Fundamental Research On Using Environmentally Friendly Gas In Gas Insulated Transmission Line

The gas insulated transmission line?GIL?has been widely used all over the world since 1970s.Depending on its excellent physical,chemical and insulating properties,Sulfur hexafluoride?SF₆?is used as a traditional gas insulated medium in GIL.However,because of its high greenhouse effect and stability in the atmosphere,SF₆ has been limited worldwide to use.Researches on the GIL using environmentally friendly insulating gas become more and more necessary.Trifluoroiodomethane?CF₃I?and its gas mixtures have quite well insulating characteristics and low global warming potential.Gas insulated electrical apparatuses using CF₃I and its mixtures as the gas insulated medium gradually catch more attentions.The surface flashover characteristics of the insulator under different gas pressures of 30%CF₃I-70%N₂ mixtures from 0.1MPa to 0.3MPa are analyzed first by taking power frequency AC experiments and lightning impulse experiments using gas discharge test platform.And also compared the results with that of SF₆ and its mixtures under the same situations.The results show that surface flashover characteristics of the insulator in30%CF₃I-70%N₂ is about 0.8 times as much as that of SF₆ and much higher than that of 20%SF₆-80%N₂ gas mixture.The reasonable operational gas pressure range by using CF₃I mixture as the insulating gas is also obtained.Then,the size of a standard single-phase line segment of 220kV new generation GIL with 30%CF₃I-70%N₂ as its insulating gas is designed.The related distributed parameters are calculated.Finally,the thermal effect and temperature rise of the GIL designed in this essay is simulated and calculated,and the size of the GIL is checked.The heat dissipation potentials of CF₃I and its mixtures are studied,and the factors that affect the temperature rise of GIL are analyzed.The results show that the heat dissipating capability of CF₃I is not very strong,but if adding a certain ratio of N₂ or CO₂,the heat dissipating capability will be increased significantly,even better than that of SF₆.The research results of this dissertation provide well design basis and theoretical foundations in designs and applications of high voltage apparatuses using CF₃I and its mixtures as their insulating gas.