Decomposing Mechanism of SF6 under Positive DC Partial Discharge in the Presence of Trace H2O

The influence of H 2 O on SF 6 decomposition characteristics under positive DC partial discharge (PD) is significant. To evaluate PD fault severity in DC SF 6 -insulated equipment using the production characteristics of SF 6 decomposition components, the corresponding relationship and mathematical expression between the production of SF 6 decomposition components and the H 2 O content should be identified and achieved. Thus, SF 6 decomposition experiments under positive DC PD are performed to reflect the influence of H 2 O on SF 6 decomposition components. Results show that the total discharge quantity and the discharge repetition rate averaged for 1 s decrease slightly when the H 2 O content increases from 0 to 970 ppmv and then increase when the H 2 O content increases from 970 to 5120 ppmv. The effective production rates of SO 2 F 2 , SOF 2 , and SO 2 increase with the H 2 O content, whereas that of SOF 4 decreases. Finally, the corresponding relationship and mathematical expression between the characteristic ratio (c(SO 2 F 2 ) + c(SOF 4 ))/(c(SOF 2 ) + c(SO 2 )) of components and the H 2 O content have been achieved, which can afford references for PD fault diagnosis in DC SF 6 gas-insulated equipment.