Partial Discharge Characteristics Influenced By Cu₂S On Oil-paper Insulation In Transformers

Over the past decade, there appeared lots of failures of transformers and reactors related to corrosive sulfur in many countries. The cases caused or suspected by cuprous sulfide for large transformers were about100units. Many domestic transformer failures in connection with the cuprous sulfide, but in view of the failure mechanism which the deposition of the cuprous sulfide in transformer and reactor has not yet conclusive in domestic power industry, so they were not directly attributed to the cause of the cuprous sulfide.Based on the problems found in engineering practice, the study tests were carried out on generating method for cuprous sulfide and the characteristics of partial discharge on inter-turn winding insulation affected by the sulfur corrosion, in the hope of getting a breakthrough in revealing the mechanism of transformer failures caused by cuprous sulfide.First of all, We used the transformer windings of the real manufacturer, design a model of inter-turn discharges, and build a partial discharge test platform. The test model can simulate the windings inter-turn insulation structure in the actual oil-paper insulation transformer, and based on the inter-turn structure in this model, the Sulfur corrosion test and the development process testing of partial discharge were studied.Secondly, we experimentally studied the cuprous sulfide deposition method by accelerating sulfur corrosion and insulation aging in the laboratory. The results show that adding sulfur in the transformer oil through the high temperature can be formed the effectiveness of copper electrode corrosion, insulating materials aging, and cuprous sulfide deposition.Third, through gradually increasing test voltage on the inter-turn insulation paper corrosion by sulfur, we studied the development process of inter-turn insulation partial discharge, and the variation law of parameters following out-applied voltage amplitude and applied time, such as the discharge pulse frequency, the average apparent discharge quantity, the total number of apparent discharge quantity and phase distribution range of discharge.The results show that the discharge pulse frequency between turns and discharge amount are substantially in accordance with the applied voltage exponentially increases; pulse gradually expand the scope of phase distribution, finally occupies nearly the entire frequency phase; the symmetry of the positive half-cycle discharge pulse and the negative half-cycle pulse is very good.Finally, this paper made comparative analysis for the differences from the inceptive voltage of partial discharge and the discharge development process between the inter-turn insulation subjected to sulfur corrosion and non-sulfur corrosive ones. The results show that the discharge development process of the test sample subjected to the sulfur corrosion is more tortuous than those without sulfur corrosion. Usually there are phenomena that they firstly reduced and later increased for the discharge; The inceptive voltages of partial discharges of the test samples subjected to the sulfur corrosion are great dispersion, but their average value is lower than that of non sulfur corrosive ones. So, the transformers that corroded by sulfur have more chance to be exposed to partial discharges.