Study on the Characteristic Decomposition Components of DC SF 6 -Insulated Equipment under Positive DC Partial Discharge

Pulses with different amplitudes occur when an inner partial discharge fault exists in SF 6 -gas-insulated DC high-voltage electrical equipment. SF 6 decomposes following complex physical and chemical processes. Discussing and quantifying the mathematical relationship of pulse discharge quantities to SF 6 decomposition component characteristics is helpful to evaluate and predict the insulation fault severity and development trends in SF 6 -insulated DC equipment. Numerous simulation experiments on SF 6 decomposition under positive DC partial discharge were performed on a needle-plane model. The DC partial discharge quantities of pulses are obtained, and decomposition characteristics based on the mechanism of SF 6 decomposition are analyzed. Results show that generation, effective generation rate and concentration ratio c(SO 2 F 2 + SOF 4 )/c(SOF 2 + SO 2 ) of components increase with partial discharge severity, and the first two act in the following order: SOF 4 > SOF 2 > SO 2 F 2 > SO 2 > CF 4 when the discharge quantity level is higher than 238,957 pC. Finally, a coefficient matrix illustrates the mathematical effects of pulses with different discharge quantities on different SF 6 decomposition components. The pulses whose discharge quantity is higher than 50 pC have obvious promotion effects on the formation of decomposition components, whereas the pulses whose discharge quantity lower than 50 pC decrease the positive promotion effects that large discharge pulses have on decomposition components. The higher the effective generation rates are, the greater the partial discharge severity is, and their change laws provide a new method to evaluate and predict insulation fault severity and development trends in DC SF 6 -insulated equipment with high reliability and detection stability.