| Power transformer is the core of electric power transmission and transition. It plays a vital role in the safeguard of power grid's operation. However, it will be affected by various factors and failure of transformer happens. The failure of oil-paper insulation is the main reason to the failure of transformer. Recently, several transformer failures happened due to the corrosive sulfur in insulation oil. Corrosive sulfur in oil can attack insulation winding, leading to the decrease of oil-paper insulation characteristic, the decrease of which brings potential safety hazard to the operation of transformer. Therefore, it is of importance to investigate the process and mechanism of sulfur corrosion on insulation winding, the effect of sulfur corrosion on oil-paper insulation characteristic as well as the failure mechanism of transformer insulation winding caused by sulfur corrosion.In this paper, experimental platform for sulfur corrosion was established according to the purpose of experiment, winding used for transformer were aged in mineral oil in lab. Secondly, the effect of AC/DC electric field and field intensity on the sulfur corrosion was investigated through analyzing the sulfur corrosion difference of winding under the effect of signal-thermal and electric-thermal aging. The corrosion mechanism under the effect of electric field was studied as well. Furthermore, the formation of deposition on paper in winding and diffusion law among paper layers in winding was studied, Fick's law was adapted to establish the corrosion deposition diffusion dynamical model according to the deposition formation and diffusion law on winding. Finally, the law of characteristic parameters of oil-paper in the corrosion process was studied and the relation between parameters and sulfur corrosion was investigated as well. According to the corresponding experiments, the failure mechanism of transformer winding is investigated. The main innovative achievements of this paper are as following:?1? The sulfur corrosion mechanism under the effect of electric field was studied and obtained. Copper ions was produced due to the electrochemistriy. Copper ions contributed to the formation of deposition due to its reaction with sulfur substance. At the same time, copper ions accelerated the aging of oil, which produced acid. The acid contributed to the dissolution and decomposition of DBDS-Cu2. The Intensifying role played by acid on sulfur corrosion can be represented as the effect of electric field on sulfur corrosion to a great extent.?2? The formation and diffusion of deposition on winding is investigated, Fick's second law is put forward to establish to deposition diffusion dynamical model. It was found that the deposition was formed mainly on the innermost paper surface, and the deposition will transfer from innermost paper to outermost paper due to concentration difference. The diffusion of deposition is conducted by the DBDS-Cu2 and it decomposed to Cu2 S after diffusion. The deposition on the second, third and fourth paper surface was derived from the DBDS-Cu2 on the innermost paper, whereas the deposition on the outermost paper was derived from the both ends of winding. Diffusion dynamical Dodel was established based on Fick's second law and its expression was D=217×10-5exp?-9176.13/T?.?3? The failure mechanism of winding under the effect of sulfur corrosion was obtained. The conductive Cu2 S produced by sulfur corrosion will be attached to paper surface, the electric field in deposition location will be distorted.Cu2 S and copper ions will decrease the insulation resistance. PD will be formed easily due to distorted field and decreased resistance. PD attacks paper and forms damage, which cannot be recovered. The increase of dielectric loss contributes to the generation of heat and PD will also produce heat, the increased thermal resistivity leads to decreasing the ability of heat dissipation potential. The collected heat can not be removed easily and temperature will arise. The arising temperature contributes to the formation of deposition, which triggers PD and arising temperature more seriously. The insulation performance decreases continuously. This process revolves and winding will be failed when it cannot be bear the electric field. |
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