The Investigation Of Discharge Characteristics Of CF₃I-CF₄ Gas Mixtures

With the progress of science and technology and the development of electric power industry,it has become an indispensable part of social and economic development.The SF₆ gas used in transformer and GIL of transmission line and substation has the characteristics of strong insulation.But because the GWP value of SF₆ is 23900,it has been regarded as one of the greenhouse gases that should be restricted by Kyoto Protocol.As an environmentally friendly insulating gas with GWP value less than 5,CF₃I has been extensively studied and tested by researchers in recent years.However,CF₃I is the same as SF₆ gas,and its liquefaction temperature is higher,so it is difficult to use in cold areas.Therefore,buffer gas should be added into CF₃I to reduce its liquefaction temperature,so that the application range of CF₃I gas will be widened.In recent years,researchers have reduced the liquefaction temperature of CF₃I by incorporating N₂,CO₂ and air or other insulating gases such as c-C₄F₈.However,there is no CF₃I gas mixture with the same insulation strength as pure CF₃I gas or pure SF₆ gas.CF₄,as a kind of gas with good insulation,has a low liquefaction temperature of–128?.It can be mixed with CF₃I gas as a mixture of CF₃I and CF₄ to improve its insulation strength and reduce the liquefaction temperature of CF₃I,so that CF₃I can be widely used.In this thesis,the electron transport coefficient and synergistic effect of CF₃I-CF₄ gas mixture are calculated by Monte-Carlo method.Compared with pure SF₆ gas and SF₆-CF₄ gas,the conclusion about the electrical resistance of CF₃I-CF₄ gas mixture is drawn.The liquefaction temperature is calculated by Antoine equation,and the reasonable application range of CF₃I-CF₄ gas is obtained.Then,through the AC breakdown voltage testing device and impulse voltage generator device,the AC breakdown voltage and lightning resistance characteristics of mixed gases under different electrodes,different proportions,different pressure and different clearances are tested,and the relevant trend curves and pashen curves of mixed gases varying with air gap,space and CF₃I ratio are obtained.The results calculated by Monte-Carlo method are compared with the results of AC voltage test,and the electric strength at different ratios and the magnitude of the breakdown voltage of different ratio is consistent.And the CF₃I-CF₄ mixed gas'AC breakdown voltage can reach 57%-120%of pure SF₆ gas,so the CF₃I-CF₄ mixed gas has the potential to replace SF₆ gas.