Study On The Influence Of Trace H₂O And O₂on SF₆Decomposition Characteristics Under Overheating Fault

Sulfur hexafluoride (SF6), as a kind of inert gas with stable chemical propertiesunder atmospheric pressure, is widely used in gas insulated equipment for its excellentinsulation and arc performance. As the city scale expanding unceasingly and landresource increasingly nervous, SF6gas insulated equipment becomes more and morepopular among the power supply system for a series of advantages, such as small area,safe and reliable running, small electromagnetic pollution and so on.However, there are some inevitable defects inside SF6gas insulated equipmentwhich will produce abnormal heat and result in overheating fault in the actual operation.When the local temperature of SF6gas insulated equipment reaches a certain degree,SF6will decompose and recatwith impurities such as moisture and oxygen, thusgengrating a variety of oxygen containing sulfur fluoride and hydride (SOF2, SO2F2,SO2, HF, H2S, etc.). There is an association rule between these compositions andoverheating fault, so SF6decomposition components can be used to determine theseverity and development trend of gas insulated equipment overheating fault. As tracemoisture and oxygen has affected the SF6thermal decomposition process, the influenceof moisture and oxygen on SF6decomposition components must be corrected in order toimprove the accuracy of fault diagnosis. However, the influence rules are not clear atpresent. Therefore, it is needed to study the influence of trace moisture and oxygen onSF6thermal decomposition characteristics deeply to establish perfect expertdecision-making system of SF6gas insulated equipment.In this article, a series of artificial thermal fault decomposition experiments withdifferent different moisture and oxygen contents (volume fraction) were conducted onthe designed SF6thermal decomposition experimental system. The local hightemperature was produced by a stainless steel hot electrode and the contents ofdecomposed components were measured by gas chromatograph, chromatography-massspectrometry and fourier transform infrared spectroscopy. The influence mechanism oftrace moisture and oxygen on SF6decomposition characteristics under partial thermalfault has been preliminary explored. Results show that, no matter how much H2Ocontent is, SF6can decompos into CO2, SOF2, SO2, SOF4, SO2F2and H2S when thefault temperature is340℃. The concentrations of all these decomposition characteristicsincrease with the time extended, but change differently with the increase of H2O and O2 content, beacuse moisture and oxygen plays different role in the formation process ofeach decomposition product, eventually leading the influence of moisture and oxygenon effective gas rate of each product and ratios of c(SOF4+SO2F2)/c(SOF2+SO2),c(sulfur product)/c(CO2) and c(SO2)/c(total product) differently. However, the influencecan be corrected by the constructing fixed expressions. The variation of H2O and O2content not only affects the production of the decomposition characteristic components,but also changes the type of the main components of SF6thermal decomposition. Theinjection of H2O and O2makes SO2and HF gradually evolved into the maincomponents and increases the proportion of SO2F2in total gas, respectively. Therefore,the influence of trace H2O and O2on diagnosis results must be considered whencharacteristics component gas analysis method is used to diagnose overheating fault ofgas insulated equipment.