Influence regularity of trace H2O on SF6 decomposition characteristics under partial discharge of needle-plate electrode

SF
₆
decomposition characteristics under partial discharge (PD) are not only associated with insulation fault type and its severity but also closely related to the H
₂
O content of in the equipment. This paper studies the decomposition characteristics of mixture gas SF
₆
/H
₂
O with six different gradients of trace H
₂
O under the same PD energy, selects SO
₂
F
₂
, SOF
₂
, CO
₂
, and CF
₄
as the characteristic components, and analyzes the influence regularity of trace H
₂
O on each of the component concentration, effective formation rate and characteristic ratio. Results show that H
₂
O creates favorable conditions for generating SO
₂
F
₂
and SOF
₂
owing to the capacity to capture F atom and inhibit low fluorine sulfides from recombining into SF
₆
. As a result, the concentration and effective formation rate of SO
₂
F
₂
and SOF
₂
is positively related with H
₂
O. Whereas H
₂
O has no evident influence on CO
₂
, it can consume intermediate by-products CF
₂
and CF
₃
which restrain CF
₄
generation. Each characteristic ratio decreases sharply and then becomes stable with increment of H
₂
O. The defined effective characteristic ratio effectively reflects its relationship with H
₂
O, whereas obtained mathematical expression between each effective characteristic ratio and trace H
₂
O lays solid foundation for fault diagnosis of SF
₆
insulated equipment based on SF
₆
decomposition characteristics.