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Some cases reported recently indicate flow electrification that becomes obvious due to aging deterioration of insulating oil and cellulose insulation in aged oil-immersed transformers. It is supposed that the inclusion of minor components influences the aging deterioration of mineral insulating oil, but details including the aging mechanism have not been clarified. This paper examines the influence of various compounds on the electrostatic charging tendency (ECT) of insulating oil. Mineral insulating oil mainly consists of hydrocarbon compounds, but it also contains extremely small amounts of sulfur compounds, nitrogen compounds and oxygen compounds. Sample oil was prepared by adding various compounds to synthetic oil suffering from small aging changes of the ECT. After heating the sample oil, the ECT was measured, and the influence of various compounds was examined. Aging changes of the ECTs were small in pure hydrocarbon compounds. On the other hand, increases by aging were detected in the ECTs of the sample oils to which impurities such as sulfur compounds and nitrogen compounds were added. In particular, outstanding increases were detected in the ECTs of sample oil to which sulfide compounds and sulfoxide compounds classified as sulfur compounds were added. It has been estimated that sulfur compounds influence the increase by aging of the ECT of mineral insulating oil. It has been also estimated that the increase by aging of the ECT of mineral insulating oil starts from sulfide compounds contained in new oil and that the ECT increase process triggered by sulfide compounds progresses by the production of sulfoxide compounds and compounds of high ECT. Index Terms--Aging, Copper, Electrostatic measurements, Electrostatic processes, Insulation, Insulators, Nitrogen compounds, Oil insulation, Oxidation, Oxygen, Oxygen compounds, Petroleum, Sulfur, Sulfur compounds, Transformers.

This paper describes the surface breakdown characteristics of silicone oil which has the possibility of application to innovative switchgears and transformers as an insulating medium. At the first step, we have experimentally studied the impulse breakdown characteristics of the configuration with a triple-junction where a solid insulator is in contact with the electrode. The test configuration consists of solid material (Nomex[R] or pressboard) and liquid insulation oil (silicone or mineral oil). We have discussed the experimental results based on the maximal electric field at the triple-junction. As the second step, we have studied the configuration which may improve the surface breakdown characteristics by lowering the electric field on the insulator surface. Index Terms--Surface breakdown, Electric power apparatus, silicone oil, triple junction, discharge inception voltage.

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 chlorideimpregnated 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 chlorideimpregnated 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. [ABSTRACT FROM PUBLISHER]