C4F7N

as the most promising SF6 alternative gas in high-voltage switchgear

is crucial for advancing large-capacity eco-friendly gas circuit breakers by studying pressure buildup characteristics within the chamber during the arcing process. This study establishes an arc magnetohydrodynamic simulation model that accounts for nozzle ablation and degradation

with its accuracy verified through type test. Then

the pressure buildup characteristics of C4F7N/CO2/O2 gas mixture and its differences from SF6 are investigated

and the influence of different arcing times and interrupter structures on interruption performance are analyzed. The results indicate the following: The simulated arc voltage of C4F7N gas mixture

considering nozzle ablation and degradation

aligns well with experimental results. The peak pressure in the expansion chamber with SF6 is nearly 35% lower than that with the C4F7N gas mixture

but the latter exhibits a faster pressure relief rate

and the increased energy in the chamber due to the hot PTFE vapor produced by the nozzle ablation is the main reason for the pressure increase. At the zero-crossing moment

the pressure in the expansion chamber is approximately 14% higher without considering nozzle degradation than with degradation

and the throat enlargement due to nozzle degradation significantly reduces the pressure buildup effect and accelerates the relief process. An improved design with a moderately reduced nozzle throat diameter and an extended throat length can establish higher pressure in the expansion chamber and enhance interruption performance by improving convective cooling.