Research on Influence of Nozzle Ablation on Decomposition Products of SF₆ Switchgear Under Arc Discharge

The nozzle will be eroded by the arc in case of interruption of SF₆ switchgear. The degree of nozzle ablation is closely related to the SF₆ decomposition products. However，the characteristic products of nozzle ablation under the condition of arc discharge are not clear，which seriously restricts the application of SF₆ decomposition product analysis method in fault diagnosis. In order to explore the characteristic products of nozzle ablation and its relationship with arc energy，an arc discharge test platform is set up based on 40.5 kV SF₆ circuit breaker. The arc discharge tests in SF₆ and He atmosphere are performed under the condition of installation and removal of the nozzle. The gas after the interruption tests is qualitatively and quantitatively detected and analyzed by gas chromatography. It is found after 10 times of interruption test at 5 kA that CF₄，C₂F₆ and CO₂ produced by nozzle ablation in SF₆ atmosphere account for 99.8%，77.1% and 70.3% of the total generation respectively，and C₃F₈ produced by nozzle ablation in He atmosphere accounts for 100% of the total generation. Therefore，CF₄，C₂F₆，C₃F₈ and CO₂ are suitable as indicators to characterize the degree of nozzle ablation. Furthermore，the correlation degree with nozzle ablation from strong to weak is CF4>C2F6≈C3F8>CO2.