| Power transformer is the core equipment of energy transmission and distribution in power grid system.Once the fault occurs,it will bring the society inestimable economic loss and serious safety problem.In recent years,the power transmission and transformation equipment faults caused by the influence of corrosive sulfur in insulation oil on transformer windings have attracted the attention of many research institutions at home and abroad.Grid International set up special working groups in 2005 and 2009 to address the problem.The industry has also developed standards to strictly control the corrosive sulfur content of insulating oils in the hope of controlling sulfur corrosion at the source.Grid companies at home and abroad are made of metal passivator is added to the insulating oil measures,although has obtained the good inhibiting the effect of sulfur corrosion,but in the process of transformer running for a long time,passivation agent consumption will gradually lose their protection,and research shows that stray gases generated by a passivator is dissolved in insulating oil,interfere with the fault diagnosis result of dissolved gas in transformer oil.Through the research of relevant enterprises and scientific research institutions,the reaction mechanism between corrosive sulfur and windings has been preliminarily agreed,but so far there is no other effective means to restrain the corrosion of windings except adding metal passivator to the insulation oil.Therefore,it is of great academic significance and engineering value to find a new effective way to restrain the winding corrosion to ensure the transformer safe,stable and reliable operation.Grain boundary characteristic distribution refers to the improvement of special grain boundary ratio and adjustment of internal grain boundary network structure through appropriate deformation and heat treatment process for copper with middle and low stacking fault energy of face centered cubic metal,so as to significantly improve the corrosion resistance of copper.In this paper,based on grain boundary engineering technology,by optimizing the deformation and heat treatment parameters in the production process of copper windings and adjusting the content and distribution of special grain boundary inside the windings,the anti-corrosion performance of windings was effectively improved.Then,the corrosion resistance of grain boundary engineering windings under different influence factors and electrothermal combined action and its influence on oil-paper insulation are investigated.Finally,the anti-corrosion mechanism of grain boundary engineering windings is revealed from three different perspectives,namely energy and distribution at grain boundary,molecular dynamics and reaction thermodynamics.The main innovative achievements obtained through the above research papers are as follows:(1)The copper windings of transformer are optimized by grain boundary characteristic distribution,and the deformation and heat treatment parameters with excellent corrosion resistance of the windings are obtained on the premise of both conductivity and mechanical properties.The effects of different winding deformation variables,different rolling passes,different annealing temperature and different annealing time on the special grain boundary ratio inside the winding and its resistance to oil-sulfur corrosion were investigated.It is concluded that the windings optimized by grain boundary distribution have excellent corrosion resistance.(2)The corrosion resistance of GBCD windings and the influence of oil-paper insulation properties under different influencing factors were studied.For the original winding,the increase of temperature,DBDS concentration,the presence of oxygen and the increase of electric field strength will accelerate its corrosion.Significant corrosion products were found on the surface of the original winding and the surface of the insulating paper.The copper content in the insulating oil and the insulating paper increased gradually with the strengthening of the influencing factors,and the insulating performance of the oil-paper deteriorated seriously.GBCD windings show good corrosion resistance under various influencing factors.Temperature rise,DBDS concentration increase,oxygen presence and electric field strength increase do not accelerate the corrosion of GBCD windings.The content of copper on insulating oil and insulating paper is relatively low,which makes the insulation performance of oil-coated paper relatively good.(3)The corrosion resistance of GBCD winding under single thermal,AC electric thermal and DC electric thermal for a long time and its influence on the insulation property of oil-paper were studied.The test results show that the corrosion of the original winding will deepen gradually with the prolongation of time under the single thermal.In addition,the winding corrosion is more obvious under the electro-thermal combination,especially DC electro-thermal combination,which further leads to the increase of copper content in insulating oil and insulating paper,thus seriously reducing the insulation performance of oil-paper.Under the single thermal,AC electric thermal and DC electric thermal,the GBCD winding has no obvious corrosion with the extension of the corrosion time.Even in the electro-thermal combination,especially under the action of DC electro-thermal combination,there is still no obvious corrosion,and it has excellent anti-corrosion performance.The content of copper element in insulating oil and insulating paper is relatively low,and the insulating performance of oil-paper is better.(4)The mechanism of resistance to sulfur corrosion of GBCD winding is revealed.Firstly,through electrochemical corrosion test,it is concluded that the optimized winding with a large number of special grain boundaries not only reduces the interface energy of the winding,but also breaks the random grain boundary network structure and blocks the corrosion channel of the winding,thus effectively improving the anti-corrosion performance of the winding.Then,through corrosion tests at different temperatures,the reaction temperature and activation energy of the windings and corrosive sulfur were calculated respectively.It was concluded that the winding of optimized reaction temperature was 135.2?,while the reaction temperature of the ordinary windings was 104.5?.The optimized winding reaction activation energy is32557.62J/mol,while the reaction activation energy of ordinary winding is9375.61J/mol.The optimized winding has not only a higher reaction temperature than ordinary winding,but also a higher reaction activation energy,thus showing better corrosion resistance. |
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