Research On The Insulation Properties Of SF₆/CF₄ Gas Mixture Under The Power Frequency AC Voltage

Because of excellent insulation performance and breaking capacity,SF₆ gas has been widely applied to power system.But the further application of SF 6 is limited due to the high liquefaction temperature property and a very high liquefaction temperature index.However,no other alternative pure insulation gas has been found,which with better indices than SF₆ among insulation property,liquefaction temperature,economy and safety.In present research works,mixture gas that containing buffer gas in SF₆ is a valid way to improve the comprehensive performance of insulation gas and it is also one of the major research categories.Most of the research is conducted on two kinds of mixture gas,SF 6/N₂ and SF₆/CO2,seldom on the mixture gas SF₆/CF₄.As a kind of insulation low cost gas,CF₄ presents many excellent features,such as low liquefaction temperature,low degree of greenhouse effect index and high quality of arc-quenching performance.What's more,CF₄ is also a electronegative gas.Conducting research on mixture insulation gas SF₆/ CF₄ is of great value of academic research and industrial application.This paper studied SF₆/CF₄ mixed gas insulation performance under power frequency AC voltage,mainly completed the following work:1.Introduce a test chamber,which is of good sealing performance,has a distance-adjustable electrode and can withstand both positive and negative pressure,providing a stable test environment for the mixed gas pressure test.2.Under the circumstance of power frequency AC voltage,a gas pressure test that uses two kinds of gas mixture of SF₆/N₂ and SF₆/CF₄ has been carried out.Including the test under different forms of electric field,various pressure,different mixing ratio and different electrode distance,next processing the test data and finally analyzing the influence of the above factors on the breakdown voltage :?1?Within the range of pressure and with the same mixing ratio k,the breakdown voltage of mixture gas SF₆/CF₄ almost increases linearly with the increase of pressure p.?2?With a constant value of distance of electrodes d and a constant value of pressure p,the breakdown voltage of mixture gas SF₆/CF₄ increases non-linearly with the mixing ratio k,showing a saturation trend.Namely,when the proportion of SF₆ is low,the breakdown voltage would increase greatly with the increase of content SF₆ at first.And then the increase rate would be declining.?3?Under the condition of highly non-uniform electric field,when mixing ratio k and pressure p are constant,breakdown voltage of mixture gas SF₆/CF₄ increases non-linearly with the distance between electrodes d.When d is larger than 10 mm,the increase rate would be declining.Namely d equals to 10 mm is the inflection point.3.According to the ratio of breakdown voltage of mixture gas SF 6/CF₄ to that of mixture gas SF₆/N₂ and the known empirical formula of mixture gas SF₆/N₂,the dielectric strength of mixture gas SF₆/CF₄ can be obtained.4.Comparing mixture gas SF₆/CF₄ with mixture gas SF₆/N₂,the synergy of mixture gas SF₆/CF₄ is much better.From view point of dielectric strength,mixture gas SF₆/CF₄ is a good choice for alternating pure gas SF₆ and mixture gas SF₆/N₂ in gas insulation devices.It lays foundations for studying on mixture gas with SF₆ and has important reference to future research.