Study On Insulation Characteristics Of C₄F₇N/CO₂ And C₄F₇N/N₂ Mixed Gases Under Different Voltage Forms

This thesis from all over the world have been striving to find environmentally friendly gases that can replace SF6.In recent years,C4F7N is considered to be one of the most potential environmentally friendly gases to replace SF6 in the high voltage field and has been favored by researchers in many countries for its excellent insulation performance and lower global warming potential.However,because of its high liquefaction temperature,it is restricted to use in alpine regions and needs to be used in combination with certain buffer gases(currently the most used in the high voltage field are CO2 and N2).In order to better optimize the C4F7N mixed gas configuration scheme and provide key guidance for engineering applications,this thesis compares the insulation properties of C4F7N/CO2 and C4F7N/N2 mixed gases with different electric field forms f,different gas pressures p and different gas mixing ratios k by applying different voltage forms and chooses a better configuration plan.The main contents are as follows:Firstly,from the perspective of the discharge mechanism of gas,several factors affecting gas insulation are analyzed,including:pressure p,electric field form f and mixing ratio k;analysis and calculation from the liquefaction temperature angle to determine the mixing ratio k of the mixed gas studied(4%,7%,10%,13%),pressure p(0.1 Mpa,0.2Mpa,0.3Mpa,0.4Mpa,0.5Mpa).Designing the test cavity to simulate GIL:It is able to withstand the gas pressure of 0.7Mpa,can replace test electrodes of different shapes,and can determine the shape of the test electrode(plate-plate electrode and ball-plate electrode).According to the actual situation of GIL normal operation,the test cavity has the ability to adjust the gap distance d.Providing a good environment for the overall test.Secondly,the gap distance is fixed to d 3mm,maintaining the test environment temperature at 23 ℃.Using the designed test cavity under the two electric field forms(f=1 and 1.7)to carry out power frequency AC and positive and negative impact breakdown test.The mixing ratios k and gas pressure p are changed in the test,and under the same discharge conditions the insulation properties of C4F7N/CO2 and C4F7N/N2 mixed gases are compared and analyzed.From the test point of view,an environmentally friendly gas buffering scheme with better insulation performance is selected.Finally,since the C4F7N gas-related collision cross-section parameters are still under study,the experimental results are analyzed from the theoretical calculation point of view.In this paper,BOLSIG+ is used to analyze the discharge characteristics of N2 and CO2,and their electron energy distribution function(EEDF)is obtained.The experimental results are theoretically analyzed from the C4F7N gas adsorption electron capacity mechanism.