Abstract
Pulses with different amplitudes occur when an inner partial discharge fault exists in SF6-gas-insulated DC high-voltage electrical equipment. SF6 decomposes following complex physical and chemical processes. Discussing and quantifying the mathematical relationship of pulse discharge quantities to SF6 decomposition component characteristics is helpful to evaluate and predict the insulation fault severity and development trends in SF6-insulated DC equipment. Numerous simulation experiments on SF6 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 SF6 decomposition are analyzed. Results show that generation, effective generation rate and concentration ratio c(SO2F2 + SOF4)/c(SOF2 + SO2) of components increase with partial discharge severity, and the first two act in the following order: SOF4 > SOF2 > SO2F2 > SO2 > CF4 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 SF6 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 SF6-insulated equipment with high reliability and detection stability.
Highlights
SF6 is widely used as a gaseous dielectric in gas insulation power transmission and transformation equipment for its excellent arc-interrupting ability and insulation performance [1,2,3,4]
SF6 can decompose into SO2 F2, SOF2, SOF4, SO2 and CF4 under different forms of electrical discharges due to the different types of insulation faults existing in SF6 -gas-insulated high-voltage electrical equipment, no matter whether DC equipment [5,6,7,8] or AC equipment [9,10,11,12,13,14]
The characteristic decomposition components of SF6 in DC SF6 -insulated equipment under positive DC partial discharge are discussed in this paper
Summary
SF6 is widely used as a gaseous dielectric in gas insulation power transmission and transformation equipment for its excellent arc-interrupting ability and insulation performance [1,2,3,4]. DC partial discharge (PD) pulses with different amplitude lead to deterioration of the insulating qualities of gas or SF6 -gas-insulated equipment, further corrode the internal parts of equipment, and seriously affect DC equipment operation safety [12,13]. The magnitudes of positive DC PD on needle-plane electrodes are non-uniform and large, and larger than the magnitudes of negative PD that occurs in AC or negative DC under same conditions, whereas the repetition rate is much lower. The difference may be due to the electron initiation that mainly occurs via field-enhanced collision detachment of negative ions for positive DC PD or via field emissions from the point electrode for negative PD [15]
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