Experimence Study of Trace Water and Oxygen Impact on SF6 Decomposition Characteristics Under Partial Discharge

It is common practice to identify the insulation faults of GIS through monitor the contents of SF6 decomposed components. Partial discharges (PD) could lead to the decomposition of SF6 dielectric, so new reactions usually occur in the mixture of the newly decomposed components including traces of H2O and O-2. The new reactions also cause the decomposed components to differ due to the different amounts of H2O and O-2 even under the same strength of PD. Thus, the accuracy of assessing the insulation faults is definitely influenced when using the concentration and corresponding change of decomposed components. In the present research, a needle-plate electrode was employed to simulate the PD event of a metal protrusion insulation fault for two main characteristic components SO2F2 and SOF2, and to carry out influence analysis of trace H2O and O-2 on the characteristic components. The research shows that trace H2O has the capability of catching an F atom, which inhibits low-sulfide SF from recombining into high-sulfide SF6. Thus, the amount of SOF2 strongly correlates to the amount of trace H2O, whereas the amount of SO2F2 is weakly related to trace H2O. Furthermore, the dilution effect of trace O-2 on SOF2 obviously exceeds that of SO2F2.