T. Ke

Bio: T. Ke is an academic researcher. The author has contributed to research in topics: Transformer oil & Corrosion. The author has an hindex of 1, co-authored 1 publications receiving 7 citations.

Failure mechanism of transformer oil-immersed cellulosic insulation induced by sulfur corrosion

Abstract: The life of transformer oil-paper insulation is determined by the insulation property of transformer cellulosic insulation. Existing studies have shown that sulfur corrosion poses a serious threat to the properties of transformer oil-immersed cellulosic insulation due to the reaction of corrosive sulfur dissolved in oil with copper winding. This paper investigated the effect of sulfur corrosion on the characteristics of transformer cellulosic insulation, cellulosic insulation winding samples with different degrees of sulfur corrosion were obtained through an accelerated thermal aging experiment. Then, short-/long-term withstand voltage tests for the cellulosic insulation winding were conducted. Experimental results showed that the contamination of sulfur corrosion had a minimal effect on the power–frequency breakdown voltage of the cellulosic insulation winding but considerably decreased its long-term electrical life. Combined with the analysis of the electrical/physical and chemical parameters of oil-immersed cellulosic insulation, the failure mechanism of transformer oil-immersed cellulosic insulation induced by sulfur corrosion was synthetically discussed and analyzed.

Effects of Thiophene Degradation on the Corrosiveness of Oil and the Properties of Oil–Paper Insulation in the Oil-Immersed Transformers

Abstract: As a non-corrosive inactive sulfur, thiophene is one of the most common sulfides in mineral oil, which are retained in oil and used for improving the oxidation stability of the oil. However, thiophene may be decomposed and form low-molecular sulfide with strong corrosiveness because of rapid energy accumulation under operating conditions of the oil-immersed power transformer. Thus, this study explored the effect of thiophene degradation on the corrosiveness and properties of insulating oil under thermal and electrical aging conditions, including a case investigation of sulfur corrosion of a 500-kV electric reactor and the accelerated aging experiments of oil–paper insulation. The results showed that the degradation and pyrolysis of thiophene depend on energy accumulation induced by thermal and electric fields in the oil-immersed transformers. Under the premise of thiophene without degradation and transformation, thiophene can still delay the deterioration of insulating oil due to its high oxidation resistance. The continuous energy accumulation induced by thermal and electric fields may cause the molecular chains of thiophene molecules to break and form some corrosive low-molecular sulfides, thereby resulting in the increase of the corrosiveness of oil, the decrease of the properties of oil–paper, and posing a huge corrosion threat to the oil-immersed transformer.

Investigation on the equilibrium distribution of methanol in transformer oil-immersed cellulosic insulation

Abstract: Methanol in oil was used to indirectly evaluate the aging status of cellulosic paper insulation for oil-immersed transformers. However, the distribution of methanol in oil is affected by many factors, not only related to the oil–paper adsorption equilibrium, but also may be affected by the vapor–liquid phase transition. In this study, the adsorption experiments of mineral oil and standard cellulosic Kraft paper for methanol were designed to explore the adsorption equilibrium process at different oil–paper mass ratios under room temperature. The vapor–liquid equilibrium experiments of methanol between oil and gas were carried out to explore the effects of temperature and phase volume ratios. It turned out that: firstly, compared with mineral oil, the Kraft paper has a stronger adsorption capacity for methanol, which makes most of methanol adsorbed in paper when equilibrium at room temperature. Secondly, the increase of oil–paper mass ratios reduces the adsorption of Kraft paper for methanol and makes the equilibrium time longer. Particularly, at a higher oil–paper mass ratio, due to the less paper mass, methanol would “reverse diffusion” from paper to oil standard solution in the early stage of equilibrium. Finally, the presence of methanol in gas phase cannot be ignored. The increase of temperature makes more liquid methanol in oil transferred to the gas phase by the phase transition process, while increasing the oil–gas phase volume ratios in constant volume system can inhibit this process.