Decomposition characteristics of SF₆ under three typical defects and the diagnostic application of triangle method

Detection of decomposition products is a widely studied method for condition diagnosis of SF₆ insulated equipment because of its anti-electromagnetic interference and high sensitivity. A 90 L discharge chamber with adjustable defect was designed to simulate typical failures including metal protrusion defect, floating potential defect and insulator defect. Primary products of both the former two defects are SOF₂, SO₂F₂, CO₂, and SO₂. Concentration ratios including Φ(SOF₂+SO₂F₂+SO₂)Φ(CO₂) and Φ(SOF₂+SO₂)/Φ(SO₂F₂) could be used to distinguish these two defects which have different structures and discharge energy. Influence of essential conditions such as applied voltage, pressure, and moisture content has been investigated under metal protrusion defect. For the insulator defect, several extra carbon containing by-products, namely, CF₄, CO, and CS₂, are found to be critical characteristic decomposition products. Moreover, a triangle method utilizing composition of decomposition products is proposed. It is proved to be a graphical method which helps to follow the faults more easily and more precisely.