Correlation between SF6 Decomposed Products and Defect Type and Partial Discharge State in DC GIS

In order to study the relationship between SF
₆
decomposed products and the type and severity of the insulation defect in gas-insulated switchgear (GIS), two defect models of metal tip and free metal particle were developed, and the pulse signal characteristics during the partial discharge (PD) development process were studied. It is proposed to use qv and nv as the characteristic parameters to divide the PD development process into three stages. Then, the SF
₆
decomposition experiment was carried out in each PD stage. The results showed that SF
₆
was decomposed and produced stable products such as CF
₄
, SO
₂
, CO
₂
, SO
₂
F
₂
and SOF
₂
. Under the tip defect, CO
₂
, SO
₂
F
₂
and SOF2 were the main decomposed products; under the particle defect, SOF
₂
was the main product. Finally, the correlations between the concentration and defect type, as well as the concentration ratio and PD state were studied separately. It is proposed to use C(CO2), C(SO2F2) and C(SOF2) to identify the two defects, and use R(CF4/CO2) and R[SO2F2/(SOF2+SO2)] to assess the PD state of two defects.