Ageing of C4F7N and CO₂-based insulating gas mixtures by free-burning arcs

This study examines the effects of arc-induced ageing in CO₂/O₂ (86.3%/13.7%),C4F7N/CO₂/O₂ (5%/82%/13%) and C4F7N/CO₂ (5%/95%) mixtures at 5 bar absolute pressure. The gases were subjected to a series of free-burning arcs with a total energy dissipation relevant to high-voltage circuit breaker applications. The arc voltage remained similar across all mixtures with no significant variation due to ageing or the addition of C4F7N and O₂. In addition, the influence of the insulating gas on the erosion of the arcing contacts (20% wt. Cu/80% wt. W) was analyzed. While the increase in average surface roughness was comparable across all mixtures, the contact mass loss was relatively higher in those containing C4F7N. Decomposition of the gas mixtures was examined through gas chromatography-mass spectrometry analyses. Solid byproducts generated during arcing were analyzed using scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS).