Research On The Correlation Characteristics Between Partial Discharge Quantity And SF₆Decomposition Components Under Different Insulation Defects

Under common conditions, the sulfur fluoride （SF₆） as a good insulation mediumwith a strong electric negative, high resistance to electric intensity and excellent arcingability, was widely used in gas insulated Switchgear （GIS for short）. In normalcircumstances, SF₆had stable chemical properties, not easy to break down. When therewas PD in the equipment, SF₆gas would some extent decompose into sub-fluoride suchas SF₂, SF₄and SF₃; For pure SF₆, these sub-fluoride would quickly and efficiently tocompound into SF₆. But there was inevitably impurities gas specially as traces of airand water in GIS, which would take complex chemical reactions with these sub-fluorideto produce many steady components such as SOF₂、SO₂F₂、SOF₄、SO₂、DF₄、CO₂、HF、H₂S and so on. Among them, the acidic gas formed by HF, SO₂saluting into waterhad strong corrosive effect on metal and insulating material internal equipment, andwhen existing for long-term, they would reduce insulation performance, accelerateinsulation degradation, endanger the safety operation of the equipment, even seriouslycause sudden insulation fault.Preliminary studies both at home and abroad suggested that, severity of PD hadgreat influence on the types, contents and forming rules of SF₆decomposition, but theinfluence law of PD strength on SF₆decomposition characteristics was not clear.Therefore it was necessary to study correlation characteristics between partial dischargequantity and SF₆decomposition components, which helped to judge partial dischargedegree caused by defects through testing decompose components, establish therelationship between components and partial discharge, and lay the foundation for GISand fault diagnosis.Based on the already constructed PD testing apparatus, the author constructeddefects of needle-plate, gap and free metal particle; By adjusting the experimentalvoltage or particle number, PD of different strength was produced to drive SF₆decompose, and the average power per second QSECwas selected to correlated withdecomposition components. Study found that the contents and the production rates ofDF₄and CO₂didn’t change with the PD strength obviously, unsuitable as the relatedcomponents; while it was opposite of SOF₂and SO₂F₂that was suitable. Theconcentration of SOF₂and SO₂F₂had a “linear-saturated” growth with QSECincreasement （only SOF₂under free metal particle defect）, while the order of transition time from “linear” to “saturated” is free metal particle defect <gap defect <needle-plate defect; the production rates of SOF₂and SO₂F₂similarly grew in way of“linear-saturated” with QSEC, while the production rate of SO₂F₂could be seen assaturated growth from beginning of PD under gap defect. DF₄/CO₂and SOF₂/SO₂F₂could be chosen to construct code tree to distinguish defect, and the codes ofneedle-plate, gap and free metal particle were01or1x、00、2x. Besides,（SOF₂+SO₂F₂）/（CO₂+DF₄） grew with QSEC, so such to determine PD strength, and thecorrelation characteristics between them could be divided into three steps to reflect PDdevelopment.