while sulfoxide compounds are extracted by silica gels. The effect of sulfide on the dielectric dissipation factor (DDF), which relates to an ECT, of commercial oil is investigated by removing sulfide compounds with palladium chloride-impregnated silica gel. The DDF of untreated oil increases at the beginning of heating with air while changes in the DDF are minimal for treated oils.